Structure of a Neuron😊

Structure of a Neuron

2. Myelination

3. Demyelinating Diseases

• Loss of myelin sheath ⇒ ↓↓ conduction velocity of action potentials

Functional Areas of the Neuron

Graded Electrogenesis:

• Formation of a local potential by different synapses

• Examples:
• Excitatory Postsynaptic Potential (EPSP)
• Inhibitory Postsynaptic Potential (IPSP)

• Site in CNS: Surface of dendrites >> Surface of cell body (soma)

Action Potential Generation Site:

• Generated by voltage-gated sodium channels.

• Voltage-gated sodium channel density: (lowest threshold)
• Node of Ranvier > Initial segment > Totodendria > Surface of myelin

• Initiation site:
• Sensory neurons: Node of Ranvier
• Motor neurons: Initial segment

Gibbs Donnan Effect

• Presence of large impermeable molecules on one side of a membrane.

• Key impermeable molecule:
• Protein
• Typically negatively charged at normal pH.
• More abundant inside the cell
• Attracts positive ions (e.g., sodium)
• Repels negative ions (e.g., chloride)

• Important for differential ion distribution

Equilibrium Potential

• Isoelectric potential.

• No net ion movement occurs.

• At EP: Concentration gradient = Electrical gradient

Determining Factors

• Concentration

• Charge

Nernst Equation:

• Calculates equilibrium potential for a single ion.
• Simplified:
• Eq = +61 mV / Z log10 ([Ion] outside / [Ion] inside)
• (Z = valency including charge)
• Answer: Sodium

• Equilibrium Potentials:

Ions	Equilibrium Potentials	Notes
Potassium (EK+)	-90 mV	Closest to RMP of all vertebrate cells ↳ Generally everyone is pottan Equal to RMP of myocardium, skeletal muscle ↳ Pottan has a good muscle and heart
Chloride (ECl-)	-70 mV	Equal to RMP of neuron (-70 mV) ↳ Nuclear → Neuron, Chloride → 70
Sodium (ENa+)	+63 or +61 mV	ㅤ
Calcium (ECa2+)	+132 mV	ㅤ

Nernst Equation

• Where:
• z = – 1 (for Cl⁻)
• [outside] = 100 mmol/L
• [inside] = 10 mmol/L
• Answer → - 60

Resting Membrane Potential (RMP)

• Aka Diffusion potential
• Considering permeability of multiple ions
• D/t K+>> Cl, Na

Goldman-Hodgkin-Katz Equation

• Consider multiple ions based on :
1. Concentration
2. Permeability

• Applied Aspect:
• Action Potential

• Mnemonic:
• EP avano → Ni ayikko (EP → Nernst)
• Registered Medical Practitioner avano
• Golden Opp (RMP → Goldman Hodgkin Katz)

Driving Force (DF)

DF = RMP - EP

• Example: DF (Na⁺) = -70 - (+60 mV) = -130 mV

• Implication: Intracellular Negative Force
• Cation (Na⁺): Enters cells
• Anion (Cl⁻): Moves out of cells

Action Potential

Action Potential – Overview

• Definition: Change in membrane voltage over time after stimulation.

Resting & Local Potentials

• Stimulation → RMP (-70 mV) changes → Local Potential generated

Spike Potential

• Portion of action potential above threshold

• Includes:
• Depolarization
• Repolarization

Ionic Permeability Changes:

Refractory Period