Synaptic Transmission Flashcards
What are the four primary regions of a neuron?
Dendrites, cell soma, axon (covered with a myelin sheath), synaptic terminals
In a neuron, what is the primary area for receiving and integrating complex information?
dendrites
What is the name for the region where the axon emerges from cell body?
axon hillox
What is the function of the presynaptic terminal?
convert electrical signal that was propagated down the axon into chemical signals (neurotransmitter
Describe postsynaptic potentials?
small graded changes
What does the axoplasm contain?
parallel arrays of microtubules and neurofilaments that give stability and means of transport
Which direction does kinesin move?
Anterograde (from cell body to presynaptic terminal)
Which direction does dynein move?
Retrograde (from presynaptic terminal to cell body)
Describe the speed and directionality of electrical synapses?
Extremely fast and usually bidirectional
How are electrical synapses transmitted?
Allow direct passive flow of electrotonic current between cells by gap junctions
What are gap junctions composed of?
6 connexins form connexons. Then 2 connexons in adjacent cells form a hemi- channel which results in a gap junction
Benefit of chemical synapses?
Provide directionality, amplification, potential for excitation and inhibition, plasticity, and integration in space and time
What are the criteria for chemical neurotransmitters?
1- present in the presynaptic terminal
2- released in a voltage and calcium dependent manner
3- specific receptors present in the postsynaptic target cell
4- means to inactivate the neurotransmitter
What are the 7 steps in synaptic transmission?
1- Transmitter molecules are synthesized and packaged in vesicles
2- an action potential arrives at the terminal
3- depolarization of terminal opens volt gated calcium channels
4- increased calcium in terminals triggers vesicle fusion
5- transmitter diffuses across cleft & binds to postsynaptic receptors
6- a postsynaptic response occurs
7- transmitter molecules are cleared/ inactivated by enzymatic degradation, uptake, or diffusion
What are active zone in presynaptic terminals?
regions where a subset of vesicles are “docked”
What is the the electron dense region in the postsynaptic cell?
Postsynaptic density (they are alighed with the active zones of presynaptic cells)
How are neurotransmitters released from presynaptic cells?
exocytosis
What are the V-snares involved in neurotransmitter release?
synaptobrevin and synaptotagmin (Calcium sensor)
What are the T-snares involved in neurotransmitter release?
SNAP-25 and syntaxin
How is vesicle membrane recycled?
endocytosis
What are the two classifications of postsynaptic receptors?
ionotropic and metabotropic
What are the properties of an ionotropic receptor?
Contains an ion channel as part of its structure and transmitter binding triggers a rapid response
What are the properties of a metabotropic receptor?
Linked to G-proteins that transduce a slower biochemical signal
What type of receptors does acetylchole bind to?
Both ionotropic (fast response) and etabotropic (slow response)
How are postsynaptic potentials produced?
Conductance changes due to ion channel openings lead to ionic current flow through the channels that lead to changes in the membrane potential
What do excitatory PSPs do?
Increase the probability that an action potential will be triggered
What do inhibitory PSPs do?
Decrease the probability that an action potential will be triggered
What type of NT is glutamate?
Major excitatory NT that binds to ionotropic and metabotropic receptors
What is the fast/ ionotropic receptor for glutamate?
AMPA. Allow for flow of Na+ and K+ down their electrochemical gradient
What is the slow/ ionotropic glutamate receptor?
NMDA. Allow for flow of Na+, K+, and Ca2+ ions
What type of NT is GABA?
Major inhibitory transmitter that binds to ionotropic and metabotropic receptors
The binding of GABA to ligand gated channels causes?
Hyperpolarization of the target cell
What is decremental conduction?
the large amount of potential that is lost by leakage through the membrane of the dendrite before EPSPs can reach the cell soma
What are synaptic potential changes?
Local passive events that become progressively smaller at greater distances from the stimulus
What is temporal stimulation?
Involves EPSPs produced at one synapse by two sequential action potentials. The membrane time constant plays a role in how fast the first synapse dissipation (with a longer time constant the first EPSP is still present)
What is spacial summination?
When action potentials in two neurons produce EPSPs at their synapses, which propagate by passive conduction to the soma and axon hillox
The membrane time constant plays a role if the synapses summate (happens when the time constant is longer)
When does temporal stimulation occur?
When EPSPs from the same cell arrives in rapid succession
When does spatial summation occur?
When EPSPs are received simultaneous from multiple cells.
