Cns 4

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Cns 4

  1. 1. Reflexes <ul><li>Automatic responses coordinated within spinal cord </li></ul><ul><li>Through interconnected sensory, motor, and interneurons </li></ul><ul><li>Produce simple and complex reflexes </li></ul>
  2. 2. Neural Reflexes <ul><li>Rapid, automatic responses to specific stimuli </li></ul><ul><li>Basic building blocks of neural function </li></ul><ul><li>1 neural reflex produces 1 motor response </li></ul>The Reflex Arc <ul><li>The wiring of a single reflex </li></ul><ul><li>Beginning at receptor </li></ul><ul><li>Ending at peripheral effector </li></ul><ul><li>Generally opposes original stimulus (negative feedback) </li></ul>
  3. 3. 5 Steps in a Neural Reflex <ul><li>Step 1: Arrival of stimulus, activation of receptor </li></ul><ul><ul><li>physical or chemical changes </li></ul></ul><ul><li>Step 2: Activation of sensory neuron </li></ul><ul><ul><li>graded depolarization </li></ul></ul>Figure 13–14 <ul><li>Step 3: Information processing by postsynaptic cell </li></ul><ul><ul><li>triggered by neurotransmitters </li></ul></ul><ul><li>Step 4: Activation of motor neuron </li></ul><ul><ul><li>action potential </li></ul></ul><ul><li>Step 5: Response of peripheral effector </li></ul><ul><ul><li>triggered by neurotransmitters </li></ul></ul>
  4. 4. Five Essential Components to the Reflex Arc Figure 12.17
  5. 5. 4 Classifications of Reflexes <ul><li>By early development </li></ul><ul><ul><li>How reflex was developed: </li></ul></ul><ul><ul><li>innate reflexes :basic neural reflexes, formed before birth </li></ul></ul><ul><ul><li>acquired reflexes : rapid, automatic, learned motor patterns </li></ul></ul><ul><li>By type of motor response- Nature of resulting motor response: </li></ul><ul><ul><li>somatic reflexes : </li></ul></ul><ul><ul><ul><li>involuntary control of nervous system </li></ul></ul></ul><ul><ul><ul><ul><li>superficial reflexes of skin, mucous membranes </li></ul></ul></ul></ul><ul><ul><ul><ul><li>stretch reflexes (deep tendon reflexes) e.g., patellar reflex </li></ul></ul></ul></ul><ul><ul><li>visceral reflexes (autonomic reflexes): </li></ul></ul><ul><ul><ul><li>control systems other than muscular syste </li></ul></ul></ul>
  6. 6. <ul><li>By complexity of neural circuit </li></ul><ul><ul><li>monosynaptic reflex : </li></ul></ul><ul><ul><ul><li>sensory neuron synapses directly onto motor neuron </li></ul></ul></ul><ul><ul><li>polysynaptic reflex : </li></ul></ul><ul><ul><ul><li>at least 1 interneuron between sensory neuron and motor neuron </li></ul></ul></ul><ul><li>By site of information processing </li></ul><ul><ul><li>spinal reflexes : </li></ul></ul><ul><ul><ul><li>occurs in spinal cord </li></ul></ul></ul><ul><ul><li>cranial reflexes : </li></ul></ul><ul><ul><ul><li>occurs in brain </li></ul></ul></ul>
  7. 7. Spinal Reflexes <ul><li>Range in increasing order of complexity: </li></ul><ul><ul><li>monosynaptic reflexes </li></ul></ul><ul><ul><ul><li>simplest of all reflexes </li></ul></ul></ul><ul><ul><ul><li>Just one synapse </li></ul></ul></ul><ul><ul><ul><li>The fastest of all reflexes </li></ul></ul></ul><ul><ul><ul><li>Example – stretch-knee-jerk reflex </li></ul></ul></ul><ul><ul><li>polysynaptic reflexes </li></ul></ul><ul><ul><ul><li>more common type of reflex </li></ul></ul></ul><ul><ul><ul><li>Most have a single interneuron between the sensory and motor neuron </li></ul></ul></ul><ul><ul><ul><li>Example – withdrawal reflexes </li></ul></ul></ul>
  8. 8. Clinical classification <ul><li>Superficial reflexes </li></ul><ul><li>Deep reflexes </li></ul>
  9. 9. Reflex name How to elicit Response Centre Supinator jerk Radial styloid process Flexion of elbow C 5,6 Biceps Biceps tendon Flexion of elbow C 5,6 Triceps Triceps tendon Extension of elbow C 6,7 Knee jerk Patellar tendon Extension of Knee joint L 2,3,4 Ankle jerk Tendoachilis Plantar flexion of ankle L5, S1,2 Jaw jerk Chin Lower jaw goes up sharply Brain stem Planter reflex Scratching the outer border of the sole of the foot Planter flexion L 5, S1 Abdominal reflex Scratching over the abdomen Contraction T 7-12
