Neurons and APs

Neurons are individual cells in the nervous system that communicate with each other.
Early understandings viewed the brain as a continuous network, but advancements have shown neurons are distinct entities.

Initial studies involved cutting the brains of small animals and observing them under microscopes.
Scientists believed neurons were interconnected tubes resembling a superhighway, lacking gaps.

Kameo Golgi developed staining techniques that enhanced visualization of neurons using silver nitrate, enabling better viewing of neuron structures.

Ramon Cajal's work with younger animal brains revealed neurons are individual cells that do not connect like highways but instead are adjacent to each other.
Noted the unique structure of pyramidal and Purkinje cells.
Formulated the Neuron Doctrine, establishing that the nervous system is composed of individual neurons communicating with one another.

Neurons have cell bodies with dendrites and axons that facilitate communication and processing information.

Action potentials are electrical impulses generated when a neuron communicates information.

At rest, neurons maintain a polarized state, being relatively negatively charged inside compared to outside (approximately -70 mV).
Positively charged ions are outside, while potassium ions are typically at a higher concentration inside.

Ion channels, particularly sodium and potassium channels, are crucial for generating action potentials.
The lipid bilayer of the cell membrane prevents ion passage unless channels are open.

Stimulus Initiation
- A stimulus causes sodium channels to open, allowing sodium ions to flow into the neuron, depolarizing the membrane.
- If enough sodium enters, the membrane potential reaches the threshold (around -50 mV), triggering more sodium channels to open.
Action Potential Peak
- The charge flips, reaching approximately +50 mV, which is the peak of the action potential.
- Sodium channels close afterward, and potassium channels open, allowing potassium to exit, returning the membrane to a negative state.
Refractory Period
- Following an action potential, the neuron enters a refractory period where it cannot fire again until the resting state is restored.
- This prevents overstimulation and ensures the action potential travels in one direction.

Neurons can communicate excitatory or inhibitory signals.
Excitatory postsynaptic potentials (EPSPs) slightly depolarize the next cell, potentially triggering a new action potential.
Inhibitory postsynaptic potentials (IPSPs) hyperpolarize and reduce the likelihood of the next neuron firing.

Spatial Summation: Multiple excitatory inputs from different neurons can collectively trigger an action potential in a postsynaptic neuron.
Temporal Summation: Rapid firing of the same presynaptic neuron can summate to reach the firing threshold.

The synapse is the gap between presynaptic and postsynaptic neurons, where neurotransmission occurs.
Upon arrival at the terminal, the action potential releases neurotransmitters across the synapse to the next neuron.

Neurotransmitters bind to receptors on the postsynaptic neuron, facilitating communication between neurons.
Reuptake pumps can retrieve neurotransmitters after they have acted on receptors.

Issues like multiple sclerosis interrupt the efficiency of neuronal communication by damaging myelin sheaths, affecting neurotransmission efficiency.