Nervous System: Neuronal Action & Communication Notes

Ion Concentrations and Potential Differences: Understand how varying ion concentrations impact the resting membrane potential.
Definitions: Master the meanings of hyperpolarization and depolarization.
Action Potential Phases: Familiarize with the different phases of an action potential.
Synapse Function: Comprehend the mechanics of synapse transmission.
Neuroreceptors: Identify and explain the essential properties of neuroreceptors.

Neurotransmitters: Chemicals that facilitate neuronal communication.
Graded Potential: Changes in membrane potential that vary in size and are localized.
Action Potential: A rapid, all-or-nothing electrical impulse that travels along an axon.

Definition: The electrical potential difference across a neuron's membrane when at rest, typically about -70 ext{ mV}.
Creation of Membrane Potential: Similar to stored energy in a battery; an ion concentration gradient contributes to this potential.
Ion Channels: Structures that control the flow of ions (Na+, K+, Cl-) and thus influence membrane potential.

Electrochemical Gradient: The combination of concentration gradients and electrical gradients influencing ion flow.
- Ions move from high to low concentration and towards opposing charges (cations to anions and vice versa).
Types of Ion Channels:
1. Leak Channels: Allow ions to diffuse freely (e.g., K+). Found in all cells.
2. Mechanically-Gated Channels: Open in response to physical force (e.g., touch).
3. Ligand-Gated Channels: Open when specific chemicals (neurotransmitters) bind (e.g., pain receptors).
4. Voltage-Gated Channels: Open in response to changes in membrane potential (e.g., Na+ channels in axons).

Definition: Localized changes in membrane potential due to ion channel activity (e.g., opening of K+ channels leading to hyperpolarization or Na+ channels leading to depolarization).
Location: Typically occur at dendrites and the cell body of neurons.
Characteristics: Vary in duration and amplitude depending on stimulus strength and duration of channel opening.

Threshold Potential: A critical level of depolarization around -55 ext{ mV} that must be met to initiate an action potential.
Depolarizing Phase:
- Voltage-gated Na+ channels open, allowing Na+ influx, thus increasing positive charge within the neuron.
Repolarization Phase:
- Na+ channels close and K+ channels open, allowing K+ to exit, restoring the negative internal environment.
After-Hyperpolarizing Phase: A brief period where the membrane potential becomes even more negative than at rest.

Sodium-Potassium Pump: An active transport mechanism that moves Na+ out of and K+ into the cell, using ATP to maintain resting potential by keeping higher K+ and lower Na+ concentrations inside the neuron.

Mechanism: Action potentials propagate along the axon without losing strength due to local depolarization opening adjacent voltage-gated channels—a domino effect.
Myelin Sheath: Increases conduction speed by allowing the impulse to jump between nodes (Nodes of Ranvier).

Function: An action potential causes the opening of voltage-gated Ca2+ channels in the presynaptic neuron, which facilitates neurotransmitter release into the synaptic cleft.
Post-Synaptic Effects: Neurotransmitters bind to receptors on the postsynaptic membrane, leading to changes in ion permeability and local potentials.
Fate of Neurotransmitters: After binding, they may diffuse away, be reabsorbed by the presynaptic neuron, or be enzymatically broken down.

Neurotransmitters: Various types, each having specific effects based on their corresponding receptors (e.g., GABA, serotonin).
Psychotropic Drugs: Affect neurotransmission by altering release, receptor interaction, reuptake processes, or enzymatic breakdown.