Term
| what is the function of the basal ganglia structures? |
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Definition
| modulation of *upper motor neuronal activity originating in the premotor cortex. the cerebellum also plays a role in this modulation. |
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Term
| what are the structures of the basal ganglia? |
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Definition
| the striatum (gray matter which projects through the internal capsule: caudate nucleus, nucleus accumbens, putamen), globus pallidus (aka: lenticular nucleus - major output structure: external and internal segments), subthalamic nucleus (small interneuronal nucleus), and substantia nigra (parkinson's affects this: compact and reticular parts) |
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Term
| what is most likely to damage the basal ganglia? |
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Definition
| tumor or stroke - it is fairly protected from trauma |
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Term
| what is the final output for muscle movement signals? |
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Definition
| the thalamus (crosstalk from which goes to the cerebral cortex) |
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Term
| what is unique about the subthalamic nucleus? |
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Definition
| most of the interconnecting subnuclear groups have an inhibitory effect, but the subthalamic nucleus has a major excitatory effect. |
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Term
| what is the dividing line between the caudate nucleus and thalamus from the putamen and globus pallidus? |
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Definition
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Term
| what is the "shape" of the midbrain? |
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Definition
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Term
| what creates the dark coloration of the substantia nigra? |
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Definition
| neuromelanin - which starts to disappear in parkinson's (cell loss) |
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Term
| what are the 4 basic circuits of the basal ganglia? |
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Definition
| the motor loop, the cognitive loop, the limbic loop, and the oculomotor loop - all of which begin and end in the cortex. |
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Term
| what characterizes the motor loop of the basal ganglia? |
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Definition
| this involves *learned types of movements. the initial projection is from the somatosensory cortex to the putamen, which then projects to other subnuclear groups - eventually modulating the thalamus and back to the premotor cortex to modulate movement before final output. |
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Term
| what characterizes the cognitive loop of the basal ganglia? |
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Definition
| this involves *motor intentions, as the basal ganglia helps modulate thinking about a movement before carrying it out. |
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Term
| what characterizes the limbic loop of the basal ganglia? |
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Definition
| this involves the *emotional aspects of movement, w/the first major site of integration being the nucleus accumbens. |
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Term
| what characterizes the oculomotor loop of the basal ganglia? |
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Definition
| this involves voluntary saccadic eye movement w/integration from the subthalamic nucleus to the superior colliculus |
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Term
| are the basal ganglia involved in writing? |
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Definition
| yes, writing is more or less a subconscious movement which the basal ganglia is involved with. a stroke here can thus strongly affect a pt's ability to write. |
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Term
| what characterizes the primary input from the cerebral cortex to the basal ganglia? |
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Definition
| the primary input from the cerebral cortex to the basal ganglia is excitatory and uses the NT glutamate (released on caudate nucleus, putamen, subthalamic nucleus, and the nucleus accumbens). |
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Term
| what characterizes the principle output from the basal ganglia to the cerebral cortex? |
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Definition
| the principle output from the basal ganglia to the cerebral cortex is from the globus pallidus internal segment and substantia nigra reticular region using the inhibitory NT GABA directed at the thalamus. the thalamus itself secretes the NT glutamate (excitatory) directed at the cerebral cortex. |
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Term
| what characterizes the excitatory interconnections within the basal ganglia? |
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Definition
| the putamen receives excitatory neurostimulation from the cerebral cortex and thalamus (glutamate). the putamen then has inhibitory neurotransmission on the globus pallidus (which then sends inhibitory signals to the subthalamic nucleus), substantia nigra, and subthalamic nucleus (GABA). the subthalamic nucleus then has excitatory neurotransmission back to the globus pallidus. the substantia nigra has excitatory and inhibitory neurotransmission back onto the putamen. |
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Term
| what is the basic outline of the basal ganglia's influence on the thalamus and cerebral cortex? |
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Definition
| either the putamen/striatum inhibits the globus pallidus's inhibition of the thalamus (leads to more cerebral cortex motor output) or the subthalamic nucleus sends excitatory signals to the globus pallidus, encouraging its inhibition of the thalamus (leads to less excitatory signaling from the thalamus to the cerebral cortex, and thus less motor output from the cerebral cortex). |
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Term
| what effects do the disorders of the basal ganglia include? |
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Definition
| slowed/diminished movements, involuntary movements, and generalized alterations in muscle tone |
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Term
| what characterizes parkinson's disease? |
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Definition
