PT 505 Muscle Contraction

Excitation, Excitation-Contraction Coupling, Contraction, Relaxation

What are the four phases of muscle contraction and relaxation?

neuron

Muscle excitation begins with ________ AP transitioning to a muscle AP

VGCC

First step of muscle excitation involves a neuron AP opening what kind of channels?

vesicle

Influx of calcium into the axon terminal causes _____________ fusion to release neurotransmitters

ACh, AChRs

Third step of muscle excitation involves this specific neurotransmitter. What does this neurotransmitter bind to?

depolarization

What happens when ACh is bound to muscle after being released from the axon terminal in the NMJ?

end-plate potentials

the depolarizations of skeletal muscle fibers caused by a neurotransmitter (ACh) binding to the sarcolemma of the NMJ

passively

EPPs are local potentials, which are spread passively or actively?

EPPs

What brings the skeletal muscle to its AP threshold?

sodium

Once skeletal muscle is brought to threshold, voltage gated ______________ channels depolarize it

potassium

Once skeletal muscle is brought to threshold and depolarizes voltage gated ______________ channels repolarize it

excitation-contraction coupling

events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract

myosin

Muscle action potentials ultimately expose _________ binding sites

T-tubules

Muscle action potentials are propagated here

Calcium released from terminal cisterns

As the AP travels down the T-tubules, what processed occurs?

troponin

Calcium entering the muscle binds to this structure in order to change shape

tropomyosin

Once Ca2+ is bound to troponin, it pulls on this structure

tropomyosin

Myosin binding sites are normally covered by ___________________

decrease

During skeletal muscle contraction, increase in tension corresponds to a(n) ______________ in length

Sliding filament theory

theory that actin filaments slide toward each other during muscle contraction, while the myosin filaments are still

one

How many things can myosin hold on to at one time?

ATP actin ADP

Myosin binding preference in order

cross-bridge

Myosin-ADP binding to actin forms:

ADP

Once the cross bridge is formed, myosin releases:

power stroke

Myosin's release of ADP results in the:

ATP

Myosin binds to ________ to break the crossbridge

recovery stroke

Return of the myosin head to its original position after cross-bridge release

hydrolyzing ATP

Myosin performs the recovery stroke by doing what?

True

Different myosin heads are at different parts of the contraction cycle. (Asynchronous and jerky strokes). True or False

50

At any time, ____% of myosin heads bind to actin to prevent slippage

40

Fibers shorten by up to _____% during contraction

antagonist, gravity

Return to resting tension and length is assisted by what two things?

ACh

Once a motor neuron rests, what is no longer released, leading to relaxation?

AChE

In order to activate relaxation, the remaining ACh in the synaptic cleft is broken down by:

Reabsorbed by sarcoplasmic reticulum

For relaxation to occur, what happens to the calcium ions in the muscle?

False

ACh degradation and Ca2+ absorption only occur during relaxation. True or False?

troponin

In order to relax the muscle, calcium unbinds from ___________

tropomyosin

Last stage of skeletal muscle relaxation involves _____________ covering myosin binding side on actin, returning the muscle to its original length

length

Tension generated by a muscle depends on:

length tension relationship

The resting length of a muscle and the tension the muscle can produce at this resting length.

minimal additional contraction

Overly contracted muscle leads to:

minimal actin myosin contacts

Overly stretched muscle leads to:

resting

Muscles are usually near optimum ___________ length

anatomical limitations, muscle tone

Two things which influence optimal resting length of muscle

tonic muscle contractions, tonic motor neuron input

Factors increasing muscle tone

maintain resting potential, clean up Ca2+, cross bridge cycle

3 roles of ATP in skeletal muscle contraction-relaxation cycle

Sodium Potassium pump (3 Na out, 2 K in)

ATP maintains resting membrane potential by supplying the:

1

How many ATP are required to supply the calcium pumps and the sodium-potassium pumps

Calsequestrin

calcium-binding protein within the sarcoplasmic reticulum which aids in storage and clean up of intracellular Ca2+

1-2

How many Calcium ions can one 1 ATP molecule clean up?

breaking cross bridge, fueling recovery stroke

ATP's 2 roles with the cross bridge:

Rigor Mortis

stiffness of the body that sets in several hours after death

we stop "paying the bill"

Why does Rigor Mortis occur?

ATP

Once we dies, we first deplete our _______ stores

Vm maintenance, Ca2+ clearance, cross bridge breakage

Depletion of ATP stores prevents what 3 things?

SR release of calcium

Deterioration/Degradation contributes to what early process?

myofibril relaxation

Deterioration/Degradation contributes to what late process?

tension

Whole muscle contraction generates _____________

shortens

If tension exceeds load, then muscle _____________

lengthens

If load exceeds tension, then muscle _____________

latent period, contraction, relaxation

twitch phases

internal tension

What builds up in the latent period?

excitation, excitation-contraction coupling, elastic tensing

What 3 processes occur in the latent period

external tension

What is created in the contraction phase of twitch

continuous calcium release

What process occurs during the contraction phase

relaxation phase

Phase slower than contraction, which involves calcium sequestration

increases

Fiber strength __________ with temperature and stimulus frequency

fatigue

Fiber strength decreases with:

fiber

Muscle strength depends on ____________ strength

little

Small motor units would lead to _________ strength

more

Large motor units would lead to _________ strength

temporal summation

Summation by a postsynaptic cell of input from a single source over time.

asynchronous

______________ motor unit activity leads to smooth muscle contractions

tetanus

a sustained muscular contraction resulting from a rapid series of nerve impulses

size principle

motor units are recruited from smallest to largest

neuron

Motor unit size is based on the _________ size

isometric phase

muscle tension rises but muscle does not shorten

isotonic phase

muscle begins to shorten and move the load

isometric

What contraction phase is motor unit recruitment?

isotonic

What contraction phase is motor unit maintenance?

concentric, eccentric

Two types of isotonic contractions