Neuron Structure and Function

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.

Transmission of Information

• Nerve: A bundle of axons traveling together, capable of long-distance transmission.
• Neuron Decision: Based on incoming signal strength, a neuron decides to pass the signal (action potential).

Action Potential

• Ion Movement: Transmission depends on ions (sodium, potassium, chloride).
• Resting State: More sodium outside, more potassium inside the cell.
• Electrochemical Gradient: Difference in charge across the membrane (resting potential ≈ -70 mV).

Ion Channels and Membrane Potential

• Ion Channels: Facilitate ion movement across membranes.
  • Voltage-gated Channels: Open at specific membrane potentials.
  • Ligand-gated Channels: Open when bound by specific molecules.
  • Mechanically-gated Channels: Open due to physical forces.
• Graded Potential: Small changes in membrane potential, can be positive or negative.

Sodium-Potassium Pump

• Function: Restores ionic balance by transporting sodium out and potassium in.
• Energy Use: Accounts for 20%-40% of brain's energy use.

Action Potential Process

• Threshold Voltage: From -70 mV to -55 mV triggers action potential.
• Depolarization: Sodium channels open, sodium enters cell, potential becomes less negative.
• Repolarization: Potassium channels open, potassium exits the cell.
• Hyperpolarization: Membrane potential becomes more negative than resting potential.

Refractory Periods

• Absolute Refractory Period: Neuron cannot fire another action potential.
• Relative Refractory Period: Larger stimulus needed to trigger action potential.

Action Potential Characteristics

• All-or-Nothing: Action potential amplitude does not change with stimulus size.
• Frequency: Frequency of firing can increase with stronger stimulus.

Conduction Velocity

• Myelin Sheaths: Increase speed of transmission (saltatory conduction).
  • Peripheral Nervous System: Myelin formed by Schwann cells.
  • Central Nervous System: Myelin formed by oligodendrocytes.
• Nodes of Ranvier: Gaps in myelin sheath where action potential "jumps."

Summary

• Resting Potential: No stimulus, membrane potential at rest.
• Graded Potential: Small stimulus causes variable response.
• Action Potential: Stimulus above threshold causes neuron to fire.