1. Nerve Signals
11.2
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2. Nerve Impulses there are about 100 billion neurons in the human brain
neurons can transmit nerve impulses per second

3. (Image from:http://www.thenutritionpost.com/tag/brain-scans)
Electroencephalography – measuring brain activity…what is it actually measuring?

4. Potential Difference
caused by relative concentrations of positive ions (Na+ and K+) on either side of the membrane
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5. Neuron Membrane K channel Na/K pump
(Image from: Na channel
K channel
Na/K pump

6. Resting Potential (-70 mV)
inside of cell is more negative (-70 mV) than outside
membrane is “polarized”
Na+/K+ active transport pump establishes resting potential, pumping out 3 Na+ for every 2 K+ in

7. Na+/K+ Pump
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Re-establishes the potential difference as well as the relative ion concentrations across the membrane

8. Action Potential depolarization + repolarization
+ restoration of resting potential
= action potential

9. Depolarization (+40 mV) stimulus causes depolarization
if threshold potential reached, Na+ channels open
Na+ ions enter, causing rapid depolarization
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10. Repolarization (-70+ mV)
Na+ channels shut
K+ channels open
K+ moves out of cell
slow closure of K+ channels causes hyperpolarization
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11. Action Potential
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12. Animation & Quiz
The dry but informative McGraw-Hill narrated animation & quiz:

13. Refractory Period
from the peak of an action potential until the membrane reaches resting potential again
a few milliseconds
ensures action potential travels in one direction only

14. All-Or-Nothing
intensity of stimulus is indicated by the frequency of action potentials, not the size
action potentials per second
rate of conduction increases with diameter of nerve (up to 25 m/s)

15. Myelinated Axons
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16. What happens when the action potential reaches the axon terminals?

17. Chemical Synapse
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18. Synaptic Transmission
Ca2+ ions actively pumped out of neurons
action potential in presynaptic neuron causes calcium channels to open
Ca2+ ions flow in and cause synaptic vesicles to fuse with plasma membrane

19. Synaptic Transmission
neurotransmitters released into the synaptic cleft
diffuse across cleft and bind to receptors on postsynaptic cell
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20. Neurotransmitters
acetylcholine (excitatory) causes Na+ channels to open in postsynaptic neuron, propagating the action potential
many drugs interfere with action of neurotransmitters

21. Anti-anxiety drugs
depressants such as diazepam (Valium) act by increasing the amount of inhibitory neurotransmitters at synapses
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22. Endorphins endorphin = endogenous morphine(
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(Loves makes us produce endorphins!)

23. Animation & Quiz Quick McGraw-Hill narrated animation with quiz: