lecture 10-spinal cord, brainstem, cortex control of motor function

Question 1

describe anterior motor neurons (efferents)

Answer 1

alpha motor neurons give rise to A alpha (A-alpha) fibers

Question 2

describe interneurons

Answer 2

30X as numerous as anterior motor neuron. small and highly excitable. capable of spontaneous activity. responsible for most of spinal cord integrative function

Question 3

describe a motor unit

Answer 3

composed of a single motor neuron and the muscle fibers it innervates. composed of extrafusal fibers

Question 4

describe motor neuron pool

Answer 4

group of motor neurons that innervate fibers within the same muscle

Question 5

describe recruitment in a motor neuron

Answer 5

refers to the increase in tension of muscle contraction by the activation of additional motor units (size principle)

Question 6

describe small motor neurons

Answer 6

innervate a few muscle fibers, lowest threshold, fire first, generate smallest force

Question 7

describe large motor neurons

Answer 7

innervate many muscle fibers, highest threshold, fire last, generate largest force

Question 8

define renshaw cells

Answer 8

inhibitory cells in anterior horns of spinal cord

Question 9

where do renshaw cells receive collateral branches from

Answer 9

alpha motor neurons

Question 10

what does the transmission of inhibitory signals to surrounding motor neurons by renshaw cells result in

Answer 10

results in lateral inhibition and enhance fluidity of limb movement.

Question 11

describe the muscle spindle

Answer 11

group Ia and II afferents. arranged in parallel with extrafusal fibers. detect both dynamic and static changes in muscle length

Question 12

describe golgi tendon organ (muscle sensor)

Answer 12

group Ib afferents. arranged in series with extrafusal fibers. detect muscle tension.

Question 13

describe pacinian corpuslces as muscle sensors

Answer 13

group II afferents. detect vibration

Question 14

describe free nerve ends (muscle sensors)

Answer 14

groups III and IV afferents. detect noxious stimuli

Question 15

what are muscle spindles innervated by

Answer 15

small gamma motor neurons (group II afferents)

Question 16

how do muscle spindles run in comparison to extrafusal fibers

Answer 16

run parallel to them

Question 17

describe the central region of spindle

Answer 17

has no contractile fibers; functions as a sensory receptor

Question 18

what does stretching of central region of intrafusal fires stimulate

Answer 18

sensory fibers

Question 19

what do muscle spindles detect

Answer 19

changes in muscle length

Question 20

describe nuclear bag fibers

Answer 20

detect rate of change in muscle length. innervated by group Ia afferents and dynamic gamma efferents. multiple nuclei located in a central bag-like configuration

Question 21

describe nuclear chain fibers

Answer 21

detect static change in muscle length. Innervated by group II afferents and static gamma efferents. more numerous than nuclear bag fibers. multiple nuclei arranged in a single row

Question 22

what does stimulation of muscle spindle sensory fibers result from

Answer 22

lengthening of entire muscle. contraction of ends of itnrafusal fibers

Question 23

what are muscle spindle gamma motor neurons coactivated with

Answer 23

alpha motor neurons

Question 24

descirbe A gamma motor nuerons

Answer 24

supply small intrafusal fibers in middle of muscle spindle

Question 25

descrie gamma-dynamic motor neurons

Answer 25

excite nuclear bag intrafusal fibers

Question 26

describe gamma static motor neurons

Answer 26

excite nuclear chain intrafusal fibers

Question 27

what brain areas control gamma fibers

Answer 27

bulboreticular region of brain stem, cerebellum, basal nuclei, cerebral cortex

Question 28

describe the dynamic stretch reflex

Answer 28

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

Question 29

describe static reflex

Answer 29

transmitted by both primary and secondary endings, causes degree of muscle contraction to remain relatively constant

Question 30

how are golgi tendon organs arranged in respect to extrafusal fibers

Answer 30

in series with them

Question 31

what do golgi tendon organ detect

Answer 31

muscle tension

Question 32

describe the circuitry of golgi tendon organ

Answer 32

type Ib afferent –> inhibitory interneuron –> anterior motor neuron

Question 33

what does the anterior part of the premotor cortex develop

Answer 33

a motor image of the total muscle movement that is to be performed

Question 34

what does the posterior motor cortex send signals to

Answer 34

primary motor cortex, basal nuclei and thalamus, primary motor cortex

Question 35

where are pyramidal cells located in the motor cortex

Answer 35

5th layer

Question 36

where are input signals located in the motor cortex

Answer 36

layers 2-4

Question 37

where do upper motor neurons originate

Answer 37

cerebral cortex, cerebellum, brainstem

Question 38

where do lower motor neurons begin

Answer 38

in CNS from anterior horns of spinal cord and from brainstem cranial nerve nuclei