motor control

Question 1

upper motor system (cerebral)

Answer 1

complex movements
learning

Question 2

lower motor system (spinal)

Answer 2

reflexes
pattern generation

Question 3

lower motor neurons

Answer 3

• located in the ventral horn of the spinal cord
• innervate muscles: alpha - extrafusal muscle, generates force (motor unit); gamma - intrafusal fibers in spindles (sensing stretch)

Question 4

3 types of motor units

Answer 4

• fast fatigable (FF) - large force, but become fatigued after a couple mins; running, jumping
• fast fatigue-resistant (FR) - intermediate force, don’t fatigue as rapidly; jogging and finger movements
• slow (S) - low force, but don’t fatigue due to many mitochondria; posture and other sustained actions like walking

Question 5

motor units undergo plasticity with training

Answer 5

• muscle fibers increase
• motor neurons increase in size and dendritic complexity, and change excitability

Question 6

size recruitment principle

Answer 6

motor units are activated so that small force units are activated first (due to their low threshold for activation), if more force is required the FR are activated, and if maximal force is needed, FF units are activated

Question 7

spinal stretch reflex loop

Answer 7

allows for stabilization of sudden loads, which stretch muscle
unexpected stretch activates spindles, which activate alpha motor neurons causing tension in muscle to counteract stretch

Question 8

negative feedback from Golgi tendon organs

Answer 8

regulates the force generated by the muscle, preventing excessive force that could cause damage

Question 9

flexion-crossed extension reflex

Answer 9

strong cutaneous stimuli cause withdraw of ipsilateral leg (hazard avoidance) and extension of contralateral leg (for balance)

Question 10

reflexes can be overridden by

Answer 10

top-down control
descending commands from the brain via gamma motor neurons and/or spinal interneurons

Question 11

central pattern generation

Answer 11

neurons in periphery (spinal) that are able to generate patterns for typical rhythmic coordinated movement of torso and extremities
- can be refined and modulated by inputs from sensory systems and the CNS

Question 12

efference copy

Answer 12

a copy of the muscle command that is used by the brain to anticipate movement and posture without having to wait for feedback from Golgi tendon organs and muscle spindles

Question 13

feed forward controller

Answer 13

using a model of the body/world, the controller can anticipate future states and act accordingly before sensory info arrives

Question 14

cerebral cortex involvement in movement

Answer 14

1. multiple pre-motor areas that have a variety of complex functions for planning movement
2. primary motor cortex (M1) which has a rough topographic map of the contralateral body and initiates movement

Question 15

M1 neurons typically fire most rigorously for movement in

Answer 15

one direction

Question 16

mirror neurons

Answer 16

neurons in premotor cortex that respond to the observation of a movement and the execution of the movement

Question 17

afferent (inputs) projections to cerebellum

Answer 17

• frontal cortex (motor and sensory signals)
• parietal cortex (sensory signals)
• inferior olive (teaching signal for errors)
• vestibular nucleus (balance)
• spinal cord (proprioception)

Question 18

efferent (output) projections from cerebellum

Answer 18

• projections go to the deep cerebellar nuclei, which project to the thalamus/cerebral cortex involved in motor control, and to brainstem structures involved in motor control

Question 19

cortico-cerebellar loops

Answer 19

cerebellum forms a loop with premotor, motor, and parietal regions of cerebral cortex - with additional postural info from the brainstem
- helps fine tune motor output and is part of the feed forward model for motor control

Question 20

structure of cortex of the cerebellum

Answer 20

• purkinje cells have a fan-like dendritic structure that are in parallel with other purkinje neurons
• parallel fibers pass through the fans
• climbing fibers wind around the dendrites -> activate during motor error and drive synaptic plasticity so as to modify future motor programs and avoid object