APC 100 Neuro Powerpoint 2011 part 3

APC 100 Neuro Powerpoint 2011 part 3 - Nervous Nervous...

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Nervous System Anatomy and Functional Organization Part 3 Jim Sharp DVM, PhD jwsharp@ucdavis.edu APC Anatomy 100
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Stretch Reflex Involuntary Tendon-tap reflex = stretch reflex Lengthens muscle spindle Activates afferent neuron Synapses with lower motor neuron Muscle contracts Stretch reflex important postural reflex, maintains constant muscle length Reflexes
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Muscle Spindle Muscle spindle detects stretch Encapsulated intrafusal fibers Extrafusal fibers normal muscle Muscle spindles located near muscle-tendon junction Stretch Reflex Intrafusal fibers - nuclear bag and nuclear chain fibers Nuclear bag fibers dynamic stretch Nuclear chain fibers static stretch
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The center portion of intrafusal fibers – no actin or myosin Contains multiple nuclei Primary annulospiral and secondary sensory endings Stretch causes annulospiral ending to depolarize Muscle Spindle Stretch Reflex A depolarized primary annulospiral ending causes AP in large sensory neuron
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Gamma Loop Muscle spindle receives motor innervation – gamma motor neurons Sets “tone” of muscle spindle Upper motor neurons affect activity of gamma motor euron Reflexes neuron > tone results in increased stretch of interfusal fibers This > activity of afferent neurons More motor neurons discharge – alpha motor neurons More muscle cells contract Gamma neuron activity affects intensity of reflex response
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Withdrawal Reflex Withdrawal or flexor reflexes – protective reflexes Touch something hot - withdrawal reflex Reflex involves three or more neurons Requires activation of several muscle groups Afferent fibers and interneurons travel up and down cord to activate appropriate lower motor neurons Elbow flexors C5-C7 Inhibition of extensors Typically involves heat and mechano receptors Pain is usually after the fact, as most pain transmission is slow Reflexes
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Motor and Sensory Systems
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Spinothalamic Pathway Primary afferent fiber Secondary or tertiary neuron decussates Ascends lateral funiculus Synapse in VPN of thalamus Thalamic neurons then project to sensory cortex in parietal lobe eat, cold, pain, less discriminative General Sensory Systems Heat, cold, pain, less discriminative aspects of touch
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Medial Lemniscus Pathway Discriminative aspects of touch Proprioception, vibration Most fibers decussate Fibers from caudal limbs (legs) &caudal body synapse in nucleus gracilis Fibers from upper limb and cranial portion of body synapse in nucleus cuneatus These fibers synapse in VPN of thalamus General Sensory Systems Thalamic fibers synapse in somatosensory cortex
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APC 100 Neuro Powerpoint 2011 part 3 - Nervous Nervous...

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