Action

Question 1

Motor

structures

Answer 1

• Muscles, Motor Neurons, Spinal Cord

• Subcortical motor structures
– Basal Ganglia
– Cerebellum

• Cortical regions involved in motor control
– Primary motor area
– Premotor cortex
– Supplementary motor area
– Parietal reach areas.

Question 2

Effectors

Answer 2

parts of the body that can move.

– Arms, legs
– Head, neck, tongue

Question 3

Muscles

Answer 3

– Control effectors via spinal cord.
• Via Cortical
• Via Subcortical

Question 4

Muscles, Motor Neurons, Spinal Cord

Answer 4

• Paired agonist and antagonist muscles.
(e.g, extensor and flexor)

• Innervation from alpha motor
neurons in spinal cord.

• Excitatory to one muscle,
inhibitory to other.

Question 5

Reflexes

Answer 5

Simplest form of motor control.

They don’t even require brain interaction; they go to the spinal cord and then return.

Question 6

Stretch Reflex

Answer 6

• Sensory Signal (stretch)
>>>>>
• Spinal Cord (dorsal root)
>>>>
• Alpha Motor Neuron
>>>>
• Contract Quadriceps Muscle

Question 7

Cortical Areas Involved

in Motor Control

Answer 7

• Primary motor area (M1)
– Somatotopic map
(motor humunculus)
– Contralateral organization
   = left brain controls right side
      of body

• Secondary motor areas
– Pre-motor cortex (PMC)
– Supplementary motor area (SMA)
– Planning voluntary actions

• Association motor areas
– Parietal cortex
(dorsal stream; multisensory
integration areas)

Question 8

Motor Planning
vs
Execution

Answer 8

• fMRI study
– Simple movements
(tapping finger) >>> 
Primary motor cortex
– Complex movements
(tap fingers in specific sequence) >>> 
primary & supplementary motor areas
– Imagining movements >>> only SMA

• TMS study
– Over motor cortex:
movement halted or wrong key pressed.
– Over SMA: effect delayed
(~3 key presses after TMS)

Question 9

Premotor
vs
Supplementary Motor Area

Answer 9

• Both are involved in motor
planning.

• PMC:
– Externally-­guided movement
– Connections w/ parietal lobe
(visually-­‐guided reaching)

• SMA:
– Internally-­guided movement
– Connections w/ frontal lobe
(goals/preferences)

Question 10

Basal Ganglia

Answer 10

Selecting, initiating actions

Question 11

Brainstem

Answer 11

• ­‐ cranial nerves

- ­‐ Controlling face/reflexes.

Question 12

Cerebellum

Answer 12

• ­‐ Balance

- ­‐ Hand-­eye coordination

Question 13

Neural Coding of Movement

Answer 13

• M1: neurons code direction of movement
• Individual neurons
have preferred directions
• Summed activity over all neurons
= Population Vector
• Direction of population vector predicts direction of movement
• Cells represent planned movement before execution
of movement
• Implications for neuroprosthetics!

Question 14

Applying what we know:

Neuroprosthetics

Answer 14

Training monkeys to use robotic arms:

1. Monkey reaches toward &
   grasps objects at different
   locations.
2. Recordings from motor cortex used to create corresponding population
   vectors.
3. Population vectors used to control robotic arm
4. Monkey learns to control robotic arm just by thinking
   about moving it.

Question 15

Human Brain‐Machine Interface

BMI

Answer 15

PaQent M.N.:
25 yr-old quadriplegic
• Array of microelectrodes implanted into motor cortex
• Trained BMI by imagining
different movements
• Can control computer mouse
and robotic arm

Question 16

Hemiplegia

Answer 16

– Loss of voluntary movement
on 1 side.

– Damage to primary motor cortex (contralateral M1)

– No voluntary control

– Reflexes?
• Initially no reflexes either
• Reflexes return later
(and are often hyperactive)

– Spasticity
(increased muscle tone)
due to lack of voluntary control.

Question 17

Apraxia

Answer 17

– Loss of skilled action
(motor planning, not muscle related)

– Parietal damage
(often of the left hem)

– Coordination problem

– Ideomotor type:
rough sense of desired action but problems executing it

– Ideational type:
more severe; disrupted knowledge of action
(e.g., appropriate use of tool)

“Show me how you would slice bread.”

Question 18

Cerebellum

Answer 18

Motor Execution
Motor Planning
Balance and Eye Movements

Smooth control of action
– Especially axial muscles (body and trunk)
– Sensitive to alcohol

Question 19

Cerebellar Ataxia

Answer 19

– Can select & initiate movement.
– Clumsy, irregular, erratic motions.
– Cannot smoothly terminate
actions.

Question 20

Parkinson’s

Answer 20

– Movement Disorder of the Basal Ganglia.

– Loss of dopamine neurons
in substantia nigra

– Less input from basal ganglia to motor cortex &raquo_space;> reduction in movement
• Slowness in execution
of movements
(Bradykinesia)
• Reduction in voluntary movements (Hypokinesia)
• Reduced flexibility in modulating movements
(e.g., varying force)

– Treatments
• L-­‐dopa therapy (synthetic
precursor to dopamine).
Can cause opposite effects
(hyperkinesia, tremors)
• Deep brain stimulation
therapy (stimulate regions not getting enough dopamine)

Question 21

Huntington’s

Answer 21

– Movement Disorder of the Basal Ganglia.

– Degenerative disease of striatum.

– Loss of inhibition >>>
too much input to motor cortex
>>>
increase in movement
(hyperkinesia)
• Clumsiness, balance problems, increase in involuntary movements (chorea)

– Not restricted to the motor system, general dementia

Question 22

The Case of the

Frozen Addicts

Answer 22

– 1980s: several young people suddenly presenting with severe
Parkinson’s-like symptoms
(completely frozen)

– Had taken contaminated batch of
synthetic heroin
• MPPP (synthetic heroin)
• MPTP (destroys dopamine cells)

– http://www.time.com/time/magazine/article/
0,9171,1101850408–]141542,00.html

– Treated patients with L-dopa

– Huge advance in understanding
Parkinson’s
• Animal models