Revise: Muscle Terminology
There are around 640 named muscles in the human body - in addition
to thousands of smaller (un-named) muscles.
Knowledge of muscle structure and familarisation with the major
muscles of the body is an essential part of training in many therapies
- such as Massage, Aromatherapy, Accupuncture, Shiatsu, and many
others.
This page contains some definitions of key terms about muscles
and muscle functions.
The following table lists key terms in alphabetical order.
Term
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Definition
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Abduction
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Movement of a bone, and the limb of which it is a part,
away from the mid-line of the body.
Verb: To abduct
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Abductor
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Any muscle that moves one part of the body away from
another - or away from the midline of the body.
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Action
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Movement (usually of skin or bone) caused by muscle
contractions.
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Group Actions:
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Most movements occur when several skeletal muscles
act in groups, as opposed to individually.
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Most skeletal muscles are arranged at joints,
in opposing pairs.
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The muscle that causes an action is referred
to as the prime mover or agonist (= leader).
Often another muscle, called the antagonist
(ant = against), relaxes while the prime mover
contracts.
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Most movements also involve muscles called synergists,
which help the prime mover function more efficiently
by reducing unnecessary movement.
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Some muscles in a group also act as fixators,
stabilizing the origin of the prime mover so that
the prime mover can act more efficiently.
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Under different conditions and depending on the
movement, many muscles act at various times as
prime movers, antagonists, synergists,
or fixators.
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Adduction
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Movement of a bone, and the limb of which it is a part,
towards the mid-line of the body.
Verb: To adduct
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Adductor
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Any muscle that moves one part of the body towards
another - or towards the midline of the body.
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Dorsiflexion
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Backward flexion of a foot or hand, or of their digits.
That is, bending fingers or toes backwards towards the
upper surface of the foot or hand.
Put another way: Bending of the foot (or hand) in the
direction of the dorsum (superior surface), e.g. when
standing on ones heels.
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Extension
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Increasing the angle between articulating bones, often
to restore a part of the body to the anatomical position
after it has been flexed.
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Fatigue
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The inability of a muscle to contract forcefully after
prolonged activity.
One important factor in muscle fatigue is the lowered
release of calcium ions from the sarcoplasmic reticulum,
resulting in a decline of Ca2+ level in the sarcoplasm.
Other factors that contribute to muscle fatigue include
depletion of creatine phosphate, insufficient oxygen,
depletion of glycogen and other nutrients, build-up
of lactic acid and ADP, and failure of nerve impulses
in the motor neuron to release enough acetyl-choline.
Because increased lactic acid would cause a decrease
in the pH of body fluids, muscle fatigue may be viewed
as a homeostatic mechanism that prevents the pH from
dropping below the normal acceptable range.
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Flexion
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Decreasing the angle between articulating bones. For
example, "Plantar Flexion" is the bending
of the toes (or fingers) downwards towards the sole
(or palm).
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Flexor
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A muscle that causes a limb or other body-part to bend.
Examples include the mucles of the arms, legs, fingers,
and toes.
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Insertion
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The position at which the other end of the muscle (i.e.
from its origin) is attached, by means of a tendon,
to the moveable bone.
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Origin
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The attachment of muscle (by means of a tendon) to
the stationary bone.
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Plantarflexion
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Flexion of a foot or hand, or of their digits. That
is, bending fingers or toes towards the lower surface
of the foot or hand. For example, bending the foot in
the direction of the plantar surface, as when standing
on your toes - as opposed to ones heels.
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Pronation
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Movement of the forearm so that the palm is turned
backward or downward.
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Rotation
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Movement of a bone such that it revolves around it's
own longitudinal axis (e.g. turning the head from side
to side at the joint between the atlas and axis).
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Supination
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Movement of the forearm so that the palm is turned
forward or upward.
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Tone
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Even when a whole muscle is not contracting, a small
number of its motor units are involuntarily activated
to produce a sustained contraction of the muscle fibers.
The process gives rise to muscle tone.
To sustain muscle tone, small groups of motor units
are alternately active and inactive in a constantly
shifting pattern. Muscle tone keeps skeletal muscles
firm, but it does not result in a contraction strong
enough to produce movement.
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This is the end of this page but information about
anterior muscles,
posterior muscles,
and muscles of facial
expression are included on other pages of
this website.
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... End of Article ...
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