Muscle Basics Over 600 muscles in the body Each is attached to bones or other structures by no fewer than 2 points 1.Origin: the immovable (or less movable) bone 2.Insertion: movable end of a bone

Interactions of Skeletal Muscles in the Body: skeletal muscles may work together or in opposition to each other skeletal muscles only contract or shorten, they do not lengthen 1. prime mover or agonist: the muscle providing the major force behind a movement Ex: biceps brachii and brachialis are prime movers for elbow flexion 2. antagonist: muscles that oppose or reverse a movement Ex: triceps brachii antagonists to elbow flexion

3. synergists: muscles that “help” the agonist a. promote same movement b. reduce unnecessary movements (wrist and fingers) 4. fixators: synergists that immobilize a bone or a muscles origin Ex: muscles that stabilize vertebral column and anchor scapula to thorax

Naming Skeletal Muscles: 1. Location: by the bone or body region that it is near Ex: rectus abdominis 2. Shape: named for a shape it resembles Ex: deltoid (triangle) 3. Size: minimus, maximus, longus etc. Ex: gluteus maximus

4. Direction of fibers: the way in which muscle fibers run based on the midline of the body or the longitudinal axis of a bone 5. # of origins: Ex: biceps brachii, triceps brachii etc.

6. Location of a muscle’s origin and / or insertion: muscles are named through these two points; the origin is usually named first Ex: sternocleidomastoid 7. Action of the muscle: flexor, adductor, extensor, etc

Arrangement of Fascicles

Circular: fascicles are arranged in concentric rings Ex: orbicularis oculi

Convergent: muscle has a broad origin and narrows toward a single tendon Ex: pectoralis major

Parallel: long axes of facsicles run parallel to the long axis of the muscle

Pennate (feather) : the fasicles are short and attach obliquely to a tendon

Unipennate: Fascicles insert on 1 side of tendon

Bipennate: fascicles insert into 2 sides of tendon

Multipennate: muscles insert from several different sides of tendon