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1. MUSCLE SPINDLE & GOLGI
TENDON ORGAN
BY :
MMANTTHAN PUROHIT

2. WHAT IS MUSCLE SPINDLE ???
Basically, muscle spindle is the major sensory organ of
muscle and is sensitive to quick and sustained stretch.
It is one of the neurophysiological properties of
contractile tissue, which may influence the muscle’s
response to stretch.
The main function of the muscle spindle is to receive and
convey information about changes in the length of the
muscle and the velocity of the length changes.

3. DEFINITION
MUSCLE SPINDLE is defined as,
ÏT IS A SPINDLE SHAPED
PROPRIOCEPTOR SITUATED IN THE SKELETAL
MUSCLE. IT IS FORMED BY MODIFIED SKELETAL
MUSCLE FIBERS CALLED INTRAFUSAL FIBERS.

5. MUSCLE SPINDLE CONSIST OF...
 Muscle spindles are small, encapsulated receptors composed of
afferent sensory fiber endings, efferent motor fiber endings, and
specialized muscle fibers called INTRAFUSAL FIBERS.
 Each spindle contains 6-14 intrafusal fibers, which are of 2 types :
1) NUCLEAR BAG FIBERS
2) NUCLEAR CHAIN FIBERS
 NUCLEAR BAG FIBERS contains the nucleus in the central
portion of the receptor and it gives the bag like structure.
APPROX 2-5
 NUCLEAR CHAIN FIBERS look like the chain, nuclei are
arranged in the form of a chain. APPROX 6-10

7. INNERVATION OF MUSCLE SPINDLE…
 The muscle spindle is innervated by both sensory & motor nerve
fibers.
 SENSORY SUPPLY :
1) GROUP 1a FIBERS( primary sensory endings)
2) GROUP 2 FIBERS( secondary sensory endings)
 The primary ending supplying both the nuclear bag fibers as well
as nuclear chain intrafusal fibers are stimulated when the muscle
spindle is stretched.
 Secondary endings innervate the receptor portion of mainly
nuclear chain fiber, the nerve ending respond mainly to sustained
stretch, therefore measure the length.

11. INNERVATION OF THE MUSCLE SPINDLE...
 MOTOR SUPPLY :
 The end portion of the muscle fiber is supplied by gamma efferent
neurons.
 Gamma motor neurons are of 2 types.
1) GAMMA-S
2) GAMMA-D
 GAMMA-S fibers excite the nuclear chain fibers and enhance the static
response in the muscle spindle.
 GAMMA-D fibers excite the nuclear bag fiber and enhance the dynamic
responses in the muscle spindle.

13. FUNCTION OF THE MUSCLE SPINDLE…
 The muscle spindle fibers are sensitive to the length and the velocity
of lengthening of the muscle fibers.
 They send messages to the brain about the state of stretch of the
muscle fiber.
 When the muscle fiber shortens, the spindle stop sending messages
because they are no longer stretched.
 When the signal decreases, the higher centers send a message to
intrafusal muscle fibers in the spindle to shorten so that they once
again are able to respond to the length change in the muscle spindle.

14. STATIC RESPONSE
 When the muscle spindle is stretched, the receptors which is present
in that spindle is activated and it sends the impulses to the nervous
system.
 It sends the messages to the nervous system through group 1a and
group 2 fibers.
 Whenever the muscle spindle is stretched slowly, the proportion of
the impulse transmit impulses many more minutes is called static
response.
 It occurs due to the stretching of the nuclear chain fibers because it
supplied by both the group 1a and group2 nerve fibers.

15. DYNAMIC RESPONSE
 If the muscle spindle structures stretched suddenly the nerve ending
is stimulated powerfully and it is called dynamic response of spindle.
 It occurs when the nuclear bag fibers stretched because it is
innervated by type 1a fibers.

16. MUSCLE SPINDLE AS THE RECEPTOR
ORGAN FOR STRETCH REFLEX
 Stimulation of muscle spindle elicits the stretch reflex.
 Intrafusal fibers are situated parallel to the extrafusal fibers and are
attached to the tendon of the muscle by means of capsule.
 So, stretching of the muscle causes stretching of the muscle spindle
also. This stimulates the muscle spindle and it discharges the
sensory impulses.
 These impulses are transmitted via the primary and secondary nerve
fibers to alpha motor neurons in the spinal cord.
 Alpha motor neuron in turn send motor impulses to muscle through
their fibers and cause contraction of extrafusal fibers.

