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29 September Today Neurons Axonal transport Resting Membrane potential Next class Action potentials Conduction of action potentials Lab next week: Measuring action potential conduction velocity in human ulnar nerve. Slide 2 1QQ # 10 for 8:30 class 1.High levels of cortisol a)Can lead to weight loss b)Can suppress inflammation c)Are characteristic of Addisons disease d)Can be the result of prolonged sleep deprivation or pain e)Are associated with subnormal sensitivity to EPI. 2.Which are expected of a 10 year old boy who develops secondary hypersecretion of growth hormone? a)He will have high levels of IGF in his plasma. b)His GHRH level will be low c)Bones of his face, hands and feet will grow disproportionately large relative to the rest of his body d)His hypothalamus is secreting excessive amounts of a tropic hormone Slide 3 1QQ # 10 for 9:30 class 1.A woman in menopause who is not receiving hormone replacement therapy would be expected to a)Have high levels of estradiol b)Have high levels of FSH c)Have high levels of gonadotropin releasing hormone d)Be at higher risk for breast cancer e)Be at higher risk of osteoporosis. 2.Which are expected of a 10 year old boy who develops primary hypersecretion of growth hormone? a)He will have high levels of IGF in his plasma. b)His GHRH level will be low c)Bones of his face, hands and feet will grow disproportionately large relative to the rest of his body d)His hypothalamus is secreting excessive amounts of a tropic hormone Slide 4 Ch 6 Nervous SystemPart A and B Ch 6 Part A: Basic terms Cell types of Nervous Tissue Components of a neuron Components of a reflex arc Axonal regeneration: PNS and CNS Origin of resting membrane potential Equilibrium Potentials (Nernst potentials) S 2 Slide 5 Important Terms (well know these and many more as we move through Chapter 6 Myelin Axon Terminal Node of Ranvier Cell Body (soma) Astrocyte = Astroglia Microglia Ependymal cell Schwann cell Dendrite Neurotransmitter Oligodendrocyte Axon with axon hillock Axonal pathfinding Synapse Afferent Neuron Efferent Neuron Interneuron S 3 Slide 6 Common symbols S 4 Slide 7 Nervous tissue = Neurons (for electrical signaling) and Glial cells (for...) Know functions of CNS Glial cell types. Schwann cells wrap axons in PNS CNS = Brain + Spinal Cord; PNS = axons & ganglia S 5 Slide 8 Excitable membranes & special structures make Neurons good Electrical Communicators } receiving } sending ligand-gated ion channels in membranes of dendrites and soma. Graded potentials voltage-gated ion channels in membrane of axon hillock and axon.. Action potentials = all or nothing! Axon hillock integrates. Decremental conduction in dendrites and somatic membranes Unidirectional Non-decremental conduction in axons Synapse on other neurons, skeletal muscle, smooth muscle, cardiac muscle, glands S 6 Slide 9 Fig. 06.02 In PNS In CNS Nodes of Ranvier ~1mm apart Not all axons are myelinated, although all axons are enveloped by Schwann cells in CNS or Oligodendrocytes in PNS What are the advantages of myelination? Lightly myelinated axon S 9 Slide 10 Communication in The Vertebrate NS Signaling over short and long distances Blood pressure Blood gases and pH Muscle stretch Pain Skin temperature Hair movement Light, Taste, Odor Touch, Pain, Temperature, Etc. Dimensions of neurons Reflexes require some part of the CNS (i.e. frog lab) Peripheral nerves are mixed (have afferent & efferent axons) S 10 Slide 11 Descending neurons (interneurons) from brain to spinal cord Sensory (afferent) neurons from hoof to brain If Nodes of Ranvier are 1 mm apart: How many Schwann cells to myelinate the 2 meters of a sensory axon from hoof to dorsal root ganglion near spinal cord? How many oligodendries to myelinate the 2 meters of the sensory axon ascending in spinal cord to brain? S 11 Slide 12 Fig. 06.03 S 12 Orthograde = anterograde retrograde Slide 13 Axonal Transport Orthograde = Anterograde = from soma to terminals slow1-2 mm/day fast ..200-400 mm/day (kinesin) Retrograde = from terminals to soma fast.200-400 mm/day (dynein) What gets transported and why? Axonal transport is too slow for rapid signaling, so S 13 Slide 14 Who Cares? Slide 15 Alayna Davis October 1992 Age 5 October 31, 1992 October 1998 Slide 16 Damaged axon of the Peripheral Nervous System regenerate about 1 mm per day (dependent upon slow orthograde axonal transport!) Slide 17 Regeneration in CNS? So how can PNS axon regenerate and what prevents CNS axons from regenerating? Slide 18 Bioelectricity is chemistry + physics Membrane potentials Ohms law Resting Membrane Potential The Nernst Equation The Goldman Equation Slide 19 Fig. 06.07 From physics: Ohms Law Voltage = Current x Resistance Slide 20 Fig. 06.08 Virtues of Squid Giant Axon Slide 21 Fig. 06.09 Slide 22 Fig. 06.10 Slide 23 Fig. 06.10a There is a concentration gradient favoring the diffusion of Na+ and K+ through the selectively permeable membrane which has ion channels only for potassium. Slide 24 Fig. 06.10b With K+ channels open, K+ diffuses down its concentraiton gradient, leaving behind CL- ions which are not permeable through the membrane. As more and more K+ move to the left, the compartment they leave becomes more and more negatively charged. Slide 25 Fig. 06.10c Slide 26 Fig. 06.10d Soon, the accumulation of negative charges seriously impeded the diffusion of K+ as the electrostatic force builds up in opposition to the concentration driving force. Slide 27 Fig. 06.10e Equilibrium potential = Nernst potential = diffusion potential Eventually, the electrostatic force that impedes diffusion of K+ is exactly equal to the driving force favoring diffusion based on a concentration gradient. When these two driving forces are equal and opposite, the membrane potential reaches an equilibrium at which the voltage is called So which compartment corresponds to intracellular fluid? E ion+ = 61/Z log ([conc outside]/ [conc inside]) E K+ = 61/1 log (5/150) E K+ = -90 mV Slide 28 The Nernst Equation Calculate the membrane potential if only one ion species is permeable and the concentrations are known on both sides of the membrane.