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Synaptic Knob

End of an axon that contains vesicles filled with the neurotransmitter acetylcholine


A functional level of muscle tissue made up of actin and myosin filaments. These are responsible for muscle contractions


Basic functional unit of a muscle cell.

Muscle Tone

A partial but sustained muscle contraction. Common in muscles of the back

All-or-none Response

When a muscle fiber descides to contract, it will contract completely

Isometric contractions

Contraction of muscles without changing the length of the muscle. Example: standing at attention, pushing a wall

Creatine Phosphate

An energy supply for the synthesis of ATP molecules.


Protein molecule that stores oxygen


Muscle growth from training or usage


Lack of muscle usage leading to decrease size, tone, and power

Isotonic Contractions

Contraction of muscles that changes the length of the muscle. Examples: lifting objects, running


Energy source for muscle contractions. Without it muscles may cramp and not contract

Skeletal Muscle

Voluntary, striated muscle found through out the entire body

Cardiac Muscle

Involuntary, striated muscle found only in the heart. Contains intercalated disks

Smooth Muscle

Involuntary, non-striated muscle found in vessels and organs.


Less moveable end of muscle attachment. Fixed end


Moveable end of muscle attachment.


The movement made based on the muscle. Example: flexion

Rectus abdominus

AKA "six-pack" inserts on the superior surface of the pubis and around the symphysis

Biceps brachii

Muscle that when contracted causes the arm to flex

Triceps brachii

Muscle that when contracted causes extension of the arm. Extends arm during push ups

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