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Neuroscience
| Question | Answer |
|---|---|
| 2 anatomic divisions of the nervous system | CNS: brain & spinal cord PNS: cranial and spinal nerves & ganglia |
| structural division of PNS | Neurons: Receive, integrate & relay impulses Glia: support, insulate & nourish neurons |
| Grey matter primarily consists of... | Neurons |
| White matter primarily consists of.. | myelinated nerve fibers |
| Function of Somatic Nervous System: | Voluntary Sensory & Motor System (Brain & Spinal Cord) |
| Function of Visceral Motor System (Autonomic Nervous System): | Sympathetic Parasympathetic. regulate functions not under voluntary control ("automatic functions') |
| Higher Level Functions | Cognition Learning Memory Reasoning Comprehension Personality |
| Nervous system derived from... | embryonic exoderm |
| PNS derived from.. | Neural Crest |
| CNS derived from.. | Neural tube |
| Neurulation | As the neural groove deepens, the neural crests close along the midline. The neural groove transforms into the neural tube |
| The 3 Primary Brain Vesicles are.. | Forebrain MidBrain Hindbrain (formed at the 4th week) |
| The caudal end of the neural tube forms.... | the spinal cord |
| An important reference point of orientation in the brain | Lentiform Nucleus |
| Cerebrum.. | Consists of 2 cerebral hemispheres which are separated by the longitudinal fissure |
| The 2 cerebral hemispheres | are connected by a mass of myelinated nerve fibers (Commissure Fibers) |
| The cerebral hemispheres are composed of: | gray matter (externally) white matter (internally) |
| Sulci are.... | -Fissures: deep, they extend through the entire depth of the hemisphere. Fissures are really deep sulci - Cortical sulci: limited to the cortex |
| The 4 lobes of the cerebral hemisphere: | Frontal, Parietal, Temporal and Occipital |
| Main Sulci: 1. Longitudinal Fissure | • mid-sagittal fissure •incompletely separates the 2 hemispheres • contains the falx cerebri & the superior & inferior sagittal sinus |
| 2. Lateral sulcus (Sylvian Fissure) | • = the deepest sulcus • mostly horizontal • separates the frontal & temporal lobes |
| 3) Central Sulcus (Rolando) | • starts at longitudinal fissure & courses downward (& slightly forward) to lateral sulcus • Separates frontal & parietal lobes |
| 4) Parieto-occipital sulcus | • Separates the parietal & occipital lobes • Medial surface |
| 5) Calcarine Sulcus | •Medial surface • Starts at the posterior end of corpus callosum & continues back towards occipital pole |
| Cortical Areas of Frontal Lobe: Primary Motor Area Brod #4 | • voluntary movement • controls movement on opposite side of body • bilateral control tongue, larynx, pharynx, etc |
| Primary motor area has.. | Pyramidal cells with their axons being the beginning of the motor pathway •corticobulbar tract: motor pathway of cranial nerves • corticospinal tract: motor pathway of spinal nerves |
| Cortical Areas of Frontal Lobe: Premotor Area Brod #6 | •has no giant pyramidal cells • stores programs of motor activity • programs the activity of primary motor area |
| Cortical Areas of Frontal Lobe: Supplementary Motor Complex (SMC) | • Between motor & pre-frontal cortex • Anterior to Brodmann #4 • Direct projections to spinal cord • Function not clear, appears to control voluntary actions |
| T-junction | On it lie the Frontal eye field which controls voluntary scanning movements of the eye & independent of visual information |
| Cortical Areas of Frontal Lobe: Broca’s Area (Brod. #44, 45) | [Pars opercularis (#44) & triangularis (#45)] • Motor speech area for formation of words • Important in dominant (left) hemisphere – 98% • ablation in Broca's area results in speech paralysis |
| Prefrontal Association Cortex | • extensive • concerned with individual personality • regulation of feelings •lateral surface: cognitive processes • medial & inferior surface: emotional behavior & regulation of ANS |
| Cortical Areas of the Parietal Lobe: Primary Somesthetic (somatosensory) Area (Brod. #3,1,2) | • receives sensations from the contralateral side of body • has to do with all forms of conscious sensations e.g. touch, pressure, temperature, pain, etc. |
| Superior Parietal Lobule | • Quadrangular convolution • Association Cortex |
| Inferior Parietal Lobule | • Constituted by 2 semicircular gyri • Sensory Speech Area of Wernicke |
| Cortical Areas of the Parietal Lobe: Somatosensory Association Area (Brod. #5,7) | • superior parietal lobule • receive & integrate different sensory modalities • stereognostic sense |
| Cortical Areas of the Parietal Lobe: Primary Auditory Cortex (Brod. #41,42) | •includes gyrus of Heschle •found in inferior wall of lateral sulcus |
| Cortical Areas of the Temporal Lobe: Sensory Speech area of Wernicke, Brod #39,40 | Visual Area of Speech Brod. #39: angular gyrus Auditory Area of Speech #40 : supra-marginal gyrus |
| Cortical Areas of the Occipital Lobe: Primary Visual Cortex (Brod. #17) | situated on the walls of the calcarine sulcus |
| Cortical Areas of the Occipital Lobe: Secondary Visual Area (Brod. #18,19) | function relates visual info received by primary area with past experience for recognition |
| Cortex | layer of gray matter that covers the surface of the hemispheres |
| Cellular Elements of Cortex: | • Pyramidal cell • Granular (Stellate) cell • Fusiform cell (modified pyramidal) • Horizontal cells of Cajal • Cells of Martinotti |
| Nerve fibers consist of: | • Radial fibers • Tangential fibers |
| Pyramidal cells: | apex: 1 apical dendrite basal angles: basal dendrites axon: terminate is deeper layers or enters white matter as a projection, association or commissural fiber |
| Betz cells | giant pyramidal cells |
| Stellate (or granular cells) | • small polygonal shape • multiple branching dendrites • 1 relatively short axon (terminates on nearby neurons) |
| Fusiform cells | •long axis vertical to surface • deeper layers • axon from inferior pole which enters the white matter as a projection, an association or a commissural fiber |
| Horizontal cells of Cajal | • small, fusiform cells • oriented horizontally •found in superficial layers • axon is parallel to surface & makes synapses with pyramidal cells |
| Cells of Martinotti | • small, multipolar cells •found in all layers • short dendrites |
| Radial Fibers | • right angle to surface • afferent entering fibers: terminate in cortex • efferent exiting fibers: axons from pyramidal, stellate & fusiform cells • projection, association & commissural fibers |
| Tangential Fibers | • parallel to surface • collateral & terminal branches of afferents • axons of stellate & horizontal cells • collaterals of pyramidal & fusiform cells • most concentrated in layers of 4 &5 Bands of Baillarger (sensory cortex) |
| The 6 cell layers of the cerebral cortex: | Ι – Molecular Layer ΙΙ – External Granular Layer ΙΙΙ – External Pyramidal Layer ΙV - Internal Granular Layer V - Internal Pyramidal Layer VΙ - Polymorphic Layer |
| Heterotypical areas: | do not show all 6 layers |
| Homotypical aeas: | show all 6 layers |
| The inner part of Cerebral Hemispheres consists of: | -White matter - Basal Ganglia - Ventricular system - Limbic System - Diencephalon |
| Association Fibers: | connect different parts of same cerebral hemisphere |
| Projection Fibers: | connect cortex of cerebral hemisphere with caudal parts of the brain and spinal cord |
| Commissural Fibers: | connect two cerebral hemispheres passing across the midline |
| Corpus Callosum: | The largest commissure of the brain, which connects the two cerebral hemispheres passing across the midline Coordinates the activities of the two cerebral hemispheres |
| Parts of CC: | - Rostrum - Genu - Body - Tapetum - Splenium |
| The forceps minor: | - Connects the frontal lobes - Can be found in the genu of CC |
| The forceps major: | - Forms a prominence called the bulb - Connects the occipital lobes - Can be found n the splenium of CC |
| The tapetum: | - Separates the fibers of the optic radiations from the temporal horn Can be found in the upper part of the body and splenium of CC |
| Anterior Commissure: | - Located at the upper end of the lamina terminalis - Interconnects the olfactory bulbs of the two cerebral hemispheres |
| Posterior Commissure: | - Epithalamic commissure - Has fibers from the pretectal nuclei that are involved in the pupillary light reflex |
| Fornix: | - C shape structure - Consists mainly of hippocampomamillary tract fibers - VIP in limbic system |
| Parts of the fornix: | 1. fimbria 2. crus 3. commissure 4. body 5. columns |
| Habenular Commissure: | A small bundle of nerve fibers that cross the midline in the superior part of the root of pineal stalk |
| Short association fibers: | - Lie beneath the gray substance of the cortex - Connect adjacent gyri of same hemisphere |
| Long association fibers: | - Connect distant areas of the same hemispheres |
| Superior longitudinal fasciculus (SLF): | - Largest bundle - Connects parietal and occipital lobe with ipsilateral frontal lobe |
| Inferior longitudinal fasciculus: | - Connects occipital with temporal lobe - Runs lateral and inferior the optic radiation fibers |
| Cingulum: | - C- shaped structure right above CC - Allows communication between components of the limbic system |
| Anterior Cingulum: | Linked with emotions - apathy, depression |
| Posterior Cingulum: | Linked with cognitive functions; attention, spatial skills, memory |
| Uncinate fasciculus: | - Connects the inferior part of the frontal lobe with the anterior temporal lobe |
| 2 segments of uncinate fasciculus: | -Upper segment: unites gyri on the frontal lobe with the cortex of the more lateral temporal gyri -Lower Segment: connects the orbital surface of the frontal lobe with the medial surface of the temporal lobe |
