5. Basal Ganglia

caudate and putamen - neostriatum

continuous ventrally and anteriorly in the forebrain, but then the internal capsule penetrates and separates them more posteriorly striated by fibre bundles of internal capsule which pass through it caudate and putamen which are separated during development by the internal capsule input from most areas of the cerebral cortex and from the substantia nigra pars compacta Send most of their output to the globus pallidus, comprised of external and internal segments, and substantia nigra of midbrain project to the eGP (inhibitory) and SubNig

organisation of fibres in the internal capsule

corticobulbar fibres (to the medulla, controlling head and neck muscles) and the corticospinal fibres lie close to the genu ("bend") Afferent thalamocortical fibres runs around the lateral ventricle then posteriorly

gene of the internal capsule

corticospinal fibres to the head, neck & part of the upper limb are located most affected by striate artery blockage

pyramidal disorders

damage to the internal capsule or motor cortex

extra pyramidal disorders

damage to the striatum

Huntington's chorea

death of cells in the neostriatum, spontaneous unnecessary and unwanted complex limb movements are produced. Huntingtin protein causes damage

Symptoms of parkinson's disease

degeneration of dopaminergic neurons of the substantia nigra pars compacta slowness in the execution of movement (bradykinesia), rigidity and tremor excessive inhibition in the thalamus

What are the two major divisions of the substantia nigra

dopaminergic- pars compacta (innervates neostriatum) non-dopaminergic (pars reticulata)

deep brain stimulation

electrical stimulation of deep brain nuclei applied through surgically implanted electrode Deep nuclei usually targeted include the subthalamic nucleus, globus pallidus interna, ventral anterior thalamus, and pedunculopontine nucleus disrupt pathological patterns of neural activity

corticopontine tract

fibres from PMC and SMA go to the pontine nuclei, which in turn project to the cerebellum

Where is the caudate nucleus located

follows the course of the lateral ventricle located in the wall of the anterior horn, body and inferior horn of the lateral ventricle grey matter - tadpole shaped large head in lateral wall of the middle part of the lateral ventricle narrow flat tail curling with the lateral ventricle into the roof of the inferior horn

What are functionally linked to the striatum and globus pallidus

nuclei of the diencephalon: thalamus, subthalamic nuclei nucleus of the midbrain: Substantia nigra

Endoscopic third ventriculostomy

placing a camera (known as an endoscope) first through the frontal lobe into the lateral ventricle, then through the foramen of Munro into the third ventricle makes a hole ('ventriculostomy') in the floor of the third ventricle to allow CSF to pass from the ventricle into the subarachnoid space and then onwards to be absorbed prevents hydrocephalus and raised ICP e.g. tumour obstructing aqueduct of Sylvius

substantia nigra pars compacta

recieves input from caudate and putamen nuclei within the basal nuclei that release dopamine to modulate the function of the striatum; part of the motor pathway dark pigmented area in the midbrain next to the cerebral peduncles In a cross section through the midbrain, where myelin has been stained (Figure 5.4), it appears as a lighter area.

Where does the subthalamic nucleus lie

similar cross-sectional location to the SN but at the junction of the midbrain and diencephalon - difficult to see recieves input from external segments of the globus pallidus project to internal globus pallidus = regulates the output of the entire striatum given inputs and outputs

indirect pathway > inhibits movement

striatum inhibits eGP •EGP neurons inhibit the subthalamic nucleus •Increased activity > disinhibition of subthalamic nucleus •STN are excitatory to the iGP •increase activity in internal globus pallidus, increasing inhibition in the thalamus and preventing movement

Blood supply of the striatum and internal capsule

supplied by small arteries originating from the middle and anterior cerebral arteries, are effectively end-arteries. Striate arteries from MCA site for cerebrovascular accident

treatments for Parkinson's disease

L-DOPA, pallidotomy of iGP deep brain stimulation of ST nucleus (inhibits it) reducing internal globus pallidus output or excitation by subthalamic nuclei (surgical interventions)

nucleus accumbens

Located where the caudate and putamen are joined in the ventral striatum - anterior-ventral Involved in reward

basal ganglia

a set of subcortical structures that directs intentional movements and have cognitive functions forebrain and midbrain structures: -neostraiatum (caudate nucleus and putamen) -globus pallidus outputs relay in thalamus (as does outputs from cerebellum)

Dopamine

activates the inhibitory direct pathway to the internal globus pallidus via D1 receptors > disinhibition of the thalamus > movement suppresses the inhibitory projections to external globus pallidus (part of the indirect pathway) via D2 receptors.

