skeletal servomechanism
- 1. THE SKELETAL MUSCLE SERVO MECHANISM 1
- 2. CONTENTS • DEFINITION • ANATOMY • MECHANISM • ALPHA LOOP CONTROL • GAMMA LOOP CONTROL • SCHEMATIC DIAGRAM 2
- 3. 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
- 4. 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
- 5. 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
- 6. 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
- 7. 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
- 8. 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
- 9. 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
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- 11. • 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
- 12. • The spindle cells secondary afferent conduct more slowly through a multi synaptic connection 12
- 13. • A local feedback loop exist in the spinal cord called renshaw cell to the local motor neuronal pool • This feedback is inhibitory. 13
- 14. a 1a Descending influence (UMN) MUSCLE Muscle spindle GAMMA LOOP CONTROL Activation of the -loop results in increased muscle tone 14
- 15. • 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
- 16. SCHEMATIC OF SKELETAL MUSCLE CONTROL SYSTEM 16
- 17. 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
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- 19. References • en.wikipedia.org/wiki/spindle mechanism • www.slideshare.net • John H.Milsum text book 19