1. Neural Conduction and Synaptic Transmission
(i.e., Electricity and Chemistry)

2. Neurons
Figure 2.5 A typical neuron and synapse Klein/Thorne: Biological Psychology © 2007 by Worth Publishers
Figure 2.6 The four major types of synapses Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

3. Neural Conduction
An Electrical Process

4. Resting Membrane Potential

5. Figure 4.2 Recording the resting membrane potential of a neuron Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

6. Ions and the resting membrane potentialK+
Potassium ions, positive charge

7. Ions and the resting membrane potential
Na+
Sodium ions, positive charge

8. Ions and the resting membrane potential
Cl-
Chloride ions, negative charge

9. Ions and the resting membrane potential
Inside the neuron K+
Protein-
Outside the neuron
Na+
Cl-

10. What the ions naturally want to do
Force of diffusion
It’s getting crowded in here
Electrostatic pressure
Opposites attract
Similarities repel
Figure 4.4 The influence of diffusion and electrostatic pressure on the movement of ions into and out of the neuron Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

11. What the neural membrane is making the ions do
Differential permeability
Playing favorites
K+ and Cl- pass through easily
Na+ -- not so easy to pass through the membrane
Proteins: not a chance!
Ion channels: like doors

12. What the neural membrane is making the ions do
Sodium-potassium pump
Three Na+ out for every two K+ cells in
Figure 4.5 The sodium-potassium pump Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

13. Putting it all together…
Na+ ions
Want to go inside neuron because
There are fewer of them inside (force of diffusion)
There is a negative charge inside (opposite to their positive charge)
But
Neuron’s membrane not very permeable to Na+ ions
Sodium-potassium pump keeps kicking them out
Therefore, most Na+ ions stay outside neuron

14. Putting it all together…
K+ ions
Want to go outside neuron because
There are fewer of them outside (force of diffusion)
Neuron’s membrane very permeable to K+ ions
But
There is a positive charge outside (similar to their positive charge), so they are repelled by the outside
Sodium-potassium pump keeps kicking them back into neuron
Therefore, most K+ ions stay inside neuron

15. Putting it all together…
Cl- ions: can’t make up their minds
Want to go inside neuron because
There are fewer of them inside
Neuron’s membrane very permeable to Cl- ions
Also want to stay outside of neuron because
The charge outside is positive (and their own charge is negative
Therefore, Cl- ions keep going back and forth, distribution of Cl- ions is held at equilibrium.
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16. Postsynaptic Potentials
Getting the membrane potential to change from -70 mv

17. Figure 2.6 The four major types of synapses Klein/Thorne: Biological Psychology © 2007 by Worth Publishers
Figure Overview of synaptic transmission Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

18. Like relay team passing a baton
Causes something called “postsynaptic potentials” to happen

19. Postsynaptic potentials can do one of 2 things…
Depolarize neuron
Hyperpolarize neuron

20. Postsynaptic potentials
Depolarize
Decrease resting potential
Become less negative
E.g., from -70 mV to – 67 mv
De/hyper polarize receptive membrane, why called “post” synaptic

21. Postsynaptic potentials
Increase likelihood that neuron will fire
Excitatory postsynaptic potentials: EPSPs
De/hyper polarize receptive membrane, why called “post” synaptic

22. Postsynaptic potentials
Hyperpolarize
Increase the resting potential
Become more negative
E.g., from -70 mV to -72 mV
De/hyper polarize receptive membrane

23. Postsynaptic potentials
Decrease likelihood that neuron will fire
Inhibitory postsynaptic potentials: IPSPs
De/hyper polarize receptive membrane

24. Characteristics of EPSPs and IPSPs
Notes

25. There are a bunch of EPSPs and IPSPs happening in the same neuron at once

26. How EPSPs or IPSPs add up
Spatial summation
A bunch of EPSPs/IPSPs combine together
Figure Spatial summation and temporal summation Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

27. How EPSPs or IPSPs add up
Temporal summation
When EPSPs/IPSPs are coming in real fast, the next one happens before the previous one fades away
They add together over time
Figure Spatial summation and temporal summation Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

28. Getting a neuron to fire
EPSPs and IPSPs travel until they reach near the axon hillock

29. Getting a neuron to fire
Remember…
EPSP make membrane’s resting potential less negative (e.g., from -70 mv to -68 mv)
IPSPs make membrane’s resting potential more negative (e.g., from -70 mv to -75 mv)
When combined they cancel each other out, and whichever is stronger wins

30. Getting a neuron to fire: Example 1
EPSPs add up to change resting potential from -70 mv to -60 mv (change of +10 mv)
IPSPs add up to change resting potential from -70 mv to -75 mv (change of -5 mv)

31. Getting a neuron to fire: Example 1
Net difference of +5 mv, from -70 mv to -65 mv
The resting membrane potential to become less negative
The end result is the membrane is depolarized

32. Figure 4.7 Changes in the membrane potential during the action (spike) potential Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

33. Getting a neuron to fire: Example 2
EPSPs add up to change resting potential from -70 mv to -68 mv (change of +2 mv)
IPSPs add up to change resting potential from -70 mv to -75 mv (change of -5 mv)

