Neurotransmission: The electrochemical process by which neurons communicate.
Neuron Structure
Anatomical Features:
Dendrites: Receive signals from other neurons.
Cell Body (Soma): Processes incoming signals.
Axon: Transmits signals away from the cell body.
Synaptic Terminals: Release neurotransmitters to communicate with other neurons.
Resting Potential
Definition: The state of a neuron when it is not actively sending a signal, characterized by a negative charge.
Polarization: Due to unequal distribution of ions:
More positively charged ions (Na+) outside
More negatively charged ions (K+, Cl-) inside
Sodium-Potassium Pump: Maintains resting potential by transporting 3 Na+ out and 2 K+ into the cell.
Synapses and Neurotransmitter Action
Synapse: Connection point between two neurons.
Neurotransmitter Binding: Released by the pre-synaptic neuron; binds to receptor sites on post-synaptic neuron.
If primarily excitatory, fires an action potential.
If primarily inhibitory, leads to hyperpolarization (silencing the neuron).
Action Potential
Definition: A brief and rapid shift in electrical charge, resulting in a positive internal charge in the neuron.
Triggering an Action Potential:
Occurs when sufficient excitatory neurotransmitters cause Na+ influx, reaching the threshold of excitation.
Initiated at the axon hillock where the axon meets the cell body; contains many voltage-gated Na+ channels.
Propagation of Action Potential
Depolarization Wave: Subsequent opening of Na+ channels along the axon, allowing for continuing depolarization.
Node of Ranvier: Gaps between myelin sheaths; allows for faster conduction via saltatory conduction.
All or None Law: Action potentials are fully triggered or not at all; no partial action potentials.
Signal Strength: Measured by frequency of action potentials rather than amplitude.
Neurotransmitter Reuptake and Refractory Period
Reuptake: Process where most neurotransmitters are reabsorbed by the pre-synaptic neuron after triggering an action potential in the post-synaptic cell.
Refractory Period: A ~2 ms period following an action potential where the neuron cannot fire again, allowing it to return to resting potential and prepare for new signals.