0414 action potential propagation and synaptic integration Flashcards
What does the membrane resistance of an axon describe? What does the internal resistance describe?
The membrane resistance describes the permeability of the axon membrane to ions (is affected by myelinnation and presence of channels). The internal resistance generally refers to the diameter of the axon
What is a passive membrane and what is an excitable membrane? Where in the neuron is each of these found
Passive membrane = no voltaged gated channels (e.g. the dendrites, the myelinnated parts of the axon). Excitable membrane = voltage gated ions (e.g. the axon hillock, the nodes of ranvier)
What is the length constant ?How does internal and membrane resistance affect it (what factors influence these resistances)
The length constant is the distance when membrane potential = 0.37 original MP. Increasing internal resistance increases length constant (e.g. myelinnation). Increasing the membrane resistance decreases length constant (e.g. thinning of axon)
Why do action potentials propagate in one direction? Explain the mechanism
Due to ion channel inactivation. Once a VG channel is open, an inactivation gate subsequently blocks the openning (0.5-1ms). It resets when the membrane repolarises. Thus, inactivating the gates until the AP has moved far enough to not stimulate another AP
What is the absolute and relative refractory period.
The absolute refractory = second AP cannot be initiated (basically depolarisation to repolarisation). Refractory period = second AP requires stronger stimulus (basically hyperpolarisation)
What cells maintain and produce myelin sheaths in the CNS and PNS
Oligodendrocytes =CNS and schwann cells = PNS. Just think oleg plays with swans. Also, oleg is close to us (therefore in our head)
What are nodes of ranvier? Why are they more sensitive to firing
Nodes of ranvier are gaps between adjacent myelin sheaths on the axon. They are more sensitive to firing because of increase [Na channels]. The ‘boost’ the AP signal
What is saltatory conduction
Saltatory conduction is the depolarisation jump from one node to another
Describe the process of neuronal computation and Synaptic integration
Synaptic integration is the integration of all EPSP and IPSP inputs from the dendrites to determine either firing or non-firing of the axon hillock. Neuronal computation is the computation or decision making trait of neurons
Describe some factors that would affect a signal (EPSP or IPSPs) influence on synaptic integration
The strength of the signal, the frequency of the signal, the type of connection (from dendrite to postsynaptic location) and these same factors for the other signals (i.e. are there other EPSPs and IPSPs)
What is the ‘decision’ of whether to fire or not to fire made in the neuron
At the axon hillock (aka trigger zone)
Most dendrites do not have voltage gated channels. List 2 examples of cells that are exceptions
Sensory neurons and pyramidal cells (cortex)
Which constants govern spatial summation and temporal summation
Spatial summation is governed by length constant (how far an AP traveks). Temporal summation is governed by time constant (how long an AP lasts)
What are the 4 types of synaptic configurations and what type of input are they generally (excitatory, inhibitory or modulatory)
Axodendritic (excite), axosomatic (inhibit), axoaxonic ( modulate) and dendrodendritic/somasomatic (no common)
True or false:synaptic contacts near the cell boy and trigger zone have greater influence (compared to other connections)
True