| Arcuate Fasciculus: | 3 segments: -long direct segment -anterior indirect segment -posterior indirect segment |
| Long direct segment function: | connects posterior superior temporal gyrus (Wernicke’s) to inferior frontal gyrus (Broca’s) |
| Anterior, indirect segment: | connects inferior frontal gyrus (Broca’s) to inferior parietal lobule |
| Posterior, indirect segment: | connects inferior parietal lobule to posterior superior temporal gyrus (Wernicke’s) |
| Functional asymmetry of arcuate fasciculus: | Left AF: language & verbal memory damage: conduction aphasia (difficulty to repeat) Right AF: visuospatial language |
| Projection fibers: | Consist of fibers uniting the cortex with lower parts of the brain and spinal cord. Fibers are arranged in a radiating pattern called he corona radiata |
| Projection Fibers/ Corona Radiata: | There are afferent fibers conveying impulses to cerebral cortex and efferent fibers carrying impulses away from the cortex |
| Internal Capsule: | consists of projection fibers connecting cortex of cerebrum to any lower centers |
| Parts of Internal Capsule: | 1. Anterior limb 2. Posterior limb 3. Genu 4. Retrolentiform part 5. Sublentiform part |
| Corticospinal Tract: | Is the direct voluntary motor pathway which originates from the motor areas of the cerebral cortex. Its axons can be found in the medullary pyramids. Also called as pyramidal tract. |
| Lateral corticospinal tract: | 90% of corticospinal fibers cross in the pyramidal decussation to for the lateral corticospinal tract in the spinal cord |
| Anterior corticospinal tract: | Fibers that do not cross in the pyramidal decussation form the anterior corticospinal tract |
| Corticopontine Tract: | Its fibers are involved in a circuit tat involves the cerebellum The information is relayed to the cerebellum via the middle cerebellar peduncle.Corticobulbar Tract |
| Corticobulbar Tract: | Originates in the ventral precentral gyrus, and passes through the internal capsule with the corticospinal tract. Gives off branches to the motor nuclei of trigeminal, facial, vagus, hypoglossal and spinal accessory nerves. |
| Corticostriate Tract: | Made fom afferent fibers from many parts of the cerebral cortex that descend to the caudate nucleus & putamen in the corpus striatum. Topical organization in frontal , parietal, occipital and temporal lobes. |
| Afferent fibers: | Thalamocortical fibers: from thalamus to all parts of the cerebral cortex |
| Ventricular System: | 4 interconnected cavities within which flows the cerebrospinal fluid: 2 lateral ventricles, the 3rd ventricle and the 4th ventricle |
| How are ventricles connected? | Through specific openings: 1. Foramen of Monro: lateral with 3rd ventricle 2. Cerebral Aqueduct (Sylvius): 3rd w 4th ventricle 3. Foramen of Lushka & Magendie: 4th ventricle w subarachnoid space |
| CSF pathway: | Exits the 4th ventricle & flows through the subarachnoid space over and through the brain and spinal cord & eventually reabsorbed into the venous system through arachnoid granulations |
| Choroid Plexus: | Produces CSF Mostly is formed in the LATERAL VENTRICLES |
| Functions of CSF: | 1. Protects the CNS from trauma 2. Mechanical support for the brain 3. Assists in the regulation of the contents of the skull 4. Removes metabolites from the CNS 5. Serves as a pathway for pineal secretions to reach the pituitary gland |
| Absorption of CSF into dural venous sinuses: | By arachnoid villi: form arachnoid granulations |
| CSF pressure | >>> pressure in the sinus |
| Hydrocephalus | Due to the increased production of CSF OR decreased reabsorption which leads to accumulation of CSG in the brain |
| Divisions of the lateral ventricles: | -the anterior horn -the body -the atrium or trigone -the inferior or temporal horn -the posterior or occipital horn |
| Central canal: | Opens superiorly into the fourth ventricle |
| Meninges: | Are the membranes covering the brain and the spinal cord: 3 membranes: 1. The dura mater 2. The arachnoid mater 3. The pia mater |
| Dura Mater: | Strong: Consists of: 1. Falx cerebri 2. Falx cerebelli 3. Tentorium cerebelli 4. Diaphragma sella |
| Arachnoid Mater: | Spidery Holds Blood vessels Separated from dura by the subdural space Separated from pia by the subarachnoid space witch is filled with CSF |
| Pia Mater: | - It extends out over the cranial nerves & fuses with their epineurium - Forms the TELA CHOROIDAE which fuse with ependyma to form the choroid plexus which forms the CSF |
| Pituitary Gland: | Also known as hypophysis: Endocrine gland which rests within the sella turcica -Anterior pituitary: regulates stress, growth, reproduction -intermediate lobe: secretes & synthesizes melanocyte stimulating hormone -posterior pituitary: hypothalamus |
| Pituitary Adenomas: | Slow-growing benign tumors of the pituitary gland; they can be divided in secreting and non-secreting Can cause bitemporal hemianopsia due to compression of the optic chiasm |
| Dural Nerve Supply | Branches of the trigeminal, vagus, first three cervical nerves and branches from the sympathetic system pass to the dura |
| Headaches: | Stretching of dura |
| Dural arterial supply: | internal carotid maxillary ascending pharyngeal occipital vertebral VIP: middle meningeal artery (MMA) |
| Epidural hematoma is produced from... | an injury of the middle meningeal artery |
| Dural venous drainage: | Meningeal veins |
| Subdural hematoma is caused from... | A rupture of the superior cerebral veins |
| Subarachnoid Cisterns: | -Openings in the subarachnoid spaces -Contain neurovascular contents |
| Suprasellar means: | Superior to the pituitary |
| Interpenduncular means: | Between the cerebral peduncles and Liliequist membrane |
| Liliequist membrane is... | arachnoid membrane that seperates the supasellar, interpeduncular and ambient cistern |
| Perimesencephalic means: | Around the mesencephalon. This connects the suprasellar with the quadrigeminal cistern |
| Quadrigeminal is: | Inferior of the splenium of the corpus callosuu and posterior of the pineal |
| 2 types of synapses: | Electrical & Chemical |
| Excitatory postsynaptic potential is... | Local depolarization of the postsynaptic membrane |
| Inhibitory postsynaptic potential is... | Local hyperpolarization of the postsynaptic membrane |
| Formation of a new action potential in a neuron usually requires ......... | The summation of many excitatory postsynaptic potentials in a short period of time. |
| In a presynaptic neuron we find... | Neurotransmitters |
| In a postsynaptic neuron we find.... | Receptors |
| Receptors can be.. | Ionotropic Metabotropic |
| Main excitatory neurotransmitter: | Glutamic acid |
| Main inhibitory neurotransmitter: | GABA |
| Resting potential of cellular membrane is.. | In most neurons −70 mV |
| Graded Potential is.. | Change in the transmembrane potential that does not travel far from the area of stimulation because it decreases as it goes. It is called graded because it can have several different values. |
| Local membrane potentials are .... | Graded Potentials |
| Action potential of cellular membrane is... | around –55 mV |
| Gastrulation: | the process of establishing all three germ layers (3rd week). |
| Neurulation: | -(3-4th week) formation and closure of the neural tube -commences with the formation of the neural plate under the inducive influence of the notochord. -completions of neurulation with closure of the caudal neuropore (27th day). |
| Organogenesis: | early embryonic period (3th to 8th week) |
| Notochord formation (week 3) | Primitive node of the primitive streak -> Notochordal process -> Notochord |
| Formation of the neural plate and neural tube: | -Lateral edges rise to form the neural folds. -Neural folds rise further and fuse in the midline to form the neural tube. - Fusion is delayed at cephalic and caudal ends of the neural tube - The neural tube contains amniotic fluid. |
| Chordoma: | - incidence: 1/million/year - slowly growing, metastatic neoplasm deriving from remnants of the notochord. -most commonly in the sacral (50%) or base of the skull (35%) - prognosis: 46% 10-year survival |
| Cranium bifidum (“cleft skull”): | ❑ Incomplete formation of the cranial vault usually in the occipital area. ❑ defect of closure of the neural tube |
| Neural crests derive from... | the ectoderm of the neural folds from which they detach and form two longitudinal columns on either sides of the dorsal aspect of the neural tube |
| Neural crest: cephalic part | - The cephalic neural crest secretes FGF-8, which induces the expression of BF-1, which controls the development of the telencephalon. |
| Neural crest: trunk | -Under the influence of BMP-4 &7, which are secreted by the nonneurogenic ectoderm. |
| Hirschprung’s disease (congenital aganglionic megacolon)) | - 1: 5000 births - mutations of ret, EDNRB, neuregulin 3 genes -congenital lack of parasympathetic plexuses of Auerbach and Meissner due to incomplete migration of neural crest cells. |
| Histogenesis: wall of the neural tube | -initially the neuroepithelium forms a pseudostratified cylindrical neuroepithelium - Neuroepithelial cells exhibit intense mitotic activity |
| Histogenesis: proliferation phase | • Ventricular zone • rate: 250,000/min • Daugther cells remain in «postmitotic stage» |
| Histogenesis: ventricular zone | -initial wave of differentiation to neuroblasts which migrate to the intermediate zone. - next wave of differentiation to glioblasts which migrate to the intermediate and marginal zones. |
| Histogenesis: intermediate zone | - Neuroblasts differentiate to neurones - Glioblasts differentiate into astrocytes, oligodendrocytes and oligodendrocyte progenitors cells. - The intermediate zone will become gray matter |
| Histogenesis: marginal zone | -contains the axons of the neurons of the intermediate zone - contains glioblasts from which astrocytes and oligodendrocytes derive. -the marginal zone becomes white matter |
