Motor Functions of Spinal Cord

Question 1

reciprocal inhibition

Answer 1

when a stretch reflex excites one muscle it often simultaneously inhibits the antagonist muscles, the neuronal circuit that causes this reciprocal relation is called reciprocal innervation

Question 2

positive supportive reaction

Answer 2

pressure on the footpad of a decerebrate animal causes the limb to extend against the pressure applied to the foot

Question 3

cord righting reflex

Answer 3

when a spinal animal is laid on its side, it will make uncoordinated movements to try to raise itself to standing position

Question 4

crossed extensor reflex

Answer 4

about 0.2 to 0.5 sec after a stimulus elicits a flexor reflex in one limb, the opposite limb begins to extend

Question 5

magnet reaction

Answer 5

in positive support reactions, pressure on one side causes extension in that direction.

Question 6

the oscillation back and forth between flexor and extensor muscles in rhythmic stepping movements results from?

Answer 6

mutually reciprocal inhibition circuits within the matrix of the cord itself, oscillating between neurons controlling agonist and antagonist muscles

Question 7

stumble reflex

Answer 7

if the top of the foot encounters an obstruction during forward thrust, the forward thrust will temporarily stop then in rapid sequence the foot will be lifted higher and proceed to be placed over the obstruction.

Question 8

mark time reflex

Answer 8

if a well healed spinal animal is held up and its legs are allowed to dangle freely the stretch on the limbs occasionally elicits diagonal stepping between the forelimbs and hindlimbs

Question 9

galloping reflex

Answer 9

when almost equal stretch or pressure stimuli are applied to the limbs on both sides of the body at the same time unequal stimulation elicits diagonal walking reflex

Question 10

scratch reflex

Answer 10

it is initiated by itch or tickle sensation. it involves two functions:

• position sense
• to and fro scratching movement

Question 11

mass reflex

Answer 11

in a spinal animal the spinal cord suddenly becomes excessively active causing mass discharge in large portions of the spinal cord

Question 12

usual stimulus of mass reflex

Answer 12

strong pain stimulus to skin

excessive filling of a viscus

Question 13

what are the effects of mass reflex?

Answer 13

• major portions of bodys skeletal muscles go into flexor spasm
• colon and bladder evacuate
• the arterial pressure rises to maximal values
• body breaks out into profuse sweating

Question 14

mass reflex mechanism is similar to that of

Answer 14

epileptic seizures

Question 15

spinal shock

Answer 15

when the spinal cord is suddenly transected in the upper neck at first essentially all cord functions including the cord reflexes immediately become depressed to the point of complete silence

Question 16

after-effects of spinal shock

Answer 16

• arterial blood press falls drastically
• all skeletal muscle reflexes are blocked during initial stages of shock (first to return is the stretch reflex)
• sacral reflexes for bladder and colon emptying are blocked in the first few weeks

Question 17

types of neurons in each spinal cord segment

Answer 17

sensory relay neurons
anterior motor neurons
interneurons

Question 18

anterior motor neurons

Answer 18

• located in anterior gray matter
• are of two types alpha motor neurons, which give rise to type A alpha motor nerve fibers which go to extrafusal fibers and gamma motor neurons, which give rise to type A gamma motor nerve fibers which go to intrafusal fibers of skeletal muscle

Question 19

motor innervation of extrafusal skeletal muscle

Answer 19

alpha efferent fibers

Question 20

Renshaw Cells

Answer 20

• located in anterior horns of spinal cord in association with motor neurons.
• almost immediately after the anterior motor neuron axon leaves the body of the neuron collateral branches from the axon pass to the renshaw cells
• they are inhibitory, thus stimulation of each motor neuron inhibits adjacent motor neurons (lateral inhibition)
• renshaw cells help in focus and sharpening of signals

Question 21

more than half of the nerve fibers that ascend and descend in the spinal cord are:

Answer 21

propriospinal fibers, they aid in multisegmental reflexes including reflexes that coordinate simultaneous movements in forelimbs and hindlimbs

Question 22

muscle sensory receptors

Answer 22

• muscle spindles (in belly) send info about length/ change in length
• golgi tendon organs (in tendons) send info about tendon tension/ change in tension

Question 23

motor innervation of intrafusal skeletal muscle

Answer 23

gamma efferent fibers

Question 24

central receptor area of muscle spindle has:

Answer 24

primary and secondary afferent endings

Question 25

primary afferent endings

Answer 25

aka annulospiral ending
type la
17 micrometer
transmits sensory signals at a velocity of 70-120m/s
excited by both the nuclear bag and nuclear chain fibers

Question 26

secondary afferent endings

Answer 26

type ll
8 micrometers
spreads like branches on a bush
excited by nuclear chain fibers only

Question 27

types of muscle spindle intrafusal fibres:

Answer 27

nuclear bag muscle fiber(1-3 in each spindle)

nuclear chain fibers (3-9 in each spindle)

Question 28

static response

Answer 28

when the receptor portion of the muscle spindle is stretched slowly the number of impulses transmitted from both the primary and secondary endings increase almost directly in proportion to the degree of stretchung and continue to transmit these impulses for a few seconds

Question 29

the gamma efferent system is controlled

Answer 29

• primarily by bulboreticular facilitatory region (involved in antigravity contractions)
• secondarily by impulses transmitted to bulboreticular area from the cerebellum basal ganglia and cerebral cortex

Question 30

clonus

Answer 30

muscle jerks oscillate

Question 31

transmission of impulses from the tendon organ into the cns is done by:

Answer 31

type lb fibers

Question 32

lengthening reaction

Answer 32

when tension on the muscle and therefore on the tendon becomes extreme, the inhibitory effect of the golgi tendon organ can be so great that it leads to a sudden reaction in the spinal cord that causes instantaneous relaxation of the entire muscle

Question 33

dorsal spinocerebellar tracts carry

Answer 33

instantaneous information from both the muscle spindles and the golgi tendon organs directly to the cerebellum at 120m/s (fastest in brain/spinal cord)

Question 34

pathway for flexor reflex (pain/nociceptive)

Answer 34

i. diverging circuits
ii. reciprocal inhibition circuits
iii. circuits for discharge