Graded Potentials and Action Potentials

Flashcards covering graded potentials, action potentials, and related concepts from a physiology lecture.

Graded Potentials

Variable strength, used for short-distance communication.

Action Potentials

Very brief, large depolarizations, rapid signaling over long distances.

Graded Potential Initiation

Can initiate an action potential if the depolarizing graded potential is strong enough when it reaches the trigger zone within a neuron.

Reasons Graded potentials lose strength

Current leak and cytoplasmic resistance

Graded Potentials

small, local changes in membrane potential that happen at dendrites and cell bodies in response to neurotransmitter binding and can summate.

Action Potentials

Large, all-or-nothing electrical signals that travel down the axon once the graded potentials are strong enough to reach the threshold at the axon hillock.

Presynaptic Neuron

The neuron sending the signal.

Postsynaptic Neuron

The neuron receiving the signal.

Synapse

The gap between two neurons.

Neurotransmitters

Chemicals released from the presynaptic neuron.

Ligand-gated ion channels

Receptors on the postsynaptic membrane that open in response to neurotransmitters.

Depolarize

Membrane potential becomes less negative (toward zero or positive).

Hyperpolarize

Membrane potential becomes more negative.

Receptor potentials

Occur in specialized sensory receptor cells; due to the opening of different channels.

TRPV1

Transient receptor potential vanilloid 1; a calcium-permeable ion channel

Excitatory postsynaptic potentials (EPSPs)

Increase the likelihood of a postsynaptic action potential occurring (excitatory neurotransmitter).

Inhibitory postsynaptic potentials (IPSPs)

Decrease the likelihood of a postsynaptic action potential occurring (inhibitory neurotransmitter).

Endplate potentials (EPPs)

Occur in muscle cells; generally, very similar to EPSPs.

Axon Hillock/Trigger Zone

The location where the action potential will occur.

Action Potentials

Very brief, large depolarizations with constant amplitude that do not decrease in strength with distance; an all-or-none phenomena.

Depolarization

The membrane potential becomes less negative.

Overshoot

The peak of the action potential where the membrane potential is positive.

Repolarization

The membrane potential returns toward the resting membrane potential.

Hyperpolarization

The membrane potential becomes more negative.

Action Potential Threshold

The white line rises as the voltage nears the threshold of -55 mV. At -55 mV, numerous voltage-gated sodium channels open, allowing a surge of positively charged sodium ions to rush into the cell.

Voltage-Gated Channels

As the neuronal membrane potential reaches ~ +30 mV, voltage-gated sodium (Na⁺) channels inactivate, halting further Na⁺ influx. At the same time, voltage-gated potassium (K⁺) channels open, allowing K⁺ ions to flow out of the cell.

Hyperpolarization cause

The membrane becomes hyperpolarized as K⁺ ions continue to leave the cell