Basal Ganglia and Cerebellum Flashcards
Basal Ganglia Roles
multiple roles in the nervous system and include fine-tuning movements, reward functions, cognition, and memory
Basal Ganglia Regions
subcortical regions, including the putamen, caudate, nucleus accumbens, globus pallidus (interna and externa), the subthalamic nucleus, and substantia nigra
Basal Ganglia - other terminologies for regions
striatum: caudate, nucleus accumbens, and putamen
lenticular nucleus: putamen, globus pallidus (has the external and internal segments)
striatum
caudate, nucleus accumbens, and putamen
lenticular nucleus
putamen, globus pallidus (external and internal segments)
Basal ganglia image
Direct Pathway Net Effect
increase (or initiate and maintain) movement
DISINHIBITS the thalamus, which facilitates the EXCITATORY thalamocortical pathway
Direct Pathway - primary neuron receptors
D1 receptors
Direct Pathway
cortex projections travel to the putamen which sends inhibitory projections to the globus pallidus interna (GPi) and substantia nigra reticulatum (SNr). The GPi/SNr, in turn, sends inhibitory outflow to the thalamus
Indirect Pathway - net effect
suppress movement.
activity from indirect pathway excites the GPi/SNr which INHIBITS the thalamocortical pathway
Indirect Pathway primary neuron receptor
D2 receptors
Indirect Pathway
cortex projections travel to the putamen, which sends inhibitory projections to the globus pallidus externa (GPe), where inhibitory projections then extend to the subthalamic nucleus (STN), with the result of disinhibiting the STN. STN, in turn, has excitatory projections to the GPi
Hypokinetic movement disorders
due to REDUCED activity in the DIRECT pathway
hyperkinetic movement disorders
due to REDUCED activity in the INDIRECT pathway
Parkinson’s disease presentation
rigidity, masked facies, and resting pill-rolling tremor due to loss of dopaminergic neurons in the substantia nigra
lesions to substantia nigra
can cause parkinsonism
hemiballismus
rapid violent uncontrolled flailing movements of an extremity (usually the arm), classically associated with lesions of the subthalamic nucleus
lesions of subthalamic nucleus caused by
hemiballismus
loss of dopaminergic neurons in substantia nigra cause
parkinson’s disease
chorea
described as “dancing”
typically more proximal
number of layers in the cerebellar cortex
3
athetosis
described as “snake-like”
usually more distal
layers of the cerebellar cortex
granule layer
Purkinje cell layer
molecular layer
Granular layer
innermost layer containing tightly packed small granule cells that provide excitatory output to other cerebellar cells via parallel fibers
Purkinje layer
the middle layer, containing the cell bodies of Purkinje cells which provide inhibitory input to the deep cerebellar nuclei
Molecular layer
outermost later, contains the dendrites and axons of interneurons (Golgi, basket, and stellate cells)
basket and stellate cells
receive excitatory input from granule cells via parallel fibers and inhibit Purkinje cells
Golgi cells
receive excitatory inputs from granule cell parallel fibers and provide feedback inhibition to granule cells
number of layers in cortical tissue
6
only cells to inhibit deep cerebellar nuclei
Purkinje cells
cerebellum macroscopic anatomy
2 lateral hemispheres and a midline vermis
dorsal to the pons and medulla and separated from the occipital lobe via the tentorium
folia
cerebellar hemispheres’ marked infoldings
atrophy of the folia seen in
patients with chronic alcohol use
mass lesions, swelling, or elevated intracranial pressure causes
cerebellum can herniate through the foramen magnum and compress the brainstem
cerebellar peduncles
connect cerebellum to other brain structures via 3 paired major white matter tracts
superior cerebellar peduncle
mostly EFFERENT/output fibers that relay to the thalamus and spinal cord
middle cerebellar peduncle
contains INPUT from various regions of the cerebral cortex
inferior cerebellar peduncle
contains INPUT from the spinal cord and lower brainstem
deep cerebellar nuclei
located in cerebellar white matter
from lateral to medial: dentate, emboliform, globose, and fastigial nuclei
main output centers of the cerebellum, efferent fibers exiting via superior cerebellar peduncle
cerebellar nuclei mnemonic
“Don’t Eat Greasy Food”
Dentate, Emboliform, Globose, Fastigial
dentate nucleus
largest
dysfunction can lead to hiccups or palatal myoclonus as it is part of Mollaret’s triangle
Mollaret’s triangle
ipsilateral red nucleus
ipsilateral inferior olivary nucleus
contralateral dentate nucleus
emboliform and globose nuclei
sometimes called interposed nuclei
help with initiating movements and keeping movements smooth
fastigial nuclei
receive inputs from the vermis and help with walking and stability while standing
cerebellar lesion symptoms
input/output fibers “double-cross” with a net result of having ipsilateral symtpoms
climbing fibers
originate from the contralateral inferior olivary nucleus
enter cerebellum via inferior and middle cerebellar peduncles
provide excitatory input to the granule and Purkinje cells
mossy fibers
originate from several locations throughout the cortex, vestibular nuclei, and spine
enter cerebellum via inferior and middle cerebellar peduncles
provide excitatory input to the granule and Purkinje cells
vascular supply to the cerebellum
three main arteries: posterior inferior cerebellar artery (PICA), anterior inferior cerebellar artery (AICA), and the superior cerebellar artery (SCA)
cerebellum vascular territories
posterior inferior cerebellar artery (PICA)
arises from the vertebral artery
largest vascular supply to the cerebellum
PICA supplies
lateral medulla and most of the posterior and inferior portions of the cerebellum
PICA strokes
high risk for cerebellar herniation due to large vascular territory
most common cerebellar stroke
PICA stroke presentation
vomiting, vertigo, horizontal ipsilateral nystagmus, and truncal ataxia
if other PICA-supplied structures are affected, can present with lateral medullary syndrome
head impulse test
can help differentiate posterior circulation stroke from peripheral vertigo. a normal head impuse testing in the setting of vertigo, nausea, and vomiting are more suggestive of brainstem insult. peripheral vertigo will have significant lag with corrective saccades with movement in one horizontal direction only
head impulse test peripheral vertigo
significant lag with corrective saccades with movement in one horizontal direction only
head impulse test brainstem insult
stroke from peripheral vertigo. a normal head impuse testing in the setting of vertigo, nausea, and vomiting
anterior inferior cerebellar artery (AICA)
supplies the inferior lateral pons, the middle cerebellar peduncle, and a strip of the anterior cerebellum between the territories of the PICA and SCA
AICA strokes
very rare
vessel occlusion leads to sudden dysmetria and vertigo, and ipsilateral sensorineural hearing loss
labyrinthine/internal acoustic artery
branch of the AICA, which supplies the inner ear
occlusion contributes to hearing loss
superior cerebellar artery (SCA)
supplies the upper lateral pons, superior cerebellar peduncle, and most of the superior half of the cerebellar hemisphere including the deep cerebellar nuclei
SCA stroke
ataxia, nystagmus, and dysarthria
