Neurophysiology
The
Resting
Membrane
Potential
-70 mV
V
Intracellular
(soma)
V
Extracellular
Three Concepts
1. Concentration Gradients
2. Electrical gradients
3. Selective permeability
of the membrane
Solid barrier in place
100 NaCl
0 NaCl
Outside
Inside
Solid barrier in place
0
100 Na+
100 Cl0
Outside
0 Na+
0 Cl0
Inside
Barrier removed
100 Na+
100 Cl0
0 Na+
0 Cl0
Outside
Inside
Na+ Concentration gradient = 100
Cl- Concentration gradient = 100
Barrier removed
50 Na+
50 Cl0
50 Na+
50 Cl0
Outside
Inside
Na+ Concentration gradient = 0
Cl- Concentration gradient = 0
Measure voltage difference
System at equilibrium
0
50 Na+
50 Cl0
50 Na+
50 Cl0
Outside
Inside
Na+ Concentration gradient = 0
Cl- Concentration gradient = 0
Solid barrier in place
0
100 Na+
100 Cl0
Outside
0 Na+
0 Cl0
Inside
Replace with Na+
permeable membrane
0
100 Na+
100 Cl0
0 Na+
0 Cl0
Outside
Inside
Na+ Concentration gradient = 100
Replace with Na+
permeable membrane
+100
50 Na+
100 Cl-
50 Na+
0 Cl-
-50
+50
Outside
Inside
Na+ Concentration gradient = 0
Replace with Na+
permeable membrane
+100
50 Na+
100 Cl-
50 Na+
0 Cl-
-50
+50
Outside
Inside
Na+ Concentration gradient = 0
Replace with Na+
permeable membrane
System at equilibrium
+50
75 Na+
100 Cl-
25 Na+
0 Cl-
-25
+25
Outside
Inside
Na+ Concentration gradient = 50
Replace with Clpermeable membrane
+50
75 Na+
100 Cl-
25 Na+
0 Cl-
-25
+25
Outside
Inside
Cl- Concentration gradient = 100
Replace with Clpermeable membrane
-50
75 Na+
50 Cl-
25 Na+
50 Cl-
+25
-25
Outside
Inside
Cl- Concentration gradient = 0
Replace with Clpermeable membrane
System at equilibrium
-25
75 Na+
62.5Cl-
25 Na+
37.5 Cl-
+12.5
-12.5
Outside
Inside
Cl- Concentration gradient = 25
-70 mV
V
Intracellular
(soma)
V
Extracellular
Ion Concentrations in Neurons
(-70mV resting potential)
Ion
[X]I
[X]O
Na+
50mM
460mM
c
e
Cl-
40mM
540mM
c
e
K+
400mM
10mM
c
e
ENa+ = +55mV
ECl -= -65mV
EK+ = -90mV
Nernst
Equilibrium
Potentials
Resting Membrane
Potential: Animation
A + B: Summation of EPSPs
C + D: Summation of IPSPs
A + C: EPSP + IPSP
Postsynaptic
Potentials
• may be excitatory (EPSP)
or inhibitory
excitatory potentials bring the
membrane potential closer to
the the cell’s threshold
inhibitory potentials prevent
the membrane potential from
reaching threshold
•open Na+ channels: excitatory
•open K+ channels: inhibitory
•open Cl- channels: inhibitory
ENa+ = +55mV (above threshold)
ECl -= -65mV (below threshold)
EK+ = -90mV (below threshold)
Postsynaptic
Potentials
•are graded potentials, as
opposed to the all-or-none
action potential
•summate over space (spatial
summation) and time (temporal
summation)
•decay with time and distance
•trigger an action potential if, and
only if, their summed effect
raises the membrane above
threshold at the axon hillock
The Action
Potential: Animation
Exocytosis: Process of neurotransmitter
release, which is Ca2+-dependent.
Pinocytosis, or endocytosis: Process of
recovering synaptic vesicle.
Ca2+
(Calcium influx
required for
neurotransmitter
release)
Synaptic Transmission:
Animation
Two Modes of Coupling Between
Receptors and Ion Channels
1. Ionotropic synapses
Receptor protein also acts
as ion channel
2. Metabotropic synapses
Receptor proteins and ion
channels distinct; linked by
a second messenger system
Ionotropic
Metabotropic
~~~~~~~~~~~~~~~~~~~~~~~~~~
Fast
Slow
Wasteful
Economical
Stereotyped
Modifiable
Autoreceptors
found on presynaptic terminal
sensitive to neurotransmitter
released from that terminal
regulate neurotransmitter release
usually inhibit further release
different receptor subtype