Neuronal Signalling… Take 2
Summary of Potentials…
Membrane Potential
- the potential of the cell membrane of any cell.
Resting Potential
- membrane potential of a neurone that is not being stimulated
(determined by the Goldman Equation)
Equilibrium Potential
- the potential of the membrane, for a single ion that that stops further
movement of that ion across the membrane (Nernst Equation)
Reversal Potential
- potential at which no further charge movement across the membrane
occurs
For a single ion Erev=Eeq
2. The Action Potential…
Once the action potential is generated, it must propagate along the
axon.
Summation…
when many different EPSPs and IPSPs are integrated
when the integration is sufficiently excitatory to raise the membrane
potential to the point where Na+ channels open
This point is known as the THRESHOLD
The threshold is the point when the action potential is fired
The opening of these ion channels causes small excitatory/ inhibitory
changes in the cell, which combine to potentially trigger the firing of an
action potential signal
A single receiving (post-synaptic) neuron can have 1000’s of synapses
with different incoming (pre-synaptic) axon terminals
each synapse is either excitatory or inhibitory
INTEGRATION = simultaneous stimulation at many synapses is
“evaluated” by the cell body
Action potential is an “all or nothing” phenomenon – it either occurs or it
doesn’t
Two processes of summation:
Integration - cumulative
effects of more than one
graded potential
Summation – 2 mechanisms
, 1. Temporal summation - multiple stimulation at one synapse in a short
period of time – additive. Pushes the membrane potential towards the
threshold value.
2. Spatial summation – more
common summation process.
Simultaneous stimulation from
two or more nearby synapses;
each synapse is excitatory or
inhibitory
- reinforcing or opposing
effects
- equal excitatory and inhibitory
graded potentials cancel each
other out
Action potential results from sequential opening of voltage-sensitive
channels…
1) Depolarisation – when
stimulus causes the membrane
potential to rise above the
threshold value, voltage-gated
Na+ channels open, leading to
an influx of Na+ ions into the
axon and the “all or none”
action potential spike. This is depolarisation – the inside of the membrane
is more positively charged than the outside.
2) Repolarisation – closing of Na+ channels and the opening of voltage-
gated K+ channels. This allows K+ to diffuse out of the axon, restoring the
negative membrane potential.
3) Hyperpolarisation – these open potassium channels may cause brief
hyperpolarisation, the efflux of K+ ions meaning that the membrane
potential becomes more negative than at resting potential.
Inactivation of Na+ channels…
Summary of Potentials…
Membrane Potential
- the potential of the cell membrane of any cell.
Resting Potential
- membrane potential of a neurone that is not being stimulated
(determined by the Goldman Equation)
Equilibrium Potential
- the potential of the membrane, for a single ion that that stops further
movement of that ion across the membrane (Nernst Equation)
Reversal Potential
- potential at which no further charge movement across the membrane
occurs
For a single ion Erev=Eeq
2. The Action Potential…
Once the action potential is generated, it must propagate along the
axon.
Summation…
when many different EPSPs and IPSPs are integrated
when the integration is sufficiently excitatory to raise the membrane
potential to the point where Na+ channels open
This point is known as the THRESHOLD
The threshold is the point when the action potential is fired
The opening of these ion channels causes small excitatory/ inhibitory
changes in the cell, which combine to potentially trigger the firing of an
action potential signal
A single receiving (post-synaptic) neuron can have 1000’s of synapses
with different incoming (pre-synaptic) axon terminals
each synapse is either excitatory or inhibitory
INTEGRATION = simultaneous stimulation at many synapses is
“evaluated” by the cell body
Action potential is an “all or nothing” phenomenon – it either occurs or it
doesn’t
Two processes of summation:
Integration - cumulative
effects of more than one
graded potential
Summation – 2 mechanisms
, 1. Temporal summation - multiple stimulation at one synapse in a short
period of time – additive. Pushes the membrane potential towards the
threshold value.
2. Spatial summation – more
common summation process.
Simultaneous stimulation from
two or more nearby synapses;
each synapse is excitatory or
inhibitory
- reinforcing or opposing
effects
- equal excitatory and inhibitory
graded potentials cancel each
other out
Action potential results from sequential opening of voltage-sensitive
channels…
1) Depolarisation – when
stimulus causes the membrane
potential to rise above the
threshold value, voltage-gated
Na+ channels open, leading to
an influx of Na+ ions into the
axon and the “all or none”
action potential spike. This is depolarisation – the inside of the membrane
is more positively charged than the outside.
2) Repolarisation – closing of Na+ channels and the opening of voltage-
gated K+ channels. This allows K+ to diffuse out of the axon, restoring the
negative membrane potential.
3) Hyperpolarisation – these open potassium channels may cause brief
hyperpolarisation, the efflux of K+ ions meaning that the membrane
potential becomes more negative than at resting potential.
Inactivation of Na+ channels…
