Synapse and Neurotransmission - Vocabulary (Physiology 2024)

Vocabulary flashcards covering key terms from the lecture notes on synapses and neurotransmission.

Synapse

Functional connection between two neurons or between a neuron and an effector cell; a specialized gap through which chemical signals pass, typically one-way.

Presynaptic membrane

Membrane of the transmitting neuron terminal that contains neurotransmitter vesicles.

Synaptic cleft

The extracellular gap (about 200–300 angstroms) between the presynaptic and postsynaptic membranes where neurotransmitters diffuse.

Postsynaptic membrane

Membrane of the receiving neuron that has receptors for the neurotransmitter.

Action potential

Electrical impulse generated at the axon hillock; travels along the axon and triggers neurotransmitter release at the terminal.

Sherrington

Charles Scott Sherrington coined the term synapse to describe the gap between neurons.

Chemical synapse

Communication between neurons via neurotransmitter release and receptor binding; transmission is typically unidirectional.

Electrical synapse

Direct electrical communication through gap junctions allowing ions to pass between cells; fast and usually bidirectional.

Gap junction

Direct cytoplasmic connections between cells in which ions pass; formed by connexin proteins.

Connexin

Protein subunits that form gap junction channels.

Neurotransmitter

Chemical messenger released from the presynaptic terminal that acts on receptors of the postsynaptic cell to influence activity.

V-SNARE (synaptobrevin)

Vesicle-associated SNARE protein that participates in docking/fusion of the vesicle with the presynaptic membrane.

T-SNARE (syntaxin)

Target membrane SNARE protein on the presynaptic membrane that forms SNARE complex with v-SNARE.

SNAP-25

Presynaptic membrane protein that helps SNAREs fuse to form the fusion complex.

Synaptotagmin

Calcium sensor on synaptic vesicles that triggers vesicle fusion when Ca2+ enters the terminal.

SNARE complex

Tightly coordinated proteins (v-SNARE, t-SNARE, SNAP-25) that mediate docking and fusion of vesicles.

Docking

Process of vesicles attaching to the presynaptic membrane in preparation for fusion.

Priming

Preparation of docked vesicles for rapid fusion upon Ca2+ influx.

Fusion

Membrane fusion of vesicle with presynaptic membrane releasing neurotransmitter.

Release (exocytosis)

Exocytotic discharge of neurotransmitter into the synaptic cleft.

Endocytosis

Membrane retrieval to recycle vesicle components after transmitter release.

Clathrin

Protein that coats vesicles for endocytosis and recycling.

Endosome

Vesicular compartment where recycled vesicle membranes are reused and refilled.

Vesicle

Membrane-bound storage sac containing neurotransmitter in the presynaptic terminal.

Reuptake

Transport of neurotransmitters back into the presynaptic terminal to terminate signaling.

Acetylcholine (ACh)

A common neurotransmitter; usually excitatory; at NMJ stimulates skeletal muscles; also in autonomic neurons; degraded by acetylcholinesterase.

Acetylcholinesterase (AChE)

Enzyme that inactivates acetylcholine in the synaptic cleft.

Myasthenia gravis

Disease with decreased acetylcholine receptors leading to muscle weakness.

Botulinum toxin

Toxin that inhibits acetylcholine release, causing flaccid paralysis.

Tetanus toxin

Toxin that disrupts synaptobrevin, preventing transmitter release and causing spastic paralysis.

Glutamate

Major excitatory CNS neurotransmitter; involved in memory and long-term potentiation; precursor to GABA; high levels can be neurotoxic.

GABA

Major inhibitory neurotransmitter in the brain; GABA-A (ionotropic) causes IPSPs; GABA-B (metabotropic) modulates via G proteins.

Glycine

Inhibitory neurotransmitter mainly in the spinal cord; blocked by strychnine.

Strychnine

Glycine receptor antagonist that increases spinal neuron excitability.

Dopamine

Neurotransmitter involved in movement control and reward; deficits in Parkinson's; excess linked to schizophrenia; released more with amphetamine.

Norepinephrine (noradrenaline)

CNS: arousal; PNS: smooth muscle, cardiac muscle, glands; increases blood pressure; derived from tyrosine.

Serotonin (5-HT)

Neurotransmitter implicated in mood, sleep, appetite, memory; precursor to melatonin; SSRIs block reuptake.

Histamine

Excitatory neurotransmitter involved in wakefulness; high levels linked to headaches and mood; low levels linked to fatigue.

