Muscle Smooth - uninucleate, fusiform cells without striations. Visceral function. ANS innervation. Cardiac - Uninucleate (mostly) cells which are striated, branch and communicate via intercalated discs. Intrinsic beat. ANS Striated - multinucleated cells which are striated. Voluntary control. Somatic functions. Sarcomere is contractile unit.

Classification Based on Function Somatic: orient and move animal within environment located in body wall, appendages and tail originate in myotomes include (1) muscles of body wall, (2) hypobranchial and tongue muscles, (3) extrinsic eye muscles and (4) appendicular muscles

Visceral: maintain homeostasis innervated by autonomic n.s. include (1) branchiomeric, (2) cardiac, (3) intrinsic eye and erector muscles, and (4) smooth muscles of tubes, vessels, and hollow organs Skeletal vs non-skeletal: skeletal attach and move skeletal elements non-skeletal include all other muscles (involuntary)

Skeletal Muscles Muscular and tendinous elements Tendons attach muscle to bone - extensions of the epimysium (fascia). Red fibers - high myoglobin content and a rich blood supply. Contract slowly, resist fatigue, allow extended function. White fibers - lack myoglobin, contract rapidly, fatigue quickly.

Origin, Insertion, Action Origin - site of attachment that remains fixed and does not move. Insertion - attachment site that is displaced when muscle contracts. Action - describes the function movement of the muscle.

Names and Homologies Names - denote fiber direction (oblique, rectus), location or position (supraspinatus), number of subdivisions (quadriceps), shape (deltoid), origin and/or insertion (sternocleidomastoid), action (levator scapulae), size (pectoralis major) or other criteria...

Homologies - even though muscles in two species have the same name they may not be homologous. Muscles may alter shape, size and attachment site(s) during evolution. Homologous muscles have the same embryonic origin rather than the adult characteristics.