Muscle Physiology Lecture Notes

These vocabulary flashcards cover the structural characteristics, microscopic anatomy, physiology of contraction, fiber types, and dynamic responses of skeletal and smooth muscle based on the Chapter 10 transcript.

Excitability

The ability of muscle tissue to change its electrical state.

Elasticity

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

Extensibility

The ability of muscle tissue to stretch or extend.

Contractility

The ability of muscle tissue to shorten with force.

Skeletal Muscle Tissue

Voluntary muscle composed of long fibers with multiple nuclei and striations.

Cardiac Muscle Tissue

Involuntary, striated muscle found only in the heart, characterized by short branched fibers, single nuclei, and intercalated discs.

Smooth Muscle Tissue

Involuntary, non-striated muscle made of spindle-shaped, uninucleate cells found in vessel walls, organ linings, and sphincters.

Tendon

A cord of dense regular connective tissue that attaches muscle to bone.

Aponeurosis

A broad, sheet-like connective tissue that serves the same function as a tendon, such as the thoracolumbar aponeurosis.

Fascicles

Subdivided bundles within a skeletal muscle, each containing $20$ to $80$ muscle fibers.

Epimysium

The connective tissue membrane that surrounds the entire muscle and blends into the tendon.

Perimysium

The connective tissue membrane that surrounds individual muscle fascicles.

Endomysium

The connective tissue membrane that surrounds individual muscle fibers.

Sarcolemma

The plasma membrane of a muscle fiber.

Sarcoplasm

The cytoplasm of a muscle fiber.

Sarcoplasmic Reticulum (SR)

Modified endoplasmic reticulum in muscle fibers that is specialized to store $Ca^{2+}$.

Myofibrils

Rod-shaped organelles within muscle fibers formed from contractile proteins arranged in a repeating pattern.

T-tubules

Pits in the sarcolemma that lead down and wrap around myofibrils to conduct electrical signals.

Terminal cisternae

Two rings of the sarcoplasmic reticulum that form on both sides of a T-tubule where $Ca^{2+}$ is stored.

Sarcomere

The repeating functional unit of a myofibril composed of actin and myosin; it is the section between two Z-discs.

Actin

Thin filaments within a sarcomere that are anchored to Z-discs.

Myosin

Thick filaments within a sarcomere that are anchored to the M-line.

Z-discs

The borders of a sarcomere which serve as attachment points for thin filaments.

M-line

The center point of a sarcomere where thick filaments are attached.

I-band

The light region of a sarcomere that contains only thin (actin) filaments.

A-band

The dark region of a sarcomere where thick and thin filaments overlap.

Action Potential

An electrical signal transmitted by neurons or across the sarcolemma to trigger muscle contraction.

Neuromuscular Junction

The site where a motor neuron interacts with a muscle fiber, consisting of the axon terminal and the motor end plate.

Acetylcholine (ACh)

A neurotransmitter stored in synaptic bulbs that is released into the synapse to trigger an electrical impulse in the muscle fiber.

Acetylcholinesterase

An enzyme that quickly degrades Acetylcholine (ACh) in the synapse to cease muscle contraction.

Botulinum toxin

A neurotoxin produced by Clostridium botulinum that blocks the release of ACh, causing muscle paralysis.

Troponin-Tropomyosin complex

Proteins that shield actin filaments at rest, with tropomyosin specifically blocking myosin binding sites.

Sliding Filament Model

The theory that skeletal muscle fibers contract as thin filaments are pulled and slide past thick filaments.

Cross bridge formation

The process where myosin heads bind to exposed binding sites on actin while cocked with $ADP + P_i$.

Power stroke

The movement of the myosin head forward after releasing $ADP + P_i$, dragging actin toward the middle of the sarcomere.

Muscle Tension

The force generated by the contraction of a muscle via the shortening of sarcomeres.

Isotonic contraction

A contraction where muscle tension remains constant throughout the movement of a load.

Concentric contraction

A type of isotonic contraction where the muscle shortens to move a load.

Eccentric contraction

A type of isotonic contraction where the muscle lengthens as muscle tension diminishes.

Isometric contraction

A contraction where the muscle produces tension but the joint angle does not change and no load is moved.

Motor Unit

A single motor neuron and all the group of muscle fibers it innervates.

Recruitment

The progressive activation of more and larger motor units to increase the strength of muscle contraction.

Muscle Twitch

A single contraction of muscle fibers in a motor unit produced by a single action potential.

Wave Summation

The additive effect of successive action potentials resulting in a sustained muscle contraction.

Incomplete Tetanus

A state of almost continuous muscle contraction where the frequency of action potentials increases and relaxation time decreases.

Complete Tetanus

A state where action potential frequency is so high that the muscle fibers do not relax at all, resulting in a flat plateau of tension.

Slow Oxidative (SO) fibers

Small-diameter muscle fibers that contract slowly using aerobic respiration and possess myoglobin; used for posture and joint stability.

Fast Oxidative (FO) fibers

Muscle fibers that produce fast contractions primarily via aerobic respiration and are used for movements like walking.

Fast Glycolytic (FG) fibers

Large-diameter muscle fibers that use glycolysis to generate ATP quickly for powerful movements, but fatigue quickly.

Creatine phosphate

A high-energy molecule used to regenerate ATP during the first $5$ to $8$ seconds of intense muscle contraction.

Hypertrophy

The increase in the diameter of muscle fibers due to training.

Atrophy

A decrease in the diameter of muscle fibers, often caused by lack of use.

Sarcopenia

Muscle atrophy specifically associated with aging.

Angiogenesis

The generation of new blood vessels produced during endurance training to supply more $O_2$ and nutrients.

Calmodulin

A protein in smooth muscle that binds to calcium to activate the enzyme myosin kinase.

Myosin kinase

An enzyme in smooth muscle activated by calmodulin that allows myosin to bind to actin for contraction.

Dense bodies

Structures on the sarcolemma of smooth muscle cells where thin filaments are anchored.