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Motor functions of Spinal Cord- Reflex Action

Motor functions of Spinal Cord- Reflex Action. The Pattern Generator. Objectives. At the end of this lecture you must be able to: Define a reflex action& know components of Reflex arc. Types of reflexes & their level of integration Physiological Significance of these reflexes.

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Motor functions of Spinal Cord- Reflex Action

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  1. Motor functions of Spinal Cord-Reflex Action The Pattern Generator

  2. Objectives • At the end of this lecture you must be able to: • Define a reflex action& know components of Reflex arc. • Types of reflexes & their level of integration • Physiological Significance of these reflexes. • Stretch Reflex and its practical Imporatnce

  3. Connectionsof Peripheral Sensory fibers & Corticospinal fibers with Interneurons & Ant. Motor N (α & γ + Renshaw Cells)

  4. Reflex • Is a quick, involuntary stereotype reaction of the body in response to stimulus. • All reflexes functions through a Reflex Arc. • Reflex Arc: is comprised of -Receptor -> -Afferent Nerve -> -Interneuron( +) ->(integration Centre) -Efferent Nerve -Effector

  5. Classification of Reflexes On the basis of Innate or Acquired: • Unconditioned Reflexes.- Present since birth • Conditioned Reflexes: - Learned after birth On the basis of Number of Synapses: - Asynaptic – e.g. Axon Reflex - Monosynaptic – e.g.Stretch Reflex -Polysynaptic – e.g. Withdrawal Reflex, Crossed Extensor Reflex

  6. Classification of Reflexes • Clinically: - Superficial – Abdominal Reflex - Deep ------- Knee jerk -Visceral ------ from any viscera -Pathological – Babinski Sign PROPEERTIES of reflexes: Already discussed in properties of synapses

  7. Stretch Reflex • Defnition. Whenever a muscle is stretched, it responds in the form of contraction. (Monosynaptic) • TYPES: 1. Static ( Tonic ) 2. Dynamic ( Phasic) Stretch Receptor: Muscle Spindle To understand these types muscle spindle ?

  8. Muscle Spindle Is a type of Stretch Receptor present in Muscles lying Parallel to Extrafusal muscle fibers . 3-10 u Long . Attached to Glycocalyx of surrounding Extrafusal fibers Comprised of Two types of Fibers. 1.Nuclear chain Fibers 2.Nuclear Bag Fibers (Intrafusal fibers) .3-12 in number

  9. Innervations of Muscle Spindle

  10. Innervation of Intrafusal Fibers of Muscle Spindle Afferent: Primary- Annulospiral endings ( group- I a) Secondary-Flower spray endings (group- II ) Efferent: Dynamic -- (Gamma-1) - Plate endings Static - (Gamma-2) - Trail endings a

  11. Excitation of Muscle Spindle Can be Excited by TWO ways; 1. Stretching the who muscle > Stretching of mid portion of the spindle >Excitation 2. Contraction of the end portion of the Spindle without stretching the muscle will also lead to Stretching the central part > Excitation

  12. Functions of Muscle Spindle • Maintenance of Muscle Length by feedback: - Stretching of muscle > Reflex Shortening of muscle Oppositeif Muscle contracts Hence Detects Change in length & Rate of change in length. 2. Damping (smoothing) of Oscillations by Primary Endings. 3. Excitation of Alpha Motor Neurons.

  13. Functions of Muscle Spindle contd. 4. Maintenance of ά- motor Neuron discharge throughout the muscle contraction 5. Stabilizes body Position during Tense action (Bulboreticular facilitatory area send excitatory signals to Gamma motor Neuron) 6. Tendon Reflexes 7. Muscle Tone

  14. Clinical Example of Stretch Reflex1. (Knee Jerk)2. Clonus

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