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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 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. • Stretch Reflex and its practical Imporatnce
Connectionsof Peripheral Sensory fibers & Corticospinal fibers with Interneurons & Ant. Motor N (α & γ + Renshaw Cells)
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
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
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
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 ?
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
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
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
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.
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