Lab 7: Muscle Physiology

Muscle tone

A sustained, partial contraction of portions of a skeletal or smooth muscle in response to activation of stretch receptors or a baseline level of action potentials in the innervating motor neurons.

Contraction Phase

Ca2+ binds to troponin, myosin binding sites on actin are exposed, and cross bridges are formed- 10-100 msec

Wave summation

Wave summation is an increase in muscle contraction strength based on how rapidly a muscle is stimulated. Wave summation occurs because muscles that are rapidly stimulated are not able to relax between repeated stimulations.increased strength of a contraction that occurs when a second stimulus arrives before the muscle fiber has relaxed completely following a previous stimulus

Twitch

a brief spasmodic contraction of muscle fibers; also : a slight jerk of a body part caused by such a contraction.

Motor unit

a motor neuron together with the muscle fibers it stimulates

Multiple motor unit recruitment

is a measure of how many motor neurons are activated in a particular muscle, and therefore is a measure of how many muscle fibers of that muscle are activated. The higher the recruitment the stronger the muscle contraction will be.

Latent Phase

the muscle action potential sweeps over the sarcolemma and Ca2+ is released from the SR~ 2msec

all or nothing principle

the strength by which a nerve or muscle fiber responds to a stimulus is independent of the strength of the stimulus. If that stimulus exceeds the threshold potential, the nerve or muscle fiber will give a complete response; otherwise, there is no response.

Isotonic contraction

the tension developed in the muscle remains almost constant while the muscles change length- body movements and moving objects

Isometric contraction

the tension generated is not enough to exceed the resistance of the object to be moved and the muscle does not change length

Relaxation Phase

- Ca2+ is actively transported back into the SR, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, and tension in the muscle fibers decrease- 10-100msec

Muscle Fatigue

Inability of a muscle to maintain its strength of contraction or tension; may be related to insufficient oxygen, depletion of glycogen, and/or lactic acid buildup.

Tetanus

• Unfused tetanus- a sustained, muscle contraction with partial relaxation between stimuli • Fused tetanus- a sustained, muscle contraction without partial relaxation between stimuli tetanus in which stimuli to a particular muscle are repeated so rapidly that decrease of tension between stimuli cannot be detected.