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Chapter 8 Neurons, Part 1

Chapter 8 Neurons, Part 1 - Ch 8 Neurons Cellular and...

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Unformatted text preview: Ch 8: Neurons: Cellular and Network Properties, Part 1 Part Objectives: Describe the Cells of the NS Explain the creation and propagation of an Explain electrical signal in a nerve cell electrical Outline the chemical communication and signal Outline transduction at the synapse transduction Review of the Nervous System System New 3rd division: Enteric NS (p 246, and Chapter 21) The afferent and efferent axons together form the together A. Central nervous system B. Autonomic division of the nervous system C. Somatic motor division of the nervous system D. Peripheral nervous system E. Visceral nervous system Autonomic neurons are further subdivided into the A. Visceral and somatic divisions B. Sympathetic and parasympathetic divisions C. Central and peripheral divisions D. Visceral and enteric divisions E. Somatic and enteric divisions Processes or appendages that are part of neurons include A. Axons B. Dendrites C. Neuroglia D. A and B E. A, B and C Cells of NS Cells • 1. Nerve cell = Neuron Fig 8-2 – Functional unit of nervous system – excitable – can generate & carry electrical signals • Neuron classification either Neuron structural or functional (?) structural Fig 8-3 Cells of NS Cells • 1. Neurons • 2. Neuroglia = Support cells – Schwann Cells (PNS) – Oligodendrocytes (CNS) – Astrocytes – Microcytes – Ependymal Cells Fig 8-3 Some Terminology Some Pre- and Postsynaptic membrane, terminal, neuron, etc. Ganglion Interneuron Synaptic Cleft Neurotransmitter Sensory and Motor Functional categories of neurons include A. Afferent neurons B. Sensory neurons C. Interneurons D. Efferent neurons E. All of these are included as functional categories of neurons Axonal Transport of Membranous Organelles Organelles Retrograde Anterograde or normograde Axonal Transport Axonal What is it? Why is it What necessary? necessary? Slow axonal transport (0.2 2.5 mm/day) 2.5 Carries enzymes etc. that Carries are not quickly consumed – Utilizes axoplasmic flow axoplasmic Fast axonal transport (up to 400 mm/day) 400 Utilizes kinesins, dyneins Utilizes and microtubules Actively walks vesicles up or down axon along a or microtubule Which of the following is the main glial cell of the PNS? A. Microglia cell B. Astrocyte C. Schwann cell D. Oligodendrocyte E. All of these are found in the PNS 2. Neuroglia cells 2. In CNS: 1. Oligodendrocytes (formation of myelin) 2. Astrocytes (BBB, K+ uptake) 3. Microglia (modified MΦ ) 4. In PNS: 5. 6. (Ependymal cells) What does this mean? Schwann cells (formation of myelin) Satellite cells (support) See Fig 8-5 Resting Membrane Potential (Electrical Disequilibrium) Ch 5, p160-167 Ch Recall that most of the solutes, Recall including proteins, in a living system are ions system Recall also that we have many Recall instances of chemical disequilibrium across membranes disequilibrium Opposite (+ vs. -) charges attract, Opposite thus energy is required to maintain separation separation The membrane is an effective The insulator insulator Resting Membrane Potential (Electrical Disequilibrium) Ch 5, p160-167 Ch Membrane potential = unequal Membrane distribution of charges (ions) across cell membrane K+ is major intracellular cation Na + is major extracellular cation Na Water = conductor Water Cell membrane = insulator Cell Review of Solute Distribution in Body Fluids Distribution Electro-Chemical Gradients Electro-Chemical • Allowed for, and maintained by, the cell membrane • Created via – Active transport (Na+ pump) – Selective membrane permeability to certain ions and molecules Fig 5-36 Separation of Electrical Charges These Measurements are on a relative scale ! Resting Membrane Potential Difference Membrane Difference • All cells have it All • Resting ⇒ cell at rest • Membrane Potential ⇒ separation of charges creates potential energy charges • Difference ⇒ difference between electrical charge inside and outside of cell (ECF by convention 