Membrane PotentialActive Electrical Properties of the Neuron Synaptic Transmission (Principles of Neuroscience Ch6, Ch7, Ch8, Ch9, Ch11, Ch12)

Neuron as the functional units of nervous systemStructure of a neuron1x Neuron: carrying signals50x Supporting cells: protect, insulate, reinforce, assist neuronsMultiple sclerosis (MS): immune system-myelin sheathloss of signal conduction, muscle control, brain function

Drawing of the fluid-mosaic model of membranes, showing the phospholipid bilayer and imbedded proteins.

Ion Channels Are Important for Signaling in the Nervous SystemIon channels have three important properties 1. They conduct ions 2. They recognize and select specific ions 3. They open and close in response to specific electrical, mechanical, or chemical signals.

Gates: voltage-gated channels, ligand-gated channels, mechanically gated channels, non-gated channels

Ion Channels Are Proteins That Span the Cell Membrane ion channelNa+ d = 0.095 nm electric field strengthK+ d = 0.133 nm

ionchannel 1 ms, bindingNa+ K+Lipid bilayer: 6-8 nmChannel selective

Several types of stimuli control the opening and closing of ion channels

[Ca++]iVoltage-gated channel

Only a very thin shell of charge differenceis needed to establish a membrane potential.

Resting potential: the voltage across the plasma membrane of a resting neuron

A nerve signal originates as a change in the resting potential: The action potentialSquid giant axonsHodgkin and Huxley, 1940saction potential (nerve signal) Vg Na+ channel openVg K+ channel openAny + ion

One direction:refractory period (Vg Na+ channel inactivation)

all or nonenot vary in size

Synapse (relay point, junction)1. Electrical synapse2. Chemical synapseChemical synapse

Action potentialVg Na+ channel openVg K+ channel openAny + ionMembrane potential (Ch 7)Ion channel (Ch 6)Passive electrical properties of the neuron (Ch 8)Active electrical properties of the neuron (Ch 9)Synaptic transmission (Ch 10, 11, 12)

Action potential()1. -70 mV, K+ permeability, 2. ,Na+, Na+3. , Na+Na+ () +35 mV Na+K+,K+ () 4. K+, (K+)(K+ permeability) Na+-K+ pump

Membrane Potential1. Resting membrane potential 2. Action potential +100 mV-200 mV

AAB BBA

+ AB0 no net - BA

Ln x = 2.303 log xA + B + permeable membraneElectrochemical potential ()Electrochemical potential ()=driving force

Electrochemical Equilibrium and the Nernst Equation29 2.303 RT/F = 60 mVA BX29 EK+-60 mVion

ion (K+ ) ionion

K+Na+Nernst equationion

Goldman EquationResting membrane potentialAction potentialK+ (~Na+25)Na+Cl-K+ (~-75 mV)Na+Na+Na+ (~+55mV)equation

A nerve signal originates as a change in the resting potential: The action potentialGiant squid axonsHodgkin and Huxley, 1940saction potential (nerve signal) Vg Na+ channel openVg K+ channel openAny + ion

Action potential()1. K+ permeability, K+2. ,,Na+, Na+3. , Na+Na+ () +35 mVNa+,Na+K+,K+ () 4. K+, (K+)(K+ permeabilityK+) Na+-K+ pump

Vg Na+ channel openVg K+ channel openNa+voltage clampaction potential V()= I () x R (1/Rchannel)

Refractory period ()

Opening of voltage-gated channels is all-or-nonePatch-clamp

Genes encoding the K+, Na+, and Ca2+ channels stem from a common ancestor

Gating of the Na+ channel is thought to rely on redistribution of net charge in the S4 region

Action potentials move rapidly along myelinated axons because the only parts of the neuronal membrane that undergo ion movementsare the section at the Nodes of Ranvier.

Active Electrical Properties of the Neuron1.2.3. All or none4. Vg Na+ and K+ channel5. 6. 7. Myelin sheath

Synaptic Transmission

Chemical synapse:

Chemical synapse: neuromuscular junction1.very accessible to experimentation2.one muscle one neurotransmitter3.one presynaptic axon4.simple mechanism5.single type of ion channel

Chemical synapse: neuromuscular junction

Nicotinic receptor

Electrophysiological properties: end-plate potential (EPP) in muscle cellCurare (: ACh receptor antagonist

Vg Ca2+ channelNicotinic receptorNa+K+depolarizationN receptorVg Na+Vg K+ Channel--APSummary: neuromusclar junction

Skeletal muscle AP1. Ca++i 2. Ca++Ca++ pump 3. Ca++ATP

Four primary neurons communicate to one secondary neuron.One primary neuron communicates to four secondary neurons.Central Nervous System

IPSP and EPSP

1. Spatial summation ()2. Temporal summation ()

receptor

Chemical synapse: many to one

Four primary neurons communicate to one secondary neuron.One primary neuron communicates to four secondary neurons.Central Nervous System

(A4 10/31 ) action potential synaptic transmission ()