Anatomy Muscle Physiology

Excitability

The ability of muscle tissue to respond to a stimulus.

Contractility

The ability of muscle tissue to shorten and generate force.

Extensibility

The ability of muscle tissue to be stretched or extended.

Elasticity

The ability of muscle tissue to return to its original length after being stretched.

Fascicles

Bundles of muscle fibers that make up skeletal muscle.

Perimysium

The connective tissue layer that surrounds each fascicle.

Epimysium

The connective tissue that encloses the entire muscle.

Endomysium

The connective tissue that surrounds individual muscle fibers within a fascicle.

Myofibrils

Structures within muscle fibers that contain functional units called sarcomeres.

Sarcoplasmic reticulum (SR)

A network of membranes that stores, releases, and retrieves calcium ions.

T-tubules

Inward extensions of the sarcolemma that carry action potentials into the muscle fiber.

Troponin

A protein complex on the actin filament that binds calcium ions and moves tropomyosin.

Tropomyosin

A protein that covers myosin-binding sites on actin, preventing contraction in a relaxed muscle.

A band

The dark band in a sarcomere representing the entire length of the myosin filament.

I band

The light band in a sarcomere representing the area where only actin filaments are present.

Z discs

The boundaries of the sarcomere where actin filaments are anchored.

M line

The center of the H band in a sarcomere where myosin filaments are anchored.

Skeletal Muscle Finer Contraction

Activation of motor neuron, signal transmitted to muscle at the neuromuscular junction (NMJ); Excitation of muscle fiber, Excitation-Contraction coupling, Contraction (sliding filament mechanism), Relaxation

Motor unit

A motor neuron and all the muscle fibers it innervates, responsible for muscle contraction.

Neuromuscular Junction(NMJ)

Connection between motor neuron and muscle fiber(“synapse”)

Acetylcholine (ACh)

A neurotransmitter released into the synaptic cleft that binds to receptors on muscle fibers.

Acetylcholinesterase

An enzyme that breaks down acetylcholine in the synaptic cleft, stopping the muscle contraction signal.

Muscle twitch

A single contraction and relaxation cycle of a muscle fiber in response to a single stimulus.

Overly contracted muscles

Generate less tension due to actin filaments overlapping, blocking cross-bridge formation.

Motor unit recruitment

Increasing muscle tension by activating more motor units.

Incomplete Tetanus

A state of sustained muscle contraction with partial relaxation between contractions (weightlifting)

Complete tetanus

A state of sustained muscle contraction with no relaxation between contractions. (carrying a piano across house)

Isometric contraction

Muscle tension increases without any change in muscle length.

Isotonic contraction

Muscle length changes while tension remains constant.

Load

Force exerted by the object on muscle

Tension

Force exerted by the muscle on object

Isotonic Concentric Contraction

Muscle shortens, tension remains constant (tension>load)

Isotonic Eccentric Contraction

Muscle lengthens while maintaining tension; movement down (tension<load)

Catabolism

Break down; energy releasing reactions

Anabolism

Synthesis; energy storing reactions

Cofactors

inorganic molecule needed for enzyme function (Fe+2-iron, Mg+2-Magnesium, Ca+2-Calcium)

Coenzymes

Organic factors derived from vitamins; niacin, riboflavin (NAD+, FAD)

Electron Transport Chain

NADH+H+ and FADH2 to make ATP; regenerate shuttles(NAD+ and FAD); NO O2=“traffic jam”=NO ATP

Oxygen in Cellular Respiration

FINAL electron acceptor in the Electron Transport Chain; combines with electrons and protons to form water making the continuous flow electrons and production of ATP

Aerobic Respiration Equation

C6 H12 O6 + 6O2 → 6CO2 + 6H2O + (32) ATP

Phosphagen System (immediate)

Borrows Phosphate from other molecules; buys time for other mechanisms to kick in (~5-8 secs of intense act.)

Glycolysis/Anaerobic Fermentation (short)

Glycogen in muscle/glucose in blood; 2 ATP per glucose (30-40 secs of intense act.) [not for too long cuz lactic acid=toxic]

Aerobic Respiration (long)

Glycogen from muscle; 32 ATP per glucose (glucose + fatty acids from blood)

Oxygen debt

The extra oxygen consumed after exercise to restore the body to its resting state.

Fatigue

The inability to maintain a desired or expected force or power output.

High intensity, short duration (fatigue factors)

^ K(Potassium) in ECF=muscle less excitable; accumulation of inorganic molecules like phosphates, lactic acid, depletion of ATP and creatine phosphate. (^ ADP + Pi → ^ADP=,CB cycling rate ^Pi=,Ca+2 from SR)

Lower intensity, long duration (fatigue factors)

decrease in glycogen/glucose, electrolytes, and CNS output to muscles; less electrolytes and dehydration means muscle cells less excitable

Slow-twitch fibers (Type I)

Fibers that use aerobic respiration; high fatigue resistance, rich in myoglobin(red)

Fast-twitch fibers (Type II)

Fibers that use glycolysis and phosphagen system; low fatigue resistance, less myoglobin(white/pale)