Motor System and Basal Ganglia and Cerebellum

Question 1

Explain the motor system hierarchy

Answer 1

Lower level: Spinal cord
Level 2: Brainstem
Level 3: motor cortex (primary cortex and supplementary)
Level 4: association cortex (contains parietal and frontal)

Question 2

Describe the function of the primary motor cortex (M1)

Answer 2

Found in the pre-central gyrus, anterior to the central sulcus, it’s function is fine motor control, discrete, precise voluntary movement. Provide descending signals to execute movement.

Penfields homuculus

Question 3

Describe the 2 descending motor pathways

Answer 3

Lateral and anterior corticospinal tracts. Both start in the primary motor cortex, descend through the Brainstem.

In lateral, the cross over happens at the medulla (pyramid cells) and then to spinal cord. Whereas the anterior, cross over occurs at spinal level.

Question 4

Describe the role of promoter cortex

Answer 4

Frontal lobe anterior to M1. Involved in planning movements, regulates externally caused movement. Eg catching an apple, requires arm and body.

Question 5

Describe the role of the supplementary motor area

Answer 5

Plan complex movements, programming sequencing of movements, regulates internally driven movements (eg speech) SMA becomes active when thinking about movements

Question 6

Describe the role of association cortex

Answer 6

Posterior parietal cortex - movement is targeted accurately

Prefrontal cortex - appropriate movements for particular course of action.

Question 7

Describe the upper motor and lower motor neurone lesion.

Answer 7

Upper motor neuron lesions: loss of function, paresis, paralysis, increased abnormal motor function, spasticity, hyper reflexia, clonus.

Lower motor: weakness, hypotonia, hyporeflexia, muscle atrophy, fasicukations, twitch, fibrillation

Question 8

Describe apraxia and MND

Answer 8

Apraxia: disorder of skilled movement, aren’t weak but forgot how to do skilled movements.

MND: progressive degenerative disorder of the motor system, spectrum of disorder eg ALS.

Question 9

Describe the structure and function of the basal ganglia

Answer 9

Basal ganglia is extra pyramidal, part of the corticospinal tract. Contains 1. Caudate nucleus, 2. Lentiform nucleus, 3. Subthalamic nuclei, 4. Substantia niagra.

Functions:

1. Elaborating associated movements (eg swinging arms when walking)
2. Modulating and coordinating movement (suppressing unwanted movements)
3. Performing movements in order.

Question 10

Describe the cause and effect of Parkinson’s

Answer 10

Neurodegeneration of the dopaminergic neurones that originate in the substantia nigra and project to the striatum.

Motor signs: bradykinesia, hypomimic face, akinesia, rigidity, tremor at rest.

Question 11

Describe the cause and effect of Huntington’s

Answer 11

Genetic neurodegeneratuve disorder on chromosome 4, autosomal dominant, CAG repeat. Degeneration of GABAergic neurones in the striatum, caudate and then putamen.

Motor signs: choreic movements, speech impairment, difficulty swallowing, unsteady gait, cognitive decline and dementia.

Question 12

Describe the structure of cerebellum

Answer 12

3 layers: molecular, pisiform and granular.

Divisions : 1. Vestibulocerebellum - hair, posture, coordination

2. Spinocerebellum - speech muscle tone and coordination
3. Cerebrocerebellum - skilled movements, cognitive function , attention language

Question 13

Describe the effects of loss of cerebellar function

Answer 13

Depends on the localisation. Look at notes.