Neurotransmission and Ion Channels

Action Potential

Synaptic Transmission

• Occurs at the synapse, the gap between two neurons
• Involves the release of neurotransmitters from the presynaptic neuron and their binding to receptors on the postsynaptic neuron
• Types of synaptic transmission:
  • Chemical synaptic transmission: involves the release of neurotransmitters into the synapse
  • Electrical synaptic transmission: involves direct electrical communication between neurons

Ion Channels

• Proteins embedded in the neuronal membrane that regulate the flow of ions
• Types of ion channels:
  • Voltage-gated ion channels: open or close in response to changes in membrane potential
  • Ligand-gated ion channels: open or close in response to binding of neurotransmitters
  • Mechanosensitive ion channels: open or close in response to mechanical stimuli

Depolarization

• A decrease in the negative charge of the neuronal membrane, making it less negative
• Causes:
  • Influx of positively charged ions (e.g. sodium) into the cell
  • Efflux of negatively charged ions (e.g. potassium) out of the cell
• Results in the generation of an action potential if the depolarization is strong enough

Repolarization

• A return to the resting state of the neuronal membrane, making it more negative
• Causes:
  • Efflux of positively charged ions (e.g. potassium) out of the cell
  • Influx of negatively charged ions (e.g. chloride) into the cell
• Occurs during the falling phase of the action potential
• Restores the resting membrane potential, ready for the next action potential

Action Potential

Synaptic Transmission

• Synaptic transmission occurs at the synapse, the gap between two neurons, and involves the release of neurotransmitters from the presynaptic neuron and their binding to receptors on the postsynaptic neuron
• There are two types of synaptic transmission: chemical and electrical
• Chemical synaptic transmission involves the release of neurotransmitters into the synapse
• Electrical synaptic transmission involves direct electrical communication between neurons

Ion Channels

• Ion channels are proteins embedded in the neuronal membrane that regulate the flow of ions
• There are three types of ion channels: voltage-gated, ligand-gated, and mechanosensitive
• Voltage-gated ion channels open or close in response to changes in membrane potential
• Ligand-gated ion channels open or close in response to binding of neurotransmitters
• Mechanosensitive ion channels open or close in response to mechanical stimuli

Depolarization

• Depolarization is a decrease in the negative charge of the neuronal membrane, making it less negative
• Depolarization occurs when positively charged ions (e.g. sodium) flow into the cell or negatively charged ions (e.g. potassium) flow out of the cell
• If depolarization is strong enough, it generates an action potential

Repolarization

• Repolarization is a return to the resting state of the neuronal membrane, making it more negative
• Repolarization occurs when positively charged ions (e.g. potassium) flow out of the cell or negatively charged ions (e.g. chloride) flow into the cell
• Repolarization occurs during the falling phase of the action potential
• It restores the resting membrane potential, ready for the next action potential