Electrical Signals and Neurotransmission Flashcards

Flashcards covering electrical signals, action potentials, post-synaptic potentials, neurotransmitters, receptor types, and neurotoxins based on the lecture notes.

Action Potential

An electrical signal generated in the axon that always involves depolarization, repolarization, and hyperpolarization, has a constant amplitude, is actively conducted without diminishing, and is initiated by opening voltage-gated channels.

Post-synaptic Potential (PSP)

An electrical signal generated in dendrites and soma that passively spreads through the cytosol with diminishing amplitude, initiated by opening or closing chemically gated ion channels.

Threshold ($T$)

The level of axonal membrane depolarization required to open voltage-gated $\text{Na}^+$ and $\text{K}^+$ channels, normally about $-55\text{ mV}$.

DDT and Pyrethroids

Insecticides that bind to voltage-gated $\text{Na}^+$ channel proteins, slowing their dynamics so they stay open for a prolonged time and disrupt action potential production.

Invertebrate Axon Strategy

Adaptation using large diameter axons to maximize action potential conduction velocity by minimizing cytosolic resistance ($r_i$).

Vertebrate Axon Strategy

Adaptation that maximizes action potential conduction velocity by wrapping axon segments in myelin to increase membrane resistance ($r_m$) against current leak.

Oligodendrocytes

Glial cells that wrap axonal segments in myelin within the Central Nervous System (CNS).

Schwann Cells

Glial cells that wrap axonal segments in myelin within the Peripheral Nervous System (PNS).

v-SNARE

SNARE proteins located on the synaptic vesicle that bind $\text{Ca}^{2+}$, changing shape to bind with t-SNAREs on the pre-synaptic membrane.

t-SNARE

SNARE proteins located on the pre-synaptic membrane that bind with v-SNAREs to enable membrane fusion and pore opening.

Fast Synaptic Responses

Simplest post-synaptic responses mediated by receptors located directly on ion channels, where neurotransmitter binding opens the channel allowing ion movement across the post-synaptic membrane.

Excitatory Post-Synaptic Potential (EPSP)

A localized depolarization of $V_m$ caused by $\text{Na}^+$ crossing the post-synaptic membrane, moving $V_m$ towards threshold ($T$) for action potential initiation.

Inhibitory Post-Synaptic Potential (IPSP)

A localized hyperpolarization of $V_m$ caused by $\text{Cl}^-$ or $\text{K}^+$ crossing the post-synaptic membrane, moving $V_m$ away from threshold ($T$).

Spatial Summation

The summing of post-synaptic potentials arising from inputs of spatially separated axon terminals that arrive at the exact same time.

Temporal Summation

The summing of post-synaptic potentials that occur sequentially over time from the same presynaptic fiber firing action potentials in quick succession.

Absolute Refractory Period (ARP)

Period lasting $1\text{ msec}$ in duration that sets the upper limit of action potential frequency to $1\text{ AP/msec}$.

Slow Synaptic Responses

Responses mediated by single membrane-spanning receptors linked to G-proteins (metabotropic receptors) that can open/close ion channels or alter protein synthesis and metabolism.

Ionotropic Receptors

Receptors directly associated with ion channels that produce fast post-synaptic potentials upon neurotransmitter binding.

Metabotropic Receptors

Receptors linked to G-proteins that produce slow synaptic responses and can alter cell metabolism or protein synthesis.

Nicotinic Receptors

Cholinergic receptor subtype consisting of 5 protein subunits with 2 ACh binding sites, where binding of ACh or nicotine opens chemically gated channels.

Muscarinic Receptors

Cholinergic receptor subtype activated by muscarine whose activation leads to hyperpolarization in the target cell.

Botulinum Toxin

Bacterial neurotoxin that destroys SNARE proteins inside axon terminals, blocking neurotransmitter release.

Latrotoxin

Black widow venom neurotoxin that damages the pre-synaptic membrane to allow cation influx, triggering continuous neurotransmitter release until depleted.

Cobratoxin and Alpha-bungarotoxin

Competitive inhibitors found in cobra and banded krait snake venom that block nicotinic receptors on muscle fibers, causing paralysis.

Succinylcholine (Sux)

Surgical paralytic agent that binds nicotinic receptors and holds them open, depolarizing muscle fibers to cause paralysis.

Carbamate and Organophosphate Pesticides

Pesticides that inhibit the enzyme breaking down acetylcholine in the synaptic cleft, prolonging ACh action and causing muscle spasms.

Substance P

Peptide neurotransmitter used in CNS pain pathways that stimulates pain transmission.

Endorphins

Peptide neurotransmitters used in CNS pain pathways that inhibit pain transmission.

Catecholamines

Subcategory of amine neurotransmitters derived from tyrosine, which includes epinephrine, norepinephrine, and dopamine.

Serotonin ($5\text{-Hydroxytryptamine}$)

An amine neurotransmitter derived from the amino acid tryptophan.