Motor Functions of Spinal Cord and Reflexes

Question 1

what is the name of the reflex that happens when you move your hand away very quickly when you put your hand on a hot burner

Answer 1

withdrawal of flexion reflex

Question 2

what are the 3 neuronal organizations of the spinal cord

Answer 2

sensory neurons
motor neurons
interneurons

Question 3

describe sensory neurons (ganglion, where does it transmits signals to, where is the synapse and what does it elicit)

Answer 3

-dorsal root ganglion
-transmits signals to higher centers
-synapse at the spinal cord level to elicit motor reflexes

Question 4

describe motor neurons (horn, what do they innervate, what are the 2 types of MN and what does they excite)

Answer 4

-anterior horn,
-directly innervate skeletal m. fibers
-alpha MNs (A-alpha axons) excite extrafusal muscle fibers (motor units), muscle contraction
-Gamma MNs (A-gamma axons) excite intrafusal fibers (muscle sensory receptors)

Question 5

describe interneurons (they have connections with what, what can they do)

Answer 5

-local neurons that have connections with sensory and motor neurons
-they can be inhibitory or excitatory

Question 6

what are sensory receptors of the muscle and what are they stimulated by

Answer 6

mechanoreceptors and they are stimulated by mechanical displacement of the muscle

Question 7

describe muscle spindles (where are they, what do they sense)

Answer 7

-distributed throughout the muscle belly (midportion of intrafusal fibers)
-sense muscle length (stretched, relaxed, contracted) and rate of change of length

Question 8

what are sensory signals transmitted through in muscle spindles

Answer 8

1a (primary sensory endings) fibers
2 (secondary sensory endings) fibers

Question 9

describe golgi tendon organs (where are they, what do they sense and what are sensory signals transmitted thru)

Answer 9

-are located in the muscle tendon
-sense tendon tension and rate of change of tension
-sensory signals are transmitted thru 1b fibers

Question 10

sensory receptors within the body of a muscle that primarily detect changes in the length of a m

Answer 10

muscle spindles

Question 11

what is the function of a muscle spindle

Answer 11

to provide info on the position of body parts (proprioception)

Question 12

describe primary sensory endings of the muscle spindle (type 1a fibers) (where do they terminate, respond to what)

Answer 12

-terminate on nuclear bad and nuclear chain fibers
-respond to the rate of changes in muscle length (dynamic) and to the degree of stretch of the muscle (static)

Question 13

describe secondary sensory endings of the muscle spindle (type 2 fibers) (where do they terminate, respond to what)

Answer 13

-terminate on nuclear chain fibers
-respond mostly to the degree of stretch of the muscle (static response)

Question 14

what is alpha-gamma coactivation

Answer 14

causes the tension on the muscle spindles to be maintained as the muscle shortens; thus sensitivity to stretch is maintained

Question 15

what needs to happen to send signals to the CNS

Answer 15

muscle spindles must be stretched

Question 16

for the biceps curl example:
A) elbow is ___ = ____ and ____ fibers are ____= muscle spindles are responding by sending signals to the ____

Answer 16

elbow is extended = extrafusal and intrafusal fibers are stretched = muscle spindles are responding by sending signals to the CNS

Question 17

for the biceps curl example:
B) during biceps curl, ____ are activated to contract ____ –> muscle spindles get ___ and can no longer send signals to the___

Answer 17

during biceps curl, alpha motorneurons (Mns) are activated to contract muscle fibers –> muscle spindles get shorten and can no longer send signals to the CNS

Question 18

for the biceps curl example:
C) to avoid the B situation, ___ are activated to contract ____ fibers –> muscle spindles get ____ and respond by sending signals to the ___

Answer 18

C) to avoid the B situation, gamma are activated to contract intrafusal fibers –> muscle spindles get stretched and respond by sending signals to the CNS

Question 19

what are encapsulated sensory receptor through which muscle tendon fibers pass

Answer 19

golgi tendon organs

Question 20

golgi tendon organ are stimulated when muscle fibers are

Answer 20

tensed by the contraction or the stretching of the muscle (sensitive to muscle tension)

