Anatomy of the Muscular System

A Few Facts… There are more than 600 skeletal muscles in the body They constitute 40-50% of our body weight Along with the skeleton they determine the form and contours of our body

Skeletal Muscle Structure

Connective Tissue Components Muscles cells (fibers) are covered by a delicate connective tissue membrane called the endomysium. Groups of skeletal muscle fibers are called fascicles, and bound together by a tougher connective tissue envelope called the perimysium. The muscle as a whole is covered by a course sheath called the epimysium.

Skeletal Muscle Structure

Aponeurosis – broad, flat sheet of connective tissue Tendon – bands or cords of fibrous connective tissue that attach a muscle to a bone or other structure Aponeurosis – broad, flat sheet of connective tissue Fascia – surrounds the muscle organ and outside the epimysium Superficial Deep

Size, Shape, and Fiber Arrangement Skeletal muscles are organs Vary widely in size and shape Muscle fiber arrangement differs Parallel to the long axis of the muscle Converge to a narrow attachment Oblique and pennate (like a feather pen) Bipennate (double-feathered) Curved -- sphincter

Fiber Arrangement Parallel Convergent Pennate Bipennate Sphincter

Attachment of Skeletal Muscle Most muscles span at least one joint and attach to both articulating bones Origin – attachment of a muscle to the bone, which does not move when contraction occurs Insertion – attachment of a muscle to the bone that it moves when conctraction occurs

Muscle Attachment

Muscle Actions Most muscles act in groups and not alone—some contract while others relax Agonist (prime mover) – used to describe a muscle or group of muscles that directly performs a specific movement. Example: biceps brachii is the prime mover in the flexion of the forearm. Antagonists – muscles that, when contracting, directly oppose prime movers – they relax while the prime mover is contracting

Synergists – muscles that contract at the same time as the prime mover Fixator muscles – generally function as joint stabilizers Most muscles function not only as prime movers but also as antagonists, synergists, and fixators. A prime mover in a particular movement , such as flexion, may be an antagonist during extension

Lever Systems A lever is any rigid bar free to turn about a fixed point called its fulcrum. Bones serve as levers and joints serve as fulcrums

First Class Lever

Second Class Lever

Third Class Lever

How Muscles are Named Most are Latin in origin (some Greek) Location (gluteus = buttock) Function (adductor) Shape (deltoid = triangular)

Muscle Naming Continued… Direction of fibers (rectus = straight) Number of heads of divisions (biceps = two points of origin) Points of attachment (sternocleidomastoid = origin on the sternum and clavicle and inserts on the mastoid process) Size of muscle (maximus = largest)