Stretch reflex, muscle spindle physiology | alpha gamma coactivation | CNS physiology

Summary

This educational video script delves into the stretch reflex, a fundamental topic in first-year MBBS exams. It explains the reflex's components, including the muscle spindle's sensory role, the types of nuclear back and chain fibers, and their respective static and dynamic functions. The script clarifies the monosynaptic nature of the stretch reflex, its role in maintaining muscle length through negative feedback, and the clinical significance of assessing motor system integrity. It also discusses the importance of alpha-gamma co-activation in voluntary muscle movements and the impact of gamma motor neuron activity on muscle tone and reflex sensitivity.

Takeaways

• 📚 The stretch reflex is a fundamental topic in first-year MBBS exams and is crucial for understanding muscle response mechanisms.
• 💪 The stretch reflex operates within skeletal muscles and involves a complex interaction between sensory and motor components.
• 🔍 Muscle spindles, containing nuclear bag and nuclear chain fibers, serve as the sensory receptors for the stretch reflex, detecting both static and dynamic stimuli.
• 🧬 The afferent nerve fibers, classified as Group 1A and Group 2, supply the muscle spindles and convey information about muscle length and velocity of change.
• 🌟 The stretch reflex is monosynaptic, meaning it involves a single synapse between the afferent nerve fibers and the alpha motor neurons.
• 🏋️‍♂️ Alpha motor neurons are responsible for contracting the extrafusal muscle fibers, which are the main contractile components of the muscle.
• 🔄 Gamma motor neurons play a key role in adjusting the sensitivity of the stretch reflex by supplying the contractile ends of the intrafusal fibers.
• ⏱️ The reaction time of the stretch reflex is between 19 to 24 milliseconds, indicating its rapid response to muscle stretch.
• 🔄 Alpha-gamma co-activation is essential for voluntary muscle movement, preventing the stretch reflex from opposing muscle contractions during movement.
• 🏥 Clinical assessment of the stretch reflex, such as the knee-jerk, is important for evaluating the integrity of the motor system in patients with paralysis.
• 🚑 Hyperactive stretch reflexes can indicate upper motor neuron lesions, as the inhibitory control over gamma motor neurons is disrupted, leading to increased sensitivity of the reflex.

Q & A

What is the stretch reflex?

The stretch reflex, also known as the myotatic reflex, is an involuntary response that occurs when a muscle is stretched. It helps maintain muscle tone and posture by contracting the muscle back to its original length when stretched.

What are the components of the stretch reflex?

The components of the stretch reflex include a receptor (muscle spindle), an afferent limb (sensory nerve fibers), a central nervous system processing center (spinal cord), and an efferent limb (motor neurons).

What are the two types of fibers found in the muscle spindle?

The two types of fibers found in the muscle spindle are nuclear bag fibers and nuclear chain fibers. They serve as receptors for the stretch reflex.

What is the difference between static and dynamic nuclear back fibers?

Static nuclear back fibers are important for detecting a static stimulus, such as maintaining muscle tone. Dynamic nuclear back fibers are important for detecting a dynamic stimulus, such as changes in muscle length during movement.

How are the muscle spindle fibers supplied by nerve fibers?

Muscle spindle fibers are supplied by efferent nerve fibers classified as Group Ia and Group II fibers. Group Ia fibers supply both static and dynamic components of the muscle spindle, while Group II fibers supply only the static component.

What is the role of the alpha motor neuron in the stretch reflex?

The alpha motor neuron is responsible for supplying the extrafusal muscle fibers, which are the contractile fibers of the skeletal muscle. When activated by the stretch reflex, these neurons cause the muscle to contract.

What is the role of the gamma motor neuron in the stretch reflex?

The gamma motor neuron supplies the contractile ends of the intrafusal muscle fibers (muscle spindle). It plays a role in adjusting the sensitivity of the stretch reflex and is involved in maintaining muscle tone and posture.

What is the significance of the monosynaptic nature of the stretch reflex?

The monosynaptic nature of the stretch reflex means it involves only one synapse between the afferent nerve fibers and the alpha motor neurons. This allows for a rapid response time, which is crucial for the reflex's function in maintaining muscle tone and posture.

