Physioex 9.0 Exercise 3

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Activity 1
1.Increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels because the membrane is permeable to K+ ions. Therefore, the K+ ions will diffuse down its concentration gradient from a region of higher concentration to a region of lower concentration. 2.Increasing extracellular K+ causes the membrane potential to change to a less negative value because the K+ ions diffuse out across the membrane. My results went well compared to my prediction because I predicted that the resting membrane potential would become less negative. 3.The extracellular Na+ did not alter the membrane potential in the resting neuron because the Na+ channels were mostly closed. 4.Na+ and K+ both have a relative permeability of 0 voltage outside a resting neuron and a relative negative permeability inside a resting neuron. 5.A change in Na+ or K+ conductance would affect the resting membrane potential because if the membrane is permeable to a particular ion, that ion will diffuse down its concentration gradient from a region of higher concentration to a region of lower concentration. Activity 2

1.The passive channels that are likely found in the membrane of the olfactory receptor are chemical, in the membrane of the Pacinian corpuscle are pressure, and in the membrane of the free nerve ending are several different modalities because the sensory end of the nerve is less specialized. 2.The term graded potential is meant to describe the amplitude of the receptor when there is an increase in stimulus intensity with an appropriate stimulus. 3.The stimulus modality that induced the largest-amplitude receptor potential in the Pacinian corpuscle was pressure with high intensity. My results went well compared to my prediction because I predicted that high intensity pressure would induce the largest-amplitude receptor potential in the Pacinian corpuscle. 4.The stimulus modality that induced the largest-amplitude receptor potential in the olfactory receptors was chemical with high intensity. My results went well compared to my prediction because I predicted that high intensity chemical would induce the largest-amplitude receptor potential in the olfactory receptors. 5.The Pacinian corpuscle and free nerve ending will likely not have a membrane protein that recognizes other molecules because their stimulus modality are not chemical unlike the olfactory receptors. 6.The type of sensory neuron that would like respond to a green light would be photoreceptors.

Activity 3
1.The term threshold as it applies to an action potential is the voltage at which you first observe an action potential. 2.Depolarization in membrane potential triggers an action potential because nearby axonal membranes will be depolarized to values near or above threshold voltage. 3.The action potential at R1 (or R2) stayed the same as I increased the stimulus above the threshold voltage. My results did not compare well with my prediction because I predicted that the peak value of the action potential would increase. 4.The phrase “all-or-nothing” describes action potential because it only occurs when you reach threshold voltage. 5.The part of the neuron that was investigated in this activity was the axon. Activity 4

1.TTX blocks the voltage-gated Na+ channels between R1 and R2, which blocks the propagation of the action potential from R1 to R2. 2.Lidocaine blocks the voltage-gated Na+ channels between R1 and R2, which blocks the propagation of the action potential from R1 to R2. The effect of lidocaine differs from the effect of TTX because the lidocaine has a peak of response up to 6 seconds while TTX does not. 3.The response at R2 after lidocaine application will necessarily be zero because lidocaine blocks the propagation of the action potential from R1 to R2. 4.Fewer action potentials are recorded at R2 when TTX is applied because TTX blocks the voltage-gated Na+ channels between R1 and R2, which blocks the...
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