Lecture on Neurons and Signal Transmission

Structure of a Neuron

• Dendrites: Receive information.
• Cell Body: Processes and integrates information.
• Axon: Carries information long distances.
• Axon Terminal: Transmits information to the next cell.
• Nerve: A bundle of axons traveling together.

Signal Transmission and Action Potential

• Dendrites receive incoming signals.
• Neuron decides to pass signal based on stimulation strength.
• Action Potential: When signal is strong enough, neuron "fires."
• Ion Movement: Transmission depends on movement of ions (sodium, potassium, chloride).

Resting State of Neurons

• Sodium Ions: Higher concentration outside the cell.
• Potassium Ions: Higher concentration inside the cell.
• Chemical Gradient: Ionic separation at membrane creates a gradient.
• Electrical Gradient: More positive ions outside than inside.
• Electrochemical Gradient: Combination of chemical and electrical gradients.
• Membrane Potential: Resting potential is approximately -70 millivolts.

Ion Channels and Membrane Potential

• Ion Channels: Allow ions to move across the membrane.
  • Voltage-Gated Channels: Open at certain membrane potentials.
  • Ligand-Gated Channels: Open when bound by specific molecules.
  • Mechanically-Gated Channels: Open in response to physical forces.
• Graded Potential: Small, transient changes in membrane potential.
• Sodium-Potassium Pump: Restores ionic gradients using ATP.

Action Potential Process

• Threshold Voltage: -55 millivolts triggers action potential.
• Sodium Channels: Open, allowing sodium influx and depolarization.
• Overshoot: Membrane potential becomes positive.
• Repolarization: Potassium exits the cell, returning to negative potential.
• Hyperpolarization: Membrane potential temporarily more negative than resting.
• Absolute Refractory Period: Neuron cannot fire another action potential.
• Relative Refractory Period: Larger stimulus needed to fire due to hyperpolarization.

Action Potential Characteristics

• All-or-Nothing Principle: Action potential either occurs or does not.
• Frequency of Action Potentials: Can change depending on stimulus intensity.

Factors Affecting Conduction Velocity

• Myelin Sheaths: Increase conduction speed via saltatory conduction.
  • Peripheral Nervous System: Schwann cells form myelin sheaths.
  • Central Nervous System: Oligodendrocytes form myelin sheaths.
  • Nodes of Ranvier: Gaps between myelin sheaths where action potential jumps.

Summary

• Resting Potential: No stimulus, membrane at resting potential.
• Graded Potential: Small stimulus causes a change in potential.
• Action Potential: Stimulus above threshold causes neuron to fire.