0 mV) cell Fig 5-33 Measuring Membrane Potential Differences Differences Equilibrium Potential for K+ (Ch 5, p 163) (Ch Equilibrium = Membrane potential difference at which movement down concentration gradient equals movement down electrical gradient Definition: electrical gradient equal to and Definition: opposite concentration gradient opposite Equilibrium potential for K+ = -90 mV Fig 5-34 Potassium Equilibrium Potential Potassium On the planet Endor (where all known physical laws are obeyed), animals have evolved a unique nervous system. Neurons in these animals are exclusively permeable to Ca2+ at their normal resting membrane potential. In these animals, there is a 10-fold higher Ca2+ concentration outside the cell than there is inside. The resting membrane potential of these cells could be approximately A. – 58 mV B. – 29 mV C. 0 mV D. + 29 mV. E. Either A or B is possible Resting Membrane Potential (Ch 5, p 160) (Ch of most cells is between -50 and -90 mV (average ~ -70 mV) Reasons: • Membrane permeability: Membrane K+ > Na+ at rest • Small amount of Na+ leaks into cell into • Na+/K+-ATPase pumps out 3 -ATPase Na+ for 2 K+ pumped into cell Na Equilibrium Potential for Na+ Equilibrium • Assume artificial cell Assume with membrane permeable to Na+ but to permeable nothing else nothing • Redistribution of Na+ until movement down concentration gradient is exactly opposed by movement down electrical gradient gradient • Equilibrium potential Equilibrium for Na+ = + 60 mV for Fig 5-35 Ions Responsible for Membrane Potential Potential Cell membrane Cell – impermeable to Na+, Cl - & Pr – Cl – permeable to K+ ⇒ K+ moves down concentration gradient (from inside to outside of cell) ⇒ Excess of neg. charges inside cell Excess ⇒ Electrical gradient created Electrical Neg. charges inside cell attract K+ back into cell cell Change in Ion Permeability • leads to change in membrane potential • Terminology: Stimulus Stimulus Depolarization Repolarization Hyperpolarization Fig 5-37 Explain Explain • Increase in membrane potential • Decrease in membrane potential • What happens if cell becomes more What permeable to potassium • Maximum resting membrane potential Maximum a cell can have • Membrane potential changes play Membrane important role also in non-excitable tissues! tissues! • Insulin Secretion Insulin p 166 166 β-cells in pancreas have two special channels: • Voltage-gated Ca2+ channel • ATP-gated K+ channel Fig 5-38 Fig 5-38 p 167 Fig Resting membrane potential changes are important in A. Neurons. B. muscle cells. C. In all kinds of different types of cells. D. Both A and B are correct. E. A, B and C are correct. What is the direction of the driving force(s) for the movement of sodium ions when a nerve cell is at rest? nerve A. Inward chemical gradient B. Outward electrical gradient C. Outward chemical gradient D. Both A and B E. Both B and C If the membrane potential is equal to chloride’s equilibrium potential, in which direction will Cl- ions move if a chloride channel opens while the cell remains at resting membrane potential A. Inward B. Outward C. Ions move equally in both directions D. No ions will move through the channel E. Three chloride ions will move out for every two chloride ions that move in. Return to Ch 8: p. 252 Electrical Signals in Neurons Electrical Changes in membrane potential are the Changes basis for electrical signaling basis Only nerve and muscle cells are excitable Only (= able to propagate electrical signals) GHK Equation: Resting membrane potential = Resting combined contributions of the conc. gradients and membrane permeability gradients for Na+, K+ (and Cl-) for Control of Ion Permeability Control • Gated ion channels – alternate between open Gated and closed state and – – – Mechanically gated channels Chemically gated channels Voltage-gated channels • Net movement of ions de- or hyperpolarizes Net cell cell 2 types of electrical signals types Graded potentials, travel over short distances Graded Action potentials, travel very rapidly over longer travel distances distances ...
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