Excitatory and Inhibitory Neurotransmission Flashcards
What does an entry of +ve ions or an exit of -ve ions result in?
A positive change
What does an exit of +ve ions or entry of -ve ions result in?
A negative change
What do neurons regulate regarding transmitter discharge?
The timing and location by invoking the mechanisms of excitation and inhibition
What occurs in the opening of Na channels?
Inward flow - depolarisation, excitatory
What occurs in the opening of Ca channels?
Inward flow - depolarisation, excitatory
What occurs in the opening of Cl channels?
Inward flow- hyperpolarisation, inhibitory
What occurs in the opening of K channels?
Outward flow- hyperpolarisation, inhibitory
Does a Na channel agonist cause excitation or inhibition?
Excitation
Does a Na channel antagonist cause excitation or inhibition?
Inhibition
Does a K channel agonist cause excitation or inhibition?
Inhibition
Does a K channel antagonist cause excitation or inhibition?
Excitation
What can inactivate neurotransmitters?
Enzymes
What happens when neurotransmitters are returned to axon terminals?
Reuse, transported into glial cells
How can neurotransmitters leave the synaptic cleft?
Diffusion
In what two ways may neurotransmitters act on ion channels?
Directly or indirectly
What is direct gating carried out by?
Ionotropic receptors
What is indirect gating mediated by?
Activation of metabotropic receptors
What is a key feature of an ionotropic receptor?
Receptor is an integral component of the molecule that forms the channel it controls
What is significant about metabotropic receptors and the channel it controls?
They are distinct
Which ligand-gated channels are pentamers?
GABAa, Glycine and ACh (nicotinic) channels
Which ligand-gated channels are tetramers?
Glutamate channels
How can ionotropic glutamate receptors be classified?
Via their response to non-endogenous agonists that mimic glutamate
What do non-NMDA receptors do?
Bind the agonists kainate or AMPA controlling a channel permable to Na+ and K+. Mediate fast excitatory transmission
What do NMDA receptors do?
Control a channel permeable to Na+, Ca2+ and K+. Contribute a slow component to the excitatory synaptic potential
Why are NMDA receptors thought to promote neurotoxicity?
High permeability to Ca2+
What 2 receptors does GABA act on?
Ionotropic GABAa receptor (Cl- channel) and metabotropic GABAb receptor (K+ channel)
What is benxodiazepines moa?
Positive allosteric modulator of the GABAa receptor so enhance Cl entry, decrease rmp, and enhance inhibition in presence of GABA
What are barbiturates moa?
Similar to benzos and potentiates the effect of GABA at the GABAa receptor
What is Baclofen’s moa?
Agonist of the GABAb receptor so enhances the K current (and increase inhibition)
What is glycine released by in the spinal cord?
Interneurones to inhibit antagonist muscles motoneurones
What do ionotropic channels function as?
On-off switches
Which receptor gating of ion channels if faster?
Ionotropic (ms), metabotropic is slower (tens of ms)
What kind of action do metabotropic receptors have?
Modulatory synaptic actions
What are some modulatory actions of metabotropic receptors?
Acting on channels in presynaptic terminal to modulate transmitter release, modulating transmitter-gated channels to regulate the size of the post synaptic potential, modulate resting and voltage-gated ion channels in the neuronal soma to alter resting Em and AP firing pattern
What is a fast EPSP due to?
Activation of nicotinic (ionotropic) ACh receptors. Channels conduct Na+ and K+
What does a slow EPSP follow?
Activation of muscarinic (GPCR) ACh receptors. ACh closes a K+ channel (M-type)
What is the EPSP?
A depolarizing change in rmp caused by the actions of excitatory neurotransmission. Multiple EPSPs or very large EPSPs can cause rmp to cross threshold and result in an Action Potential (AP)
What is the IPSP?
Negative change in rmp caused by release of an inhibitory neurotransmitter. Inhibits crossing of the threshold and inhibits AP.
What is the graded potential?
A change in the rmp caused by an EPSP or IPSP, such a change is caused by (inhibitory or excitatory) neurotransmitter release and is not of a magnitude large enough to cross threshold and result in an AP
What increases the amplitude of the graded potential, and what does this mean?
Sodium entry, the higher the amplitude the further the spread of signal
What is an interneurone?
A locally-acting neurone, typically releases GABA and so brings about an IPSP and inhibition, function is local processing of information
What are neurotransmitters released in?
Discrete packages called quanta
What are some strategies to increase quantal release?
Extensive innervation, mega humongous presynapse
