Spinal Cord Reflexes

Question 1

What specific neural structures do spinal reflexes require?

Answer 1

An afferent limb (sensory) and efferent limb (motor)

Question 2

What supplies the lower motor neurons of lamina IX?

Answer 2

the efferent/motor limb

Question 3

What are the afferent/sensory limb provided by?

Answer 3

primary sensory neurons that enter the cord through the dorsal roots of spinal nerves

Question 4

What tpe of receptor is a neuromuscular spindles?

Answer 4

enscapsulated receptors

Question 5

What do neuromuscular spindles in skeletal muscle monitor?

Answer 5

1) stretch/tension/length of skeletal muscle (flexing vs extending a muscle)
2) velocity of tension/length/stretch changes of skeletal muscle (slow stretch vs reflex stretch)

Also known as proprioception

Question 6

Where is the greatest distribution of neuromuscular spindles found?

Answer 6

Greatest in muscles near where it joins its tendon and in muscles that perform skilled moevemnts

Question 7

What is the shape of neuromuscular tendons?

Answer 7

Fusiform shaped

Question 8

How are neuromuscular spindles attached in regards to skeletal muscles?

Answer 8

They are attached in parallel therefore the capsule of connective tissue of the spindle is attached to the CT that encloses the extrafusal fiber (spindle lies side beside the extrafusal fibers)

Question 9

Where are intrafusal muscle fibers enclosed?

Answer 9

Enclosed in capsular tissue

Question 10

What happens when extrafusal muscle fibers do when they are stretched?

Answer 10

When extrafusal muscle fibers are stretched it should increase the tension of a neuromuscular spindle

Question 11

What happens when extrafusal muscle fibers do when relaxed?

Answer 11

When extrafusal muscle fibers relax it decreases tension of neuromuscular spindle

Question 12

How many fibers are found in each spindle?

Answer 12

2-14 fibers per spindle

Question 13

Which are smaller, extrafusal or intrafusal fibers?

Answer 13

Intrafusal muscle fibers

Question 14

What are the two types of intrafusal fibers?

Answer 14

nuclear chain fibers

nuclear bag fibers

Question 15

When tension in neuromuscular spindles increase what happens to the firing of fibers?

Answer 15

Increases firing of type Ia and type II fibers

Question 16

When tension in neuromuscular spindles decrease what happens to the firing of fibers?

Answer 16

Decreased firing of the type Ia and type II fibers

Question 17

How many types of fibers supply sensory innervation t neuromuscular spindles?

Answer 17

2 types of fibers:
Group A alpha fibers
Group A beta fibers

Question 18

What is another name for group A alpha fibers?

Answer 18

Type Ia fibers

Question 19

What do type Ia fibers spiral around and form?

Answer 19

These endings spiral around intrafusal fibers forming annulospiral endings of the muscle spindle

Question 20

What is another name for Group A beta fibers?

Answer 20

Type II fibers

Question 21

What do type II fibers form?

Answer 21

flower spray endings of the spindle

Question 22

When are type Ia and II fibers activated?

Answer 22

When a muscle is stretched at an appropriate rate.

Question 23

What does the activation of type Ia and II fibers do?

Answer 23

Stretch leads to lengthening (increased tension) in neuromuscular spindles and the endings are stimulated and generating proprioceptive data that travels to the CNS/spinal cord via primary afferents

Question 24

What is the motor innervation of neuromuscular spindles achieved by?

Answer 24

Gamma motor neurons

Question 25

What do gamma motor neurons control?

Answer 25

The length and tension of neuromuscular spindles and determines the sensitivity of the nm spindle to stretch

Question 26

What does an increasing in firing of gamma motor neurons result in?

Answer 26

Contraction of intrafusal fibers and increases the sensitivity (lowers the threshold) of the nm spindle to a stretch stimulus

Question 27

What can intense gamma motor neuron activity initiate?

Answer 27

Initiates spindle discharge and results in an increase in firing of type Ia and II fibers

Question 28

What is a stretch reflex also known as?

Answer 28

a deep tendon reflex

Question 29

What are the 2 neurons required for a stretch reflex to occur?

Answer 29

Afferent limb | Efferent limb

Question 30

What is the afferent limb of a deep tendon reflex?

Answer 30

Sensory fibers from a nm spindle (Ia and II fibers)

Question 31

What is the efferent limb of a deep tendon reflex?

Answer 31

Alpha motor neurons

Question 32

What is an example of a stretch reflex that only requires 2 neurons?

Answer 32

Monosynaptic reflex

Question 33

What is required to initiate the stretch reflex of a muscle?

Answer 33

High velocity stretch

Question 34

In the stretch reflex, what occurs with spindle activation and afferent information?

Answer 34

Enter into the spinal cord visa type Ia and II fibers

Question 35

In the stretch reflex, where do central processes of primary afferents travel?

