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Spinal cord reflexes
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- 2. Student Preparation Textbook ofMedical Physiology Guyton and Hall, Ch. 54 2
- 3. Definition - Spinalreflex arc • A neuronal circuit extending from a peripheral receptor through the spinal cord to a peripheral effector. 3
- 4. Classification of reflexarcs • 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
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- 6. Classification of reflexarcs 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. Classification of reflexarcs 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. Classification of reflexarcs 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. Classical signs ofinfection: • Calor – heat • Dolor – pain • Rubor – redness • Tumor - swelling 9
- 10. Classification of reflexarcs 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. Classification of reflexarcs According to origin of the receptor and termination of the effector • Viscerovisceral reflex • Axonal Reflex • Ganglionic reflex 11
- 12. Classification of reflexarcs • 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. Classification of reflexarcs • 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. Classification of reflexarcs • 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. Classification of reflexarcs • 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. Functional components ofa 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. Functional components ofa 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. Examples – Major Reflexes 18
- 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
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- 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. Local sign • Theresponse 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. Reciprocal innervation • Neuronalcircuits 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. Reciprocal inhibition isrequired with the monosynaptic reflex 25
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- 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. Crossed-extensor reflex Flexor reflex 28
- 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. 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
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- 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
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- 34. Canine Dermatomes –Skin Areas Innervated By Spinal Nerves Shingles in humans – Herpes zoster