  10. 10. 1. Monosynaptic Reflexes – patellar reflex
  11. 11. <ul><li>Move body part away from stimulus (pain or pressure): e.g., flexor reflex :pulls hand away from hot stove </li></ul><ul><li>Strength and extent of response: </li></ul><ul><ul><li>depends on intensity and location of stimulus </li></ul></ul>2. Polysynaptic Reflexes <ul><li>More complicated than monosynaptic reflexes </li></ul><ul><li>Interneurons control more than 1 muscle group </li></ul><ul><li>Withdrawal or flexor reflex is an example </li></ul>
  12. 12. Motor Unit and Neuron Pool <ul><li>Skeletal muscles are innervated by  -motor neurons from the spinal cord ventral horn & brain stem </li></ul><ul><li>Motor unit = muscle fibers innervated by one  -motor neuron </li></ul><ul><li>Neuron pool = all  -motor neurons that innervate one muscle </li></ul>
  13. 13. Muscle Spindle & Golgi Tendon Organ - Proprioceptors <ul><li>Muscle spindle - fusiform shaped </li></ul><ul><ul><li>3-12 or more intrafusal fibers </li></ul></ul><ul><ul><li>Parallel attachment to sheaths of extrafusal skeletal muscle fibers </li></ul></ul><ul><ul><li>Detect stretch of skeletal muscle </li></ul></ul><ul><li>Golgi tendon organ - capsular structure located in muscle tendons </li></ul><ul><ul><li>Connected in series to extrafusal skeletal muscle fibers </li></ul></ul><ul><ul><li>Detect changes in muscle tension </li></ul></ul>
  14. 14. Muscle spindles are in parallel with extrafusal muscle fibers
  15. 15. Muscle spindle
  16. 16. Muscle Spindle Intrafusal Fibers <ul><li>Central region devoid of contractile elements </li></ul><ul><li>Contain several nuclei </li></ul><ul><li>Nuclear bag fibers - nuclei clumped in central region (dynamic responders) </li></ul><ul><li>Nuclear chain fibers - nuclei arranged in rows (static responders) </li></ul>
  17. 17. Efferent innervation of skeletal muscles: Extrafusal fibers –  motor neurons Intrafusal fibers –  motor neurons
  18. 18. Sensory Innervation of Intrafusal Fibers <ul><li>Primary spindle afferent – group Ia afferent , annulospiral ending; spirals around and innervates the central region of both nuclear bag and nuclear chain fibers </li></ul><ul><li>Secondary spindle afferent – group II afferent , flower spray ending; mostly innervate distal ends of nuclear chain fibers </li></ul>
  19. 19. Sensory innervation of the muscle spindle
  20. 20. Muscle spindle function <ul><li>Primary spindle afferents (Ia) - respond primarily to dynamic changes in muscle length (rate of change in length) </li></ul><ul><li>Secondary spindle afferents (II) - respond primarily to static changes in muscle length (steady state changes) </li></ul><ul><li>Contraction of extrafusal fibers causes collapse of intrafusal fibers with cessation of discharge </li></ul>
  21. 21. Role of  motor neurons – to increase the sensitivity of muscle spindles
  22. 22. Motor innervation (  ) of muscle spindle <ul><li>Dynamic gamma fiber (  -d) - excites mainly nuclear bag intrafusal fibers </li></ul><ul><li>Static gamma fiber (  -s) - excites mainly nuclear chain fibers </li></ul>
  23. 23. Function of muscle spindle cont. <ul><li>Stimulation of  -d fibers enhances the dynamic response of the primary afferent </li></ul><ul><li>Stimulation of  -s fibers enhances the static response of the secondary afferent </li></ul><ul><li>Fusimotor fibers (  ) contract intrafusal fibers (usually during active extrafusal contraction) and resensitizes them for accurate detection of muscle length over a wide range </li></ul>
  24. 24. Spindle responses to passive muscle stretch dynamic static
  25. 25. Primary spindle responses to passive stretch without and with  stimulation Primary = dynamic muscle spindle
  26. 26. Secondary responses to passive stretch without and with  stimulation Secondary = static muscle spindle
