Neuromuscular Junction and Muscle Contraction Vocabulary

Comprehensive vocabulary flashcards covering resting membrane potentials, action potential propagation down axons, synaptic transmission at the neuromuscular junction, the sliding filament model, NMJ toxins, and rigor mortis based on the lecture material.

Resting Membrane Potential

The difference in electrical charge across the plasma membrane when a cell is not receiving input, where the outside is more positively charged than the inside.

Axon Hillock

The region at the junction of the cell body and axon where incoming stimulus signals accumulate to generate an action potential if they exceed the threshold.

Action Potential

A temporary reversal in resting membrane potential that travels down the length of an axon through rapid sequential depolarization and repolarization.

Depolarization

The rapid change in membrane potential where the inner surface becomes positively charged and the outer surface becomes negatively charged, driven by the inflow of $\text{Na}^+$ ions.

Repolarization

The restoration of the negative internal charge of the membrane after an action potential passes, accomplished by inactivating $\text{Na}^+$ channels and opening additional $\text{K}^+$ channels.

Node of Ranvier

Unmyelinated gaps along an axon membrane where ion diffusion occurs, allowing action potentials to jump from node to node in saltatory conduction.

Neuromuscular Junction (NMJ)

The specialized synapse or motor end plate where an axon terminal of a motor neuron meets a muscle fiber.

Synapse

Any point of functional contact or interaction where a neuron meets and transmits signals to a target cell.

Synaptic Cleft

The narrow extracellular space separating the presynaptic axon terminal from the postsynaptic muscle fiber membrane.

Synaptic Vesicles

Membrane-bound sacs inside the presynaptic axon terminal that contain chemical neurotransmitters such as acetylcholine.

Acetylcholine (ACh)

The neurotransmitter released by motor neurons across the synaptic cleft to bind receptors on the sarcolemma and trigger muscle depolarization.

Acetylcholinesterase (AChE)

An enzyme present in the synaptic cleft that breaks down acetylcholine to stop muscle cell stimulation and allow muscle relaxation.

Sarcolemma

The plasma membrane surrounding a muscle fiber that receives neurotransmitters and propagates action potentials.

T Tubules (Transverse Tubules)

Infoldings of the sarcolemma that conduct electrical impulses deep into the interior of the muscle fiber toward the sarcoplasmic reticulum.

Terminal Cisternae

Enlarged sacs of the sarcoplasmic reticulum adjacent to T tubules that store and release $\text{Ca}^{2+}$ ions into the sarcoplasm when excited.

Sarcoplasmic Reticulum

The smooth endoplasmic reticulum of a muscle cell responsible for storing, releasing, and re-sequestering calcium ions necessary for contraction.

Tropomyosin

A regulatory strand protein wrapped around actin that physically blocks myosin-binding sites when a muscle fiber is relaxed.

Troponin

A regulatory protein bound to tropomyosin that binds $\text{Ca}^{2+}$ ions, undergoing a conformational change that shifts tropomyosin to expose active sites on actin.

Myosin-Actin Cross-Bridge

The structural bond formed when an activated myosin head attaches to an exposed binding site on a thin actin filament.

Power Stroke

The step in contraction where the myosin head releases $\text{ADP}$ and inorganic phosphate ($\text{P}_i$), flexing to pull the attached actin filament toward the M line.

Recovery Stroke

The process following cross-bridge detachment where myosin hydrolyzes a newly bound $\text{ATP}$ to $\text{ADP} + \text{P}_i$ and recocks back into its high-energy position.

Sliding Filament Mechanism

The model describing muscle contraction wherein thin actin filaments are pulled along thick myosin filaments toward the center of the sarcomere without changing individual filament length.

Botulinum Toxin

A potent toxin produced by Clostridium botulinum that inhibits the release of acetylcholine at the NMJ, causing flaccid paralysis.

Tetanus Toxin

A deadly toxin produced by Clostridium tetani that blocks the release of inhibitory neurotransmitters, resulting in rigid spastic paralysis.

Latrotoxin

A neurotoxin found in black widow spider venom that induces excessive acetylcholine release, leading to severe muscle contraction and pain.

Tetrodotoxin

A deadly biological poison found in puffer fish that blocks voltage-gated ion channels in neurons, preventing membrane depolarization.

Rigor Mortis

Postmortem muscle stiffening caused by calcium leakage into sarcoplasm and continuous cross-bridge attachment in the absence of cellular $\text{ATP}$.