68. Voluntary Movement

Question 1

What tracts are in Lateral and Medial Descending Systems?

Answer 1

Lateral - control of distal musculature
CS Tract
Rubrospinal tract - hand coordination

Medial - control of proximal musculature
Reticulospinal - neck/back/leg muscle tone/pain control
Vestibulospinal - neck/back/leg reflexes/muscle tone
Tectospinal - neck - attention/orientation

Question 2

What are the inputs to the primary motor cortex?

What motor loops exist in the brain?

What is the physiology of the M1 neurons in the PMC?

Answer 2

1. Parietal, “Where”, Action Stream
2. Temporal, “What”, Perception Stream (via limbic system/prefrontal cortex)

Loops: through BG and cerebellum for complex, coordinated movement

M1: signal FORCE and DIRECTION
force - rate of AP = magnitude of contration
direction - certain neurons only fire for certain directions

Question 3

What are the 2 main premotor cortical areas and what are they active for?

What happens when you damage the 2 main inputs to the PMC?

What is the HIGHEST premotor cortex? How do these neurons work? What happens with damage here?

Answer 3

1. Premotor Cortex: active for visually guided movement (translate x,y,z world into muscle actions), lateral to SMC
2. Supplementary Motor Cortex: active for internally-guided/previously learned movement, medial to PreMC

Damage to Parietal Stream (Where, Action) = OPTIC ATAXIA (can’t move hand into slot, but can describe it)
Damage to Temporal Stream (What, Perception) = VISUAL AGNOSIA (can’t describe orientation)

Parietal Cortex - multisensory integration
Damage = HEMISPATIAL NEGLECT
Parietal Neurons: EXTRINSIC COORDINATES - encode ONLY direction of movement (not if you need more/less force)

Question 4

The cerebellum relates to what side of the body?
The cerebellar loop performs what type of action on movement?

What are the 4 clinical signs of damage?

Answer 4

IPSILATERAL SIDE OF BODY (communication with cerebrum requires decussation)
INHIBITORY action - control/termination of movement and learning from motor error

1. Dysdiadochokinesia - difficulty with alternating movement
2. Decompensation of Movement - lack of coordination of steps
3. Dysmetria: makes too large of movments
4. Intention Tremor: larger tremors when approaching final target of movment

Question 5

How do the clinical signs relate to the cerebellar region involved?

Answer 5

More lateral lesions = more distal problems

1. Vermis damage = POSTURAL instability, TRUNK ataxia, dysmetric head/eye movement (eye wobbling)
2. Intermediate Cerebellum = Ataxia of Arm/Leg movements and GAIT problems
3. Hemispheres = impairs fine movement of HANDS/FEET, motor planning

Question 6

What is the function of the Purkinje Cell? What NT does it secrete?

Describe the internal circuitry of the cerebellum

Answer 6

Purkinje: GABA inhibitory = only outputs to deep nuclei (no direct motor projections)

1. mossy fibers - granular cells - parallel fibers - purkinje dendrites
2. climbing fibers - wind around purkinje dendrites
3. Golgi Cell: input from parallel fibers, inhibit granular cell (negative feedback)
4. Deep nuclear neuron: input from Purkinje (inhibitory), and mossy/climbing fibers (excitatory)