Muscles

Skeletal muscle functions

Produces movement, protects, provides dynamic joint stability, supports posture, and produces body heat.

Aggregate muscle action

Muscles working in groups to achieve a given joint motion.

Muscle action

A specific joint movement resulting from a concentric contraction of a muscle crossing the joint.

Ways muscles can be named

Appearance, location, function, shape, size, number of divisions, fiber direction, and points of attachment.

Deltoid naming example

Named based on shape.

Gluteus maximus naming example

Named based on size.

Triceps brachii naming example

Named based on number of divisions.

External abdominal oblique naming example

Named based on fiber direction.

Rectus femoris naming example

Named based on location.

Coracobrachialis naming example

Named based on points of attachment.

Supinator naming example

Named based on action.

Two major muscle fiber arrangements

Parallel and pennate.

Parallel muscle fibers

Fibers run parallel to the length of the muscle.

Pennate muscle fibers

Fibers run diagonally toward a tendon.

Advantage of parallel muscle fibers

They generally allow a greater range of movement.

Types of parallel muscles

Flat, fusiform, strap, radiate, and sphincter/circular.

Types of pennate muscles

Unipennate, bipennate, and multipennate.

Muscle fiber arrangements producing the strongest contractions

Bipennate and unipennate.

Irritability/excitability

The ability of a muscle to respond to stimuli.

Contractility

The ability of a muscle to contract and develop tension.

Extensibility

The ability of a muscle to be passively stretched beyond its normal resting length.

Elasticity

The ability of a muscle to return to its original resting length after stretching.

Extensibility vs. elasticity

Extensibility is the ability to stretch; elasticity is the ability to return to the original length.

Isometric contraction

A contraction in which muscle tension develops without changing muscle length.

Concentric contraction

A contraction in which the muscle shortens while producing tension.

Eccentric contraction

A contraction in which the muscle lengthens while producing tension.

Isokinetic contraction

A contraction performed at a constant speed.

Agonist

The muscle primarily responsible for producing an action.

Antagonist

A muscle that produces an action opposite the agonist.

Stabilizer

A muscle that helps stabilize or fixate a body part.

Synergist

A muscle that works with another muscle to help produce an action.

Methods for determining muscle action

Palpation, EMG, electrical muscle stimulation, anatomical lines of pull, anatomical dissection, and models.

Palpation

Using touch to feel or examine a muscle as it contracts.

EMG

Electromyography; detects electrical activity produced by muscles.

Electrical muscle stimulation

Using electrical stimulation to cause muscle activity and observe the resulting joint action.

Anatomical line of pull

The direction of force produced by a muscle based on its attachments and position.