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UKCD Histo Nerve
Test objective answers for nerve
| Question | Answer |
|---|---|
| List the two major divisions of the nervous system and what they comprise. | Central nervous system (CNS - brain and spinal cord); Peripheral nervous system (PNS - cranial/spinal) |
| What is the third division of the nervous system? Its function and its two subdivisions. | Autonomic nervous system (ANS). It controls the activity of smooth and cardiac mm. as well as glands. The ANS is composed of sympathetic and parasympathetic divisions. |
| Differentiate the components of the CNS from the PNS. | CNS : neurons + supporting cells (neuroglia) organized into gray matter (cell bodies located here) and white matter (NO cell bodies, only cell processes); PNS |
| What are the supporting cells of each division of the nervous system? | CNS: neuroglial cells; PNS: Schwann cells, satellite cells, capsule cells. |
| How the cell processes and cell bodies in each are are aggregated? | Cell bodies: CNS- gray matter (nuclei); PNS -ganglia; Cell processes: CNS -white matter (fiber tracts); PNS- nerves. |
| What is the structural/functional unit of nerve tissue? | The neuron. |
| Match up the type of neuron morphology observed in cells that have various functions within the nervous system (i.e. motor, sensory, special sense) | Bipolar neurons - neurons of special sense (sight, smell, etc); multipolar neurons- motor neurons (of spinal cord); pseudounipolar neurons- general sensory neurons (dorsal root ganglia). |
| List the types of synapses as classified on a morphological basis. | axo-axonic; axo-dendritic; axo-somatic. |
| What is a dendritic spine? What occurs here? What do they represent? | A raised projection on the surface of the dendrite. They serve as synapse sites for incoming axons. They increase in number with learning (skills). |
| How do the pre and post-synaptic faces of a typical synapse differ? | The presynaptic face exhibits numerous neurotransmitter vesicles fusing with it. The postsynaptic face is thickened as has no vesicular fusion associated with it. |
| On which side of the synapse would neurotransmitter vesicles be commonly observed? | On the pre-synaptic face. |
| What role do neurotubules (microtubules) play in the axon? | important role in neurotransmitter vesicle transport. They transport the filled vesicles from the cell body (soma) down through the axon to the terminal bouton. They then transmit empty vesicles back up to the Golgi for membrane recycling. |
| What is myelin? What is its function? | Layer upon layer of Schwann cell (PNS) or Oligodendrocyte (CNS) membrane, b/c membrane has large lipid component, functions in insulating the cell processes (mainly axons) so that impulses do not “jump” to adjacent axons, speeds impulse transmission |
| What cell forms myelin in the PNS? in the eNS? | PNS- Schwann cell; CNS- oligodendrocyte. |
| How do Schwann and oligodendrocyte myelinating cells differ in their ability to myelinate? | Schwann cells can myeilnate a single internode of a single axon. Oligodendrocytes myelinate single internodes on as many adjacent axons as the cell has processes. |
| What is neurokeratin? | The proteinaceous skeleton of the membranes involved in forming the meylin sheath. It is visible only after the lipid component is removed. |
| What are clefts of Schmidt-Lanterman? What is their function? Are they found in the eNS? | Defects in myelination of axons in PNS, small blips of Schwann cell membrane,known to be a cytoplasmic continuity b/w inner and outer collars of Schwann cell cytoplasm, help maintain inner aspects of myelin sheath, NOT found in CNS |
| What is/are the function(s) of myelin? | Insulate axon preventing leakage/loss of electrical charge of the membrane potential passing along the axon. It also ensures the membrane capacitance is low ensuring a small change is required to produce a significant voltage difference along the axon. |
| What is an intraperiod line? A major dense line? | An intraperiod line is the fused external aspects of adjacent membranes + the small portion of extracellular matrix stuck between them. A major dense line is the inner (cytioplasmic) surfaces fusing with a remnant of cytoplasm between them. |
| What helps "stick" the membranes of the myelin sheath together in the PNS? the eNS? | CNS Proteolipid protein (PLP) sticks exoplasmic surfaces of oligodendrocyte membrane together in myelin sheath, MBP links cytoplasmic surfaces, PNS PO protein associates w/ MBP form a major dense line |
| Which of the 3 adhesion proteins is common to both the eNS and PNS? | Myelin Basic Protein. |
| How is myelin maintained? | Through extensions of cytoplasm from the parent myelin-forming cells (oligos - CNS; Schwann cells - PNS). |
| Name 4 sites where myelin maintenance is a functional feature interface. | 1. Adjacent to the axon - inner collar; 2. between lamellae - Clefts of Schmidt Lantermann; 3. at the ends of each internode - paranodal areas, and 4. adjacent to the cell body - outer collar. |
| What are nodes of Ran vier? What is their function? | Bare areas of axon found between the termination of one myelinated internode and the start of the adjacent internode. They help speed impulse transmission. |
| Do nodes vary in structure between the PNS and the eNS? | Nodes in the CNS are typically bare, whereas those in the PNS are partially covered by tongues of adjacent Schwann cells. |
| What is the difference in the way a Schwann cell handles a myelinated axon compared to unmyelinated axons in the PNS? | Schwann cells can only myelinate a single internode (region) of a single axon in the PNS. In the unmyelinated state however, they can support a single region of numerous cell processes that they invaginate into their cytoplasm. |
