Skeletal Muscles

• Morphology - the architecture of a muscle will determine its strength and excursion. The strength of a muscle is directly proportional to its cross sectional area.

1 Parallel, or nearly parallel (fan shaped) - muscle fibers run parallel or nearly parallel to each other and to the length of the muscle; this gives the greatest degree of movement

2 Pinnate - literally means feather-like; it means that the tendon runs nearly the length of the muscle and the fibers insert into the tendon at an angle

· unipinnate - fibers insert at an angle along one side of the tendon

· bipinnate - fibers insert at angles along two sides of the tendon

· multipinnate - the tendon has many septa into which fibers insert

· circumpinnate - the tendon runs through the center of the muscle and receives fibers all around the tendon

• Muscle names - muscles are named for the following:

· shape or geometry

· action

· attachment(s)

· location

• Muscle movement

1 Role in motion - one muscle may have more than one role, depending on the motion

· prime mover - a single (generally) muscle which is mostly responsible for a particular action

· antagonist - a muscle which produces the opposite action

· synergist - a muscle which assists the prime mover; it assists in the desired movement or prevents undesired movement

· fixator - a muscle which stabilizes a joint so other muscles can act more efficiently

2 Types of movement

· flexion - to narrow (reduce) the angle of a joint (in the foot, it is also called plantar flexion)

· extension - to increase the angle of a joint (in the foot, it is also called dorsiflexion)

· abduction (take away) - movement away from the midline (or midpoint of the

· hand/foot)

· adduction (add to)- movement toward the midline (or midpoint of the hand/foot)

· pronation - rotating the forearm so the dorsum of the hand faces anteriorly

· supination - rotating the forearm so the palm of the hand faces anteriorly

· circumduction - circular motion of the shoulder or the hip; involves flexion, extension, abduction, adduction, rotation

· protraction - moving anteriorly, as in protracting the scapula

· retraction - moving dorsally, as in retracting the scapula

· opposition - drawing of the thenar pad toward contact with the hypothenar pad (reposition is to return thumb to anatomical position)

· elevation - to raise superiorly

· depression - to move inferiorly

· lateral bending - to move the trunk of the body away from the median plane

· rotation - to move the body or extremaity around a longitudinal axis

a) lateral - to rotate a joint externally, away from the median plane

b) medial - to rotate a joint internally, toward the median plane

· inversion (also called supination) - to rotate the medial border of the foot superiorly

· eversion (also called pronation) - to rotate the lateral border of the foot superiorly

· hyperextension - to extend beyond normal range

Category: Anatomy Notes