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Neuromuscular Function
N/A
19
Anatomy
Undergraduate 2
09/19/2012

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Term
neuromuscular junction
Definition
  • point where nerve and muscle communicate
  • product of communication will be muscle twitch rather than an action potential (AP)
Term
motor unit
Definition
  • consists of a motor neuron, its axon, and muscle fibers it innervates
Term
terminal endplate (motor endplate)
Definition
end of axon of motor neuron
Term
acetylcholine (Ach)
Definition
only neurotransmitter dumped into the active zone (cleft) of neuromuscular junction
Term
miniature endplate potential (MEPP)
Definition
  • if there are sufficient MEPPs, muscle AP will be generated
  • it takes many activated regions to excite muscle fiber
  • you need to activate many muscle fibers to actually move muscle and do work
  • one will not be enough to make muscle contract
Term

striated (skeletal) muscle

 

Definition
  • long ropelike structure made up of strands of muscle fiber
  • each muscle fiber is made up of long myofibrils
  • each myofibril is composed of either thin or thick myofilaments
Term
muscle fiber contraction
Definition
  • occurs as result of complex chemical reactions
  • many myofilaments make up one muscle fiber
  • muscle fibers make up a muscle bundle
Term
muscle control
Definition
  • neuromotor innervation
  • slow and fast twitch muscle fibers
Term
neuromotor innervation
Definition
  • each muscle fiber is innervated by one motor neuron
  • but each motor neuron may innervate a large number of muscle fibers
Term
multiple motor unit summation
Definition
  • use of many motor neurons to activate muscle
  • more motor neurons that are activated; greater number of fibers that will contract
Term
stretch or myotatic reflex
Definition
  • most simple reflex
  • classic example is knee jerk reflex
  • monosynaptic or two-neuron reflex (one synapse or one sensory neuron and one motor neuron)
Term
knee jerk reflex
Definition
  • tap patellar tendon of quadriceps muscle
  • leads to brief stretch of muscle, which stimulates sensory endings of spindles
  • sends volley of impulses to alpha-motor neurons
  • activation of alpha-motor neurons causes a quick contraction (muscle jerk) of same muscle
Term
stretch reflexes
Definition
  • common element in all stretch reflexes: stretched muscle contracts after very brief delay
  • crossed extensor reflex (for your information)
Term
annulospiral (primary) sensory endings
Definition
  • central region of intrafusal fiber is wrapped by these sensory endings
  • fast-conducting
  • two types of intrafusal fibers: nuclear bag fibers and nuclear chain fibers
Term
types of sensory fibers
Definition
it is not necessary for this course to differentiate between type Ia (fast) and type II (slow) fibers
Term
stretch of spindles
Definition
  • as spindles stretch, surge of sensory input is directed to alpha-motor neurons, which reflexively contract muscle mass to decrease muscle length progressively
  • contraction of entire muscle halts stretch of spindles
  • stretching of central portion of intrafusal fibers can induce stretch reflex
Term
reflex motor response
Definition
stereotyped movement to sensory information
Term
neuronal circuitry for spinal reflex
Definition
  • neuronal circuitry for spinal reflex
  • circuitry includes following structures: muscle spindles, afferent fibers, alpha motor neurons (efferent fibers), neuromuscular junction, and muscle tissue
Term
reflex functions of spinal cord
Definition
  • mostly, independent of voluntary control
  • however, reflexes are indirectly influenced by descending impulses from motor cortex and brainstem motor centers
  • clinical example: in case of an upper motor neuron (UMN) lesion, spinal cord reflexes are released from higher levels of motor control and become hyperactive
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