Cell Signaling and Action Potential Conduction in Neurobiology

Action Potential

Rapid change in membrane potential during neuron signaling.

Myelinated Axons

Axons insulated with myelin for faster signal conduction.

Unmyelinated Axons

Axons without myelin, slower signal conduction.

Refractory Period

Time during which neuron cannot fire another action potential.

Absolute Refractory Period

No stimulus can trigger an action potential.

Relative Refractory Period

Only stronger stimulus can initiate action potential.

Graded Potentials

Variable changes in membrane potential, not all-or-nothing.

Chemical Synapse

Connection where neurotransmitters transmit signals between neurons.

Presynaptic Cell

Neuron sending the signal at a synapse.

Postsynaptic Cell

Neuron receiving the signal at a synapse.

Synaptic Bouton

Terminal of presynaptic neuron releasing neurotransmitters.

Synaptic Vesicle

Membrane-bound structure containing neurotransmitters.

Synaptic Cleft

Gap between presynaptic and postsynaptic neurons.

Gap Junctions

Direct cytoplasmic connections between adjacent cells.

Autocrine Signals

Signals affecting the same cell that produces them.

Paracrine Signals

Signals affecting nearby cells in the same tissue.

Endocrine Signals

Hormones released into the bloodstream affecting distant cells.

Neurotransmitter

Chemical messenger transmitting signals across synapses.

Neurohormone

Hormone produced by neurons, released into blood.

Second Messenger

Intracellular molecule mediating cellular response to signals.

G-Protein-Coupled Receptor

Receptor activating G-proteins to trigger signaling pathways.

Amplifier Enzyme

Enzyme that increases the concentration of second messengers.

Rising phase

Initial depolarization during action potential.

Falling phase

Repolarization following action potential peak.

After-hyperpolarization

Period after action potential where membrane potential is lower.

Resting potential

Stable membrane potential before action potential initiation.

Proximal axon

Part of axon closest to cell body.

Active region

Area of axon where action potential is generated.

Distal inactive region

Part of axon farthest from cell body.

Myelin sheath

Insulating layer around axons, speeds up conduction.

Nodes of Ranvier

Gaps in myelin sheath where ion channels are concentrated.

Saltatory conduction

Jumping of action potentials between nodes.

Velocity of axons

Speed of action potential propagation, e.g., 70-120 m/s.

Synaptic terminal

End of presynaptic neuron where neurotransmitter release occurs.

Graded depolarization

Change in membrane potential leading to neurotransmitter release.

Termination of synaptic transmission

Processes that stop neurotransmitter action at synapse.

Primary messenger

Molecule that initiates signal transduction pathway.

Receptor-channel

Protein that opens in response to ligand binding.

Receptor-enzyme

Receptor that has enzymatic activity upon activation.

Nicotinic receptor

Type of acetylcholine receptor that is ionotropic.

Muscarinic receptor

Type of acetylcholine receptor that is metabotropic.

Alpha receptor

Type of adrenergic receptor responsive to norepinephrine.

Beta receptor

Type of adrenergic receptor with different signaling pathways.

Action Potentials

Rapid electrical signals along neurons.

Electrical Synaptic Transmission

Direct electrical communication between neurons.

Contact-Dependent Signaling

Cell communication requiring direct contact.

Autocrine Signaling

Cell signals affecting itself.

Paracrine Signaling

Cell signals affecting nearby cells.

Endocrine System

Hormonal signaling over long distances.

Ligand

Molecule that binds to a receptor.

Receptor

Protein that binds ligands to initiate signaling.

Hydrophilic Signals

Cannot cross the cell membrane.

Lipophilic Signals

Diffuse through membranes to bind receptors.

Nicotinic Acetylcholine Receptor (nAChR)

Ion channel activated by acetylcholine.

G Proteins

Molecules that transmit signals from receptors.

G-Protein Coupled Receptor (GPCR)

Receptor that activates G proteins upon ligand binding.

Muscarinic AChR

GPCR activated by acetylcholine, not in skeletal muscle.

Signal Amplification

Process enhancing cellular response to signals.

Second Messengers

Intracellular molecules that mediate signaling pathways.

α-bungarotoxin

Nicotinic AChR antagonist from kraite venom.

Insulin Receptor

Receptor that mediates insulin signaling.

Epinephrine

Hormone that triggers fight-or-flight response.

α-adrenergic Receptors

GPCRs responding to norepinephrine and epinephrine.

β-adrenergic Receptors

GPCRs mediating responses to epinephrine.

Chemical Synaptic Transmission

Release of neurotransmitters across synapses.