lecture 9

Question 1

what happens when sensory fibers enter the spinal cord?

Answer 1

they are transmitted to higher centers or they synapse locally to elicit motor reflexes

Question 2

where are the motor neurons located?

Answer 2

they are located in the anterior portion of the cord of the cord aka the ventral horn

Question 3

how much bigger are the motor neurons located in the anterior portion of the cord compared to other motor neurons?

Answer 3

50-100% times bigger

Question 4

where are the sensory neurons located?

Answer 4

they are located in the dorsal horn and so they receive a stimulus and transmit to the higher centers of the nervous system

Question 5

]what the two types of anterior motor neurons?

Answer 5

alpha (lower motor neurons) and gamma motor neurons(which work on sensory apparatus called muscle spindles or intrafusal fibers)

Question 6

what are the alpha motor neurons?

Answer 6

they give rise to large alpha A fiber, upon stimulation they excite extrafusal fibers (collectively called a motor unit) and these neurons go to the muscle cell

Question 7

what are the gamma motor neurons?

Answer 7

give rise to smaller type A gamma fibers and go to small special skeletal muscle fibers called intrafusal fibers; note that more of these neurons makes the muscle more sensitive

Question 8

what is important to note about interneurons?

Answer 8

they help us create reflex type movements and comprise the neural circuitry for the motor reflexes

Question 9

define the Renshaw Cell Inhibitory System

Answer 9

immediately after the anterior motor neuron axon leaves the body of the neuron, collateral branches from the axon pass to adjacent Renshaw cells. These are inhibitory cells that transmit inhibitory signals to the surrounding motor neurons

Question 10

Renshaw cells are inhibitory cells that transmit inhibitory signals to the surrounding motor neurons, T/F?

Answer 10

T

Question 11

what are propiospinal fibers?

Answer 11

they travel up and down the cord for 1-2 segments and provide the pathways for multisegmental reflexes, like the registration of pain and temperature

Question 12

when we initiate voluntary muscle movements, what fibers are we innervating?

Answer 12

the extrafusal fibers

Question 13

what are the two types of sensory receptors of the muscle?

Answer 13

muscle spindle and golgi tendon organ

Question 14

what is the muscle spindle?

Answer 14

these sense muscle length and change in length

Question 15

what is the golgi tendon organ?

Answer 15

these sense tendon tension and change in tension, these consist of sensory nerve endings interwoven among collagen and are type 1b afferent motor neuron

Question 16

what type of neuron is the golgi tendon organ?

Answer 16

Type 1b afferent motor neuron

Question 17

what are the signals from the mentioned sensory receptors (muscle spindle and golgi tendon organ) of the muscle for?

Answer 17

intrinsic muscle control

Question 18

in terms of the the muscle spindle, there are two important endings, what are they?

Answer 18

primary ending and secondary ending

Question 19

what type of neurons are the primary endings of the muscle spindle? where do these go?

Answer 19

these are Type 1a afferent motor neuron and they go to the bag fiber

Question 20

how would you describe the shape of the primary ending?

Answer 20

annulospiral ending located in the center of the receptor area and encircles the central portion of each intrafusal fiber

Question 21

what type of neurons are the secondary endings of the muscle spindle? where do these go?

Answer 21

type II afferent fibers and these innervate the chain fibers

Question 22

how would you describe the actions of the secondary fibers?

Answer 22

innervate the receptor region on one or both sides of the primary ending and they spread like branches on a bush, hence the word, chain fibers

Question 23

what are the extrafusal fibers?

Answer 23

alpha motor neurons that give rise to large type A alpha fibers and are collectively called a motor unit and are outside and around the muscle

Question 24

what are the intrafusal fibers?

Answer 24

these are gamma motor neurons that are small, special skeletal muscle fibers within the muscle spindle

Question 25

in terms of physiologic function of the muscle spindle, what do we call the simplest manifestation of muscle spindle function?

Answer 25

muscle stretch reflex

Question 26

what happens when a muscle is stretched suddenly?