| the basal ganglia in parkinson's inhibit the cerebral motor cortex to the point of insufficient muscle activation. this initially is due to depigmentation of the substantia nigra (loss of neuromelanin) and subsequent loss of the dopaminergic receptors on the striatum. the main effect is overinhibition of the thalamus = pill rolling, tremors, muscle rigidity, impairment of postural reflexes, bradykinesia, and hypokinesia. the limbic system's output through the thalamus is also inhibited = dementia/lack of expression. |
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Term
| what tx has been developed for parkinson's? |
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Definition
| deep brain stimulation (pacemaker for the brain) which electrically stimulates the thalamus, subthalamus and globus pallidus (restores excitation/inhibition to the thalamus). this does not destroy brain tissue and has been proven to be successful in early stages of the disease. |
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Term
| what characterizes huntington's chorea and hemiballism? |
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Definition
| the basal ganglia allow do not inhibit the cerebral motor cortex enough = excess muscle activation = involuntary muscle movement. |
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Term
| what is huntington's chorea specifically? |
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Definition
| this is fatal, presents between 30-50 y/o, and is genetic (chr 4). initially the *caudate nucleus is decreased as well as the *putamen which leads to rapid, involuntary movements of the face/tongue/limbs as well as some dementia and personality changes. on a film, the size of the lateral ventricles can tell you if the caudate nucleus is still normal size/functional - b/c the caudate nucleus should compress the lateral ventricles and in a huntington's pt, this does not occur. |
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Term
| what is hemibalism specifically? |
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Definition
| this is due to a lesion (usually a stroke in the PCA) in the *contralateral subthalamic nuclei, which usually inhibits the globus pallidus's inhibition of the thalamus - however w/the loss of the subthalamic nuclei, the thalamus no longer dampens its excitatory neurotransmissions to the cerebral motor cortex = wild flailing movements of the arm and leg. |
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Term
| what characterizes the cerebellum? |
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Definition
| it is often called the "little brain" as it is the largest structure in the posterior fossa and makes up 10% of the brain's total weight. it is located behind the brainstem at the level of the pons and is attached by the superior, middle, and inferior peduncles. its functions include: coordination of voluntary movements (basal ganglia are more subconscious), equilibrium, muscle tone, postural control, and cognitive functions (procedural memory like riding a bike etc). |
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Term
| what are the important structures of the cerebellum? |
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Definition
| the anterior lobe which is divided by the primary fissure from the posterior lobe. the nodulus (part of the vermis) which is divided from the anterior portion of the posterior lobe by the posterolateral fissure. there is a horizontal fissure in the posterior portion of the posterior lobe. the tonsils are found on the inferior portion of the posterior lobe (can herniate into foramen magnum). the flocculus are found lateral to each nodulus. the vermis is the midline ridge on the dorsal and ventral surface between the L and R halves of the cerebellum. |
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Term
| what are the cerebellar functional lobes? |
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Definition
| the vestibulocerebellum/flocculonodular lobe: balance and gait. the spinocerebellum (midline+posterior hemispheres): coordination of limb musculature adjustment and comparison between intended and actual movements. cerebrocerebellum (lateral cerebellar hemispheres): coordination of voluntary motor activities and motor planning |
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Term
| what are the deep cerebellar nuclei? |
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Definition
| the fastigial nucleus (under vermis: postural adjustments and eye movement), interposed nucleus (composed of emboliform/globulose nucleus, under medial hemisphere: adjusting limb movements), and dentate nucleus (under lateral hemisphere: planning initiation and control of voluntary movements) |
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Term
| what is the cellular organization of the cerebellum? |
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Definition
| the major neuron in the cerebellum is the purkinje cell (like pyramid cell in cerebrum). there are 3 layers of the cerebellar cortex which start w/the outermost *molecular layer (axons+dendrites from purkinje cells and parallel fibers from the granular cells). then the *purkinje layer (composed of purkinje cells). then the innermost *granular cell layer (granular cells which send out unmyelinated parallel fibers and interneurons). there are 2 afferent/input fibers: climbing fiber (from contralateral inferior olivary nucleus to synapse on purkinje dendrite) and mossy fiber (from brainstem/spinal cord nuclei to synapse on granule cell dendrite) |
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Term
| what are the folia? arbor of vitea? |
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Definition
| folia: the cortical ridges on the cerebellar surface. arbor of vitea: white matter. |
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Term
| what is the flow of information in the cerebellum? |
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Definition
| input synapses in the cerebellar cortex, which then projects signaling to the deep cerebellar nuclei, which then projects to output targets (brainstem/thalamus). NTs used in the cerebellum are glutamate (excitatory) and GABA (inhibitory). |
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Term
| what is the synaptic organization of the basic cerebellar circuit? |
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Definition
| the purkinje cell (main cerebellar fiber) is inhibitory (GABA) on the deep cerebellar nuclei; a relationship which is modulated by interneurons (mossy/climbing/parallel fibers). the deep cerebellar nuclei send excitatory (glutamate) signals to the brainstem/thalamus when not completely dampened by the purkinje cells (end result similar to basal ganglia = modulation of the thalamus). there is also a slight amount of inhibitory (GABA) signals sent from the deep cerebellar nuclei to the inferior olivary nucleus. |
