Lecture on Neurons and Neural Transmission

Main Parts of a Neuron

• Dendrites: Receive information.
• Cell Body: Processes and integrates information.
• Axon: Carries information long distances within the neuron.
• Axon Terminal: Transmits information to the next cell.
• Nerve: A bundle of axons, can transmit information over long distances.

Transmission of Neuronal Signals

• Action Potential: Neuron fires if incoming stimulation is strong enough.
• Ions in Neural Transmission:
  • Key ions: Sodium (Na⁺), Potassium (K⁺), Chloride (Cl⁻).
  • Unequal distribution creates electrochemical gradients.

Resting Membrane Potential

• Chemical Gradient: Higher Na⁺ outside, higher K⁺ inside.
• Electrical Gradient: More positive outside than inside.
• Membrane Potential: Resting potential is approximately -70 mV.
• Electrochemical Equilibrium: Balance of chemical and electrical gradients.
• Ion Channels: Mediate ion movement across membranes.

Types of Ion Channels

• Always Open Channels
• Voltage-Gated Channels: Open at specific membrane potentials.
• Ligand-Gated Channels: Open when bound by specific molecules.
• Mechanically-Gated Channels: Open in response to physical forces.
• Channels are selectively permeable.

Neuronal Firing and Action Potentials

• Threshold Voltage: Action potential triggers at -55 mV.
• Depolarization: Influx of Na⁺ makes membrane potential less negative.
• Repolarization: Efflux of K⁺ returns potential to negative.
• Hyperpolarization: Temporary state when membrane potential is more negative than resting potential.
• Sodium-Potassium Pump: Restores ion concentrations using ATP.

Refractory Periods

• Absolute Refractory Period: No new action potential can be triggered.
• Relative Refractory Period: Larger stimulus required to trigger an action potential.

Characteristics of Action Potentials

• All-or-Nothing: Action potential either happens or doesn't.
• Frequency: Can change based on stimulus intensity.

Factors Influencing Conduction Velocity

• Myelin Sheaths: Increase speed via saltatory conduction.
• Nodes of Ranvier: Gaps in myelin where action potentials jump.
• Schwann Cells: Form myelin in PNS.
• Oligodendrocytes: Form myelin in CNS.

Summary

• Resting Potential: Membrane potential with no stimulus.
• Graded Potential: Result of small stimulus.
• Action Potential: Triggered when stimulus is above threshold, neuron fires.