1. Chapter 37:
Neurons, Synapses and Signaling
FIGURE 37.1: CONE SNAIL!

2. Concept 37.1: Neuron structure and organization reflect function in information transfer2

4. Neuron Organization
Sensory neurons
Motor neurons
Association neurons

5. Dendrites Axon Cell body Portion of axon Sensory neuron Interneurons
Figure 37.5
Dendrites
Axon
Cell
body
Figure 37.5 Structural diversity of neurons
Portion
of axon
Sensory neuron
Interneurons
Motor neuron 5

6. Figure 37.4: THREE PARTS OF INFO PROCESSING!
Sensory input
Integration
Sensor
Motor output
Figure 37.4 Summary of information processing
Processing center
Effector 6

8. Concept 37.2: Ion pumps and ion channels establish the resting potential of a neuron Sodium-Potassium Pump REVIEW (Bio I/AP) WHY IS IT IMPORTANT?!

9. Resting Membrane Potential http://bcs. whfreeman
Potential difference exists across every cell’s plasma membrane.
Cytoplasm side=
Extracellular fluid=
Occurs when a
Value= ____mV
What makes it negative?
IONS!

10. Table 37.1
Table 37.1 Ion concentrations inside and outside of mammalian neurons 10

11. Key OUTSIDE Na OF CELL K Sodium- potassium pump Potassium channel
Figure 37.6
Key
OUTSIDE
OF CELL
Na K
Sodium-
potassium
pump
Figure 37.6 The basis of the membrane potential
Potassium
channel
Sodium
channel
INSIDE
OF CELL 11

12. Figure 37.7: Modeling A Mammalian Neuron
Inner
chamber
−90 mV
Outer
chamber
Inner
chamber
62 mV
Outer
chamber
140 mM
KCI
5 mM
KCI
15 mM
NaCI
150 mM
NaCI
Cl− K
Na
Cl−
Potassium
channel
Sodium
channel
Artificial
membrane
Figure 37.7 Modeling a mammalian neuron
(a) Membrane selectively permeable
to K
(b) Membrane selectively permeable
to Na
5 mM
140 mM
150 mM
15 mM
EK  62 mV
log
 −90 mV
ENa  62 mV
log
 62 mV 12

13. Concept 37.3: Action potentials are the signals conducted by axons

14. Ions Change in membrane potential (voltage) Ion channel
Figure 37.9
Ions
Change in
membrane
potential
(voltage)
Ion
channel
Figure 37.9 Voltage-gated ion channel
(a) Gate closed: No ions
flow across membrane.
(b) Gate open: Ions flow
through channel. 14

15. (a) Graded hyperpolarizations produced by two stimuli
Figure 37.10a
(a) Graded hyperpolarizations
produced by two stimuli
that increase membrane
permeability to K
Stimulus
50
Membrane potential (mV)
Threshold
−50
Figure 37.10a Graded potentials and an action potential in a neuron (part 1: hyperpolarizations)
Resting
potential
Hyperpolarizations
−100 1 2 3 4 5
Time (msec) 15

16. (b) Graded depolarizations produced by two stimuli
Figure 37.10b
(b) Graded depolarizations
produced by two stimuli
that increase membrane
permeability to Na
Stimulus
50
Membrane potential (mV)
Threshold
−50
Figure 37.10b Graded potentials and an action potential in a neuron (part 2: depolarizations)
Resting
potential
Depolarizations
−100 1 2 3 4 5
Time (msec) 16

17. Strong depolarizing stimulus
Figure 37.10c
(c) Action potential
triggered by a
depolarization that
reaches the threshold
Strong depolarizing stimulus
50
Action
potential
Membrane potential (mV)
Threshold
−50
Figure 37.10c Graded potentials and an action potential in a neuron (part 3: action potential)
Resting
potential
−100 1 2 3 4 5
Time (msec) 17

18. Rising phase of the action potential
Figure 37.11
Key
Na K 3
Rising phase of the action potential 4
Falling phase of the action potential
50
Action
potential 3
Membrane potential
(mV) 2 4
Threshold
−50 1 1 5
Resting potential 2
Depolarization
−100
Time
Figure The role of voltage-gated ion channels in the generation of an action potential
OUTSIDE OF CELL
Sodium
channel
Potassium
channel 5
Undershoot
INSIDE OF CELL
Inactivation loop 1
Resting state 18

19. Key Na K Resting state OUTSIDE OF CELL Sodium channel Potassium
Figure 37.11a
Key
Na K
OUTSIDE OF CELL
Sodium
channel
Potassium
channel
Figure 37.11a The role of voltage-gated ion channels in the generation of an action potential (part 1: resting state)
INSIDE OF CELL
Inactivation loop 1
Resting state 19

20. Key Na K Depolarization 2 Figure 37.11b
Figure 37.11b The role of voltage-gated ion channels in the generation of an action potential (part 2: depolarization) 2
Depolarization 20

21. Rising phase of the action potential
Figure 37.11c
Key
Na K
Figure 37.11c The role of voltage-gated ion channels in the generation of an action potential (part 3: rising phase) 3
Rising phase of the action potential 21

22. Falling phase of the action potential
Figure 37.11d
Key
Na K
Figure 37.11d The role of voltage-gated ion channels in the generation of an action potential (part 4: falling phase) 4
Falling phase of the action potential 22

23. Key Na K Undershoot 5 Figure 37.11e
Figure 37.11e The role of voltage-gated ion channels in the generation of an action potential (part 5: undershoot) 5
Undershoot 23

