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SPINAL CORD REFLEXES

Lecture - 2 Dr. Zahoor Ali Shaikh. SPINAL CORD REFLEXES. Spinal Reflex. What is Reflex? -- It is a response that occurs automatically without conscious effort. Reflex. Components of reflex arc are Five: 1- Sensory Receptor 2- Afferent pathway 3- Center 4- Efferent pathway

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SPINAL CORD REFLEXES

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  1. Lecture - 2 Dr. Zahoor Ali Shaikh SPINAL CORD REFLEXES

  2. Spinal Reflex • What is Reflex? -- It is a response that occurs automatically without conscious effort.

  3. Reflex Components of reflex arc are Five: 1- Sensory Receptor 2- Afferent pathway 3- Center 4- Efferent pathway 5- Effector organ

  4. Components of reflex arc

  5. REFLEX • Receptor responds to the stimulus and produces action potential (AP) • AP is taken by afferent pathway to the integrating center (usually CNS) • Spinal cord and brain integrate basic (automatic) reflexes

  6. REFLEX • Integrating center processes all the information and makes the decision about the response • Instruction from integrated center are sent via efferent pathway to the Effector organ (muscle or gland)

  7. Classification of reflexes • Monosynaptic or stretch reflex or tendon jerk eg. Bicep jerk ,tricep jerk, supinator jerk knee jerk, ankle jerk • Polysynaptic reflex eg. Withdrawal reflex Abdominal reflex Plantar reflex • Visceral reflex eg. Micturation, defecation reflex Jendressik Phenomenon

  8. Stretch Reflex [monosynaptic] • Sudden stretch to a muscle leads to contraction of that muscle is known as stretch reflex.

  9. Stretch Reflex [monosynaptic] • Stretch Reflex is basic (automatic) spinal reflex. We will take example Knee jerk • There are 5 components of Stretch Reflex 1- Sensory receptor – muscle spindle in skeletal muscle 2- Afferent pathway – 1a fibers 3- Center – spinal cord 4- Efferent fibers – α motor neuron 5- Effector organ – skeletal muscle contraction

  10. Types of muscle fibers • Extrafusal muscle fibers ( cause muscle contraction supplied by α - motor neuron) • Intrafusal muscle fibers or muscle spindle (receptor for stretch reflex, supplied by γ - motor neuron)

  11. Fig 13.3 – Sensory receptors in muscle Silverthorn 2nd Ed

  12. MUSCLE SPINDLE (INTRAFUSAL FIBERS)

  13. MUSCLE EXTRAFUSAL FIBERS MUSCLE INTRAFUSAL FIBERS

  14. Muscle spindle • Nuclear bag fiber • Nuclear chain fiber Sensory innervations of muscle spindle • Ia – nuclear bag & nuclear chain fibers • II – nuclear chain fibers Motor supply – γ motor neuron Dynamic & Static

  15. Types of motor neuron • α – motor neuron (supply Extrafusal fibers ) • γ - motor neuron (supply Intrafusal fibers)

  16. Patellar Tendon Reflex KNEE JERK – MONOSYNAPTIC REFLEX

  17. Polysynaptic Reflex • In polysynaptic reflex, there are many synapses between inter-neurons in the reflex pathway • We will study withdrawal reflex

  18. POLYSYNAPTIC REFLEXES Withdrawal Reflex • When a person touches a hot stove or pin prick, a withdrawal reflex occurs from the painful stimulus • 1. Receptor- pain and Temperature Receptors stimulated • 2. Afferent impulse travels via Action potential • 3. Center– Spinal cord.( Excitatory interneuron stimulated that stimulate efferent fibers).

  19. POLY SYNAPTIC REFLEX • 4 .Efferent fibers to Biceps to cotract ( flextion of arm ) and inhibitory neuron stimulated to inhibit contraction of Triceps. • This type of connection causing stimulation of nerve supply to one muscle and simultaneous inhibition of the nerve to its Antagonistic muscle is known as RECIPROCAL INNERVATION.

  20. Withdrawal reflex – Polysynaptic reflex

  21. Poly synaptic reflex Important • Afferent neuron stimulate also interneuron that carry signals to the Brain ( Ascending tracts in the spinal cord ) • Therefore Brain can modify the with drawl reflex. How? • By sending impulses via descending pathways to the efferent motor neuron supplying the involved muscles and prevent contracting of biceps inspite of painful stimulus e.g. pin prick

  22. DIFFERENT REFLEXES SHOWN JendressikPhenomenon (Reinforcement)

  23. Jendressik Phenomenon (Reinforcement) Superficial Reflexes

  24. Summary

  25. TRANSVERS SECTION OF SPINAL CORD

  26. Dermatomes of Spinal roots and divisions of trigeminal nerve (V1 ,V2, V3)

  27. Cranial Nerve Spinal Cord Reflexes

  28. Other Reflexes • 1- Golgi tendon Reflex • 2- Crossed Extensor Reflex We will discuss first Golgi endon Reflex

  29. Golgi Tendon Organs • Composed of: • Nerve fiber endings that wind between collagen fibers inside connective tissue capsule • If muscle is stretched: • Free nerve endings are pinched and they fire • Activation of Golgi tendon organs: • Inhibits alpha motor neurons and decreases muscle contraction

  30. The Golgi tendon reflex (inverse stretch reflex)

  31. Fig 13.6 – Muscle reflexes Silverthorn 2nd Ed

  32. Crossed Extensor Reflex

  33. POLYSYNAPTIC REFLEX

  34. Clinical Importance of reflexes • To test the integrity of reflex arc. • Localization of neurological lesion. • Identifying the type of lesion. • Monitoring the progress of neurological deficit.

  35. Clinical Importance of reflexes • Deep tendon reflexes are absent in lower motor neuron lesion. • The become exaggerated in upper motor neuron lesions. • Pendular jerks are observed in cerebellar lesions.

  36. Thank you

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