| Migration | • initially just soma and primitive axon (undifferentiated) • start exhibiting excitability and production of neurotransmitters • Radial glia act as guidewires and define the course • they have no dendrites |
| Neural tube: differentiation | Cells exit the proliferation phase,remain in contact to the basement membrane and differentiate to neuroblasts, glioblasts |
| Development of processes - Synaptogenesis | • When migration is complete axons and dendrites acquire their normal, mature shape and size. • Axons bearing growth cones and dendrites form synapses with other neurons • Growth cones follow chemotactic factors to reach their target |
| Synaptogenesis | ❑ Formation of new synapses ❑ Depends on the presence of glial cells and particularly astrocytes ❑ Exchange of chemical signaling between pre and post synaptic cells is essential for the formation of synapses. ❑ Synaptic pruning |
| Death of neuronal cells | • 40-75% of neurons that will form will undergo apoptosis after migration- death is essential • Neurons die due to their inability to compete for chemical signals from their targets • Νeurotrophins |
| Myelination | -Myelination in the spinal cord starts in the 4th month from the ventral (motor) roots. -CNS myelination by oligodendrocytes whereas in the PNS by Schwann cells (← neural crest cells) |
| Alar plates: | dorsolateral thickening of the intermediate zone as a result of proliferation of sensory neuroblasts → dorsal horn of the spinal cord (somatic and visceral afferents) |
| Sulcus limitans: | longitudinal sulcus which separates the alar from the basal plates (persists in the rhomboid fossa but not in the spinal cord). |
| Basal plate: | ventrolateral thickening due to fast proliferation of motor neuroblasts → ventral and lateral horns of the SC (somatic and visceral efferents) |
| Development of the spinal cord | ❑ The intermediate zone contains neuroblasts and forms the gray matter of the spinal cord ❑ The marginal layer contains the processes of the neuroblasts and forms the white matter of the spinal cord. |
| Development of the spinal cord | ❑ dorsally→ intermediate neurons (induced by greater conc of BMP4+7 dorsally) ❑ ventrally→ motor neurons (induced by greater conc of Shh from notochord) |
| Spina bifida | ❑ vertebral arches not forming properly leaving a bone defect usually in the lumbosacral region ❑ due to neural tube defect ❑ unknown aetiology associated with genetic, environmental and nutritional factors (B complex vitamin or folate deficiency). |
| Spina bifida occulta | ❑ incomplete formation of the dorsal part of the vertebrae (spinous process) during embryogenesis, usually in the lumbar column ❑ The spinal cord remains intact – usually asymptomatic but may coexist with tethered cord syndrome ❑ In 10% of births |
| Tethered cord syndrome: | ❑ Tight connective tissue attachment of the spinal cord to the sacral column which hinders the ascend of the spinal cord. ❑ the spinal cord may be found at a lower level than expected for the developmental stage. ❑ part of spina bifida syndrome |
| Spina bifida with meningocoele | ❑ bone defect in the dorsal part of the vertebrae usually in the lumbar column with protrusion through the cleft of meningeal containing CSF but not nervous tissues. ❑ Spinal cord intact – usually asymptomatic |
| Spina bifida with myeloschisis | ❑ bony and skin defect in the lumbosacral region with protrusion of spinal cord and/or cauda equina through the skin. |
| Development of the PNS | Basal plate of the neural tube: ▪ Motor neurons ▪ Preganglionic neurons of the ANS • Neural crest: ▪ Sensory nerves and dorsal root ganglia ▪ Postganglionic neurons of the ANS • Mesoderm: connective tissue of epineurium, perineurium and endoneurium |
| Development of the ANS | ❑ preganglionic sympathetic fibres (lateral spinal horns T1-L3) ← basal plates of neural tube ❑ postganglionic fibers (paravertebral and prevertebral ganglia, chromafin of the adrenal medula) ← neural crest |
| Development of the metencephalon | ❑ the metencephalon extends from the pontine flexure to the isthmus of the rhombencephalon ❑ from the metencephalon develop the pons and the cerebellum ❑ Roof plate from a single layer of ependymal cells covered with vessel rich mesenchyme (pia matter). |
| Basal plate | Somatic efferent column (medial): abducent nucleus, facial nerve nucleus and motor nucleus of the trigeminal nerve |
| Alar plate | Somatic afferent column: (lateral) pontine sensory nucleus of the trigeminal nerve and vestibular and cochlear nuclei VIII |
| Development of the cerebellum | the dorsolateral segments of the alar plates of the metencephalon develop toward the midline and form the rhombic lips which join in the midline to form the cerebellar plate. |
| Development of the mesencephalon | ❑ marginal zone forms cerebral peduncles ❑ lumen: Sylvian aqueduct |
| Development of the diencephalon | ❑ the diencephalon develops from the prosencephalic primitive vesicle ❑ the basal plates of the neural tube at the level of the prosencephalic vesicle degenerate ❑ from the middle part of the prosenchalic vesicle |
| Development of the hypophysis | ❑ Infundibulum + posterior lobe a downward extension of the diencephalon ❑ anterior lobe ← anterior wall of Rathke’s pouch (ectodermal outpocketing of the stomodeum) |
| Development of the hypophysis | ❑ pars tuberalis ← small extension of Rathke’s pouch round the infundibulum. ❑ Intermediate lobe (pars intermedia) ← posterior wall of Rathke’s pouch. |
| Development of the telencephalon: primitive vesicles | ❑ Hemispheres start forming by the 5 th week as a result of a lateral extension of the prosencephalic (forebrain) vesicle. ❑ In the telencephalon the basal (motor) plates degenerate and only the alar (sensory) plates remain. |
| Holoprosencephaly | ❑ failure to split the primitive prosencephlic vesicle into two telencephalic vesicles- (telencephalon with a single ventricle). ❑ agenesis of olfactory bulbs and tracts (arrhinencephaly) |
| Development of the telencephalon | ❑ The walls of the primitive telencephalic vesicles are organized in ventricularintermediate and marginal zones like the rest of the neural tube. ❑ Neuroblasts migrate from the ventricular to the most superficial parts of the hemispheres. |
| Development of the cortex | ❑ Temporary formation of a cortical plate and a subplate zone between the intermediate and marginal zone. ❑ The intermediate zone will form the white matter of the hemispheres ❑ The marginal zone will form the molecular layer of the Cx. |
| Cortical interneurons are generated from the ventral telencephalon | Radial migration from the dorsal region ventricular zone give rise to projection neurons |
| Development of the telencephalon | ❑ In the beginning of the 7 th month the cortical surface is smooth ❑ During the last two months of the cortex develops rapidly forming gyri which are separated by sulci and fissures. |
| Lissencephaly | ❑ Smooth cortical surface due to failure to form gyri and sulci ❑ a defect of neuronal migration ❑ associated with genetic causes, intrauterine infections and poor fetal blood supply |
| Schizencephaly | ❑ cleft between the cortical surface and the lateral ventricles which is lined by ectopic cortex. ❑ the cleft contains CSF and communicates with the lateral ventricles. ❑ manifests with learning difficulties movement disorders, epileptic fits |
| congenital hydrocephalus (obstructive) | Ι. congenital stenosis of the aqueduct ❑ heritable ❑ congenital infections (CMV, rubella, toxoplasma) ΙΙ. Atresia of Luschka and Magendi foramina (Dandy-Walker syndrome) III. Arnold- Chiari dysplasia |
| Basal ganglia | -subcortical structures compromised by neuronal cell bodies -surrounded by white matter -no direct projections to spinal cord |
| Movement planning - execution | prefrontal cortex -> premotor/supplementary motor area -> basal ganglia -> thalamus -> motor cortex -> corticospinal / corticonuclear tracts |
| Basal Ganglia Function: | Motor function; Control of voluntary motor movements Procedural learning Emotion Cognition Reward learning |
| Direct Pathway | Inhibitory projecions to globus pallidus internus cause inhibition of GPi and downregulation of inhibitory activity of the GPi-Thalamic circuit |
| Indirect pathway | Inhibitory projections t globus pallidus externus -> inhibition of GPe -> downregulation of inhibitory activity of GPe on subthalamic nucleus -> upregulation of excitatory signals from subthalamic nucleus to Gpi |
| substantia nigra | acts as an amplifier of movement by modulating both pathways through a common neurotransmitter, dopamine |
| Parkinson's disease | -neurodegenerative disease - movement disorder -progressive degeneration of dopaminergetic neurons in the substantia nigra -direct pathway mainly affected |
| Gracile fasciculus | provides conscious proprioception of the lower limbs and trunk to the brainstem |
| Cuneate fasciculus | transmits fine touch, fine pressure, vibration, and proprioception information from spinal cord |
| Lateral funiculus | transmits the contralateral corticospinal and spinothalamic tracts |
| Area postrema | >> center of vomiting • Hypoglossal triangle (trigone) • Vagal triangle (trigone) |
| Obex | the most inferior point of 4th ventricle → here starts the central canal |
| Hypoglossal trigone | position of underlying hypoglossal nucleus (CN XII) |
| Vagal trigone | position of underlying dorsal motor nucleus of the vagus nerve (CN X) |
| Level of Decussation of Pyramids | • distribution of white & gray matter = similar to cord • central canal • decussation of pyramids (corticospinal fibers) •Anterior column of gray matter – cut off |
| Level of Decussation of Lemnisci | • appearance still similar to spinal cord • nucleus gracilis & nucleus cuneatus increased greatly in size • underneath gracile & cuneate tubercles • central canal • pyramids |