Answer 26

excitation of the spindles causes a reflex contraction of the large skeletal muscle fibers of the stretched muscle and also of closely allied synergistic muscles

Question 27

what is the importance of the coactivation of alpha and gamma motor neurons?

Answer 27

they keep the length of the receptor portion of the muscle spindle from changing during the course of the muscle contraction and so this phenomenon keeps the muscle spindle from opposing the muscle contraction

Question 28

T/F, coactivation of the alpha and gamma motor neurons maintains the proper damping function of the muscle spindle, regardless of change in muscle length

Answer 28

T

Question 29

when alpha motor neurons are stimulated by upper centers, what other motor neuron is stimulated?

Answer 29

gamma motor neurons are also stimulated (both extrafusal and intrafusal fibers contract at the same time)

Question 30

In terms of the role of muscle spindles in voluntary motor activity, what percent of motor nerve fibers to the muscle are small type A gamma efferent fibers?

Answer 30

31%

Question 31

what is the name of the efferent fibers that make up 31% of the motor nerve fibers to the muscle, this is in terms of the role of muscle spindles in voluntary motor activity.

Answer 31

type A gamma efferent fibers

Question 32

in terms of the role of muscle spindles in voluntary motor activity when alpha motor neurons are stimulated, what other motor neurons are stimulated? what is this called? what is the effect on extrafusal and intrafusal fibers?

Answer 32

gamma motor neurons; coactivation of alpha and gamma neurons; it causes them to contract at the same time

Question 33

what is the golgi tendon organ?

Answer 33

these sense tension and change in tension

Question 34

what so golgi tendon organs consist of?

Answer 34

sensory nerve ending interwoven among collagen

Question 35

what motor neurons are the golgi tendon organ?

Answer 35

type 1b afferent motor neuron

Question 36

in terms of coactivation of alpha and gamma motor neurons what happens if gamma motor axons are cut?

Answer 36

the spindle loses activity when muscle contracts

Question 37

what is maintained during alpha-gamma coactivation?

Answer 37

maintains spindle function when muscle contracts

Question 38

during active contraction of the muscle, what motor neurons cause the contraction of the extrafusal muscle fibers with consequent relation of intrafusal fibers?

Answer 38

alpha motor neurons

Question 39

in active contraction are the spindles activated?

Answer 39

no

Question 40

what is the tension like in active contraction?

Answer 40

tension is slow, no adjustment made to increase resistance

Question 41

during muscle contraction is the golgi tendon organ activated? effect?

Answer 41

yes; causes relaxation

Question 42

in active contraction of the muscle, what fibers and motor neurons are involved?

Answer 42

type Ib fibers and alpha motor neurons

Question 43

what is active contraction with Gamma Coactivation?

Answer 43

Intrafusal and extrafusal fibers contract; spindles activated, reinforcing contraction stimulus via 1a fibers in accord with resistance

Question 44

in active contraction with Gamma Coactivation, is the golgi tendon organ activated? effect?

Answer 44

Tendon organ is activated, causing relaxation if load is too big

Question 45

in the damping mechanism in smoothing muscle contraction what happens when the spindle is not working properly?

Answer 45

the muscle contraction is jerky

Question 46

in neuronal circuitry of the stretch reflex, what is the monosynaptic pathway?

Answer 46

pathway allows a reflex signal to return with the shortest time delay to the muscle after excitation of the spindle

Question 47

in the neuronal circuitry of the stretch reflex, what is the monosynaptic stretch?

Answer 47

a single synapse between the afferent and efferent neurons

Question 48

what does the monosynaptic reflex oppose?

Answer 48

sudden changes in muscle length

Question 49

what is the purpose in the clinical application of the stretch reflex?

Answer 49

To determine how much background excitation or tone the brain is sending to the spinal cord

Question 50

what is being tested in the clinical application of the stretch reflex?

Answer 50

the facilitation of gamma efferents

Question 51

what is the effect of cortical lesions in the clinical application of the stretch reflex?

Answer 51

increase muscle stretch reflexes

Question 52

what is the name of the reflex tested in the clinical setting?

Answer 52

knee jerk reflex

Question 53

what is spinal reflex circuit?

