Synaptic Transmission Flashcards
synapse
junction between two cells, often two neurons, but can be any 2 cells
can be electrical or chemical
convergence
many pre-synaptic neurons affecting a single post-synaptic neuron.
can recieve signals from ~10,000 cells.
action potentials are often a result of the sum on all the connections
Do we physically change when we learn?
We change the number and quality of our dendrites
There is no difference in the number of neurons, but there is a difference in the number of neuronal connections
Electrical Synapses
- These are rare
- Are formed between 2 cells that are connected by gap junctions
- The junctions are big enough so that many types of molecules can be shared vetween the adjacent cells
- Signal passes extremely rapidly
- Signal can be bidirectional, or pore configurations can limit direction
- passage of signal is guaranteed and does not require amplification
Chemical synapses
Includes a presynaptic neuron in which the AP triggers release of a chemical into the extracellular space. The chemical binds to chemically gated ion channels on post-synaptic neuron triggering a graded potential and potentially an action potential in the post-synaptic neuron
Where are ribosomes located?
Just outside the nucleus
Which protein does anterograde NT transport?
Kinesin
Which protein does retrograde NT transport?
Dynein
Anterograde transport
- Transport from the cell body to the axon terminal
- Transports nutrients, enzymes, mitochondria, neurotransmitters
- uses kinesin
- can moce up to 15 inches a day
Retrograde transport
- transports from the axon terminal to the cel body
- moves recycled vesicles, and recycled NT
- uses Dynein
Neurotransmitter release
The end product of AP in many neurons.
NT are encased in vesicles
Vesicle-cell membrane fusion is required for release
Divergence
Then one presynaptic neuron has many acon terminals and forms many synapses
What voltage gated ion channels are at the axon terminal?
Na, K, Ca
What happens with Ca when the depolarization reaches the axon terminal
Voltage gated ion Ca channels open and Ca2+ rushes into the cell.
Ca then binds to receptors on the vesicle membrane, triggering a shape change that allows the vesicle membrane to fuse with the cell membrane.
Explain the events in the synaptic cleft
NT moves throuhg the synapse by diffusion, and binds to the receptors on the post synaptic cell. (This occurs slowly ~0.2ms)
What can change the efficiency of NT signalling in the synaptic cleft?
- The concentration of receptors on the post synaptic cell
- The concentration of NT in the synapse.
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What happens when there is more NT in the synapse?
More NT=more receptors bound=Bigger Graded potential
What are three methods for removing NT from the synapse?
- Re-uptake
- Diffusion
- Breakdown by enzymes in the presynaptic cleft
Reuptake
NT is actively transported back into the presynaptic neuron or the surrounding glial cells
Can presynaptic synapses release more than one NT?
Yes
Which ion triggers synaptic vesicles to merge with the plasma membrane?
Ca
What triggers Ca channls to open?
A + intracellular voltage
What is true about a relative refractory period?
Some Na channels are inactivated, and some are closed.
An AP can occur if the stimuli is strong enough.
Can graded potentials moce the cell closer to and further from threshold?
Yes
Can action potentials moce the cell closer to and further from threshold?
No. They are all or nothing and always depolarize to the same amplitude.
Excitatory post-synaptic potential (EPSP)
If the binding of an NT to a receptor on the post synaptic neuron results in depolarization
One EPSE changes the RMP 0.5mV (a 15mV change is needed to reach threshold)
Inhibitory post synaptic potential (IPSP)
the binding of an T to a receptor on the post synaptic neuron results in hyperpolarization.
Can happen either by allowing + ions out of the cell(like K), or letting - ions into the cell (chloride)
Summation
adding graded potentials together to reach threshold and spark an action potential
Temporal Summation
Fires EPSP after EPSP within a short period of time, so the membrane does not have time to repolarize, and summation occurs to reach threshold.
Spatial Summation
Multiple EPSPs from different presynaptic neurons, adding up to reach threshold
Factors that effect synaptic strength/summation
- Availability of NT/NT precursor molecules
- Availability of Ca outside the presynaptic neuron
- Receptor concetration/sensitization on post synaptic neuron
- Enzymatic destruction of NT in synaptic cleft
- diffusion factors
Synaptic plasticity
- Receptor expression can be up/down regulated.
- Another set of chemicals, neuromodulators can effect the availability og NT in eurons
- receptors can desensitise