| internal arcuate fibers | emerge from anterior aspects of nuclei gracilis cuneatus The fibers cross-over = decussation of lemnisci |
| inferior olivary nucleus | • belongs to extrapyramidal system • associated with regulation of coordinated voluntary muscle movement |
| vestibular nuclear complex | 4 nuclei: medial, inferior, lateral & superior |
| Cochlear nuclei | 2 nuclei: anterior & posterior |
| Nuclei of Vagus Nerve (X) | dorsal vagal nucleus nucleus tractus solitarius nucleus ambiguus |
| Hypoglossal nucleus | 2 nuclei: anterior & posterior |
| Tectum | Roof of the brainstem: superior colliculi, inferior colliculi: corpus quadrigemina |
| Tegmentum | Anterior cell body-rich areas, floor of brainstem: red nuclei, substantia nigra, reticular formation |
| Anterior Circulation of Willis | v Internal Carotid Artery v Middle Cerebral Artery v Anterior Cerebral Artery |
| Course Internal Carotid Artery (ICA) (1) | • The ICA enters the skull through the carotid canal •Turns 90 degrees anteromedially within the canal to run through the petrous temporal bone • It exits the canal and turn 90 degrees superiorly in the carotid sinus |
| Course Internal Carotid Artery (ICA) (2) | • Turns 90 anteriorly to travel along the roof of the cavernous sinus, where it grooves the body of the sphenoid • Another 90 turn to pass the anterior clinoid process then t divides into the middle and anterior cerebral branches . |
| (ICA) - Segments | 1. cervical segment (C1) 2. petrous (horizontal) segment (C2) 3. lacerum segment (C3) 4. cavernous segment (C4) 5. clinoid segment (C5) 6. ophthalmic (supraclinoid) segment (C6) 7. communicating (terminal) segment (C7) |
| ACA Segments | 1. A1 (horizontal): origin from the ICA to the anterior communicating artery (ACOM) 2. A2 (vertical): from ACOM to the origin of the callosomarginal artery 3. A3 (callosal): distal to the origin of the callosomarginal artery |
| MCA Branches (1) | • M1 medial lenticulostriate penetrating arteries lateral lenticulostriate penetrating arteries anterior temporal artery polar temporal artery • M2 Superior terminal branch Inferior terminal branch |
| MCA Branches (2) | • M3 Sylvian branches • M4 Cortical branches |
| Posterior Circulation of Willis | v Vertebral Arteries v Basilar Artery v Posterior Cerebral Arteries (+ posterior communicating) |
| Vertebral Artery (VA) | •Branch of the subclavian art •Passes – foramen transvesarium C6 -1 •Enters through foramen magnum – perforates the dura & arachnoid mater – enters subarachnoid space •passes medulla oblongata •Lower border of pons – joins opposite side->BASILAR art |
| VA Segments | V1 (preforaminal):origin to transverse foramen of C6 V2 (foraminal):from transverse foramen of C6 to transverse foramen of C2 V3 (atlantic, extradural or extraspinal): from C2 to dura V4 (intradural):from dura to confluence to form basilar art |
| Branches VA | V1: segmental cervical muscular and spinal branches V2: anterior meningeal art, muscular and spinal branches V3: posterior meningeal art V4: anterior and posterior spinal art, perforating branches to medulla, posterior inferior cerebellar art (PICA) |
| Basilar Artery | The basilar art runs cranially in the central groove of the pons towards the midbrain within the pontine cistern It bifurcates at the upper pontine border into the two posterior cerebral arteries |
| Branches BA | v anterior inferior cerebellar artery (AICA) v labyrinthine artery (variable origin; more commonly a branch of AICA) v pontine arteries v superior cerebellar artery (SCA) |
| Vascular Territories | Anterior cerebral artery: ACA has part of the frontal and the parietal lobe and the anterior CC, basal ganglia, internal capsule Anterior Choroideal artery: AChA has part of the hippocampus, the posterior internal capsule and part of the thalamus |
| Vascular Territories | Middle cerebral artery: branches supply the lateral surface of the hemisphere, except for the frontal and the parietal, temporal lobe Lenticulo-striate arteries: lateral LSA' s are deep penetrating arteries of the MCA , vascularize: basal ganglia. |
| Vascular Territories | Posterior Inferior Cerebellar Art:territory is on the inferior occipital surface of the cerebellum and is in equilibrium with the territory of the AICA Superior Cerebellar Art: territory is in the superior and tentorial surface of the cerebellum. |
| Vascular Territories | Branches from vertebral and basilar: These supply the medulla oblongata and the pons |
| Vascular Territories | Post cerebral art:P1 extends from PCA to post. communicating art, contributing to circle of Willis.Post. thalamoperforating arts branch off&supply the midbrain &thalamus.Branches of PCA supply the temporal l.,occipital pole,visual cortex,&splenium of CC |
| Clinical Applications | v Stroke: ◦ Blockage in the artery – cerebral infarction ◦ Carotid artery ◦ Basilar artery ◦ Bleeding within the brain – intracerebral hemorrhage ◦ Aneurysm ◦ AVM ◦ Intracerebral haemorrhage - hypertension |
| Aneurysms | v Definition: weakness in the wall of a cerebral artery causes a localized dilation or ballooning of the blood vessel v Management ü Observation (unruptured) ü Surgery (clipping/bypass) ü Endovascular treatment |
| Characteristics of the cerebral veins | v do not have arterial pattern v thin walled (absence of muscular tissue) v no valves v run in subarachnoid space |
| Superficial Cerebral Veins | • Drain the surface of the cerebral hemisphere (cortex) i. superior cerebral veins ii. middle cerebral veins iii. inferior cerebral veins |
| Deep cerebral veins | v Internal Cerebral Veins v Basal vein of Rosenthal v Great vein of Galen |
| Internal Cerebral Veins | v Union of 3 veins: 1. thalamostriate vein 2. septal vein 3. choroidal vein |
| Basal Vein & v. of Galen | v Deep middle cerebral vein joins the anterior cerebral vein and striate vein to form the basal vein of Rosenthal v Basal vein of Rosenthal, internal cerebral veins and inferior sagittal sinus are joining the great vein of Galen à straightsinus |
| Superior Sagittal Sinus | It resides in base of falx cerebri Receives tributaries from several superior cerebral veins that run deep to arachnoid mater on both hemispheres. Veins pierce the arachnoid & dura as they approach sagittal sinus, where they drain their contents. |
| Inferior Sagittal Sinus | • Along its journey, it receives tributaries that drain from the medial part of the cerebral hemispheres • At the tentorium cerebelli, it drains into the straightsinus |
| Straight Sinus | • Located on the midline and lies within the posterior end of the falx cerebri and the middle of the tentorium cerebelli • Terminates at level of the internal occipital protuberance • The great cerebral vein of Galen drains to the straight sinus |
| Transverse Sinus | • The left and right transverse sinuses travel in the base of the tentorium cerebelli, along the occipital bone • It communicates with the straight sinus, superior sagittal sinus and the occipital sinus at a point called the confluence of sinuses |
| Sigmoid Sinus | •Paired, bilateral, s-shaped set of sinuses that course along the floor of the posterior cranial fossa • They are the terminal parts of the dural venous sinuses that continue from the transverse sinuses at the level of the tentorium cerebelli |
| Hippocampal formation | • At the floor of the temporal horn of the lateral ventricle Consists of the: • Hippocampus (Ammon’s horn) • Dentate gyrus • Endorrhenal cortex of the parahippocampal gyrus • Fimbria |
| Dentate gyrus I | ❖ Thin indented strip of cortex on the upper surface of the parahippocampal gyrus. |
| Dentate gyrus II | ❑ Three-layers archicortical structure with the exception that pyramidal neuronshave been replaced by granular neurons o The principal input pathway of the hippocampal formation |
| Hippocampal formation: internal connections | 1: afferent fibres from sensory association Cx to the entorrhenal Cx 2: perforant pathway 3: DG granular cells project to CA3 4: CA3 pyramidal neurons project to the alveus and to CA1 (Schaffer collaterals) 5: CA1 neurons project to the subiculum |
| Hippocampal formation: internal connections | 6: Alvear pathway 7: Subiculm neurons projecting to the entorrhinal Cx 8: Entorrhinal Cx neurons projecting to the association Cx |
| Hippocampal formation: afferent connections | • From the cingulate gyrus (via the entorhinal Cx.) • From the septal nuclei (fornix) • From the contralateral hippocampus (commissure of the fornix) |
| Hippocampal formation: afferent connections | • From the indusium griseum of the corpus callosum (medial and lateral longitudinal striae) • From the olfactory Cx and sensory association cortex (via the entorhinal Cx) • Mesencephalic reticular formation |
| Hippocampal formation: efferent connections | All efferent connections via the fornix (glutamatergic projection) • To mamillary bodies (hypothalamus) • To ant nuclei of thalamus • To mesencephalic tegmentum • To septal nuclei • To lat preoptic area and ant hypothalamus • To habenular nuclei |
| Fornix | • Arch-shaped white matter tract comprising of commissural and associative fibres • Alveus → fimbria hippocampi → crura fornicis → corpus fornicis-→ anterior columns → mamillary bodies |
| Hippocampal formation: functional role | • Acute emotional response • Recent memory (transformation of recent to long-term memory) • Generation of new neurons and migration toward the olfactory cortex and the rest of the CNS (rostral migratory stream) • Stress reaction |
| Indusium griseum and longitudinal striae | • It lies on top of the corpus callosum. • It condenses to form the lateral and medial longitundinal striae (fibre bundles). • They connect the hippocampus to the cingulate gyrus and the diagonal band of Broca. |
