Chapter 11: The Muscular System

Muscular System

consists only of skeletal muscles, no smooth muscles

Muscular System Organization

affects power, range, and speed of muscle movement

Muscle Fibers

organized into fascicles (bundles)

Skeletal Muscles

classified by fascicle organization, relationship of fascicles to tendons

Skeletal Muscle Classification

parallel, convergent, pennate, circular

Parallel Muscles

• fibers are parallel to the long axis of muscle

• tension depends on number of myofibrils

Convergent Muscles

• broad area converges on attachment site e.g. tendon, aponeurosis, raphe

• fibers pull in different directions depending on stimulation

Pennate Muscles

• forms an angle with tendon

• less movement than parallel muscles

• contain more myofibrils and develop more tension than parallel muscles

Circular Muscles (Sphincters)

open and close to guard body entrances

Skeletal Motion

• skeletal muscles attach to skeleton, causing movement

• type of muscle attachment affects poewr, range, and speed of muscle movement

Muscle Attachment: Skeletal Motion

• bone acts as a lever

• joint is a fulcrum (fixed point)

• muscle provides force

Three Classes of Levers

first class, second class, third class

First Class Lever

force and load are balanced e.g. seesaw

Second Class Lever

small force moves a large weight e.g. wheelbarrow

Third Class Lever

larger force moves a smaller load e.g. catapult

Origins and Insertions

• most muscles originate or are inserted on the skeleton

• origin is usually proximal to insertion

Origin

fixed point of attachment

Insertion

moving point of attachment

Actions

• movements produced by muscle contraction e.g. flexion, extension, abduction, adduction

• described in terms of bone, joint, and/or region

Muscle Interactions

• muscles work in groups to maximize efficiency

• smaller muscles reach maximum tension first

• larger muscles take longer to reach maximum tension

Agonist

produces a particular movement

Antagonist

opposes movement of a particular agonist

Synergist

a small muscle that assists larger agonist

Fixator

aids in initiation or stabilization of agonist

Muscle Opposition

• agonist and antagonist muscles work in pairs

• one contracts, the other stretches

• flexor-extensor, abductor-adductor

Flexor

muscle lines of action cross the anterior side of a joint

Extensor

muscle lines of action cross the posterior side of a joint

Abduction/Abductor

muscle lines of action cross the lateral side of the joint

Adduction/Adductor

muscle lines of action cross the medial side of a joint

Lateral Rotation

lines of action cross the posterior side of joint, when muscle contracts, produces lateral rotation

Medial Rotation

lines of action cross anterior side of joint so when muscle contracts it produces medial rotation

Naming Skeletal Muscles

location in body, origin and insertion, fascicle organization, relative position, structural characteristics, action

Location in the Body

identifies body regions e.g. temporalis muscle

Origin and Insertion

first part of name is origin, second part of name is insertion e.g. genioglossus muscle

Fascicle Organization

describes fascicle orientation within the muscle e.g. rectus (straight)

Relative Position

externus, internus, extrinsic, intrinsic

Externus

superficialis, visible at body surface

Internus

profundus, deep muscles

Extrinsic

muscles outside an organ

Intrinsic

muscles inside an organ

Structural Characteristics

number of tendons e.g. biceps, tripceps, shape e.g. trapezius, size e.g. longus

Action

movements (flexor, extensor, retractor) and occupations (e.g. risor (laughter))

Abdominal

abdomen

Ancon

elbow

Auricular

Ear

Brachial

arm

Capitis

head

Carpi

wrist

Cervicis

neck

Coccygeal

coccyx

Costal

rib

Cutaneous

skin

Femoris

thigh

Glossal

tongue

Hallux

great (big) toe

Ilium/Inguinal

groin