Muscle Structure and Function Chapter 8 Day 3

Review Questions : What chemical exposes the binding site for actin and myosin? Calcium What is the source of energy for a contraction? ATP What is the name of the step in which the actin filament is actively contracted? Powerstroke What 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 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 Fibers Slow-Twitch Muscle FibersFast-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 expressions o moving your neck o 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 minimi 14

Find the muscles on your body.