Answer 53

when a skeletal muscle is abruptly stretched and a reflexive contraction of the same muscle occurs, increasing muscle tension and opposing the stretch.

Question 54

for what is the spinal reflex circuit strong? what is this reflex also called?

Answer 54

in physiological extensor muscles; myotatic reflex

Question 55

what is the knee jerk reflex?

Answer 55

A light tap on the patellar tendon deflects the tendon, which then pulls on and stretches the quadriceps femoris muscle

Question 56

what neurons are affected in the knee jerk reflex?

Answer 56

type 1a sensory neurons

Question 57

what happens physiologically to the body when we use the knee jerk reflex?

Answer 57

Passive stretching a skeletal muscle causes a reflexive contraction of that same muscle and relaxation of the antagonist muscle

Question 58

what is stimulated in the reflexive contraction of the knee jerk response?

Answer 58

The reflex stimulates in the spinal cord → the motor neurons to the extensor muscles → inhibits the motor neurons to the flexor muscle

Question 59

what does the stretch reflex depend on?

Answer 59

the nervous system and requires sensory feedback from the muscle

Question 60

what abolishes the stretch reflex?

Answer 60

Cutting the dorsal (sensory) roots to the lumbar spinal cord

Question 61

what is the effect of the knee jerk reflex?

Answer 61

the stretch reflex in the quad

Question 62

so in the knee jerk reflex, we see reciprocal innervation. What is this?

Answer 62

As the knee jerk reflex causes contraction of the quadriceps muscle → there is an antagonist relaxation during contraction (semitendinosus muscle antagonist to knee jerk reflex)

Question 63

what neuron are affected in reciprocal innervation?

Answer 63

Branches of the group Ia sensory axons excite specific interneurons that inhibit the α motor neurons of the antagonists

Question 64

what is the reflex the inverse myotatic reflex is also called?

Answer 64

golgi tendon reflex

Question 65

in the inverse myotatic reflex, what is the effect of the golgi tendon organs?

Answer 65

they become aligned in series with the muscle and super sensitive to the tension of a tendon and respond to force generated by muscle

Question 66

what sensory axons are involved in the Golgi tendon reflex?

Answer 66

group 1b sensory axons and these excite both the excitatory and inhibitory interneurons within the spinal cord This circuit inhibits the muscle in which tension has increased and excites the antagonist muscle (opposite of stretch reflex)

Question 67

what does the inverse myotatic reflex inhibit?

Answer 67

the motor neurons to the extensor muscle and stimulates the motor neurons to the flexor muscle

Question 68

T/F, the inverse myotatic reflex uses more of the golgi tendon organ then it uses the sensory type 1b neuron?

Answer 68

T

Question 69

why does the golgi tendon want to equalize the force among muscle fibers?

Answer 69

to prevent too much tension on the muscle

Question 70

what is the inhibitory nature of the tendon reflex?

Answer 70

if the tension on the muscle and tendon is too high than inhibitory effect occurs providing relaxation of the entire muscle (lengthening reaction)

Question 71

what is the purpose of the protective mechanism in the golgi tendon reflex?

Answer 71

prevents tearing of the muscle or avulsion of the tendon from its attachments to the bones

Question 72

what type of reflex happens when you touch a hot pan?

Answer 72

reflexive

Question 73

what are the neurons that stimulate the flexor reflex?

Answer 73

from fast pain afferent neurons in the skin

Question 74

how is the flexor reflex different from a simple stretch reflex?

Answer 74

Unlike simple stretch reflexes, coordinate movement from entire limb or even pairs of limbs

Question 75

so in a leg that feels pain, what does the reflex inhibit? what about the opposite leg?

Answer 75

the motor neurons to the extensor muscle and stimulates the motor neurons to the flexor muscle; In the opposite leg, the reflex stimulates the motor neurons to the extensor muscle and inhibits the motor neurons to the flexor muscle (supports the body weight when the other leg flexes)

Question 76

how do reflexes affect movement?

Answer 76

it affects coordination of several muscle groups Reflexive Movement - Spinal integration, input to the brain Postural reflexes - Cerebral integration, maintains balance, input to cortex