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.
1QQ # 10 for 8:30 class • High levels of cortisol • Can lead to weight loss • Can suppress inflammation • Are characteristic of Addison’s disease • Can be the result of prolonged sleep deprivation or pain • Are associated with subnormal sensitivity to EPI. • Which are expected of a 10 year old boy who develops secondary hypersecretion of growth hormone? • He will have high levels of IGF in his plasma. • His GHRH level will be low • Bones of his face, hands and feet will grow disproportionately large relative to the rest of his body • His hypothalamus is secreting excessive amounts of a tropic hormone
1QQ # 10 for 9:30 class • A woman in menopause who is not receiving hormone replacement therapy would be expected to • Have high levels of estradiol • Have high levels of FSH • Have high levels of gonadotropin releasing hormone • Be at higher risk for breast cancer • Be at higher risk of osteoporosis. • Which are expected of a 10 year old boy who develops primary hypersecretion of growth hormone? • He will have high levels of IGF in his plasma. • His GHRH level will be low • Bones of his face, hands and feet will grow disproportionately large relative to the rest of his body • His hypothalamus is secreting excessive amounts of a tropic hormone
S 2 Ch 6 Nervous System Part 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 3 Important Terms (we’ll know these and many more as we move through Chapter 6 Cell Body (soma) Afferent Neuron Astrocyte = Astroglia Axon Terminal Myelin Dendrite Microglia Node of Ranvier Neurotransmitter Interneuron Schwann cell Axon with axon hillock Oligodendrocyte Synapse Ependymal cell Axonal pathfinding Efferent Neuron
S 4 Common symbols
S 5 CNS = Brain + Spinal Cord; PNS = axons & ganglia Nervous tissue = Neurons (for electrical signaling) and Glial cells (for...) Know functions of CNS Glial cell types. Schwann cells wrap axons in PNS
S 6 Excitable membranes & special structures make Neurons good Electrical Communicators ligand-gated ion channels in membranes of dendrites and soma…. Graded potentials }receiving Axon hillock “integrates.” Decremental conduction in dendrites and somatic membranes Unidirectional Non-decremental conduction in axons Synapse onother neurons, skeletal muscle, smooth muscle, cardiac muscle, glands }sending voltage-gated ion channels in membrane of axon hillock and axon…..Action potentials = “all or nothing!”
S 9 Fig. 06.02 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? In PNS In CNS Lightly myelinated axon
S 10 Communication in The Vertebrate NS Reflexes require some part of the CNS (i.e. frog lab) Blood pressure Blood gases and pH Muscle stretchPain Skin temperature Hair movement Light, Taste, Odor Touch, Pain, Temperature, Etc. Peripheral nerves are “mixed” (have afferent & efferent axons) Signaling over short and long distances Dimensions of neurons
Descending neurons (interneurons) from brain to spinal cord Sensory (afferent) neurons from hoof to brain S 11 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 12 Fig. 06.03 Orthograde =anterograde retrograde
S 13 Axonal Transport • Orthograde = Anterograde = from soma to terminals • slow……1-2 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…
Alayna Davis October 1992 Age 5 October 1998 October 31, 1992
Damaged axon of the Peripheral Nervous System regenerate about 1 mm per day (dependent upon slow orthograde axonal transport!)
Regeneration in CNS? So how can PNS axon regenerate and what prevents CNS axons from regenerating?
Bioelectricity is chemistry + physics • Membrane potentials • Ohm’s law • Resting Membrane Potential • The Nernst Equation • The Goldman Equation
Fig. 06.07 From physics: Ohm’s Law Voltage = Current x Resistance
Fig. 06.08 Virtues of Squid Giant Axon
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.
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.
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.
Fig. 06.10e Equilibrium potential = Nernst potential = diffusion potential E ion+ = 61/Z log ([conc outside]/ [conc inside]) E K+ = 61/1 log (5/150) E K+ = -90 mV 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?
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.