Please enable JavaScript.
Coggle requires JavaScript to display documents.
2 Electrical Signals Of Nerve Cells and Basic Neuropsysiology - Coggle…
2 Electrical Signals Of Nerve Cells and Basic Neuropsysiology
Membrane Potential
The neuron membrane is a lipid bilayer which is impermeable to ions.
Membrane Proteins
ATP driven pumps create gradients of ions across the membrane.
Voltage gated ion channels render the membrane selective to specific ions depending on the voltage across the membrane.
Resting membrane potential
The resting membrane potential can be calculated using the Goldman-Hodgkin-Katz Equation.
At rest, the membrane is mainly permeable to K+. The resting membrane potential is therefore close to the equilibrium potential of K+ (between -75 mV and -55 mV).
Created by
Lots of non-permeable anions Inside = Net Negative Charge Inside!
Lots of more Na+ outside = Na+ “wants” to go inside because of both diffusive AND electrostatic forces
Lots of more K+ inside because:
Electrical forces make K+ “want” to stay inside, BUT diffusive forces make it want to go outside
Unique Cell resting membrane potential
Each cell has its own unique resting membrane potential dictated by its surrounding ions. For example, in mammalian hippocampal neurons, this is around -70 mV, for the squid axon, this is around -65 mV.
Equilibrium potential
The equilibrium potential (or reversal potential) is the potential at which there is no flow of ions from one side to the other and can be calculated using the Nernst Equation.
Two forces generate membrane potential
Diffusion
(concentration gradient)
Electrostatic
Action Potential
Needs
The action potential (spike) requires an initial depolarization and is mediated by voltage gated Na+-channels and voltage gated K+-channels residing in the membrane.
Starts at
The depolarization increases the probability of Na+ channels opening and once enough Na+ channels are open, it crosses a “threshold” for the initiation of a spike.
This membrane potential threshold is unique to every cell, but it is usually around -40 mV.
Behaviour of voltage gated channels
These voltage gated channels open at specific periods during the generation of an action potential: the permeability of the Na+ and K+ ions change over the course of the action potential.
Propagation of action potential
The propagation of an action potential is unidirectional (in most cases) because of the inactivation of the voltage gated Na+ channels.
Effect of myelin
Isolates the axon and makes the action potential jump or "saltate" from one node og Ranvier to the next
Synaptic Potential
Electrical Synapses
Chemical Synapses
On recieving neurotransmitters
Neurotransmitter bind to ligand gated ion channels or metabotropic receptors. This alters the permeability of the postsynaptic membrane to certain ions.
Effects from synaptic potentials
Excitatory and inhibitory synaptic potentials (EPSPs and IPSPs) are generated at the postsynaptic membrane and then summated at the soma of the postsynaptic neuron.
This may lead to the generation of an action potential if the threshold for the opening of the voltage gated Na+ channels is reached.
Summation of synaptic potential is dependent on:
Temporal clustering of inputs.
Spatial clustering of inputs.
Stochastic properties of the synapse (i.e., short-term plasticity, see future lecture.)
Different receptors per neurotransmitter
Acetylcholine
Glutamate
GABA
Types of receptors
G-protein couple/Metabotropic
Ligand-gated ion channels
Types of synaptic potentials
Excitatory postsynaptic potentials (EPSPs) are primarily driven by glutamate receptors on the postsynaptic neuron.
Inhibitory postsynaptic potentials (IPSPs) are primarily driven by GABA receptors on the postsynaptic neuron.
The Neural Code
Voltage gated ion channels are unevenly distributed on the neuronal membrane.
Action potentials are often initiated at the axon initial segment (AIS).