| Amygdala or amygdaloid body or complex | The amygdaloid body consists of several nuclei the most important of which are the: ❖ corticomedial group ❖ Basolateral group ❖ Central group |
| Amygdaloid complex: afferent connections | 1. Ventral posterior nucleus of the thalamus. 2. Lateral and medial geniculate body 3. Brainstem (mesencephalic reticular formation, locus coeruleus) 4. To corticomedial nuclear complex |
| Amygdaloid complex: afferent connections | 5. To basolateral nuclear complex: prefrontal Cx, sensory association Cx, cingulate Cx and the subiculum. 6. Endorrhenal Cx 7. Insula of Reil (emotional response to pain) 8. Nucleus basalis of Meynert (alertness) |
| corticomedial nuclear complex: | olfactory bulb, septal nuclei, bed nucleus of the stria terminalis, intralaminar nuclei thalami, hypothalamic nuclei, nucleus tractus solitarius |
| Amygdaloid complex: efferent connections I | 1. From corticomedial nuclear complex (stria terminalis): 1. olfactory bulb and cortex 2. hypothalamic nuclei 3. MD nucleus thalami, 4. Corpus striatum 5. Bed nucleus of the stria terminals 6. Nucleus accumbens |
| Amygdaloid complex: efferent connections II | 2. From the basolateral nuclear complex (via stria terminalis and amygdalofugal pathway) to: 1. prefrontal Cx, sensory association Cx, cingulate Cx, endorrhenal cx, 2. ventral striatum and thalamus 3. Nucleus basalis of Meinert 4. Septal area |
| Amygdaloid complex: efferent connections III | 3. Opposite amygdaloid complex→ stria terminalis→ anterior commissure→ opposite AC |
| Amygdaloid complex: efferent connections IV | 4. From Central nuclear group projections to brainstem 1. periaquaductal gray m. 2. Locus coeruleus 3. Dorsal nucleus vagi 4. Medial parabranchial nucleus (pneumotaxic respiratory centre) 5. Nucleus Accumbens 6. Bed nucleus of stria terminalis |
| Amygdaloid complex: functional role | ❑ Emotional responses: ❑ fear, anger, stress ❑ Aggressive or defensive behaviour ❑ Determines which memories will be stored as memories and in which brain area depending on their significance. ❑ Role in defense and survival. |
| Stria terminalis | • White matter tract (associative fibres) emerging from the (corticomedial group) posterior end of the amygdaloid complex. • Forms part of the floor of the corpus of the lateral ventricles. |
| Bed nucleus of the stria terminalis (BST) | ❖ A cluster of about 12 nuclei surrounding the caudal part of the ant commissure, deep in the cerebral hemi. ❖ The anterior group (BSTant) seems to specialize in energy balance ❖ Posterior group (BSTpost) may contribute more to reproduction and defense. |
| Cingulate gyrus | • Posterior part: alertness , emotional response to external stimuli, response to painful stimuli. • Ant part: cognitive functions, movement control, decisionmaking, empathy • Afferents via the neocortex and thalamus and projects to the endorhinal Cx. |
| Nucleus accumbens (NAcc) | • Part of the ventral striatum (at the junction between putamen and caudate). • Electrical stimulation causes pleasure, reward response (augmentation of dopaminergic transmission). |
| Nucleus accumbens and amygdala | Connections and neurotransmitters involved in craving and stress |
| Septal area and septal nuclei | • Located below the anterior end of the corpus callosum and anterior to the anterior commissure • Septal nuclei associated with: – Sexual behaviour – Aggressive behaviour – Emotional behaviour – Modification of memory and attention |
| Septal nuclear connections | • Afferent connections (A): 1. amygdala (→ diagonal band of Broca crossing the anterior perforate substance) 2. Hippocampus (fornix) 3. Paraventricular + anterior and lateral hypothalamus 4. Olfactory bulb 5. Mesencephalon |
| Septal nuclear connections | Efferent connections (B): 1.Habenular nucleus (stria medullaris) 2.Dentate gyrus ( fornix) 3.Medial dorsal nucleus thalami (MD) (stria medullaris thalami (glutaminergic) 4. mesencephalic tegmentum 5.Anterior+ medial ventral and lateral hypothalamus |
| Septal area: functional role | ❑ Antipsychotics may be acting by modifying the dopaminergic input to the septal area ❑ Euphoric feelings associated with drug abuse may be due to the modification of the ascending pathway from the mesencephalon to the septal area. |
| Medial forebrain bundle (MFB) | • The principal afferent and efferent pathway containing ascending and descending fibres passing through the hypothalamus. • Connects the hypothalamus to the olfactory cx, orbitofrontal cx and mesencephalon. |
| Limbic system: Papez circuit (1930) | ❑ Connection between cognitive (cortical)+emotional experience + expression) ❑ Originally proposed as the anatomical substrate of emotional expression |
| Kluver-Bucy syndrome | ❑ In case of bilateral temporal lobe lesions in monkeys 1. Hypersexuality 2. Hyperorality: place objects in their mouth to explore them 3. personality changes: aggression or passivity 4. psychic blindness or visual agnosia: do not recognize danger |
| Wernicke-Korsakoff syndrome | ❑ Lesions of the mammillary bodies, thalamus, fornix, superior colliculi and hypothalamus due to lack of thiamin (vitamin B1) usually associated with alcoholism or intractable vomiting |
| Wernicke-Korsakoff syndrome | ❑ Manifestations: ❑ Wernicke encephalopathy: ophthalmolplegia+ ataxia+ delirium (may be reversible) ❑ Korsakoff psychosis (dementia): memory disturbance, confabulation (irreversible) |
| Explicit memory / Declarative memory: | – conscious intentional recollection of facts, experiences and concepts that can be reported verbally. – Encoded by the hippocampus and endorrhenal cortex but are stored in other parts of the CNS. |
| Implicit memory/Procedural memory: | – Unconscious memory/knowledge of cognitive (knowing how to read) and motor skills (e.g. knowing how to tie shoe-laces or ride a bike). – Encoded and probably stored in the cerebellum and the corpus striatum. |
| Alzheimer’s disease | ❑ Degeneration of the hippocampus, amygdaloid complex and anterior nucleus thalami ❑ Failure of recent memory ❑ Disinhibition |
| Diencephalon | ü thalamus ü hypothalamus ü subthalamus ü epithalamus |
| Thalamus | o Large, paired structure of gray matter o Lies immediately lateral to 3rd ventricle o It is positioned deep to the posterior half of the insula and the lower part of the pre- and postcentral gyri and adjacent part of the superior temporal gyrus |
| Thalamus – massa intermedia | o The Thalami meet and fuse in the midline forming a bridge of gray matter across the 3rd ventricle à interthalamic adhesion or massa intermedia |
| Pulvinar of the Thalamus | o Pulvinar: the prominent posterior part of the thalamus o It presents in the wall of three different supratentorial compartments: 1. the posterolateral part of the pulvinar forms the lateral half of the anterior wall of the atrium |
| Arterial Supply | o PCA: perforators, thalamogeniculate, posterior choroidal o PCOM: thalamoperforators o Anterior Choroidal (ICA branch) |
| Function | o relay station for all sensory pathways o recognition of pain, thermal & tactile sensations o Influences voluntary movements through basal ganglia & cerebellum – cerebral Cx– cortico-nuclear / cortico-spinal pathways o Maintains alertness |
| Thalamus – Internal structure | o Thalamus consists mainly of grey matter (nuclei) o Superior surface is covered by a thin layer of white matter called stratum zonal |
| Thalamic nuclei | v Thalamus (dorsal) o Anterior nuclei: part of limbic system o Medial nuclei: decision making, memory and behavior o Lateral nuclei: : part of limbic system |
| Clinical Significance | o Lesions of the thalamus can cause: v Sensory loss (light touch, discrimination, muscle joint sense) v Thalamic Pain (thalamic overreaction) v Motor Dysfunctions v Changes in consciousness and alertness |
| Thalamic Syndromes | Posterolateral thalamic syndrome v sensory disorders / speech v Dejerine-Roussy syndrome (pain) o Medial thalamic syndrome v disorders of consciousness, neglect, amnesia o Anterolateral thalamic syndrome v paresis, ataxia, motor incoordination |
| Hypothalamus | o The hypothalamus is located below the thalamus and above the midbrain - diamond shaped o Rostral: it extends from the anterior commissure, lamina terminalis, and optic chiasm o Caudal: it extends to the periaqueductal gray matter of the midbrain |
| Hypothalamic nuclei | Anterior (or chiasmatic) region: between the lamina terminalis and the anterior infundibular recess o Median (or tuberal) region: proceeds to the anterior column of the fornix o Posterior region: stretches to the caudal mammillary bodies |
| Hypothalamus – physiology overview | the nuclei of the hypothalamus act as a conduit between the nervous and endocrine systems via the pituitary gland o Function: regulates homeostatic functions such as hunger, thirst, body temperature, and circadian rhythms |
| Subthalamus | o Continuous caudally to midbrain o Contains the subthalamic nucleus o Function: role in motor control and is interconnected with the basal ganglia o DBS to treat patients with Parkinson |
| Epithalamus | o The epithalamus is the dorsal posterior segment of the diencephalon o It includes: ü the habenula and the habenular commissure ü the stria medullaris ü the pineal body |
| Epithalamus | o A main function of the epithalamus is the secretion of melatonin by the pineal gland o It is connected with both the limbic system and the basal ganglia |
| Circadian rhythm: | : The “internal body clock” that regulates the 24-hour cycle of biological processes |
| Pineal gland: | A small, pinecone-shaped endocrine gland found near the center of the brain that produces melatonin |
| Melatonin | A hormone related to serotonin that is secreted by the pineal gland; it is involved in the sleep/wake and reproductive cycles |
| anatomy of cerebellum | - 2 large hemispheres which are connected w the vermis in the midline - surface is divided by numerous curve transverse fissures giving to it a laminated appearance - horizontal fissure extends separating a superior and inferior surface |
