Week 6 Content 1

Basal ganglia and cerebellum

Basal ganglia

Collection of five anatomical and functionally related grey matter structures = caudate, putamen, globus pallidus, subthalamic nuclei, substantia nigra

Globus pallidus

Consists of internus and externus sections - GPi and GPe

Substantia nigra

Consists of pars compacta SNpc and pars reticulata SNpr

Blue area

Striatum - caudate and putamen

Yellow area

Globus pallidus externus

Red area

Globus pallidus internus

Green area

Subthalamic nuclei STN

Purple area

Substantia nigra

Functions of BG

Circuits withing basal ganglia that provide insight into function

Four circuits of BG

Goal directed behaviour loops, social behaviour loop, emotion loop, motor loop - all non motor except for motor loop

BG movement control

Regulates desired movements and inhibits undesired movements by sending information to motor cortex via the thalamus

Motor loop

Cortico-basal ganglia-thalamic loop with three pathways = hyperdirect, direct and indirect

Direct pathway function

Allows movements by inhibiting globus pallidus internus and therefore allowing thalamus to activate

Direct pathway sequence

Dopamine from substantia nigra pars compacta and information from motor cortex to striatum, striatum releases GABA to inhibit globus pallidus internus, globus pallidus cannot inhibit thalamus and therefore allows movement

Indirect pathway function

Prevents undesired movements by inhibiting globus pallidus externus and therefore inhibits thalamus

Internal pathway sequence

Dopamine from substantia nigra pars compacta and information from motor cortex to striatum, striatum releases GABA to inhibit globus pallidus externus, allows subthalamic nuclei to release glutamate to globus pallidus internus to inhibit thalamus and therefore, inhibit movement

Dopamine

Fuel of basal ganglia

Dopaminergic producing neurons

Found in SNpc, enhanced action of direct pathway and inhibits action of indirect pathway with net effect of facilitation of movement

Hypokinetic movement disorder

Below normal amount of human movement due to overactive indirect pathway - parkinsons

Hyperkinetic movement disorder

Above normal amount of human movement due to overactive direct pathway - huntingtons

Cerebellar cortex

More regular than cerebral cortex, contains folds, fissures and gyri

First cortical layer of cerebellum

Molecular layer = few neurons, contains axons of granule cells and dendrites of purkinje cells

Second cortical layer of cerebellum

Purkinje cells = single row of huge cells, unique to cerebellum

Third cortical layer of cerebellum

Granular layer = numerous densely packed neurons

Structures of cerebellum

Two large cerebellar hemispheres with three lobes in each = anterior, posterior and flocculonodular

Cerebellum connection to rest of CNS

Connected by passing information via three cerebellar peduncles found on brainstem

First cerebellar peduncle

Superior cerebellar peduncle, located on midbrain, primarily cerebellar efferent fibres via thalamic nuclei to cortex

Second cerebellar peduncle

Middle cerebellar peduncle, located on pons, entirely afferent fibres, information to cerebellum from cerebru

Third cerebellar peduncle

Inferior cerebellar peduncle, located on medulla, afferent fibres from spinal cord and vestibular apparatus, efferent fibres to vestibular nuclei and reticular formation

Blood supply to cerebellum

Basilar artery gives rise to anterior inferior cerebellar artery, superior cerebellar artery and posterior inferior cerebellar artery

Functions of cerebellum

Coordinates human movement, depends on feedback for normal function, critical role in normal motor function, works as comparator

Roles of cerebellum

Maintaining posture and balance via input from vestibular receptors and proprioreceptors, coordination of timing, force, synchronisation of voluntary movement, motor learning

Functional areas of cerebellum 1

Spinocerebellum located in vermal and paravermal sections of cerebellum, has extensive connections with spinal cord

Spinocerebellum input

Movement commands from cortex, activity levels of spinal cord neurons

Spinocerebellum role

Role in making anticipatory, corrective and responsive adjustments or otherwise movement would be uncoordinated

Functional area of cerebellum 2

Vestibulocerebellum, located in flocculonodular lobe

Vestibulocerebellum input

Input from ipsilateral vestibular apparatus and ipsilateral vestibular nuclei in brainstem

Vestibulocerebellum output

Vestibular nuclei and reaches motor neurons via vestibulospinal tracts and tracts coordinating head and eye movement

Functional areas of cerebellum 3

Cerebrocerebellum, located in lateral cerebellar hemispheres, extensive connections with cerebral cortex

Cerebrocerebellum input

Input from cerebral cortex via pontine nucleus

Cerebrocerebellum output

Output from motor and premotor cortex via dentate and motor thalamus

Cerebrocerebellum role

Role in timing movements, planning movements, coordination of voluntary movements - influences corticospinal corticobrainstem and rubrospinal tracts

Cerebellum ataxia

Posture and balance impariments, dysmetria, intention tremor, nystagmus, dysarthria, dysdiadochokinesia, dyssynergia, decomposition of movement

Dyssynergia

Impairment of multijoint movements - movements are not properly sequenced or of proper range or direction

Cerebellar vs somatosensory ataxia

Movement coordination should be compared with eyes open vs eyes closed, cerebellar lesions cause ataxia regardless of use of vision

Vestibulocerebellum dysfunction signs

Unsteadiness, truncal ataxia, nystagmus

Spinocerebellum dysfunction signs

Intention tremor, ataxic gait, dysarthria, dysdiadochokinesia, dysmetria, movement decomposition