Neurophysiology. The Resting Membrane Potential Intracellular (soma) Extracellular VV -70 mV.

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Presentation transcript:

Neurophysiology

The Resting Membrane Potential

Intracellular (soma) Extracellular VV -70 mV

Three Concepts 1. Concentration Gradients 2. Electrical gradients 3.Selective permeability of the membrane

100 NaCl Solid barrier in place 0 NaCl OutsideInside

100 Na+ 100 Cl- 0 Na+ 0 Cl- Solid barrier in place 0 00 OutsideInside

100 Na+ 100 Cl- 0 Na+ 0 Cl- OutsideInside Barrier removed Na+ Concentration gradient = Cl- Concentration gradient = 100

50 Na+ 50 Cl- 50 Na+ 50 Cl- OutsideInside Barrier removed 00 Na+ Concentration gradient = 0 Cl- Concentration gradient = 0

50 Na+ 50 Cl- 50 Na+ 50 Cl- 00 OutsideInside Measure voltage difference 0 Na+ Concentration gradient = 0 Cl- Concentration gradient = 0 System at equilibrium

100 Na+ 100 Cl- 0 Na+ 0 Cl- Solid barrier in place 0 00 OutsideInside

100 Na+ 100 Cl- 0 Na+ 0 Cl- Replace with Na+ permeable membrane 0 00 OutsideInside Na+ Concentration gradient = 100

50 Na+ 100 Cl- 50 Na+ 0 Cl- Replace with Na+ permeable membrane OutsideInside Na+ Concentration gradient = 0

50 Na+ 100 Cl- 50 Na+ 0 Cl- Replace with Na+ permeable membrane OutsideInside Na+ Concentration gradient = 0

75 Na+ 100 Cl- 25 Na+ 0 Cl- Replace with Na+ permeable membrane OutsideInside Na+ Concentration gradient = 50 System at equilibrium

75 Na+ 100 Cl- 25 Na+ 0 Cl- Replace with Cl- permeable membrane OutsideInside Cl- Concentration gradient = 100

75 Na+ 50 Cl- 25 Na+ 50 Cl- Replace with Cl- permeable membrane OutsideInside Cl- Concentration gradient = 0

75 Na+ 62.5Cl- 25 Na Cl- Replace with Cl- permeable membrane OutsideInside Cl- Concentration gradient = 25 System at equilibrium

Intracellular (soma) Extracellular VV -70 mV

Ion Concentrations in Neurons Ion[X] I [X] O Na+50mM460mM Cl-40mM540mM K+400mM10mM c c e e c e (-70mV resting potential) E Cl - = -65mV E K+ = -90mV Na+ = +55mV E Na+ = +55mV Nernst Equilibrium Potentials

Resting Membrane Potential: Animation

A + B: Summation of EPSPs C + D: Summation of IPSPs A + C: EPSP + IPSP

Postsynaptic Potentials may be excitatory (EPSP) or inhibitory excitatory potentials bring the membrane potential closer to the the cell’s threshold inhibitory potentials prevent the membrane potential from reaching threshold open Na + channels: excitatory open K + channels: inhibitory open Cl - channels: inhibitory E Cl - = -65mV (below threshold) E K+ = -90mV (below threshold) Na+ = +55mV (above threshold) E Na+ = +55mV (above threshold)

Postsynaptic Potentials are graded potentials, as opposed to the all-or-none action potential summate over space (spatial summation) and time (temporal summation) trigger an action potential if, and only if, their summed effect raises the membrane above threshold at the axon hillock decay with time and distance

The Action Potential: Animation

Exocytosis: Process of neurotransmitter release, which is Ca 2+ -dependent. Pinocytosis, or endocytosis: Process of recovering synaptic vesicle.

Ca 2+ (Calcium influx required for neurotransmitter release)

Synaptic Transmission: Animation

Two Modes of Coupling Between Receptors and Ion Channels 1. Ionotropic synapses Receptor protein also acts as ion channel 2. Metabotropic synapses Receptor proteins and ion channels distinct; linked by a second messenger system

Ionotropic Metabotropic FastSlow WastefulEconomical StereotypedModifiable ~~~~~~~~~~~~~~~~~~~~~~~~~~

Autoreceptors found on presynaptic terminal sensitive to neurotransmitter released from that terminal regulate neurotransmitter release usually inhibit further release different receptor subtype