17. ROLE OF MUSCLE SPINDLE IN THE
MAINTENANCE OF MUSCLE TONE
 Muscle tone is defined as the state of continuous and passive partial
contraction of muscle with certain vigor and tension.
 It is also defined as resistance offered by the muscle to stretch.
 Gamma motor neurons and muscle spindle are responsible for the
development and maintenance of muscle tone.
 Development of muscle tone :

18. DEVELOPMENT OF MUSCLE TONE
1) Impulses from the gamma motor neuron cause contraction of end portion of
intrafusal fibers.
2) This stretches and activates the central portion of the intrafusal fiber, which initiates
the stretch reflex action for the development of muscle tone by discharging the
impulses.
3) Impulses from the central potion of the intrafusal fibers pass through primary
sensory nerve fibers and reach the anterior gray horn of the spinal cord.
4) These impulses stimulates the alpha motor neurons in the anterior gray horn.
5) Alpha motor neuron in turn send impulses to extrafusal fibers of the muscle through
spinal nerve fibers.
6) These impulses produce partial contraction of the muscle fibers resulting in
development of muscle tone.

22. GOLGI TENDON ORGAN

23. DEFINITION
GOLGI TENDON ORGAN is defined as,
It is a sensory organ located near the
musculotendinous junction of extrafusal fibers. Which senses
any change in the tension of the muscle.

24. STRUCTURE OF GTO
GOLGI TENDON ORGAN is situated in the tendon of skeletal
muscle near the attachment of the extrafusal muscle fibers.
It is placed in series between the muscle fibers and the
tendon.
Golgi tendon organ is formed by a connective tissue
capsule.

26. NERVE SUPPLY TO GTO
 Sensory nerve fiber supplying the GTO belongs to 1b type.
 Normally, the responses from the spinal cord or from the CNS are
mostly relaxation of the muscle.
 When tension develops in a muscle, the GTO fires, inhibit alpha motor
neuron activity, and decreases tension in the muscle-tendon unit
being stretched.

27. FUNCTIONS OF THE GOLGI TENDON
ORGAN
 GOLGI TENDON ORGAN gives response to the change in the force or
tension developed in the skeletal muscle during contraction.
1) ROLE OF GTO IN FORCEFUL CONTRACTION :
 During the powerful contraction, tension in the muscle increases and
stimulates golgi tendon organ, which discharge the sensory impulses.
 Impulses are transmitted by 1b sensory nerve fiber to an inhibitory
interneuron in the spinal cord.
 Inerneuron, in turn causes the development of IPSP in motor neurons,
which supply the muscle.

28. 2) Role of GTO in inverse stretch reflex :
 Inverse stretch reflex is the sudden decrease in resistance due to relaxation when a
muscle is stretched excessively.
 Inverse stretch reflex is actually the inhibition of contraction due to excessive
stretching. So, it is also called autogenic inhibition.
 MECHANISM :
 Excessive stretch to the muscle leads to the activation of the GTO, which send
afferent impulses which cause :
A. Stimulation of inhibitory internuncial neuron, which in turn inhibits alpha motor
neuron of the stretched muscle resulting in relaxation.
B. Stimulation of excitatory internuncial neuron, which in turn activates alpha motor
neuron of antagonistic muscle. It leads to contraction of antagonistic muscle and
relaxation of stretched muscle.

30. 3) ROLE OF GTO IN LENGHENING REACTION :
 When tension increases during muscular contraction caused by
stretch reflex, the GTO is activated.
 It causes the development of spinal reaction, which is called the
lengthening reaction.

32. NEUROPHYSIOLOGICAL RESPONSE OF
MUSCLE TO STRETCH
 When a stretch force is applied to muscle-tendon unit either quickly or
over a prolonged period of time, the primary and secondary afferent
nerve fibers of intrafusal muscle fibers sense the length changes and
activate the extrafusal fiber via alpha motor neurons in the spinal
cord, thus activating a stretch reflex and increasing a tension in the
muscle being stretched.
 The increased tension causes resistance to lengthening and in turn, it
is thought to compromise the effectiveness of the stretching
procedure.

33.  When stretch reflex is activated in a muscle being lengthened, decreased
activity in the muscle on the opposite side of the joint, referred as reciprocal
inhibition.
 In contrast, the GTO, which monitors tension in the muscle fibers being
stretched, has an inhibitory impact on the level of muscle tension in the
muscle tendon unit in which it lies, particularly if the stretch force is
prolonged. This effect is called autogenic inhibition.
 Originally, the GTO was thought to fire and inhibit muscle activation only in
the presence of high levels of muscle tension as a protective mechanism.
 However, the GTO has since been shown to have a low threshold for
firing(fires easily), so it can continuously monitor and adjust the force of
active muscle.

35. QUIZ TIME
 What is the difference between muscle spindle and GTO???
 What is the motor supply of extrafusal fibers ???
 What is reciprocal inhibition ???
 What is autogenic inhibition ???
 What is stretch reflex ???
 What is inverse stretch reflex ???