Transcript Neuronal Excitability - STCC Faculty Webpages

Neuronal Excitability
Resting, Action, and Postsynaptic
Potentials
Resting Potential
 The
concentration gradient
on K+ is out of the cell.
 The concentration gradient
of Na+ is strongly into the
cell.
 The neuronal membrane is
not very permeable to these
ions at rest (just through the
few leak pores)
 The Na+/K+ pump (in red)
maintains these gradients.
Action Potential
occurs in axon
 Na+ voltage-gated
channels open first
 depolarization occurs
 K+ delayed rectifier
opens (and Na+
voltage-gated
channels close)
 repolarization occurs

The synapse transfers the
information from the action potential
 The
action potential reaches the axonal
terminal and is the electrical signal that
activates calcium voltage-gated channels
 Calcium floods into the axonal terminal
(from the extracellular solution) through its
now-open channels
 Calcium causes neurotransmitter-containing
vesicles to be released
What happens at the postsynaptic
membrane???
 Neurotransmitter
binds to protein receptors.
 These receptors are part of the “signal
transduction” function of membranes…
they have to receive information and then
respond to it.
 Most receptors can do this because they are
actually ligand-gated channels. The
neurotransmitter is the ligand, so they open.
 A postsynaptic potential (p.s.p.) results
What’s a postsynaptic potential?
 The
postsynaptic potential is the electrical result
of the synapse
 When a neuron responds to the neurotransmitter
postsynaptically, it does so by allowing ions to
move across its membrane
 The movement of ions changes the membrane
potential of the postsynaptic neuron
 The change in the membrane potential is the
“postsynaptic potential” and will get integrated
with other postsynaptic potentials in the cell body
Types of postsynaptic potentials
EPSP:
IPSP:
 excitatory postsynaptic  inhibitory postsynaptic
potential
potential
 can help lead to the
 can help to prevent the
production of an
production of an
action potential
action potential
 causes a
 causes a
depolarization
hyperpolarization
Postsynaptic potentials are small
Each psp is typically
less than 5 mV in size
(whereas an action
potential is a change
of over 100 mV)
 Psps can sum together
in the cell body to
trigger Na+ voltagegated channels to open

What does the p.s.p. mean to the
neuron?
If the p.s.p.s all sum together in the cell body,
the axon hillock can detect this electrical
summing…
This is the “some electrical event occurs” that
begins the action potential at the axon
hillock.
Pretty neat, huh?