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Neurons
Neurons are highly specialized cells.
• A neuron has four parts.
1. cell body has nucleus and organelles
2. dendrites receive impulses as signals (message)
3. axon carries impulses as signals
4. terminal converts electrical impulses to chem. signals
terminal 4
1 Cell body
3 axon
2
dendrites
Resting Potential
• Defined: Neuron
at rest
• Neuron Exterior:
– Positive charge
– Mainly Na+
outside the cell
• Neuron Interior:
– Negative
charge
– K+ inside the
cell
Action Potentional
• Defined: a moving electrical impulse.
– generated by a
stimulus.
– Na+ enters, and cell
becomes + charged.
– K+ leaves, and area of
+ charge moves.
imp
ulse
Na+
Na+
+
+
+
Na
Na
Na
+
+
+
+
+
+ K+
Na
Na
Na
Na
+
Na
Na
Na
+
K
+
Na
Na
+
+
+
+
+ Na+
K
Na
Na
+
+
Na
Na
Na
Na
Na+Na+
Na+
+
+
+
+
+
Na
Na
+
+
+
Na
Na
Na
+
K
Na
Na
+
+
Na
+
Na
Na
Na
Na+
Na+ Na+ Na+
Na+
Na+
K+
K+
Na
K+
K+
Na+
K+
Na+
Na+
Na+
Na+
+
+
K
K
K+
negative
+
impulse
+
Na
+
K+
Na+
Na+
K+ K+
K+
K+
K+
Na+
Na+
Na+
K+ K+
K+
K+
K++
Na
K+
K+
K+
K+
K+
Na+
K+
K+
Na+
K+
K+
K+
K+
Na+
Na+
Na+Na+ Na+
+
Na+
Na+ Na
+
Na
+
+
Na+ Na Na+ Na+ Na Na+
K+
K+
Na+
K+
K+ K+ K+
Na+
Na+
K+
+Na
Na
K+
+
Na+
Na+
Na
+
Na
Na+
K+ Na+ Na+
Na+ Na+
+
Na+
Na+
Synapse
• Defined: Gap between
neurons
• Problem: Impulse cannot
cross the gap
• Solution: Impulse converted
into chemical molecules
that stimulate the next cell,
called neurotransmitters
• Steps:
– Impulse reaches
neuron’s end
– Vesicle releases
neurotransmitters
– Neurotransmitters attach
to neighboring neuron
– New impulse created
Impulse stimulates a
vesicle, which
contains
neurotransmitters
Vesicle exits the
cell and dissolves
impul
se
End of one
cell
Start of
another cell
Neurotransmitters
stimulate a new
impulse
Neurotransmitters
cross the synapse
and attach to
receptors of a
neighboring neuron
imp
ulse
End of one
cell
imp
ulse
Start of
another cell
Brain
Feet
Motor neurons reach the muscles
• Impulse causes the muscles to stretch and
contract…this causes MOVEMENT!