Muscle Contraction Physiology and Excitation

Vocabulary flashcards covering excitable membrane potentials, neuromuscular junctions, the sliding filament mechanism, energy sources, and clinical conditions in muscle physiology.

Resting Membrane Potential (RMP)

The electrical charge difference across the plasma membrane of excitable cells at rest, maintained at $-90\,mV$ in neurons and muscle cells with the outside positive and inside negative.

$Na^+/K^+$ ATPase Pump

A membrane transport protein that uses ATP to move $3\,Na^+$ out of the cell and $2\,K^+$ into the cell, maintaining the resting electrochemical gradient.

Ligand-Gated Ion Channel

A membrane channel that opens when a specific chemical attaches to it, such as acetylcholine binding at the motor end plate.

Voltage-Gated Channel (VGC)

A membrane channel that opens or closes in response to a change in electrical charge across the plasma membrane.

Motor Unit

A single motor neuron and all the muscle fibers it stimulates, allowing several muscle fibers to contract simultaneously.

Neuromuscular Junction (NMJ)

The region where the motor neuron and the muscle fiber sarcolemma come together.

Acetylcholine (ACh)

A neurotransmitter stored in synaptic vesicles of the motor neuron that is released into the synaptic cleft to stimulate muscle contraction.

Synaptic Cleft

The microscopic extracellular space located between the motor neuron synapse and the sarcolemma of the motor end plate.

End Plate Potential (EPP)

The local depolarization of the muscle fiber membrane caused by $Na^+$ influx through channels, raising the membrane potential to $+30\,mV$.

Transverse Tubules (T-Tubules)

Membranous tunnels through which action potentials travel deep into the interior of the muscle cell to trigger $Ca^{2+}$ release.

Sarcoplasmic Reticulum

An intracellular organelle in muscle fibers that stores $Ca^{2+}$ and releases it into the sarcoplasm when voltage-gated channels open.

Troponin

A regulatory protein on actin that binds $Ca^{2+}$, unlocking and moving tropomyosin away from the myosin-binding sites.

Tropomyosin

A regulatory protein on actin that covers myosin-binding sites when the muscle fiber is at rest to prevent contraction.

Power Stroke

The mechanical step in contraction where $ADP$ and inorganic phosphate ($P_i$) are released from the myosin head, pulling the actin filament toward the M-line.

Crossbridge Cycle

The repeating sequence in which the cocked myosin head binds actin, performs a power stroke, and detaches upon binding a new ATP molecule.

Acetylcholinesterase

An enzyme that rapidly breaks down acetylcholine in the synaptic cleft, preventing continual muscle contraction and allowing relaxation.

Botox

A substance used in cosmetics that blocks acetylcholine channels on muscles, preventing muscle contraction.

Myasthenia Gravis

A neuromuscular disease in which antibodies block acetylcholine channels on muscle fibers, impairing muscle excitation.

Rigor Mortis

Post-mortem stiffening of muscles that occurs when calcium leaks out from the sarcolemma and lack of ATP prevents myosin from detaching from actin.

Muscle Cramp

An unexpected tightening of muscle fibers (also known as a charley horse) that can occur due to an insufficiency of ions.

Creatine Phosphate

An anaerobic energy source that transfers a phosphate to $ADP$ to produce ATP and creatine during short-duration, high-intensity exercise of about $10\,\text{seconds}$.

Anaerobic Glycolysis

A metabolic pathway that breaks down glucose without $O_2$, producing $2\,\text{ATP}$ and lactic acid, which causes muscle burn during $30\text{--}40\,\text{seconds}$ of exercise.

Aerobic Cellular Respiration

An oxygen-dependent metabolic pathway in mitochondria that produces large amounts of ATP for prolonged exercise durations.

Muscle Fatigue

A physiological state in which a muscle cannot contract even though it continues to be stimulated.