Question 21

GTOs react intensively (static and dynamic responses) when

Answer 21

when muscle tension suddenly increase (dynamic) or settles down rapidly to a lower level of steady state tension (static)

Question 22

what are GTO signals transmitted thru

Answer 22

Ib fibers

Question 23

Ib fibers in GTO inhibit indirectly (through interneurons) what and to allow what

Answer 23

alpha motor neuron at the spinal cord to allow the muscle to relax and thus to relieve the tension on the tendon

Question 24

what are named mechanism by which sensory impulses are automatically converted into a motor effect

Answer 24

spinal cord reflexes

Question 25

what are the reactions in the spinal cord reflexes and what are they controlled by

Answer 25

involuntary and rapid reactions controlled by the spinal cord integration centers

Question 26

what can spinal cord reflexes do to the body

Answer 26

protective mechanism to the body (e.g prevent an over stretch (or contraction) of the muscle, withdrawal from a painful stimulus…)

Question 27

what is a stretch reflex

Answer 27

sudden stretch of the muscle activates the muscle spindles (of the same muscle)

Question 28

what are the associated fibers to the stretch reflex and what do they transmit

Answer 28

associated sensory fibers (Ia &II) transmit impulses at the spinal cord level

Question 29

in stretch reflex what fibers synapse directly with what and causes what

Answer 29

type Ia and II fibers synapse directly with alpha motor neurons causing the muscle to contract

Question 30

the stretch reflex is a ____ reflex because of the connection between the sensory and the motor nerve fiber

Answer 30

monosynaptic

Question 31

describe the neuronal circuits of the stretch reflex in a patellar reflex (what happens, what is the function, what are the endings for the afferent signals, where is the synapse, what results, what is the innervation, what send the efferent signals)

Answer 31

-striking the patellar tendon elicits a sudden kicking movement of the lower leg
-function of the stretch reflex is to oppose sudden changes in muscle length (stretching)
-afferent signal via primary (Ia) and secondary (II) sensory endings
-synapse in spinal cord with alpha motor neurons
-muscle contraction results to oppose stretch
-reciprocal innervation (Collateral 1a synapses inhibitory interneurons)
-inhibitory interneuron sends efferent signal to antagonist (relaxation of antagonist m.)

Question 32

what is the function of Golgi tendon reflex

Answer 32

relieve excess tension on the tendon

Question 33

contracting of a muscle creates a ___ on the ___ attached to the same muscle and thus ___ the golgi tendon organs

Answer 33

tension
tendon
activates

Question 34

golgi tendon sensory fibers (1b) transmits ____ at a ____ _____ to ____

Answer 34

impulses at a higher frequency to spinal cord

Question 35

in the golgi tendon reflex:
sensory neurons synapse with what, that inhibit what, and causes what
sensory neurons synapse with what, that excite what, and causes what

Answer 35

sensory neurons synapse with inhibitory interneurons that inhibit alpha motor neurons and cause the contracted muscle to relax
sensory neurons synapse with excitatory interneurons that excite alpha motor neurons of antagonist muscles and cause the muscle to relax

Question 36

what are the five steps of golgi tendon reflex

Answer 36

1- increased tension stimulates sensory receptor (tendon)
2-sensory neuron excited
3-within integrating center (sc), sensory neuron activates inhibitory interneuron
4-motor neuron inhibited
5-effector (muscle attached to same tendon) relaxes and relieves excess tension

Question 37

extrafusal fibers are activated by which types of motor neurons

Answer 37

alpha motor neurons

Question 38

what is the flexion reflex

Answer 38

is initiated by a painful stimulus that causes automatic withdrawal of the threatened body part

Question 39

in flexion reflex; sensory neurons synapse with interneurons that…

Answer 39

-excite motor neurons of the flexor muscle (e.g biceps) and cause muscle to contract
-inhibit motor neurons of the extensor muscle (e.g triceps) and cause the muscle to relax