BIO 116 EXAM #3 - PART 4

chapter 13 muscular system

functions of muscular system

• tone and posture support

• movement including breathing

• maintains body temperature

• movement of bodily fluids

• protection of organs and joints

fascicle

bundle of skeletal muscle fibers, found inside muscle

tendon

fibrous connective tissue that connects skeletal muscle to bone

motor unit

combination of motor neurons and the muscle cell it innervates

three types of muscle

• skeletal → voluntary movement of the body, straited

• smooth → involuntary movement of substances in organs, not straited, single nucleus

• cardiac → involuntary movement pumping blood, striated, single nucleus

structure of skeletal muscle

• origin → attachment to bone, stationary

• insertion → attachment to bone that moves when muscle contracts

• body → main part of the muscle

how do muscles generate movement?

convert chemical energy (ATP) into mechanical energy

agnostic muscle pairs

one muscle contracts, the other muscle relaxes

• biceps and triceps

• quadriceps and hamstrings

t-tubules

inward extension of sarcolemma that transmits impulses

what is stored in the sarcoplasmic reticulum and why is it important?

has calcium ions important for contraction proteins to interact with T-tubules

myosin

thick filaments in myofibrils, has myosin heads

actin

thin filaments in myofibrils

myofibril

bundle of myofilaments (protein filaments)

A band

contains actin and myosin filaments

H band

contains myosin filaments only (when not contracted)

I band

contains actin filaments only

Z-lines

dark bands that separate sarcomeres

muscle contraction steps

1. nerve impulse stimulates the release of calcium

2. calcium binds to troponin and exposes myosin attachment sites

3. ADP + P allows myosin to bind to actin

4. myosin pulls actin towards the center of the sarcomere, shortening the muscle fiber

5. ATP releases myosin, prepares it for next contraction

what is the role of acetylcholine in muscle contraction?

a neurotransmitter that stimulates muscle contraction

what is the role of calcium in muscle contraction?

exposes the binding sites on actin, permission signal for contraction

what is the role of ATP in muscle contraction?

powers myosin head cycle

rigor mortis

happens when there is no more ATP available to release actin filaments, causing muscles to become stiff usually after death

“all-or-none” response for muscle fibers

a muscle will contract only if threshold stimulus is reached

twitch contractions

• quick, jerky responses to stimulus

• too weak to be useful

tetanic

• sustained, steady muscular contractions

• caused by a series of stimuli bombarding a muscle in rapid succession

• motor units cannot relax between stimuli

tetanus

• maximum sustained contraction

how do your muscles make ATP for short, intense bursts of exercise?

• creatine phosphate → creatine + ATP

• glycogen → lactate + ATP (fermentation)

how do your muscles make ATP for long, lower intensity exercise?

glycogen or fatty acids → CO₂ + H₂O + ATP (cellular respiration)

strain

injury from overextension or trauma, stretching/tearing of muscle fibers

sprain

injury near a joint, ligament damage

cramps

painful muscle spasms, involuntary twitches

muscular dystrophy

group of genetic disorders characterized by muscle atrophy