Session 5: Neurotransmitters Flashcards
True or false. Receptor (generator) potentials and postsynaptic potentials are both graded.
True.
Both potentials are graded changes of membrane excitability that decay away form the site of stimulation.
In the graded potentials, at what location must the membrane potential reach a threshold level? What is contained here?
The critical point on the axon (initial segment, axon hillock), which contains the voltage-gated channels.
What happens if threshold depolarization is not achieved at the axon hillock?
No action potential is initiated.
What are the two possible mechanisms that neurotransmitters influence the postsynaptic cell?
- Ionotropic
2. Metabotropic
What are ionotropic receptors?
localized receptors that act directly on an ion channel
What are metabotropic receptors?
receptors are located at some point on the membrane, but activate an ion channel some distance away via a second messenger system (aka g-protein-coupled receptor).
What is required internally for a second messenger system?
Internal cellular mechanism that may be long acting via changes in enzyme/protein expression.
What are neurotransmitters co-localized with? Where?
Neuropeptides in axonal terminals.
Give examples of neurotransmitters co-localized with neuropeptides.
GABA has been found with various classes of calcium binding proteins specific to different structures/regions in the brain:
- GABA/calbindin in the frontal lobe
- GABA/paralbumin in occipital lobe
Exact function of colocalization is not clear, but what is a possible explanation?
The peptide acts as a neuromodulator by modifying the activity of the cell during neurotransmission, as well as prolonging membrane activity.
What determines the action (excitatory vs. inhibitory) of the neurotransmitter? Give examples.
The post-synaptic receptor determines the action, i.e. what kind of ion channel the receptor is located on.
- ACh (nicotinic) with Na+ channels
- GABA and glycine with Cl- channels.
True or False. Fast neurotransmitters are associated with ionotropic receptors, not metabotropic receptors.
False. While Fast neurotransmitters are associated with ionotropic receptors, they also act on metabotropic receptors.
What is acetylcholine?
A fast, excitatory neurotransmitter. Ionotropic but may also have a metabotropic receptor.
What is gamma-aminobutyric acid?
GABA is a fast inhibitory neurotransmitter. Ionotropic but may also have a metabotropic receptor.
What are catecholamines? Give examples.
Fast excitatory neurotransmitters. Only act through metabotropic receptors.
Examples: norepinephrine, epinephrine, dopamine
