Muscles and muscle tissues

Skeletal muscle…

Voluntary, striated, multinucleated

Cardiac muscle…

Involuntary, striated, intercalated discs

Smooth muscle…

Involuntary, non-striated

Excitability…

Ability to receive and respond to stimuli

Contractility…

Ability to shorten forcibly

Extensibility…

Ability to stretch

Elasticity…

Ability to recoil to resting length

Epimysium…

Surrounds entire muscle

Perimysium…

Surrounds fascicles

Endomysium…

Surrounds individual muscle fibers

Fascicle…

Bundle of muscle fibers

Sarcolemma…

Muscle fiber membrane

Sarcoplasm…

Muscle cell cytoplasm

Myofibrils…

Rod-like structures containing sarcomeres

Sarcomere…

Contractile unit between Z discs

Z disc…

Anchors actin filaments

A band…

Dark band, overlapping actin + myosin

I band…

Light band, thin filaments only

H zone…

Thick filaments only

M line…

Middle of sarcomere; holds thick filaments

Titin…

Elastic protein that stabilizes and recoils sarcomeres

Actin (thin filaments)…

Contains myosin binding sites

Myosin (thick filaments)…

Has heads that form cross-bridges

Tropomyosin…

Blocks binding sites on actin at rest

Troponin…

Binds calcium to move tropomyosin

Cross-bridge formation…

Myosin heads bind actin

Power stroke…

Myosin pulls actin toward M line

ATP role in contraction…

Detaches myosin head from actin

Filaments during contraction…

Slide, but do NOT shorten

Acetylcholine (ACh)…

Neurotransmitter released at NMJ

Motor neuron…

Nerve cell controlling muscle fiber

Motor unit…

Motor neuron + all muscle fibers it innervates

Acetylcholinesterase (AChE)…

Breaks down ACh in synapse

Synaptic cleft…

Space between neuron and muscle fiber

T-tubules…

Carry action potential into muscle fiber

Sarcoplasmic reticulum…

Stores calcium for contraction

Calcium’s role…

Binds troponin, exposing actin binding sites

Action potential triggers…

Opening of Ca²⁺ channels in SR

Relaxation occurs when…

Calcium pumped back into SR

Creatine phosphate system…

First, fastest ATP source

Anaerobic glycolysis…

Produces ATP without oxygen; forms lactic acid

Aerobic respiration…

Most efficient ATP producer; occurs in mitochondria

Muscle fatigue…

Caused by ionic imbalances and ATP challenges

Myoglobin…

Oxygen-binding pigment in muscle

Isotonic contraction…

Muscle changes length (movement)

Isometric contraction…

Tension increases, length stays same

Twitch…

Single, brief contraction

Tetanus (fused)…

Sustained maximal contraction

Muscle tone…

Constant, slight contraction for posture

All-or-none principle…

Muscle fiber contracts fully or not at all

Rigor mortis…

Stiffening after death due to lack of ATP

Recruitment…

Increasing number of motor units activated

Synaptic vesicles…

Store ACh in axon terminal

Threshold stimulus…

Minimum stimulus needed to generate AP