Nervous System: Part III How the Neuron Works: RESTING VS. ACTION POTENTIAL

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1 Nervous System: Part III How the Neuron Works: RESTING VS. ACTION POTENTIAL 1

2 RESTING VS. ACTION POTENTIAL 2

3 How does a neuron cause the transmission of informa4on? 3

4 Cells: surrounded by charged ions Cells live in a sea of charged ions anions (nega4ve) more concentrated within the cell Cl -, charged amino acids (aa - ) ca4ons (posi4ve) more concentrated in the extracellular fluid Na + K + K + Na + Na + Na + Na + Na + Na + K + Na + Na + Na + Na + Na + K + aa - Cl - Cl - Cl - Cl - K + aa - aa - aa - K + K + aa - Cl - aa - Cl - +

5 Measuring cell voltage Voltage measures the difference in concentra4on of charges. The posi4ves are the hole you leave behind when you move an electron. unsfmulated neuron = resfng potenfal of -70mV

6 Cells have voltage! Opposite charges on opposite sides of cell membrane charge gradient stored energy (like a bapery)

7 How does a nerve impulse travel? S4mulus: nerve is s4mulated Na + ions diffuse into cell charges reverse at that point on neuron posi4ve inside; nega4ve outside The 1st domino goes down! Na

8 How does a nerve impulse travel? Wave: nerve impulse travels down neuron change in charge opens next Na + gates down the line Na + ions con4nue to diffuse into cell wave moves down neuron Gate + channel closed + + channel open The rest of the dominoes fall! Na wave

9 How does a nerve impulse travel? Re-set: 2nd wave travels down neuron K + channels open up more slowly than Na + channels K + ions diffuse out of cell charges reverse back at that point nega4ve inside; posi4ve outside Set dominoes back up quickly! K Na wave

10 How does a nerve impulse travel? Combined waves travel down neuron wave of opening ion channels moves down neuron Ready for next time! signal moves in one direc4on flow of K + out of cell stops ac4va4on of Na + channels in wrong direc4on Na wave K +

11 How does a nerve impulse travel? Ac4on poten4al propagates wave = nerve impulse, or ac4on poten4al brain finger 4ps in milliseconds! In the blink of an eye! K Na wave

12 Structure & function! Voltage-gated channels Ion channels open & close in response to changes in charge across membrane Na+ channel closed when nerve isn t doing anything. Na + channels open quickly in response to depolariza4on & close slowly K + channels open slowly in response to depolariza4on & close slowly Na wave K +

13 How does the nerve re-set itself? A\er firing a neuron has to re-set itself both are moving against concentra4on gradients need a pump!! A lot of work to do here! K + K + Na + Na + K + Na + Na + K + Na + Na + Na + Na + Na + Na + Na Na + Na + K + K + Na + K + K+ K + K + Na + Na + Na + K wave K +

14 How does the nerve re-set itself? _Dominoes need to set back up again. Na/K pumps are one of the main drains on ATP produc4on in your body. ac4ve transport protein in membrane requires ATP _Your brain is a very expensive organ to run! re-sets charge across membrane ATP That s a lot of ATP! Feed me some sugar quick!

15 Neuron is ready to fire again Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + K + aa - K + K + K + K + K + aa - aa - aa - K + aa - K + aa - K + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + resfng potenfal

16 Res4ng Poten4al and Ac4on Poten4al 16

17 Key Points Guided Notes on Key Points begin now: 17

18 KP1: Res4ng poten4al is negafve inside the cell and posifve outside This is maintained by: Sodium-potassium pumps that move Na outside and K inside Because there is a difference in charge inside/outside the cell, we say the cell is polarized. 18

19 KP1: Res4ng poten4al is negafve inside the cell and posifve outside The cell says Na to Na (and pumps 3 out) and says OK to potassium (and pumps 2 in) 19

20 Sodium/Potassium Pumps 3 sodium (Na+) ions pumped out for every 2 potassium (K+) ions pumped in Requires ATP!!! Creates a negafve resfng potenfal (-70mV charge inside the cell) Aka polarized 20

21 KP2: Ac4on poten4als cause previously gated Na + and K + channels to open The posi4ve ions flooding the cell signals neighboring gated channels to open This causes signals to propogate or flow down a neuron As this happens, the cell is depolarized (the separa4on of charge from inside/outside is lost) The sodium-potassium pumps and potassium channels re-establish res4ng poten4al (polariza4on) 21

22 Genera4on of Ac4on Poten4als: A Closer Look At res4ng poten4al: 1. Most voltage-gated sodium (Na + ) channels and voltage-gated potassium (K + ) channels are closed during the res8ng state.

