Anatomy of Basal Ganglia

Question 1

What are basal ganglia, what is their general location and function?

Answer 1

Refers to a number of sub cortical nuclear masses that lie in the inferior part of the cerebral hemisphere, lateral to the thalamus
They are a group of nuclei that are anatomically interconnected and have important motor functions

Question 2

Name the components of the basal ganglia

Answer 2

caudate nucleus
putamen
globus pallidus
substantia nigra
subthalamic nuclei
amygdala (due to developmental origin, but functionally part of limbic)
claustrum (function unknown)

Question 3

What are the components of the lentiform nucleus?

Answer 3

putamen (outer part of the LN) and globus pallidus (inner part)

Question 4

What are the divisions of the corpus striatum? What are the components of each division?

Answer 4

Dorsal striatum - caudate nucleus and putamen

Ventral striatum - nucleus accumbens + olfactory tubercle

Question 5

Describe the shape of the caudate nucleus

Answer 5

Curved, tadpole shaped. parts - head, body and tail

Question 6

What is the substantia nigra and where is it found? Name its two parts

Answer 6

Collection of neurones in the midbrain immediately behind the crus cerebri. It is divided into two parts: pars compacta and pars reticulata

Question 7

Describe the subthalamic nucleus: shape, location and function

Answer 7

Shaped like a biconvex lens in the subthalamic region. Found at junction of internal capsule and crus cerebri. Responsible for integrating and smoothening movements

Question 8

What are the relations of the caudate nucleus (as in the structures near it)?

Answer 8

Corpus callosum lies above head and body. Thalamus lies medial to most of body. Between thalamus and CN, u find the stria terminalis and the thalamostriate vein.
It is separated from the lentiform nucleus by the anterior limb of the internal capsule

Question 9

What is the main function of the basal ganglia?

Answer 9

Motor refinement, preventing unwanted movements by modulating theexcitatory inputto the cerebral cortex. Thus prevents excessive and exaggerated movements.
Each side influences the cerebral cortex of its same side. This means it influences the contralateral body.

Question 10

What are the 4 loops/circuits of the basal ganglia and their function?

Answer 10

Motor (learned movements e.g. writing), cognitive (motor intentions - preparing for movements), limbic (emotional aspects of movement), oculomotor (voluntary saccades - using the eye muscles to look at an object)

Question 11

Draw a diagram of the direct pathway of the motor loop, and does it incr or dec motor activity

Answer 11

Cerebral cortex (CS fibres + glutamate, exc) -> dorsal striatum (SP fibres + GABA, inhib) -> medial segment of globus pallidus (PT fibres so ansa lenticularis + fasciculus lenticularis, inhib) -> VL nucleus and VA nucleus in thalamus (ex)-> back to cerebral cortex so this pathway increases motor activity
Inhibition of inhibitory fibres, so we get excitation

Question 12

Draw a diagram of the indirect pathway of the motor loop and does it incr or dec motor activity

Answer 12

Cerebral cortex (CS fibres + glutamate exc) -> dorsal striatum (SP fibres + GABA inhib) -> lateral segment of GP (inhib) -> subthalamus (exc) -> medial seg of GP (inhib) -> thalamus (exc) -> back to cortex
Excitation to inhibitory pathway causes decrease in motor activity

Question 13

How does dopamine affect the motor loop and tf motor activity?

Answer 13

Dopamine stimulates the direct pathway and inhibits indirect pathway and so increases motor activity

Question 14

Draw a diagram of the limbic loop and its functions/features (what NT does it use)

Answer 14

Prefrontal cortex -> ventral striatum (nucleus accumbens) -> ventral pallidum -> thalamus (meliodorsal nucleus) -> back to prefrontal cortex
It is involved in giving motor expression to emotion (through smiling, gestering etc). The loop is rich in dopaminergic nerve endings.

Question 15

Why may someone with parkinson’s disease have a very neutral or reduced facial expression?

Answer 15

Their limbic loop (has dopaminergic neurones) may be declining, so this may account for their masked facies (reduced

Question 16

What can damage to the basal ganglia cause?

Answer 16

Dyskinesia
Disturbance of muscle tone (rigidity)

Question 17

What is dyskinesia and what are the types and its symptoms? What can cause it?

Answer 17

Disorder in movement. Hyperkinesia - tremors, athetosis, chorea, ballism. Hypokinesia - parkinson’s disease.

Question 18

What is a tremor?

Answer 18

Is a rhythmical, alternating abnormal involuntary activity having a relatively regular frequency and amplitude

Question 19

What is athetosis?

Answer 19

Is characterised by movements that are involuntary, slow and writhing involving particularly the distal muscles of the extremities

Question 20

What is chorea and name the two types?

Answer 20

Quick, jerky, irregular involuntary movements that are non-repetitive.
Sydenham’s chorea and huntington’s chorea.

Question 21

Describe two features of sydenham’s chorea

Answer 21

Disease of childhood and is associated with rheumatic heart disease

Question 22

Describe huntington’s chorea (gene, areas of BN involved, what does CT scan show)

Answer 22

It is autosomal dominant. Dopamine secreting neurones of the SN are overactivated. NS pathway inhibits the caudate nucleus and putamen, this leads to degeneration of caudate nucleus. CT shows enlarged lateral ventricle due to degeneration of caudate nucleus.

Question 23

What is hemiballismus and what BN problem causes it?

Answer 23

This is violent, forceful movement confined to one side of the body. It involves the proximal extremity musculature i.e., muscles of shoulder and pelvic girdle.
Lesion in subthalamic nuclei, due to thrombosis in the branch of posterior cerebral artery supplying the subthalamus

Question 24

What is parkinsonism (symptoms)?

Answer 24

It is a clinical syndrome comprising of: impairment of voluntary movement (hypokinesis - delay in initiation, paucity and lack of precision of movements), rigidity, tremor at rest expressionless face, stooped posture.

Flexed elbows, wrists, hip and knees. Shuffling, short stepped gait.

Question 25

What is the cause of parkinsons disease?

Answer 25

Lesion in the substantia nigra and damage to nigrostriatal pathway which uses dopamine as NT. Pathology - cellular loss and depigmentation of SN