Flashcards in Synaptic Integration Deck (27):
two types of summation
Temporal and spatial
occurs when a single presynaptic input fires repeatedly at high frequency
occurs when inputs from different presynaptic neurons arrive simultaneously
Temporal summation depends on these two factors
frequency (how closely spaced these APs are)
decay time (how slowly the membrane potential returns back to base line)
3 passive electrical properties of dendrites
1. Rm (membrane resistance) = 1/g
2. Cm (membrane capacitance)
3. Ri or Ra (internal or axial resistance)
Is internal/axial resistance low or high in a dendrite? Why
The resistance of current down axial will be low, because dendrite is a good conductor, filled with salty solution (high conductance, g, = low resistance, 1/g)
In absence of channels, the membrane resistance Rm is (high/low)
Fewer channels > low conductance > higher Rm
What do capacitors store?
Ability to store an electrical charge
Effect of membrane capacitance
Changes in membrane potential are slower than changes in current (Because of time to charge and discharge the capacitance)
when open channel, immediately get current flowing through, but you get rounded change for membrane potential
temporal summation constant and equation
tao = Rm x Cm
Where is Cm relatively constant?
(no myelin in dendrites!)
In axons, myelin increases/decreases Cm
Myelin reduces Cm (harder to store electrical charge when telephone book vs piece of paper)
Rm depends on
# of channels
Short time constant =
short decay time for membrane potential
How can you increase Rm? What is specific best target?
Close channels, specifically K channels
Spatial summation constant and equation
lambda = square root(Rm/Ra)
Explain Ra relation to diameter (thickness)
Ra is inversely proportional to diameter (thicker diameter, can carry more charge, less resistance)
Determines how far the charge in membrane potential can passively spread out before dying
Myelin (increases/decreases) conduction speed
Effects of myelin insulation on:
-increases Rm (myelin is an insulator, and thus fewer channels blocked by myelin, lowers g increases Rm)
-decreases Cm (capacitance depends on separation of charge. increasing that distance when wrap myelin around, so greatly reduce membrane capacitance / interaction bw outside and inside charges)
Effects of myelin insulation on:
- decrease time constant = faster charging of membrane
(time constant = Rm x Cm > myelin increases Rm, decreases Cm > Cm is more dramatic change)
-increase length constant = greater distance between notes
(length constant = square root(Rm/Ri) > myelin increases Rm, no effect on Ri > longer length constant
The further you separate nodes, the faster the propagation down the axon. Why? How does myelin relate to this?
-nodes require sodium voltage gated channels, which are active processes
-have to be placed to regenerate AP before it dies out
-channels are slower because take time to open and close.
-Area between nodes (myelinated) is passively spread, and passive spread is faster
-Unmyelinated is much slower because constantly opening channels.
Dendrites integrate synaptic potentials:
-longer time constant = ?
-longer length constant = ?
longer time constant = better temporal summation
longer length constant = better spatial summation
Axons faithfully propagate action potentials:
-shorter time constant = ?
-long length constant = ?
shorter time constant = faster conduction velocity
longer length constant = faster conduction velocity
In axon, myelin leads to increased length constant, which means what?
greater distance between nodes