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25 Cards in this Set

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Motor Neurons
Each muscle fiber is supplied by only one motor nerve fiber.
The Motor Unit
one nerve fiber and all the muscle fibers it innervates
behaves as a single functional unit
Motor units vary in size. Muscles for eye movement have 23 muscle fibers per motor unit. The large thigh muscles have 500-1000 fibers per motor unit.
"work in shifts”
synapse.
The point of contact between a neuron and its target cell
neuromuscular junction
When the target cell is a muscle cell
synaptic cleft
There is a tiny gap between the two cells
RMP is measured in mV, and is determined by
1) diffusion of ions down their concentration gradients
2) selective permeability of the plasma membrane
3) electrostatic attraction
Electric potential
potential energy that results from a polarized state.
action potential.
When a nerve or muscle cell is stimulated, ion gates in the membrane open, sodium ions rush in, and potassium ions rush out, resulting in changes in membrane voltage called
Low-level tension and resistance to stretch
Controlled by the spinal cord
Random, asynchronous motor unit contractions
Energy Transfer
During exercise, muscles use energy produced by aerobic respiration and anaerobic fermentation (when oxygen is limited and lactic acid accumulates).
For short, quick spurts of energy, muscle tissue relies on ________________ to supply ATP.
direct phosphorylation
Muscle fatigue, the progressive weakness and loss of contractility, is due to a variety of causes:
ATP synthesis declines as glycogen is consumed.
The ATP usage slows down to maintain the resting membrane potential.
Lactic acid lowers the pH of the sarcoplasm and impairs the action of enzymes.
The accumulation of potassium ions reduces the membrane potential.
Motor nerve fibers use up their Ach.
The CNS fatigues for unknown reasons
Oxygen debt
the difference between the resting state of oxygen consumption and the elevated rate following an exercise
Slow-twitch fibers are small and produce twitches _______________
up to 100 msec long
Fast-twitch fibers are larger and produce twitches ____________
as short as 7.5 msec
Individuals are _______ with different ratios of slow- to fast-twitch fibers
born
Athletic conditioning cannot change the __________________
genetic component of ability
Training can only what you _________ have
optimize
90/10 rule
90% of your training effort must be invested to reach the last 10% of your genetic capability.
Muscle strength depends on
muscle size
fascicle arrangement
size of active motor units
multiple motor unit summation (recruitment)
temporal summation
the length-tension relationship
fatigue
Growth results mostly from ______________
cellular enlargement
The central nervous system occasionally triggers painful, spasmodic contractions
cramps
Cramps are initiated by..........
extreme cold, heavy exercise, lack of blood flow, electrolyte depletion, dehydration, hormone imbalances, and low blood glucose
Muscular Dystrophy
A group of familial diseases of skeletal muscle
Usually the result of one faulty (mutated) gene
Duchenne MD is the most common 1 in 3500 males (usually only in males)
Lack of the dystrophin gene
Smooth Muscle
Different anatomy than skeletal muscle
Wraps around blood vessels and digestive organs
Controlled by the autonomic NS