Introduction to the Muscular System

Organization of Skeletal Muscle Fibers fascicles fibers fibers of a single fascicle always parallel fascicles of a muscle can be arranged in various ways Tendon – mostly made of collagen fibers

Muscles are classified by how the fascicles are organized Parallel (e.g., biceps brachii muscle) most common arrangement Convergent (e.g.,pectoralis muscle) fascicles fan or triangle shaped, converge to attach

Muscles are classified by how the fascicles are organized Pennate (unipennate, bipennate and multipennate) fasicles form angle toward tendon Circular (e.g.,orbicularis oris) sphincter, contracts to reduce diameter of opening

Classification of Muscle Skeletal- found in limbs Cardiac- found in heart Smooth- Found in viscera Striated, multi- nucleated Striated, 1 nucleus Not striated, 1 nucleus voluntary involuntary

Origins and Insertions The ends of skeletal muscles are always attached to other structures fixed end is called ORIGIN usually attached to bone or cartilage movable end is called INSERTION usually attached to the bone it moves

How are muscles named? location in the body Origin and Insertion e.g., temporalis muscle Origin and Insertion first part = origin, 2nd part = insertion Fascicle Organization e.g., Rectus means “straight” e.g., transverse means “across” e.g., oblique means “oblique angle”

How are muscles named? Relative Position e.g., superficialis, internus, lateralis, etc… Structural Characteristics (shape and size) e.g., deltoid, rhomboid, major, longus, etc… Action e.g., abductor, extensor, rotator, etc…

Characteristics of Muscle Skeletal and smooth muscle are elongated Muscle cell = muscle fiber Contraction of a muscle is due to movement of microfilaments (protein fibers) All muscles share some terminology Prefixes myo and mys refer to muscle Prefix sarco refers to flesh

Muscular Actions Agonists (prime mover) Antagonist Synergists Fixators responsible for a particular movement Antagonist against movement of agonist Synergists aid agonists, stabilize an action Fixators specialized synergists immobilize the origin of agonist so all tension is exerted at the insertion point