BIO 102 Chapter 6

Motor unit size, the number of motor units active at any one time, and the frequency of stimulation of individual motor units

Three factors that determine how much muscle tension is generated by muscle

Isotonic contractions

When a muscle shortens while maintaining a constant force

Isometric contractions

When a muscle tension increases, and the muscle may even shorten a little as tendons are stretched slightly, but ones and objects do not move

Insertion

One end of skeletal muscle that attaches to another bone across a joint

Summation

Increasing muscle cell force by increasing the rate of stimulation of motor units

Recruitment

Increasing tone (or force) by activating more motor units

Relaxation

Muscle cell returns to its original length

Antagonistic muscles

Muscle groups that oppose each other

Synergistic muscles

Muscle groups that work together to create the same movement

Voluntary muscle

Muscle movement over which we have conscious control

Involuntary musle

Muscle movement which is generally beyond our conscious control

Origin

One end of the skeletal muscle that joins to a bone that remains relatively stationary

Cardiac muscle

Rhythmic contractions of this type of muscle found in the heart pumps blood throughout the body

Contract

Shorten

Intercalated disks

Structures which join cardiac muscle cells

Excitable

The characteristic of all muscle cells which means they contract in response to chemical and/or electrical signals from other organ systems

Muscle tension

The mechanical force that muscles generate when they contract

Motor unit

The muscle neuron and all the muscle cells it controls; the smallest functional unit of muscle contraction

Action potential

The stimuli for muscle contraction

Latent period

The time between stimulation and the start of muscle contraction

Contraction

The time during which the muscle cell actually shortens

Skeletal muscle

The type of muscle that interacts with the skeleton and causes bones to move (or prevents them from moving) relative to each other

Slow-twitch fibers

This type of skeletal muscle fiber breaks down ATP slowly, and so it contracts slowly; they tend to make ATP as they need it by aerobic metabolism (called "red" muscle).

Fast-twitch fibers

This type of skeletal muscle fiber contracts quickly because it breaks down ATP quickly. They have fewer mitochondria, fewer blood vessels, and little or no myoglobin (called "white" muscle).

Twitch

A complete cycle of contraction and relaxation

Muscle fatigue

A decline in muscle performance during exercise

Single muscle

A group of individual muscle cells, all with the same origin and insertion and all with the same function

Motor neuron

A single nerve cell which controls each group of muscle cells

All-or-none principle

According to this, muscle cells are completely under the control of their motor neuron; muscle cells never contract on their own.

Pacemaker cells

Cardiac cells with the fastest rhythm of contraction and relaxation; the rest of the cells follow their faster pace.