Key Na + K + +50 Membrane potenfal (mv) -50 0 Threshold 1 OUTSIDE OF CELL Sodium channel

23 Key Na + K Membrane potenfal (mv) Threshold 1 OUTSIDE OF CELL Sodium channel Potassium channel -100 ResFng potenfal Time INSIDE OF CELL InacFvaFon loop 1 ResFng state

24 AcFon potenfal is generated: 2. Voltage-gated Na + channels open first and Na + flows into the cell, depolarizing it. 3. During the rising phase, if the threshold is crossed, the membrane poten4al increases to and past zero

Key Na + K + +50 Membrane potenfal (mv) -50 0 Threshold 2 1 2 DepolarizaFon OUTSIDE OF CELL

25 Key Na + K Membrane potenfal (mv) Threshold DepolarizaFon OUTSIDE OF CELL Sodium channel Potassium channel -100 ResFng potenfal Time INSIDE OF CELL InacFvaFon loop 1 ResFng state

26 Key Na + K OUTSIDE OF CELL Rising phase of the acfon potenfal DepolarizaFon Sodium channel Potassium channel Membrane potenfal (mv) AcFon potenfal Threshold ResFng potenfal Time INSIDE OF CELL InacFvaFon loop 1 ResFng state

27 4. During the falling phase, voltage-gated Na + channels inacfvated; voltage-gated K + channels open, and K + flows out of the cell

Key Na + K + 3 2 OUTSIDE OF CELL Rising phase of the acfon potenfal DepolarizaFon Sodium channel Potassium channel Membrane

28 Key Na + K OUTSIDE OF CELL Rising phase of the acfon potenfal DepolarizaFon Sodium channel Potassium channel Membrane potenfal (mv) AcFon potenfal Threshold ResFng potenfal Time INSIDE OF CELL InacFvaFon loop 1 ResFng state

Key Na + K + 3 2 OUTSIDE OF CELL Rising phase of the acfon potenfal DepolarizaFon Sodium channel Potassium channel Membrane potenfal (mv) +50-50

29 Key Na + K OUTSIDE OF CELL Rising phase of the acfon potenfal DepolarizaFon Sodium channel Potassium channel Membrane potenfal (mv) AcFon potenfal Threshold ResFng potenfal Time Falling phase of the acfon potenfal 4 INSIDE OF CELL InacFvaFon loop 1 ResFng state

30 5. During the undershoot, membrane permeability to K + is at first higher than at rest, then voltage-gated K + channels close and res4ng poten4al is restored. Hence, there is an undershoot or hyperpolarizafon that persists un4l the membrane potassium permeability returns to its usual value.

Key Na + K + 3 2 OUTSIDE OF CELL Rising phase of the acfon potenfal DepolarizaFon Sodium channel Potassium channel Membrane potenfal (mv) +50-50 -100 0

31 Key Na + K OUTSIDE OF CELL Rising phase of the acfon potenfal DepolarizaFon Sodium channel Potassium channel Membrane potenfal (mv) AcFon potenfal Threshold 2 1 ResFng potenfal Time Falling phase of the acfon potenfal INSIDE OF CELL InacFvaFon loop 1 ResFng state 5 Undershoot

32 Axon 1 AcFon potenfal Na + Plasma membrane Cytosol

33 Axon 1 AcFon potenfal Na + Plasma membrane Cytosol K + AcFon potenfal 2 Na + K +

34 Axon 1 AcFon potenfal Na + Plasma membrane Cytosol K + AcFon potenfal 2 Na + K + K + AcFon potenfal 3 Na + K +

$KP3: Inac4vated Na+ channels cause a refractory period when no ac4on poten4al can occur During the refractory period a\er an ac4on$

35 KP3: Inac4vated Na+ channels cause a refractory period when no ac4on poten4al can occur During the refractory period a\er an ac4on poten4al, a second ac4on poten4al cannot be ini4ated The refractory period is a result of a temporary inac4va4on of the Na + channels

$KP3: Inac4vated Na+ channels cause a refractory period when no ac4on poten4al can occur The refractory period ensures that$

36 KP3: Inac4vated Na+ channels cause a refractory period when no ac4on poten4al can occur The refractory period ensures that ac4on poten4als only travel in one direc4on (towards the synapse) This makes sure that ac4on poten4als cannot propagate backwards

37 KP4: Myelin sheaths increase the speed of signal transmission Ac4on poten4al speed increases with the axon s diameter In vertebrates, axons are insulated by a myelin sheath Myelin sheaths are made by glia* Oligodendrocytes in the CNS Schwann cells in the PNS *Glia are not neurons, they are gluing cells that hold neurons in place, provide nutri4on, and insulate them.

