Muscle Tissue Types, Structure, and Physiology: A&P Chapter 10

Excitability

The ability of plasma membranes to change electrical states (respond to a stimulus).

Elasticity

The ability of muscle to return to its original length when relaxed.

Extensibility

Muscle can stretch or extend.

Contractility

The ability of muscle to shorten and pull on attachment points with force.

Skeletal Muscle

Is attached to the skeleton, is striated, and is controlled voluntarily.

Smooth Muscle

Mostly located in the walls of hollow organs, is not striated, and is controlled involuntarily.

Cardiac Muscle

Forms the heart, is striated, and is controlled involuntarily.

Epimysium

Most superficial sheath that covers entire muscle, made of dense irregular connective tissue.

Perimysium

Surrounds the fascicles or bundles of muscle fibers (cells).

Endomysium

Connective tissue that surrounds each individual muscle fiber.

Plasma membrane

Also known as sarcolemma.

Cytoplasm

Also known as sarcoplasm.

Smooth endoplasmic reticulum

Also known as sarcoplasmic reticulum (SR).

Thin filament

Actin.

Thick filament

Myosin.

Sarcomere

Functional unit of muscle made of actin and myosin (myofilaments) and regulatory proteins troponin and tropomyosin.

Z disc

Anchors actin myofilaments.

Actin

Thin filaments.

Myosin

Thick filaments.

I band

Actin only.

A band

Entire length of myosin plus overlapping parts of actin.

H zone

Light zone in midsection of A band that contains myosin only (visible in relaxed muscle fiber).

M line

Dark vertical line in H zone that anchors myosin.

Action potential (AP)

Travels along the motor neuron until it reaches the neuromuscular junction.

Acetylcholine (ACh)

A neurotransmitter released into the synaptic cleft.

Excitation-Contraction Coupling

AP moves by depolarization along sarcolemma down T-tubules to the interior of the cell where the membrane can then be in contact with sarcoplasmic reticulum (SR).

Triad

Made of two SR on either side of a T-tubule.

Calcium (Ca++)

Triggers the release from the SR and binds to troponin starting the contraction process.

Tropomyosin

A protein that blocks myosin-binding sites on actin.

Troponin-tropomyosin complex

Formed when tropomyosin and troponin bind together.

Ca++

Binds to troponin which then pulls tropomyosin away from the myosin-binding sites on actin.

Thin filaments

Are pulled along thick filaments toward the center of the sarcomere.

Myosin head

Can only pull actin a small distance before it must be detached and re-cocked, an action which requires ATP.

Muscle contraction end

Occurs when Ca++ is pumped back into the SR or there is no more ATP, resulting in relaxation.

Z lines

Move closer together during sarcomere contraction.

I bands

Become smaller during sarcomere contraction.

Creatine phosphate

In a resting muscle, ATP is converted to ADP and creatine phosphate; when energy is needed, it quickly transfers its phosphate to ADP creating ATP.

Glycolysis

Produces less ATP than creatine phosphate and creates lactic acid.

Aerobic respiration

In the presence of oxygen, this process produces 95% of the ATP needed by muscles and takes place in the mitochondria.

Isotonic contractions

The tension in a muscle stays constant and a load is moved.

Isometric contractions

The muscle produces tension but the load is not moved.

Motor Unit

The group of muscle fibers in a muscle innervated by a single motor neuron.

Recruitment

The increasing activation of motor units producing a stronger muscle contraction.

Muscle Twitch

One single contraction of all muscle fibers in a motor unit.

Latent period

AP is moving along sarcolemma and Ca++ are released from SR.

Contraction phase

Ca++ binds to troponin, cross-bridges form, and sarcomere shortens.

Relaxation phase

Ca++ ions are pumped out, cross-bridge cycling stops, and muscle returns to resting state.

Wave summation

Fibers are stimulated while a previous twitch is still occurring, making the second twitch stronger.

Tetanus

If the relaxation phase completely disappears, contractions become continuous resulting in tetanus.

Treppe

Occurs when a muscle fiber is stimulated immediately after the relaxation period ends, resulting in a slightly higher contraction than the previous maximum contraction.