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Stretch reflex 2 Internal ear 1 by P.R.Desai Prof & HOD Physiology, DYPMCKOP

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Definition of MuscleTone
Significance of Muscle Tone
Spinal & Supraspinal Mechanism of Muscle Tone
Decerebrate Rigidity

Veröffentlicht in: Gesundheit & Medizin
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Stretch reflex 2 Internal ear 1 by P.R.Desai Prof & HOD Physiology, DYPMCKOP

  1. 1. Stretch Reflex Dr Mrs Padmaja R Desai Professor & Head Department of Physiology D Y Patil Medical College Kolhapur
  2. 2. Specific Learning Objectives • Definition of MuscleTone • Significance of Muscle Tone • Spinal & Supraspinal Mechanism of Muscle Tone • Decerebrate Rigidity
  3. 3. Muscle Spindle
  4. 4. Myotatic reflex or stretch reflex:-
  5. 5. • When the muscle is stretched, stretch receptors i.e. muscle spindles are stretched and therefore stimulated. From stretch receptors afferent impulses are carried by Group Ia and group II fibres and they directly synapse with the alpha motor neurons without interposition of any interneurons.Efferents from alpha motor neuron carry impulses to the extrafusal fibres of the muscle from where the muscle spindle fibres originated and cause its contraction. • This is a monosynaptic reflex.
  6. 6. • Tone:- • It is a sustained partial state of contraction of skeletal muscle at rest. • Importance of tone:- • It is important for maintenance of posture. • To perform various voluntary movements. • It is important for lifting of load.
  7. 7. • Tone of skeletal muscles is maintained by two fundamental mechanisms. • The spinal mechanism i.e. stretch reflex. • The supraspinal mechanism i.e. the descending tracts both pyramidal and extra pyramidal which influence the stretch reflex.
  8. 8. Spinal Mechanism • Tone is maintained reflexely by monosynaptic stretch reflex. • The central nuclear bag region of the muscle spindle is stretched either due to • Stretching of the extrafusal fibres when the muscle is stretched. • OR • When the intrafusal fibres contract
  9. 9. • Though this reflex is spinal but the supraspinal pathways modify this reflex.
  10. 10. Supraspinal mechanism • The descending tracts i.e. both the Pyramidal and extra pyramidal terminate on α or r motor neurons either directly or through interneuron’s and modify their activity. Thus these tracts influence the stretch reflex. Mainly the extrpyramidal tract is responsible for maintaining the tone.
  11. 11. • It consists of Basal ganglia motor nuclei of reticular formation of brainstem, vestibular nuclei and descending fibers converging impulses to spinal cord.
  12. 12. • Normal muscle tone is due to continuous impulses send by facilitatory areas to spinal motor neurons (i.e. α and r motor neurons).
  13. 13. Decerebrate rigidity • When the brain stem is transected at the intercollicular level i.e. between the superior and inferior colliculus there is increase in the muscle tone and this rigidity produced is called as decerebrate rigidity
  14. 14. References 1. Text book of Medical Physiology -Guyton & Hall, 12th edition. 2. Ganong’s review of Medical Physiology - 23rd edition. 3. Text book of Medical Physiology - 2nd edition 4. Net sources ( Acknowledge for all online source) 5. Text book of Medical Physiology - Prof. A.K.Jain

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