THE SKELETAL MUSCLE SERVO MECHANISM

1

CONTENTS

• DEFINITION

• ANATOMY

• MECHANISM

• ALPHA LOOP CONTROL

• GAMMA LOOP CONTROL

• SCHEMATIC DIAGRAM

2

SERVO MECHANISM

• servomechanism, automatic device used to correct the performance of a mechanism by means of an error-sensing feedback. The term servomechanism properly applies only to systems in which the feedback and error-correction signals control mechanical position or one of its derivatives such as velocity or acceleration.

3

ANATOMY

• EXTRAFUSAL CONTRACTING FIBERS

1. Extra fusal muscle fibers is the term

given to standard Muscle fibers

2. Extrafusal muscle fibers are innervated

by alpha motor neurons and generate

tension by contracting, thereby

allowing for skeletal movement.

4

INTRAFUSAL MUSCLE FIBER

• Intrafusal muscle fibers are

skeletal muscle fibers that

comprise the muscle spindle

and are innervated by gamma

motor neurons.

• These fibers are proprio-

-ceptors that detect the

amount and rate of change in

length of a muscle.

5

Intrafusal fibers are wrapped by two types of afferent endings that send sensory

inputs to the CNS

• Primary afferent endings (annulo-spiral endings)– group 1 fibers

– Innervate the center of the spindle

• Secondary afferent endings(flower spray endings)– Type II fibers

– Associated with the

ends of the spindle

6

MECHANISM

• The extrafusal fibres are attached to bone through tendons exhibit a finite spring stiffnesss,and which are embedded in golgi tendon organs

• These organs are mechano receptors sensitive to the total muscle tension.

7

Alpha loop control• The tendon organs provides inhibitory

feedback to the alpha motor neuron but do not constitute the basic positive feedback element for this servomechanism

8

Loop control

• Activating the motor neurons that stimulate

the distal ends of the intrafusal fibers to contact thus stretching the mid-portion of the spindle (internal stretch)

• Whatever the stimulus, when the spindles are activated their associated sensory neurons transmit impulses at a higher frequency to the spinal cord

9

10

• The spindle cells primary afferents have an excitatory effect on alpha motor neurons travel via spinal cord in a fast mono synaptic reflex arc

11

• The spindle cells secondary afferent conduct more slowly through a multi synaptic connection

12

• A local feedback loop exist in the spinal cord called renshaw cell to the local motor neuronal pool

• This feedback is inhibitory.

13

a

1a

Descending influence (UMN)

MUSCLE

Muscle spindle

GAMMA LOOP CONTROL

Activation of the -loopresults in increased

muscle tone

14

• Branches of the afferent fibers also synapse with inter- neurons that inhibit motor neurons controlling the antagonistic muscles

• Inhibition of the antagonistic muscles is called reciprocal inhibition

15

SCHEMATIC OF SKELETAL MUSCLE CONTROL SYSTEM

16

CONCLUSION

• Servo mechanics can apparently be driven by either of two reference command inputs from higher nervous centers,so called as alpha and gamma efferent pathways.

• Firing frequency of spindle’s primary afferent in the steady state is approxiamately propotional to muscle extension over the physiological range.

17

18

References

• en.wikipedia.org/wiki/spindle mechanism

• www.slideshare.net

• John H.Milsum text book

19