Muscle Structure

and Function

Chapter 8Day 3

Review Questions:What chemical exposes the binding site for actin and myosin?

•CalciumWhat is the source of energy for a contraction?

•ATPWhat is the name of the step in which the actin filament is actively contracted?

•PowerstrokeWhat chemical must be present in order for the actin and myosin filaments to separate?

•ATP

Think it over

•The boat (myosin) does not move far in one cycle, a muscle contraction requires many cycles▫ If a muscle is contracted what happens if a new molecule of ATP is not available?▫ Muscle stays contracted – cramps!

•Why does rigor mortis occur? (Hint: What chemical is no longer available to the body?)▫ ATP is not available to control calcium release so contractions are continuous 6-8 hours after death. ▫ Body relaxes 16-24 hours as enzymes break down contractile structures.

Muscle Fiber Contraction Speed•Muscle fibers differ in:▫Contraction speed

Slow twitch Fast twitch

▫Production of ATP Oxidatively – presence of oxygen Glycolyitically – in absence of oxygen

•The speed of contraction and aerobic capacities of the fibers reflect the specialized functions of the muscle

Muscle FibersSlow-Twitch Muscle Fibers Fast-Twitch Muscle Fibers

• Nickname: red fibers• Contain red, oxygen-storing

pigment myoglobin▫ Well supplied with oxygen-

carrying blood• Contain a ton of mitochondria▫ Enables the aerobic cycle of

cellular respiration to occur• Fibers have a high respiratory

capacity▫ Generate ATP fast enough to deal

with the ATP breakdown• Can contract for a long period of

time without fatiguing • Found in muscles of the back

• Nickname: white fibers• Have few myoglobin▫ Poor blood supply

• Few mitochondria• Extensive sarcoplasmic reticulum,

store Calcium▫ ATPase (enzyme that

transports various ions) is faster

• Contract rapidly▫ Fatigue as lactic acid builds▫ ATP depletes quicker, causes

fatigue as well • Found in muscles of the hands,

feet, eyes

Uh oh, there’s a third fiber…•Fast-twitch fatigue-resistant

▫Nickname: intermediate fibers▫Have the fast-twitch speed like the white fibers▫Also have the substantial oxidative capacity of red

fibers

•Some muscles have only one fiber type or another, majority of muscles include a combination of fiber types

There are 4 basic functions of head and neck muscles:

o swallowing and chewing (mastication)o making facial expressionso moving your necko supporting your head

Head and Neck Muscles

Muscles of the Head and Neck

Posterior neck muscles

The muscles in the neck help to support the head. How much do you think an average adult head weighs?

(over 11 pounds)

Limb muscles

Muscles of the limb function in:•movement•grasping•balance

Color Key

•Purple: Muscles that move the arm•Orange: Muscles that move the

forearm•Brown: Muscles that move the

hand

Anterior superficial muscles of

the shoulder and arm

Posterior superficial muscles

of the arm Extensor digiti

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Find the muscles on your body.