Home Work Instructions.
Anatomy/Physiology (Dr. Doumen)
Spring 2015

Go to your Mastering A&P site

On the left side, click on “Study Area” and then click on the blue link that
reads “Access the Self Study Area”

In the Column on the left, find “Interactive Physiology” link and click on
it.

You should now see a Table with several Interactive Physiology activities.
Your job is to execute Nervous System I: Ion Channels and Nervous
System I : Membrane potentials.

To get started, click on Nervous System I : Ion Channels. On the new
page, click on the link at the top of the page under TOPIC. Do the same
afterwards for Nervous System I : Membrane potentials.

You will need to fill out questions on a worksheet. The worksheet for both
topics is attached below. DO NOT download the worksheet on the study
area site since it is not what I want you to do.

You will provide ALL your answers in dark blue ; type out your answers
below each question, fill in the blank lines or fill in the tables. Where blank
lines appear, eliminate them and replace with your answer(s). It should be
self-explanatory. The worksheet is a word document and everything needs
to be typed in and kept neat. Thus, do not cut tables off and/or create wild
convoluting margins. Presentation counts !
Your Name :
Topic 1 : The Nervous System: Ion Channels
1.
Why does a cell membrane need ion channels? Explain in several sentences.
2.
Ion channels are selective for specific ions. What three characteristics of
the ions are important for this selectivity?
a.
b.
c.
3.
Channels can be classified as either gated or non-gated channels. A sodium
channel that is always open would be classified as a/an ___________channel. In
class we defined a channel that is always open as a __________ channel.
4.
From our discussion in class and from this presentation, explain in what direction
a sodium ion would move when a cell has open sodium channels available in the
membrane.
5.
What two forces are involved that direct the movement of sodium into the cell ?
6.
What is the membrane potential of a neuron at rest?
What is the reason for this membrane potential? (we have seen this in class and
the presentation tells you without going in detail)
7.
If you observe the presentation carefully, you will be able to test at what voltage
potential across the membrane the voltage-gated channels open and close . Fill
those Membrane Potentials in this Table. (pay close attention)
Channels
Open
Close
Potassium
Sodium
8.
9.
Acetylcholine (ACh) and GABA are neurotransmitters that open chemically-gated
channels. What ions pass into the cell when these channels are activated?
a. ACh:
ions
b. GABA:
ions
Ion channels are regionally located and functionally unique. List all the areas on
the neuron and the type of potential dependent on the following types of ion
channels:
Channels
Areas on the neuron
Type of potential
Nongated
Chemically-gated
Voltage-gated
9.
Where do action potentials occur in a neuron and why? (the table above should
tell you now).
10.
11.
From the quiz, place an “X” by the characteristics of voltage-gated sodium channels.
_____
Always open
_____
Found along the axon
_____
Important for action potential
_____
Opened and closed by gates
_____
Found on the dendrites and cell bodies
_____
Important for resting membrane potential
Name two kinds of channels through which chloride ions could pass into the cell.
a.
b.
12.
Do some research and provide me with a half page discussion regarding
Tetrodotoxin . This presentation already mentions one source where one can find
this toxin. In your discussion, include this animal and one other animal that
contains this toxin. Furthermore discuss the physiological reason why this toxin is
deadly and provide more details regarding this toxin. ( for example, what kind of
toxin is it, who makes it, what other animals have it …. ).
Topic 2 : The Nervous System: Membrane Potential
1.
Record the intracellular and extracellular concentrations of the following ions
(mM/L) according to the presentation .
Intracellular
Extracellular
Sodium (Na+)
Potassium (K+)
Chloride (Cl–)
2.
What negative charged particles are present inside the cell to balance the positive
charged ions?
3.
How would the following alterations affect the membrane permeability to K+?
Use the words “increase” or “decrease” to indicate the change in permeability.
a. An increase in the number of passive (leakage) K+ channels ___________
b. Opening of voltage-gated K+ channels __________
c. Closing of voltage-gated K+ channels __________
d. Adding more passive (leakage) Na+ channels __________
4.
What mechanisms do excitable cells such as neurons use to change the
permeability of the membrane for a certain ion?
5.
Looking back at question 6 in Topic 1, what can we measure in a cell that will tell
us that the permeability for a certain ion has changed?
6.
a. What acts as a chemical force that pushes K+ out of the cell?
b. What force tends to pull K+ back into the cell?
7.
When the two forces listed above are equal and opposite in a cell permeable
only to K+, this is called the ____________ potential for K+
8.
In Class we have seen how to calculate this potential for a single ion. It is called
The _________ equation.
9.
Write out this equation below and define all elements in that equation.
10.
Calculate the Eq. Potential for each ion using the previous Table.
Eq. Potential in mV
Sodium (Na+)
Potassium (K+)
Chloride (Cl–)
11.
If a neuron at rest were ONLY permeable to sodium, what would the resting
membrane potential be ?
If a neuron at rest were ONLY permeable to potassium, what would the resting
membrane potential be ?
12.
Since the neuron is permeable to Na+ as well as K+, the resting membrane
potential is not equal to the equilibrium potential for any ion, instead it is
_____________
13.
What is the reason that nerve cells have this specific resting membrane potential
mentioned in the question above ?
14.
Although a cell has chloride leakage channels, it is sometimes said that chloride
ions do not provide much current to a cell and do not contribute much to the
resting membrane potential. Why do you think this is ? The above discussion
should give you clues.
15.
At the resting membrane potential, what kind of current (ion flow) do we have for
Na+ : ______________
K+ : _______________
16.
What important membrane protein resets the gradients for these ions across the
membrane ? __________________
17.
What will happen to the resting membrane potential of an excitable cell if the
following conditions happen below (Depolarize or Hyperpolarize )
a.
an increase in extracellular fluid concentration of K+? _____________
b.
a decrease in extracellular fluid concentration of K+? ______________
c.
an increase in extracellular fluid concentration of Na+? _______________
d.
a decrease in number of leakage Na+ channels? ________________
18.
We have seen that K+ always tends to “leave” the cell. But under what conditions
would K+ actually start entering the cell through leakage channels ? Explain.
19.
Which ion channels are not present in Glial cells according to this presentation ?
20.
In a half page discussion, present evidence that confirms or refutes the response
given in question 19 according to the Interactive Physiology presentation. Do
some brief internet research and provide me some details and with at least one
credible reference.
______________________________________________________________________
Final questions not related to the presentation.
A. What is Hyperkalemia and why would a person develop this condition. I like to see
at least a half page presentation
B. Complete the Table below . Assume that the intracellular concentration for K+ is a
constant 150 mM. Calculate the Eq. Potential for K+ at each concentration
mentioned in the left column. The EK+ for the situation where extracellular K+ is
equal to 5 mM has already been calculated. Do this now for the rest of the data. In
addition, knowing that the RMP is always about 17 mV more positive than EK+, fill in
the estimated RMP at each value for K+ as well.
Extracellular
K+(in mM)
1
2
3
4
5
6
8
10
12
EK+
RMP
-88.6 mV
-70 mV
14
C. Voltage gate sodium channels have two gates. They open at ~ - 55 mV and close at
around + 30 mV. They will be re-activated for opening if they see a Membrane
potential more negative than -50 mV. Given that information, and using the
information in table above, explain why potassium needs to stay low in the
extracellular fluids ( and blood) and why hyperkalemia can cause death.