7 neurons


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7 neurons

  1. 1. Neurons & The Nervous System
  2. 2. Neural Signaling Response to stimulus involves: •detection of stimulus •conduction of signal •processing •response
  3. 3. receives information nucleus & organelles integrates info carries signal to other cells neuroglial cell synaptic terminal
  4. 4. p887 Speed of impulse – 30-90 m/sec
  5. 5. p887
  6. 6. Neuroglia • structural & functional support of neurons (surround axons) • two important neuroglial cells: -Schwann cells (PNS) -oligodendrocytes (CNS) •Cells wrap around axons several times to form myelin sheath (Figure). Function? •Nodes of Ranvier (1-2 mm apart) Louis Antoine Ranvier 1878 discovered myelin and nodes.
  7. 7. CNS -brain -spinal cord PNS (peripheral nervous system) -sensory neurons -motor neurons Interneurons link CNS & PNS p886
  8. 8. p894
  9. 9. Ganglion Cell bodies Myelin sheath Artery Vein Axon 100 µm Nerve-consists of hundreds (thousands) of axons wrapped together in connective tissue. bullfrog -A mass of nerve cell bodies.
  10. 10. Initiation of action potential all or nothing must reach a threshold -Membrane potential is the voltage difference across a cell’s membrane (cytoplasm is more negative than outside the cell – resting potential is -70mV) -Nerve impulses are detected as a wave of electrical activity. (electrochemical change) -With an all or nothing response, how is intensity detected?
  11. 11. Resting Potential p889
  12. 12. Resting Membrane Potential-Polarized K+ leak Na+ /K+ ATP channel pump K+ leak channels maintain negative voltage inside the cell. There are few Na+ leak channels.
  13. 13. p893
  14. 14. p893
  15. 15. & Potassium Channel 1. 2. 3. 4. channel inactivated
  16. 16. Propagation of nerve impulse polarized depolarized repolarized
  17. 17. Voltage gated Na+ channel How do voltage gated channels work?
  18. 18. Science 4/3/10 K+ voltage gated channels
  19. 19. Area of depolarization Potassium channel Sodium channel Area of repolarization Area of depolarization Action potential Action potential
  20. 20. Resting state Depolarization Repolarization Return to resting state Extracellular fluid Sodium channel Potassium channel Cytoplasm 1 2 3 4 2 1 3 4
  21. 21. Na+ /K+ ATP Pump -Average neuron contains 1,000,000 pumps. -Speed – 200 Na+ ions & 135 K+ ions per second.
  22. 22. Fig. 44.11 p878
  23. 23. p894
  24. 24. Neural circuits Convergence Divergence
  25. 25. Synaptic vesicles Neurotransmitter molecules Receptor Plasma membrane of postsynaptic neuron Presynaptic terminal Synaptic cleft Na+ 0.25 µm presynaptic neuron postsynaptic neuron synaptic terminal What happens to the neural transmitter? 20 nM (10-9 M)
  26. 26. p896
  27. 27. Excitatory Neurotransmitter Promotes Depolarization of Postsynaptic Neuron
  28. 28. Inhibitory Neurotransmitter Hyperpolarizes the cell
  29. 29. p898
  30. 30. Green = excitatory Rust = inhibitory
  31. 31. Events at the Synapse p897
  32. 32. Cocaine -Binds the dopamine transporters and prevents reuptake of the neurotransmitter. -Dopamine continues to stimulate the postsynaptic cell.
  33. 33. Effect of Alcohol on the NS •Increases absorbance of K+ -neuron cannot repolarize -no repolarization - prevents propagation of action potential. -no action potential, no influx of Ca+2 , hence no release of neural transmitter. •Leads to slurred speech, slow reflexes, blurred vision & loss of inhibition.
  34. 34. Sensory Receptors •Mechanoreceptors - pressure •Energy Detecting Receptors heat cold light - photoreceptors •Chemoreceptors concentration of a particular compound How do they work? mechanoreceptors – stretch receptors -fire when stimulated - no adaptation sensory receptors – fire at a continuous basal level - undergo adaption Ex. – chemoreceptors & photoreceptors thermal
  35. 35. Ruffini corpuscle (pressure) Dermis 500 µm Pacinian corpuscle (deep pressure, touch) Hair follicle receptor (hair displacement) Merkel disc (touch, pressure) Meissner corpuscle (touch, pressure) HairFree nerve endings (pain) Epidermis Subcutaneous tissue
  36. 36. Pressure Sodium channel opens Sodium channel closed
  37. 37. papilla – location of taste buds. “wall-like” “leaf-like” “mushroom-like”
  38. 38. Taste buds – a collection of chemosensitive epithelial cells associated with a sensory neuron. Circumvallate papilla
  39. 39. Each taste bud is “onion” shaped structures of between 50-100 taste cells. Molecules in the food dissolve in saliva and contact the taste receptors through the taste pores.
  40. 40. Smith &Margolskee Scientific American March 2001 Salts Na+ ions enter Na+ channels & depolarize the cell. The cell repolarizes by opening K+ gates.
  41. 41. Smith &Margolskee Scientific American March 2001 Sour - Acids 1. H+ directly enter channels. 2. H+ bind to Na+ channels causing them to open. 3. H+ bind to K+ channels and close these channels (no K+ leaves). Taste Cell
  42. 42. Smith &Margolskee Scientific American March 2001 Sugar molecules bind to a receptor. This activates a G-protein & and the secondary messenger cAMP causing K+ leak channels to close. The Na+ leak channels allow Na+ in a & the neuron depolarizes.
  43. 43. G protein GTP K+ channel open Adenylyl cyclase Protein kinase A Sugar molecule Receptor K+ channel closes activates 1 2 3 4 5 6 Gustducin cAMP closes K+ leak channels, but Na+ leak channels stay open.
  44. 44. The Tongue Taste Map Smith &Margolskee Scientific American March 2001 1. Although each neuron responds more strongly to one type of tastant, it can also generate a stimulus to other dissimilar molecules. 2. Specific tastes might be distinguished by the brain due to a pattern of activity across neural networks. 3. Smith & Margolskee claim that taste discrimination depends on the relative activity of different neuron types, each of which must contribute to the overall pattern of activity in order to distinguish between different stimuli.