Chemical Synaptic & Neuromuscular Transmission

A complete set of vocabulary flashcards covering chemical synaptic transmission, neuromuscular transmission, associated clinical disorders, and pharmacological agents.

Synapse

Specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands.

Presynaptic terminal

The part of the axon where the action potential arrives to trigger the release of neurotransmitters.

Postsynaptic membrane

The surface of the cell receiving the signal at a synapse, containing specific receptors for neurotransmitters.

Synaptic vesicles

Membrane-bound structures within the presynaptic terminal that contain neurotransmitter molecules.

Synaptic cleft

The gap between the presynaptic terminal and the postsynaptic membrane across which neurotransmitters diffuse.

Exocytosis

The process by which neurotransmitter release occurs from synaptic vesicles into the synaptic cleft following calcium influx.

Excitatory postsynaptic potential (EPSP)

A depolarizing potential caused by the influx of sodium through $Na^+$ channels, driving the membrane potential toward threshold.

Inhibitory postsynaptic potential (IPSP)

A hyperpolarizing potential caused by the influx of chloride through $Cl^-$ channels, driving the membrane potential away from threshold.

Acetylcholine (ACh)

A neurotransmitter synthesized from Acetyl CoA and Choline, used in both central synaptic and neuromuscular transmission.

Glutamate and Aspartate

Examples of excitatory amino acid neurotransmitters.

GABA and Glycine

Examples of inhibitory amino acid neurotransmitters.

Biogenic amines

Derivatives of amino acids including Epinephrine, Norepinephrine, Dopamine, Serotonin ($5-HT$), and Histamine.

Neuropeptides

Amino acid chains acting as neurotransmitters, such as Endorphin, Enkephalin, Oxytocin, and Vasopressin.

Nitric Oxide

A gas neurotransmitter also known as Endothelial Derived Relaxing Factor (EDRF).

Alzheimer’s disease

A clinical condition characterized by memory loss due to the degeneration of acetylcholine-neurons in the brain.

Parkinson’s disease

A disorder characterized by tremors and rigidity caused by the degeneration of dopamine-neurons in the basal ganglia.

Schizophrenia

A form of psychosis characterized by personality disorder due to hyperactivity of dopamine-secreting neurons.

Neuromuscular junction (NMJ)

The specific chemical synapse between the axon terminal of a motor neuron and a skeletal muscle fiber.

Motor unit

Comprises a single motor neuron and all the skeletal muscle fibers it innervates.

Small motor units

Motor units involved in fine motor activities, such as those controlling facial expressions.

Large motor units

Motor units involved in gross muscular activities, such as the quadriceps used for running.

Junctional folds

Specialized folds in the postsynaptic muscle membrane at the neuromuscular junction.

Motor end plate

A specialized region on the postsynaptic muscle membrane which contains nicotinic acetylcholine receptors.

Choline acetyl transferase (CAT)

The enzyme responsible for forming acetylcholine from Acetyl CoA and Choline.

Acetylcholinesterase (AChE)

The enzyme on the motor end plate that degrades acetylcholine into choline and acetate to terminate its signal.

Nicotinic receptors

Specific receptors on the motor end plate to which acetylcholine binds to open $Na^+$ and $K^+$ channels.

End Plate Potential (EPP)

The potential due to depolarization of the motor end plate caused by $Na^+$ influx dominating over $K^+$ efflux.

Miniature End Plate Potential (MEPP)

A small change in membrane potential ($0.4\,mV$) produced by the release of a single synaptic vesicle.

Botulinum toxin

An agent that blocks the release of ACh from presynaptic terminals, leading to skeletal muscle paralysis and potential death.

Curare

A substance that competes with ACh for nicotinic receptors, decreasing the size of the End Plate Potential.

D-Tubocurarine

A form of Curare used therapeutically as an anesthetic due to its ability to cause skeletal muscle relaxation.

α-Bungarotoxin

A neurotoxin present in krait venom that binds irreversibly to acetylcholine receptors.

Myasthenia gravis

An autoimmune disease where antibodies are formed against acetylcholine receptors on the motor end plates.

Ptosis

The medical term for drooping eyelids, a primary clinical feature observed in Myasthenia gravis.

Diplopia

The clinical term for double vision, often seen in patients with Myasthenia gravis.

Dysphagia

Difficulty in swallowing, which can occur due to muscle weakness in Myasthenia gravis.

Dysarthria

Difficulty in speech resulting from the involvement of facial and throat muscles in Myasthenia gravis.

Tensilon (Edrophonium)

A reversible acetylcholinesterase inhibitor used specifically for the diagnosis of Myasthenia gravis.

Neostigmine and Pyridostigmine

Anticholinesterase agents used to treat Myasthenia gravis by prolonging the presence of ACh in the synaptic cleft.

Lambert-Eaton syndrome

A condition where antibodies destroy voltage-gated calcium channels in the presynaptic terminal, causing muscle weakness.

Voltage-gated $Ca^{2+}$ channels

Channels in the presynaptic terminal that open upon depolarization to allow calcium influx.

Axon

The long projection of a neuron that conducts electrical impulses away from the cell body.

Dendrites

The branched projections of a neuron that receive signals from other neurons.

Synaptic knobs

The rounded tips of axon terminals that participate in synapses.

Hyperpolarization

A change in membrane potential that makes it more negative than the resting potential, seen in IPSPs.

Depolarization

A change in membrane potential toward a more positive value, seen in EPSPs and EPPs.

$Na^+$-choline cotransporter

The mechanism by which choline is taken back into the presynaptic terminal after ACh degradation.

Motoneuron pool

The collection of motor neurons that innervate a specific muscle.

Basal ganglia

The area of the brain where dopamine-neuron degeneration leads to Parkinson’s disease.

Action Potential

The electrical signal that travels down the motor neuron to trigger the sequence of events in transmission.