Skeletal muscle

Skeletal muscle

Voluntary, striated muscle that moves bones, works in pairs or more and is attached to bones by tendons

Cardiac muscle

Striated muscle fibers (cells) that form the wall of the heart; uni- or binucleated; involuntary muscle tissue found only in the heart.

Smooth muscle

under involuntary control, moves internal organs, cells contain a single nucleus, are spindle-shaped, and do not appear striated; each cell is a fiber; found inside many internal organs of the body

Muscle fibres

The long cylindrical multinucleated cells that make up skeletal muscles

Striated

muscle tissue in which the contractile fibrils in the cells are aligned in parallel bundles, so that their different regions form stripes visible with a microscope.

Voluntary

A muscle that is under conscious control

Involuntary

A muscle that is not under conscious control.

Excitability

muscles receive and respond to stimulation

Contractility

ability to shorten forcibly when stimulated

Extensibility

ability to be stretched

Elasticity

The ability of a material to bounce back after being disturbed

Epimysium

a sheath of fibrous elastic tissue surrounding the entire muscle.

Perimysium

Connective tissue surrounding a fascicle

Endomysium

Connective tissue surrounding a muscle fiber

Insertion

The attachment of a muscle tendon to a moveable bone or the end opposite the origin

Origin

attachment of a muscle that remains relatively fixed during muscular contraction

Aponeurosis

strong sheet of tissue that acts as a tendon to attach muscles to bone

Sarcolemma

plasma membrane of a muscle fiber

Sarcoplasm

cytoplasm of a muscle fiber

Sarcoplasmic Reticulum

Organelle of the muscle fiber that stores calcium.

glycosomes

granules of stored glycogen that provide glucose during periods of muscle cell activity

Myofibrils

Microscopic protein filaments that make up muscle cells.

Sarcomere

the structural, contractile unit of a myofibril in striated muscle, consisting of a dark band and the nearer half of each adjacent pale band.

A band

dark area; extends length of the thick filaments

I band

light band; thin filaments only

H zone

The region at the center of an A band of a sarcomere that is made up of myosin only. The H zone gets shorter (and may disappear) during muscle contraction.

M line

middle of the sarcomere; supporting proteins that hold the thick filaments together in the H zone

Z disc

at the center of the light band; provides anchorage for thin filaments and elastic filaments

Myosin

The contractile protein that makes up the thick filaments of muscle fibers

Actin

A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.

Tropomyosin

A protein of muscle that forms a complex with troponin regulating the interaction of actin and myosin in muscular contraction

Troponin

A globular protein of muscle that together with tropomyosin forms a regulatory protein complex controlling the interaction of actin and myosin and that when combined with calcium ions permits muscular contraction

Elastic filament

composed of protein titin

Holds thick filaments in place; helps recoil after stretch; resists excessive stretching

Titin

are strands of elastic protein

reach from tips of thick filaments to the Z line

stabilize the filaments; responsible for allowing the sarcomere to stretch and recoil

Dystrophin

links the thin filaments to the integral proteins of the sarcolemma

T tubules

Also called transverse tubules, these are deep invaginations of the plasma membrane found in skeletal and cardiac muscle cells. These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell.

Triads

formed by t tubules that run between the paired teminal cisternae of SR; organelles come into closest contact here; encircle each sarcomere

Action potential

the change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.

Ion channel

A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.

Chemically gated ion channels

channel-linked receptors that open to let a specific ion pass in response to a ligand

ACh receptor

a transmembrane protein in the sarcolemma of the neuromuscular junction that binds to ACh

Voltage-gated ion channels

A specialized ion channel that opens or closes in response to changes in membrane potential

Neuromuscular junction/ motor end plate

Interface between the end of a motor neuron and a muscle fiber (synaptic area.) Acetylcholine and Cholinesterase are active in this region

Axon terminal

The endpoint of a neuron where neurotransmitters are stored

synaptic knob (terminal button)

Rounded areas (knobs) at the end of axon terminals that store neurotransmitters and assist in the transmission of neural information.

Synaptic cleft

The narrow gap that separates the presynaptic neuron from the postsynaptic cell.

