Postsynaptic Potential
- brief changes in membrane potential of the postsynaptic cell caused by the release of neurotransmitters
Whether cell excites or inhibits is dependent on the neurotransmitter
Excitatory postsynaptic potential (EPSP)
- pushes the postsynaptic cell closer to threshold for AP
- -> Depolarizing
Synaptic delay
- Delay between arrival of Ap at axon terminal + creation of a postsynaptic potential
- Reflects the time needed for neurotransmitters to diffuse into synaptic cleft
Inhibitory postsynaptic potential (IPSP)
- moves postsynaptic cell away from threshold for AP
- -> Hyperpolarizing
- increase of resting membrane potential
Spatial summation
The simultaneous summation of potentials ( E / IPSP ) from different locations ( dif. postsyn. membr. ) across the cell body
Temporal summation
- not absolutely simultaneous
- -> the closer they are in time - the greater the overlap
Role of distance in EPSPs
Simultaneous EPSPs from synapses closer to the axon hillock will produce a larger sum than those farther away
Ligand
- molecule of the perfect/correct shape for a receptor
- -> Schlüssel-Schloss Prinzip
-can activate or block the receptor
Endogenous ligands
Neurotransmitters/Hormones made inside the body
Exogenous ligands
Drugs/Toxins that work as neurotransmitters from outside the body
Agonist
Molecule that acts like a neurotransmitter
--> high efficacy
Antagonist
Molecule that prevents the action of a transmitter
--> low efficacy
Ionotropic receptors
control ion channels directly
–> when bound, ion channels open immediately
Metabotropic receptors
activate G-Proteins, which in turn activate ion channels
–> indirect control of ion channel
G-protein
molecule,
- either directly opens ion channel
- or activates another chemical signal which then opens the ion channel
Degradation
Special enzyme breaks transmitter down into pieces
--> products are recycled to make more of the transmitter in the axon terminal
Reuptake
Special receptors of the transmitter are located in the presynaptic membrane and bring the transmitter back inside its the help of transporters
Convergence
Type of neural circuit
- many cells send signals to one
Divergence
Type of neural circuit
- one cell sends signals to many
Binding Affinity
the degree of chemical attraction between ligand and receptor
Efficacy
Propensity (Neigung) of a ligand to activate the receptor to which it is bound
Partial Agonist
A partial agonist is a drug that has a very
high affinity for a particular receptor but activates that
receptor less than the normal ligand does
Division of a Synapse
- Presynaptic Membrane = usually axon terminal
- Synaptic Cleft = gap between pre- and postsynaptic membrane
- Postsynaptic Membrane = usually dendrite
Synaptic Transmission
- AP arrives at axon terminal
- Depolarization opens voltage-gated Ca2+ channels in the membrane of axon terminal
- -> Ca2+ ions enter the terminal
- Exotysis= Ca2+ causes vesicles to fuse with presynaptic membrane, rupture, release transmitter into synaptic cleft
- -> mediated by V/T-Snare and Synaptotagmin
- transmitter molecules cross the cleft to bind to special receptors in postsynaptic membrane
- ion flow creates a local E/IPSP in the postsynaptic neuron
- Synaptic transmitter is either inactivated (Degradation) or removed (Reuptake) from synaptic cleft by transporters
- Synaptic transmitters may also activate presynaptic autoreceptors
