Psyc 6, week 1
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This 4 page Class Notes was uploaded by Sabrina Straus on Friday September 16, 2016. The Class Notes belongs to PSYC 6 at Dartmouth College taught by Catherine Cramer in Fall 2016. Since its upload, it has received 5 views. For similar materials see Introduction to Neuroscience in Psychology (PSYC) at Dartmouth College.
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Date Created: 09/16/16
3. 9/14/16 Class Notes THE NEURON AT REST ~cells have electrical potentials I. Recording from the giant axons of squid i n vitro~ when the electrode enters the axon, it records a negative potential (inside of cell is negative) methodology and first recordings resting potential ~occurs because of membrane II. The semipermeable membrane phospholipid bilayerseparates inside from outside/ occasionally punctuated by channels and separates charge ion channelsmovement of ions III. Forces on ions resulting from the semipermeable membrane osmotic pressure (aka diffusion)opposite direction but same magnitude as electrostatic pressure electrostatic pressureattract same charge and repel opposites ~never fully satisfied cations (+) anions () dynamic equilibrium Nernst equation E(lectrical potential) = k log (Xout/Xin) } version for 1 ion Represents dynamic equilibrium at a particular temperature for 1 ion ~assumes that the membrane is permeable to the ion and that no other ions are involved IV. Ions that matter (for neurons at rest) chloride (Cl) can move most freely because smallest sodium (Na+) big on outside/ doesn’t pass easily through membrane potassium (K+) Calcium (Ca2+) V. Putting them all together i n vivo selective permeabilities goldman equationmore complicated form of nernst equation that factors in various ions and their relative permeabilities sodiumpotassium pump also working to maintain concentration gradients across the membrane ~rests around 65mV Chapter Notes Chapter 3: Neuronal Membrane at Rest nervous system: collect, distribute, and integrate info > neuron conducts info over large distances by using electrical signals along the axon ~action potential: nerve impulse that overcomes biological constraints ~excitable membrane: on cells capable of generating and conduction action potentials ~resting membrane potential: difference in electrical charge across the membrane cast of chemicals: salty fluids, membrane, and proteins >cytosol + extracellular fluid: water is the main ingredient in neuron, the extracellular fluid, and cytosol}allows for charge 1. Water uneven distribution of electrical charge 2. Ions: atoms that have a net charge a. Monovalent: difference between numbers of protons and electrons is 1 b. Divalent: 2 c. cations= + charge d. anions= charge ● Important ions: Na+ K+ Ca2+ Cl 3. Phospholipid membrane has hydrophobic layer (nonpolar covalent bond)> lipid contribute to resting and action potentials by forming a barrier to water soluble ions a. Contain long nonpolar chains of carbon atoms b. Polar phosphate group ~ polar head and nonpolar tail ~isolates cytosol of the neuron from the extracellular fluid 4. Protein a. enzymes catalyze chemical reactions b. Cytoskeleton gives neuron shape c. Receptors sensitive to neurotransmitters ~provide routes for ions to cross the neuronal membrane 1. Structure: made up of 20 dif amino acids (have a central carbon atom, 4 molecular groupshydrogen, amino group, carboxyl, and r group) a. Synthesized by ribosomes} forming peptide bonds i. Polypeptides:proteins made of a single chain of amino acids b. 4 structures i. Primary: chain of amino acids ii. Secondary: 1. Alpha helix: spiral 2. Beta sheet iii. Tertiary: w/ interactions among Rgroups iv. Quaternary structure made of subunits 2. Channel proteins: hydrophobic inside and philic exposed part a. Ion channels: ion selective + gating (open and closed by changes in microenvironment) 3. Ion pumps enzymes that use the energy released by the breakdown of ATP to transport certain ions across the membrane ex: Na+ and Ca2+ movement of ions 1. Diffusion: movement of ions from high concentration to low concentration over the concentration gradient 2. Electricity: opposite charges attract forming an electrical current (measured in amps)} cation to cathode and anion to anode a. Electrical potential/ voltage: force exerted on a charged particle (reflects difference in charge between anode and cathodehigher current as difference increases) b. Electrical conductance: relative ability of an electrical charge to migrate (measured in siemens)} depends on the number of ions available to carry electrical charge (also can be described as electrical resistancerelative inability of an electrical charge to migrate (measured in ohms)) ~Ohms law > V=IR ~required for ion movement: permeable membrane + electrical potential difference ion basis of resting membrane potential >membrane potential:voltage across the neuronal membrane} measured with microelectrode and voltmeter measures the electrical potential difference between the microelectrode and a wire (reveals neuronal membrane is negative) >equilibrium potentials: diffusional and electrical forces are equal and opposite} ionic equilibrium potential Notes: 1. Large changes in membrane potential are caused by small changes in ionic concentration 2. Net difference in electrical charge occurs at the inside and outside surfaces of the membrane} capacitance (membrane’s ability to store electrical charge) 3. Ions are driven across the membrane at a rate proportional to the difference between the membrane potential and the equilibrium potential a. Ionic driving force: difference between the real membrane potential and equilibrium potential 4. If the concentration difference across the membrane is known for an ion, the equilibrium potential can be calculated for that ion a. Nernst equation: exact value of eqlm potential >distribution of ions across the membrane ● Concentrations arise due to ion pumps ○ Sodiumpotassium: enzyme that breaks down ATP in the presence of Na+ (energy drives pump and exchanges Na+ for K+) ○ Calcium: enzyme that actively transports Ca2+ out of the cytosol across the cell membrane *mutations of these pumps can cause neurological disorder >relative ion permeabilities of the membrane at rest (because permeable to more than 1 ion) ● Goldman equation: considers the relative permeability of the membrane to different ions ● Importance of regulating the external potassium concentration: due to high permeability, the membrane is sensitive to extracellular changes ○ Ex: depolarization: change in membrane potential from the normal resting value to a less negative value (thus increasing extracellular potassium depolarizes neurons) ○ Sensitivity has led to barriers ■ blood brain barrier: specialization of walls of brain capillaries to limit movements of potassium ■ Glia can also take up extracellular K+ esp. Astrocytes } potassium spatial buffering ● Exception: muscle cells
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