| A | B |
|---|
| Sarcomere | The repeating unit of myofibril |
| Neuron | The functional unit of the nervous system, a nerve cell |
| Synapse | The interface between a nerve cell and another cell |
| Neurotransmitter | A chemical released by a neuron. This chemical travels across the synaptic cleft, allowing the neuron to communicate with another cell. |
| Motor Unit | One motor neuron and all the muscle fibers it innervates |
| All-or-none law of skeletal muscle contraction | An individual muscle fiber contracts with equal force in response to each action potential |
| Subthreshold Stimulus | A stimulus too small to create an action potential in a neuron |
| Threshold Stimulus | A stimulus strong enough to create one action potential in a neuron |
| Submaximal Stimuli | Stimuli of increasing strength that create more action potentials along more neurons |
| Maximal Stimulus | A stimulus which is strong enough to create action potentials in all the motor neurons innervating a whole muscle |
| Muscle Tone | The state of partial contraction in a muscle, even when the muscle is not being used |
| acetylcholinesterase | enzyme that inactivates acetylcholine |
| acetylcholine (ACh) | neurotransmitter that stimulates muscle fibers |
| muscle fiber | muscle cell |
| fascicles | bundles of muscle cells |
| endomysium | collagen layer that wraps each muscle cell |
| perimysium | collagen layer which wraps a fascicle |
| epimysium | collagen layer that wraps around one whole muscle |
| sarcolemma | plasma membrane of the muscle fiber |
| sarcoplasmic reticulum | endoplasmic reticulum of the muscle fiber |
