Neurons, Synapses, & Signaling

1. Neurons, Synapses, & Signaling Campbell and Reece Chapter 48

2. nerve cells that transmit information within the body • communication between neurons consists of: • long distance electrical signals • short distance chemical signals Neurons

3. use pulses of electrical current to receive transmit regulate the flow of information over long distances w/in the body Neurons

4. Neuron Organization

5. Nervous System

6. Sensory Neurons • transmit information (senses) from body  brain • are afferent • specialized dendrites that initiate action potential when stimulated Types of Neurons

7. 2. Motor Neurons • transmit signals to muscle fibers & glands • are efferent Types of Neurons

8. 3. Interneurons • majority of neurons in brain • form local circuits connecting neurons Types of Neurons

9. junction between axon terminal & next cell (another neuron, muscle fiber, gland cell) • neurotransmitters are chemical messengers released @ most synapses that pass action potential to receiving cell Synapse

10. presynaptic cell: cell releasing neurotransmitter & passing on action potential • postsynaptic cell: receiving neurotransmitter • synaptic cleft: physical space between the 2; neurotransmitter released into this space & diffuses across it attaching to receptors on postsynaptic cell Synapse

11. Synapse

12. cells that support neurons • Greek: glue • aka neuroglia • nourish neurons • insulate axons • regulate ECF surrounding neurons Glial Cells

13. ions unequally distributed across plasma membrane • inside of cell slightly (-) compared to outside cell • source of potential nrg • called the membrane potential • resting potential: the membrane potential of neuron @ rest = • -60 to –80 mV Ion Pumps

14. Resting Potential

15. Na+/K+ pump generates & maintains the ionic gradients of membrane potential • 1 turn of pump • 1 ATP • 3 Na+ out • 2 K+ in Formation of Resting Potential

16. Membrane Potential

17. pores that span the membrane allowing ions to diffuse across (in or out) • membranes are selectively permeable and variations in how easily any particular ion can cross a membrane depends on the # of channels & how often they are open Ion Channels

18. Types of Ion Channels

19. neurons have gated ion channels that open or close in response to stimuli • open/close changes permeability for that ion • neurons have K+ channels • when open K+ diffuses out of cell • changes resting potential from: -60 mV to -90 mV Action Potentials

20. K+ Ion Channels in Neurons

21. http://bcs.whfreeman.com/thelifewire/content/chp44/4401s.swf • http://www.dnatube.com/video/1105/Understanding-Action-Potential-and-Nerve-Impulses Resting & Action Potentials

22. when K+ channels open & resting potential decreases to -90 mV inside of cell becoming more (-) than normal resting potential called: hyperpolarization Hyperpolarization

23. when Na+ ion channels open Na+ diffuse into cell making inside less (-) compared to outside cell • membrane potential shifts toward (+) mv • this reduction in magnitude of membrane potential called depolarization Depolarization

24. any shift in membrane potential • magnitude of shift varies with strength of stimulus • induce a small electrical current that flows along the membrane leaking out of the cell • so only lasts short distance from source Graded Potentials

25. electrical signal that propagates along the membrane of a neuron as a nongraded (all or nothing) depolarization • have a constant magnitude & can regenerate in adjacent regions of the membrane • travel long distances Action Potential

26. ion channels that open/close based on membrane potential passing a particular level • Na+ channels in neurons are voltage gated: open when depolarization occurs  Na+ diffuses into cell  becomes more depolarized  more Na+ channels open (+ feedback) Voltage-Gated Ion Channels

27. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html • Interactive site to try at home: http://outreach.mcb.harvard.edu/animations/actionpotential_short.swf

28. Action potentials occur when a depolarization increases the membrane voltage to a particular value (the threshold) • for mammals the threshold is a membrane potential ~ -55mV • once started the action potential has a magnitude independent of the strength of triggering stimulus Threshold

29. + feedback loop of depolarization & channel opening triggers an action potential whenever the membrane potential reached the threshold • membrane depolarization opens both Na+ & K+ channels but Na+ opens faster initiating the action potential • Na+ channels become inactivated as action potential proceeds (gates close) & remain so until after membrane returns to resting potential

31. (-) membrane potential restored by inactivation of Na+ channels, which increases K+ outflow • This is followed by a refractory period: • no matter how strong the stimulus to initiate next action potential is cannot initiate one during refractory period Refractory Period

33. Conduction of Action Potentials

34. glial cells oligodendrocytes (CNS) and Schwann cells (PNS) form layers of electrical insulation along length of axons Myelin Sheaths

35. Saltatory Conduction

36. >100 neurotransmitters belonging to 5 groups: • Acetylcholine • Amino Acids • Biogenic Amines • Neuropeptides • Gases Neurotransmitters