Muscle Contraction and Neuromuscular Physiology

Vocabulary flashcards covering the physiological steps of skeletal muscle contraction, energy production, and types of muscle movement as described in the lecture.

Membrane potential

The difference in electrical charge across a cell's membrane, typically ranging between $-60$ and $-90\,mV$ for most cells.

Millivolt ($mV$)

A unit of electrical measurement equal to a thousandth of a volt, used to describe the charge of a cell's membrane.

Sodium-potassium pump

A cellular mechanism that pushes three sodium ions ($Na^+$) out of the cell for every two potassium ions ($K^+$) it lets in, maintaining a negative internal charge.

Action potential

A special kind of electrical current or "zap" produced by neurons and muscle cells that travels down the cell to control activity.

Neuromuscular junction

The specific synapse or place where a neuron's axon meets a skeletal muscle cell.

Axon terminal

The knob-like ending of a neuron, also called the synaptic terminal or synaptic knob, where neurotransmitters are released.

Synaptic cleft

The microscopic, fluid-filled space between the axon terminal and the motor end plate of a muscle cell.

Motor end plate

The specialized part of the muscle cell membrane ($sarcolemma$) at the neuromuscular junction that drops down and becomes wavy.

Acetylcholine ($ACH$)

The specific neurotransmitter chemical that acts as a ligand to open sodium channels on the muscle cell during contraction.

Ligand-gated channel

An ion channel that opens or closes in response to the binding of a specific chemical, such as a neurotransmitter.

Voltage-gated channel

An ion channel that opens or closes in response to changes in electrical current or voltage across the membrane.

Acetylcholinesterase

An enzyme that breaks acetylcholine into acetic acid and choline to stop the stimulus and close the sodium channels.

Sarcoplasmic reticulum

A modified smooth endoplasmic reticulum in muscle cells that stores and releases calcium ions ($Ca^{2+}$).

Triad

A combination of one transverse tubule ($t$-tubule) and two terminal cisternae of the sarcoplasmic reticulum.

Troponin

The "bouncer" protein on actin that binds to calcium; this binding causes it to move the tropomyosin rope away from binding sites.

Tropomyosin

The rope-like protein that blocks the myosin-binding sites on actin when a muscle is at rest.

Cross bridge

The connection formed when a myosin head grabs onto the binding site of an actin filament.

Power stroke

The flexing motion of the myosin head at its hinge that pulls the thin filament toward the center of the sarcomere.

Sliding filament theory

The concept that thin filaments slide over thick filaments toward the $M$-line, shortening the sarcomere and the overall muscle.

Rigor mortis

A state of skeletal muscle contraction after death caused by the lack of $ATP$ and the leaking of calcium into the cytosol.

Creatine phosphate

A high-energy molecule that stores a phosphate group to quickly regenerate $ATP$ from $ADP$ during the first $15$ seconds of contraction.

Creatine kinase

The enzyme that facilitates the transfer of a phosphate group from creatine phosphate back to $ADP$ to create $ATP$.

Anaerobic metabolism ($glycolysis$)

The process of breaking down glucose into pyruvate in the cytoplasm without oxygen, yielding an immediate $2\,ATP$ per glucose molecule.

Aerobic metabolism

The mitochondrial process requiring oxygen that utilizes the citric acid cycle and electron transport chain to produce $34$ to $36\,ATP$.

Lactate ($lactic\,acid$)

A byproduct of anaerobic metabolism that causes a burning sensation and contributes to muscle fatigue.

Cori cycle

The recovery process where the liver absorbs lactate and converts it back into pyruvate and then glucose.

Hypertrophy

The enlargement of a muscle due to an increase in the number of myofibrils within the muscle cells, typically caused by resistance training.

Atrophy

The reduction in muscle size, tone, and power due to a lack of use or stimulation.

Isotonic concentric contraction

A contraction where the muscle tension exceeds the load and the muscle shortens while doing work.

Isotonic eccentric contraction

A contraction where the muscle tension is less than the load, causing the muscle to lengthen while maintaining tension.

Isometric contraction

A contraction where the muscle tension increases but the length of the muscle does not change, such as when maintaining posture or bulk.