Chapter 12 Muscular System

Origin (muscle)

The stationary bone that a muscle is attached to.

Insertion (muscle)

The bone that moves when a muscle contracts, located on the opposite side of a joint.

Action (muscle)

The movement caused when the insertion is pulled toward the origin.

Skeletal Muscle Actions

Muscle actions categorized as exterior, flexor, and abductor.

Fascia

The connective tissue covering the surface of a muscle.

Fascicles

Bundles of muscle fibers within a whole muscle.

Sarcolemma

The specialized plasma membrane surrounding a muscle fiber.

Sarcomere

The functional unit of muscle contraction composed of actin and myosin.

Neuromuscular Junction

The synapse between a nerve fiber and a muscle fiber.

Motor Unit

A motor neuron and all the muscle fibers it innervates.

Innervation Ratios

The tradeoff between strength and fine control based on the number of muscle cells per motor unit.

Muscle Tension

The mechanical force generated by muscles during contraction.

Cross Bridge Cycle

The process by which myosin heads interact with actin during muscle contraction.

Excitation-Contraction Coupling

The physiological process linking muscle excitation to contraction.

Muscle Twitch

A single contraction/relaxation event recorded when an electrical shock is applied.

Summation

The increase in contraction strength when a second stimulus is applied before complete relaxation.

Tetanus

A sustained muscle contraction due to continuous stimulation.

Phosphocreatine

A reserve of high-energy phosphate in muscle that can rapidly regenerate ATP.

Muscle Spindle

Stretch receptors in skeletal muscles that respond to muscle stretching.

Golgi Tendon Organ

Stretch receptors located in tendons that signal the level of muscle tension.

Monosynaptic Reflex

A reflex that involves a single synapse between a sensory neuron and a motor neuron.

Cardiac Muscle

Striated muscle found in the heart, capable of spontaneous contraction.

Gap Junctions

Electrical synapses that connect myocardial cells, allowing impulses to spread.

Smooth Muscle

Involuntary non-striated muscle that lacks sarcomeres and can contract in response to stretch.

Multiunit Smooth Muscle

Smooth muscle where individual cells are controlled separately, without gap junctions.

Single Unit Smooth Muscle

Smooth muscle where cells are electrically connected and contract as a single unit.