Basal Ganglia

Question 1

Describe function of following connections of basal ganglia:
1. Cortical
2. Between nuclei
3. Brain sten

Answer 1

1. Inhibits excessive activity of motor cortical area (4&6), inform basal ganglia about program & intention of movement
2. Control intrinsic activity
3. Regulation of muscle tone & body posture

Question 2

Describe caudate circuit & its function

Answer 2

Sensory & motor association areas —caudate nucleus—globus pallidus—thalamus—supplementary motor, premotor & prefrontal areas
F, cognitive control of sequences of motor movements. This subconciously determines within seconds patterns of movement which will be used together to achieve a goal.

Question 3

Describe putamen circuit & its function

Answer 3

Premotor, supplementary motor & somatosensory areas —putamen—globus pallidus—thalamus—primary motor & premotor areas
Execute learned patterns of movement

Question 4

Enumerate connections of basal ganglia to brain stem

Answer 4

Reticular formation, red nucleus, vestibular nucleus

Question 5

Mention neurotransmitters in basal ganglia

Answer 5

Cerebral cortex release glutamate on corpus striatum
Intrastriatal interneurons release Ach
Substantia nigra release dopamine on corpus striatum
Coprus striatum release GABA on substantia nigra
Basal ganglia release NE, ecephalin & Serotonin on brain stem

Question 6

Describe effect of stimulatiry & inhibitory circuits

Answer 6

Stimulatory, facilitate muscle activity especially at beginning if voluntary movement like rising from sitting or beginning to walk
Inhibitory, inhibit unwanted muscle activity

Question 7

Describe the direct pathway

Answer 7

Cortical fibers stimulates striatum by glutamate, striatum inhibits to GPi (GABA, inhibitory), which disihibits the thalamus & thalamic projections excite motor neurons.
This functions to maintain ongoing motor activity

Question 8

Describe the indirect pathway

Answer 8

Cortical input to stiatum in excitatory (glutatmate), striatum inhibits GPe (GABA, inhibitory) thus the subthalamic nuclei are released from GPe inhibition thus cause increased GPi activity which inhibitsvthe thalamus & the net effect is cortical inhibition & suppression of muscle activity.

Question 9

Effects of dopamine & acetylcholine

Answer 9

1. Dopamine in nigrostriatal fibers activates direct pathway (D1) & inactivates indirect pathway (D2) thus facilitatory to movement.
2. Acetycholine is present in balance with dopamine to facilitate the movement

Question 10

What happens with degeneration in the dopamine releasing neurons?

Answer 10

Decreased activity of direct pathway & increased activity of indirect pathway, thus hypokinesia & slow voluntary movements take place, known as parkinsonism.

Question 11

Mention functions of basal ganglia

Answer 11

1. Regulation of muscle tone
2. Role in voluntary movements
3. Automatic associated movements
4. In lower animals, BG is highest motor center

Question 12

Describe role of BG in muscle tone

Answer 12

Caudate is stimulatory, lentiform is inhibitory there is net inhibition.
It decreases the activity of alpha motor neurons through decreasing the activity of motor cortex
It decreases the activity of gamma motor neurons through stimulation of inhibitory reticular formation

Question 13

Describe role of BG in voluntary movements

Answer 13

There are no direct descending tracts from basal ganglia, but it affects voluntary movements by extra-pyramidal tracts
1. Storage of programs of some learned voluntary movements in putamen circuit, lesion results in motor apraxia
2. Planning of motor activity through caudate circuit
3. Provision of postural background for the fine voluntary movements, adjust muscle tone of proximal muscles via ventro-medial pathways to facilitate more regulated fine skilled actions

Question 14

Causes of chorea

Answer 14

Lesion in the caudate nucleus & degenrenation of GABA releaseing striatal fibers to GPe leading to decreased activity of indirect pathway:
1. As a complication of rheumatic fever, but no dementia
2. Congenital (Huntington’s chorea) = progressive dementia

Question 15

C/P of chorea

Answer 15

1. Hypotonia & pendular knee jerk
2. Involuntary movements: sudden semipurposeful movements
3. Dancing movements of arms, legs, face, head & trunk, increase by emotions decrease by sleep

Question 16

Mention causes of athetosis

Answer 16

Lesion of lentiform nucleus mainly globus pallidus (degeneration of GABA releasing neurons which project to thalamus)

Question 17

C/P of athetosis

Answer 17

1. Hyoertonia
2. Involuntary movements = slow twisting movements. Involving distal parts, snake-like movements. Increase by emotions decrease by sleep.

Question 18

Cause of hemiballismus

Answer 18

Lesion in subthalamic nuclei, when glutamate decreases in it, it can’t carry out its normal function in exciting GPi which becomes inhibited

Question 19

C/P of Hemiballismus

Answer 19

1. Hypertonia
2. Involuntary movements: attacks of rapid violent movements. Involving half of body that may cause loss of balance, may be fatal due to respiratory muscle spasm.

Question 20

Causes of parkinsonism

Answer 20

1. Idiopathic due to unknown neurotoxin or oxidation reactions with free radical generation
2. Viral encephalitis, vascular, trauma, poison
3. Drug-induced by antipsychotics, antiemetics, reserpine, tetrabenazine, methyldopa

Question 21

Describe C/P of parkinsonsim

Answer 21

1. Rigidity
2. Static tremors
3. Akinesia
4. Postural deficits & tendency to frequent fall
5. Cognitive impairment as depression

Question 22

Describe rigidity of parkinsonism

Answer 22

Stiffness of muscle during movement. In both flexor & extonsor but f is more.
Alpha rigidity
Mechanism: net effect of basal ganglia is inhibitory so its lesion causes increased excitability of motir neurons

Question 23

Describe static tremors of parkinsonism

Answer 23

Involuntary, regular rapid movements disappear during sleep exaggerated by fatigue & emotions, diminished by voluntary movement.
It may be due to oscillatory discharge (on & off) of globus pallidus interna & thalamic nuclei leading to alternative activation & inactivation of cortical motor areas

Question 24

Describe manifestations of parkinsonian akinesia

Answer 24

1. Difficulty in initiating voluntary movement, no automatic subconscious movements
2. Difficulty in buttoning shirt & necktie before shirt
3. Mask face & no blinking, staring look
4. Monotonous slow slurred speech
5. Shuffling gait with trunk bent forward

Question 25

Mechanism of akinesia in parkinson

Answer 25

1. Increased thalamo-cortical inhibition is associated with decreased activity of supplementary motor area, due to loss of planning & programming functions of BG
2. The increased muscle tone & rigidity interferes with initiation of movement. All lead to avoidance to do any movement as simplest acts require great mental effort.