34. Getting a neuron to fire: Example 2
Net difference of -3 mv, from -70 mv to -73 mv
The resting membrane potential to become more negative
The end result is the membrane is hyperpolarized

35. Figure 4.7 Changes in the membrane potential during the action (spike) potential Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

36. Getting a neuron to fire
The end result that matters is how the EPSPs and IPSPs cancel each other out near the axon hillock

37. Getting a neuron to fire
If it so happens that, near the axon hillock
The net combination of EPSPs/IPSPs
Depolarizes the membrane (makes it less negative)
To a point called threshold potential

38. Figure 4.7 Changes in the membrane potential during the action (spike) potential Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

39. Action potential Membrane becomes depolarized to about 40 mV
All-or-nothing

40. Voltage-activated ion channels
When a neuron’s membrane reaches the threshold of excitation, ion channels open
Na+ ions (previously could not permeate the membrane) can now rush into the neuron
As a result, membrane potential goes to about 40mv

41. Voltage-activated ion channels
K+ ions (they start out being inside the neuron) now rush out of the neuron
Force of diffusion
When membrane potential is now positive, also driven out by electrostatic pressure

42. Refractory period Absolute refractory period Lasts 1 to 2 milliseconds
Impossible for another action potential to happen
Figure 4.7 Changes in the membrane potential during the action (spike) potential Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

43. Refractory period Relative refractory period
Possible for another action potential to happen
But need extra-strength stimulation
Figure 4.7 Changes in the membrane potential during the action (spike) potential Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

44. Action potential travels down axon
Figure 4.9 Propagation of the action potential along an unmyelinated axon Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

45. Action potential travels down axon
Action potentials are nondecremental – do not become weaker as they travel
Travel very slowly

46. Action potential only causes those ion channels in one small spot of the membrane to open
To travel down the axon, needs to nudge the adjacent ion channels

47. Conduction of Action Potential in Myelinated Axons
Figure Propagation of the action potential along an myelinated axon Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

48. Conduction of Action Potential in Myelinated Axons
This time,
Action potential travels rapidly
Action potential simply hops from one node of Ranvier to another
Saltatory conduction (saltare = dance)
Action potential grows weaker as it travels
But, still strong enough to initiate another action potential at the next node of Ranvier
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49. Synaptic Transmission of Signals
A Chemical Process

50. Chemical signals
In your nervous system there are chemicals called “neurotransmitters.”
Neurons produce neurotransmitters.

51. Neurotransmitters Neurotranmsitters are packed into synaptic vesicles.
Synaptic vesicles are found at the terminal buttons.

52. Release of neurotransmitters
Action potential travels down axon and reaches synapse
This causes Ca2+ (calcium) ion channels to open
Figure Overview of synaptic transmission Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

53. Release of neurotransmitters
Ca2+ ions cause synaptic vesicles to join to presynaptic membrane
Vesicles release neurotransmitters into synaptic cleft
Neurotransmitters get passed on to the next neuron
Figure Overview of synaptic transmission Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

54. It’s like playing pinball
What happens next?
It’s like playing pinball

55. Back to where we started…
Neurotransmitter binds with receptor, causes ion channels to open
If Na+ channels open, then Na+ ions enter neuron, depolarizes membrane  EPSP

56. Back to where we started…
If chloride channels open, the Cl- ions enter neuron, hyperpolarizes membrane  IPSP
If potassium channels open, the K+ ions leave the neuron, hyperpolarizes membrane  IPSP

57. What happens to the leftover neurotransmitters?
Reuptake
Neurotransmitters return to presynaptic buttons
Figure Termination of neural transmission Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

58. What happens to the leftover neurotransmitters?
Degradation
Neurotransmitters broken apart in the synapse by enzymes
Figure Termination of neural transmission Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

59. Chemicals in the Nervous System
Neurotransmitters
Chemicals in the Nervous System

60. Neurotransmitters Acetylcholine (Ach) Gamma-aminobutyric acid (GABA)
Muscles
Memory: Alzheimer’s
Gamma-aminobutyric acid (GABA)
Seizures
Huntington’s disease

61. Neurotransmitters Epinephrine (aka adrenaline) Norepinephrine
Activation of cardiovascular system

62. Neurotransmitters Dopamine Serotonin Schizophrenia Parkinson’s
Depression
Aggression
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63. Agonists and Antagonists

64. Agonists Synthesis of neurotransmitter Helps with release
Obstructs autoreceptor
Pretends to be neurotransmitter
Prevents reuptake
Figure Autoreceptors Klein/Thorne: Biological Psychology © 2007 by Worth Publishers

65. Antagonists Obstacle to synthesis Obstacle to neurotransmitter release
Fools autoreceptor
Blocks receptor

66. How some drugs work Cocaine Agonist of norepinephrine and dopamine
Prevents reuptake of leftover norepinephrine and dopamine
Therefore, effects of these neurotransmitters are increased

67. How some drugs work Botulinium toxin Antagonist of acetylcholine
Prevents acetylcholine from being released
Therefore, effects of these neurotransmitters are decreased
Small amounts used to paralyze certain muscles