Neuroscience Lecture 4 Quiz

Lecture 4 PHCL2610: Nervous System

• Topics covered include Synaptic Transmission, Neurotransmitters, Receptors, and Postsynaptic Potentials.
• Primary material is Vander's Human Physiology 16th Edition, Chapter 6, Section C: Synapses.
• Synaptic transmission is the process of communication between neurons or a neuron and a target cell across a synapse.
• A synapse or synaptic cleft is a microscopic space between neurons or between a nerve terminal and a target cell.
• Neurotransmitters (NTs) are chemical messengers released from axon terminals of presynaptic neurons.
• NTs bind to receptors on post-synaptic neurons and can be excitatory or inhibitory.

Synaptic Transmission

• The process by which a neuron communicates with a target cell (neuron or tissue cell).
• Involves the transmission of signals across a synapse.

Neurotransmitters

• Chemical messengers released by presynaptic neurons.
• Types include: Acetylcholine (ACh), Biogenic amines (e.g. Catecholamines, Dopamine, Norepinephrine, Epinephrine, Serotonin, Histamine), Amino acids (e.g., glutamate, GABA, glycine), Neuropeptides, Gases (e.g., nitric oxide), Purines (e.g., adenosine, ATP), and Lipids (e.g., prostaglandins, endocannabinoids).

Criteria Defining Neurotransmitters

• NTs must be produced within a neuron.
• NTs must be released when a neuron is stimulated. This stimulation is Ca2+ dependent.
• NTs must be inactivated after release.
• Released NTs must produce physiological responses (affecting a post-synaptic receptor).

Removal of Neurotransmitter

• Mechanisms depend on the specific neurotransmitter.
• Reuptake: NT is transported back into the presynaptic terminal for reuse or metabolism.
• Enzymatic transformation: NT is transformed into inactive substances, like acetylcholine destruction at the synaptic cleft. Other transformations occur inside the cell.
• Diffusion: NT diffuses away from the receptor site at the synapse.

Neurotransmitter Receptors

• Neurotransmitters bind to ligand-gated receptors in the synaptic cleft to produce an effect.
• Two categories:
  • Ionotropic Receptors: Ligand-gated ion channels.
  • Metabotropic Receptors: G-protein coupled receptors (GPCRs).

Ionotropic Receptors

• Ligand-gated ion channels.
• Fast neurotransmission. Two functional domains important for this reaction:
  • Extracellular NT binding site
  • Membrane spanning domain that forms an ion channel.
• Include GABA(Gamma-aminobutyric acid), Acetylcholine, Glycine, and serotonin.

Metabotropic Receptors

• G protein-coupled receptors (GPCRs).
• Slow neurotransmission.
• The ion channel is not part of the receptor structure.
• Examples include: Glutamate, Acetylcholine, and monoamines.

How Does a GPCR Work?

• NT binds to the receptor, activating it and changing its conformation.
• The activated receptor activates a G protein.
• The G protein dissociates from the receptor and binds to an effector.
• The effector activity changes.
• Examples of G protein effects include activation/inhibition of effectors.
• Resultant effects include second messenger production or channel activation.

G Proteins and Ion Channels

• G proteins can directly or indirectly open/close ion channels.
• Examples of relevant channels include Ca2+ channels.

Postsynaptic Potentials

• Activation of receptors results in membrane potential changes.
• Excitatory postsynaptic potential (EPSP): Slight depolarization in postsynaptic membrane increasing the likelihood of an action potential.
• Inhibitory postsynaptic potential (IPSP): Slight hyperpolarization in the postsynaptic membrane where generating an action potential is more difficult.

Summation

• Summation is the process through which EPSPs and IPSPs at a postsynaptic neuron are accumulated.
• Summation can be either spatial or temporal.