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SPINAL CORD REFLEXES



                   1
Student Preparation
Textbook of Medical Physiology
   Guyton and Hall, Ch. 54




                                 2
Definition - Spinal reflex arc
• A neuronal circuit extending from a
  peripheral receptor through the spinal
  cord to a peripheral effector.




                                           3
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
Somatosomatic reflex




                       5
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
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
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
Classical signs of infection:
•   Calor – heat
•   Dolor – pain
•   Rubor – redness
•   Tumor - swelling




                       9
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
Classification of reflex arcs
        According to origin of the receptor
          and termination of the effector

• Viscerovisceral
  reflex
• Axonal Reflex
• Ganglionic reflex




                                              11
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
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
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
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
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
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
Examples – Major
   Reflexes



                   18
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
Monosynaptic reflex




                      20
Monosynaptic
reflex




          21
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
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
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
Reciprocal inhibition is required with
the monosynaptic reflex                  25
Polysynaptic
flexor reflex




        26
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
Crossed-extensor reflex




  Flexor reflex
                          28
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
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
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
Panniculus Reflex




                    33
Canine Dermatomes – Skin
Areas Innervated By Spinal
         Nerves
                       Shingles in
                       humans –
                       Herpes zoster

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Spinal cord reflexes

  • 2. Student Preparation Textbook of Medical Physiology Guyton and Hall, Ch. 54 2
  • 3. Definition - Spinal reflex arc • A neuronal circuit extending from a peripheral receptor through the spinal cord to a peripheral effector. 3
  • 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
  • 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. 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. 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. Classical signs of infection: • Calor – heat • Dolor – pain • Rubor – redness • Tumor - swelling 9
  • 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. Classification of reflex arcs According to origin of the receptor and termination of the effector • Viscerovisceral reflex • Axonal Reflex • Ganglionic reflex 11
  • 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. 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. 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. 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. 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. 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. 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
  • 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 • 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. 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. Reciprocal inhibition is required with the monosynaptic reflex 25
  • 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
  • 31. 31
  • 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
  • 34. Canine Dermatomes – Skin Areas Innervated By Spinal Nerves Shingles in humans – Herpes zoster