1. Nerves & signaling Ch 37

2. I. Nerves =  A. Cells called neurons bundled together in a sheath of connective tissue

3. II. Neurons:(fits form to function)  A. cells that transmit impulses  B. Neuron structure  1. Dendrites : fine branches that receive signals  2. Cell body : nucleus & organelles  3. Axon : transmits signal  4. Synaptic terminal : passes signal to next cell

4. III. Synapse / synaptic cleft  A) Interstitial space between synaptic terminal and next cell  B) signaling neuron is the presynaptic cell  C) receiving cell is the Postsynaptic cell

5. IV. Neurotransmitters  A. signaling molecules (chemical messengers)  B. Carry signal from synaptic terminal to receptors on postsynaptic cell

7. V. Glia  Cells that  support neurons  Nourish  Regulate surrounding interstitial fluid  Oligodendrocytes – make myelin in CNS  Schwan cells – make myelin in PNS

8. VI. Information Processing : three stages  1. sensory input  2. integration  3. motor output

9. A. Sensory neurons: signal integrators  1. External  a. mechanoreceptors  b. chemoreceptors  c. photoreceptors  2. Internal  a. baroreceptors (pressure)  b. muscle tension  c. pain receptors ( nociceptors)

10. B. Integrators  1.Found in CNS : central nervous system  2. called interneurons :connect neurons in brain & longitudinal nerve cord  3. process info sent in by sensory neurons

11. C. Motor output  1. motor neurons transmit signal from CNS to effector cells  a. muscle cells  b. endocrine cells

12. VII. Movement Across Cell Membrane  A. Simple diffusion  1. very small, not charged  B. facilitated diffusion (protein channel)  C. active transport –against conc. Grad  1. protein pump or co-transporter

13. VIII. Resting Potential  A. Sodium potassium pump  1. active transport  a. 3Na + out and 2K + into cell  b. creates concentration gradients  1. high Na + outside High K + inside  B. K + channels leak ions back out  1. electrical gradient slightly positive outside cell  2. -70 mV potential energy…voltage

14. 2 K + in for every 3 Na + out more K+ leaks out than Na+ leaks in

15.  C. Equilibrium Potential = magnitude of voltage across membrane  1. E K =-90 mV  2. E Na = +62 mV  3. Resting potential ≈ -70 mV bcs  more K + leaking so closer to K +  4. Hyper polarization = inside even  more negative…increase K diffusing out  5. Depolarization = inside becomes less negative…open Na channels

16.  6. Graded potentials..  different levels of hyper/depolarization  a. different neuron responses  b. no response or action potential  c. depolarization signals are summative

17. Graded potential:  Low grade: small stimulus, depolarization does not reach trigger zone with high enough energy = no action potential sent down axon  High grade: intense or long lasting  Signal reaches trigger zone at or above threshold level  Action potential send down axon

18. IX. Action Potential: massive depolarization  A. Sum of depolarization signals causes  depolarization level to reach threshold  B. voltage-gated Na channels open  C. positive feed back opens more  D. Flow of Na in brings E closer to + E na  E. voltage gated K channels open  F. restore negative cytoplasm  G. undershoot = too much negative charge inside  H. resting potential restored by NaK pumps

19. Action potential initiation  http://www.mind.ilstu.edu/curriculum/neurons_intro/ne urons_intro.php http://www.mind.ilstu.edu/curriculum/neurons_intro/ne urons_intro.php

21. X.Action potential:quick reversal of polarity  http://www.youtube.com/watch?v=7EyhsOewnH4&feature=related http://www.youtube.com/watch?v=7EyhsOewnH4&feature=related  A.Action potential is all or nothing  B.Na + flow in as fast as possible for.5ms  C.Then Na + gates shut and K + gates open

22. XI. Propagation of action potential  http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0014- swf_action_potenti.swf http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0014- swf_action_potenti.swf  http://www.youtube.com/watch?v=CvktREcRMAo&feature=related http://www.youtube.com/watch?v=CvktREcRMAo&feature=related  A. One patch of membrane activates the Na + gates next to it by becoming positive inside…..causes more Na + gates to open  B. Propagation is 1 way due to gate inactivation.  1. refractory period = Na gated channels are inactivated

23. C. Saltatory conduction  1. Myelin prevents conduction of ions.  2. spaces between myelin sheath called nodes of Ranvier.  Nerve impulse  jumps between  nodes of Ranvier

24. XII. Transduction of Action Potential  A. Electrical synapse: electric charge transmitted directly to postsynaptic cell  1. gap junctions=rapid unvarying response  B. Chemical Synapse  1. Polarization opens Ca + channels  2. Ca+ causes synaptic vesicles to release neurotransmitters by exocytosis  3. Neurotransmitters diffuse to postsynaptic cell & bind to receptors

25. C. Neurotransmitters – 2 categories  1. excitatory : causes depolarization  2. inhibitory : causes hyperpolarization  3. Ach = acetylcholine ( muscle) both excitatory and inhibitory  4. serotonin = mood/ memory/sleep  5. epinephrine/norepinephrine=excitatory  (called adrenalin & noradrenalin in endocrine function)

26.  4. Receptors are ligand-gated ion channels  a. neurotransmitter = the ligand  b. binding the ligand opens the gate  c. some let in K + & Na + to depolarize  d. some let in K + or Cl - to hyperpolarize

27. D. Integration=postsynaptic response  1. EPSP=excitatory postsynaptic potential and enhances the chance of the ps cell reacting  2. IPSP=inhibitory and pulls the cell back from threshold (restores resting polarization)  3. integration = summation of EPSP & IPSP determines response of cell  a. spatial summation : multiple synapses of same cell receive signal  b. Temporal summation : rapidly repeated signal

28. E. Clearing of synaptic cleft  1. Neurotransmitters cleared by…  a. diffusion  b. re-uptake into pre-synaptic cell  c. enzyme mediated breakdown

29. IX