Na+K+ Pump: Essential for Cell Functions

1. The beauty of the Na+K+ pump • Found along the plasma membrane of all cells. • Establishes gradients, controls osmotic effects, allows for cotransport

2. Na+K+ pump Nerve cells have a Na+K+ pump and selective permeability to Na+andK+ that set up a potential Na+K+ pump transports 3 Na+ out for every 2 K+ in. Na+–K+ pump

3. Cotransport p. 61

4. The setup… Cotransport…the result

5. Cotransport

6. The Na+K+ pump also establishes chemical gradients and ultimately influences electrical gradients Electrochemical gradient = electrical and chemical (concentration) gradient combined

8. Electrochemical gradients of neurons Neurons and muscles are excitable cells With stimulation, potential across membrane changes from negative inside the cell to being positive inside

9. Membrane ICF ECF Concentration gradient for K+ Electrical gradient for K+

10. K+ effects More K+ diffuses out compared to the diffusion of Na+in K+ would diffuse until it is balanced by its electrical gradient EK+ = –90 mV

11. Na+ effects ECF ICF Gradient for Na+ into the cell Na+ would diffuse until balanced by its electrical gradient Concentration gradient for Na+ Electrical gradient for Na+ ENa+ = +60 mV

12. Na+ and K+passive (leak) channels Na+ leak channel K+ leak channel

13. Na+ and K+ movement together establish the resting potential ECF More K+ leak channels Na+–K+ pump (Passive) (Active) Na+ channel K+ channel (Active) (Passive) ICF

14. Large net diffusion of K+ outward makes EK+ of –90 mV Outside Inside No diffusion of A– Small net diffusion of Na+ inward neutralizes some of the potential created by K+ diffusion Resting membrane potential = –70 mV

15. Cell communication

16. decrease increase

17. Gated ion channels Gated channels allow specific ions to pass only when gates are open • Note difference bwgated and leak channels Triggered by: potential change (voltage), chemical binding, temperature change, stretching

18. Voltage-Gated Na+ Channel ECF Activation gate Slow closing Inactivation gate ICF Closed but capable of opening Inactivated Open (activated)

19. Voltage-Gated K+ Channel ECF ICF Delayed opening Open Closed

20. Na+ and K+ gated channels Depolarization causes: • Na+ gates to open, then slowly close • Delayed opening of K+ gates FirstLater Delayed opening

21. Graded potentials Graded potential Resting potential Time Magnitude of stimulus Stimuli applied

22. Graded potentials Below threshold Signal dies out over distance

23. Graded potentials Initial site of potential change Loss of charge Loss of charge Current flow Current flow

24. Triggering an action potential Na+ equilibrium potential At threshold, Na+ channels briefly open, which causes a large depolarization K+ open during spike, and slowly close, resting potential returns Threshold potential Resting potential Triggering event K+ equilibrium potential

26. 1) Input zone receives incoming signals from other neurons. Dendrites 2) Trigger zone initiates AP’s Axon hillock 3) Conducting zone conducts action potentials Axon terminals 4) Output zone releases neurotransmitter that influences other cells. Dendrites Cell body Axon

27. Conduction of signal interstitial fluid cytoplasm

28. Conduction of signal Na+ Na+ Na+

29. Conduction of signal K+ K+ K+ Na+ Na+ Na+

30. Conduction of signal K+ K+ K+ Na+ Na+ Na+ Na+ K+

31. Action potentials • All or nothing • No degradation of signal over distance • Conduction in one direction

32. Refractory period Action potentials travel in one direction bc of the refractory period

33. Myelination

34. unsheathed node axon Schwann cells of a myelin sheath Na+ action potential resting potential resting potential K+ Na+ resting potential restored action potential resting potential

35. Chemical Synapse Voltage-gated Ca2+ channels Chemically gated Na+, K+, or Cl- channels

36. Calcium influx causes vesicles to perform exocytosis

37. Neurotransmitters A synapse will use only one type of neurotransmitter • Ex: dopamine, serotonin, epinephrine, GABA Neurotransmitters are quickly removed once they bind to receptors • Reuptake or inactivated

38. Neurotransmitters activate gated ion channels Excitatory synapse: Na+ channels Inhibitory synapse: K+ or Cl- channels

39. Signal at the synapse excites or inhibits the postsynaptic neuron Excitatory synapse: • Causes an influx of Na+ into postsynaptic neuron. • This produces an EPSP and depolarizesthe neuron. Inhibitory synapse: • Causes an outflow of K+ from the postsynaptic neuron. It can also cause an influx of CL- • This produces an IPSP and hyperpolarizes the neuron.

40. Inhibitory synapse Excitatory synapse Activation of synapse Activation of synapse EPSP IPSP PSP= Postsynaptic potential

43. Temporal summation: PSPs occur close together in time from a single presynaptic neuron. Spatial summation: PSPs originate from several presynaptic inputs.

45. Some neuron shapes Hippocampus neuron Pyramidal neurons Bipolar neurons - retina Purkinje neurons

46. Drug effects If a drug affects the nervous system, it usually changes synapse function Drug molecules can: • mimic neurotransmitters • falsely stimulate neurotransmitter release • block neurotransmitters, or their reuptake These drugs all mimic natural endorphin

47. How stimulants and sedatives work In a part of the brain stem (RAS), excitatory synapses (norepinephrine) cause wakefulness, inhibitory synapses (GABA) cause drowsiness

48. How stimulants and sedatives work In a part of the brain stem (RAS), excitatory synapses (norepinephrine) cause wakefulness, inhibitory synapses (GABA) cause drowsiness Caffeine, amphetamines, ecstasy (MDMA) norepinephrine in RAS Alcohol, valium, barbiturates, & marijuana activate GABA receptors.