Lecture 4 Flashcards
Post Synaptic Receptors
a transmitter agent diffuses across a synapse and bind to a specific site on a receptor protein embedded in postsynaptic membrane
Ionotropic
directly opens channels
Metabotropic
initiates a metabolic cascade to activate enzymes
2 types of receptors
1) ionotropic
2) metabotropic
Ionotropic Effects
ligand binding opens an ion channel
Metabotropic Effects
Binding of the ligand to the post-synaptic metabotropic receptor activates an enzyme that is usually G-protein coupled
4 Ligands for ionotropic receptors
- Acetylcholine
- Glutamate
- GABA
- Glycine
Beta- Adrenoreceptor
A metabolic receptor for noradrenalin (NA)
6 Ligands for Metabotropic Receptors
- ACh: muscarinic receptor
- Peptides: substance P, Beta-endorphin, ADH
- Catecholamines: noradrenaline, dopamine
- Serotonin
- Purines: adenosine, ATP
- Gases: NO, CO
PSPs (Postsynaptic potential)
are generated in in excitable membrane (are neuronal dendrites and cell bodies- does not have high density of voltage-gated Na+ channels thus, can NOT initiate an AP)
Nearest excitable membrane is at the ___________ of the axon (trigger zone )
beginning
Spread of PSPs
the binding of a transmitter generates PSP
- PSP must spread through passive conduction across the membrane to get to the initial segment of the axon
EPSPs
excitatory postsynaptic potential
PSP Summations
loss of current (AP) occurs along the membrane due to the poor cable property of biological tissues before the AP reaches its trigger zone
2 Types of Summations
- spatial summation
- temporal summation
Spatial summation
minimum of 10-30 synchronous EPSPs in dendritic tree, each generated at a different synapse
Temporal summation
only a few active synapses, but each generating EPSPs at high frequency; summated potentials reach threshold over a period of time
Spatial Summation
Large number of EPSPs in synchrony
Temporal Summation EPSPs
last for about 30-40 ms in duration before dying out, thus, successive inputs on any given synapse generates subsequent EPSPs that add on to pre-existing EPSPs (e.g. 10 ms apart)
Inhibitory Post-Synaptic Potential
IPSPs tend to be preferentially located on the cell soma, interposed ½ way between the site where EPSP is generated and the trigger zone
IPSP (Cl- Channel)
- IPSP involves the opening of the Cl- channel
- The equilibrium potential for Cl- is very close to the resting MP (-70 mV)
- Therefore at rest, opening of the Cl- channel would result in little change
After Hyperpolarization
Voltage-gated K+ channels at trigger zone cause after hyperpolarizations
A Spike Train
the sequence of neuronal firing timings, where a spike refers to the firing of an action potential.
