Lecture 6: Motor Functions of Spinal Cord and Reflexes

Question 1

what are the 3 neurons part of Neuronal Organization of the Spinal Cord

Answer 1

sensory neurons
motor neurons
interneurons

Question 2

Where do you find the sensort neurons in the spinal cord

Answer 2

dorsal root ganglion

Question 3

where do you find the motor neurons in the spinal cord

Answer 3

anterior horn

Question 4

What is the function of sensory neurons in the spinal cord

Answer 4

transmit signals to higher centers

Question 5

what is the function of motor neurons in the spinal cord

Answer 5

directly innervate skeletal muscle fibers

Question 6

Where do sensory neurons synapse and why

Answer 6

Synapse at the spinal cord level to elicit motor reflexes

Question 7

what are the 2 types of motor neurons of the spinal crod

Answer 7

Alpha MNs

Gamma MNs

Question 8

What is the fucntion of Alpha MN? Gamma MN?

Answer 8

excite extrafusal muscle fibers (motor units), muscle contraction
A-gamma axons) excite intrafusal (spindles) fibers (muscle sensory receptors)

Question 9

Which motor neuron excites intrafusal msucle fibers

Answer 9

gamma MN

Question 10

Which motor neurons excites extrafusual muscle fibers

Answer 10

alpha

Question 11

What is the “typical muscle fiber”

Answer 11

alhpa

Question 12

What are interneurons and what are the two types

Answer 12

Local neurons that have connections with sensory & motor neurons
They can be inhibitory or excitatory

Question 13

true or false: Interneurons are only excitatory

Answer 13

false, theyre excitatory and inhibitor

Question 14

What kind of receptors are sensory receptors of the muscle?

Answer 14

MECANORECEPTORS (i.e. stimulated by mechanical displacement of the muscle)

Question 15

What are the two sensory receptors (mecanoreceptors) of the msucle>

Answer 15

MUSCLE SPINDLES

GOLGI TENDON ORGANS

Question 16

Where are muscle spindles located

Answer 16

Are distributed throughout the muscle belly (midportion of intrafusal fibers)

Question 17

What do muscle spindles sense

Answer 17

Sense muscle length (stretched, relaxed, contracted) and rate of change of length

Question 18

Sensory signals in the muscle spendles are transmitte through what type of fibers?

Answer 18

1a (primary sensory ending) fibers

II (secondary sensory ending) fibers

Question 19

Whree are golgi tendon organs lcocated?

Answer 19

in the muscle tendon

Question 20

what do golgi tendons sense?

Answer 20

Sense tendon tension and rate of change of tension.

Question 21

what are the Sensory signals of the golgi tendon transitted through

Answer 21

1b fibers

Question 22

be able to locate the primary sensory endings, secondary sensory endings and 1b fibers

Answer 22

/

Question 23

rank by 1a, 1b and II by conduction velocity

Answer 23

Ia, Ib, II

Question 24

What is thje function of the msucle s[indles

Answer 24

Function: To provide info on the position of body parts (proprioception)

Question 25

Where do the Primary sensory endings of the muscle spindle (type Ia fibers) terminate?

Answer 25

Terminate on nuclear bag and nuclear chain fibers

Question 26

true or false: muscle spindles respond to both dynamic and static changes in the muscle length and stretch

Answer 26

true!! `

Question 27

explain how muscle spindle fibers respond to dynamic and statoic

Answer 27

Respond to the rate of change in muscle length (dynamic) and to the degree of stretch of the muscle (static) type 1a and type 2

Question 28

where do sSecondary sensory endings of the muscle spindle (type II fibers) terminate and what do they respond to ?

Answer 28

Terminate on nuclear chain fibers | Respond mostly to the degree of stretch of the muscle (static response)

Question 29

understand the diagram of passive muscle strecth vs primary and secondary endings

Answer 29

.

Question 30

When there is a dynamic change in muscle strentch BLANK are very good at detecting and sending out the signal

Answer 30

primary sensory endings

Question 31

WHat is the function of Alpha-Gamma Coactivation

Answer 31

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

Question 32

true or false: to send signals to the CNS, muscle spindles MUST be stretched

Answer 32

true

Question 33

explain the steps to how alpha-gamma coactivation works in extension

Answer 33

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

Question 34

explain what would happen wihtout the alpha gamma coactivation if we contracted our muscles

Answer 34

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 (doesn’t exist in reality)

Question 35

explain what happens in reality to allow muscle spiindles to be strecthed during flexion/ contraction

Answer 35

as alphas are activated to contract extrafusal, gamma are activated to contract intrafusal fibers → muscle spindles get stretched and respond by sending signals to the CNS= COACTIVATION

Question 36

TRUE OR FALSE: GTO are Encapsulated sensory receptor through which muscle tendon fibers pass

Answer 36

true

Question 37

when are golgi tendons stimulated?

Answer 37

“Tensed” by the contraction or stretching of the muscle (sensitive to muscle tension)

Question 38

Golgi tendons have a static response, dyanmic, or both?

