Basal Ganglia Flashcards
Describe the extrapyramidal system
Involved in movements of the axial and proximal limb musculature
Initiates movement patterns through its complex subcortical loops providing the framework for all focal motor activity
Includes the basal ganglia, cerebral cortex and dorsal thalamus
What is the principal subcortical loop of the EPS?
The striatal loop and one of the EPS’s indirect descending pathways is the corticorubrospinal pathway
What are the components of the EPS?
Ventral anterior and ventral lateral nuclei
Often called the motor nuclei of the thalamus
Form a critical link in the merging, integration, and processing of info from the striatum, cerebellum and cortex during all stages of motor pattern development
Describe the globus pallidus
Located on the lateral aspect of the genu of the internal capsule
One of the principal sources of efferents from the basal ganglia
Efferent fibers from this originally formed a single bundle known as the lateral forebrain bundle
What are the associated structures of the basal ganglia?
Globus pallidus, caudate nucleus, putamen, substantia nigra, red nucleus, subthalamus and nucleus accumbens
What is the caudate nucleus?
An elongated tear drop shaped nucleus located on the surface of the lateral ventricle
Functionally similar to connections of the putamen by the internal capsule
What is the putamen and where is it located?
Largest nucleus of the basal ganglia
Located lateral to the globus pallidus
What are the two subdivisions of the substantia nigra?
Pars reticularis and pars compacta
What is the pars reticularis?
Forms the anterior portion of the SN and contains serotonin and GABA
Source of most efferent fibers from the SN
What is the pars compacta?
Contain dopamine and melanin
Neurons in this region are destroyed in Parkinson’s disease
What is the red nucleus?
Subdivision of the reticular formation
Most of its fibers project to the inferior olivary nucleus via the central tegmental fasciculus as part of the subcortical loop to the cerebellum
Unilateral lesions of the red nucleus and midbrain tegmentum cause what?
Benedikt’s syndrome
Pt presents with ipsilateral oculomotor palsy and contralateral motor dysfunction such as tremor, ataxia or choreiofrm movements
Describe the subthalamus
Subdivision of the thalamus but is mainly formed by a rostral extension of the reticular formation
Regulates the output of the basal ganglia
Unilateral lesions of the subthalamus result in what?
A reduction or loss of inhibition (GABA) upon the globus pallidus by the subthalamus causing contralateral hemiballismus
Characterized by violent, involuntary, flinging movements of the UE and LE
Always associated with hypotonus
Describe the nucleus accumbens (NAc)
A small accumulation of gray matter b/w the putamen and caudate below the internal capsule
NAc + olfactory tubercle comprise the ventral striatum which links the amygdala and hippocampus to the dorsomedial nucleus of the thalamus and globus pallidus
Dopaminergic neurons of the mesolimbic pathway project into the GABAnergic neurons of the ventral striatum
What is the function of the nucleus accumbens (NAc)?
May play a role in motivational and emotional aspects of movement
Involved in the encoding of new motor programs and cognitive processing of aversion, motivation, reward and reinforcement learning
Has a significant role in addictive behavior of all types
What forms the connections to the globus pallidus?
Dorsal and ventral divisions of the ansa lenticularis
Classified as pallido-thalamic fibers
Describe the dorsal division of the ansa lenticularis
Commonly called the lenticular fasciculus
Join with fibers from the ventral division of the ansa lenticularis to form the thalamic fasciculus
Which fibers form the connections to the substantia nigra?
Nigro-thalamic and nigro-striatal fibers
What are nigro-thalamic fibers?
Non-dopaminergic fibers that originate from the pars reticularis of the SN and terminate in the VA and VL thalami nuclei
Fibers from the globus pallidus and the SN do not terminate in the same areas of the VA and VL nuclei
What are nigro-striatal fibers?
Dopaminergic fibers that originate in the pars compacta of the SN and terminate in the caudate and putamen (striatum)
Destruction of the inhibitory GABA-nergic fibers in the striatonigral fibers are involved in what disease?
Huntington’s chorea which is an autosomal dominant motor disorder
Common features include dementia, chorea and behavioral disturbances
Choreiform movements which are characterized by sudden irregular, involuntary and jerky purposeless movements
Sx may be due to excessive dopaminergic influence in the degenerated area or loss of inhibit from GABAnergic neurons of the striatonigral pathway
Describe the intermediate division of the ansa lenticularis (subthalamic fasciculus)
Subthalamic nucleus (STN) receives major input from the globus pallidus and motor cortex Contain glutamate and exert an excitatory influence
What is Parkinson’s disease?
A subcortical degeneration disorder involving the substantia nigra, globus pallidus, upper brainstem nuclei (mainly RF) and occasionally post ganglionic sympathetic neurons
What are the three major causes of Parkinson’s?
Postencephalitic, arteriosclerosis and drug induced
What are the signs and sx associated with Parkinson’s disease?
Bradykinesia, tremor during rest, rigidity (abnormal passive resistance to movement in all directions), masked face with a positive glabellar reflex, postural embarrassment
Cortical/subcortical feedback loops play important roles in what?
In initiating motor movement patterns and integrating them with the cerebellum, cerebral cortex and limbic system
Which fibers are excitatory?
Cortico-striatal fibers
Which fibers are primarily inhibitory upon specific motor thalamic nuclei?
Pallidothalamic and nigrothalamic fibers
The cerebellum acts to adjust the intensity of what?
The motor movement patterns to the appropriate level for the task
What is the principal discharge pathway for the motor system?
The corticospinal and corticobulbar tracts
Lesions of the motor system show what?
Dysfunction of the system in the absence of the damaged component rather than its particular function
What is the striatal loop?
Cerebral cortex -> striatum (globus pallidus + SN) -> striatothalamic and nigrothalamic fibers -> VA and VL nuclei -> primary and premotor cortices -> cerebral cortex
What is the cerebellar loop?
Primary and premotor cortices —> via corticopontine fibers to the pontine nuclei —> cerebllum via pontocerebellar fibers —> VA and VL nuclei -> primary and premotor cortices
