Nervous System 2015
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Transcript Nervous System 2015
Nervous System
AP Biology
2007-2008
Essential Knowledge:
Animals have nervous systems that
detect external and internal signals,
transmit and integrate information and
produce responses.
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Nervous system cells
Neuron
signal
direction
a nerve cell
dendrites
cell body
Structure fits function
many entry points
for signal
one path out
transmits signal
axon
signal direction
myelin sheath
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dendrite
cell body axon
synaptic terminal
synapse
Myelin sheath
Axon coated with Schwann cells
signal
direction
Insulation material (lipid)
speeds up signal
saltatory conduction
150 m/sec vs. 5 m/sec
(330 mph vs. 11 mph)
myelin sheath
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action potential
saltatory
conduction
Na+
myelin
axon
+
+
+
+
+
–
–
Na+
Multiple Sclerosis
immune system (T cells)
attack myelin sheath
loss of signal
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Neuron Functional Differences
Integrates and coordinates
info from afferent, sends out
response to efferent
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Neuron at Resting Potential
Opposite charges on opposite sides of
cell membrane
membrane is polarized
negative inside; positive outside
charge gradient (-70mv)
stored energy (like a battery)
+ + + + + + + + + + + + + + +
– – – – – – – – – – – – – –
– – – – – – – – – – – – – –
+ + + + + + + + + + + + + + +
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What makes it polarized?
Cells live in a sea of charged ions
anions (negative)
more concentrated within the cell
Cl-, charged amino acids (aa-)
cations (positive)
Na+ more concentrated in the extracellular fluid
Na+
Na+
K+
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aa-
K+
Na+
aaCl-
Na+
ClK+
Na+
aa-
Na+
K+
aa-
K+
Na+
ClCl-
Na+
aa-
Na+
Na+
Na+
Claa- Cl-
–
K+
+
channel
leaks K+
Salty
Banana!
How does a nerve impulse travel?
Stimulus: nerve is stimulated
reaches threshold potential
open Na+ channels in cell membrane
Na+ ions diffuse into cell
charges reverse at that point on neuron
positive inside; negative outside
The 1st
domino
goes
down!
cell becomes depolarized
– + + + + + + + + + + + + + +
+ – – – – – – – – – – – – – –
Na+
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+ – – – – – – – – – – – – – –
– + + + + + + + + + + + + + +
Depolarization
Wave: nerve impulse travels down neuron
The rest
of the
dominoes
fall!
Gate
change in charge opens
+ –
next Na+ gates down the line
“voltage-gated” channels
channe
l
closed
Na+ continues to diffuse down neuron
“wave” moves down neuron = action potential
+
+
channe
l open
– – – + + + + + + + + + + + +
+ + + – – – – – – – – – – – –
Na+
+ + + – – – – – – – – – – – –
– – – + + + + + + + + + + + +
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wave
Voltage-gated channels
Ion channels open & close in response to
changes in charge across membrane
Structure
& function!
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Repolarization
Re-set: 2nd wave travels down neuron
K+ channels open
K+ channels open up more slowly than Na+ channels
K+ ions diffuse out of cell
charges reverse back at that point
negative inside; positive outside
Set
dominoes
back up
quickly!
K+
+ – – – – + + + + + + + + + +
– + + + + – – – – – – – – – –
Na+
– + + + + – – – – – – – – – –
+ – – – – + + + + + + + + + +
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wave
How does a nerve impulse travel?
wave of opening ion channels moves down
neuron
flow of K+ out of cell stops activation of Na+
channels in wrong direction
Ready
for
next time!
Animation
K+
+ + + – – – – + + + + + + + +
– – – + + + + – – – – – – – –
Na+
– – – + + + + – – – – – – – –
+ + + – – – – + + + + + + + +
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wave
How does the nerve re-set itself?
Sodium-Potassium pump
active transport protein in membrane
requires ATP
3 Na+ pumped out
+
2 K pumped in
re-sets charge
across
membrane
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That’s a lot
of ATP !
Feed me some
sugar quick!
ATP
Action potential graph
1. Resting potential
2. Stimulus reaches
40 mV
4
30 mV
Membrane potential
threshold potential
3. Depolarization
Na+ channels open;
K+ channels closed
4. Na+ channels close;
K+ channels open
5. Repolarization
reset charge gradient
6. Undershoot
+ channels close slowly
K
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20 mV
10 mV Depolarization
Na+ flows in
0 mV
–10 mV
3
–20 mV
Repolarization
K+ flows out
5
–30 mV
–40 mV
–50 mV
Threshold
–60 mV
2
–70 mV
–80 mV
1
Resting potential
Hyperpolarization
(undershoot)
6 Resting
All or nothing response
Once first one is opened, the rest open
in succession
a “wave” action travels along neuron
have to re-set channels so neuron can
react again
How is a nerve impulse
similar to playing with
dominoes?
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What happens at the end of the axon?
Impulse has to jump the synapse!
junction between neurons
has to jump quickly from one cell
to next
How does
the wave
jump the gap?
Synapse
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The Synapse
axon terminal
action potential
synaptic vesicles
synapse
Ca++
receptor protein
neurotransmitter
acetylcholine (ACh)
ion-gated channels open
muscle cell (fiber)
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We switched…
from an electrical signal
to a chemical signal
Action potential
depolarizes membrane
Opens Ca++ channels
Neurotransmitter vesicles
fuse with membrane
Release neurotransmitter
to synapse diffusion
Neurotransmitter binds
with protein receptor
Neurotransmitter
degraded or reabsorbed
Neurotransmitters
Acetylcholine
transmit signal to skeletal muscle
Epinephrine (adrenaline) & norepinephrine
fight-or-flight response
Dopamine
affects sleep, mood, attention & learning
lack of dopamine in brain associated with
Parkinson’s disease
excessive dopamine linked to schizophrenia
Serotonin
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affects sleep, mood, attention & learning
Weak point of nervous system
Any substance that affects
neurotransmitters or mimics them affects
nerve function
Ex: Gases, drugs, poisons
Acetylcholinesterase inhibitors =
neurotoxins!
Ex: snake venom, insecticides
Snake toxin blocking
acetylcholinesterase
active site
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Vertebrate Brains
Evolutionary trends towards
“Cephalization”
Central region for integrating and
coordinating information.
Different regions have different functions:
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How are they similar?
How are they different?
More mass, more
neurons, more
connections….
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Ponder this…
Any Questions??
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2007-2008