AP Biology

1
AP Biology

• Nervous Systems
• Part 2

2
Animation

• http//www.youtube.com/watch?v90cj4NX87Yk

3
Membrane Potential and ion concentrations
CYTOSOL
EXTRACELLULAR FLUID
Na 150 mM
Na 15 mM
K 150 mM
K 5 mM
Cl 120 mM
Cl 10 mM
A 100 mM
Plasma membrane
4
Na/K pumps
EXTRACELLULAR FLUID
Na
Na high K low
Na
Na
Na
Na
Na
Na
Na
ATP
Na low K high
P
Na
P
CYTOPLASM
ADP
Phosphorylation causes the protein to
change its conformation, expelling Na to the
outside.
Cytoplasmic Na bonds to the
sodium-potassium pump
Na binding stimulates phosphorylation by
ATP.
K
K
K
K
K
P
K
P
Extracellular K binds to the protein,
triggering release of the phosphate group.
Loss of the phosphate restores the
proteins original conformation.
K is released and Na sites are receptive
again the cycle repeats.
5
Resting Potential
Stimuli
Stimuli
Stronger depolarizing stimulus
50
50
50
Action potential
0
0
0
Membrane potential (mV)
Membrane potential (mV)
Membrane potential (mV)
Threshold
Threshold
50
50
Threshold
50
Resting potential
Resting potential
Resting potential
Depolarizations
Hyperpolarizations
100
100
100
4
1
4
1
1
5
3
2
0
5
3
2
0
5
4
3
2
0
6
Time (msec)
Time (msec)
Time (msec)
Graded potential hyperpolarizations
Graded potential depolarizations
Action potential
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Impulse generation
Na
Na
Na
Na
K
K
Rising phase of the action potential
Falling phase of the action potential
50
Action potential
Na
Na
0
Membrane potential (mV)
Threshold
50
K
Resting potential
100
Time
Depolarization
Na
Na
Potassium channel
Extracellular fluid
Activation gates
Na
K
Plasma membrane
Undershoot
Cytosol
Sodium channel
Inactivation gate
K
Resting state
7
Propagation
Axon
Action potential
Na
An action potential is generated as Na flows
inward across the membrane at one location.
Action potential
K
Na
K
The depolarization of the action potential
spreads to the neighboring region of the
membrane, re-initiating the action potential
there. To the left of this region, the membrane
is repolarizing as K flows outward.
Action potential
K
Na
K
The depolarization-repolarization process is
repeated in the next region of the membrane. In
this way, local currents of ions across the
plasma membrane cause the action potential to be
propagated along the length of the axon.
8
Saltatory Conduction
Schwann cell
Depolarized region (node of Ranvier)
Cell body
Myelin sheath
Axon
9
Reflex Arc