Junctional folds

folds IN SARCOLEMMA at motor end plate that contain acetylcholine receptors; provide a large surface area for millions of ACh receptors located here

Endplate potential

the postsynaptic potential that occurs in the motor endplate in response to release of acetylcholine by the terminal button

Motor End Plate

specialized part of a muscle fiber membrane at a neuromuscular junction

Neuromuscular junction

region where a motor neuron comes into close contact with a skeletal muscle cell

Acetylcholinesterase

the enzyme that breaks down acetylcholine in the synaptic cleft

Excitation-contraction Coupling

The sequence of events from motor neuron's signaling to a skeletal muscle fiber to the contraction of the fiber's sarcomeres.

Creatine phosphate

An energy storage molecule used by muscle tissue. The phosphate from creatine phosphate can be removed and attached to an ADP to generate ATP quickly.

Creatine Kinase

enzymes that catalyzes the transfer of phosphate from CP to ADP

Motor unit

A motor neuron and all of the muscle fibers it innervates

Myogram

a chart of the timing and strength of a muscle's contraction

Muscle twitch

the response of a muscle to a single brief threshold stimulus

Latent period

time between application of a stimulus and the beginning of a response in a muscle fiber

Period of contraction

cross bridges are active, from the onset to the peak of tension development, and the myogram tracing rises to a peak

Period of relaxation

final phase, lasting 10-100ms, is initiated by reentry of Ca2+ into the SR; muscle tension decreases to zero and tracing returns to baseline

Treppe

the gradual increase in muscular contraction following rapidly repeated stimulation

Wave summation (temporal summation)

If stimulus frequency set at about 20 per second

Relaxation is not completed between twitches

Contractile forces add up to produce higher tensions

unfused/incomplete tetanus

Further increase in stimulus frequency causes muscle to progress to sustained, contraction generating more force with very brief periods of incomplete relaxation; frequency of stimulation allows only incomplete relaxation; generates submax. sustained contraction

fused/complete tetanus

when the muscle is stimulated so rapidly that no evidence of relaxation is seen and the contractions are completely smooth and sustained and generate maximum tension

Multiple motor unit summation

the more motor units activated the stronger the contraction

Sub-threshold stimuli

stimuli that produce no observable contractions

Threshold stimulus

stimulation level that must be exceeded to elicit a nerve impulse or a muscle contraction

Maximal stimulus

A stimulus which is strong enough to create action potentials in all the motor neurons innervating a whole muscle

Muscle tone

The state of partial contraction in a muscle, even when the muscle is not being used.

Isotonic contractions

muscle length changes and moves the load, the tension remains relatively constant through the rest of the contractile period; come in two flavors concentric and eccentric

Concentric contractions

those in which the muscle shortens and does work, such as picking up a book or kicking a ball;

Eccentric contractions

muscle generates force as it lengthens

Isometric contractions

muscular contraction that increases tension but does not produce movement.

Glycolysis

the breakdown of glucose by enzymes, releasing energy and pyruvic acid.

Lactic acid

Produced in muscle cells from the reduction of pyruvate (under anaerobic conditions) to regenerate NAD+ so that glycolysis can continue. A rise in lactic acid usually accompanies an increase in physical activity.

Anaerobic glycolysis

Energy-yielding conversion of glucose to lactic acid in various tissues, notably muscle, when sufficient oxygen is not available.

Aerobic respiration

Respiration in which oxygen is consumed and glucose is broken down entirely; water, carbon dioxide, and large amounts of ATP are the final products. This metabolic process in which pyruvate is broken down in the Kreb's cycle and the electron-carrier molecules produced are used to produce ATP through electron transport

Aerobic endurance

the length of time a muscle can continue to contract using aerobic pathways

Muscle fatigue

Inability of muscle to maintain its strength of contraction or tension after prolonged activity; may be related to insufficient oxygen, depletion of glycogen, and/or lactic acid buildup

Excess post-exercise oxygen consumption

additional oxygen consumed immediately after an exercise bout when the body is no longer exercising

Myoblasts

stem cells that fused to form each muscle fiber early in development

Myosatellite cell

stem cells that function in the repair of damaged muscle tissue

prime mover (agonist)

muscle that produces most of the force during a particular joint action

Antagonist

muscle that opposes or reverses a prime mover

Synergist

muscle that aids a prime mover in a movement and helps prevent rotation

Fixator

Muscle that immobilizes one or more bones, allowing other muscles to act from a stable base.