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 ce**ntral 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 re**main 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 l**esions** 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 1**5 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? ## Footnote  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 sp**inal cord on inhibitory interneurons** that in **turn terminate directly on the motor neurons**