Muscle Physiology and Contraction Lecture Notes

Flashcards covering the phases of muscle twitches, types of contractions, fiber classification, energy metabolism, and motor unit recruitment based on lecture notes.

Muscle twitch

A muscle contraction recorded on a myogram, described as a three-act play including the latent, contraction, and relaxation periods.

Latent period

The opening scene of a muscle twitch where the stimulus occurs but no visible action happens; events like calcium release prepare the muscle.

Contraction period

The climax of a muscle twitch where sarcomeres shorten and generate tension.

Relaxation period

The resolution of a muscle twitch where tension fades as calcium returns to storage.

Isotonic contractions

Contractions where muscles create tension to move, keeping the same tone while changing length.

Concentric contractions

A type of isotonic movement where the muscles shorten.

Eccentric contractions

A type of isotonic movement where the muscles lengthen.

Isometric contractions

Contractions where a muscle creates tension but the resistance is too great to move the load, so the muscle stays the same length.

Wave summation

Occurs when skeletal muscles are stimulated rapidly at $20-50$ stimuli per sec, preventing full relaxation and increasing muscle strength and tension.

Incomplete tetany

A state where stimulation frequency increases so muscles have less time to relax between contractions.

Complete tetany

Defined by a stimulation rate of $40-50$ stimuli per second where contractions fuse into a prolonged, sustained state.

Tonic contraction

The ability of a muscle to maintain continuous tone.

Fiber power

Depends on fiber diameter; larger fibers produce stronger contractions because they have more myofibrils.

Fiber speed

Relates to myosin ATPase activity which determines how quickly a fiber contracts.

Fast twitch fibers

Fibers that contract quickly ($0.01\text{ m sec}$) with shorter durations ($7.5\text{ ms}$), excelling in rapid, powerful movements.

Slow twitch fibers

Fibers that contract slower ($0.2\text{ m sec}$) but can sustain contractions longer ($100\text{ ms}$).

Creatine phosphate

Stores energy in muscles for short bursts of activity, providing $10-15\text{ secs}$ of power by helping make ATP.

Pyruvate (with oxygen)

Enters the mitochondria for energy production.

Pyruvate (without oxygen)

Turns into lactate to keep glycolysis going.

Lactate

A byproduct that can return to muscle cells for energy, enter the blood for the heart, or go to the liver for the Cori Cycle.

Cori Cycle

The process by which the liver converts lactate back into glucose.

Oxygen debt

Occurs when muscles use more oxygen than available during exercise; extra oxygen is needed later to restore myoglobin, ATP, and glycogen.

Motor unit

Consists of one motor neuron and all the muscle fibers it controls.

Recruitment of multiple motor unit

The process where more motor units activate as stimulation voltage increases, causing stronger muscle contractions.

Length-tension relationship

Explains how muscle tension changes based on filament overlap; maximum tension occurs at resting length.