Synaptic Transmission and Neuromuscular Junction

Vocabulary flashcards covering action potential propagation, axonal conduction, local anesthetics, neurotoxins, post-synaptic potentials (EPSP/IPSP), and neuromuscular junction physiology.

Action Potential Resting State

The baseline state of a neuron where voltage-gated ion channels are closed and membrane potential is around $-65\,mV$, maintained primarily by $\text{K}^+$ leak channels.

Nodes of Ranvier

Unmyelinated gaps along an axon where voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels are concentrated, allowing the action potential to regenerate during axonal conduction.

Saltatory Conduction

The mode of action potential propagation along myelinated axons in which the electrical signal travels rapidly and passively beneath myelin sheath segments and regenerates actively at the Nodes of Ranvier.

Reversible Antagonist

A drug type—such as local anesthetics procaine, lidocaine, novocaine, and cocaine—that temporarily binds to and blocks voltage-gated $\text{Na}^+$ channels to prevent pain signals before eventually unbinding.

Tetrodotoxin (TTX)

A potent neurotoxin produced by animals like puffer fish (fugu) that acts as an irreversible antagonist by permanently blocking voltage-gated $\text{Na}^+$ channels, potentially causing fatal asphyxiation.

Excitatory Post-Synaptic Potential (EPSP)

A localized depolarization of the postsynaptic membrane caused by neurotransmitter binding that opens ligand-gated channels to allow $\text{Na}^+$ entry into the neuron.

Inhibitory Post-Synaptic Potential (IPSP)

A localized hyperpolarization of the postsynaptic membrane caused by neurotransmitter binding that opens ligand-gated channels to allow $\text{Cl}^-$ entry into the neuron.

Glutamate

The most common excitatory neurotransmitter in the central nervous system, which binds to postsynaptic receptors to cause $\text{Na}^+$ influx and generate an EPSP.

Gamma-AminoButyric Acid (GABA)

The most common inhibitory neurotransmitter in the central nervous system, which binds to postsynaptic receptors to cause $\text{Cl}^-$ influx and generate an IPSP.

Pyramidal Cells

Neurons found in the cerebral cortex that integrate synaptic inputs from tens of thousands of presynaptic sources.

Purkinje Cells

Large neurons located in the cerebellum that feature highly branched dendritic trees capable of receiving and integrating hundreds of thousands of synaptic inputs.

Neuromuscular Junction (NMJ)

Also known as a motor end plate, the specialized chemical synapse formed between the terminal of a motor neuron and a skeletal muscle fiber.

Alpha Motor Neuron

A motor neuron with its cell body located in the ventral portion of the spinal cord whose axon extends to innervate a group of muscle fibers.

Acetylcholine (ACh)

The neurotransmitter released from the presynaptic terminals of motor neurons at the neuromuscular junction to stimulate muscle fiber depolarization.

Nicotinic Acetylcholine Receptor-Channel

A ligand-gated ion channel located on the postsynaptic muscle membrane that opens when bound by two $\text{ACh}$ molecules, allowing $\text{Na}^+$ influx and $\text{K}^+$ efflux.

End-Plate Potential (EPP)

The localized postsynaptic depolarization produced at the muscle endplate by net $\text{Na}^+$ influx through activated acetylcholine receptor-channels.