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Reflexes The typical pattern of a neural “circuit” is an arc. sensory afferents  integration in CNS  motor efferents  effector tissue Reflexes are the.

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Presentation on theme: "Reflexes The typical pattern of a neural “circuit” is an arc. sensory afferents  integration in CNS  motor efferents  effector tissue Reflexes are the."— Presentation transcript:

1 Reflexes The typical pattern of a neural “circuit” is an arc. sensory afferents  integration in CNS  motor efferents  effector tissue Reflexes are the simplest form of integration by CNS. –spinal cord and brain stem only –monosynaptic –polysynaptic Somatic reflexes –effector tissue = skeletal muscle Fig

2 Skeletal Muscle Proprioceptors Muscle Spindles –detect muscle length inhibit muscle stretch Golgi Tendon Organs –detect muscle tension inhibit over-contraction

3 Golgi Tendon Organ Fig Type Ib fibers

4 Muscle Spindles fus- = spindle intrafusal fibers – specialized muscle fibers of the spindle extrafusal fibers – regular skeletal muscle fibers AA AA Type II fiber Type Ia fiber Fig

5 The (Ia) sensory nerve ending is a stretch receptor, wrapped around the center of an intrafusal fiber. The intrafusal fibers have sarcomeres only on their ends. A  stimulation of intrafusal fibers will cause contraction of the ends and stretch of the middle. There is always some tonic discharge by the A  motor neurons. Therefore, the stretch receptors are always slightly stimulated – warmed up and ready to respond to any stretch of the muscle. Fig. 6-3 Ganong Muscle Spindles

6 Stretch Reflex a monosynaptic reflexa monosynaptic reflex e.g., the knee-jerk reflex negative feedback ipsilateral stimulation of extension (simultaneous inhibition of flexion – polysynaptic) AA Fig

7 Polysynaptic Reflexes via interneurons –sensory neuron from skin  [interneuron(s)]  A  motor neuron examples –withdrawal (flexor) reflex –crossed extensor reflex

8 Withdrawal Reflex = stimulatory + = stimulatory = inhibitory - = inhibitory Fig a flexor reflex –ipsilateral stimulation of flexion inhibition of extension

9 Crossed Extensor Reflex Fig an extensor reflex –contralateral stimulation of extension inhibition of flexion

10 Somatic Motor Pathways (from brain) organizing principles –phylogenetic lateral and medial motor systems –medial tracts are more primitive (see ventral/anterior columns) »control proximal muscles: posture and gross movements –lateral tracts are more advanced »control distal muscles: fine, skilled movements –clinical pyramidal and extrapyramidal systems –pyramidal system (direct pathway) –extrapyramidal systems (indirect pathways)

11 Somatic Motor System The frontal lobe is a major control center for somatic motor functions. –precentral gyrus 30-60% of cortical motor fibers originate here. Fig

12 Pyramidal System direct pathway –The axon of one neuron travels from the cerebral cortex to lower motor neurons (such as the A  motor neurons). –two paths lateral corticospinal tracts ventral corticospinal tracts Fig. 13.6

13 lateral corticospinal tracts –lateral motor system –major importance only in primates –precise control of voluntary movements in distal muscles –In humans, 80-90% of cortical motor fibers travel in these tracts. –cross over in the pyramids of the medulla giving the “pyramidal” system its name ventral corticospinal tracts –medial motor system –cross over (via interneurons) in the spinal cord, at the level of the lower motor neuron Fig Ganong

14 Medullary Pyramids Fig Fig. 14.9


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