Neuro1 RMP PDF

Generation and Conduction of Nerve Impulses RESTING POTENTIAL AND ACTION POTENTIAL ION CHANNELS Bear et al. 1996 • An opening (pore) formed by 4-6 membrane spanning protein molecules embedded in the cell membrane • The diameter of the pore determines ion selectivity • Gating is the property of...

Generation and Conduction of Nerve Impulses RESTING POTENTIAL AND ACTION POTENTIAL ION CHANNELS Bear et al. 1996 • An opening (pore) formed by 4-6 membrane spanning protein molecules embedded in the cell membrane • The diameter of the pore determines ion selectivity • Gating is the property of ion channels to open and close depending on changes in the cell membrane • Functional states: closed and activatable [at rest], open [active], and closed and non-activatable [refractory, inactive] Gated ion channels A. Ligand (chemical transmitter) gated channels B. Phosphorylation gated channels C. Voltage gated channels Kandel et al. 4th Edition D. Mechanically gated channels Resting Membrane Potential • Determined by non-gated ion channels (channels that are always open) • Results from the membrane distribution of the major ions (Na, K pump) • Diffusion of ions and the resulting electromagnetic forces contribute to the resting membrane potential which is typically -70mV (-40 to -90mV). • Depolarization: Vm>-70mV • Hyperpolarization: Vm<-70mV Ion Distribution in the motor neuron at rest • Extracellular fluid: sodium Na+, chloride Cl– • Intracellular fluid: potassium K+, organic anions • Equilibrium potential: what would happen if each ion was able to move in or out of the cell in the absence of the others • Na+ would go in and polarize the membrane to +55mV • Cl- would go in and polarize the membrane to -60mV • K+ would go out and polarize the membrane to -75mV Na+ ClK+ A- 3Na+ 2K+ K+ - - - - -75mV Na+ Cl- + + + + 55mV - - - - - - - -60mV KKKKKKKKKKK Na Na Na - - - - - - - - - - - - + + + - - - 70mV 2K+ 3Na+ Resting Membrane Ion Permeability • Permeability is determined by the number of non-gated ion channels present in the membrane • The permeability of potassium is higher than the permeability of sodium • The concentration gradient is maintained by the Na/K pump which sends 3Na+out and 2K+ in • So, K+ is inside while Na+ is outside • There are more K+ non-gated channels than Na+ channels • A lot of K+ goes out and some Na+ comes in so that the resting membrane potential is closer to the K+ equilibrium -75mV than the Na+ 55mV • The Na/K pump moves the ions against their concentration gradient keeping Na out and K in