Voluntary Motion: Cortical and Cerebellar Controls

Question 1

Cortical Areas of Voluntary Motion

Answer 1

• primary motor cortex
• supplementary motor cortex
• pre-motor cortex
• parietal cortex

Question 2

Pre-Motor Cortex

Answer 2

• receives sensory info required to move
• dorsally: applies the rules that determine whether it is appropriate to move
• identifies intent of motion and decides what motion to produce
• “goal” of motion

Question 3

Supplementary Motor Cortex

Answer 3

• organizes motor sequence/identifies what is needed
• acquire motor skills
• executive control (switch actions if needed)
• two parts:
  1. Supplementary Motor Area: posture
  2. Pre-supplementary area: plans motor program for action

Question 4

Primary Motor Cortex

Answer 4

• precentral gyrus
• controls specific movements esp related to arms/hands to face
• code the motions required for goal
• arranged in columns

Question 5

Columns of Primary Motor Cortex

Answer 5

• 2 sets of neurons/column, one to start motion and one to maintain
• layer 4 receives sensory input
• layer 5 is output for corticospinal path
• stimulation of any column produces a specific motion
• if area controls fine motion = contraction of single muscle
• if area controls general motion = contraction of group of muscles
• neighboring columns control related motions, not neighboring muscles
• columns also divided into activation/inactivation segments for agonist/antagonist muscle

Question 6

Dorsal Visual Pathway

Answer 6

• contains axons from occipital cortex that travel to parietal/frontal cortex
• enables us to complete acts based on visual input-allows for reaching and grasping objects

Question 7

Voluntary Motion Pathway: Reaching

Answer 7

1. visual cortex > parietal cortex (V6A, PEc, VIP, and MIP areas)
2. VIP creates rough map of surrounding space
3. info goes from VIP > F4 within premotor cortex
4. F4 creates detailed map of space - neurons fire more with closer object
5. F2 area receives input about where limb is in space
6. F2 makes a map of location of limb relative to body

Question 8

Voluntary Motion Pathway: Grasping

Answer 8

1. anterior intraparietal and PFG respond to seeing object to grasp (visually dominant), grasping object (motor dominant), and both seeing and grasping (visuomotor neurons)
2. anterior intraparietal and PFG > relay info to F5
3. neurons in F5 fire with GOAL of action and not actual motor act itself

Question 9

Reaching Components

Answer 9

Visual pathway: dorsal
Parietal Areas: V6a, PEC, MIP, VIP
Creation of maps: 2
Map of space with object: rough map for VIP and detailed map for F4
Map of body in space: F2 
Awareness of goal: no
encoding of motor act: no

Question 10

Grasping Components

Answer 10

Visual pathway: dorsal
Parietal Areas: AIP Cortex, PFG
Creation of maps: no 
Map of space/body: no
Awareness of goal: Yes via F5
Encoding of Motor act: no

Question 11

Cerebellum Role in Voluntary Motion

Answer 11

• sequence complex acts
• correct force/direction
• balance + eye movements
• learning of complex actions

Question 12

Spinocerebellum: Central Area

Answer 12

• posture control of ongoing motions
• inputs: vestibular, visual and auditory, efferent copy (intended motion)
• outputs: interpositus n, fastigial n, rubrospinal tract

Question 13

Cerebrocerebellum

Answer 13

• plan complex motions
• sequence of rapid motions
• inputs: all regions of cerebral cortex
• outputs: dentate, back to cortex

Question 14

Vestibulocerebellum

Answer 14

• balance/eye movements
• input: vestibular apparatus
• output: fastigial n, vestibular n, ascend or descend

Question 15

Deep Cerebellar Nuclei

Answer 15

• transmit outputs from cerebellum
• dentate nucleus
• fastigial nucleus
• interpositus (globose and emboliformis)

Question 16

Spinocerebellum: Lateral Areas

Answer 16

• force and direction of motion
• control ballistic motions
• inputs: muscle afferent, efferent copy (goal)
• output: interpositis nucleus, rubrospinal tract

Question 17

Basal Ganglia Function

Answer 17

• involved in planning/programming of movement
• initiation of movement
• also control end of movement to some extent
• work by inhibition and withdrawal of inhibition (to start movement)

Question 18

Basal Ganglia Direct Pathway

Answer 18

• striatonigal GABA-ergic pathway
• permissive to motion
  1. axons from striatum project to SNPR and GPi
  2. pre-synaptic terminal releases GABA in SNPR and GPi
  3. inhibition of neurons in SNPR and GPi via Cl channel

Question 19

Parkinson’s Disease

Answer 19

• substantia nigra pars compacta input abolished
• less DA
• direct pathway is difficult to activate
• indirect pathway difficult to inhibit
• inability to initiate motion

Question 20

DA Effect on Direct Pathway

Answer 20

source: SNPC
location of dopamine synapse: striatum
receptor on striatal neuron: D1
effect of DA binding: excitation
overall effect on pathway: activation

Question 21

DA Effect on Indirect Pathway

Answer 21

source: SNPC
location of dopamine synapse: striatum
receptor on striatal neuron: D2
effect of DA binding: inhibition
overall effect on pathway: inhibition

Question 22

Integration of Motor Control

Answer 22

1. pre-frontal cortex plans actions and carries out thought process
2. interactions with parieto-temporal-occipital association area and all levels of motor cortex and cerebellum
3. association of frontal, supplementary, pre-motor cortex, and cerebrocerebellum
4. interactions between frontal, premotor SMC, and basal ganglia determine if motion will occur
5. columns in primary motor cortex are activated
6. action potentials travel down axons of pyramidal cells and activate alpha motor neurons of muscles
7. Gamma motor neurons reduce sensitivity of muscle spindles in antagonist muscle
8. Spino cerebellum ensures motion is correct after motion starts