| anatomy of cerebellum | primary fissure divides the cerebellum into an anterior and posterior lobe |
| Arbor vitae | - white matter of cerebellum - brings sensory and motor info to and from cerebellum |
| Deep cerebellar nuclei | ❑ There are 4 pairs of nuclei in the deep white matter of the cerebellum. ❖ Fastigial n. ❖ Emboliform n. ❖ Globose n. ❖ Dentate n. ❑ major projection pathway of the cerebellum. |
| Cerebellar peduncles | Connect cerebellum to the brainstem and contain afferent and efferent pathways |
| Superior cerebellar peduncle | ❑ mostly efferent fibres to thalamus and nucleus ruber ❑ afferent fibres from ventral spinocerebellar tract |
| Middle cerebellar peduncle | ❑ Fibres from contralateral pontine nuclei (fronto-ponto-cerebellar tract) |
| Inferior cerebellar peduncle | ❑ dorsal spinocerebellar and cuneocerebellar tracts ❑ Olivocerebellar tract (climbing fibres) ❑ Efferents and afferents to vestibular nuclei |
| Cerebellar afferents | ❑ All afferents are excitatory and terminate at the cerebellar Cx ❑ Afferents also provide collaterals terminating on neurons of the deep cerebellar nuclei. |
| Cerebellar afferents | 1. Climbing fibres 2. Mossy fibres 3. Serotoninergic projections from the Locus Coeruleus to the cerebellar cortex 4. Noradrenergic projections from the Raphe nuclei to the cerebellar cortex |
| Cerebellar efferents (primarily from deep nuclei) | 1. Dentato-rubro—thalamocortical pathway 2. Projection to vestibular nuclei bilaterally via the inf. Peduncle 3. Projection to RF contralaterally via the inf. peduncle |
| Purkinje cells | ❑ dendrites fan-out in a single plane in the molecular layer where they receive excitatory synapses from T-parallel fibres from granule cells ❑ Project to ipsilateral deep cerebellar nuclei ❑ inhibitory (Gaba-ergic) |
| Granule cells | ❑ In the granule cell layer ❑ Axons to molecular layer where they bifurcate and form T parallel fibres ❑ The only excitatory cells in the cerebellar cortex (Glutamatergic) |
| Stellate cells | ❑ receive excitatory synapses from T-parallel fibres from granule cells ❑ form inhibitory synapses on Purkinje cells |
| Golgi cells | ❑ receive excitatory synapses from T-parallel fibres from granule cells ❑ Form inhibitory synapses on granule cells |
| Basket cells | ❑ receive excitatory synapses from T-parallel fibres from granule cells ❑ Form inhibitory synapses on Purkinje cells |
| Cerebellar blood supply | ❑ Superior cerebellar artery (SCA) ( basilar A) ❑ Anterior inferior cerebellar artery (AICA) ( basilar A) ❑ Posterior inferior cerebellar artery (PICA) (Vertebral A): ❑ Venous drainage: great cerebral vein of Galen or adjacent venous sinuses. |
| Characteristics of cerebellum | Consists of 3 distinct functional systems: ❑ Archeocerebellum ❑ Paleocerebellum ❑ Neocerebellum |
| Cerebellar ataxia: | the sum of all the signs and symptoms of cerebellar malfunction (Gordon Holmes) |
| Anatomical organization I | ❑ Extends along the whole length of the midline tegmentum to the hypothalamus and thalamus superiorly and to the spinal cord inferiorly. |
| Anatomical organization II | The RF can be divided into three columns based on their histological and functional organization. ❑ Median ❑ Medial ❑ Lateral |
| Anatomical organization IV | Median column ❑ Consists of the Raphe nuclei of the midbrain, pons and medulla ❑ Medium-size neurons with long ascending and descending projections ❑ Contain serotoninergic neurons |
| Anatomical organization V | Lateral column ❑ Lateral part of the tegmentum ❑ Consists of small neurons ❑ Contains may nuclei such as: the locus coeruleus, the pedunculopontine nucleus, the parvocellular nucleus and lateral parabranchial nucleus. |
| Anatomical organization VI | Locus coeruleus ❑ Group of bluish (noradrenergic) neurons in the lateral part of the pontine and dorsal midbrain tegmentum ❑ Role in respiration and REM sleep ❑ Afferent connections from nucleus tracti solitarii Anatomical organization VI |
| Connections of the Reticular Formation: afferents I | 1.Spinal cord sensory spinoreticular fibres mediating all kinds of sensations. 2.Collateral fibres from vestibular and trigeminal nuclei. |
| Connections of the RF: afferents I | 3.Collaterals from the medial lemniscus carrying acoustic impulses 4.Collaterals from the tectoreticular fasciculus bear visual stimuli (the RF becomes activated by auditory> vestibular >>> and to a lesser extent by visual stimuli). |
| Connections of the RF: afferents II | 5. Cerebral cortex (precentral and postcentral gyrus) 6. Cerebellar Cx (cerebello-reticular tract) 7. Red nucleus (rubroreticular tract) 8. Corpus striatum 9. Limbic system (Medial forebrain bundle) 10. hypothalamus |
| Connections of the RF: efferents I | 1. Spinal cord (reticulospinal tract)- axons that modulate: ❑ medial pontine reticulospinal tract: controls extensor muscles ❑ lateral medullary reticulospinal tract: inhibits axial extensor muscles and controls autonomic functions of breathing. |
| Connections of the RF: efferents I | ❑ spinal reflex activity- modulate muscle tone ❑ spinal autonomic activity (lateral horns Sy. and Parasy neurons) |
| Connections of the RF: efferents II | 2. Brainstem (reticulobulbar tract) to the motor nuclei of the brainstem 3. Cerebellar Cx ( mossy fibres) 4. Substantia nigra and nucleus ruber ( pedunculopontine nucleus) |
| Connections of the RF: efferents III | 5. reticulothalamic fasciculus: projection to the thalamus ❑ truncothalamus (=reticular, medial and intralaminar nuclei) ❑ project in turn to most of the cortex determining the activity of cortical neurons. 6. Neocortex |
| Connections of the RF: efferents III | 7. Limbic system ( medial forebrain bundle) 8. Hypothalamus and septal area. 9. Quadrigeminal nuclei |
| Functional role of the RF I: level of consciousness | 1. Midbrain 2. diencephalon 3. Bilateral lesion of cerebral cortex 4. Diffuse process |
| Functional role of the RF II | Sensory system • RF structures project to the dorsal horns of the spinal cord and modulate all sensory input (GATING THEORY) • Raphe nuclei 5HT • Pontine paragigantocellular RF NA |
| Functional role of the RF III | Movements of the eyeballs ❑ Mesencephalic RF: centre for vertical gaze ❑ Pontine RF: centre for horizontal gaze |
| Functional role of the RF IV | • Sleep-wake cycle regulated by RF in hypothalamus and brainstem. • Not a passive turning-off of neuronal activity • Raphe system (serotoninergic) may be responsible for bringing on sleep |
| Functional role of the RF IV | • Locus coeruleus (noradrenergic) activation may be responsible for REM sleep • Neurons in the pontine RF begin to discharge just before the onset of sleep. • Lesions of the pons produce a state of hyper-alertness and much reduced sleep. |
| Functional role of the RF V | Autonomic control ❑ In the RF, the CVC/RC, urination centre, deglutition, sneezing, coughing and other autonomic centres are found ❑ Descending fibers from the hypothalamus to the lumbosacral autonomic neurons pass in the reticulospinal tracts. |
| Locus coeruleus: | (lateral pontine tegmentum) contains synaptic centres of respiratory control ❑ Neurons responsible for inspiration found in lower medulla (4) and neurons responsible for expiration found posterolaterally to the inspiratory centre (5). |
| Cardiovascular centre: | ❑ Heart rate and blood pressure are controlled by the Dorsal nucleus vagi and the nucleus tracti solitarii. |
| Cardiovascular centre: | ❑ The CVC suppression centre consists of reticular nuclei located in the lower medulla and the CVC excitatory centre consists of reticular neurons of the other parts of the brainstem RF. |
| Functional role of the RF VIII | Arousal-attention ❑ Afferent input to the RF conducted by collaterals from the somatosensory, auditory, visual, and visceral sensory systems. ❑ The RF projects to the non-specific thalamic nuclei and these in turn project to the cortex |
| Functional role of the RF VIII | ❑ All specific sensory systems (unimodal) transmit to the RF that is multimodal (nonspecific)→ INTEGRATION→ projection to many cortical areas→ regulation of level of excitability of Cx→ alertness |
| Functional role of the RF IX | Arousal-attention cont. ❑ Every new stimulus added leads to increased alertness. ❑ Behavioural arousal is independent of the modality of stimulation and is associated by increases in activity over much of the cortex. |
| Functional role of the RF X | Control of neuroendocrine functions ❑ Stimulation of certain RF areas has been shown to regulate via hypothalamic RFactors or RIFactors the secretions of adenohypophysis |
| Functional role of the RF X | Control of biological rhythms ❑ Mediated via connections to suprachiasmatic nucleus of the hypothalamus |
| Tethered cord syndrome | ❑ Tight connective tissue attachment of the spinal cord to the sacral column which hinders the ascend of the spinal cord. ❑ The spinal cord may be found at a lower level than expected ❑ may be part of spina bifida syndrome |
| cervical enlargement | begins roughly at C4 and extends to T1 site of motor neurons that innervate the upper limbs |
| lumbar enlargement | extends from T11 through the L1 site that innervates lower limbs |
| central canal | tube that pierces the gray commissure of the spinal cord |
| anterior median fissure and posterior median sulcus | deep clefts partially separating left and right halves |
| gray matter | neuron cell bdies, dendrites, axons. divided into horns: posterior dorsal horn anterior dorsal horn lateral horn |
| white matter | myelinated axons divided into three columns ventral dorsal lateral |
| commissures | connections between left and right hales gray mater with white matter in the central canal |