  27. 27. Connections of Ia afferent fibers within the spinal cord <ul><li>Cell body in dorsal root ganglion </li></ul><ul><li>Alpha motor neuron in ventral gray </li></ul><ul><li>Single synapse </li></ul><ul><li>Motor effector same (homonymous) muscle </li></ul><ul><li>Purpose - oppose stretch and maintain tone or posture </li></ul>
  28. 28. Connections of group II fibers in spinal cord <ul><li>Cell body in dorsal root ganglion </li></ul><ul><li>Alpha motor neuron in ventral gray </li></ul><ul><li>Single synapse </li></ul><ul><li>Motor effector same (homonymous) muscle </li></ul><ul><li>Purpose - oppose stretch and maintain tone or posture; locomotion </li></ul>
  29. 29. Spinal reflex connections of Ia afferent fibers <ul><li>Excitatory to motor neurons of the homonymous muscle </li></ul><ul><li>Excitatory to neurons of synergistic muscles (facilitation) </li></ul><ul><li>Inhibitory to neurons of antagonistic muscle </li></ul>
  30. 31. Golgi tendon organ <ul><li>Golgi tendon organ - capsular structure located in muscle tendons </li></ul><ul><li>Connected in series to extrafusal skeletal muscle fibers </li></ul><ul><li>Detects changes in muscle tension </li></ul>
  31. 33. Golgi tendon organ Ib afferent
  32. 34. Excess muscle stretch (tension) fires Golgi tendon organ muscle spindle Golgi tendon organ
  33. 35. Contrast Golgi tendon organ and primary spindle during contraction <ul><li>Golgi tendon organ (Ib) responds to increased tension during extrafusal muscle contraction </li></ul><ul><li>Muscle spindle (Ia) is silent during muscle contraction </li></ul>
  34. 36. Spinal connections of Ib afferent fibers(Inverse stretch reflex) <ul><li>Inhibitory to neurons of homonymous m. </li></ul><ul><li>Inhibitory to neurons of synergistic muscles </li></ul><ul><li>Excitatory to neurons of antagonistic muscle </li></ul><ul><li>Purpose - oppose development of excessive muscle tension </li></ul>
  35. 37. Spinal cord circuits <ul><li>1a afferents: activated by stretch of muscle; innervate alpha motor neurons, causing reflex contraction of muscle </li></ul><ul><li>1b afferents: activated by contraction of muscle; innervate interneurons, that inhibit alpha motor neurons, causing reflex relaxation of muscle </li></ul>
  36. 38. <ul><li>Quick stretch of muscle distorts nuclear bag (muscle spindle) </li></ul><ul><li>Afferent signal via primary sensory nerve (Ia) </li></ul><ul><li>Monosynapse in spinal cord with α-motor neuron </li></ul><ul><li>Efferent signal via α-motor neuron </li></ul><ul><li>Muscle contraction results to oppose stretch </li></ul><ul><li>Reciprocal innervation Collateral Ia synapses inhibitory interneurons </li></ul><ul><li>Inhibitory interneuron sends efferent signal to antagonist -> relaxation of antagonist muscle </li></ul>I. Stretch Reflex Patellar reflex (knee jerk)
  37. 39. Stretch Reflex Figure 13.16
  38. 40. Stretch reflexes <ul><li>1. passive stretch of muscle (e.g. by tapping tendon) activates Ia afferents, which activate alpha motor neurons, causing contraction of stretched muscle: monosynaptic reflex </li></ul><ul><li>2. passive contraction of muscle (stimulation of alpha motor neurons) causes decreased activity of muscle spindles, leading to decreased activity of alpha motor neurons </li></ul>
  39. 41. Stretch reflex
  40. 42. Stretch reflexes <ul><li>3. gamma loop: supraspinal input (e.g. corticospinal) activates gamma motor neurons, activating intrafusal fibers that stretch the muscle spindle, activating Ia fibers, which activate alpha motor neurons </li></ul><ul><li>4. voluntary muscle contraction against a load: corticospinal fibers activate both alpha and gamma motor neurons, allowing Ia fibers to continue to sense muscle length while muscle is contracting: alpha-gamma coactivation </li></ul>
  41. 43. Gamma efferents allow continued response of spindle during voluntary contraction
