Synaptic Transmission Overview

Overview of Synaptic Transmission

• Synapses are connections between two neurons where communication occurs
• Synapses can be of two types: electrical and chemical
• Electrical synapses involve direct electrical connections between neurons via gap junctions
• Chemical synapses have a synaptic cleft between the pre-synaptic and post-synaptic neurons

Types of Chemical Synapses

• Axodendritic: Pre-synaptic neuron's axon connects to post-synaptic neuron's dendrite
• Axosomatic: Pre-synaptic axon connects to post-synaptic neuron's cell body
• Axoaxonic: Pre-synaptic axon connects to post-synaptic axon

Neurotransmitter Release and Action

• Neurotransmitters are stored in synaptic vesicles in the pre-synaptic terminal
• Arrival of action potential triggers Ca2+ influx, causing vesicle fusion and neurotransmitter release into synaptic cleft
• Neurotransmitters then bind to receptors on the post-synaptic neuron

Ionotropic vs Metabotropic Receptors

• Ionotropic receptors have ion channels that open directly upon neurotransmitter binding
• Metabotropic receptors activate G-protein signaling cascades to indirectly modulate ion channels

Excitatory vs Inhibitory Synapses

• Excitatory synapses cause depolarization and increased likelihood of action potential generation
• Inhibitory synapses cause hyperpolarization and decreased likelihood of action potential

Neurotransmitter Types

• Small molecule neurotransmitters (e.g. acetylcholine, glutamate, GABA)
• Amino acid neurotransmitters (e.g. glutamate, aspartate)
• Biogenic amine neurotransmitters (e.g. dopamine, serotonin, norepinephrine)

Neurotransmitter Removal

• Diffusion out of synaptic cleft
• Enzymatic degradation
• Reuptake by pre-synaptic neuron### Neurotransmitters and Neuropeptides
• Neurotransmitters are molecules that transmit signals across the synapse between neurons.
• Examples of neurotransmitters:
  • Excitatory neurotransmitters: glutamate, aspartate
  • Inhibitory neurotransmitters: GABA, glycine
• Neurotransmitters can be classified into two categories:
  • Small molecule neurotransmitters (e.g., acetylcholine, dopamine)
  • Neuropeptide neurotransmitters (e.g., substance P, neuropeptide Y)

Inhibitory Neurotransmitters

• GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter that reduces neuronal activity.
• Glycine is another inhibitory neurotransmitter that can cause muscle relaxation and reduce pain.

Biogenic Amines

• Biogenic amines are a class of neurotransmitters that include:
  • Norepinephrine (also known as noradrenaline)
  • Serotonin (also known as 5-hydroxytryptamine)
  • Dopamine
• These neurotransmitters play a role in various physiological and psychological processes, such as:
  • Mood regulation
  • Emotional response
  • Motor control
  • Reward and motivation

Nitric Oxide

• Nitric oxide (NO) is a gas neurotransmitter that:
  • Relaxes smooth muscles
  • Dilates blood vessels
  • Plays a role in neurotransmission and neuromodulation
• NO is synthesized on-demand and is not stored in synaptic vesicles.

Carbon Monoxide

• Carbon monoxide (CO) is another gas neurotransmitter that:
  • Has anti-inflammatory effects
  • Regulates insulin release
  • Plays a role in thermoregulation and memory formation
• CO is also synthesized on-demand and is not stored in synaptic vesicles.

Neuropeptides

• Neuropeptides are short chains of amino acids that function as neurotransmitters.
• Examples of neuropeptides:
  • Substance P: involved in pain modulation
  • Neurotensin: involved in pain modulation and gut function
• Neuropeptides can have various effects on the body, including:
  • Pain modulation
  • Gut function
  • Mood regulation

Overview of Synaptic Transmission

• Synapses are connections between two neurons where communication occurs
• There are two types of synapses: electrical and chemical

Types of Synapses

• Electrical synapses involve direct electrical connections between neurons via gap junctions
• Chemical synapses have a synaptic cleft between the pre-synaptic and post-synaptic neurons

Types of Chemical Synapses

• Axodendritic: pre-synaptic neuron's axon connects to post-synaptic neuron's dendrite
• Axosomatic: pre-synaptic axon connects to post-synaptic neuron's cell body
• Axoaxonic: pre-synaptic axon connects to post-synaptic axon

Neurotransmitter Release and Action

• Neurotransmitters are stored in synaptic vesicles in the pre-synaptic terminal
• Arrival of action potential triggers Ca2+ influx, causing vesicle fusion and neurotransmitter release into synaptic cleft
• Neurotransmitters then bind to receptors on the post-synaptic neuron

Receptors

• Ionotropic receptors have ion channels that open directly upon neurotransmitter binding
• Metabotropic receptors activate G-protein signaling cascades to indirectly modulate ion channels

Synaptic Function

• Excitatory synapses cause depolarization and increased likelihood of action potential generation
• Inhibitory synapses cause hyperpolarization and decreased likelihood of action potential

Neurotransmitters

• There are several types of neurotransmitters:
  • Small molecule neurotransmitters (e.g. acetylcholine, glutamate, GABA)
  • Amino acid neurotransmitters (e.g. glutamate, aspartate)
  • Biogenic amine neurotransmitters (e.g. dopamine, serotonin, norepinephrine)
• Examples of neurotransmitters:
  • Excitatory neurotransmitters: glutamate, aspartate
  • Inhibitory neurotransmitters: GABA, glycine

Neurotransmitter Removal

• Neurotransmitters can be removed through:
  • Diffusion out of synaptic cleft
  • Enzymatic degradation
  • Reuptake by pre-synaptic neuron

Biogenic Amines

• Biogenic amines are a class of neurotransmitters that include:
  • Norepinephrine (also known as noradrenaline)
  • Serotonin (also known as 5-hydroxytryptamine)
  • Dopamine
• These neurotransmitters play a role in various physiological and psychological processes, such as:
  • Mood regulation
  • Emotional response
  • Motor control
  • Reward and motivation

Gas Neurotransmitters

• Nitric oxide (NO) is a gas neurotransmitter that:
  • Relaxes smooth muscles
  • Dilates blood vessels
  • Plays a role in neurotransmission and neuromodulation
• Nitric oxide is synthesized on-demand and is not stored in synaptic vesicles
• Carbon monoxide (CO) is another gas neurotransmitter that:
  • Has anti-inflammatory effects
  • Regulates insulin release
  • Plays a role in thermoregulation and memory formation
• Carbon monoxide is also synthesized on-demand and is not stored in synaptic vesicles

Neuropeptides

• Neuropeptides are short chains of amino acids that function as neurotransmitters
• Examples of neuropeptides:
  • Substance P: involved in pain modulation
  • Neurotensin: involved in pain modulation and gut function
• Neuropeptides can have various effects on the body, including:
  • Pain modulation
  • Gut function
  • Mood regulation