skeletal muscle system

skeletal muscle

striated, voluntary, multinucleated ex: biceps, triceps and quadriceps and attached to bones

cardiac muscle

involuntary, striated, one or two nuclei per cell. intercelated discs

smooth muscle

involuntary, found in hallow organs, non-striated, uninucliated. slow contractions that last longer. ex: digestive tract and arteries

origin of skeletal muscle

the fixed attachment point of the muscle (doesn't move during contraction)

insertion

the moveable attachment point of the muscle ( moves during contraction

movement

when a muscle contracts, the insertion moves toward the origin

Epimysium

outer connective tissue layer that surrounds the entire muscle

Perimysium

connective tussue that surrounds a bundle of muscle fibers called a fascicle

endomysium

connective tissue that surrounds invidual muscle fibers

muscle fiber (cell)

contains multiple nuclei and mitochondria

Myofibrils

rod-like structures inside muscle fibers that allow contraction

sarcolemma

the cell membrane of a muscle fiber

sarcoplasmic reticulum

stores calcium ions for contraction

T-tubules

channels that caryr electrical signals deep into the muscle

neuromuscular junction

Synapse between motor neuron and muscle fiber.

nerve signal arrives- a nerve impulse (action potential) reaches the axon terminal.

step 1

Acetylcholine (ACh) Release: The nerve releases ACh, a neurotransmitter, into the synaptic cleft.

step 2

ACh Binds to Receptors: ACh binds to receptors on the motor end plate (part of the sarcolemma).

step 3

Sodium (Na⁺) Channels Open: Sodium ions rush into the muscle cell, triggering depolarization.

step 4

Action Potential Propagation: The electrical signal spreads along the sarcolemma and into T-tubules.

step 5

Calcium Release: The sarcoplasmic reticulum releases calcium ions, initiating contraction.

step 6

sarcolemma membrance potential

The sarcolemma's membrane potential is controlled by ion movement across the cell membrane.

resting potential

The cell's stable, negative charge when inactive (~ -70mV

depolarization

Sodium (Na⁺) rushes into the cell, making the inside less negative.

repolarization

Potassium (K⁺) rushes out of the cell, returning the inside to its negative state.

hyperpolarization

the cell becomes too negative before stabilizing

restoration of resting potential

The sodium-potassium pump restores the original ion balance.

z-discs

boundary lines marking the ends of each sarcomere

a-band

the dark area where thick filaments(myosin) are present

i-band

the light area containing think filaments (actin)

H-zone

the middle of the sarcomere that only contains myosin when relaxed

m-line

the center of the sarcomere that holds thick filaments together

sliding filament mechanism

Calcium Release: Calcium binds to troponin, which moves tropomyosin, exposing actin's binding sites.

Cross-Bridge Formation: Myosin heads attach to the exposed actin sites.

Power Stroke: Myosin heads pull actin toward the M-line, shortening the sarcomere.

ATP Attachment: ATP binds to myosin heads, causing them to detach from actin.

Cycle Continues: This process repeats, shortening the muscle fiber and causing contraction.