Dr Straub Flashcards
Estimated neurons in CNS human
- 10^11 neurones and >10^14 synapses
Describe complex neuronal actiity
multiple contact sites for neurons!
Why is synaptic integration important
Neurons receive multiple synaptic inputs:
- From the same and/or different neurons
Neurons provide multiple synaptic outputs
- To the same and/or different neurons
- synaptic integration enables information processing in the CNS
- integration of synaptic inputs determines nervous system function
What parameters effect neuronal integration (3 + explain)
1)Neuronal morphology and synapse distribution
Complexity of neuritic processes
Distance of synapse to soma
Relative position of synapses to each other
2)Synaptic properties
Amplitude of current flow at synapse - most single synapses only produce relative modest postsynaptic membrane potential changes (~ 1-2 mV at the soma) multiple synaptic inputs are required to depolarise neuron sufficiently to trigger action potential
3)Membrane properties
Length constant affects spatial summation
Time constant affects temporal summary
What are the two aspects of synaptic integration?
- Spatial
- Temporal
Describe spatial synaptic integration
- What happens if multiple impuses arive from different synapses on the same cell (from one neuron multiple contact sites)
- Or activity in more than one presynaptic neuron sites on dendretic tree activated simutaneously (many neurons coinciding)
- Summartive (add them up) eg Purkinje cell beautiful dentretic trees multipolar - recieve two types of impulse, from climbing fibres (one per purkinje multiple contact sites) - Parallel fibre ( thousans of parallel fibres single synaptyic contact between one and one tree, multiple parrallel cells)
Describe temporal synaptic integration
- Passive so will decrease over distance - how much is termined by legnth constant
- Decays exponentially
- lambda length constant is the point when it has declined to 37% so Vm = VEPSPmax X e^(-x/lambda)
Whats the different between the parallel and climbing on impulse
Parallel - single contact small synaptic current and pptential
Climbing - large synaptic current and potential fro multiple contact triggers complex spike
SUMMAAARY
Temporal and spatial integration of synaptic inputs is dependent on passive membrane properties (time constant and length constant)
Postsynaptic potentials decay exponentially with time and distance from site of origin
time: V(t)=Vmax x e^(-t/t) t = rm x cm
distance: V(x)=Vmax x e^(-d/l) length constant = root(rm / ra)
Synaptic inputs alter the passive properties of dendrites (length constant and time constants) affects (inhibits) spread of membrane potential changes
Describe the legnth constant
- passive membrane property
- determined by membrane resistance (rm) and resistance along the dendrite (ra)
- describes the spatial characteristic of membrane potential changes,i.e. how a potential change will decrease along a dendrite
- LArge membrane resistance means long length constant if exon resistance is high there will be a low length constant
When can/can’t AP be combined
- when two passively progating signals meet
- It can’t at a new synapse because:
Activity at synapse 1 opens ion channels
Change in membrane resistance
Change in length constant (decrease)
Effect of synapse 2 and/or synapse 3 on cell soma potential is changed
The effect of the time constant on AP
- Short PSP- o temporal summation
- Long PSP - temporal summation (PSPs add up)
- time constant— Vm=VEPSPmax X e^(-t/tau)
- tau=RmxCm
- greater membrane resistance means less leakage so a PSP lasts longer
- greater Cm means can store more meaning longer PSP
SUMMARY leccy 2
Time constant determines whether neuron acts as temporal integrator (rate coding) or coincidence detector
EPSP and IPSP summate, but summation is only linear when synapses are on different dendrites so that changes in membrane resistance do not affect spread of EPSP or IPSP
“Silent” postsynaptic inhibition: Inhibitory synapses can affect EPSPs, even if they do not cause a change in membrane potential
Synaptic integration can be studied using photo-release of ‘caged’ glutamate to simulate effect of glutamate release at individual synapses
Overall effect of synaptic inputs is strongly dependent on the order/precise timing of synaptic inputs
SUMMARY L3
Synapses can undergo short-term activity dependent changes
Synaptic facilitation
Synaptic depression
Synapses with low release probability are more likely to show synaptic facilitation and synapses with high release probability depression
Heterosynaptic modulation of synapse function:
Altering sensitivity of postsynaptic neuron to presynaptic transmitter release – can lead to facilitation or depression of synapse
Altering presynaptic transmitter release by modulation of presynaptic calcium influx – can lead to facilitation or depression of synapse
LTP is a mechanism of long-term synaptic plasticity and considered as a cellular mechanism for learning
What is a temporal integrator
long time constant means majority of EPSPs contribute to the AP and the timeing of APs is only weakly linket to impu pattern but gives a good average