38 Axon Myelin sheath Schwann cell Nodes of Ranvier Node of Ranvier Schwann cell Nucleus of Schwann cell Layers of myelin Axon 0.1 µm

39 The sheaths help signals move more quickly by allowing the action potential to jump from each node of Ranvier to the next.

40 GUIDED PRACTICE 40

41 Take a moment to put these in the correct order Depolariza4on Res4ng state Repolariza4on Hyperpolariza4on Res4ng state

42 Sequenced in order of occurrence Res4ng state Depolariza4on Hyperpolariza4on Repolariza4on Res4ng state

43 +50? Membrane potenfal (mv) Res4ng state Depolariza4on Hyperpolariza4on -50 0? Repolariza4on Res4ng state Time?

44 What is represented by each ques4on mark??: Res4ng Poten4al?: Threshold?: Ac4on Poten4al 44

45 Describe what is occurring at 1,2,3,4,5 using the words: Res4ng state, depolariza4on, repolariza4on, and hyperpolariza4on 45

46 At ResFng PotenFal: 1. Most voltage-gated sodium (Na + ) channels and voltage-gated potassium (K + ) channels are closed during the res8ng state AcFon potenfal is generated: 2. Voltage-gated Na + channels open first and Na + flows into the cell, depolarizing it. 3. During the rising phase, if the threshold is crossed, the membrane poten4al increases to and past zero 4. During the falling phase, voltage-gated Na + channels inacfvated; voltage-gated K + channels open, and K + flows out of the cell 5. During the undershoot, membrane permeability to K + is at first higher than at rest, then voltage-gated K + channels close resul4ng in repolariza8on and res8ng poten8al is restored 46

47 A(n) in Na + permeability and/or a(n) in K + permeability across a neuron s plasma membrane could shi\ membrane poten4al from 70 mv to 80 mv. a. increase; increase b. increase; decrease c. decrease; increase d. decrease; decrease

48 A(n) in Na + permeability and/or a(n) in K + permeability across a neuron s plasma membrane could shi\ membrane poten4al from 70 mv to 80 mv. a. increase; increase b. increase; decrease c. decrease; increase d. decrease; decrease

49 Adding a poison that specifically disables the Na + /K + pumps to a culture of neurons will cause a. the res4ng membrane poten4al to drop to 0 mv. b. the inside of the neuron to become more nega4ve rela4ve to the outside. c. the inside of the neuron to become posi4vely charged rela4ve to the outside. d. sodium to diffuse out of the cell and potassium to diffuse into the cell.

50 Adding a poison that specifically disables the Na + /K + pumps to a culture of neurons will cause a. the resfng membrane potenfal to drop to 0 mv. b. the inside of the neuron to become more nega4ve rela4ve to the outside. c. the inside of the neuron to become posi4vely charged rela4ve to the outside. d. sodium to diffuse out of the cell and potassium to diffuse into the cell.

51 Name three specific adap4ons (transport proteins) of the neuron membrane that allow it to specialize in conduc4on 51

52 (transport proteins) of the neuron membrane voltage-gated K + channels, sodium/potassium pumps, voltage-gated Na + channels. 52

53 Independent Prac4ce: Label the graph of the ac4on poten4al 53

54 Figure 48.11a Independent Prac4ce +50 AcFon potenfal Membrane potenfal (mv) Threshold Time ResFng potenfal

55 CLOSING hpp://bcs.whfreeman.com/webpub/ektron/ Hillis%20Principles%20of%20Life2e/Animated %20Tutorials/ pol2e_at_3402_the_ac4on_poten4al/ pol2e_at_3402_the_ac4on_poten4al.html 55

Nervous System: Part II How A Neuron Works

Nervous System: Part II How A Neuron Works Essential Knowledge Statement 3.E.2 Continued Animals have nervous systems that detect external and internal signals, transmit and integrate information, and