3- Synapses Flashcards
Define synapses ?
Area of contact between 2 neurons
Synaptic knob site ?
Distal end of the axon
Synapses classified according to site ? (3) ( most common)
1- axo-dendritic (80-95% ) least excitable & most common
2- axo-axonic most excitable
3- axo-somatic junction
Types of synapses ?
Electrical & chemical
Define electrical synapses ?
Presynaptic & postsynaptic neuron membrane come close together forming area of fusion= gap junction
Gap junction form a —— resistance bridge that allows ———- conduction of electrical potentials ?
Low , rapid
impulse in the pre-synaptic axon causes secretion of ——————- at the synapse ?
chemical transmitter
chemical transmitter act on receptors in the ?
Postsynaptic neuron
Process of synaptic transmission involves ? (3)
1- release of transmitters into synaptic cleft
2- action of transmitter on postsynaptic
3- termination
Depolarization of synaptic knob membrane cause ————————?
Transient opening of voltage gated Ca++ = inflow
Neurotransmitter released into synaptic cleft is proportional to ————- entered synaptic knob ?
Calcium
Ligand channels 2 types ? Mention them
1- cation channels
2- anion channels
Cation channels allow passage ——-,——,—— ?
Sodium , potassium, calcium
Na+ influx is ———- than K+ efflux leading to ——————of postsynaptic membrane ?
Grater
Depolarization
Na+ influx is grater than K+ efflux leading to depolarization of postsynaptic membrane
The Transmission that produces this effect is called ?
Excitatory transmission ( Adrenalin or acetylcholine)
Excitatory postsynaptic potentials is ?
Opening of ion channels which leads to depolarization & the inside of postsynaptic become less negative
Anion channels allow mainly ————- postsynaptic membrane?
Chloride
Chloride ion reflux leads to —————of postsynaptic membrane thus ————- postsynaptic neuron ?
Hyper polarization, inhibit
Neurotransmitter that open chloride ion channels is called ?
Inhibitory transmission
Hype polarization is produced by ?
Inc rate of k+ outflow
Second messages receptor system is ?
G-protein
(slide 18)
The movement of a component freely within the postsynaptic cell leads to?
1- Opening of specific ion channels e.g. second messenger gated K+ channels K+ efflux & hyper-polarization of postsynaptic membrane
2- Activation of particular enzyme systems that control the metabolic pathways in the neuron as CAMP, and cGMP.
3- Regulation of gene transcription & formation of new protein.
Summation 2 types ?
Spatial & temporal
Spatial summation is ?
Many synaptic knobs discharged at same time = EPSP leading to action potential
Temporal summation is ?
Single presynaptic knob discharge repetitively = EPSP produced by preceding stimulus
Post-synaptic inhibition?
The pre-synaptic neuron secretes inhibitory chemical substance that causes hyper-polarization of post-synaptic neuron by increase chloride influx or increase potassium efflux resulting in IPSP.
Pre-synaptic inhibition?
In pre-synaptic inhibition the inhibitory knobs lies directly on the termination of the excitatory pre-synaptic fiber.
- release inhibitory chemical transmitter which decreases the release of chemical transmitter by the pre-synaptic terminal.
Presynaptic facilitation?
lie on terminal nerve fibrils
• neurotransmitter chemicals secreted at such terminals frequently cause facilitation
• Circuits of this type could lead to short- term memory.
