what does the term basal ganglia refer to?
- loosely grouped collection of large subcortical nuclear (gray) masses located deep within each cerebral hemisphere
- more specifically to the corpus striatum and 2 related nuclei (subthalamic nucleus and substantia nigra)
- --- nuclei are reciprocally connected w/ and functionally related to the corpus striatum but technically not structual parts of basal ganglia
what is the principle motor role of the basal ganglia?
- (along w/ corticospinal system)
- specifically the corpus striatum and related nuclei
- to control complex patterns of any skilled motor activity
- exp: using scissors, hammering nails, shooting basketballs
does the basal ganglia have a direct path to the spinal cord?
- interacts w/ areas of cerebral cortex that give rise to descending motor pathways through a number of feedback loops
- (connects to the extrapyramidal pathways and influences that output to the cord)
what was the basial ganglia originally called back in 1664 by Thomas Willis?
- corpus striatum
- believed to by the sesnorium commue (by Aristole)
- was thought to receive all sensory info and initiate all motor acts
what part of the basal ganglia is consided the major component of the extrapyramidal motor system?
what are the components of the basal ganglia?
- corpus striatum
- basal forebrain
- subthalamic nucleus
- substantia nigra (not a part of basal ganglia but functionally related)
what are the major functions of the corpus striatum and related nuclei?
- monitoring the progress of movement
- transfer and modification of info from neocortex to motor areas (premotor and supplementary motor areas in particular)
- automatic execution (remembering how to do something - 2nd nature activities)
- modulation of limbic activity and cognititon involving prefrontal cortex
what is the largest component of the basal ganglia?
where is the corpus striatum located?
nuclear complex is deep within each cerebral hemisphere
what are the divisions of the corpus striatum?
- 3 parts
- caudate nucleus
- globus pallidus
- 2 divisons
- neostriatum (claudate & putamen)
- paleostriatum (globus pallidus)
what is the location and physical description of the caudate nucleus?
- part of the corpus striatum
- located medial to internal capsule
- runs along the lateral ventricle (has enlarged head thta bulges into its lateral wall of the frontal horn)
where are the putamen and caudate nucleus in relation to the internal capsule?
separated incompletely by it
what gives the corpus striatum is striated appearance?
what parts of the corpus striatum comprise the neostriatum (aka striatum)
- putamen and caudate nucleus together
- (they are histologically similiar but not homogenous)
what are the two basic types of neurons within the neostriatum?
- (comprised of the caudate nucleus & putamen)
- projection neurons (inhibitory, use GABA)
- interneurons (excitatory, use Ach)
both contain neuropeptides that are co-released w/ their neurotransmitter
what parts of the corpus striatum make up the paleostriatum?
- the globus pallidus - medial to putaman, separated by the external medullary lamina
- has a pale appearance due to numerous mylinated fibers
what is the claustrum?
- part of the basal ganglia
- latin word means fence/barrier
- a thing sheet of gray matter located medial to the insular cortex and overlying the lateral surface of the putamen
what is the function of the claustrum?
- part of the basal ganglia
- functions are obscure
- widespread reciprocal connections w/ sensory (esp visual and somatosensory areas of cerebral cortex)
- receives input from hypothalamus (laterally), thalamus, and locus coeruleus
- NO subcortical projections
what is the amygdaloid nuclear complex?
- phylogenetically oldest part of the basal ganglia
- a component of the olfactory and limbic systems
- has olfactory, visceral, endocrine and behavior functions
- NO role in motor control
what other parts of the brain does the amygdaloid influence?
- hippocampus (learning and memory, limbic system - interal drive)
- hypothalamus (cardiovascular, feeding, thirst)
- and more?
what is the basal forebrain?
- aka substantia innomiata
- part of basal ganglia?
- a mass of gray matter situated ventral to the lentiform nucleus that extends anterolaterally toward the amygdaloid complex
what info does the basal forebrain receive?
- afferent projections from limbic cortex and hypothalamus, nucleus of the diagnonal band and septal area
- more functionally related to basal ganglia than limbic/olfactory system
- similiar to connections of globus pallidus
what nucleus has been implicated in Alzheimer's disease?
what is the substantia nigra?
- not a part of the basal ganglia, but functionally related (w/ reciprocal connections)
- elongated nucleus representing a component of the brainstem
- receives some striatal input that uses GABA and is inhibitory
what are the two components of the substantia nigra?
- pars reticulata (ventral)
- pars compacta (dorsal)
- both have feedback loop w/ thalamus
neurons of the substantia nigra pars reticulata use what as a neurotransmitter?
- project primarily to the neostriatum
- (contain the black pigment neuromelanin which is a product like dopamine produced from tyosine)
neurons of the substantia nigra pars compacta use what as a neurotransmitter?
- project principally to the thalamus and brain stem nuclei
what is the subthalamic nucleus and where is it located?
- one of the main driving forces of basal ganglia
- ventral to thalamus, just medial to internal capsule
what are the connections of the subthalamic nucleus?
