Lecture 10: Spinal Cord, Brainstem, Cortex Control of Motor Function I

Question 1

Interneurons

Answer 1

More numerous than anterior motor neurons; responsible for most of the spinal cord integrative function

Question 2

Motor unit

Answer 2

Composed of a single motor neuron and muscle fibers it innervates; composed of extrafusal fibers

Question 3

Motor neuron pool

Answer 3

Group of motor neurons that innervate fibers within the same muscle

Question 4

Small motor neurons

Answer 4

Innervate few muscle fibers, lowest thresholds, fire first, generate smallest force

Question 5

Large motor neurons

Answer 5

Innervate many muscle fibers, highest thresholds, fire last, generate largest force

Question 6

Renshaw cells

Answer 6

Inhibitory cells in anterior horns of spinal cord, transmit inhibitory signals to surrounding motor neurons (lateral inhibition) and to same motor neuron (recurrent inhibition)

Question 7

Muscle spindle (muscle sensor function)

Answer 7

Group Ia, II afferents; arranged in parallel with extrafusal fibers; detect dynamic and static changes in muscle length

Question 8

Golgi tendon organ

Answer 8

Group Ib afferents; arranged in series with extrafusal fibers; detect muscle tension

Question 9

Pacinian corpuscles

Answer 9

Group II afferents; detect vibrations

Question 10

Free nerve endings

Answer 10

Group III, IV afferents’ detect noxious stimuli

Question 11

Muscle spindle (motor function)

Answer 11

3-12 intrafusal fibers innervated by gamma motor neurons; run parallel to extrafusal fibers

Question 12

Central region of muscle spindle

Answer 12

No contractile fibers, functions as sensory receptor detecting changes in muscle length

Question 13

Nuclear bag fiber

Answer 13

Intrafusal; detect rate of change in muscle length; innervated by group Ia afferents/dynamic gamma efferents; nuclei arranged in bag like configuration

Question 14

Nuclear chain fiber

Answer 14

Intrafusal; detect static change in muscle length; innervated by group II afferents/static gamma efferents; more numerous than nuclear bag fibers, multiple nuclei arranged in a single row

Question 15

A-gamma motor neurons

Answer 15

Supply small intrafusal fibers in middle of muscle spindle

Question 16

Gamma-dynamic motor neurons

Answer 16

Excite nuclear bag intrafusal fibers

Question 17

Gamma-static motor neurons

Answer 17

Excite nuclear chain intrafusal fibers

Question 18

Dynamic stretch reflex

Answer 18

Signals transmitted from primary nerve endings, elicited by rapid stretch/unstretch; opposes sudden changes in to muscle length

Question 19

Static reflex

Answer 19

Transmitted by both primary and secondary nerve endings; causes degree of muscle contraction to remain relatively constant

Question 20

Circuitry of Golgi Tendon Organ

Answer 20

Type iB afferent, inhibitory interneuron, anterior motor neuron

Question 21

Flexor Withdrawal Reflex

Answer 21

Flexion on ipsilateral side, extension of contralateral side

Question 22

Premotor cortex

Answer 22

Generate a plan for movement by developing a motor image of total muscle movement that is to be performed

Question 23

Supplementary motor cortex

Answer 23

Generate a plan for movement by programming complex motor sequences and mentally rehearsing movement

Question 24

Where does the posterior motor cortex send its signals?

Answer 24

Primary motor cortex/basal nuclei and thalamus to primary motor cortex

Question 25

How does damage to Broca’s area affect speech?

Answer 25

Individual will be unable to form full words

Question 26

How does Broca’s area relate to associated respiratory and voluntary eye movement fields?

Answer 26

Affects respiratory action of vocal cords, prevents voluntary movement of eyes on different objects

Question 27

In which layer of the motor cortex do the pyramidal cells reside?

Answer 27

5th layer

Question 28

In which layer of the motor cortex do input signals enter?

Answer 28

Layers 2-4

Question 29

In which layer do neurons arise to communicate with other regions of the cerebral cortex?

Answer 29

6th layer

Question 30

Upper motor neurons

Answer 30

Entirely within CNS, form descending tracts (originate in cerebral cortex/brainstem/cerebellum)

Question 31

Lower motor neurons

Answer 31

Begin in CNS; from anterior horns of spinal cord and brainstem cranial nerve nuclei; made up of alpha motor neurons and make up spinal/cranial nerves