BIOL 2457 1st Edition Lecture 29Outline of Last Lecture Spinal Cord and Spinal Nerves Outline of Current LectureSpinal Cord and Spinal NervesLumbar Plexus Formed by the anterior rami of L1-L4. Supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs. Femoral nerves, obturator nerves.Sacral Plexus Formed by the anterior rami of L4-L5 and S1-S4. Supplies the buttocks, perineum, and lower limbs. Gives rise to the largest nerve in the body- the sciatic nerve. Coccygeal Plexus Formed by the anterior rami of S4-S5 and the coccygeal nerves. Supplies a small area of skin in the coccygeal region.Sensory & Motor Tracts The name of the tract often indicates its location in the white matter and where it begins and ends. The white matter contains both sensory and motor tracts.Reflexes Reflex - automatic, sudden, involuntary response to a stimulus Spinal reflex – occurs when the integration takes place in the spinal cord Reflex arc - pathway followed by nerve impulses that produce a reflex Reflex arc components (5 steps) Sensory receptor Sensory neuron Integrating center Motor neuron EffectorSpinal Reflexes Stretch reflex – causes contraction of a skeletal muscle in response to stretching of the muscle Tendon reflex – operates as a feedback mechanism to control muscle length by causing muscle contraction Flexor (withdrawal) reflex - causes withdrawal of a part of the body in response to a painful stimulus Works with crossed extensor reflex Crossed extensor reflex – helps to maintain balanceThe Stretch Reflex Causes contraction of a skeletal muscle in response to stretching of the muscle Monosynaptic reflex Patellar or knee-jerk reflex Stretching of a muscle →activation of muscle spindles →sensory neuron →spinal cord→motor neuron → muscle contraction IpsilateralThe Tendon Reflex Polysynaptic reflex. Controls muscle tension by causing muscle relaxation when muscle tension isgreat. Sensory receptors- Golgi tendon organs. ↑ Tension applied to the tendon → tendon organ stimulation → nerve impulse → spinal cord →motor neuron causes muscle relaxation and relieves tension.Flexor (Withdrawal) Reflex Polysynaptic reflex Ipsilateral Stepping on a tack (stimulus) → nerve impulse → activation of the interneuron → activation of the motor neuron →muscle contraction →withdrawal of the legCrossed Extensor Reflex Polysynaptic reflex. Contralateral reflex. Contraction of muscles that extend joints in the opposite limb in response to a painful stimulus. Stepping on a tack (stimulus) → nerve impulse →activation of several interneurons → activation of the motor neurons → muscle contraction causing flexion of the leg stepping on a tack & extension on the opposite side.Control of spinal reflexes Brain can facilitate or inhibit motor patterns based in spinal cord Motor control involves a series of interacting levels Monosynaptic reflexes are the lowest level Brain centers that modulate or build on motor patterns are the highest Reinforcement & inhibition Reinforcement = facilitation that enhances spinal reflexes Spinal reflexes can also be inhibited Babinski reflex replaced by planter
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