Excitable Cells, Nernst, synapses, Cell potential, action potential

Flashcards covering key vocabulary related to neural signaling, resting potential, action potentials, refractory periods, and synaptic communication based on the provided lecture notes.

Resting Potential

The state of a resting neuron where the inside is approximately -70 mV relative to the outside, due to unequal ion distribution by the Na+/K+ pump and selective membrane permeability to K+.

Na+/K+ pump

An active transport mechanism that pumps 3 Na+ ions out of the cell for every 2 K+ ions pumped in, creating concentration gradients.

Selective Permeability (at rest)

The membrane's characteristic at rest, where it is much more permeable to K+ than to Na+ due to open K+ 'leak' channels, causing the inside of the cell to become negative.

Nernst Potential (Ex)

The equilibrium potential for a single ion; the membrane voltage where the electrical force exactly opposes the chemical concentration gradient, resulting in no net ion flow.

Membrane Potential (Vm)

An electrical voltage difference across a cell's plasma membrane, essentially a tiny battery.

Goldman-Hodgkin-Katz (GHK) Equation

An equation used to calculate the actual membrane potential (Vm) by considering the concentrations and relative permeabilities of multiple relevant ions.

Action Potential (AP)

A rapid, 'all-or-none' electrical signal that travels down an axon without losing strength; the fundamental unit of long-distance communication in the nervous system.

Graded Potential

An input signal that is variable, depends on the stimulus, can be summed, is passive, and decays with distance; caused by ligand-gated, mechanical, or voltage-gated channels.

Threshold Voltage

The membrane potential (around -55 mV) that a stimulus (like summed graded potentials) must reach to trigger an action potential.

Rising Phase (Depolarization)

The phase of an action potential where voltage-gated Na+ channels open quickly, Na+ rushes into the cell, and the membrane potential rapidly shoots up towards ENa (e.g., +30 mV).

Falling Phase (Repolarization)

The phase of an action potential where Na+ channels' inactivation gates close, and slower voltage-gated K+ channels open, causing K+ to rush out and the membrane potential to become negative again.

Undershoot (Hyperpolarization)

A brief period after repolarization where K+ channels are slow to close, driving the Vm even closer to EK, causing a temporary dip below the resting potential.

Absolute Refractory Period

A period during the rising and falling phases of an AP when Na+ channels are open or inactivated and cannot be reopened, preventing APs from overlapping or traveling backward.

Relative Refractory Period

A period during hyperpolarization when Na+ channels have reset, but the cell is more negative than usual, requiring a stronger-than-normal stimulus to reach threshold.

Propagation (of Action Potential)

The process where the influx of Na+ during an AP creates a local current that depolarizes the adjacent patch of the axon to its threshold, triggering a new AP there, repeating down the axon.

Myelin Sheath

An insulating layer around myelinated axons that concentrates voltage-gated channels at gaps.

Nodes of Ranvier

Gaps in the myelin sheath where voltage-gated channels are concentrated, allowing the AP to 'jump' from node to node.

Saltatory Conduction

The process by which an action potential 'jumps' from node to node in myelinated axons, making propagation much faster than in unmyelinated axons.

Synapse

The junction where a neuron communicates with another cell (neuron, muscle, etc.).

Electrical Synapse

A type of synapse where cells are directly connected by gap junctions, allowing ions to flow freely between them for extremely fast and bidirectional signaling.

Chemical Synapse

The most common type of synapse where neurons are separated by a synaptic cleft and communicate using chemical messengers called neurotransmitters.

Neurotransmitters

Chemical messengers released from the presynaptic terminal that diffuse across the synaptic cleft to bind to receptors on the postsynaptic membrane.

SNARE proteins

Proteins critical for the fusion of synaptic vesicles (filled with neurotransmitter) with the presynaptic membrane during exocytosis.

Ionotropic Receptors

Ligand-gated ion channels on the postsynaptic membrane where neurotransmitter binding directly opens the channel, leading to a fast, short-lived response.

Metabotropic Receptors

G-protein coupled receptors on the postsynaptic membrane where neurotransmitter binding activates a second messenger system, indirectly affecting ion channels or other cellular processes for a slower, longer-lasting response.

Excitatory Postsynaptic Potential (EPSP)

A depolarization in the postsynaptic cell that brings the membrane potential closer to the threshold for firing an action potential, usually caused by opening Na+ channels or closing K+ channels.

Inhibitory Postsynaptic Potential (IPSP)

A hyperpolarization in the postsynaptic cell that moves the membrane potential further away from the threshold, usually caused by opening K+ or Cl- channels.

Temporal Summation

The adding up of multiple graded potentials from the same synapse arriving in rapid succession.

Spatial Summation

The adding up of simultaneous graded potentials from different synapses.

Axon Hillock (integrator)

The region of a neuron that integrates all incoming EPSPs and IPSPs; if the sum depolarizes it to threshold, an action potential is fired.

Enzymatic degradation (NT termination)

A mechanism to terminate neurotransmitter signaling where enzymes break down the neurotransmitter in the synaptic cleft (e.g., Acetylcholinesterase breaking down ACh).

Re-uptake (NT termination)

A mechanism to terminate neurotransmitter signaling where the neurotransmitter is transported back into the presynaptic terminal or glial cells.

Neuron

A fundamental cell of the nervous system specialized for transmitting electrical and chemical signals.

Dendrites

Branching extensions of a neuron that receive signals from other cells and transmit them towards the cell body.

Cell Body (Soma)

The main part of a neuron containing the nucleus; it integrates incoming signals and carries out basic cellular functions.

Axon

A long, slender projection that conducts electrical impulses (action potentials) away from the cell body to other neurons, muscles, or glands.

Depolarization

A decrease in the absolute value of a cell's membrane potential (e.g., from -70 mV to -50 mV or +30 mV), making the inside less negative or even positive.

Hyperpolarization

An increase in the absolute value of a cell's membrane potential (e.g., from -70 mV to -90 mV), making the inside more negative.

Presynaptic Terminal

The axon terminal of the neuron sending the signal, where neurotransmitters are released.

Postsynaptic Membrane

The membrane of the neuron or cell receiving the signal, containing receptors for neurotransmitters.

Synaptic Cleft

The narrow extracellular space between the presynaptic terminal and the postsynaptic membrane across which neurotransmitters diffuse.