Muscles

striated muscle type

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

smooth muscle type

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

cardiac muscle

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

myogenic

generate their own action potential to contract

how can the nerve system interact with cardiac muscles?

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

skeletal muscle

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

smooth muscle

includes vessels, lungs and gut

uninucleated, controlled by autonomic nerve system

sacroplasmic reticulum

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

Nesting doll muscles

Muscle → fiber bundles → muscle cell/fiber → myofibril

Sarcomere

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

Myosin filaments

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

myosin filament orientation

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

Actin filaments

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

actin filaments orientation

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

A band

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

I-band

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

sarcomere

area from z-disk to z-disk

H-zone

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

Sliding filament theory of muscle contraction

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

Myosin filaments pull _______ towards the center of the sarcomere

actin filaments

which part of the sarcomere is the only one that doesn’t shorten during contraction?

A band

Interaction of myofilaments: step 1 (starting with myosin bound to actin)

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

Crossbridge

bond between myocin headgroups and actin filaments

Interaction of myofilaments: step 2

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

Interaction of myofilaments: step 3

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

Interaction of myofilaments: step 4

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

Interaction of myofilaments: step 5

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

Interaction of myofilaments: step 6

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

______ provides the fuel to power the movement of myofilaments

ATP

_______ regulates crossbridge formation \n between myofilaments

Ca 2+ (calcium)

How does calcium moderate myosin-actin interaction?

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

tension

represents the strength of contraction

when ____ is removed tension stops increasing but remains constant

ATP

tension increases when what 2 things are present?

calcium and ATP

tension increases until ATP _______, then it waits to start decreasing until what 2 things occur?

is removed

ATP is added and calcium is absent

how do neuromuscular junctions function?

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

sarcolemma

cell membrane of a muscle cell

Excitation‐contraction coupling steps

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

calcium voltage gated protien (DHPR)

plugs and unplugs the RyR calcium channel protien

calcium is released out the RyR via ______

diffusion

RyR location

in the membrane of the sarcoplasmic reticulum

DHPR location

in the sarcolemma, specifically in the t-tubules

SERCA pumps

use ATP to put calcium back into the sarcoplasmic reticulum

changing the protien composition in muscle cells changes the ___ and ___ of the muscle cell

function and type

two types of mucle fibers

tonic and twitch

tonic fiber

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

twitch fiber

stimulated by an action potential, 3 different types

3 different types of twitch fibers

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

**be sure to memorize table