24. Membrane potential (mV)
Figure 37.11f
50
Action
potential 3
Membrane potential
(mV) 2 4
Threshold
−50 1 1
Figure 37.11f The role of voltage-gated ion channels in the generation of an action potential (part 6: graph) 5
Resting potential
−100
Time 24

25. Axon Plasma Action membrane potential Cytosol Action potential Action
Figure
Axon
Plasma
membrane
Action
potential 1
Na
Cytosol
Action
potential K 2
Na
Figure Conduction of an action potential (step 3) K
Action
potential K 3
Na K 25

26. Evolutionary Adaptations of Axon Structure
The speed of an action potential increases with the axon’s diameter
In vertebrates, axons are insulated by a myelin sheath, which enables fast conduction of action potentials
Myelin sheaths are produced by glia—oligodendrocytes in the CNS and Schwann cells in the PNS 26

27. Node of Ranvier Layers of myelin Axon Schwann cell Schwann cell
Figure 37.13
Node of Ranvier
Layers of myelin
Axon
Schwann
cell
Schwann
cell
Nodes of
Ranvier
Axon
Myelin
sheath
Nucleus of
Schwann cell
Figure Schwann cells and the myelin sheath
0.1 m 27

28. Schwann cell Depolarized region (node of Ranvier) Cell body Myelin
Figure 37.14
Schwann cell
Depolarized region
(node of Ranvier)
Cell body
Myelin
sheath
Axon
Figure Saltatory conduction 28

29. Concept 37.4: Neurons communicate with other cells at synapses
What are synapses?
Presynaptic cell
Postsynaptic cell
Synaptic cleft
Synaptic vesicles

30. K Ca2 Na Presynaptic cell Postsynaptic cell Axon Synaptic vesicle
Figure 37.15
Presynaptic cell
Postsynaptic cell
Axon
Synaptic vesicle
containing neurotransmitter 1
Synaptic
cleft
Postsynaptic
membrane
Presynaptic
membrane 3 4
Figure A chemical synapse K
Ca2 2
Ligand-gated
ion channels
Voltage-gated
Ca2 channel
Na 30

31. Synaptic Integration
Small EPSPs ADD together to bring the membrane potential closer to threshold, while IPSPs SUBTRACT from the depolarizing effect, keeping the membrane potential below the threshold.

32. Membrane potential (mV)
Figure 37.17a
Terminal branch
of presynaptic
neuron E1 E1 E2 E2
Postsynaptic
neuron
Axon
hillock I I
Threshold of axon of
postsynaptic neuron
Action
potential
Membrane potential (mV)
Resting
potential
Figure 37.17a Summation of postsynaptic potentials (part 1: subthreshold and temporal summation)
−70 E1 E1 E1 E1
(a) Subthreshold, no
summation
(b) Temporal summation 32

33. Membrane potential (mV)
Figure 37.17b
Terminal branch
of presynaptic
neuron E1 E1 E2 E2
Postsynaptic
neuron I I
Action
potential
Membrane potential (mV)
Figure 37.17b Summation of postsynaptic potentials (part 2: spatial summation)
−70
E1  E2 E1 I
E1  I
(c) Spatial summation
(d) Spatial summation
of EPSP and IPSP 33

34. Modulated Signaling at Synapses
In some synapses, a neurotransmitter binds to a receptor that is metabotropic
In this case, movement of ions through a channel depends on one or more metabolic steps
Binding of a neurotransmitter to a metabotropic receptor activates a signal transduction pathway in the postsynaptic cell involving a second messenger
Compared to ligand-gated channels, the effects of second-messenger systems have a slower onset but last longer 34

35. Neurotransmitters (and Their Functions)
Acetylcholine (ACh)
1st neurotransmitter discovered
1921—Otto Lowei
Found in both
Made by combining
HOW does it work?
How does our body get rid of it?

36. Effect of Acetylcholine
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37. Table 37.2a
Table 37.2a Major neurotransmitters (part 1: acetylcholine and amino acids) 37

38. Table 37.2b
Table 37.2b Major neurotransmitters (part 2: biogenic amines) 38

39. Table 37.2c
Table 37.2c Major neurotransmitters (part 3: neuropeptides and gases) 39

40. Amino Acids
Glutamate (rather than acetylcholine) is used at the neuromuscular junction in invertebrates
Gamma-aminobutyric acid (GABA) is the neurotransmitter at most inhibitory synapses in the brain makes post synaptic cells ______________
Glycine also acts at inhibitory synapses in the CNS that lies outside of the brain 40

41. Biogenic Amines Biogenic amines include
Norepinephrine and the chemically similar ephinephrine
Dopamine
Serotonin
They are active in the CNS and PNS
Biogenic amines have a central role in a number of nervous system disorders and treatments 41

42. The Spinal Cord
Spinal cord is a cable of neurons extending from the brain down through the backbone.
Protected by?
Function?

43. The Spinal Cord
Spinal cord is a cable of neurons extending from the brain down through the backbone.
Protected by?
Function?

44. Autonomic Nervous System
See Table 54.5 also

46. (you should be able to answer this!!)
What are G proteins?
(you should be able to answer this!!)

47. Membrane potential (mV)
Figure 37.UN03
Action potential
50
Falling
phase
Rising
phase
Membrane potential (mV)
Threshold (−55)
−50
Resting
potential
Figure 37.UN03 Summary of key concepts: action potential
−70
Depolarization
Undershoot
−100 1 2 3 4 5 6
Time (msec) 47