Chp 55 Motor function of Spinal Cord: cord reflex

Question 1

The “neuronal circuit” which causes the specific to-and-fro movements of the legs are found where?

Answer 1

Spinal cord

The brain simply sends command signals to the spinal cord to set into motion the walking process

The brain gives directions that control the sequential cord activities

Question 2

example: to promote turning movements as required, to lean the body forward during acceleration, to change the movements from walking to jumping as needed, and to monitor continuously and control equilibrium.

All this is done through Brain or Spinal Cord?

Answer 2

All this is done through “analytical” and “command” signals generated in the brain

Question 3

Define Gray Matter?

Answer 3

Grey matter refers to unmyelinated neurons and other cells of the central nervous system. It is present in the brain, brainstem and cerebellum, and present throughout the spinal cord. …

Question 4

Define Cord Grey Matter

Answer 4

The grey matter in the spinal cord consists of interneurons, as well as the cell bodies of projection neurons.

Integrated are for the Cord reflexes

Question 5

Sensory signals enter the cord almost entirely through the sensory roots, also know as?

Answer 5

posterior OR dorsal roots.

Question 6

Name two the two types of Neurons of the Spinal Cord.

Answer 6

(1) anterior motor neurons
(2) interneurons.

Question 7

Define anterior motor neurons and location

Answer 7

1. Are several thousand neurons that are 50 to 100 percent larger than most of the others
2. Located in each segment of the anterior horns of the cord gray matter.
3. They give rise to the nerve fibers that leave the cord by way of the anterior roots.
4. directly innervate the skeletal muscle fibers.

Question 8

The Anterior Motor Neurons are of two types:

Name Each.

Answer 8

1. alpha motor neurons
2. gamma motor neurons.

Question 9

Alpha Motor Neurons give rise to?

Answer 9

1. type A alpha (Aα) motor nerve fibers in the middle of the MUSCLE SPINDLE- which helps to control basic muscle “TONE”
   - these fibers branch many times after they enter the muscle
   - they innervate the large skeletal muscle fibers

Question 10

stimulation of a single alpha nerve fiber excites anywhere from ____ to several _____ _____ ____ ____, which are collectively called the ____ ____.

Answer 10

from three to several hundred skeletal muscle fibers, which are collectively called the motor unit

Question 11

gamma motor neurons:

size, location, transmit, purpose

Answer 11

1. along with the alpha motor neurons, which excite contraction of the skeletal muscle fibers, about one half as many much smaller

2. gamma motor neurons are located in the spinal cord anterior horns

3. gamma motor neurons transmit impulses through much smaller type A gamma (Aɣ) motor nerve fibers, averaging 5 micrometers in diameter, which go to small, special skeletal muscle fibers called intrafusal fibers
4. these fibers constitute the middle of the muscle spindle, which helps control basic muscle “tone”

Question 12

interneurons are present in all areas of the ____ ____ matter, in the _____ horns, ____ horns and the ____ ____ betwee them.

Answer 12

interneurons are present in all areas of the cord gray matter—in the dorsal horns, the anterior horns, and the intermediate areas between them.

Question 13

Interneuron cells are about ___ ___ as numerous as the anterior motor neurons

Answer 13

30 times

Question 14

Interneurons are ____ and ____ excitable, often exhibiting spontaneous activity and capable of firing as rapidly as ____ ____ per second

Answer 14

small and highly excitable

1500 times per second

Question 15

Interneurons they have many _____ with one another, and many of them also ____ _____ with the anterior motor neurons

Answer 15

interconnections

synapse directly

Question 16

The interconnections among the____ and _____ _______ neurons are responsible for most of the ____ _____ of the spinal cord

Answer 16

interneurons and anterior motor neurons are responsible for most of the integrative functions of the spinal cord

Question 17

almost all of incoming sensory signals to the spinal cord, are transmitted first and appropriately processed through ___ ____

Answer 17

almost all of incoming sensory signals to the spinal cord, are appropriately processed in interneurons circuit

Question 18

Renshaw cells are closely associated with the Motor Neurons…What are Renshaw Cells reponsible for and where are they found?

Answer 18

1. Are inhibitory Cells, they transmit Inhibitory Signals to Surrounding Motor Neurons causing Lateral Inhibition
2. Also located in the anterior horns of the spinal cord

Question 19

Define propriospinal fibers

Answer 19

Multisegmental Connections from One Spinal Cord Level to Other Levels

Question 20

Renshaw cells are ___ ____ that transmit inhibitory signals to the surrounding motor neurons stimulation of each motor neuron tends to _____ _____ ______neurons, an effect called _____ ____.