| substatia gelatinosa | situated at apex of posterior gay column throughout length of spinal cord receives afferent fibers concerned with pain, temperature and touch axons cross the opposite side in white commissure and ascend in lat |
| nucleus proprius | The nucleus proprius receives crude touch and pressure sensation from ipsilateral incoming central processes of dorsal root ganglion cells. -axons cross in white commissure and ascend in the anterior white matter as ant. spinothalamic tract |
| clark's dorsal nucleus | -at based of posterior gray column in T and L regons cells associated with proprioceptive impulses |
| medial group | -ventromedial & dorsomedial nuclei found in all segments of spinal cord -vip for innervating the skeletal muscles of the neck & trunk |
| lateral group | -present in cervical & lumbosacral segments of the cord & responsible for innervating the skeletal muscles of the limbs |
| central group | phrenic nucleus C3-C5 efferents supplying the diaphragm |
| reticulospinal tracts | originates at reticular formation of brain: maintain balance |
| rubrospinal tracts | originate in red nucleus of midbrain: control flexor muscles |
| tectospinal tracts | originate in superior coliculi and mediate head and eye movements towards visual targets |
| Arterial supply | Anterior spinal artery (single) ❑ formed by two branches one from each vertebral artery ❑ Runs along the anterior surface of the cervical cord and narrows a bit at the T4 level ❑ below the T4 level is called anterior medial spinal artery |
| Arterial supply | Posterior spinal arteries (paired) ❑ Branches of the vertebral arteries ❑ Branch to form the posterolateral arterial plexus ❑ Supply the dorsal white matter tracts and dorsal horns |
| Arterial supply | Radicular arteries ❑ most intercostal arteries (branches of the aorta) provide segmental radicular arteries that supply the cord from T1 to L1 |
| Adamkewicz artery (Arteria Radicularis Magna) | ❑ The largest radicular artery ❑ Enters the cord between T8 and L4 ❑ Occlusion is rare but leads to major neurological deficits (paraplegia, sensory loss in the lower limbs, bladder incontinence) |
| Arterial supply | Radicular arteries in the lumbosacral region ❑ branches of the: ❑ lumbar artery, ❑ iliolumbar artery, ❑ lateral sacral artery |
| Arterial supply | Arterial corona ❑ radicular arteries branches accompany the dorsal and ventral roots ❑ These branches unite with the posterior and anterior spinal arteries to form irregular ring arteries(ARTERIAL CORONA) with vertical connections |
| Arterial supply | Sulcal arteries ❑ Sulcal arteries branch from the arterial corona at most levels ❑ In the cervical and thoracic cord they run in the ventral sulcus ❑ They supply the ventral and lateral cord columns |
| Endoneurium | connective tissue sheath covering each nerve fibre |
| Perineurium | connective tissue covering nerve fibres fascicles and containing vessels |
| Epineurium | connective tissue covering of nerves |
| Motor nerves (efferent): | ❑ Formed by the axons of cranial nerve motor nuclei or alpha and gamma spinal motoneurons |
| Sensory nerves (afferent): | ❑ Formed by the peripheral process of pseudo-unipolar and bipolar ganglion cells e.g. sural nerve (S1, S2). |
| Mixed nerves: | ❑ composed of both sensory and motor fibres ❑ All spinal nerves and most cranial and peripheral nerves are mixed. |
| Ventral roots: | axons of α and γmotoneurons |
| Dorsal roots: | central processes of the pseudo-unipolar cells of the dorsal root ganglion |
| Dorsal root ganglion (DRG) | associated with the dorsal root |
| Dorsal branches (rami) | innervate the paravertebral muscles and the overlying skin |
| Ventral branches (rami) | form the plexuses (except in the case of the thoracic ventral rami) |
| Cervical plexus | Formed by the anterior rami of C1 to C4 in the muscles of the posterior cervical triangle |
| Cervical plexus Branches: | ❑ Anastomotic branches to the vagus, accessory, hypoglossal nerves and sympathetic chain ❑ Cutaneous sensory branches to neck and occipital area of the head ❑ Motor branches to neck muscles ❑ Phrenic nerve (C3-5): innervation of the diaphragm |
| sensory cranial nerves | from afferent nerve fibers bringing sensations to the brain -I olfactory nerve -II optic nerve -VIII vestibulocochlear nerve |
| motor cranial nerves | -III Oculomotor nerve -IV trochlear nerve -VI abducens nerve -XI accessory nerve -XII hypoglossal nerve |
| mixed cranial nerves | -V Trigeminal -VII facial nerve -IX glossopharyngeal nerve -X vagus nerve |
| Trigeminal nerve V | 3 major divisions -opthalmic V1 -maxillary V2 -mandibular V3 |
| Trigeminal neuralgia | - sudden shock like pain that lasts for a few seconds |
| Facial nerve VII | -sThe facial nerve innervates all the muscles of facial expression via zygomatic, temporal, buccal, marginal mandibular and cervical branches |
| chorda tympani | special viceral afferent fibers to taste buds on anterior 2/3 of tongue general visceral efferent fibers relayed in submandibular ganglion |
| Complications of facial nerve palsy | ❑Exposure keratitis ❑Hemifacial spasm ❑Incomplete recovery (10-15%) ❑Recurrence (same or opposite side) (7%) ❑ aberrant re-innervation- synkinesias |
| Hemifacial spasm | characterized by irregular, involuntary muscle contractions on one side of the face |
| Glossopharyngeal nerve IX | -exit he brain through retroolivary sulcus -leaves skull via jugular foramen Branches: -lingual -pharyngeal -tympanic -carotid synus |
| Vagus nerve X | branches: -reccurent laryngeal nerve -bronchial and esophageal branches -cervical cardiac branches |
| ANS neuronal pathway | sequential two- neuron efferent pathway -The preganglionic will begin at the outflow and will cross a synapse at the postganglionic, or second neuron’s cell body. -The postganglionic neuron will then create a synapse at the target organ |
| Sympathetic system: two - neuron pathway | • Spinal cord sympathetic neurons are called presynaptic (or preganglionic) neurons, while peripheral sympathetic neurons are called postsynaptic (or postganglionic) neurons. |
| preganglionic sympathetic neurons | At synapses within the sympathetic ganglia, preganglionic sympathetic neurons release acetylcholine, a chemical messenger that binds and activates nicotinic acetylcholine receptors on postganglionic neurons. |
| postganglionic neurons | • In response to this stimulus, postganglionic neurons principally release noradrenaline (norepinephrine). • Prolonged activation can elicit the release of adrenaline from the adrenal medulla. |
| Adrenal medulla: | neuroendocrine tissue composed of postganglionic sympathetic nervous system (SNS) neurons called chromaffin cells -extension of the autonomic nervous system |
| Sympathetic ganglia | located just ventral and lateral to the spinal cord. • Preganglionic nerves from the spinal cord create a synapse at one end of the chain ganglia and the postganglionic fiber extends to an effector, typically a visceral organ, in the thoracic cavity. |
| pairs of sympathetic ganglia | • There are usually 21 or 23 pairs of sympathetic ganglia: 3 in the cervical region, 12 in the thoracic region, 4 in the lumbar region, 4 in the sacral region and a single, unpaired ganglion lying in front of the coccyx called the ganglion impar. |
| Cardiac Plexus | • The cardiac plexus is situated at the base of the heart. • It is formed by the superior cardiac branch of the left sympathetic trunk and the lower superior cervical cardiac branch of the left vagus nerve. |
| Esophageal Plexus | • The esophageal plexus is formed by nerve fibers from two sources: the branches of the vagus nerve and the visceral branches of the sympathetic trunk. ---considered thoracic autonomic plexus |
| Pulmonary Plexuses | • The pulmonary plexus is an autonomic plexus formed from pulmonary branches of vagus nerve and the sympathetic trunk. It supplies the bronchial tree and the visceral pleura. |
| Abdominal aortic plexus | • It is formed by branches derived from the celiac plexus and ganglia, and receives filaments from some of the lumbar ganglia. It is situated on the sides and front of the aorta, between the origins of the superior and inferior mesenteric arteries. |
| Superior and inferior Hypogastric Plexus | • The superior hypogastric plexus is a plexus of nerves situated on the vertebral bodies below the bifurcation of the abdominal aorta. • The inferior hypogastric plexus is a plexus of nerves that supplies the viscera of the pelvic cavity. |
| Sympathetic Nervous System | • “fight-or-flight response” or sympatho-adrenal response • “activates the secretion of adrenaline (epinephrine) and, to a lesser extent, noradrenaline (norepinephrine) |
| The Fight-or-Flight Response in detail | • Acceleration of heart and lung action. -digestion slows down or stops. • Constriction of blood vessels in many parts of the body. • Dilation of blood vessels for muscles. • Inhibition of the lacrimal gland and salivation. • Dilation of pupil |
| The Fight-or-Flight Response in detail | • Inhibits digestion • Blood flow to skeletal muscles and the lungs is enhanced • Dilates bronchioles of the lung, which allows for greater alveolar oxygen exchange • Increases heart rate and the contractility of cardiac cells |
| Parasympathetic system | • Preganglionic fibers are long and synapse with short postganglionic fibers on or near the target viscera • Both preganglionic and postganglionic fibers produce Ach • “Rest& digest” division |
| The cranial nerve fibers involved in Parasympathetic system are | • CN III – lens & pupil • CN VII – lacrimal glands, submandibular & submaxillary glands (salivary) • CN IX – parotid gland (salivary) • CN X – viscera of thorax & abdomen • Sacral nerves – innervate the kidneys, colon & sex organs |
