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Do Now: 3 Types of Nerve Cells
Glue in your notebook on the next blank page!
Do Now: 3 Types of Nerve Cells
Levels of Organization
Whiteboard Activity Opinion Question
What is an ELECTROLYTE?
You have 3 minutes to talk to your lab
group and then be ready to share out.
What is an ELECTROLYTE?
DO NOT WRITE…DISCUSSION ONLY
1. All salts are electrolytes!
2. Substances that conduct an electrical current in a
solution
3. A salt is an organic compound found in the body in
the form of minerals
– Calcium and phosphorus, found in teeth and bones
– Dissolved minerals found in urine
– Sodium and potassium ions used for nerve impulses in
the brain
– Iron, found in hemoglobin, in the blood cells (this is
what makes it red in color)
Notes: How Neurons Communicate
Glue this
picture on
the next
blank page
Transmission of a Nerve Signal
• Neuron communicate similar to dominoes
– protein channels set up
– Once the 1st channel is opened, the rest open up in
succession (one after the other…)
• all or nothing response
– a “wave” action travels along neuron
– have to re-set channels so neuron can react again
Important Chemistry Vocabulary
– anions (negative)
• more concentrated IN THE CELL
– cations (positive)
• more concentrated in the extracellular fluid
(OUTSIDE THE CELLS)
K+
aa-
K+
aaCl-
Na+
ClK+
Na+
aa-
Na+
K+
aa-
K+
Na+
ClCl-
Na+
aa-
Na+
Na+
Na+
Claa- Cl-
–
Na+
Na+
Na+
+
K+
channel
leaks K+
Why is this impulse called an
ACTION POTENTIAL?
unstimulated neuron = resting potential of -70mV
How does a nerve impulse travel?
STEP 1 and 2
Step 1 - Stimulus: nerve is stimulated (ACTIVATED)
• Open channels in cell membrane
STEP
2 - Na+ ions diffuse into cell
– charges reverse at that point
The 1st
domino
goes
down!
• positive inside; negative outside
– + + + + + + + + + + + + + +
+ – – – – – – – – – – – – – –
Na+
+ – – – – – – – – – – – – – –
– + + + + + + + + + + + + + +
How does a nerve impulse travel?
STEP 3
STEP 3 - Wave: nerve impulse travels down neuron
– change in charge opens
next Na+ gates down the line
– Na+ ions continue to diffuse into cell
– “wave” moves down neuron =
The rest
of the
dominoes
fall!
action potential
Gate
+
+
–
channel
closed
+
channel
open
– – – + + + + + + + + + + + +
+ + + – – – – – – – – – – – –
Na+
+ + + – – – – – – – – – – – –
– – – + + + + + + + + + + + +
wave 
How does a nerve impulse travel?
STEP 4
STEP 4 - Re-set: 2nd wave travels down neuron
– K+ channels open
– K+ ions diffuse out of cell
– charges reverse back at that point
• negative inside; positive outside
Set
dominoes
back up
quickly!
K+
+ – – – – + + + + + + + + + +
– + + + + – – – – – – – – – –
Na+
– + + + + – – – – – – – – – –
+ – – – – + + + + + + + + + +
wave 
Checking For Understanding
1. What are the 4 steps of nerve impulse travel?
Write a paragraph or bullet points or draw a flow
chart.
Myelin sheath
 Axon coated with Schwann cells
signal
direction
insulates axon
 speeds signal

 signal hops from node to node
myelin sheath
action potential
saltatory
conduction
Na+
myelin
axon
+
+
+
+
+
–
–
Na+
Multiple Sclerosis
 immune system (T cells)
attack myelin sheath
 loss of signal
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
Chemical synapse
axon terminal
 Events at synapse
action potential

synaptic vesicles
synapse


Ca++
receptor protein

neurotransmitter
acetylcholine (ACh)

muscle cell (fiber)
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
 ion-gated channels open
neurotransmitter degraded
or reabsorbed
Nerve impulse in next neuron
K+
• Post-synaptic neuron
– triggers nerve impulse in next nerve cell
• chemical signal opens ion-gated channels
Na+
+
binding site
• Na diffuses into cell
• K+ diffuses out of cell
Here we
go again!
– switch back to
voltage-gated channel
ACh
Na+
ion channel
K+
K+
– + + + + + + + + + + + + + +
+ – – – – – – – – – – – – – –
Na+
+ – – – – – – – – – – – – – –
– + + + + + + + + + + + + + +
Na+
Neurotransmitters
• Acetylcholine
– transmit signal to skeletal muscle
• Epinephrine (adrenaline) & norepinephrine
– fight-or-flight response
• Dopamine
– widespread in brain
– affects sleep, mood, attention & learning
– lack of dopamine in brain associated with Parkinson’s
disease
– excessive dopamine linked to schizophrenia
• Serotonin
– widespread in brain
– affects sleep, mood, attention & learning
Checking For Understanding
2. How does the transmission of an action potential
from neuron to neuron represent a set of dominoes
falling down?
Write a paragraph or bullet points or draw a flow
chart.
Human Action Potential
1.
2.
3.
Everyone in your group should have at
least 1 poster. (everyone participates)
Objective: Stand up and stand on the line
(tape on the floor) to assemble a human
neuron.
The order of the posters should
demonstrate the change in electrical
charges and movement of ions (charged
particles) down the neuron.
Exit Slip
1. Work on your own.
2. Open note.
3.
When you finish your paragraph…
•
Peer grade - choose a lab group member
to read your paragraph and provide feedback.
4.
Turn in your exit slip into the exit slip tray