Explains how postsynaptic membrane receptors are split into ionotropic, ligand-gated channels with fast responses and metabotropic, G-protein coupled receptors with slower, broader effects, with GABA and dopamine receptors given as examples. It then covers postsynaptic potentials as graded potentials, spatial and temporal summation, and excitatory and inhibitory postsynaptic potentials with their ionic mechanisms.
Topic 9 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 1 section, about 649 words (4 min of reading), with 10 flashcards.
In this note
Introduction
Introduction
Postsynaptic Membrane Receptors
After neurotransmitters traverse the synaptic cleft, they interact with receptors on the postsynaptic membrane, which influence the opening or closing of ion channels. These receptors are categorized into two types: ionotropic and metabotropic.
1. Ionotropic Receptors (Ligand-gated): Fast Response
Structure: These receptors are composed of five protein subunits that form a transmembrane pore.
They are ligand-gated channels, meaning they open to allow ion passage when a neurotransmitter binds.
The ions typically permitted to pass include K^+^, Na^+^, Cl^-^, and Ca^2+^.
Example: Gamma-aminobutyric acid (GABA) receptor is a prominent type of ionotropic receptor.
Structure: Metabotropic receptors have a complex structure that spans the membrane multiple times, differing from the pore-like structure of ionotropic receptors.
Binding of a neurotransmitter to these receptors activates associated G-proteins and other protein subunits, which may then modulate nearby ion channels indirectly.
This indirect action results in slower depolarization, taking more time to reach an action potential.
While ionotropic receptors affect localized regions of the cell, metabotropic receptors can influence cellular activity more broadly.
Example: Dopamine receptors are a key type of metabotropic receptor.
Postsynaptic Potentials
Postsynaptic potentials are graded potentials, not action potentials, and they do not follow the all-or-none law. This means their magnitude can vary and they can summate to reach the threshold necessary to trigger an action potential. Unlike action potentials, which are electrical phenomena occurring when a neuron fires, postsynaptic potentials are changes in membrane potential due to the chemical action of neurotransmitters at the synapse.
Characteristics of Postsynaptic Potentials:
Graded Potentials: Their amplitude is variable, depending on the strength and number of neurotransmitter molecules binding to receptors.
Chemical Basis: The postsynaptic membrane is termed a "chemical membrane" because its potential changes are driven by the binding of chemicals (neurotransmitters), rather than by inherent electrical properties.#
Types of Summation:
1. Spatial Summation:
Description: This occurs when multiple presynaptic neurons release neurotransmitters at various synapses onto the same postsynaptic neuron simultaneously.
Effect: The combined effect of these multiple inputs can generate a significant change in the membrane potential, potentially leading to an action potential if the threshold is reached.
2. Temporal Summation:
Description: This happens when one presynaptic neuron releases neurotransmitters repeatedly in quick succession.
Effect: The rapid, repeated stimulation can increase the membrane potential incrementally, summing over time to reach or exceed the threshold for triggering an action potential.
Continue reading free
The whole note is free with an AceMed account, with its 10 flashcards. Premium adds flashcard recall, highlights and Ask AI.