Purines (ATP as transmitter)

ATP can act as a neurotransmitter or cotransmitter; present in all synaptic vesicles; has its own receptors; degraded to adenosine.

Substance P

Neuropeptide that transmits pain signals; found in brain, spinal cord, and GI tract.

Endorphins

Endogenous opioid peptides; modulate pain; morphine acts on opioid receptors; runner's high.

Enkephalins

Endogenous opioid peptides contributing to analgesia.

Dynorphins

Endogenous opioid peptides involved in pain modulation.

Opioid peptides

Group including endorphins, enkephalins, and dynorphins; endogenous opioids.

Nitric oxide (NO)

Gaseous transmitter produced on demand from L-arginine; short-acting; acts via cGMP; involved in memory and smooth muscle relaxation.

Soluble gas transmitters

Gaseous transmitters like NO that diffuse rapidly; not stored in vesicles.

SSRIs (Selective Serotonin Reuptake Inhibitors)

Drugs that inhibit serotonin reuptake, prolonging serotonin action; used as antidepressants.

Synaptic delay

Time (about 0.2–0.5 ms) between arrival of AP at the synaptic knob and postsynaptic effect, due to Ca2+ influx and transmitter release.

Synaptic plasticity

Change in synaptic strength with use; includes facilitation, depression, and long-term potentiation.

Synaptic facilitation

A short-term increase in synaptic strength when a presynaptic neuron is stimulated in quick succession.

Post-tetanic potentiation

Longer-lasting enhancement of synaptic strength after high-frequency stimulation.

Long-term potentiation (LTP)

Long-lasting increase in synaptic strength, a cellular basis for memory and learning.

Synaptic depression

Temporary decrease in synaptic strength due to depletion of releasable vesicles.

Synaptic fatigue

Reduced transmitter release with intensive stimulation due to depletion of transmitter stores.

Motor end plate

Region of the muscle fiber plasma membrane at the neuromuscular junction where motor neuron terminal contacts muscle.

End plate potential (EPP)

Depolarization of the muscle end plate caused by acetylcholine release at neuromuscular junction.

Neuromuscular junction (NMJ)

Synapse between motor neuron and muscle; acetylcholine release causes muscle contraction.

Four basic circuit types

Diverging, Converging, Reverberating, Parallel-discharge circuits; determine how signals propagate and integrate.

Diverging circuit

Incoming signal causes increasingly widespread activation, amplifying the response.

Converging circuit

Inputs from multiple neurons converge on a single output neuron; funneling effect.

Reverberating circuit

Chain of neurons with collateral connections providing positive feedback; rhythmic activity until inhibited.

Parallel-discharge circuit

Incoming signal stimulates several neurons in parallel, producing a burst of impulses at the output.

Occlusion

Two simultaneous postsynaptic impulses produce a smaller response than sum due to presynaptic sharing of the same postsynaptic neuron.

Alkalosis and acidosis effects on neurons

Alkalosis increases excitability; acidosis depresses activity; breathing can adjust CO2 to influence pH.

ACh at NMJ

Acetylcholine released at the neuromuscular junction causing muscle contraction.

Fate of neurotransmitters

Diffusion away, enzymatic degradation, or reuptake; signal must not be perpetuated.

Catecholamines

Group of biogenic amines including norepinephrine, epinephrine, and dopamine.

GABA-A

Ionotropic GABA receptor mediating fast inhibitory chloride conductance.

GABA-B

Metabotropic GABA receptor that modulates neuronal activity via G proteins.

P2Y

Example of a metabotropic receptor involved in second messenger signaling.

Post-synaptic potentials (PSP)

Electrical changes in the postsynaptic membrane due to neurotransmitter receptor activity.

Ion channels

Ligand-gated channels (Na+, K+, Ca2+, Cl−) producing rapid postsynaptic changes.

Metabotropic receptors

G protein-coupled receptors with second messenger systems; slower and longer-lasting effects.

Ca2+ and transmitter release

Calcium entry into the presynaptic terminal triggers vesicle fusion and transmitter release.

Active zone

Presynaptic site where vesicles dock and release neurotransmitter; rich in Ca2+ channels.

Enzymatic degradation (e.g., AChE)

Breakdown of neurotransmitters in the synaptic cleft by enzymes such as acetylcholinesterase.

End plate potential (EPP)

Depolarization of the muscle end plate resulting from ACh at the NMJ.

Neuromuscular junction (NMJ) activity

Motor neuron terminal releases ACh, causing muscle fiber contraction via EPP and AP in muscle.