1. Unit 2 Notes: Nerve Impulses

2. (1) Nerve Impulses What is it? Nerve Impulse = Electrical Current
Messages sent to and from neurons
Used to respond to stimuli
Ultimately maintains homeostasis
Nerve Impulse = Electrical Current
Comes from the flow of positively charged ions
Ions move across the neuron’s membrane

3. (2) Neuron Membranes & Ions
Sodium & Potassium Pumps:
In the membrane of neurons
Only open when stimulated by neurotransmitter
Na+ on the outside
K+ on the inside
Ions:
Charged particles
Sodium = Na+ = Positive Charge
Potassium = K+ = Positive Charge
Movement of Ion = Movement of Charges = Electrical Current

5. (3) Neuron Resting Potential
Resting Potential: The natural charge distribution across a neuron’s membrane.
K+ channel a little “loose”:
Some K+ leaks OUT of the neuron
Build up of MORE positive ions outside of the membrane
Inside = More Negative, Outside = More Positive
Membrane = Polarized = Imbalance

7. (4) Depolarization & Repolarization
Depolarization: (Remove imbalance)
Na+ pump opens  Na+ flows inward
Depolarization  Temporary Balance
REMEMBER: In this scenario, balance is NOT normal in this part of your body! Your body will FORCE repolarization!
Repolarization: (Imbalance Again)
K+ pump opens  TONS of K+ flows outward
Repolarization
REMEMBER: K+ needs to be in, and Na+ out!

8. http://upload. wikimedia

9. (5) Action Potential
Action Potential = Movement of Na+ and K+ ions in and out (across) the neuron membrane.
Process:
Cycle of depolarization + repolarization
Stimulus  Opening of Na+ Pumps  Movement Inward of Na+  Depolarization & Shutting of Na+ Pumps
Depolarization  Opening of K+ Pumps  Movement Outward of K+  Repolarization & Shutting of K+ Pumps

11. (6) Regaining Resting Potential
Action Potential caused Na+ to be on the inside, and K+ to be on the outside.
Change = NOT NORMAL
Not Normal  Homeostasis kicks in!
Na+ and K+ Pumps Actively Transport (using ATP) Na+ and K+ back out/in of the axon
Na+ pushes out
K+ pushes in
Resting Potential regained

12. (7) Myelin & Action Potential
Myelin = Insulation along axon
Creates “gaps” between Na+ and K+ pumps in membrane…
“Gaps”  electrical jumping
Ions fly down to the next set of pumps
Increases Speed of Current / Impulse

14. (8) Reflexes
Rapid, Unpredictable and involuntary responses to stimuli.
Reflex Arcs:
Pathway which reflex messages are sent.
1- Stimulus & Receptor
2- Message sent in thru Sensory Neuron
3- Integration at CNS
4- Action message sent out Motor Neuron
5- Effector Organ responds

15. (9) Types of Reflexes Somatic: Autonomic:
Stimulation of skeletal muscle
Movement of limbs, torso, etc.
Autonomic:
Stimulation of smooth muscle, heart and glands
Causes secretion of saliva, pupil dilation, etc.