Neurotransmitter Receptors Quiz

General Principles of Chemical Transmission

• Chemical transmission is a fundamental process in the nervous system, allowing communication between neurons and other cells.
• Learning objectives for this topic include a historical review, differentiating between electrical and chemical transmission, describing the synthesis, storage, and release of chemical transmitters, the process of chemical synaptic transmission, termination, retrograde chemical transmission, synaptic transmission (electrical and chemical), and neurotransmitter recovery and degradation.

The History of Chemical Transmission

• Understanding the function of living organisms developed from experimental physiology studies in the mid-19th century
• The peripheral and autonomic nervous systems received significant attention.
• Studies showed that electrical stimulation of nerves could elicit various physiological effects in the body.
• By 1869, it was established that muscarine mimicked vagus nerve stimulation and atropine inhibited it.
• Du Bois-Raymond (1877) proposed two mechanisms: a chemical mediator or an electrical one.
• In 1904, Elliot suggested adrenaline's role as a chemical mediator in the sympathetic nervous system.
• In 1905, Langley linked nicotine and curare to neuromuscular junctions, suggesting a chemical transmission process.

Synaptic Transmission

• A synapse is a junction where information is transmitted between cells.
• Two main types of synapses exist: electrical and chemical.
• Electrical synapses involve direct transfer of ionic current through gap junctions between cells, providing rapid and bidirectional transmission. Gap junctions are formed by connexons, allowing passage for ions and small molecules. They are common in cardiac muscle and certain smooth muscles.
• Chemical synapses involve a synaptic cleft and neurotransmitter-mediated signal transmission. Information moves across the cleft via a neurotransmitter to another neuron or non-neuronal tissue.

Chemical Synapses

• Four types of chemical synapses are present: axodendritic, axosomatic, axoaxonic, and dendrodendritic.
• The key structures involved in chemical synapses include presynaptic and postsynaptic membranes and a synaptic cleft separating them.

Principles of Chemical Synaptic Transmission

• Neurotransmitter synthesis, loading into vesicles, and vesicle fusion at the presynaptic terminal are fundamental steps.
• Neurotransmitter release into the synaptic cleft is triggered by calcium influx following an action potential.
• Neurotransmitters bind to receptors on the postsynaptic cell, eliciting a cellular response.
• Neurotransmitter removal from the synaptic cleft is vital for terminating the signal.

Retrograde Chemical Transmission

• In certain cases, signals may travel from the postsynaptic neuron to the presynaptic terminal.

Neurotransmitter Synthesis and Storage

• Presynaptic nerve terminal synthesizes neurotransmitters, utilizing precursor molecules, enzymes, and intracellular transport mechanisms.
• Neurotransmitters are packaged into vesicles for storage.

Neurotransmitter Release

• Action potentials trigger neurotransmitter release through exocytosis, where vesicles fuse with the presynaptic membrane.
• Calcium influx is crucial for vesicle fusion and neurotransmitter release.

Recycling of Synaptic Vesicles

• Synaptic vesicles are recycled through endocytosis, using proteins such as clathrin.
• Vesicles return to the presynaptic terminal to be refilled and ready for reuse.

Neurotransmitter Recovery and Degradation

• Clearing of neurotransmitters is necessary to prepare neurons for subsequent transmission.
• Neurotransmitters are transported back into the presynaptic terminal or degraded by enzymes in the synaptic cleft.

Synaptic Delay

• Synaptic delay is the time required for neurotransmitter release, diffusion across the synapse, and receptor binding.
• Synaptic delay is the rate-limiting step for neural transmission.

Synaptic Receptors

• There are two main types of receptors (Ionotropic and Metabotropic) that neurotransmitters bind to.

Ionotropic Receptors

• Ion channels that open directly in response to neurotransmitter binding.
• Typically mediate fast synaptic responses.
• Less selective to ions than voltage-gated channels.

Metabotropic Receptors

• Receptors that are linked to intracellular signaling cascades via G-proteins.
• Typically cause slower, longer-lasting, and more diverse postsynaptic effects.
• More diverse responses than ionotropic receptors.

Neurotransmitter Receptor Mechanisms

• Description of how neurotransmitters interact with receptors.
• Effects of ligand binding and subsequent cellular responses.

Signal Transduction

• Processes of cellular signal transmission and alterations following neurotransmitter interaction with cell surface receptors.

Second Messenger System

• Different second messenger systems and interactions.

Neurotransmitters (Amino acids, Amines and Peptides)

• Classification of neurotransmitters based on chemical structure (amino acids, amines, peptides).
• Examples of each class.

Neurotransmitters (Amino acids)

• Description of specific amino acid neurotransmitters' synthesis and function.

Neurotransmitters (Peptides)

• Description of specific peptide neurotransmitters' synthesis and function.

Nonpeptide Transmitters

• Neurotransmitters synthesized in the presynaptic nerve terminal.

Peptide Transmitters

• Neurotransmitters synthesized in the cell body.

Dissolved Gases (NO, CO)

• Excitatory and Inhibitory mechanisms. Describe the gaseous transmitters' actions on neurons (and other cells.)

Acetylcholine

• Synthesis, release, degradation, and receptor types.

Nicotinic ACh Receptors

• lonotropic, nonselective cationic channels.
• Ligands bind to specific regions on the receptor causing the channel to open.

Muscarinic ACh Receptors

• Metabotropic receptors.
• Five subtypes known as M1 to M5 (all G protein-coupled).

Distribution and Functions of Muscarinic Receptors (M1, M2, M3, M4, M5)

• Locations within the nervous system and general functions (e.g., excitatory or inhibitory effects on smooth muscle).
• Specific functions of each subtype discussed.

Glutamate (Neurotransmitter)

• Major excitatory neurotransmitter in the CNS.
• Synthesis and function.
• Distinct subtypes of ionotropic glutamate receptors, including AMPA, Kainate, and NMDA.

Biogenic Amines (Norepinephrine, Dopamine, Serotonin, Histamine)

• Describe synthesis and function.