What is the reaction time of the stretch reflex?

The reaction time of the stretch reflex is between 19 to 24 milliseconds, which is the time gap between the stimulus (muscle stretch) and the response (muscle contraction).

How is the stretch reflex involved in voluntary muscle movements?

During voluntary muscle movements, the stretch reflex is modulated by alpha-gamma co-activation. This co-activation prevents the reflex from opposing the movement and allows for smooth, controlled muscle contractions.

What is the clinical significance of the stretch reflex?

The stretch reflex is clinically significant as it is used to assess the integrity of the motor system in patients with paralysis or other neurological disorders. Hyperactive stretch reflexes may indicate upper motor neuron lesions.

Outlines

00:00

📚 Introduction to Stretch Reflex in MBBS

The script begins by introducing the topic of stretch reflex, a crucial subject for first-year MBBS students and a favorite for multiple-choice questions (MCQs). The stretch reflex is described as a complex but essential reflex involving the skeletal muscle. The components of the stretch reflex include the muscle spindle, which acts as a sensory component, and the contractile muscle fibers known as extrafusal fibers. The script explains the role of nuclear bag and nuclear chain fibers within the muscle spindle, and how they are innervated by different types of nerve fibers (1A and 2), which are responsible for detecting both static and dynamic stimuli. The explanation also covers the afferent and efferent pathways, culminating in the activation of alpha motor neurons in the spinal cord.

05:03

🔍 Detailed Anatomy of Stretch Reflex Components

This paragraph delves deeper into the anatomy of the stretch reflex, focusing on the sensory and motor components within the skeletal muscle. It explains the function of the muscle spindle, including the nuclear bag and chain fibers, and their respective roles in detecting muscle stretch. The paragraph also discusses the gamma motor neuron, which supplies the contractile ends of the intrafusal fibers, and the distinction between the sensory and motor roles of these fibers. The summary highlights the importance of the alpha and gamma motor neurons in the reflex arc, emphasizing the monosynaptic nature of the stretch reflex and its rapid response time.

10:03

🔄 Understanding Static and Dynamic Components of Stretch Reflex

The script explains the concepts of static and dynamic components of the stretch reflex. It describes how the muscle spindle responds to changes in muscle length (static) and the rate of change in muscle length (dynamic). The static component is associated with the nuclear chain fibers, while the dynamic component involves the nuclear bag fibers. The paragraph discusses the importance of these components in proprioception and the reflex's role as a negative feedback loop to maintain muscle length. It also touches on the clinical significance of the stretch reflex, including its use in assessing motor function and the impact of gamma motor neuron activity on reflex sensitivity.

15:04

🏃‍♂️ Alpha Gamma Co-activation and Voluntary Movement

This section of the script explores the concept of alpha gamma co-activation, which is essential for voluntary muscle contraction and maintaining muscle tone. It explains how the activation of both alpha and gamma motor neurons prevents the stretch reflex from opposing voluntary movements. The paragraph also discusses the influence of descending tracts on gamma motor neuron activity and how this influences muscle tone and posture. The summary highlights the clinical relevance of assessing stretch reflexes, such as the knee-jerk, and the use of maneuvers like the Jendrassik technique to enhance reflex response.

20:05

🛡️ Clinical Applications and Impact of Upper Motor Neuron Lesions

The final paragraph discusses the clinical applications of the stretch reflex, particularly in assessing the integrity of the motor system in cases of paralysis. It explains the process of eliciting stretch reflexes and the significance of muscle support during assessment to prevent voluntary contraction. The script also addresses the impact of upper motor neuron lesions, which can result in hyperactive stretch reflexes due to the disruption of inhibitory control over the gamma motor neuron. Additionally, it mentions other factors that can increase gamma motor neuron activity, such as anxiety and unexpected movements, and their effect on tendon reflexes.

Keywords

💡Stretch Reflex

The stretch reflex, also known as the myotatic reflex, is an automatic response that occurs when a muscle is stretched. It plays a crucial role in maintaining muscle tone and posture. In the video, the stretch reflex is the central theme, with the script detailing its function as a protective mechanism that prevents muscles from being stretched too far, which could lead to injury.