Answer 35

Primary afferents enter cord and send collaterals in the ascending conscious proprioceptive pathway

Question 36

Where do collaterals in the stretch reflex terminate?

Answer 36

Directly on alpha motor neurons and facilitate them

Question 37

What do the pool of alpha motor neurons activated in the stretch reflex supply?

Answer 37

Supply extrafusal muscle fibers of the homonymous (same) muscle that was stretched

Question 38

What happens to the muscle after the pool of alpha motor neurons activate?

Answer 38

The muscle contracts or shortens

Question 39

What happens to spindles when the muscle contracts?

Answer 39

Tension in the spindle decreases resulting in: decreased firing of Ia and II fibers -> loss of facilitation on alpha motor neurons -> decreased activity of alpha motor neurons and muscle reflexes

Question 40

What other receptors help to monitor tension generated in muscle tendon units?

Answer 40

Golgi tendon organs (neurotendinous spindles)

Question 41

What are Golgi tendon organs?

Answer 41

Encapsulated receptor in the tendon, positioned in series with the muscle tendon

Question 42

Where are golgi tendon organs found?

Answer 42

In tendons mostly near muscle

Question 43

What afferent fibers supply golgi tendon organs?

Answer 43

Ib (A beta fibers)

Question 44

What occurs in golgi tendon organs when a muscle contracts?

Answer 44

Muscle contracts -> increased tension of golgi tendon organs -> increased firing of Ib fibers

Question 45

What effect does golgi tendon organs have on alpha motor neurons?

Answer 45

Afferent information of golgi tendon organs is projected along ascending conscious pathways and onto interneurons in the spinal cord gray that have an inhibitory effect on alpha motor neurons that supply the homonymous muscle

Question 46

What components are included in the gamma reflex loop?

Answer 46

``` Gamma motor neurons Intrafusal muscle fibers of nm spindles Type Ia, II fibers Alpha motor neurons Extrafusal muscle fibers ```

Question 47

What is important about the gamma reflex loop?

Answer 47

This loop of neurons and contractile fibers plays an important role in the control of muscular activity, including - involved in maintaining general tone and in control of active movement

Question 48

How is the gamma reflex loop interrupted?

Answer 48

De-afference of a muscle

Question 49

What does the de- afference of a muscle do?

Answer 49

1) Loss of muscle tone but no paralysis | 2) movements lack precision and lack control of force of contraction

Question 50

Since many descending motor control fibers from higher centers influence lower motor neurons that terminate on gamma motor neurons, what would the result after de-afference of these muscles

Answer 50

Increase sensitivity of the nm spindle to increase firing of Ia, II fibers and this directly influences alpha motor neurons which increase firing and it causes extrafusal muscle fibers to contract and move the joint

Question 51

How do upper motor neurons exert control on muscular activity via alpha motor neurons?

Answer 51

Directly, by terminating on alpha motor neurons

Question 52

How do upper motor neurons exert control on muscular activity via gamma motor neurons?

Answer 52

Indirectly, by terminating on gamma motor neurons

Question 53

What is the flexor reflex?

Answer 53

Protective reflex that results in a removal of a body part from the source of noxious stimulus

Question 54

What type of reflex is a flexor reflex?

Answer 54

Polysynaptic (more than 2 neurons required)

Question 55

What do noxious stimulus activate nad how does it travel up the cord?

Answer 55

primary pain afferents (group A delta and C fibers) that enter the cord and tract cells relay the the pain data along the ascending conscious pathway

Question 56

Where do collaterals of the primary pain afferents synapse and where do they project fibers?

Answer 56

synapse on interneurons in the dorsal horn that project fibers to alpha motor neurons in the ventral horn

Question 57

Are flexor muscles innervated with the facilitation of alpha motor neurons?

Answer 57

Yes facilitation of alpha motor neurons innervate flexor muscles

Question 58

Are extensor muscles innervated with the facilitation of alpha motor neurons?

Answer 58

no, Inhibition of alpha motor neurons innervate extensor muscles

Question 59

What is reciprocal innervation?

Answer 59

When inhibition of neurons innervate antagonist muscles

Question 60

Is a single or multiple cord levels of motor neurons required for an effective flexor response?

Answer 60

multiple cord levels

Question 61

How does pain that might enter only at 1 cord segment activate an effective flexor response?

Answer 61

1) via collaterals in Lissauer's tract that share the noxious info to adjacent cord segments 2) by neurons in the spinal cord gray that send axons through the fasciculus proprius

Question 62

What is the fasciculus proprius?

Answer 62

Made up of spinospinalis neurons and its axons can travel upstream or downstream for short and long distances

Question 63

What is a flexion - crossed extension reflex?

Answer 63

Some interneurons send collaterals to the contralateral side of the cord and they activate motor neurons that innervate extensor muscles of the extremity on the opposite side