Neurons | Noba

Neurons are the primary cells in the central nervous system involved in processing and transmitting information.
They receive sensory input and generate behavioral responses.

Neurons respond to sensory systems like vision, hearing, smell, taste, and touch.
They execute complex behaviors such as attending to stimuli, learning, and responding to threats.

Three main components:
- Dendrites: Branching extensions that receive input from other neurons.
- Soma (Cell Body): Contains the nucleus and supports cell function.
- Axon: Long projection that sends signals (action potentials) to other neurons.

Sensory Neurons: Relay information from sensory receptors to the central nervous system.
Motor Neurons: Communicate signals to muscles for movement.
Interneurons: Process input and link sensory and motor neurons to execute behavioral responses.

Santiago Ramón y Cajal established neurons as distinct units of the nervous system through his research using Golgi-stained tissues.
His findings contradicted the prevailing theory of a continuous nerve network proposed by Joseph von Gerlach.
Cajal shared the Nobel Prize in Medicine with Camillo Golgi in 1906.

Synaptic Structure:
- Communication occurs at the synapse, where the axon terminal of one neuron meets the dendrite of another.
- Small synaptic gap (5 nm) exists between these structures.
- Neurotransmitters, contained in synaptic vesicles, are released into the synaptic cleft and influence the postsynaptic neuron.

Resting Membrane Potential:
- Neurons typically maintain a resting membrane potential of -70 mV.
- Generates through the selective permeability of the cell membrane to various ions (Na+, K+, Cl-, A-).
**Ion Movement Influences: **
- Diffusion: Ions move from areas of high to low concentration.
- Electrostatic Pressure: Positively charged ions are attracted to negative areas and vice versa.

An action potential is a transient all-or-nothing electrical signal that occurs when a neuron is stimulated enough to reach the threshold of excitation (-50 mV).
Initiation:
- Depolarization occurs when Na+ channels open, allowing Na+ influx, raising membrane potential to approximately +40 mV.
Two important phases:
- Rising Phase: Rapid influx of Na+ causes depolarization.
- Falling Phase: K+ channels open, leading to K+ efflux and re-establishment of the resting potential.
Refractory Period: Prevents the action potential from traveling backward along the axon.

Myelin sheaths insulate axons, enhancing signal transmission speed via saltatory conduction (action potentials jump between nodes of Ranvier).

Neurotransmitter: Chemical messengers released into the synaptic gap.
Equilibrium Potential: The membrane potential at which no net ion flow occurs.
Threshold of Excitation: The critical level a cell’s membrane potential must reach to trigger an action potential.
Excitatory Postsynaptic Potentials (EPSPs): Depolarizing events that bring the membrane closer to the threshold.
Inhibitory Postsynaptic Potentials (IPSPs): Hyperpolarizing events that move the membrane potential further from the threshold.

A neuron receives inputs (EPSPs and IPSPs) from various sources.
If the total input reaches the threshold of excitation, an action potential is generated.
The action potential travels down the axon and triggers neurotransmitter release into the next synapse.
The cycle repeats in the postsynaptic neuron as it receives signals.