  42. 44. Stretch reflexes <ul><li>5. reciprocal inhibition: activation of agonist and inhibition of antagonist muscles; stretch of muscle spindles activates Ia fibers, which monosynaptically activate agonist alpha motor neurons, and Ia fibers also activate glycinergic interneurons which inhibit antagonist alpha motor neurons </li></ul>
  43. 45. Stretch reflex
  44. 46. Stretch reflexes <ul><li>6. flexor reflex: activation of A-delta and c fibers by nociceptive stimuli activates excitatory and inhibitory interneurons in ventral horn, which activate flexor alpha motor neurons and inhibit extensor motor neurons; involves several spinal cord segments </li></ul>
  45. 47. Flexor reflex
  46. 48. Stretch reflexes <ul><li>7. crossed extensor reflex: activation of A-delta and c fibers by nociceptive stimuli activates excitatory and inhibitory interneurons in ventral horn, which project across midline to activate or inhibit interneurons, resulting in activation of extensor and inhibition of flexor motor neurons </li></ul>
  47. 49. Crossed extensor reflex
  48. 50. The Tendon Reflex <ul><li>Prevents skeletal muscles from: </li></ul><ul><ul><li>developing too much tension </li></ul></ul><ul><ul><li>tearing or breaking tendons </li></ul></ul><ul><ul><li>tendon reflex is less sensitive than the stretch reflex, it can override the stretch reflex when tension is great, making you drop a very heavy weight, for example. </li></ul></ul>
  49. 51. Crossed Extensor Reflexes <ul><li>Occur simultaneously, coordinated with flexor reflex </li></ul><ul><li>e.g., flexor reflex causes leg to pull up: </li></ul><ul><ul><li>crossed extensor reflex straightens other leg </li></ul></ul><ul><ul><li>to receive body weight </li></ul></ul><ul><ul><li>maintained by reverberating circuits </li></ul></ul>
  50. 52. The Babinski Reflexes <ul><li>Normal in infants </li></ul><ul><li>May indicate CNS damage in adults </li></ul>Figure 13–19
  51. 53. <ul><li>Regulate internal organs </li></ul><ul><li>Integrate in spinal cord or lower brain </li></ul><ul><li>Coordinate with hormones & pacemakers </li></ul>Autonomic Reflexes: “visceral reflexes”
  52. 54. Autonomic Reflexes: “visceral reflexes” Figure 13-2: Autonomic reflexes
  53. 55. <ul><li>Muscle tone </li></ul><ul><li>Stretch reflex </li></ul>Muscle Spindles: Mechanism
  54. 56. <ul><li>Myotactic unit: all pathways controlling a joint </li></ul><ul><li>Example: elbow joint – all nerves, receptors, muscles </li></ul>A Myotactic Unit and Stretch Reflex Illustrated Muscle reflexes
  55. 57. <ul><li>Force pulls collagen fibers which squeeze sensors </li></ul><ul><li>Overload causes inhibition of contraction </li></ul>Golgi Tendon Reflex: Response to Excessive Force Figure 13-6b: Muscle reflexes
  56. 58. <ul><li>Tendon strike stretches quads- reflexive contraction </li></ul><ul><li>Reciprocal (hamstring) muscle is inhibited </li></ul>Knee Jerk Reflex: Stretch & Reciprocal Inhibition Reflexes
  57. 59. Knee Jerk Reflex: Stretch & Reciprocal Inhibition Reflexes : The knee jerk reflex
  58. 60. <ul><li>Pain stimulus </li></ul><ul><li>Nociceptors </li></ul><ul><li>Spinal integration </li></ul><ul><li>Flex appendage away </li></ul><ul><li>Signal to brain (feel pain) </li></ul>Flexion Reflex: Pull away from Painful Stimuli
  59. 61. Flexion Reflex: Pull away from Painful Stimuli
  60. 62. Properties of Reflex <ul><li>1. Delay </li></ul><ul><li>2. Adequate stimulus </li></ul><ul><li>3. Summation </li></ul><ul><li>4. Fractionation </li></ul><ul><li>5. Occlusion </li></ul><ul><li>6. Subliminal fringe </li></ul><ul><li>7. Facilitation </li></ul>
  61. 63. Properties continued <ul><li>8. Inhibition </li></ul><ul><li>9. Recruitment </li></ul><ul><li>10. Irradiation </li></ul><ul><li>11. After discharge </li></ul><ul><li>12. Central excitatory state </li></ul><ul><li>13. Habituation and sensitisation </li></ul><ul><li>14. Final common path </li></ul>

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