Muscle Spindles

MUSCLE SPINDLES

Q. 1 Muscle spindle detects:
 A

Tension

 B

Length

 C

Proprioception

 D

Stretch

Q. 1 Muscle spindle detects:
 A

Tension

 B

Length

 C

Proprioception

 D

Stretch

Ans. B

Explanation:

Length [Ref Guyton’s Physiology 11/e,p 674-680; Ganong 22/e, p 130-134]

  • Muscle spindle and Golgi tendon organ both receptors are important component of intrinsic muscle control.

Muscle spindle            —> detects muscle length and rate of change in muscle length

Golgi tendon organ      —> detects muscletension  and rate of change in muscle tension

  • Muscle spindle acts through muscle stretch reflex. Whenever a muscle is stretched suddenly, excitation of the spindles cause reflex contraction of the large skeletal muscle fibers of stretched muscle thus maintain the muscle length & stabilize body positions during tense motor action. Stretch reflex also prevents oscillations & jerkiness of body movements.
  • However when the tension in muscle becomes great enough, contraction suddenly ceases and the muscle relaxes.

This relaxation in response to strong stretch is called the inverse stretch reflex, autogenic inhibition or lengthening reaction. The receptor for this reflex is in the Golgi tendon organ. This is a protective mechanism to prevent tearing of the muscle or avulsion of the tendon from its attachment to the bone.


Q. 2

The intrafusal fibers of the striated skeletal muscles are innervated by one of the following type of motor neurons. Choose the correct answer:

 A

Alpha

 B

Beta

 C

Gamma

 D

Delta

Q. 2

The intrafusal fibers of the striated skeletal muscles are innervated by one of the following type of motor neurons. Choose the correct answer:

 A

Alpha

 B

Beta

 C

Gamma

 D

Delta

Ans. C

Explanation:

 

C i.e. Gamma

  • The main motor supply of intrafusal fibres is (gamma) neurons.Q Y motor neuron exclusively supply intrafusal fibres.
  • Intrafusal fibres are also supplied by p fibres. p fibres also supply the extrafusal fibres [[3 for both]
  • The main motor supply of extrafusal fibres are a neurons.

Muscle spindle

–                     Each muscle spindle consists of 10 muscle fibres enclosed in connective tissue capsule.

These muscle fibres are more embryonal in character and have less striation than the rest of the fibres in the muscle (i.e. extrafusal fibres). These fibres are called intrafusal fibres

The intrafusal fibres are of two types:

  1. i)Nuclear bag fibres
  2. ii)Nuclear chain fibres

There are two kinds of sensory endings in each spindle

(i)    Primary (annulo spiral) ending – present both on nuclear chain & nuclear bag fibres.

(ii)   Secondary (flower spray) ending – present only on nuclear chain fibres

Muscle spindle

–                     Each muscle spindle consists of 10 muscle fibres enclosed in connective tissue capsule.

These muscle fibres are more embryonal in character and have less striation than the rest of the fibres in the muscle (i.e. extrafusal fibres). These fibres are called intrafusal fibres

The intrafusal fibres are of two types:

  1. i)Nuclear bag fibres
  2. ii)Nuclear chain fibres

There are two kinds of sensory endings in each spindle

(i)    Primary (annulo spiral) ending – present both on nuclear chain & nuclear bag fibres.

(ii)   Secondary (flower spray) ending – present only on nuclear chain fibres


Q. 3

What is true regarding the gamma efferent neuron?

 A

An ‘A’ group

 B

Motor neuron with a smaller diameter than that of alpha efferent neurons

 C

Innervates intrafusal fibres & Innervates muscle fibres that stretch annulospiral endings

 D

All of the above

Q. 3

What is true regarding the gamma efferent neuron?

 A

An ‘A’ group

 B

Motor neuron with a smaller diameter than that of alpha efferent neurons

 C

Innervates intrafusal fibres & Innervates muscle fibres that stretch annulospiral endings

 D

All of the above

Ans. D

Explanation:

All of the above


Q. 4

Muscle spindle is –

 A

Receptor for a variety of multisynaptic reflexes

 B

Receptor for myotatic or stretch receptor reflex

 C

Occurs only in antigravity extensor muscles

 D

Excited by both stretch and contraction of the muscles in which it is Located

Q. 4

Muscle spindle is –

 A

Receptor for a variety of multisynaptic reflexes

 B

Receptor for myotatic or stretch receptor reflex

 C

Occurs only in antigravity extensor muscles

 D

Excited by both stretch and contraction of the muscles in which it is Located

Ans. B

Explanation:

B i.e. Receptor for stretch receptor reflex


Q. 5

Find faulty statement regarding muscle spindle

 A

Central zone has no active & myosin

 B

Peripheral zone has no actin & myosin

 C

Type 1 nuclear bag fibers has low myosin ATP ase activity

 D

Type 2 nuclear bag fiber has has high level of myosin ATPase activity

Q. 5

Find faulty statement regarding muscle spindle

 A

Central zone has no active & myosin

 B

Peripheral zone has no actin & myosin

 C

Type 1 nuclear bag fibers has low myosin ATP ase activity

 D

Type 2 nuclear bag fiber has has high level of myosin ATPase activity

Ans. B

Explanation:

