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UB - PGY 300 - Class Notes - Week 3

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UB - PGY 300 - Class Notes - Week 3

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background image Lecture 9: Reflex Circuits Signals that are designed into development into nervous system, controlled 
skeletal muscle and respond to signal coming in 
Focus on Innate reflexes and Somatic Motor neurons  Classification of Neural Reflexes  Efferent division that controls the effector  Integrating regions within the central nervous system  Time at which the reflex develops  The number of neurons in the reflex loop Monosynaptic reflex Simplest reflex Has a single synapse between the afferent and efferent neurons  Only excitation Incoming neuron directly synapses on the output (efferent) neuron, comes in 
through dorsal horn, in ventral horn there is a soma of motor neuron, gets 
stimulated by afferent neuron, by way of excitatory transmitter (glutamate), 
motor neuron goes out to skeletal muscle and stimulates ACh receptor 
(nicotinic receptor), which open a channel and causes muscle contraction
Polysynaptic Reflexes More complex Two or more synapses  Uses Intervening neurons (interneurons) in central nervous systems can be excitatory or inhibitory  o Can enhance or suppress motor neuron  **Focusing on feedback system of a sensory system on a muscle** Extrafusal muscle fibers (main muscle fibers) Muscle spindle (Proprioceptor) reflex  Passive reflex: b/c automatic system  Monitors stretch of muscle Sensory Component  o When muscle is stretch, that extension of main muscle will also extend  the muscle spindle o Sits in with the main muscle 
o muscle is in resting state the muscle spindle and sensory neuron are 
still firing (modestly, few firing of neuron) o Has stretch receptors (mechanically gated), activated by extension of  muscle, which excite sensory neurons that leave muscle spindle and go
into CNS, sensory neuron stimulates a motor neuron, which then goes 
back into the muscle to contact it back
o Behaves like negative feedback system, to keep length of the muscle  constant 
background image o If muscle gets shorter the spindle stops spiking as much, and motor  neuron will tell muscle sensory to not contract as much o Both ways go back to normal state(resting) of muscle  Muscle component  o Have Intrafusal muscle fibers  Controlled by gamma motor neurons  o Voluntary control of muscle  To move arm and not have muscle spindle react, need to trick 
spindle into thinking muscle is relaxed
Stretch main muscle and relax sensory area of spindle 
(central area) loosens up the muscle spindle  
intrafusal fibers pick up the slack and central area doesn’t
change, muscle spindle doesn’t respond 
Same if muscle gets contracted:  Muscle contracts which would contract muscle spindle Instead the intrafusal fibers contract pull on the muscle 
spindle (sensory area), 
Muscle spindle doesn’t sense a change in length, and 
won’t stimulate sensory neuron to provide negative 
o Passive control of muscle When body isn’t prepared for change in muscle control Simple system(sensory) works and gamma system isn’t 
Intrafusal to extrafusal muscle circuit  Sensory neurons that measure stretch of sensory area of muscle spindle When area is stretched the neuron produces a more spiked signal through 
sensory neuron that goes to extrafusal muscle through alpha motor neurons 
Causes contraction of muscle  When muscle is longer the sensory neuron fires more than when the muscle 
returns to length it fires normally 
If muscle gets shorter, the sensory neuron fires less and produce less action 
potentials, which prevents muscle from continuing to contract 
Golgi Tendon organ  Senses tension on entire muscle Consists of sensory nerve endings interwoven among collagen fibers One model o Suppress contraction of muscle

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School: University at Buffalo
Department: Physiology
Course: Human Physiology
Professor: R Hudson
Term: Fall 2015
Name: Second Half of Week 3
Description: Lectures 9 and 10
Uploaded: 02/16/2018
6 Pages 25 Views 20 Unlocks
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