0414 - AP propagation and synaptic integration - EG Flashcards
Provide a brief overview of an action potential.
When the resting membrane potential reaches threshold (due to positive stimulus) the voltage-gated Na+ channels open, and influx of Na+ results in depolarisation of the membrane and conductance of nervous transmission. Slowly, voltage-gated K+ channels open, and efflux of K+ results in repolarisation of the membrane, and reset of membrane to resting membrane potential.
What influences the conduction velocity of an AP?
Internal resistance (Ri) and membrane resistance (Rm). The lower the internal resistance (larger diameter) the higher the length constant and increased velocity. The higher the membrane resistance (increased myelination) the higher the length constant and increased velocity.
How does Vm change in a passive membrane over distance and time?
Vm diminishes over distance dependent on the length constant and time constant. The higher the length constant the further a potential can spread.
The length constant is determined by internal resistance (axon diameter) and membrane resistance (myelination). The time constant refers to decay of Vm over time.
What is an excitable membrane?
One that can carry an AP, therefore contains voltage-gated channels.
Why does an AP only go in one direction?
Due to the inactivation of voltage-gated Na+ channels for enough time to prevent an AP from propagating backward.
Where are passive membranes in a nerve cell?
The axon is a passive membrane, so Vm decays over distance from the axon hillock.
What are nodes of Ranvier?
Gaps between two adjacent myelin sheaths along an axon that contain higher concentration of Na+ channels, making them more likely to fire at threshold. They are spaced apart sufficiently so that they can sense the change in Vm of the preceding node. Results in salutatory conduction of “jump” of depolarisation from node to node.
Can a neuron fire from one EPSP?
No as too small to reach threshold. requires either multiple EPSPs at once (spatial summation) or repetitive EPSPs that are successive enough to reach threshold (temporal summation)
What is synaptic integration?
The computation of multiple synaptic inputs (EPSPs and IPSPs) to produce a single output (fire or not fire). Occurs within the soma, and when threshold is reached triggers the axon hillock to fire an AP.
List the various synaptic configurations and their typical roles.
Axodendritic, excitatory; axosomatic, inhibitory; axoaxonic, modulatory.
What is shunting inhibition?
An effective way to inhibit a membrane potential, due to inhibitory stimulus often near the axon hillock.
What is synaptic plasticity and what receptor plays an important role in this?
Synaptic plasticity is the ability of synaptic contacts to change their connective strength. An increase is long term potentiation (LTP) and a decrease is long term depression (LTD). The NMDA receptor plays an important role as a coincidence detector to increase synaptic strength in regularly activated cells.