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Term
| what are the nuclei associated w/cerebellar function? |
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Definition
| in the brainstem: pontine nuclei, vestibular nuclei, and inferior olivary nucleus. in the spinal cord: clark's nucleus (C8-L2/3). |
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Term
| what characterizes the cerebellar peduncles? |
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Definition
| the superior peduncles send efferent signals from the deep cerebellar nuclei to the red thalamus/thalamus and brain stem (some of which *decussates at the level of the midbrain to the brain stem, but all of which decussates on the way to the thalamus). the middle cerebellar peduncles bring signals from the pontine nuclei to the cerebellum (afferent from premotor/somatosensory cortex and adjacent parts of parietal lobe -> decussates at the level of the midbrain). the inferior peduncles send afferent information from the spinal cord and brain stem (somatosensory from body/head) to the cerebellum (does not decussate, except for signals from the inferior olivary nucleus). |
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Term
| what are the major fiber tract inputs to the cerebellar cortex? |
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Definition
| the pontocerebellar pathway, the posterior spinocerebellar pathway, and olivocerebellar pathway |
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Term
| what is the pontocerebellar pathway? |
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Definition
| the pontocerebellar pathway projects from the pontine nuclei and contralaterally projects through the middle cerebellar peduncle to the cerebellar cortex (anterior/posterior lobes). this pathway controls planned motor activities such as walking and motor commands. |
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Term
| what is the posterior spinocerebellar cerebellar pathway? |
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Definition
| this originates in the clark's nucleus of the spinal cord, projects ipsilaterally through the inferior cerebellar peduncle and terminates in the ipsilateral vermis/intermediate zone. the posterior spinocerebellar cerebellar pathway is involved w/proprioceptive information. |
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Term
| what is the olivocerebellar pathway? |
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Definition
| the olivocerebellar pathway originates in the inferior/accessory olivary nuclei, projects contralaterally though the inferior cerebellar peduncle and terminates in the contralateral cerebellar hemisphere. the olivocerebellar pathway is involved w/motor coordination and motor "learning" (riding a bike etc). |
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Term
| what are the major deep cerebellar nuclei associated w/output from the cerebellum? |
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Definition
| the dentate nucleus, the interposed nucleus, and fastigial nucleus |
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Term
| what is the pathway and function associated w/the cerebellar dentate nucleus? |
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Definition
| the dentate nucleus is located in the lateral cerebellar hemisphere, projects contralaterally through the superior cerebellar peduncle and terminates in the red nucleus/thalamus (*ventral anterior and lateral regions specifically*). function: planning, initiation, and control of voluntary movements (modulated by inhibitory purkinje signals). |
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Term
| what is the pathway and function associated w/the cerebellar interposed nucleus? |
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Definition
| the interposed nucleus originates medial to the dentate nucleus and projects contralaterally through 1) the superior cerebellar peduncle to the the red nucleus/thalamus(*ventral anterior and lateral regions specifically*) and 2) through the descending limb of the superior peduncle to RAS/anterior horn of the spinal cord. function: comparator function and limb position adjustment. |
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Term
| what is the pathway and function associated w/the cerebellar fastigial nucleus? |
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Definition
| the fastigial nucleus originates medial to the interposed nucleus and projects through the inferior cerebellar peduncle to the 1) contralateral vestibular nuclei and 2) ipsilateral to the reticular formation. function: balance and gait control. |
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Term
| what is cerebellar ataxia? |
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Definition
| the most common form of ataxia - due to a dysfunction either w/in the cerebellum or in its afferent/efferent pathways |
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Term
| what is (cerebellar) posterior lobe syndrome? |
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Definition
| this results in an "intention tremor" where pts experience a loss of coordination of voluntary movement, decreased muscle tone, and to+fro movements perpendicular to the intended direction of movement. (cerebellar) posterior lobe syndrome may result from CVA, trauma, or degenerative disease. (non/less noticeable when pt is stationary) |
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Term
| what is (cerebellar) anterior lobe syndrome? |
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Definition
| this results in loss of gait stability and clumsy movement of the lower limbs and may be due to malnutrition accompanied by chronic alcoholism. |
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Term
| what is flocculonodular lobe syndrome? |
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Definition
| this results in truncal ataxia, disturbances of balance, and lack of coordination in the paraxial muscles (= walk in wide base w/trunk swaying). this may be due to a lesion of the floccular lobe/posterior vermis (medulloblastoma or stroke) |
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Term
| what is the major output from the basal ganglia? |
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Definition
| inhibitory (from the globus pallidus internus) |
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Term
| what is the major output from the cerebellum? |
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Definition
| excitatory (from the deep cerebellar nuclei) |
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