Ch 11 Postsynaptic Potentials and Neurotransmitters

Presynaptic and Postsynaptic Neurons

  • Presynaptic Neurons: Responsible for sending signals to postsynaptic neurons.
  • Postsynaptic Neurons: Receive signals through postsynaptic potentials, which can be either excitatory or inhibitory.

Postsynaptic Potentials

  • Graded Potentials: Unlike action potentials, graded potentials vary in size and can lead to excitatory or inhibitory effects.

  • EPSPs (Excitatory Postsynaptic Potentials):

    • Created when neurotransmitters bind to receptors and cause depolarization of the postsynaptic membrane.
    • Function: Bring the membrane potential closer to the threshold, increasing the likelihood of action potentials.
    • Behavior: Voltage spikes up towards the threshold.

  • IPSPs (Inhibitory Postsynaptic Potentials):

    • Generated when neurotransmitters cause hyperpolarization of the postsynaptic membrane.
    • Function: Move membrane potential further from the threshold, decreasing the likelihood of action potentials.
    • Behavior: Voltage dips down, moving away from the threshold.

Action Potentials vs. Graded Potentials

  • Action Potentials:
    • All-or-none responses that remain constant at full strength throughout the axon.
  • Graded Potentials:
    • Vary in strength and can decay with distance from the stimulus.

Neurotransmitter Effects

  • Acetylcholine (ACh):

    • Major neurotransmitter in the somatic nervous system (e.g., neuromuscular junction).
    • Can be excitatory (stimulates muscle contraction) or inhibitory (slower heart rate).

  • Norepinephrine (NE):

    • Key neurotransmitter in the autonomic nervous system related to the fight or flight response.
    • Triggers increased heart rate, breathing, and blood pressure during stress.

  • Dopamine:

    • Associated with pleasure and reward; influences positive reinforcement and motivation.
    • Connected to mood and attention, with implications for disorders like ADHD.

  • Serotonin:

    • Contributes to mood regulation and feelings of well-being.
    • Lower levels linked to depression; involved in anxiety disorders as well.

  • GABA (Gamma-Aminobutyric Acid):

    • Primary inhibitory neurotransmitter in the brain.
    • Important for pain regulation (e.g., medications like gabapentin utilize GABA pathways).

  • Endorphins:

    • Neurotransmitters that induce feelings of euphoria and act as natural pain relievers.
    • Heightened during and after physical exercise, providing a sense of well-being and relaxation.

Summary

  • The interaction between EPSPs and IPSPs determines neuron excitability and communication across synapses.
  • Different neurotransmitters have unique effects, influencing physiological responses and emotional states, critical for understanding brain function and disorders.