phys chapter 12

skeletal muscle

voluntary, striated

cardiac muscle

involuntary, striated

smooth muscle

involuntary, unstriated

functions of skeletal muscle

movement of body, posture, generation of body heat, movement of substances(ie.urinary tract), nutrient reserves, support soft tissues and organs

what is skeletal muscle linked to bones by

tendons

muscle cell is also called a

muscle fiber

components of muscle fiber

sarcoplasm, sarcolemma, and myofibril

what are myofibrils

contractile elements of the muscle fiber that are composed of myofilaments

thick filaments are composed of

myosin

thin filaments are composed of

actin

motor unit

single motor neuron and all the muscle fibers it innervates

motor end plate

area of sarcolemma where the motor neuron stimulates skeletal muscle

sarcomere

functional unit of contraction

what do myosin heads do

form cross bridges between thick and thin filaments

what is on myosin heads

actin binding sites, ATP binding site, ATPase

thin filaments regulatory proteins

troponin and tropomyosin

tropomyosin

resting, covers myosin binding sites blocking interaction

troponin

bind to tropomyosin, bind to actin, and bind to calcium

what do each actin have

special binding site for attachment with myosin cross bridges—> binding results in contraction of muscle fiber

Sliding FIlament Mechanism

contraction is accomplished by thin filaments from opposite sides of each sarcomere sliding closer together between thick filaments

Power Stroke

swiveling of myosin heads

sliding filament mechanism steps

1. attachment of myosin cross bridge to a thin filament

2. swiveling of myosin heads - power stroke

3. detach of the cross bridge from thin filament

4. reattach to a new actin binding site

5. repeat cycle

Cross Bridge cycle steps

1. resting fiber; CB is not attached to actin

2. CB bind to actin

3. P is released causing conformational change in myosin

4. Power stroke causes filaments to slide; ADP is released

5. a new ATP binds to myosin head allowing it to be released from actin

6. ATP is hydrolyzed causing CB to return to normal orientation

Functions of ATP in contraction

1. energizes CB providing energy for powerstroke

2. binding of ATP disassociates CB from actin

do myosin and actin interact at rest

no

how does muscle excitation switch on CB cycling

Calcium

calcium is ___ at rest and is stored in the ____

low, sarcoplasmic reticulum

what happens to calcium for a contraction to happen

it is released from SR —→ increase in calcium —→ contraction

how is calcium released from the SR

AP propagated into interior by transverse tubules—> Ca2+ goes through voltage-gated channels in SR-—> release of calcium

tension

force exerted on an object by contracting muscle

load

force exerted on muscle by weight of an object

twitch

response of a single muscle fiber to a single AP

Muscle contraction phases

latent period, contraction time, relaxation time

force velocity curve

for muscle to contract they must generate force that is greater than opposing forces

the greater the force the slower the contraction

two types of muscle contraction

isotonic and isometric

isotonic

change in muscle length

two types of isotonic contractions

concentric and eccentric contractions

concentric contractions

muscle shortens

eccentric contractions

muscle lengthens

isometric contractions

muscles cant shorten because load is too great, can be voluntary

nervous system in muscle tension

frequency of stimulation and motor unit recruitment

frequency of stimulation

because muscle twitch is fairly slow compared to AP many AP arrive before twitch occurs, generation of force is greater than a single twitch , summation

muscle summation

muscle stimulated again before relaxation leads to summation

tetanus

contraction is usually 3-4 greater than a single twitch

motor unit recruitment

increasing the number of active motor units, increase tension and velocity

formation of ATP by muscle

phosphoralation of ADP by creatine phosphate

oxidative phosphoralation

glycolysis

creatine phosphate