Answer 20

1. inhibitory cells
2. inhibit adjacent motor
3. lateral inhibition

Question 21

Why is Lateral Inhibition important?

Answer 21

the motor system uses this lateral inhibition to focus, or sharpen, its signals in the same way that the sensory system uses the same principle to allow unabated transmission of the primary signal in the desired direction while suppressing the tendency for signals to spread laterally

Question 22

What does proper control of muscle function require?

Answer 22

1. excitation of the muscle by spinal cord anterior motor neurons
2. also continuous feedback of sensory information from each muscle to the spinal cord, indicating the functional status of each muscle at each instant

Question 23

in order to answer what is the length of the muscle or what is its instantaneous tension or how rapidly is its length or tension changed we need to understand:

that Muscles and Tendons are supplied by aboundantly with 2 special types of sensory Receptors…

Name each

Answer 23

(1) muscle spindles
(2) Golgi tendon organs

Question 24

muscle spindles:

Answer 24

they send information to the nervous system about muscle length or rate of change of length

Question 25

Golgi Tendon:

Answer 25

located in the muscle tendons and transmit information about tendon tension or rate of change of tension

Question 26

Name 3 main points about the Two Special types of Sensory Receptors and Mame each

Answer 26

the signals from 1-Muscle Spindles and 2-Golgi Tendon Organs receptors are either entirely or almost entirely used for the purpose of intrinsic muscle control

1. they operate almost completely at a subconscious level

2 they transmit tremendous amounts of information not only to the spinal cord but also to the cerebellum and even to the cerebral cortex, helping each of these portions of the nervous system function to control muscle contraction

Question 27

Describe the structure and motor innervation of the muscle spindle

4 points of discussion:

Answer 27

1. each spindle is 3 to 10 millimeters long
2. it is built around 3 to 12 very small intrafusal muscle fibers that are pointed at their ends and attached to the glycocalyx of the surrounding large extrafusal skeletal muscle fibers
3. each intrafusal muscle fiber is a very small skeletal muscle fiber
4. the central region of each of these fibers— the area midway between its two ends—has few or no actin and myosin filaments

Question 28

central portion of the ____ ____ fiber does not contract when the ends contract, instead function as a _____ ______.

Answer 28

1. Intrafusal Muscle (tini skeletal muscle fiber)
2. Sensory Receptor

Question 29

the end portions of the Intrafusal muscle that contracts are excited by___ ____ ____ nerve fibers that originate from small type __ ____ ___neurons in the _____ ____of the spinal cord,

Answer 29

small gamma motor nerve fibers

A gamma motor

anterior horns of the spinal cord,

Question 30

(A) Gamma Motor nerve fibers in the Anterior Horns of the spinal cord are also called?

Answer 30

• called* gamma efferent fibers,
  note: in contradistinction to the large alpha efferent fibers (type Aα nerve fibers) that innervate the extrafusal skeletal muscle

Question 31

Whta do Large alpha efferent fibers innervate?

Answer 31

large alpha efferent fibers (type Aα nerve fibers) that innervate the extrafusal skeletal muscle

Question 32

T or F

The receptor portion of the muscle spindle is its central portion. In this area, the intrafusal muscle fibers have myosin and actin contractile elements

Answer 32

False

intrafusal muscle fibers do not have myosin and actin contractile elements

Question 33

sensory fibers originate in the Central Portion of the Muscle Spindle are stimulated how?

Answer 33

 they are stimulated by stretching of midportion of the spindle

Question 34

the muscle spindle receptor can be excited in two ways:

Name each:

Answer 34

1. lengthening the whole muscle stretches the midportion of the spindle and, therefore, excites the receptor
2. even if the length of the entire muscle does not change, contraction of the end portions of the spindle’s intrafusal fibers stretches the midportion of the spindle and therefore excites the receptor

Question 35

There are 2 types of sensory endings which are found in central receptor area of the muscle spindle:

Name Each:

Answer 35

1. the primary Afferent ending
2. the secondary Afferent ending

Question 36

Define primary ending

Answer 36

1. in the center of the receptor area, a large sensory nerve fiber encircles the central portion of each intrafusal fiber, forming the so-called primary ending or annulospiral ending

* this nerve fiber is a type Ia fiber averaging 17 micrometers in diameter, and it transmits sensory signals to the spinal cord at a velocity of 70 to 120 m/sec, as rapidly as any type of nerve fiber in the entire body

Question 37

Describe secondary ending

Answer 37

1. usually one but sometimes two smaller sensory nerve fibers—type II fibers with an average diameter of 8 micrometers—innervate the receptor region on one or both sides of the primary ending
2. this sensory ending is called the secondary ending; sometimes it encircles the intrafusal fibers in the same way that the type Ia fiber does, but often it spreads like branches on a bush

Question 38

What are 2 types of muscle spindle intrafusal fibers?

