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7 neurons
1) Neurons detect stimuli and transmit signals along their axons via electrical impulses. Neuroglial cells structurally and functionally support neurons. 2) An action potential is generated when a threshold stimulus causes voltage-gated sodium channels to open, depolarizing the neuron. Potassium channels then repolarize the membrane. 3) At a synapse, an action potential causes neurotransmitter release from the presynaptic neuron. This may excite or inhibit the postsynaptic neuron depending on the neurotransmitter.
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7 neurons
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- 2. Neural Signaling Response tostimulus involves: •detection of stimulus •conduction of signal •processing •response
- 3. receives information nucleus & organelles integrates info carriessignal to other cells neuroglial cell synaptic terminal
- 4. p887 Speed of impulse– 30-90 m/sec
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- 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. CNS -brain -spinal cord PNS (peripheral nervous system) -sensory neurons -motorneurons Interneurons link CNS & PNS p886
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- 9. Ganglion Cell bodies Myelin sheath ArteryVein Axon 100 µm Nerve-consists of hundreds (thousands) of axons wrapped together in connective tissue. bullfrog -A mass of nerve cell bodies.
- 10. Initiation of actionpotential 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?
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- 12. Resting Membrane Potential-Polarized K+ leakNa+ /K+ ATP channel pump K+ leak channels maintain negative voltage inside the cell. There are few Na+ leak channels.
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- 15. & Potassium Channel 1.2. 3. 4. channel inactivated
- 16. Propagation of nerveimpulse polarized depolarized repolarized
- 17. Voltage gated Na+ channel Howdo voltage gated channels work?
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- 19. Area of depolarizationPotassium channel Sodium channel Area of repolarization Area of depolarization Action potential Action potential
- 20. Resting state Depolarization RepolarizationReturn to resting state Extracellular fluid Sodium channel Potassium channel Cytoplasm 1 2 3 4 2 1 3 4
- 21. Na+ /K+ ATP Pump -Average neuroncontains 1,000,000 pumps. -Speed – 200 Na+ ions & 135 K+ ions per second.
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- 29. Excitatory Neurotransmitter Promotes Depolarization ofPostsynaptic Neuron
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- 32. Green = excitatory Rust= inhibitory
- 33. Events at theSynapse p897
- 34. Cocaine -Binds the dopamine transportersand prevents reuptake of the neurotransmitter. -Dopamine continues to stimulate the postsynaptic cell.
- 35. Effect of Alcoholon 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.
- 36. 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
- 38. Ruffini corpuscle (pressure) Dermis 500 µm Pacinian corpuscle (deep pressure, touch) Hairfollicle receptor (hair displacement) Merkel disc (touch, pressure) Meissner corpuscle (touch, pressure) HairFree nerve endings (pain) Epidermis Subcutaneous tissue
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- 40. papilla – location oftaste buds. “wall-like” “leaf-like” “mushroom-like”
- 41. Taste buds –a collection of chemosensitive epithelial cells associated with a sensory neuron. Circumvallate papilla
- 42. Each taste budis “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.
- 44. Smith &Margolskee Scientific American March2001 Salts Na+ ions enter Na+ channels & depolarize the cell. The cell repolarizes by opening K+ gates.
- 45. Smith &Margolskee Scientific American March2001 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
- 46. Smith &Margolskee Scientific American March2001 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.
- 47. G protein GTP K+ channel open Adenylyl cyclase Protein kinase A Sugarmolecule Receptor K+ channel closes activates 1 2 3 4 5 6 Gustducin cAMP closes K+ leak channels, but Na+ leak channels stay open.
- 48. The Tongue TasteMap 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.