B i.e. Peripheral zone has no action & myosin


Q. 6

Contractile part of intrafusal fiber

 A

Ends

 B

Center

 C

Both

 D

None

Q. 6

Contractile part of intrafusal fiber

 A

Ends

 B

Center

 C

Both

 D

None

Ans. A

Explanation:

A i.e. Ends


Q. 7

Find false statement regarding sensory endings

 A

Flower spray is secondary

 B

Primary ending is annulospiral

 C

Primary ending conduct la fibers

 D

Annulospiral wrap the ends

Q. 7

Find false statement regarding sensory endings

 A

Flower spray is secondary

 B

Primary ending is annulospiral

 C

Primary ending conduct la fibers

 D

Annulospiral wrap the ends

Ans. D

Explanation:

D i.e. Annulospiral wrap the ends


Q. 8

Central wraping is done by

 A

Annulospiral ending

 B

Golgitendon

 C

Type II fiber

 D

Flower spray endings

Q. 8

Central wraping is done by

 A

Annulospiral ending

 B

Golgitendon

 C

Type II fiber

 D

Flower spray endings

Ans. A

Explanation:

A i.e. Anulospiral ending


Q. 9

True is all except regarding intrafusal fibers

 A

Nuclear chain fibers are shorter & thinner

 B

Nuclear bag fibers are lesser

 C

Primary endings excited by bag fibers only

 D

Secondary endings excited by chain fibers only

Q. 9

True is all except regarding intrafusal fibers

 A

Nuclear chain fibers are shorter & thinner

 B

Nuclear bag fibers are lesser

 C

Primary endings excited by bag fibers only

 D

Secondary endings excited by chain fibers only

Ans. C

Explanation:

C i.e. Primary endings excited by bag fibers only


Q. 10

Group II sensory fibers are attached to

 A

Annulospiral ending

Flower spray ending

 B

Flower spray ending

 C

Golgi tendon

 D

All

Q. 10

Group II sensory fibers are attached to

 A

Annulospiral ending

Flower spray ending

 B

Flower spray ending

 C

Golgi tendon

 D

All

Ans. B

Explanation:

B i.e. Flower spray ending


Q. 11

Plate endings are feature of

 A

Nuclear chain fibers

 B

Nuclear bag fibers

 C

Extrafusal

 D

Golgi tendon

Q. 11

Plate endings are feature of

 A

Nuclear chain fibers

 B

Nuclear bag fibers

 C

Extrafusal

 D

Golgi tendon

Ans. B

Explanation:

B i.e. Nuclear bag fibers


Q. 12

Leksell efferents go to

 A

Interneurons

 B

Golgi bottle cells

 C

Golgi tendon organ

 D

Spindle

Q. 12

Leksell efferents go to

 A

Interneurons

 B

Golgi bottle cells

 C

Golgi tendon organ

 D

Spindle

Ans. D

Explanation:

D i.e. Spindle

Muscle spindle

It is 3-12mm long structure consisting of 3-12 very small intrafusal muscle fibers, enclosed in a connective tissue capsule. Intrafusal fibers are !Wore embryonal in character & have less distinct striations than the rest of fibers (extrafusal fibers) in the muscle. Muscle spindle acts through muscle stretch reflexQ.


Q. 13

Muscle tone is maintained by ‑

 A

Golgi tendon organ

 B

Renshaw cells

 C

Muscle spindle

 D

None of the above

Q. 13

Muscle tone is maintained by ‑

 A

Golgi tendon organ

 B

Renshaw cells

 C

Muscle spindle

 D

None of the above

Ans. C

Explanation:

Ans. is ‘c’ i.e., Muscle spindle

  • Sensory receptors (stretch receptors) for stretch reflex are muscle spindles.
  • Stretch reflex has two principal functions :

1) To maintain muscle tone

  • Tone is a tendency of a muscle to resist being stretched.
  • Muscle tone is not only important for maintaining posture but also facilitates locomotion and makes all voluntary movement smooth.

2) To make muscles respond to stretch and release

  • Stretch reflex makes a muscle respond to stretch by contraction and to release by relaxation.
  • both these responses, which oppose the triggering stimulus, help make voluntary movement smooth and graceful.

Q. 14

You are testing knee jerk reflex in a patient. The afferents in deep tendon reflexes are carried by:

 A

Dynamic intrafusal fibers

 B

Golgi tendon organ

 C

Nuclear bag and static chain fibers

 D

Both Golgi tendon and muscle spindle

Q. 14

You are testing knee jerk reflex in a patient. The afferents in deep tendon reflexes are carried by:

 A

Dynamic intrafusal fibers

 B

Golgi tendon organ

 C

Nuclear bag and static chain fibers

 D

Both Golgi tendon and muscle spindle

Ans. A

Explanation:

Ans. a. Dynamic intrafusal fibers



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