Skeletal muscle phys

4 characteristics of muscle

excitable

contractile

extensible

elastic

excitable in muscles means

able to respond to stimuli

Contractile in muscles means

able to shorten and thicken

extensible in muscles means

stretches when pulled

Elastic in muscles means

returns into original shape

what are the functions of skeletal muscles

movement

heat production

posture and facial expression

visceral (abdominal)protection

how do skeletal muscles produce heat

metabolism in muscles produce heat as waste

a single muscle is innervated by ____ neuron(s)

one

1 motor neuron can innervate ____ muscles

multiple

motor unit

one motor neuron and all the fibers it innervates

what does motor unit allow for

contract together

distribute through large muscle

at a neuromuscular junction pre-synaptic neuron is

has vessicles filled with ACh

at a neuromuscular junction post-synaptic cell is

muscle fibre that contains ACh receptors in sarcolemma

motor end plate

region of receptors on post synaptic at neuromuscular junction

synaptic cleft

seperates pre synaptic LMN and post synaptic muscle fibre

explain synaptic transmision at neuromuscluar

AP reaches axon terminal and end bulb

causes Ca2+ to enter through voltage gates

causes exocytosis of ACh

ACh binds to receptors on post synaptic sarcolemma

chem gated Na+ channels open

causes EPP

what does EPP cause in muscle fiber

opening of voltage gated Na+ channel on adjacent sarcolemma

causes AP on muscle fiber

are AP in muscle the same as AP in neuron

yes

does AP always happen at neuromuscler junction , WHY?

yes

lots of ACh and lots of receptors

what is needed to inhibit contraction of skeletal muscle

inhibition of LMN

what happens when muscle is relaxed

tropomyosin covers myosin binding sites on thin filaments (actin)

Myosin head is activated

what does it mean when myosin head is activated

myosin head is ready to bind to myosin bind sites as soon as stimulus arrives

what energy does myosin head store to use in contraction

energy released when ATP→ADP

3 steps of skeletal muscle contraction

excitation of muscle fiber

excitation-contraction coupling

Contraction

what happens during excitation of muscle fiber

sarcolemma is depolarized by influx of Na+ (causes AP)

AP spreads down T-tubles and penetrate deep into muscle fiber

Excitation-contracting coupling

couples the electrical event of AP to contractile event

what happens during Excitation-contraction coupling

AP in T-tubles cause release of Ca from terminal cisternae via mech gated Ca+ channels

Ca+ binds to troponin

Troponin-tropomyosin complex moves away and exposes myosin binding site

contraction is a ______ event

mechanical

what model is used for contraction

sliding filament mech

what happens during contraction

Active myosin head attach to mysoin binding site

energy stored in myosin head released as myosin head pivots

power stroke causes actin to slide over myosin

ATP binds and causes detach from myosin binding site

recovery stroke

Myosin head reactivates by converting ATP to ADP and storing energy

powerstroke

myosin head pivots and causes actin to slide over myosin

what is released from myosin during powerstroke

ADP and Pi

which way does actin move in powerstroke

towards middle

what happens if Ca+ remains high in sarcoplasm

continues to bind to troponin so the cycle repeats to shorten the muscle

if Ca+ is low in sarcoplasm what happens

myosin head releases from binding sites

tropomyosin blocks again and contraction stops

what happens in sliding filament mechanism

sarcomeres shorten

H Zone and I band become shorter

A band doesn’t change

during sliding filament mechanism myofibrils _______

shorten (whole fiber shortens)

do the thin and thick filaments change length during contraction

no, just overlap

what are the steps of relaxation

ACh broken down

sarcoplasmic reticulum takes up calcium

ATP binds to myosin head

Tropomyosin returns

ACh broken down into

acetic acid + choline

what happens to acetic acid once ACh broken down

used in krebs cycle to release energy

what happens to choline after ACh broken down

choline recycled to build other molecules

how does sarcoplasmic reticulum activly take up calcium

Ca2+ ATPase pupms Ca2+ from sarcoplasm to sarcoplasmic reticulum (lowers [Ca+])

cross bridges

active myosin head attached to myosin binding site

what is ATP needed for

activation of myosin and powerstroke

release of cross bridge

Activity of Ca2+ ATPase

maintains Na+/K+ ATPase / gradients

Rigor mortis

ATP production stops so corss bridge cannot detach

what leads to rigor mortis

leaky membranes leak Ca+ into sarcoplasm

causes Ca+ binding to troponin exposing myosin binding site

when does rigor mortis set in

3 hours after

peak at 12 hours

when does rigor mortis suside

gradually as cells breakdown

Myasthenia gravis

autoimmune disease that is caused by decrease number of ACh receptors

what can happen with Myasthenia gravis

EPP may not lead to AP everytime

how is Myasthenia gravis treated

Acetylcholinesterase inhibitors which increases binding of ACh to limited receptors

