Chapter 10: The Muscular System

Muscle

- Greek for "Little mouse"

- because you can see muscles moving like mice underneath skin

How many human skeletal muscles?

- about 600

- constitute about 1/2 the body weight

Three Types of Muscle

skeletal, cardiac, smooth

"Muscular System"

Refers to the skeletal system

The muscular system is specialized for one purpose which is?

converting chemical energy (ATP) into mechanical energy (motion)

Myology

study of the muscular system

Skeletal Muscle Functions

- movement

- stability

- control opening and passageways

- heat production

- glycemic control

Skeletal Muscle Function: Movement

- locomotion: move body parts and move body contents (breathing, circulation, digestion, urination, childbirth)

- communication: speech, writing, facial expressions

Skeletal Muscle Function: Stability

- maintain posture by preventing unwanted movements

- antigravity muscles: prevent us from falling over

- stabilize joints by maintaining tension

Skeletal Muscle Function: Control Openings and Passageways

- ex: sphincters: internal muscular rings that control the movement of food, blood, and other materials within the body.

Skeletal Muscle Function: Heat Production

- thermogenesis

- skeletal muscles produce about 20-30% of body heat at rest (85% when moving)

Skeletal Muscle Function: Glycemic Control

- skeletal muscles absorb, store, and use glucose which helps regulate blood sugar levels

- reduced muscle mass due to old age, obesity, or disuse associated with type 2 diabetes

Muscle Organ Arrangement

- muscles are basically cells (fibers) within a complex of connective tissue

- muscle fiber = muscle cell

The connective tissue is arranged to do what?

- provide structure

- act as passageways for vessels and nerves

- transfer the tension generated by muscle

Connective tissue components from deep to superficial (everything is connected)

- endomysium

- perimysium

- epimysium

- fascia

Endomysium

- thin sleeve of loose connective tissue around each fiber (muscle cell)

- allows room for capillaries (small blood vessels) and nerve fibers

- provides chemical environment for fiber and nerve

Perimysium

- thicker layer of connective tissue around bundles of fibers (i.e. fascicles)

- carries nerves, blood vessels, and stretch receptors

- visible to the naked eye ("grain" of meat)

Epimysium

- fibrous sheath surrounding entire fiber

- outer surface integrates with fascia; inner surface creates projections that form perimysium

Fascia (fasciae)

- sheet of connective tissue surrounding entire muscle

- separates neighboring muscle or muscle groups from each other and from the subcutaneous tissue

Fusiform

- thick in middle; tapered towards ends

- ex: biceps brachii

Parallel

- fascicles run parallel to each other

- ex: rectus abdominis

Triangular

- wide; shaped like triangle

- ex: pectoralis major

Unipennate

- half a feather; connect on one side

- ex: palmar interosseous

Bipennate

- feather; connect to 2 sides of tendon

- ex: rectus femoris

Multipennate

- connect to multiple sides of tendon

- ex: deltoid

Circular

- muscle fibers wrap around and connect to tendon

- ex: orbicularis oculi

The orientation of the fascicles affect what?

- the strength of the muscle

- direction of the pull

Muscle Attachment

- not all skeletal muscles attach to bone; may attach to other muscles, lips, skin, eyelids, etc.

- two types of attachment to bone

Two types of attachment to bone

- indirect attachment to bone

- direct (fleshy) attachment to bone

Indirect attachment to bone

- tendons connect muscle to bone

- collagen fibers of the endo, peri, and epimysium continue into the tendon and from there into the periosteum

Direct (fleshy) attachment to bone

- little separation between muscle and bone (appear connected; ex: brachialis)

- muscle and bone connected by collagen fibers

Origin

- area muscle connects

- bony attachment at stationary end of muscle

- whatever muscle is pulling against

Belly

- where all muscle fibers are

- thicker, middle region of muscle between origin and insertion

- site of contraction (part of muscle that gets shorter)

Insertion

- opposite end of origin

- bony attachment to mobile end of muscle (ex: bones being moved by muscle)

Extrinsic Muscle

- muscles isolated from region on which they act

- fingers: entrinsic muscles in the forearm

Intrinsic Muscle

- entirely contained within the region on which they act

- both origin and insertion there

Functional Muscle Groups

- muscles produce their effect (their action) either by causing or preventing movement

- four categories of muscle action

4 Categories of Muscle Action

- prime mover (agonist)

- synergist

- antagonist

- fixator

Prime Mover (Agonist)

muscle that produces most of the force during a movement

Synergist

- muscle that aids the prime mover

- may contribute additional force, modify the direction of movement, or stabilize the joint

Antagonist

- opposes the prime mover

- prevents excessive movement

- sometimes relaxes to give prime mover control over movement

- antagonistic pairs: muscles that act on opposite sides of a joint (ex: tricep and bicep)

Fixator

- muscle that prevents movement of bone

- gives prime mover something to pull against

Look at last slide

example for elbow flexion