Muscles

proteins are organized into different stripes, includes cardiac and skeletal muscle cell

same proteins as striated muscles but they aren’t organized in striped groups

can contract without signal from nerve, multibranched cell, uninucleated, myogenic, myogenic

generate their own action potential to contract

Cardiac muscles don’t need intervention from nervous system to contract, but the rate of contraction can be influenced by nerve cells from the parasympathetic or sympathetic nervous system

needs signal from nerve to contract, multinucleated, controlled by somatic nerve system

includes vessels, lungs and gut

uninucleated, controlled by autonomic nerve system

net-like structure that sits under the cell membrane draped over the myofibril, filled with fluid rich in calcium (causes contraction/relaxation)

Muscle → fiber bundles → muscle cell/fiber → myofibril

contain a specific arrangement of 2 types of protein myofilaments (Actin filaments & Myosin filaments)

thick filaments with heads containing two different types of binding sites: actin binding sites and ATP binding sites, motor protien

are attached to the m-line and go towards the z-disk

thin filaments that have troponin or tropomyosin molecules blocking their binding sites

are attached to the z-disk and go towards the m-line

area within a sarcomere where all myocin filaments are contained, contains the m-line and the area where actin and myocin filaments overlap

ONLY contains actin filaments, extends beyond the length of a single sarcomere

area from z-disk to z-disk

similar to A band but there is only myocin filaments (NO actin), is contained within 1 sarcomere, contains m-line

Interaction of actin and myosin filaments causes sarcomere width to shorten during contraction

actin filaments

A band

in rigor: myosin headgroup is attached to the actin filament and there is no ATP bound to the myosin headgroup

bond between myocin headgroups and actin filaments

ATP binds to myocin headgroup causing it to release from the actin filament breaking the crossbridge and the state of rigor

ATP is hydrolyzed breaking it down to ADP and a phosphate creating some energy that allows the next step to occur

myocin headgroup swings backwards towards the z-disk going from a 45 to 90 degree angle causing the myocin headgroup to bind to the actin filament, ADP and phospate are still bound

powerstroke: phosphate is released and myocin headgroup pulls back towards the m-line (center of sarcomere) pull the actin filament with it, shortening the sarcomere

ADP is released from the myocin headgroup putting the muscle back into a state of rigor

ATP

Ca 2+ (calcium)

when calcium is present it binds to tropon/tropomyosin causing a conformational shift in those molecules that exposes the binding sites on the actin allowing myosin headgroup to bind

represents the strength of contraction

ATP

calcium and ATP

is removed

ATP is added and calcium is absent

electric signal coming down the somatic motor fiber results in the release of a neurotransmitter called Acetylcholine

action signal gets down to the end of the presynaptic terminal of the motorneuron and opens the voltage gated calcium channels depositing calcium outside of the muscle cell

Calcium rushes inside the cell binding to the vesicles and causing the vesicles to bind to the membrane releasing the Acetylcholine that moves across the extracellular space via diffusion

it binds to receptor ion channel proteins causing it to open and ions to be able to move in and out of the muscle cell causing an action potential causing calcium to be released allowing contraction to occur

cell membrane of a muscle cell

1. Action potential is generated at the neuromuscular junction

2. Action potential is propagated along sarcolemma and into T‐tubules

3. Dihydropyrine (DHPR) and ryanodine receptors (RyR) are activated

4. Ca 2+ released from Sarcoplasmic Reticulum into sarcoplasm

plugs and unplugs the RyR calcium channel protien

diffusion

in the membrane of the sarcoplasmic reticulum

in the sarcolemma, specifically in the t-tubules

use ATP to put calcium back into the sarcoplasmic reticulum

function and type

tonic and twitch

more rare, Slow and sustained contractions stimulated by graded potentials, typically found in postural muscles

stimulated by an action potential, 3 different types

slow oxidative (SO), Fast oxidative glycolytic (FOG), and Fast glycolytic (FG)

**be sure to memorize table