Lecture on Graded Potentials and Synaptic Potentials

Types of Signals

• Graded Potentials

  • Result from ion movement through ligand-gated or mechanically-gated channels.
  • Vary in magnitude (small to large) and polarity (hyperpolarizing or depolarizing).
  • Example: Opening of a ligand-gated sodium channel causes depolarization (excitatory).
  • Stimulus increasing sodium permeability strengthens graded potential.
  • Opening potassium channels causes hyperpolarization (inhibitory).

• Action Potential

  • To be discussed in the next lecture.

Characteristics of Graded Potentials

• Effects occur at the stimulus point and as the signal is conducted.
• Decremental Conduction
  • Strength of graded potential weakens away from the origin due to electrical current leakage.
• Graded potentials can be excitatory or inhibitory:
  • Excitatory stimulus → depolarization.
  • Inhibitory stimulus → hyperpolarization.

Graded Potential Summation

• Summation of graded potentials can occur:
  • Multiple ligand-gated channels open, increasing sodium influx and creating a stronger graded potential.
  • Can be depolarizing or hyperpolarizing depending on the channel.

Synaptic Potentials

• Synapse: The junction where one neuron touches another.
  • Post-synaptic neuron: Receives chemical messenger.
  • Receptors on cell body act on these messages.

Types of Synaptic Potentials

• Excitatory Postsynaptic Potential (EPSP)
  • Results from excitatory synapses causing depolarization.
  • Example: Stimulating excitatory synapses A and B causes summation.
• Inhibitory Postsynaptic Potential (IPSP)
  • Results from inhibitory synapses causing hyperpolarization.
  • Example: Stimulating inhibitory synapse C.

Summation in Synaptic Potentials

• Both excitatory and inhibitory postsynaptic potentials can summate.
  • Example: Stimulating A (excitatory) and C (inhibitory) simultaneously leads to no net change but is still considered summation.

Conclusion

• Understand the different types of graded potentials and synaptic potentials.
• Graded potentials are crucial for determining whether an action potential is triggered, influenced by excitatory and inhibitory inputs.