PSL300H1 Lecture : Lecture 5

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raspberrycamel287

11 Dec 2011

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Action potentials start at sensory organs that detect different energies generate receptor: causes depolarization of sensory receptors upon receipt of specific energy (e. g. light, exception photoreceptors hyperpolarize (increase heat, pressure, etc. ) polarity) Transmission of signal two categories of sensory cell transmission: 1. sensory cell generates an action potential at a spike- generating zone sensory membranes are at end of axon. Epsps are generated in the post-synaptic axon post-synaptic membrane is not excitable the first excitable membrane is at a branch point synapse is present. Slowly-adapting receptor potential sustained for duration of stimulus. Repeated stimuli (identical) in succession elicit progressively weaker responses: receptor potential decreases with repeated stimulus. Class of stimulus (light, heat, etc. ) is coded by a specific type of receptor labeled line code. Within a modality, variety of stimulus qualities (e. g. colors) coded by a very restricted number of receptor types specific stimulus is coded by ratio of activity across the population of receptors.

Related Questions

Cell membranes contain openings called ion channels that allow ionsto move from the inside of the cell to the outside. Consider an ionchannel with a diameter of 0.6 nm and a length of 14 nm with R =109 O. During an action potential, this channel is open forapproximately 1.0 ms for the flow of Na+ ions with a potentialdifference across the cell membrane of about 65 mV. How many Na+ions travel through the channel?

Above is a schematic representation of a neuron with a synapse.Switch A is a synapse. R1 and R3 are the resistances of theextracellular space 2 microns from the plasma membrane. R2 is theextracellular resistance 1 mm from the plasma membrane. R5 is theintracellular resistance. When switch A is closed (synapseactivated) draw: (1) the direction of current flow in the circuit;(2) the polarity of potential changes across resistors R1-R6. (3)What are the relative magnitudes and polarities of theextracellular field potentials produced by the synaptic responserecorded at R1 and R3?

Membrane Capacitance and Conductance. For cells having simplemorphological shapes, the
intracellular voltage is nearly uniform throughout the cell suchthat any change in the membrane
potential acts equally on all parts of the membrane. If wehyperpolarize the cell or chemically block
excitable ionic conductances, the membrane potential vm ispassively related to the incoming current i
by:
Cm
dvm
dt
+Gm (vm - El ) = i (1)
where Cm is the whole-cell membrane capacitance, Gm is thewhole-cell membrane conductance, and
El is the leak potential. Most biological membranes have acapacitance of about 1 ÂµF per square
centimeter of membrane area, which allows one estimate cell size bymeasuring capacitance.
a) One way to measure the capacitance is to inject a sinusoidalcurrent i = Ie j?t and to measure the
sinusoidal perturbation in the membrane potential vm = Ve j?t . Inthe frequency domain, both the
current I and the voltage V are complex-valued numbers. Derive aformula for the cell capacitance in
terms of I and V.
b) Another way to measure cell capacitance and conductance is touse a step current injection. In this
case, the current is suddenly increased to a constant i = Io andthe voltage responds with an exponential
form. Measurement of the voltage for a known current impulseprovides a means to estimate the
capacitance and conductance. Toward this aim, find the solution ofEq. 1 for a step increase in
current. Once you have this solution, how would you use the voltageand current measurements to
estimate the passive capacitance and conductance?

PSL300H1 Lecture : Lecture 5

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