Introduction to the Muscular System

• muscle– fascicles

• fibers

• fibers of a single fascicle always parallel

• fascicles of a muscle can be arranged in various ways

Organization of Skeletal Muscle Fibers

Muscles are classified by how the fascicles are organized

1. Parallel (e.g., biceps brachii muscle)• most common arrangement

2. Convergent (e.g.,pectoralis muscle)• fascicles fan or triangle shaped, converge to attach

Muscles are classified by how the fascicles are organized

3. Pennate (unipennate, bipennate and multipennate)• fasicles form angle toward tendon

4. Circular (e.g.,orbicularis oris)• sphincter, contracts to reduce diameter of opening

Classification of MuscleSkeletal- found in limbs

Cardiac- found in heart

Smooth- Found in viscera

Striated, multi- nucleated

Striated, 1 nucleus

Not striated, 1 nucleus

voluntary involuntary 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?

1. location in the body • e.g., temporalis muscle

2. Origin and Insertion• first part = origin, 2nd part = insertion

3. Fascicle Organization• e.g., Rectus means “straight”• e.g., transverse means “across”• e.g., oblique means “oblique angle”

How are muscles named?

4. Relative Position• e.g., superficialis, internus, lateralis, etc…

5. Structural Characteristics (shape and size)• e.g., deltoid, rhomboid, major, longus, etc…

6. 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)– 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