Neuronal signalling
Cell membrane
• fosfolipid doublelayer
• ion channels
• transporters
• receptors
• synaptic membrane proteins
Extracellular and intracellular ion concentration
Ion channels and transporters
Electrochemical balance
Resting membrane potential
A difference in the electrical potential (=voltage) across the
plasma membrane of an unstimulated excitable cell.
In a typical resting neuron the electrical potential difference is
about 65 (70) mV. Because the net charge outside of the
membrane is arbitrarily defined as zero, we say the resting
membrane potential is -65 (-70) mV.
•two factors:
(1) the unequal distribution of electrically charged ions in ECF
and ICF,
(Na+-K+ pump)
(2) the selective permeability of the membrane to K+
(ion channels).
Information processing
• dendrites and body - input and integration
• axon - information transmission
• information:
– processes and soma: electrical changes (local or
action potentials)
– synapses: chemical transmitter release
Neuronal signalling
• local (graded) – receptor potential
• local (graded) – synaptic potentials
• propagated – action potential
Action potential
• short-lived reversal of membrane potential reaching
+ 30 mV
• physiologically, is triggered at the axon hillock
• threshold
• amplitude 70-100 mV
• duration 1-10 ms
• uniform response all-or-none
• propagation: without decrement, active, one direction
• refractory period
Receptor and synaptic potentials
• amplitude 0,1-10 mV (graded responses)
• duration: 5-100 ms (receptor p.),
5 ms-20 min (synaptic p.)
• propagation: with decrement, passive, electrotonic
• depolarization or hyperpolarization
Postsynaptic (=synaptic) potential
• Excitatory (Na+, Ca2+ entering the cell)
• Inhibitory (K+ leaving the cell, Cl- entering the cell)
Ion currents
Simplified view:
• Na+, Ca2+ enter the cell: depolarization
• K+ leave the cell: repolarization, hyperpolarization
• Cl- enter the cell: hyperpolarization
Neuronal signalling
Passive current flow in an axon
Propagation of action potential in
myelinated axon
Toxins
• Na+ channel:
tetrodoxin (puffer fish), saxitoxin and brevetoxin
(dinoflagellatae→shellfish)
α-toxin, β-toxin (scorpion), batrachotoxin (frog)
• K+ channels:
dendrotoxin (wasps), apamine (bees),
charybdotoxin (scorpion)
Integrating
mechanisms:
Spatial summation
Temporal summation
Divergence
Convergence
Information coding