BIOL 3510 1st Edition Lecture 11 Outline of Last Lecture I. Membrane Structure ContinuedII. Membrane TransportIII. Permeability and ImpermeabilityIV. Three Types of Active TransportOutline of Current Lecture I. Ion ChannelsII. Patch-clamp RecordingIII. Action PotentialsIV. Mechanically-gated ChannelsCurrent LectureIon channels allow the passage of molecules via passive transport, but they are not open pores.1. Selective – particular channels allow for the passage of specific ions2. Often gated – channels open and close in response to a stimulusMembrane potential is the accumulation of electric charge across a membrane. The membrane potential of a resting animal cell is negative.K+ leak channels- K+ flows out of the cell (down its conc. gradient)- K+ flows into the cells (down its voltage gradient)- Equilibrium gives a slightly negative chargePatch-clamp recording detects ion flow across a small area of membrane. Also indicates that ionchannels randomly switch between open and closed conformations. Under various conditions, one slate (open or closed) is favored over the other.Three main types of gated ion channels: voltage=gated, ligand-gated, and mechanically gated.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Voltage and ligand-gated ion channels, for example, could be neuron action potentials. An action potential is the propogation of an electrical signal (change in membrane potential) within a neuron. An action potential is triggered by a depolarization of a neuron’s membrane.Voltage-gated Na+ channels open and close in response to changes in membrane potential. Depolarization is when a membrane potential moves towards a positive value. Voltage-gated Na+ channels have three conformations.Diffusion of Na+ ions propagates the action potential along the axon. After the Na+ ions rush in…1. Voltage-gated K+ ion channels also open2. Exit of K+ ions returns the membrane potential to its resting state3. Na+-K+ pumps return the ion gradient to normalElectrical signals are converted to chemical signals and vice versa at synapses. Chemical signals =neurotransmitters. Action potentials open Ca2+ channels, prompting release of neurotransmitters into the synapse.Neurotransmitter binding opens transmitter-gated ion channels initiating membrane depolarization. They can be excitatory or inhibitory. They combine, interpret, and record signals.An example of mechanically-gated ion channels are the ion channels in the inner ear. Vibrations linked stereocilia move and ion channels
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