💡Skeletal Muscle

Skeletal muscle is the type of muscle attached to bones by tendons and is responsible for body movement. The script describes the structure of skeletal muscle, emphasizing the contractile muscle fibers and their role in the stretch reflex, where they are the primary site of action for the reflex response.

💡Muscle Spindle

A muscle spindle is a sensory organ within skeletal muscles that detects changes in muscle length. The script explains that muscle spindles contain specialized fibers, namely nuclear bag and nuclear chain fibers, which are the receptors for the stretch reflex, responding to both static and dynamic stimuli.

💡Nuclear Bag Fibers

Nuclear bag fibers are a type of intrafusal fiber found within muscle spindles. The script distinguishes between static and dynamic nuclear bag fibers, which are responsible for detecting changes in muscle length and velocity, respectively, and are crucial for the stretch reflex's activation.

💡Nuclear Chain Fibers

Nuclear chain fibers are another type of intrafusal fiber within muscle spindles that primarily detect static changes in muscle length. The script uses the term to illustrate how these fibers contribute to the stretch reflex by signaling changes in muscle length to the central nervous system.

💡Afferent Nerve Fibers

Afferent nerve fibers are responsible for transmitting sensory information from receptors to the central nervous system. In the context of the stretch reflex, the script describes how afferent fibers, specifically Group Ia and II fibers, carry signals from the muscle spindle to the spinal cord.

💡Alpha Motor Neuron

Alpha motor neurons are the final common pathway for the stretch reflex, controlling the contraction of skeletal muscles. The script explains that these neurons receive signals from afferent fibers and, upon activation, cause the extrafusal muscle fibers to contract, resulting in the reflex action.

💡Gamma Motor Neuron

Gamma motor neurons are responsible for the fine control of muscle spindle sensitivity by innervating the contractile ends of intrafusal fibers. The script discusses the role of gamma motor neurons in adjusting muscle tone and the sensitivity of the stretch reflex, particularly in the context of voluntary movement and posture.

💡Alpha Gamma Co-activation

Alpha gamma co-activation refers to the simultaneous activation of alpha and gamma motor neurons during voluntary muscle contraction. The script explains this concept as a mechanism that prevents the stretch reflex from opposing voluntary muscle movements, allowing for smooth and controlled muscle action.

💡Monosynaptic Reflex

A monosynaptic reflex is a neural pathway involving only one synapse between the afferent and efferent neurons. The stretch reflex is highlighted in the script as the primary example of a monosynaptic reflex, emphasizing its speed and directness in response to muscle stretch.

💡Negative Feedback Loop

A negative feedback loop is a biological control system that maintains stability by counteracting deviations from a set point. The script describes the stretch reflex as functioning as a negative feedback loop, where the reflex action works to restore muscle length to its original state after a stretch.

Highlights

Stretch reflex is a fundamental topic in first-year MBBS exams and a favorite for MCQs.

The stretch reflex is a reflex arc involving a stimulus, receptor, afferent, efferent, and response.

The reflex operates in skeletal muscles, involving contractile muscle fibers and tendons.

Muscle spindles are the sensory component of skeletal muscles, containing nuclear bag and nuclear chain fibers.

Nuclear back fibers are receptors for the stretch reflex, with static and dynamic varieties.

Nuclear chain fibers detect only static stimuli, unlike nuclear back fibers.

Efferent nerve fibers, classified as Group Ia and II, supply the muscle spindles.

The stretch reflex involves a direct connection between afferent fibers and alpha motor neurons.

Alpha motor neurons control extrafusal muscle fibers, which are contractile.

Gamma motor neurons supply the contractile ends of intrafusal fibers.

The stretch reflex is monosynaptic, with a single synapse between afferent and alpha motor neurons.

The reflex acts as a negative feedback loop to maintain muscle length.

The reaction time of the stretch reflex is 19 to 24 milliseconds.

Central delay in the stretch reflex is 0.6 to 0.9 milliseconds, indicating a single synapse.

Alpha-gamma co-activation is essential for voluntary muscle contraction.

Gamma motor neuron activation increases the sensitivity of the stretch reflex.

The stretch reflex is clinically used to assess the motor system's integrity.

