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