| What is a mesaxon? | The adjacent edges of the Schwann cell that almost come together and touch after invagination of the unmyelinated cell process. |
| Describe how connective tissue separates any nerve into various divisions. | pineurium surrounds an entire nerve; perineurium surrounds fascicles (bundles) of nerve cell processes within the nerve; endoneurium surrounds individual nerve cell processes |
| List the 4 types of supporting cells (neuroglial cells) in the eNS. | oligodendrocytes; astrocytes; microglia; ependyma |
| What is a perivascular foot? | A cytoplasmic footlet of a protoplasmic astrocyte that helps form the blood-brain barrier by surrounding the capillaries in gray matter. |
| What is the blood-brain barrier (BBB)? | A protective mechanism that keep injurious substances away from the cell bodies of neurons in the gray matter. |
| List the components of the BBB from the capillary lumen outward. | 1. cytoplasm of the endothelial cell; 2. basement membrane of the endothelial cell; 3. basement membrane of the astrocyte; 4. cytoplasm of the astrocyte. |
| List in order from superficial to deep, the 3 meninges (wrappings) of the eNS. | 1. dura mater; 2. arachnoid; 3. pia mater. |
| What is the subarachnoid space and what is it filled with? | The space between the underside of the arachnoid meninge and the pia mater that lines the surface of the brain/spinal cord. It is filled with cerebrospinal fluid. |
| How does the organization of white and gray matter differ between the brain and spinal cord? | Brain - gray matter external, white matter internal; spinal cord - white matter external, gray matter internal. |
| What composes white matter? | Neuronal cell process and neuroglial cells. |
| What composes gray matter? | Neuronal cell bodies, neuroglial cells, limited number of neuronal cell processes. |
| What is the distinct difference between white and gray matter? | Neuronal cell bodies ONLY found in gray matter. |
| What is a nucleus in the CNS? | An accumulation of nerve cell bodies that are responsible for a specific function (i.e. smell) |
| What is its corresponding structure in the PNS? | A ganglion. |
| List all the types of supporting cells in the PNS and their function. | Schwann cell - myelinates; capsule cell - forms a supportive capsule around neuronal cell bodies of a ganglion; satellite cells - associated with neuronal cell bodies in a ganglion. |
| How do sensory ganglia differ from autonomic ganglia? | Sensory ganglia distribute a discrete organization (cell bodies in groups; fibers in tracts); autonomic ganglia exhibit a randomly mixing (disorganized arrangement) of these structures. |
| How do sympathetic ganglia differ from parasympathetic ganglia? | Sympathetic ganglia are larger and have a more distinct CT capsule. Parasympathetic ganglia are much smaller (fewer neuron cell bodies within them) and have little or no CT capsule as they are found within the walls of organs. |
| How does scarring in the CNS differ from that in the PNS? | CNS scarring is the result of astrocytic proliferation (glial scarring), whereas in the PNS Schwann cells and fibroblasts participate in forming the scar. |
| What occurs following a severing or crushing along a peripheral nerve? | Wallerian degeneration where the distal portion of the cell process dies, the cell body exhibits swelling and the proximal stump of the severed process sprouts to re-establish contact with the target organ. |
| What is chrornatoloysis? | swelling neuronal cell body in response to distal injury. The Nissl substance is no longer required for production of neurotransmitter substance as the terminal bouton has been severed from the process, so the Nissl substance (masses of rER) breaks down. |
| What cells clean up the dead/dying debris at the injury site? | In the PNS it is Schwann cells as well as other typical C.T. phagocytotic cells (macrophages). In the CNS it is microglia and C.T. cells that invade from the lesioned blood vessels - NOT typically found in the interstital spaces of the CNS. |
| What effect does a nerve lesion have on the effector organ? | The effector organ (typically muscles) atrophies from disuse - non-stimulation. In long-standing cases muscle turns to C.T. and contraction of the limbs occurs. |
| What is the specific function of Schwann cells at the injury site? | Formation of a cell band to guide regenerating neuron cell process outgrowths. |
| What is the function of the multiple neurite outgrowths from the proximal end? | To maximize the potential for one process to find the old myelin sheath and grow through it to re-establish contact (re-innervate) with the effector organ. |
| What roles do the Schwann cells play once the neurites successfully bridge the lesion? | Form the empty myelin tube to guide the growing neurite back to the target organ. |
| How long does this regenerative process take approximately? | About 3 months. |
| What is the morphological appearance of a severed end that does not re-establish contact with its distal portion? | A club-like outgrowth of neurites. |
| What is the appearance of the target organ in this scenario? | It is atrophied (shrunken/reduced in size). |
| Major function of oligodendrocytes. | myelinate and guide developing axons |
| Major function of astrocytes. | fibrous associate preferentially with the nodes in white matter, protoplasmic comprise the blood-brain barrier in gray matter |
| Major function of microglia. | phagocytose debris; ependyma - line ventricles/central canal. |
Created by:
wiechartm
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