In upper motor neuron lesions, hyperactive stretch reflexes can be observed due to increased gamma motor neuron activity.

Anxiety and unexpected movements can also increase gamma motor neuron activity.

Transcripts

Hello friends today we are going to

discuss a very important topic comes in

first year mbbs exams also a very

favorite topic for mcqs as well but it

is a bit difficult one that is a stretch

reflex so let us see the fundamentals of

stretch reflex and its applications as

well

see first as the name suggests it is a

reflex and like all the reflexes it will

have a stimulus there will be receptor

afferent Center efferent and there will

be a response so what are the components

of this stretch reflex

stress reflex operates in a muscle

skeletal muscle so suppose this is a

skeletal muscle

that is the contractile component of the

skeletal muscle where there will be lot

of muscle fibers so these are the

contractile muscle fibers which will

extend from end to end of a muscle and

the ends of these muscle fibers will

continue as a tendon now all skeletal

muscles have a sensory component as well

that is the muscle spindle

so in the center of the skeletal muscle

there is a sensory component which is

the muscle spindle and it has two types

of fibers that is there is a nuclear

back fibers so this uh first one which I

drew it is like a back you see central

part it is like a bag so this is a

nuclear back fiber and then there is

nuclear chain fibers okay nuclear back

fibers and nuclear chain fibers

so these are the receptors for the

stretch reflex

now remember there are two components of

these nuclear back fibers that is static

nuclear back fibers

and dynamic nuclear back fibers so this

is the receptor for the stretch reflex

so that means

this receptor static receptor is

important for detecting a static

stimulus and dynamic receptor is

important for detecting a dynamic

stimulus and what is the stimulus

stretch is the stimulus so we'll see

what is the static and dynamic on the

other hand nuclear chain is only

detecting static stimulus okay

so what I do is a nuclear chain there is

C so C I make it as s so it becomes a

static nuclear chain is only static

nuclear back both static and dynamic

another way to remember

this b b becomes d right so nuclear bag

is static as well as dynamic now these

nuclear bargain nuclear static fibers

are supplied by efferent nerve fibers

and what are these efferent nerve fibers

there are one a fibers and there are two

fibers now

these names come from lieth's

classification of sensory nerve fibers

so 1A fibers and two fibers Supply these

nuclear bag and nuclear chain and which

one these fibers Supply one is supplies

all the fibers that is nuclear back

static Dynamic and nuclear chain static

one A A is for all right so they Supply

this central part of these

um muscle spindle both types of muscle

spindle and both static as well as

Dynamic con component on the other hand

type 2 fiber supplies only the static

component that is static component of

both nuclear back as well as nuclear

chain fibers

so that I am not going to draw but

remember here that these fibers are

actually 1A and two fibers one a fibers

are supplying all the types of fiber

static dynamic in nuclear pack as well

as nuclear chain and two fibers it is

supplying only static component of

nuclear back and nuclear chain fibers so

these are the afferents of the stretch

reflex then these afferents actually

make contact in the spinal cord so let

me just draw a spinal cord here we'll

get another neater diagram later so they

just go into the spinal cord and from

here they actually climb these form the

dorsal column of the ascending track but

one branch of these fibers goes and

makes contact with the Alpha motor

neurons right so motor neuron that is

the Bell imaginary law motor neuron

arises from the ventral root of the

spinal cord so that is why we are

bringing it to the ventral side and this

Alpha motor neuron supplies the external

fibers which are contractile right so

remember I told you before that there

are contractile muscle fibers which run

from end to end these contractile muscle

fibers are known as extra fusal muscle

fibers okay and this sensory component

that is the spindle shaped sensory

component that is known as intrafusal

muscle fibers so you see the sulfur

motor neuron is supplying the

contractile fibers it is not supplying

the sensory fibers

so sensory component is within and the

motor component the efferent is outside

to the extra fuser fibers however there

is another motor component

that is the gamma motor neuron so here

only there is roots for the gamma motor

neuron which Supply the ends of these

introfusal fibers understanding ends of

the introfusal fibers are supplied by

the gamma motor neuron so this

intrafusal fiber it is sensory in the

central part but there is motor

component it has contractile ends which

are supplied by the gamma motor neuron

so this is the basic structure of

stretch reflex let's see a neater

diagram now

so here we are showing the muscle

