Power Point 18 & 19 Flashcards
Under the boutons lies specialized portion of muscle membrane termed
end plate
Motor axon branches at its terminal, each branch terminates in a
synaptic bouton
Neuromuscular synapses are
cholinergic (ACh)
One action potential fired by motor neuron produces one ________ in the muscle fiber
twitch
The time it takes the twitch to reach its peak force is termed the
contraction time
Depending on biochemical properties, there are ______ twitch motor units
slow and fast
A rapid series of action potentials (resulting in temporal summation) elicits superimposed twitches, resulting in sustained contraction is known as
tetanus
Biochemical properties of a muscle fiber influence what?
contraction speed, force, and fatigability
Type I muscle fibers are what type of twitch muscles
slow twitch - produce small forces but can sustain contraction longer
Type II muscle fibers are what type of twitch muscles
fast twitch - produce large forces but are easy to fatigue
The _________ is defined as a single motor neuron and the group of muscle fibers which it innervates.
motor unit
one muscle fiber is innervated by one ______
motor neuron
fine control = few muscle fibers per neuron – type _______ fibers (motor units of less than 100 for control of eye movements)
1
large force = many muscle fibers per neuron – type _______ fibers (>1000 for single motor unit controlling leg muscles)
2
all the muscle fibers innervated by the (Same/Different) motor neuron are of the same type
same
muscle fibers in one muscle work in parallel and are subdivided into _______
motor units
motor neurons in the ventral horn of the spinal cord that control one muscle are clustered into a column termed the __________________
motor nucleous
one motor nucleus = one _______
muscle
axons from a motor nucleus exit the spinal cord in several ____________, but cluster into one nerve bundle en rout to the target muscle.
ventral roots
the force exerted by a muscle depends on:
- the number of motor units activated during contraction
* the rate at which motor neurons discharge action potentials
Force is increased during a muscle contraction by the activation of additional motor units which are recruited progressively from the __________ to the __________.
weakest, strongest
the force during the contraction at which the motor unit is activated.
Motor unit recruitment threshold
Size Principle Of Motor Neuron Recruitment
recruitment proceeds in ascending order of motor neuron size
smaller motor neurons get recruited first
sequence of motor unit recruitment is determined by spinal mechanisms (brain cannot selectively activate specific motor units)
motor units are activated in order of increasing fatigability