1. CNS in (unconscious) action: reflex arc
Simple connection of neurons that results in a reflex action in response to a stimulus
Very rapid
Depend on only 3 neurons
Not under voluntary control, happens before your brain “processed” what happened
Usually response to hot/sharp objects 1

3. Neurons

4. Neuron nerve cell, basic structural and functional unit
nucleus
cell body
axon
conducts electrochemical signals to regulate body processes
can be bundled into nerves 4

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8. surrounded by glial cells
supporting cells (nourish, defend)
often coated with an insulating layer: myelin sheath
made of Schwann cells
protective
speeds signal transmission 8

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11. Neuron Function Sensory input collects and transmits input to CNS
Integration
integrate CNS and PNS
Motor output
- transmit information from CNS to target, ex. muscles, glands 11

12. Nerves are Electrical! membrane potential
electrical charge separation across a cell membrane (potential energy)
resting membrane potential
results from difference in ion distribution inside and outside of cell (-70mV)
measured in an unstimulated, polarized neuron (no impulse) 12

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15. Forces Behind Resting Potential
1. Selective Permeability
-some molecules pass through membrane more freely than others, ex. ion channels for K+
2. Sodium-Potassium Pump
-transports 3 Na+ out of, 2 K+ into cell, using ATP
- Excess positive charge outside cell 15

16. Concentration Gradient Electrical Gradient
Result:
Concentration Gradient
Electrical Gradient 16

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21. The Action Potential how nerves send on their message
change in charge that happens with nerve depolarization 21

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23. Molecular Basis of Action Potential
An action potential is triggered when the threshold is reached.
Voltage-gated sodium channels open (-50 mV) : influx of sodium into the cell
Sodium channels close (+40 mV) and potassium channels open: K+ exits the cell
Potassium channels close and resting potential is restored. 23

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27. refractory period membrane cannot go through another action potential
Time needed for repolarization

28. the signal gets passed down the axon, in a single direction
it initiates a threshold at the junction with the next cell 28

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30. Myelin
In myelinated neurons action potentials only happen at the nodes of Ranvier
Exposed areas on neuron with many voltage-gated sodium channels, able to depolarize and pass on signal
Action potential “jumps” from node to node, causing voltage-gated Na+ channels to open 30

31. Figure 2.20  Saltatory conduction in a myelinated axon An action potential at the node triggers flow of current to the next node, where the membrane regenerates the action potential. 31

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33. Results in nerve impulse
Passing on of signal down the neuron
Much faster in myelinated neurons (120 m/s) than in non-myelinated (0.5 m/s) 33

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35. At the molecular level, sensory receptors located on the cell membrane of sensory neurons are responsible for the conversion of stimuli into electrical impulses. The type of receptor employed by a given sensory neuron determines the type of stimulus it will be sensitive to. For example, neurons containing mechanoreceptors are sensitive to tactile stimuli, while olfactory receptors make a cell sensitive to odors.[

36. The Synapse The synapse is the junction between neurons
Synapses are found between sensory receptors and sensory neurons and between motor neurons and muscle cells
The transmitting cell is called the presynaptic cell and the receiving cell is the postsynaptic cell
There are two main types of synapses
1) electrical synapses
2) chemical synapses 36

37. a) Electrical Synapse
Pre and post synaptic cells are connected by gap junctions that allow action potentials to pass directly from one cell to another 37

38. b) Chemical Synapse 38

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40. Transmission across a synapse
The electrical signal is converted into a chemical signal, and then back to an electrical signal in the post cell
Within the cytoplasm of the pre cell there are numerous sacs filled with neurotransmitters, the messenger molecules that will be released into the synaptic cleft
The neurotransmitters will cause a depolarization of the post-synaptic neuron (action potential)
Neurotrasmitters in cleft are degraded by enzymes or taken up by neurons for re-use 40

41. Chemical Synapse 41

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43. Neurotransmitters 1) Dopamine and serotonin (amines)
Technically the only two things you enjoy!
Mood regulators, linked to sensations of pleasure
Dopamine has been linked to schizophrenia and Parkinson’s disease.
Not enough serotonin is linked to depression
Serotonin and LSD (hallucinogen) have similar structures 43

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45. Endorphins (peptides, endogenous morphines)
Natural painkillers, affect emotions
Released during exercise: “runner’s high”
Similar to opiates, morphine and heroin bind to the same receptors 45

46. Norepinephrine
Complements the actions of ephinephrine, readies he body to respond to danger/stress 46

47. OK, but why do some things feel kind of good and others REALLY good?47

48. How then is stimulus intensity coded?
The All-or-None Law
The size, amplitude, and velocity of an action potential are independent of the intensity of the stimulus that initiated it.
How then is stimulus intensity coded? 48

49. Summation The figure below shows a typical neural pathway
When neuron A and Neuron B fire together an action potential is triggered in neuron D
Note that neuron C is inhibitory 49

50. Temporal and Spatial Summation50

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52. Peripheral Nervous System52

53. controls voluntary movement of skeletal muscles myelinated
divided into two parts
Somatic System
controls voluntary movement of skeletal muscles
myelinated 53

54. 2. Autonomic System
controls involuntary glandular secretions and functions of smooth and cardiac muscle
divided into: 54

55. i. sympathetic nervous system
activates “fight or flight” response
norepinephrine (neurotransmitter) works with epinephrine (hormone) to activate stress response
blood pressure increases (vasoconstriction), heart beats faster, digestion slows down, etc.
released by modern stressors: anxiety 55

56. ii. parasympathetic nervous system
involuntary control in opposition to the sympathetic nervous system
activated when the body is calm and at rest (ex. meditation)
the “break” to sympathetic NS’s “gas pedal” 56

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58. HOMEOSTASIS!!!! 58