spindle containing nuclear back and

nuclear chain fibers and there are one a

fibers which are supplying both right

and two fibers which are supplying only

the static component

and these are going to the spinal cord

then there is Alpha motor neuron which

is supplying to extra fusel fibers which

are basically contractile and there is

gamma motor neuron which is supplying

the ends of these muscle spindles so

these muscle spindle ends are actually

contractile so these two are the

efferents

so with this basic structure now let us

move on to the actual stretch reflects

what is stretch reflex

as the name suggests stretch reflects

basically stretch is the stimulus right

then there are efferents what is the

center it is the spinal cord which go to

the spinal cord and there is activation

of the difference that is the Alpha

motor neuron only we are talking about

simple stretch reflex there is

activation of Alpha motor neuron because

as I told you afferents are making

direct contact with the Alpha motor

neuron and this is stretch causes the

activation of the Alpha motor neurons

and there is contraction

so whenever the muscle is stretched it

is leading to contraction of the muscle

so this is the simple diagram for a

stretch reflex suppose the muscle is

stretched then when the muscle is

stretched you see what will happen these

intrafusal fibers will also be stretched

along with the muscle because they they

are passive okay so with the stretch of

the muscle spindle there will be

increase in efferent activity in these

1A and two fibers and they are going to

make contact with the Alpha motor neuron

so here you see it is a single synapse

that is why stretch reflex is

monosynaptic and it is the only example

of monosynaptic reflex in body

so it directly makes contact with the

Alpha motor neuron which supplies the

extra fusel fibers and there is

contraction

so this is the simple stretch reflex

but remember we talked about the dynamic

and static components so what is that

actually what are these 1A and two

fibers carrying

see what is a static component to

suppose this is your arm okay somebody's

arm very line diagram we will draw and

it is at 90 degrees so there is a

particular length of the muscle right

suppose this arm is a stretched to this

position then the length of the muscle

is increased suppose the arm is flexed

in that case suppose it is in this

position then length of the arm is

decreased okay now when the muscle is

stretched

right suppose this position this muscle

spindle will stretch and it will carry

the information to the Alpha motor

neuron and the muscle will contract back

again to its original length

similarly when the muscle is flexed okay

that means for flexing there will be

shortening of the muscle then this

afferent activity is going to decrease

why it is going to decrease because when

the muscle is shortening

along with that this introfusal fiber

length is also going to shorten here we

are talking about

whenever the muscle length is decreasing

the interfucer fiber is shortening we

will talk about voluntary contraction

little later that why we are able to

voluntary Flex the muscle why it doesn't

happen okay

anyways so when there is decrease in the

length of the muscle this will shorten

the muscle spindle and this efferent

activity in these fibers is going to

decrease okay and when this decreases

what will happen here the activation of

the Alpha motor neuron is also going to

decrease

thus causing decreased activation of

this extra fusel muscle fibers so there

will be relaxation and hence the muscle

will come back to its original position

so stretch reflexes working both ways

increase in the stretch is causing

contraction decrease in the stretch is

causing relaxation okay

so this is very simple you should

remember so basically this stretch

reflex is acting as a negative feedback

loop where it is maintaining the length

of the muscle Okay negative feedback

loop

but till now we are talking about static

stretch only see I told you that suppose

this is the muscle position but I never

talked about the dynamic component what

is dynamic component Dynamic component

is rate of the movement how fast the

muscle length is being changed from this

particular length through this

particular length so how fast the muscle

is being moved similarly here how fast

the muscle is being moved that is the

dynamic component and that information

is being carried by our 1A fibers

so basically two fibers are mainly for

the static length that currently what is

the length of the muscle and 1A fibers

is talking about the velocity of change

in the length of the muscle from one

position to other when it is going how

fast it is going so that information is

also very important because it kind of

tells the brain an anticipatory

information that how fast the correction

should be done also so that is the

meaning of static and dynamic component

now we have talked about the static and

dynamic component of the afference but

uh one thing more you remember here that

even the gamma motor neuron which are

supplying the contractile ends of these

introfusal fibers they are also of two

types that is the static and dynamic

okay so there also because this

information is going to the Alpha motor

neuron also to the top to the brain also

it is going so to make Corrections

later we will see that how voluntary

contraction this gamma motor neuron is

also activated so for that also we need

a static and dynamic component

so with this let us see certain facts

about stretch reflex one that this

stretch of the muscle when it causes a

stretch of the muscle spindle that is

known as loading of the spindle so

sometimes you should remember a loading

of the spindle stretch of the spindle is

known as loading of the spindle because

it is increasing the efferent activity

on the other hand the decrease in length

of the muscle

unloads the spindle so that is known as

unloading of spindle so that is one

second

the reaction panel for this stretch

reflex is 19 to 24 milliseconds what is

the reaction time meaning of reaction

time reaction time is basically time gap

between the stimulus and the response

right so from the time the muscle is a

stretched till the time the muscle is

contracted by the Alpha motor neuron

that is the total time taken for the

reflex so that is known as reaction time

and it is 19 to 24 milliseconds

now what is the importance of this 19 to

24 milliseconds when you see for any

negative feedback loop there is some

time involved why because there will be

some time in the activation of the

reference then carrying of this

information to the spinal cord some

conduction velocity this fiber will be

having so sometime it will take to

travel from one portion to the spinal

cord then

there will be some component involved in

this release of the neurotransmitters

activation of the Alpha motor neuron and

then there will be again velocity of

this Alpha motor neuron for getting the

information reaching the information to

the extra extra fusel a muscle fibers

right

so this is the entire time required for

the reflex but if we subtract the time

taken for traveling of the impulse then

we can get to know that how much time

this particular reflex is taking at the

level of the spinal cord and that is

known as Central delay and this Central

delay is found to be 0.6 to 0.9

milliseconds that means out of this 19

to 24 milliseconds only 0.6 to 0.9

millisecond time

is within the spinal cord rest all the

time is taken for conduction of the

impulse from the muscle spindle to the

spinal cord and again bringing the

impulse from the Alpha motor neuron to

the muscle

so this is the central delay again what

is the importance of this C

minimum time for synaptic delay what is

synaptic delay synaptic delay is

basically the time taken for the

neurotransmission in one synapse the

vesicles have to be released the

neurotransmitter has to act on the nerve

terminal so it is a chemical response

and because of this there is some

synaptic delay and that minimum delay is

0.5 milliseconds so if we know that this

is the minimum delay that means in this

stretch reflex there can be only one

synapse if there are two synapse how

much will be the delay it will be

greater than at least one millisecond

isn't it here we are talking that the

central delay is only 0.6 to 0.9

millisecond Which is less than one

millisecond so the number of synapses

involved in stretch reflexes single only

so that is why it is a monosynaptic

reflex I mean that's how we found out

that a stretch reflexes a monosynaptic

reflex by determining the total time

required for a stretch reflex and the

central delay

okay now let's move on to the next

component of stretch reflex that is

Alpha Gamma co-activation

now you see I gave you that example that

suppose this is the muscle length and if

it is changed to a different uh length

or different position

see when the muscle position is changed

when the arm is moved what will happen

the muscle length will also change so

basically lengthen the position are kind

of synonymous that is why these 1A and

two fibers are important for

proprioception they give the information

about the position of the arm anyways so

I told you that as the muscle length

will change this stretch reflex will

tend to bring the muscle back to its

original length right so if this happens

every time we move our arm we will never

be able to move because there is a

reflex operating it will always bring

the arm back to its original position

so how to move voluntarily well this is

because of Alpha Gamma co-activation

every time we wish to contract the

muscle there is Alpha Gamma

co-activation and every time we have to

relax the muscle there is Alpha Gamma

co-inhibition

so we use the word co-activation for the

contraction which is happening so what

is that I will just to redraw the

diagram quickly

so this is suppose extra fusel muscle

fiber and this is the intra-fuzer muscle

fiber and it is having the contractile

ends right so when we want to contract

the muscle

what we do from the spinal cord there is

basically information to both Alpha

motor neuron

