2. Programming and Control of Voluntary Movement: Motor Cortex

Question 1

multiple cortical motor areas

Answer 1

• 4 areas for movement of limbs and body
• 2 areas for movement of eyes
• 1 area for speech (Broca’s area)

Question 2

4 areas for movement of limbs and body

Answer 2

1. primary motor cortex (area 4)
2. dorsal premotor cortex (area 6)
3. ventral premotor cortex (area 6)
4. supplementary motor area (SMA; area 6)
   - all areas are interconnected (all project and receive projections to/from each other)
   - all receive thalamic input (from basal ganglia and cerebellum with a relay in thalamus)
   - all contribute axons to the corticospinal or pyramidal tract, which means that all can participate in initiation of movement

Question 3

area 4

Answer 3

• cytoarchitectonically (fine structure) distinct, Betz cells
• important in control of hands and fingers (fine motor control)

Question 4

Fritsch and Hitzig

Answer 4

• classic experiments
• electrical stimulation of motor cortex - brief contraction of one or few muscles on contralateral side of body, somatotropic organization (electrical stimulation will cause AP in neurons)

Question 5

Wilder Penfield

Answer 5

• tried to find “seizure focus” on epilepsy patients in order to remove it surgically but limit surgical removal to spare language, etc.
• patients stay awake and able to report experiences
• confirmation of animal work: distorted map of contralateral body musculature

Question 6

map in motor cortex

Answer 6

• enlarged representation of parts of the body with more finely controlled or skilled movement (more corticoneurons sent for fine movement)
• map is not discrete representation of single muscles
• axons descend on same side of brain until they cross (“decussate”) in the medulla
• when on opposite side of brain, descending axons are in corticospinal or pyramidal tract

Question 7

lesions of motor cortex

Answer 7

• decorticate rigidity/spasticity (descending control of stretch reflex)
• loss of ability to generate independent finger movements
• recovery of voluntary movement greater in legs than hand and arm (not permanent paralysis) - other regions must be able to issue commands for movement
• NOT paralysis (spinal cord damage), involuntary movements (damage to basal ganglia), ataxic movements (damage to cerebellum - uncoordinated movements)
• typically from injury and not from diseases (except ALS)

Question 8

plasticity in cortical maps

Answer 8

• there is a lot of plasticity in cortical organization
• increased use can result in reorganization, this is true for all areas both sensory and motor
• new PT techniques to facilitate reorganization

Question 9

premotor cortex and SMA

Answer 9

• ventral and dorsal premotor cortex (area 6): use sensory info in ongoing control of movement
• SMA: motor planning, bimanual coordination
• SMA and apraxia (skilled movement, use of tools)

Question 10

idea of bimanual coordination

Answer 10

2 hands work together but do different movements (like cutting paper, one hand cuts the other holds paper)
- damage more or less localized to SMA and cognitively intact could not demonstrate use of tools (toothbrush, scissors)

Question 11

3 types of movement as evidence for role of SMA in motor planning

Answer 11

• simple movement (motor cortex, somatic sensory cortex)
• complex movement (supplementary motor area, motor cortex, somatic sensory cortex)
• “mental rehearsal” of complex movement (supplementary motor area)

Question 12

ALS (amyotrophic lateral sclerosis)

Answer 12

• 40s-50s, more common in men
• rare frequency
• cause not known, 10% genetic, familial form

Question 13

symptoms of ALS

Answer 13

• primarily affect motor system (NOT sensory, cognitive or affective)
• gradual loss of motor control
• death by respiratory failure
• 3-5 year survival rate after diagnosis
• eye movements persist (motoneurons for extraocular muscles, CN III, IV, VI do not degenerate)

Question 14

CNS in ALS

Answer 14

• very specific cell populations and fiber tracts are affected: neurons in motor cortex whose axons descend to spinal cord (upper motoneurons) and spinal (lower) motoneurons die.
• when a neuron dies, its axon dies so the corticospinal tract degenerates
• motoneurons in CNN nuclei 3,4,6 work; some effects on mn in 5,7,9,10,12
• gammaMNs do not degenerate, only alpha

Question 15

what happens to corticospinal axons in ALS

Answer 15

• corticospinal axons die and are replaced by scar tissue –> sclerosis
• corticospinal axons are lateral in the spinal cord

Question 16

treatment of ALS

Answer 16

• no cure, supportive care only