Acetylcholine – A key chemical mediator involved in neuromuscular synaptic transmission

Action potential – An electrical impulse generated by neurons

Concentric contraction – The shorten- ing of a muscle during activation

Dynamic strength – The magnitude of isotonic or isokinetic contraction

Eccentric contraction – The lengthen- ing of a muscle during activation

Endomysium – The connective tissue surrounding a muscle cell

Epimysium – The connective tissue surrounding the entire muscle

Isokinetic – Literally “same speed”; when applied to muscle action, it implies constant velocity of shortening

Isometric – Literally “same length”; when applied to muscle action, it implies that the muscle length is held constant

Isotonic – When applied to muscle action, it implies that the load is constant

Motor end plate (neuromuscular junction) – The synapse between a motor neuron and a muscle fiber

Motor unit – The motor nerve axon and the myofibers with which it contacts

Musculotendinous junction – The area of interface between a skeletal muscle and its tendon

Myoblasts – The embryonic cells that develop into skeletal muscle cells

Myofibers – The fibers that constitute a muscle

Perimysium – The connective tissue surrounding a fascicle

Sarcolemma – Muscle-cell membrane and its associated basement membrane

Sarcomeres – The fundamental components of the contracting unit of the myofibri

Sarcopenia – The loss of muscle mass and strength as a result of aging

Sarcoplasmic reticulum – A continuous branching network of membrane, which is a specialized form of endoplasmic reticulum unique to muscle

Schwann cell – A specialized support cell that encases nerve fibers

Static strength – The magnitude of isometric contraction

Stem cells – Cells with the unlimited ability of self-renewal and regeneration; serve to regenerate tissue

Synapse –  specialized site at which an electrical signal is transmitted chemically across a junction to produce a similar electrical impulse on the opposite side

Tenocytes – The cells in tendons