| Parasympathetic nerve supply arises through three primary areas: | A. cranial nerves in the cranium, namely the preganglionic parasympathetic nerves (CN III, CN VII and CN IX) usually arise from specific nuclei in the CNS B. The vagus nerve (X) C. The pelvic splanchnic efferent preganglionic nerve cell bodies |
| Parasympathetic effects | • Heart: decreases rate • Lung: constricts bronchioles • Salivary glands: increases production of fluid • Stomach: increases motility • Pupil: constricts • Sweat glands: reduces secretions |
| • Sympathetic Division (Thoracolumbar) | - cell bodies located in lateral gray horns of thoracic & lumbar regions of spinal cord • ACh is released at preganglionic axon terminal • NE or adrenalin is released at the postganglionic axon - is more widespread and more intense and longer response |
| • Parasympathetic Division (Craniosacral) - | cell bodies found in cranial & sacral regions of the cord • ACh is released at both synapses * Effect: inhibitory/excitatory depending on receptors on effectors - a more controlled reaction with local effect and shorter duration |
| ANS neuronal pathway and pain | • General visceral afferent sensations are mostly unconscious, visceral motor reflex sensations from hollow organs and glands are transmitted to the CNS |
| Autonomic reflexes | The short reflex involves the direct stimulation of a postganglionic fiber by the sensory neuron The long reflex involves integration in the spinal cord or brain. |
| Imaging Methods for Studying Connections in Human Brain | • TDI Tractography • Diffusion tensor imaging: exploits the orientation of electron spin in order to create the WM pathways • Functional MRI - indirect (depicting areas of brain activation during certain tasks) |
| I. Hippocampal Circuitry | • Hippocampal formation: role in memory, spatial navigation and control of attention • Inputs: from entorhinal cortex (information from other association areas through peripheral cortex) • Outputs: to fornix and back to entorhinal cortex |
| Limbic System | Major nuclei: • septal nuclei • Amygdala • parts of the hypothalamus • parts of the brain stem reticular formation. |
| Amygdala | • Fear: stimulation of hippocampus and amygdala • Anger • Addiction • Pleasure • Phobias |
| Tracts of limbic system | Major fiber tracts: • Fornix • Mammillothalamic tract • Stria terminalis |
| Limbic system functions | • Provides a bridge between: • Endocrine • Visceral • Emotional • voluntary |
| Limbic system functions | Homeostasis Olfaction Memory Emotion Control of endocrine system Appetite and eating habits Autonomic control of digestive, respiratory and cardiovascular functions Reward and pleasure Addictions |
| Central Visual Pathways | After the optic chiasm decussation the fibers either • Terminate in the lateral geniculate body (LGB) of the thalamus, or • terminate in thesuperior colliculus (tectal area) and in pretectal areas. |
| Basal Ganglia Circuitry-function | • Modulation of movement -initiate movement -terminate movement • Role in cognition and learning • Role in emotional control • Motor loop • Executive loop • Limbic loop • Eye movement loop |
| Descending tracts-Pyramidal tracts | –originate in cerebral cortex, carrying motor fibres to the spinal cord and brain stem. VIP for the voluntary control of the musculature of the body and face. Corticospinal tracts –muscles of the body Corticobulbar tracts –muscles of the head and neck |
| Descending tracts- Extrapyramidal tracts | –originate in the brain stem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion |
| Premotor area (motor association area): | complex coordinated movements, such as setting the body in certain posture to perform a specific task. |
| Supplementary cortex: | planning, programming motor sequences & *Bimanual activity |
| Extrapyramidal tracts | 1. vestibulospinal tracts(no decussation, ipsilateral innervation) 2. reticulospinal tracts (no decussation, ipsilateral innervation) 3. rubrospinal tracts (decussate, contralateral innervation) 4. tectospinal tracts (decussate, contralateral innerv) |
| Corticospinal tract (pyramidal) | Fibers descend through the corona radiata internal capsule |
| Corticobulbar tracts (pyramidal) | descend through the genu of the internal capsule Projects to the: 1. nucleus ruber 2. Reticular formation 3. Crossed and uncrossed fibers to the cranial nerve motor nuclei 4. Pontine nuclei |
| vestibulospinal tracts (exrapyramidal) - medial | originate from the medial vestibular nucleus and descend both crossed and uncrossed in the Medial Longitudinal Fasciculus to reach the upper cervical cord. control reflex head movement inresponse to stimulation from semicircular canals (rotation). |
| vestibulospinal tracts (exrapyramidal) - lateral | originates from the lateral vestibular nucleus and descend uncrossed in the lateral funiculus to reach at all levels of the spinal cord.controls antigravity- extensors (neurons responsible for their innervation are in medial position in ventral horns). |
| reticulospinal tracts (exrapyramidal) - lateral | • originates from the medullary reticular formation, which receives input from both descending cortical and ascending spinoreticular fibers • descends partly crossed and partly uncrossed in the lateral funiculus |
| reticulospinal tracts (exrapyramidal) - medial | • originates from the pontine reticular formation, • Fibres descend uncrossed in the ventral funiculus -the primary action is to control posture and muscle tone by acting on alpha and gamma motoneurons. |
| rubrospinal tracts (exrapyramidal) | originates from the nucleus ruber (red nucleus) Fibres cross to the opposite side and descend through the pons and medulla to the spinal cord terminate in the ventral horns Facilitate the activity of flexor muscles |
| tectospinal tracts (exrapyramidal) | • originate from the superior colliculi of the midbrain descend in the ventral funiculus and terminate predominantly in the cervical cord the ventral horns of the cervical cord • control reflex movements in response visual stimuli |
| Ascending pathways according to perception | • Conscious perception spinothalamic system dorsal column- -medial lemniscal system Unconscious perception spinocerebellar spinoolivary spinotectal spinoreticular |
| Mechanosensors | • Pacinian corpuscles (vibration and pressure sensation) • Meissner’ s corpuscles (light touch) • Merkel’s discs (pressure receptors) • Ruffini’ s corpuscules (stretch and pressure of skin) |
| Mechanosensors | • nociceptors (noxious stimuli) • Golgi tendon organs (proprioception) • joint receptors • muscle spindles (stretch receptors) |
| Epicritic sensibility Medial Lemniscus | • Distinguish the vibration • Discriminative touch, such as surface texture, space between two spots • Perceive and recognize the form of an object in the absence of visual and auditory information (stereognosis) |
| Dorsal columnLemniscal system | • two point discrimination (fine touch, fine pressure - MC) • pressure (deep receptors - PC) • vibration (PC) • conscious proprioception (MS) (Aβ mechanoreceptors, conscious) |
| Sensitivity homunculus | • Somatotopic projection: Face and hands occupy a major part of the sensory area |
| Spinothalamic tracts | • Protopathic sensibility pain, temperature, and crude touch |
| Ventral spinocerebellar tracts | • Fibers of the ventral spinocerebellar tract decussate, ascend on the contralateral side and enter the cerebellum through the superior cerebellar peduncle • Some axons then recross within the cerebellar white matter |
| Syndrome Brown- Sequard | -Hemi section of the SC at level T10 •ipsilateral loss of proprioception, touch, and vibration sense below the lesion due to damage to the ascending dorsal columns |
| Syndrome Brown- Sequard | •contralateral loss of pain and temperature sensation 2 to 3 levels below the level of the lesion due to damage to the ascending lateral spinothalamic tract |
| Syndrome Brown- Sequard | •ipsilateral loss of motor and sensory function just at the level of the injured segments due to direct damage to ventral and dorsal grey matter |
| Anterior cord syndrome | Complete motor paralysis below the level of the lesion due to interruption of the corticospinal tract Bilateral loss of pain, temperature and light touch below the level of the lesion Autonomic dysfunction |
| Central cord syndrome | Bilateral loss of pain, temperature and light touch and pressure sensations below the level of the lesion with characteristic sacralsparing disproportionately greater motor impairment in upper compared to lower extremities |
| Sensory CNs | •I, II, VIII •Carry axons of sensory neurons •Special sensory nerves – smelling, seeing, hearing |
| Motor CNs | •III, IV, VI, XI, XII •Contain only axons of motor neurons |
| Mixed CNs | • V, VII, IX, X •Contain axons of both sensory & motor neurons |
| Ciliary body | Ciliary muscle + Ciliary epithelium |
| Photoreceptors: | Rods – Cones • Rods: Respond to dim light – no colour sensitivity • Cones: Respond to bright light – colour sensitivity – “high resolution” vision |
| Fovea-macula: | Highest concentration in Cones |
| Optic papilla: | Axons of ganglion cells enter optic nerve –physiological “blind spot” |
| Papillary oedema (or papilloedema or optic disc swelling): | Sign of increased intracranial pressure |
| VisualPathway Lesions | • Optic Chiasm compression / lesion • Bitemporal hemianopia • Meyer’s Loop lesion (or iatrogenic damage) • Contralateral superior quadrianopia • Occipital lobe lesion • Homonymous hemianopia |
| Anton–Babinski syndrome. | Bilateral occipital infarcts: Cortical Blindness. a rare neurological condition related to cortical blindness. The patients deny their blindness and affirm adamantly that they are capable of seeing |
| Visual agnosia: | : impairment in visual object recognition (“Higher level functional impairment). : impairment in visual object recognition (“Higher level functional impairment). |
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