excitable cells 3 Flashcards
(9 cards)
why does saltatory conduction happen
-Ion channels have restricted distributions
-need to have spaces between the sheets
-Myelin increases spead and distance that action potentials travel
-Focal accumulations of Na+ channels
Axons vs Dendrites
-Dendrites have voltage-sensitive channels but don’t usually produce AP’s
what’s Coding by Action Potentials
-Continuous stimulation of a neurone produces a ‘train’ of action potentials
whats the frequency of an action potential dependent on
-the size of the depolarizing stimulus
-the stronger the stimulus the higher the frequency
-this provides a way to encode stimulation intensity in the nervous system
whats the absolute refractory period
-1 ms no matter what you do, the neuron is incapable of generating another action potential
-often followed by relative refractory period (a few more ms) during which you can fire another action potential, but you would require a stronger stimulus because the ‘threshold’ is raised
what is stimulus intensity encoded by
-action potential frequency in the nervous system
-stimulus intensity can change the frequency of action potentials
-decrease in depolarisation allows increased action potential
what are graded potentials
-unlike action potentials these are not all or none, and they can be:
=excitatory - depolarising
=inhibitory - hyperpolarising
-They are caused by (1) opening of neurotransmitter-gated ion channels or (2) opening/closing of potassium channels
-they can summate- Act to integrate information from multiple neuronal imputs
-Temporal and spatial summation
what can EPSPs be shunted by
-inhibitory inputs
-Note the effect here is that by making membrane really leaky epsp is dissipated this ‘shunting’ effect can be caused by opening of non-selective cation channels in the axon membrane
what are electrical synapses
-Retinal neuronal
-Few other adult CNS neurons, (glial junctions)
-Cardiac muscle
-Smooth muscle
-rapid
-can be 2 way
