Basal Ganglia

Question 1

Describe the extrapyramidal system

Answer 1

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

Question 2

What is the principal subcortical loop of the EPS?

Answer 2

The striatal loop and one of the EPS’s indirect descending pathways is the corticorubrospinal pathway

Question 3

What are the components of the EPS?

Answer 3

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

Question 4

Describe the globus pallidus

Answer 4

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

Question 5

What are the associated structures of the basal ganglia?

Answer 5

Globus pallidus, caudate nucleus, putamen, substantia nigra, red nucleus, subthalamus and nucleus accumbens

Question 6

What is the caudate nucleus?

Answer 6

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

Question 7

What is the putamen and where is it located?

Answer 7

Largest nucleus of the basal ganglia

Located lateral to the globus pallidus

Question 8

What are the two subdivisions of the substantia nigra?

Answer 8

Pars reticularis and pars compacta

Question 9

What is the pars reticularis?

Answer 9

Forms the anterior portion of the SN and contains serotonin and GABA
Source of most efferent fibers from the SN

Question 10

What is the pars compacta?

Answer 10

Contain dopamine and melanin

Neurons in this region are destroyed in Parkinson’s disease

Question 11

What is the red nucleus?

Answer 11

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

Question 12

Unilateral lesions of the red nucleus and midbrain tegmentum cause what?

Answer 12

Benedikt’s syndrome
Pt presents with ipsilateral oculomotor palsy and contralateral motor dysfunction such as tremor, ataxia or choreiofrm movements

Question 13

Describe the subthalamus

Answer 13

Subdivision of the thalamus but is mainly formed by a rostral extension of the reticular formation
Regulates the output of the basal ganglia

Question 14

Unilateral lesions of the subthalamus result in what?

Answer 14

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

Question 15

Describe the nucleus accumbens (NAc)

Answer 15

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

Question 16

What is the function of the nucleus accumbens (NAc)?

Answer 16

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

Question 17

What forms the connections to the globus pallidus?

Answer 17

Dorsal and ventral divisions of the ansa lenticularis

Classified as pallido-thalamic fibers

Question 18

Describe the dorsal division of the ansa lenticularis

Answer 18

Commonly called the lenticular fasciculus

Join with fibers from the ventral division of the ansa lenticularis to form the thalamic fasciculus

Question 19

Which fibers form the connections to the substantia nigra?

Answer 19

Nigro-thalamic and nigro-striatal fibers

Question 20

What are nigro-thalamic fibers?

Answer 20

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

Question 21

What are nigro-striatal fibers?

Answer 21

Dopaminergic fibers that originate in the pars compacta of the SN and terminate in the caudate and putamen (striatum)

Question 22

Destruction of the inhibitory GABA-nergic fibers in the striatonigral fibers are involved in what disease?

Answer 22

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

Question 23

Describe the intermediate division of the ansa lenticularis (subthalamic fasciculus)

Answer 23

Subthalamic nucleus (STN) receives major input from the globus pallidus and motor cortex 
Contain glutamate and exert an excitatory influence

Question 24

What is Parkinson’s disease?

Answer 24

A subcortical degeneration disorder involving the substantia nigra, globus pallidus, upper brainstem nuclei (mainly RF) and occasionally post ganglionic sympathetic neurons

Question 25

What are the three major causes of Parkinson’s?

Answer 25

Postencephalitic, arteriosclerosis and drug induced

Question 26

What are the signs and sx associated with Parkinson’s disease?

Answer 26

Bradykinesia, tremor during rest, rigidity (abnormal passive resistance to movement in all directions), masked face with a positive glabellar reflex, postural embarrassment

Question 27

Cortical/subcortical feedback loops play important roles in what?

Answer 27

In initiating motor movement patterns and integrating them with the cerebellum, cerebral cortex and limbic system

Question 28

Which fibers are excitatory?

Answer 28

Cortico-striatal fibers

Question 29

Which fibers are primarily inhibitory upon specific motor thalamic nuclei?

Answer 29

Pallidothalamic and nigrothalamic fibers

Question 30

The cerebellum acts to adjust the intensity of what?

Answer 30

The motor movement patterns to the appropriate level for the task

Question 31

What is the principal discharge pathway for the motor system?

Answer 31

The corticospinal and corticobulbar tracts

Question 32

Lesions of the motor system show what?

Answer 32

Dysfunction of the system in the absence of the damaged component rather than its particular function

Question 33

What is the striatal loop?

Answer 33

Cerebral cortex -> striatum (globus pallidus + SN) -> striatothalamic and nigrothalamic fibers -> VA and VL nuclei -> primary and premotor cortices -> cerebral cortex

Question 34

What is the cerebellar loop?

Answer 34

Primary and premotor cortices —> via corticopontine fibers to the pontine nuclei —> cerebllum via pontocerebellar fibers —> VA and VL nuclei -> primary and premotor cortices