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Medicine Notes Neurology Notes

Motor Control (Spinal Reflexes) Notes

Updated Motor Control (Spinal Reflexes) Notes

Neurology Notes

Neurology

Approximately 117 pages

These notes helped me achieve a mark of 76% in my neurology exam, which is the equivalent of a 1st. The notes are based on a series of 49 lectures on the subject. This is a very good, thorough and in depth review of the nervous system. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the nervous system (e.g. physiology o...

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Lecture 12

Motor Control: Spinal Reflexes

  • Spinal and supra-spinal mechanisms

    • Spinal cord reflex

      • Very rapid, automatic and highly stereotyped response

    • Supra-spinal motor circuits

      • Volitional (deliberate) control over movements

  • Types of spinal reflexes

    • Monosynaptic reflex

      • Simplest reflex

      • Aka. Stretch or myotatic reflex

      • Mechanism for controlling muscle length

      • Prevents overstretching of muscle

      • Important in generation of muscle tone

      • LOW THRESHOLD

      • PROTECTIVE REFLEX

    • Golgi tendon reflex

      • Controls muscle tension

      • LOW THRESHOLD

      • PROTECTIVE REFLEX

    • Flexor or withdrawal reflex

      • Rapidly removes limb from painful stimulus

      • HIGH THRESHOLD

    • Crossed extensor reflex

      • Maintains body equilibrium

      • HIGH THRESHOLD

  • All these somatic reflexes have 5 common components

    1. SENSORY RECEPTOR

      • Responds to stimulus by producing a receptor potential

      • Activated

      • In periphery in most cases

    2. SENSORY NEURON

      • Axon conducts impulses from receptor to integrating center

      • Relays info into CNS

      • Afferent

    3. INTEGRATING CENTER

      • One or more regions in CNS that relay impulses from sensory to motor neurons

      • Different levels of connection complexity depending on the stimulus

    4. MOTOR NEURON

      • Axon conducts impulses from integrating center to effector

    5. EFFECTOR

      • Muscle or gland that responds to motor nerve impulse

      • Gland= autonomic

      • Motor=somatic

        • Reflex of muscles that are also involved in voluntary movement

  • Monosynaptic (stretch) reflex

    • Mechanism

      1. Stretching stimulates SENSORY RECEPTOR (muscle spindle)

      2. Sensory NEURON excited (1a)

      3. In INTEGRATING CENTER (spinal cord) sensory activates a-motor neuron

        • Direct excitatory contact

        • Provides motor signal to originally stimulated muscle

      4. (Alpha) MOTOR NEURON excited

      5. EFFECTOR (same muscle) contracts and relieves the stretching

    • General

      • Muscle spindles are PROPRIOCEPTORS- relay sensory info from muscles

      • Stretch reflex maintains muscle tone

    • EXAMPLE= Knee jerk reflex=monosynaptic (stretch reflex)

      • Lowe control from lower motor-neurons

        • In normal state, heightens response

        • Weak or absent reflex= possible lower motor-neuron lesion

      • Descending control from upper motor-neurons

        • In normal state, this dampens down response

        • Exaggerated reflex= possible lower motor-neuron lesion

    • Postsynaptic reflex-inhibitory interneuron

      • Flexors are stimulated, this a-motorneuron inhibits extensors (e.g. knee)

      • Antagonists

      • Synergists

      • Reciprocal innervation

    • Alpha and gamma motorneurons

      • Alpha motor neurons

        • Activation of these causes...

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