Answer 38

both

Question 39

explain how golgi tendons have a static and dynamic resoonse

Answer 39

GTOs react intensively when muscle tension suddenly increases (dynamic) or settles down rapidly to a lower level of steady state tension (static)

Question 40

what type of fibers are golgi tendon signals transmitted by?

Answer 40

1b

Question 41

what is a fcuntion of the 1b in the golgi tendons?

Answer 41

Ib fibers inhibit indirectly (through interneurons) alpha motor neuron at the spinal cord to allow the muscle to relax and thus to relieve the tension on the tendon.

Question 42

What type of mecanism is the spinal crod reflexes

Answer 42

Mechanism by which sensory impulses are automatically converted into a motor effect

Question 43

true or false: spinal relfexes are voluntary

Answer 43

false

Question 44

What are spinal reflexes

Answer 44

Involuntary and rapid reactions controlled by the spinal cord integration centers

Question 45

are spinal reflexes a protective mecanism or destructive?

Answer 45

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

Question 46

From a human physiology perspective, can we say that the goaltender has good or bad reflexes?

Answer 46

no

Question 47

are the strecth reflex and golgi tendon reflex the same?

Answer 47

NO COMPLETELY DIFF

Question 48

is the strectch reflex associated with the msucle spindles or the golgi tendons

Answer 48

msucle spindles

Question 49

how is the strectn reflex activated

Answer 49

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

Question 50

what are they Associated sensory fibers for stretch reflex?

Answer 50

(Ia & II)

Question 51

true or false: Type Ia and II fibers synapse directly with alpha motor neurons causing the muscle to contract

Answer 51

true

Question 52

what type of reflex is the strecth reflex?

Answer 52

monosynaptic

Question 53

what is the fucntion of the strectn reflex

Answer 53

Function of the stretch reflex is to oppose sudden changes in muscle length (stretching)

Question 54

explain the neuronal circuit of the stretch reflex

Answer 54

Sudden stretch of muscle muscle spindles sends signal to spinal through: afferent signal via primary (Ia) and secondary (II) sensory endings There is a synapse in spinal cord with α-motor neurons alpha motor neurons send back signal for muscle contraction results to oppose stretch Reciprocal innvervation: Collateral 1a synapses inhibitory interneurons Inhibitory interneuron sends efferent signal to antagonist (Relaxation of antagonist muscle)

Question 55

Does the strecth reflex have only an afferent signal>

Answer 55

no , it also has a efferent singal (Inhibitory)

Question 56

If there is a sudden stretch in my quad muscle, what will happen

Answer 56

msucle spindles will feel the stretch and send signal up through 1a and 2 to the spinal cord signal synapses with alpha motor neurons which signal contracttion of the quad muscle to oppose the stretch AT THE SAME TIME, collaterol 1a synapses with inhibiotry interneurons to send an inhibitory signal to the hamstreing

Question 57

Where does the 1a signal synpase with in the stretch reflex?

Answer 57

synapses with alpha motor neurons for contraction | synapses with inhibitory interneurons to stop hamstring

Question 58

what is the function of the golgi tendon reflex

Answer 58

: to relieve excess tension on the tendon

Question 59

true or false: Contracting of a muscle creates a tension on the tendon attached to the same muscle and thus activates the Golgi tendon organs

Answer 59

treue

Question 60

explain the neuronal circuit for the golgi tendon reflex

Answer 60

1) increased tension at the tendon 2) - Sensory neurons synapse with interneurons that inhibit alpha motor neurons and cause the muscle to relax 3) collateral: - Sensory neurons synapse with interneurons that excite alpha motor neurons of antagonist muscles and cause muscle to contract (reciprocal activation)

Question 61

true or false: Afferent impulses from golgi tendon are also transmitted to the cerebellum where it is used to adjust muscle tension.

Answer 61

true

Question 62

know the graph of golgi tendon response to muscle contraction vs stretch

Answer 62

.

Question 63

Extrafusal fibers are acitviated by which neurons

Answer 63

ALPHA MOTOR NEURONS

Question 64

what is another name for the flexion refle x/

Answer 64

withdrawal reflex

Question 65

what is The flexion reflex initiated by

Answer 65

a painful stimulus that causes automatic WITHDRAWAL of the threatened body part

Question 66

explain the senseory neuron synapse for the flexion reflex

Answer 66

Sensory neurons synapse with interneurons that: 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

Question 67

explain the flexion and cross extensor reflex?

Answer 67

1) painful stimuli detected by nociceptor 2) signal is sent to aplha motor neurons to stimulate excitatory neurons to contract the agonist 3) same time: inhibiroty neurons inhibit the antagonist msucle on the other leg!!! EXTENSORS CONTRACT while flexors inhbit to allow leg to stand on the ground

Question 68

knwo the graphs for stretch Reflexes between Controls and SCI subjects

Answer 68

;

Question 69

why do SCI have so much more reflexes

Answer 69

SCI HAVE TOO MUCH EXCITATORY ACITIVTY AT THE SPINAL CORD