Answer 38

(1) nuclear bag muscle fibers (1 to 3 in each spindle)
(2) nuclear chain fibers (3 to 9)

Question 39

Define nuclear bag muscle fibers

Answer 39

nuclear bag muscle fibers (1 to 3 in each spindle), in which several muscle fiber nuclei are congregated in expanded “bags” in the central portion of the receptor area

Question 40

Define nuclear chain fibers

Answer 40

nuclear chain fibers (3 to 9), which are about half as large in diameter and half as long as the nuclear bag fibers and have nuclei aligned in a chain throughout the receptor area

Question 41

What nerve ending is excited by both the nuclear bag intrafusal fibers and the nuclear chain fibers

Answer 41

primary sensory nerve ending is excited by both the nuclear bag intrafusal fibers and the nuclear chain fibers

Question 42

What Sensory nerve ending is usually excited only by nuclear chain fibers

Answer 42

secondary ending

Question 43

Describe the effect called static response of the spindle receptor

Answer 43

it is the response of both the primary and the secondary endings to the length of the receptor “static” response

when the receptor portion of the muscle spindle is stretched slowly, the number of impulses transmitted from both the primary and the secondary endings increases almost directly in proportion to the degree of stretching, and the endings continue to transmit these impulses for several minutes

Question 44

Define dynamic response

Answer 44

means that the primary ending responds extremely actively to a rapid rate of change in spindle length

the primary receptor transmits tremendous numbers of excess impulses to the large 17-micrometer sensory nerve fiber, but only while the length is actually increasing

Question 45

The gamma motor nerves to the muscle spindle can be divided into two types:

Answer 45

1. gamma dynamic (gamma-d)
2. gamma-static (gamma-s)

Question 46

gamma dynamic (gamma-d) Excites what fibers?

Answer 46

excites mainly the nuclear bag intrafusal fibers

Question 47

gamma-static (gamma-s) Excites what fibers?

Answer 47

mainly the nuclear chain intrafusal fibers

Question 48

T or F

stretching the muscle spindles increases the rate of firing, whereas shortening the spindle decreases the rate of firing

Answer 48

True

Question 49

How does monosynaptic pathway allows a reflex signal to return?

Answer 49

It allows a reflex signal to return with the shortest possible time delay back to the muscle after excitation of the spindle.

Monosynaptic reflexes are the simplest kind of reflexes. They include only stretch reflexes like the common knee jerk, jaw jerk, ankle jerk, etc tested in neurological consults. Their function is to maintain normal muscle length and tone.

Question 50

Describe Polysynaptic reflexes

Answer 50

Polysynaptic reflexes are much more complex and range from the simpler Golgi tendon reflex to complicated flexor and crossed extensor reflexes.

Question 51

the simplest manifestation of muscle spindle function is the ____ _____ _____

Answer 51

muscle stretch reflex

Question 52

whenever a muscle is stretched suddenly, excitation of the spindles causes _____ _____ of the large skeletal muscle fibers of the stretched muscle and also of closely allied _____ _____.

Answer 52

reflex contraction

synergistic muscles (Synergists musclesact on movable joints)

ex:

the chest, triceps and shoulder work together to do a Push-up.

The biceps and your backmuscles work together during a Pull-up to pull your body to the bar.

Question 53

the stretch reflex can be divided into 2 components:

Answer 53

1. the dynamic stretch reflex
2. the static stretch reflex

Question 54

dynamic stretch reflex is elicited by the ____ _____ _____ transmitted from the primary sensory endings of the muscle spindles, caused by ____ ____or _____.

Answer 54

potent dynamic signal

rapid stretch or unstretch

Question 55

T or F

when a muscle is suddenly stretched or unstretched, a weak signal is transmitted to the spinal cord

Answer 55

False

Strong Signal is transmitted to the spinal cord

Question 56

T or F

The dynamic stretch reflex is over within a fraction of a second after the muscle has been stretched (or unstretched) to its new length, but then a weaker static stretch reflex continues for a prolonged period there after

Answer 56

True

Question 57

weaker Static stretch reflex is elicited by the continuous static receptor signals transmitted by What?

