Lecture Notes: Neurons and Neural Communication (Vocabulary)

Neurons in the Brain

The human brain contains about 8.6\times 10^{10} neurons (approximately 86,000,000,000).
- This figure reflects the scale of neural networks in the brain and highlights the density of information processing.
Neurons operate in networks and communicate information with each other through electrical and biochemical signals.
This complexity underpins all brain function, including perception, movement, learning, and memory.
The neuron is described as one of the most complex cells in the body.

A neuron has three main parts: the axon, the dendrite, and the soma (the cell body).
Dendrites receive signals from other neurons and act as input regions, collecting information from the network.
The soma integrates incoming signals and governs metabolic processes needed to keep the cell alive.
The axon conducts the electrical signal away from the soma, acting as the output pathway of the neuron.
The axon propagates the electrical signal through ions moving in and out of the membrane, which changes the membrane potential along its length.
The axon terminus (axon terminal) is where neurotransmitters are released to communicate with other neurons.

When a neuron fires, it generates an action potential, a rapid electrical signal that travels along the axon.
Propagation occurs as ions flow across the neuron's membrane, causing the membrane potential to change over time.
When the action potential reaches the axon terminal, neurotransmitters are released into the synapse to influence the next neuron in the network.

Neurons communicate via synapses, the junctions where axon terminals release neurotransmitters into the gap between neurons.
Neurotransmitters cross the synapse and bind to receptors on the post-synaptic neuron, triggering a response.
This chemical signaling works together with the electrical signal to coordinate brain activity across networks.

Key terms and definitions:
- Neuron, axon, dendrite, soma, axon terminal, action potential, neurotransmitter, synapse.
Fundamental relationships (conceptual, with simple formulas):
- Ionic currents: I{ion} = g{ion} (Vm - E{ion})
- Membrane potential dynamics (simplified): Cm \frac{dVm}{dt} = - \sum I{ion} + I{ext}
Conceptual sequence overview: resting membrane potential, threshold, spike (action potential), and repolarization drive neural signaling.

Understanding neuronal signaling is essential for explaining how the brain processes information, controls movement, and supports cognition and behavior.
Disruptions in neural signaling underlie many neurological and psychiatric conditions; diagnosing and treating these conditions relies on knowledge of neurons and synapses.

The transcript does not discuss ethical or philosophical aspects; these notes acknowledge that such discussions are not present in the provided material.
Practical implications include applications in medicine (neuropharmacology, neuromodulation), education (learning and memory), and technology (neuro-inspired computing).