and also to gamma motor neuron so both

get excited together that is the term

Alpha Gamma co-activation so what

happens because of this

see when the Alpha motor neuron will be

activated there will be shortening of

the muscle right now as I told you

before if the muscle shortens there will

be passive shortening of the introfusal

muscle fiber also stretch reflex will be

activated no with Alpha Gamma

co-activation it doesn't happen like

that because when gamma motor neuron

gets excited and it contracts the ends

of these introfusal fibers what happens

if the contractile ends contract right

then there will be stretch of this

intrafusal muscle fiber so it will

become something like this so instead of

Contracting because of the ends

Contracting there will be stretch of the

intrafusal muscle fiber so it is like

when the extra fusel muscle fibers

shorten or contract the intrafusal

muscle fibers are kept stretched they

are not allowed to shorten by activation

of the karma motor neuron so that is why

for voluntary contraction there is Alpha

Gamma co-activation

so that is one application of Alpha

Gamma co-activation in body there is

another one also

see there are many top fibers which are

affecting the activity of gamma motor

neuron

like there is a pontine reticulospinal

tract which is stimulating this gamma

motor neuron and there is medullary

reticular spinal tract which is

inhibiting this gamma motor neuron

now suppose if the muscle is stretched

and also there is I mean suppose if the

muscle is stretched there is a

particular position in which it is

maintained suppose somebody is standing

the length of the

um leg muscles will be

some value right so length of the muscle

or the position of the muscle is some

value now if during that time the

spontane reticular spinal tract

stimulates this gamma motor neuron what

will happen

in that particular length only there

will be increased stretch of the

centrifugal muscle fiber and with that

stretch what will happen that there will

be increased activation of the Alpha

motor neuron and there will be increased

contraction of the extra Fusion muscle

fibers understanding

so basically it is increasing the tone

of the muscle in a particular length

only so this gamma motor neuron

activation what we say is increasing the

sensitivity of stretch reflex okay

increasing the sensitivity of stretch

reflex for a particular position also so

that is how the various descending

tracks actually influence the activity

of gamma motor neuron to maintain muscle

tone and posture

so that is the second application of

this Kama motor neuron

third

see this stretch reflex basically is

used clinically

in assessing the motor system so suppose

in a patient of paralysis we need to

assess the Integrity of this reflex arc

and that is done by assessing various

jerks in body jerks means this stretch

reflex that is the knee-jerk biceps drug

triceps so all these reflexes we assess

at the level of the muscle and what we

say in that it has to be supported the

muscle has to be supported why we say

because we don't want the voluntary

contraction there we don't want that

Alpha Gamma co-activation to be together

there right because we are assessing

only the stretch reflex

so that that time we hit actually the

muscle on the tendon and by hitting the

muscle on the tendon we are actually

stretching this intra-fugal muscle fiber

now sometimes it becomes difficult to

elicit this stretch reflect in that case

we ask the subject to do Chandra 6

maneuver so General six man over what

happens that there is increased

activation of this gamma motor neuron

thus increasing the sensitivity of the

stretch reflex and then only we are able

to elicit this stretch reflex

so that is another importance of only

gamma motor neuron Alpha Gamma

co-activation for voluntary

contraction of the muscle then gamma

motor neuron activation increases

sensitivity of stretch reflex generous 6

manova again increases gamma motor

neuron activity so that increased

sensitivity of the stretch reflex occurs

then there is another effect on this

gamma motor neuron suppose in case of

upper motor neuron lesions in upper

motor neuron lesions what we get we get

hyperactive stretch reflex

why is it happening because the negative

influences on the gamma motor neuron get

disrupted so this gamma motor neuron

which is generally under more inhibitory

control from the upper motor neuron that

gets interrupted and that releases the

gamma motor neuron activity and it

becomes more active causing increased

sensitivity of the stretch reflex that

is why we get hyperactive

stretch reflexes in case of upper motor

neuron lesion

then there are some other factors which

also increases gamma motor neuron

activity and these are like anxiety

unexpected movements all these also

increase gamma motor neuron activity

that is why an anxiety also we get

hyperactive tendon reflexes tendon

reflexes again another term for stretch

reflex jerks okay

so that was all about the stretch reflex

hope you have understood the concept

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