L18 Flashcards
What is the concentration of Na+ outside and inside the cell
High outside, Low inside
What is the concentration of K+ outside and inside the cell
Low outside, High inside
Process of Chemical Ion Channel Gating
-Chemical signalling neurotransmitter binds onto binding site of channel
-Causes shape change which opens it
-Allows ions to move across membrane with electrochemical gradient
-Neurotransmitter unbinds and closes
Voltage Ion channel gating
-Activation gate is closed
-When change in membrane potential both gates open allowing movement of ions
-When influx of ions cause too positive voltage, inactivation gate closes
Mechanical Ion Channel Gating
-Channels open in response to physical forces
What parts of the neuron is chemically and voltage gated
Chemical: Cell body, Dendrites, axon hillock
Voltage: Axon and Axon terminals
What are local potentials
-Movement of Na+ ions increase the membrane voltage in close proximity
What is depolarisation
When membrane potential increases due entry of Na+
What is repolarisation
after stimilus is removed and excess sodium ions are transported out of cell reducing membrane potential back to resting
What is Hyperpolarsation
When membrane potential decreases due to exit of K+
What is local potential summation
Local potentials can add together over time and space eg a excitory excitory leads to larger depolarisations and excitory-inhibitory leads to no change
What is the inital segments
-Point where cell body and axon join
-High density of voltage gated Na+ channels
-For and Action potential to be generated local potentials must sum and reach threshold (10mv)
How can the intial segment reach threshold?
-Depolarizing local potentials may open voltage gated Na+ channels which snowballs
-Leading to large influx of Na+ reaching potential
What is an action potential
-Brief increase of permeability of Na+ into cell and termination of Na+ permeability
-Increase of permeability of K+ ions which restores insides original negative
What is absolute Refractory period and what is it caused by?
-No matter how large stimulus is, another AP cannot be generated during this time
-Caused by VG Na+ channel inactivation
Relative refractory period
-AP can be produced only by large stimulus
Explain Unmyelinated axon AP propagation
-Slow transmission
-As VG Na+ channels open influx of Na+ into cell.
-Na+ local current moves onto neighbouring VG channels which causing the membrane potential to increase and thus opening their channel and continues down the axon