- recieves projections from cerebral cortex
- impt reciprocal connections w/ globus pallidus (principle source of afferent in the form of BABAergic axons)
- connections leaving here innervate the globus pallidus and substantia nigra using glutamate.
what occurs when vascular lesions are restricted to the subthalamic nucleus?
results in involuntary movements of a violent nature in the CONTRALATERAL limbs
what are the important connections of the basal ganglia?
- striatal afferents (to the neostriatum)
- striatal efferents (from the neostriatum)
- pallidal afferents (to the globus pallidus)
- pallidal efferents (from the globus pallidus)
what is the major input source to the corpus striatum?
- (part of the striatal afferent connections)
- from frontal lobes of cerebral cortex
- almost the entire cortex projects to caudate and putamen
what areas from the cerebral cortex project primarily to the putamen (striatal afferent connections)?
primary motor, premotor, supplementary motor and somatosensory area
what areas from the cerebral cortex project primarily to the caudate (striatal afferent connections)?
association cortex of prefrontal and parietal lobes
projections from the cerebral cortex to striatum are inhibitory or excitatory?
excitatory, mediated by glutamate
in addition to input from cerebral cortex, what other area of the brain has striatal afferent input to the striatum?
- from substantia nigra
- uses dopamine
- post-synaptic inhibition
- important in the genesis of parkinsonism
what are the striatal efferent connections out of the striatum?
- project to both internal and external segments of hte globus pallidus and to substantia nigra
- use GABA and are inhibitory
what are the pallidal afferent inputs?
- from the neostriadum (major input): uses GABA, inhibitory
- subthalamic nucleus: uses glutamate, excitatory
what is the main efferent nucleus of the basal ganglia?
what are the pallidal efferent outputs?
- project to 2 specific ipsilateral thalamic nuclei via 2 separate pathways
- -- lenticular fasciculus
- -- ansa lenticularis
what is the thalamic fasciculus?
a composite fiber bundle made up of the lenticular fasciculus and the ansa lenticularis pathways from the globus pallidius to the thalamus (efferent)
what transmitter is used in the pallidal efferent connections?
- (specifically the lenticular fasciculus and ansa lenticularis)
- GABA, inhibitory at the thalamic level
what is the path of the efferent projections from the globus pallidus to the cerebral cortex?
- globus pallidus --> (inhibitory) ventral teir of thalamic nuclei --> (excitatory) primary motor, premotor and supplementary motor areas of frontal lobe cortex
- (other globus pallidus projections descend to reticular formation)
What is a very general description of the inputs received to the basal ganglia and its output?
basal ganglia receives info from all areas of the cerebral cortex but only the frontal lobes receive output that is relayed through the thalamus
What is a very general description of the directed output from the corpus striatum?
- has no direct projections to the spinal cord
- frontal lobe is the target of most of its output
what is the purpose of the feedback loops existing btwn basal ganglia and thalamus?
- link the thalamus w/ different regions of the cerebral cortex (mainly the frontal lobe)
- influence various regions within the frontal lobe on the SAME side from which the corticospinal tracts arise which affect the lower motor neurons of the contralateral SC
what is the most well known basal ganglia / thalamic feedback loop?
- skeletomotor loop: links sensory motor and premotor areas of the corex w/ the moto, premotor, and supplementary motor cortex via ventral anterior and ventral lateral nucleus of thalamus
- basal ganglia assist in control of skeletal mm
what functionality do the basal ganglia / thalamic feedback loops involve?
- skeletomotor functions
- extraocular muscle movement
- goal directed behavior
- spatial memory
due to the basal ganglia /thalamic feedback loops, what happens w/ pathology of the striatum?
motor function disturbances on the contralateral side (unlike the cerebellum)
what happens clinically w/ disease or degeneration of the basal ganglia, cerebral cortex (and sometimes thalamus)?
- disturbances of muscle tone (rigidity)
- dyskinesia (disorders of movement) - voluntary control and regulation of movement is disordered, no paralysis
- person still has ability to plan and execute motor acts
what plays an important role in neural mechanisms of all dyskinesias?
cerebral cortex and cortiospinal tract
what exagerates / abolishes dyskinesia?
- all forms of abnormal involuntary movement are abolised by general anesthesia, removal of parts of motor cortex, or interruption of corticospinal tract, or during sleep
- exaggerated when pt becomes self-conscious, anxious, excited
two main classes of dyskinesias?
- hyperkinetic characterized by increased motor activity
- hypokinetic by decreased movement
what causes hypokinetic disorders?
excessive inhibition of the thalamus by basal ganglia
what causes hyperkinetic disorders?
abnormally low levels of basal ganglia output
what are different types of hyperkinetic disorders?
- chorea (huntingtons disease), athetosis, hemiballismus, dystonia, tics
- all characterized by excessive motor activity: abnormal, involuntary, purposeless movements, difficulty contininug and stopping ongoing movement, abnormalities of muscle tone (rigidity), and tremor
what are the characteristics of hypokenetic movement disorders are characterized by significant impairment in the initiation of movement (akinesia) and a lack, or reduction in the amplitude and velocity of movement (bradykinesia)