(stops ACh breakdown)

botulism

botox prevents exocytosis of ACh which causes flaccid paralysis

what causes botox

improper cannin

Clostridium botulinum produces ‘botox’

when is botox used

cosmetically

control crossed eyes and uncontrollable blinking

what do cramps come from

low extracellular Ca+ which leads to decreased stabilization of Na+ gated channels which causes muscle depolarization

Nicotine

causes muscle spasms

where does nicotine bind

ACh receptors by mimicking ACh

Black widow spider venom

causes massive release of ACh which causes muscle contraction and breathing to stop

Curare poisoning

prevents ACh from binding which causes flaccid paralysis

when is curare poisoning be used clinicaly

surgeries

tension

amount of force exerted by a muscle

what determines tension

total amount of cross bridges attached

4 factors that effect tension

frequency of stimulation

Fiber length

Size of muscle fiber

Fatigue

what does single stimulus produce

twitch

twitch

weak contraction followed by relexaion

is single stimulus normally in skeletal muscle

no

4 stages of single stimulus in muscle fiber and time of each

stimulus (1-2ms)

Latent / lag period (2ms)

Contraction period (10-100ms)

relaxation period (10-100ms)

explain single stimulus stage in muslce fiber

stimulus followed by action potential

what is latent or lag period

period between stimulus and contraction

what causes latent / lag period

excitation-contraction coupling

contraction period

increased tension, cross bridge attachement and sliding filaments

is max tension reached during single stimulus contraction period

no, not all myosin heads attached

what happens during relaxation period of single stimulus

Ca+ pumped back to sarcoplasmic reticulum

ATP attaches to myosin head (releasebindign site)

tropomysoi covers

tension decreases

what happens if second stimulus arrives before muscle completely relaxed

produces 2nd contraction with increased tension

why does second stimulus produce contraction with more tension

uptake of Ca+ by sarcoplasmic reticulum is not complete so more Ca+ added to whats already present so more myosin heads can attach

wave summation

stimuli at different times cause larger contractions

what does rapid sequence of stimuli result in on muscle

tension increases due to summation and increased Ca+ availibilty

is there relaxation in rapid sequence of stimuli

Incomplete tentanus

incomplete tetanus

partial relaxation between contractions

what happens with high frequency stimulation

highest tension, all troponin saturated with Ca+

is there relaxtion in high frequency of stmulation

complete tetanus

complete tetanus

no relation between contractions

what temp is the muscle with high frequency of stimulation

warm

fast fibers are what colour, why

white

very little myoglobin and few capillaries

slow fibers are what colour, why

red

more myoglobin and many capillaries

how do fast fibers produce energy

glycolysis and fermentation ( few mitochindria)

what are fast fibers used for

intesne short activity (throwing)

fast fibers

contract and relax rapidly

slow fibers

contract and relax slowly

how do slow fibers produce energy

aerobic respiration (many mitochondria)

what are slow fibers used for

sustained contraction (slow fatigue)

what fiber length has the most tension

resting fiber length (most cross bridges attached)

how does tension change when fiber length is shorter then resting

thin filaments overlap and interfere with cross bridges (fewer cross bridge = lower tension)

how does tension change when fiber length is longer then resting

not all myosin heads near binding sites (fewer cross bridge = lower tension)

what is the max and min length of muscle fibers

70% of optimal

130% of optimal

how does the size of muscle fiber affect tension

thicker means more myofibrils per fiber and more tension

fatigue

tension reduced because cannot contract as well

what factors affect tension in whole muscles

number of fibers contracting

number of fibers per motor unit

fatigue

how does the number of fibers contracting affect tension in whole muscle

more motor units = more tension in muscle