Spinal cord reflexes

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Spinal cord reflexes

  1. 1. SPINAL CORD REFLEXES 1
  2. 2. Student PreparationTextbook of Medical Physiology Guyton and Hall, Ch. 54 2
  3. 3. Definition - Spinal reflex arc• A neuronal circuit extending from a peripheral receptor through the spinal cord to a peripheral effector. 3
  4. 4. Classification of reflex arcs• According to origin of the receptor and termination of the effector – Somatosomatic reflex - the reflex originates and terminates in the body wall (soma) – in contrast to the viscera. An example of this reflex would be the withdrawal reflex. A nociceptive stimulus applied to sensory receptors of the skin of a limb results in skeletal muscle movement which removes the limb away from the source of the stimulus. 4
  5. 5. Somatosomatic reflex 5
  6. 6. Classification of reflex arcs cont.• According to origin of the receptor and termination of the effector – Somatovisceral reflex - the reflex originates in the body wall and terminates in a visceral effector. Example - a painful (nociceptive) stimulus applied to the limb of a dog results in urination. 6
  7. 7. Classification of reflex arcs cont.• According to origin of the receptor and termination of the effector – Viscerovisceral reflex - the reflex originates and terminates in a visceral structure. Example - gastric distention results in increased intestinal peristalsis. 7
  8. 8. Classification of reflex arcs cont.• According to origin of the receptor and termination of the effector – Axonal reflex - Sensory activity ascends a single branch of a peripheral nerve to a bifurcation, and then passes back to the same tissue, causing a neuroeffector response without entering the spinal cord. Example – a painful stimulus to the skin results in vasodilation via the axonal reflex. 8
  9. 9. Classical signs of infection:• Calor – heat• Dolor – pain• Rubor – redness• Tumor - swelling 9
  10. 10. Classification of reflex arcs cont.• According to origin of the receptor and termination of the effector – Ganglionic reflex - does not involve the spinal cord. The reflex originates in a peripheral organ, synapses in an autonomic ganglion and terminates in a peripheral effector. 10
  11. 11. Classification of reflex arcs According to origin of the receptor and termination of the effector• Viscerovisceral reflex• Axonal Reflex• Ganglionic reflex 11
  12. 12. Classification of reflex arcs• According to destination of interneuron in the spinal cord – Intrasegmental reflex - all central reflex activity occurs within a single spinal cord segment. Example - dorsal root ganglion afferent enters C7, synapses with an interneuron within C7, which synapses on a C7 motor neuron, and its axon exits C7. – Intersegmental reflex- central reflex activity involves more than one spinal cord segment. 12
  13. 13. Classification of reflex arcs• According to destination of interneuron in the spinal cord – Ipsilateral reflex - central reflex activity remains on the same side of the cord. – Contralateral reflex - afferent input enters the cord on one side and motor output exits the cord on the opposite side. 13
  14. 14. Classification of reflex arcs• According to number of synapses – Monosynaptic reflex - reflex contains one central synapse. This results in minimal delay within the spinal cord and rapid response of the effector organ in reaction to the sensory stimulus. – Di (bi)-synaptic reflex - two synapses within the spinal cord. 14
  15. 15. Classification of reflex arcs• According to number of synapses – Polysynaptic reflex - multiple synapses within the spinal cord. Although (simplistically speaking) reflexes may be isolated as mono- or di-synaptic, all reflexes have polysynaptic components. 15
  16. 16. Functional components of a typical reflex arc • Sensory receptor - detects some physical or chemical phenomena and transduces it into electrical impulses • Dorsal root ganglion (cell body of the afferent neuron) 16
  17. 17. Functional components of a typical reflex arc cont. • Interneuron (internuncial or intercalated neuron) - a neuron inserted between the afferent and efferent neurons – zero, one or multiple • Ventral horn motor neuron (efferent neuron) • Effector organ - muscle or gland 17
  18. 18. Examples – Major Reflexes 18
  19. 19. Monosynaptic reflex• Synonyms - stretch reflex, myotatic reflex, muscle spindle reflex• Stimulus - stretch of the primary or secondary receptor of the muscle spindle• Receptor - muscle spindle, Group Ia or II afferents• Number of synapses - one• Purpose - reflex contraction of the stretched muscle thus opposing stretch beyond a certain length 19
  20. 20. Monosynaptic reflex 20
  21. 21. Monosynapticreflex 21
  22. 22. Flexor reflex• Synonyms - withdrawal reflex, nociceptive reflex, pain reflex• Stimulus - noxious stimulus to an extremity• Receptor - class II, III, or IV afferents• Number of synapses - multisynaptic• Purpose - to remove affected part from danger 22
  23. 23. Local sign• The response to the stimulus by the body will be determined by the location of the stimulus on the body – i.e., a noxious stimulus to the hind limb does not result in withdrawal of a forelimb. 23
  24. 24. Reciprocal innervation• Neuronal circuits that allow inhibition (reciprocal inhibition) or facilitation (reciprocal excitation) of neurons either opposing or aiding the reflex response. Example - muscle spindle reflex in biceps brachii will (through reciprocal innervation) produce reciprocal inhibition of neurons to triceps brachii and reciprocal excitation of neurons to brachialis muscle. 24
  25. 25. Reciprocal inhibition is required withthe monosynaptic reflex 25
  26. 26. Polysynapticflexor reflex 26
  27. 27. Crossed extensor reflex• Not a separate reflex, but is accessory to, or part of, the flexor reflex• Synonyms - none• Stimulus, receptors, number of synapses same as flexor reflex• Purpose - contraction of extensor muscles of contralateral limb to support weight• After discharge - contraction outlasts stimulus 27
  28. 28. Crossed-extensor reflex Flexor reflex 28
  29. 29. Extensor thrust reflex• Synonym - none• Stimulus - pressure applied to the foot pads• Receptors - tactile receptors and muscle spindles; group I, II, III, IV afferent fibers• Number of synapses - multisynaptic• Purpose - maintenance of posture 29
  30. 30. Scratch reflex• Synonyms - none• Stimulus - irritating stimulus on the skin of the dorsal or lateral surfaces of the thorax and neck• Receptors - combination of tactile and pain receptors; group II, III, IV afferent fibers• Number of synapses - multisynaptic• Purpose - to remove source of irritant 30
  31. 31. 31
  32. 32. Panniculus reflex• Synonym – cutaneous reflex• Stimulus – local stimulus to the skin, causing contraction of the cutaneous trunci muscle in the same segment• Receptors – pain and touch receptors, group III, IV afferent fibers• Number of synapses – multisynaptic• Purpose – to remove irritating stimuli – biting flies, etc. 32
  33. 33. Panniculus Reflex 33
  34. 34. Canine Dermatomes – SkinAreas Innervated By Spinal Nerves Shingles in humans – Herpes zoster

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