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Muscle Contraction Picture
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Muscle Contraction
A muscle contraction
(also known as a muscle twitch or simply twitch) occurs when a muscle
cell (called a muscle fiber) shortens. Locomotion in most higher animals
is possible only through the repeated contraction of many muscles at the
correct times.
For most muscles, contraction occurs as a result of conscious effort
originating in the brain. The brain sends signals, in the form of action
potentials, through the nervous system to the motor neuron that
innervates the muscle fiber. However, some muscles (such as the heart)
do not contract as a result of conscious effort. These are said to be
autonomic. Also, it is not always necessary for the signals to originate
from the brain. Some reflexes are fast, unconscious muscular reactions
that occur due to unexpected physical stimuli. Other actions such as
locomotion, breathing, chewing have a reflex aspect to them; the brain
will start the contractions, but continuation of the movements can
become reflexive. The action potentials for reflexes to unexpected
stimuli originate in the spinal cord instead of the brain.
There are three general types of muscle contractions: skeletal muscle
contractions, heart muscle contractions, and smooth muscle contractions.
From Wikipedia, the free encyclopedia |
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