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Neuroscience Blk 3
| Question | Answer |
|---|---|
| Functionally, what other basal ganglia structure is the substantia nigra's pars reticularis most close to? | medial globus pallidus |
| The major input of basal ganglia comes from what and is received where? | afferent excitatory signals from cerebral cortex; reception area = neostriatum |
| Name 2 places from which the neostriatum receives input that are NOT the cerebral cortex. | 1) pars compacta of substantia nigra (motor) 2) intralaminar nuclei e.g. thalamic centromedian nucleus (non-motor) |
| What neurotransmitter is produced in the pars compacta of substantia nigra? | dopamine |
| Identify the two structures that project mainly to targets outside of the basal ganglia. What do these structures project to? | medial globus pallidus and pars reticularis (both inhibitory) to VA/VL of thalamus |
| What is the course of the ansa lenticularis? | Fibers travel from the medial globus pallidus ventrally beneath the posterior limb of the internal capsule then dorsally towards the ispilateral VA/VL nuclei of the thalamus. |
| What is the course of the lenticular fasciculus? | Fibers arise from the globus pallidus and hop into those in the internal capsule,ultimately coursing towards the VA/VL of thalamus. They join what's known as the thalamic fasciculus (cerebellothalamic fibers) en route. |
| Name all 3 of the pathways terminating in the neostriatum, their NTs and their effects on its neurons. | corticostriate (glutamate, excitatory); thalamostriate (glutamate, excitatory); nigrostriatal from pars compacta (dopamine, mixed excitatory and inhibitory) |
| What 2 cortical regions do NOT likely have significant projections to the neostriatum? | primary visual cortex and auditory cortex (all other cortical areas DO) |
| Name the 2 receptor types characteristic of certain neostriatal neurons and where they project. | D1 to medial GP; D2 to lateral GP (both inhibitory, using GABA as NT) |
| What is the major target of the lateral GP and what is its effect? | subthalamic nucleus (inhibitory) |
| If I were a glutamate molecule being released from a subthalamic nucleus neuron, what would be my destination? | medial GP (excitatory) |
| What effect does the neostriatum have on the substantia nigra? | Both D1 and D2 receptor neurons are inhibitory on SN. |
| With respect to the nigrostriatal pathway, what effect does dopamine have on the neurons with receptor types D1 and D2? | D1 excited and D2 inhibited by dopamine |
| What is the primary NT of the pars reticularis? | GABA (inhibitory) |
| T/F: The substantia nigra and subthalamic nucleus derive from the same embryologic precursor. | False: subthalamic nucleus - diencephalon; substantia nigra - mesencephalon |
| Name the major connection of the subthalamic nucleus, its NT and its effect on that target. | medial GP, (excluively) excitatory, glutamate |
| Identify and explain the circuit process which characterizes the basal ganglia's function. | Disinhibition - intermittently active inhibitory neuron synapses on a tonically inhibitory neuron that, in turn, synapses on an excitatory neuron |
| Which area of the basal ganglia has the final say on outgoing signals to the thalamus? | medial GP |
| Describe the direct motor loop pathway. | The cerebral cortex excites a D1 type neuron in the neostriatum --> this inhibits neurons in the medial GP --> these can no longer inhibit the VA/VL thalamic neurons thus the thalamus is free to excite the cortex at will. |
| Identify the distinguishing feature of the alternate direct and indirect motor loop pathways. | Instead of going through the medial GP, neurons form a circuit through the pars reticulata with the same end effect. |
| What is the net effect of the indirect motor pathway? | decreasing excitatory input on the cerebral cortex from the thalamus |
| Name a few areas of origin with reference to the prefrontal and limbic loops. | frontal cortex, orbital frontal cortex, amygdala and hippocampus |
| When speaking of the non-motor functions of the basal ganglia, to what area of the thalamus do these neurons project? | dorsal medial nucleus of thalamus |
| The dorsal medial nucleus of the thalamus controls cortical areas involved in what? | cognition, memory, emotion and behavior |
| Name 2 connections from the non-motor basal ganglia neurons that are involved in hedonistic and addictive behaviors. | ventral tegmental area and nucleus accumbens |
| Lesions of the contralateral subthalamic nucleus are associated with what type of motor manifestations? | hemiballism - random, involuntary flinging of the limbs contralateral to the subthalamic nucleus of origin |
| Explain the mechanism for the manifestations seen in hemiballism. | subthalamic nucleus is obliterated, excitatory input from it to the medial GP is absent, inhibitory neurons don't exert effect on thalamus, thalamus has free reign to excite motor cortex as it pleases |
| Explain why hemiballism would be seen on the right side if the left subthalamic nucleus is involved. | left subthalamic nucleus --> left thalamus disinhibited --> left motor cortex excited --> right side of body affected |
| What histological finding is indicative of Parkinson disease? | inclusions of Lewy bodies in dopaminergic neurons in the pars compacta |
| Describe the mechanism behind the symptoms seen in idiopathic Parkinsonism. | Loss of D1 receptor neuron excitation and D2 receptor neuron inhibition --> increased activity of inhibitory neurons on GPL, decreased activity of inhibitory neuron on GPM with net effect of inhibiting the thalamus and decreases overall motor activity |
| What is the most striking feature a neuropathologist might see on autopsy of a person who suffered from Huntington disease? | atrophy and apparent loss of neurons of the caudate and putamen |
| Selective death of D2 medium spiny neurons is associated with what pathological condition? | Huntington disease |
| Describe the basal ganglia loop changes seen in Hungington disease. | D2 receptor neurons selectively die and can't inhibit GPL, increased inhibition of subthalamic nucleus, extinction of its excitation on GPM, absence of its inhibition on thalamus = increased motor cortex activation |
| Which component of the neostriatum receives relatively more motor cortical projections? | the putamen |
| Which component of the neostritatum receives relatively more non-motor cortical projections? | the caudate |
Created by:
sirprakes
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