Equations and Constants you MAY need.

oK = 273 + oC

F = 96,480 J/V.mol

R = 8.315 J/mol.oK  or  1.987 cal/mol.oK

l = (Rm/Ri)1/2

 

 

electrical force (emf) = zFVm

Eion = (RT/zF) ln (Cout/Cin)

Vm = (RT/F) ln {(pK[K+]1/zout + pNa[Na+]1/zout + pCl[Cl-]1/zout) / (pK[K+]1/zin + pNa[Na+]1/zin + pCl[Cl-]1/zin)}

 

 

BIPN 145 - Quiz 3                             

  1. (20 points) Research into the function of the nervous system has been greatly facilitated by the ability to identify specific neurons in model systems such as the leech. This allows researchers to map neuronal circuitry and show how neuronal function contributes to complex behaviours such as swimming and learning. 

Identify a Retzius cell in the picture to the right and indicate one other piece of information that would confirm your identification.

 

The two big cells are the Rz cells and they also are identifiable by their spontaneous, non-overshooting action potentials and by their electrical coupling.

 

 

  1. (20 points)You have repeatedly impaled cells in numerous leech ganglia that have rather unusual characteristics. You believe that it is a new type of neuron that has not been previously identified. Your job is to convince the editors of Science that your data unequivocally identifies the cell as a new class of neuron and deserves to be published.  Which of the following pieces of data would you use to make your strongest case? Since space in the journal Science is very limited you must make your case with only 2 pieces of data. Circle the two that you would use and explain why.

(A)   You identify the cell as being in the anterior, lateral group or packet of cell bodies.

(B)   The action potentials in these cells is 50% broader than in other known cell types.

(C)   The resting potential in these cells is different from other identified leech neurons.

(D)   The projection pattern (3D shape) of the axons is different from other known cell types.

(E)    The cell shows no tonic or phasic activity.

(F)    Action potentials in these neurons have no pronounced after potentials.

 

(A)Simply localizing a cell to a specific packet doesnot provide a lot of info as there are many different cell types in each packet.

(B) Action potantial amplitudes and shapes are highly characteristic for a particular cell type.

(C) Resting potentials can be variable so this is generally not one of the best criteria to try to use to characterize a cell but if it is very different, ie –10 or –100 mV, then it can be “diagnostic”.

(D) Project patterns of axons and dendrites are very stereotyped (why?) so can also be used to characterize a cell type.

(E) Only a few cell types show tonic activity so this is not a very good characteristic to use.

(F) Many cells lack pronounced after potentials so this is not a good characteristic to use.

 

  1. (10 points) Pick ONE of the answers you DID NOT choose and explain why it was not sufficient evidence to identify a cell type.

(see answer above)

 

(Questions 4-8 are 5 points each) CIRCLE the correct answer.

4. SN1 sensory neurons in crayfish muscle receptor organs (MROs) encode the initial degree of muscle stretch they detect by varying the ___________________ of action potentials fired. 

  1. frequency  **
  2. amplitude
  3. duration
  4. potential

 

5. ______________________________of greater magnitude result from increased stimulus intensity.

  1. Axonal action potentials
  2. Sensory receptor potentials
  3. Muscle endplate potentials
  4. Both B & C **
  5. A, B & C

 

6. Electrical synapses can be distinguished from chemical synapses by all of the following except.

a. There is no synaptic delay at electrical synapses.

b. There are no graded postsynaptic potentials in electrical synapses

c. Small molecules such as ions can diffuse across electrical synapses but not chemical synapses.

d. Electrical synapses contain gap junctions.

e. Changes in extracellular calcium would have no effect on transmission at chemical synapses. *

 

7. Which of the following is a correct statement regarding the differences between extracellular recording and intracellular recording?

a.       Only intracellular recording allow determination of resting membrane potential.*

b.      Only extracellular recordings exhibit potentials of varying amplitudes.

c.       Only intracellular recordings exhibit changes in frequency

d.      Only extracellular recordings have stimulus artifacts

8. What would you expect to be the effect of elevating extracellular potassium from 3mM to 100mM (modified solution 3 from the muscle membrane potential experiment) on recordings from a T cell in a leech ganglion?

  1. No effect
  2. A hyperpolarization of the resting membrane potential.
  3. A burst of action potentials. *
  4. An increase in the threshold for firing an action potential.

 

9. What would you expect would be the response of a neuron to the injection of a negative current into the cell?

  1. No effect
  2. A hyperpolarization of the resting membrane potential. *
  3. A burst of action potentials.
  4. An increase in the threshold for firing an action potential.

 

10. While recording intracellularly from an N cell you stimulate the neuron by injecting current and see an action potential. After removing all the extracellular sodium from the bathing medium you observe no response to the injected current. What would you expect to see following the application of normal leech saline containing a calcium channel blocker on the response to injected current?

  1. No action potential generation
  2. Only graded potential changes in response to the stimulus pulse.
  3. Action potentials of reduced amplitude
  4. Action potentials similar to those seen in normal, unadulterated leech saline.