Where does input to the caudate and putamen come from

all areas of cerebral cortex prominent projections: prefrontal -> caudate sensorimotor ->putamen substantia nigra pars compacta (dopaminergic)

globus pallidus

become visibles medial to the putamen more posteriorly (as does thalamus, with 3rd ventricle in between) has an internal and external segment input from the neostriatum

basal ganglia pathways

caudate and putamen(striatum) receive input from most areas of the cerebral cortex and SN pars compacta striatum sends inhibitory projections to globus pallidus internal segment (diret pathways) inhibitory projections to the globus pallidus external segment, removes inhibition off the subthalamic nucleus subthalamic nucleus sends excitatory input to the globus pallidus internal segment Globus pallidus internal segment sends inhibitory input to the thalamus inhibiting information flow via the thalamus to the cerebral cortex

Origin and destination of efferent corticopontine fibres (incl corticospinal)

cerebral cortex (sensorymotor, also premotor, supplementary motor and higher level sensory areas) to pons in turn many neurons in the pontine nuclei project to the cerebellum

caudate nucleus

Always visible laterally to the lateral ventricle in coronal and horizontal section

Parkison's disease

Degeneration of the dopaminergic neurons of the substantia nigra. Much more activity in the indirect pathway. excess inhibition in the external globus pallidus and reduced inhibition in the internal globus pallidus Increased stimulation of the iGP hence excessive thalamic inhibition. overall excess inhibition in the thalamus leading to reduced motor cortex activity and reduced movement

Infarction of internal capsule or striatum

Haemorrhage from the striate branches of the middle cerebral artery, or blockage of them by thrombosis or embolism contralateral hemiparesis or hemiplegia most commonly genu - corticospinal fibres to the head, neck and part of the upper limb are affected

mid horizontal section of the brain

large head of caudate anteriorly

external segment of the globus pallidus

lateral subdivision of the globus pallidus projection to the subthalamic nucleus, which sends a return projection to the internal segment of the globus pallidus

Where is the putamen located

lateral to the internal capsule medial to the insula

putamen

located lateral to the internal capsule and medial to the insula globus pallidus is medial to the putamen

Internal segment of globus pallidus

major output pathway of basal ganglia projects to motor areas of thalamus (ventro-anterior and ventro-lateral) and medial thalamus inhibitory output to the VA and VL and M thalamus.

Is the striatum only involved in motor functions

no projection from basal ganglia to the medial dorsal nucleus of thalamus then prefrontal cortex complex executive functions = cognition

substantia nigra pars reticulata

non-dopaminergic component also recieves input from caudate and putamen outuput for the basal ganglia in control of eye movements

Hemiballismus

unilateral chorea characterized by violent, forceful movements of the proximal muscles caused by lesion of the ST nucleus

What is the ventral striatum

ventral-anterior part of the caudate-putamen that is still jointed contains the nucleus accumbens

hyper direct pathway

•Connections from the motor cortex directly excite the subthalamic nucleus •ST nucleus excites the internal globus pallidus. •Very fast emergeny brake! • Activity in this pathway will abruptly inhibit the thalamus, to stop movement

direct pathway of basal ganglia --> pro movement

•corticostriate fibres activate neurons in the caudate or putamen nuclei (come from cortex) •this inhibits of neurons in globus pallidus •iGP neurons inhibit thalamic neurons, inhibition of iGP disinhibition of the thalamus