Answer 57

both primary and secondary endings

Question 58

What is the importance of the static stretch reflex ?

Answer 58

the importance of the static stretch reflex is that it causes the degree of muscle contraction to remain reasonably constant, except when the person’s nervous system specifically wills otherwise

Question 59

“Damping” is a function of which reflexes and why is it important?

Answer 59

1. function of the dynamic and static stretch reflexes
2. important function of the stretch reflex is its ability to prevent oscillation or jerkiness of body movements
3. damping OR smoothing, function of stretch reflex

Question 60

31 % percent of all the motor nerve fibers to the muscle are the _____ _____ _____ ____ efferent fibers rather than large type A alpha motor fibers

Answer 60

small type A gamma

Question 61

whenever signals are transmitted from the motor cortex or from any other area of the brain to the alpha motor neurons, in most instances the ___ ____ ___ are stimulated simultaneously, an effect called ______ of the alpha and gamma motor neurons

Answer 61

1. gamma motor neurons
2. coactivation of the alpha and gamma motor neurons

Question 62

What does Coactivation of Alpha and Gamma motor neurons cause?

Answer 62

this causes both the extrafusal skeletal muscle fibers and the muscle spindle intrafusal muscle fibers to contract at the same time

Question 63

What is the purpose of contracting the muscle spindle intrafusal fibers at the same time that the large skeletal muscle fibers contract ?

Answer 63

1. it keeps the length of the receptor portion of the muscle spindle from changing during the course of the whole muscle contraction

therefore, coactivation keeps the muscle spindle reflex from opposing the muscle contraction

2. it maintains the proper damping function of the muscle spindle, regardless of any change in muscle length

Question 64

sudden stretch of muscle spindles is all that is required to elicit a ___ _____ _____.

Answer 64

dynamic stretch reflex

Question 65

What is the purpose of “ Muscle Jerks” examination performed by neurologist ?

Answer 65

it is used to assess the degree of facilitation of spinal cord centers.

These reflexes are used most frequently in deter- mining the presence or absence of muscle spasticity caused by lesions in the motor areas of the brain or diseases that excite the bulboreticular facilitatory area of the brain stem

Question 66

Define golgi tendon reflex.

Answer 66

The Golgi tendon organ Fig 55-8 , is an encapsulated sensory receptor through which muscle tendon fibers pass.

Golgi tendon organ helps control muscle tension

Question 67

Explain why “when the tension of Muscle in a strong stretch” becomes great enough, contraction suddenly ceases and the muscle relaxes.

What is this phenomenon called and name the Receptor.

Answer 67

1. this relaxation in response to strong stretch which is called the inverse stretch reflex
2. the receptor for the inverse stretch reflex is in the Golgi tendon organ

Question 68

How many muscle fibers are usually connected to each golgi tendon organ, and the organ is

stimulated when this small bundle of muscle fibers is “tensed” by _____ or _____ the muscle

Answer 68

about 10 to 15 muscle fibers are usually connected to each golgi tendon organ

contracting or stretching the muscle

Question 69

What is the major difference in excitation of the golgi tendon organ versus the muscle spindle?

Answer 69

Difference is that the spindle detects muscle length and changes in muscle length, whereas the tendon organ detects muscle tension as reflected by the tension in itself

Question 70

tendon organ, like the primary receptor of the muscle spindle, has both a ____ ____ and a ______ response, reacting intensely when the muscle tension suddenly increases (the _____response) but settling down within a fraction of a second to a lower level of steady state firing that is almost directly proportional to the muscle tension (the _____response)

Answer 70

dynamic response

static response

dynamic response

static response

Question 71

What happens when the golgi tendon organs of a muscle tendon are stimulated by increased tension in the connecting muscle?

 this reflex is entirely ______ ?

 thus, this reflex provides a ____ _____mechanism that prevents the development what?

Answer 71

1. signals are transmitted to the spinal cord to cause reflex effects in the respective muscle

 inhibitory

 negative feedback mechanism that prevents the development of too much tension on the muscle

Question 72

Golgi tendon organs make up what rapidly conducting sensory nerve fibers?

Answer 72

Ib group of myelinated, rapidly conducting sensory nerve fibers

Question 73

Stimulation of which fibers leads to the production of IPSPs on the motor neurons?

What does it supply?

Answer 73

Ib fibers leads to the production of IPSPs on the motor neurons that supply the muscle from which the fibers arise

Question 74

Where do the Ib fibers end in the spinal cord?

Answer 74

the Ib fibers end in the spinal cord on inhibitory interneurons that in turn terminate directly on the motor neurons