Midterm 1 Key

Answers in italics

Multiple choice:   As always, choose the best answer for each multiple-choice question.  Answer on your scantron form.  Each question (except #1) is worth 3 points.

1. Fill in your scantron form as follows:  (1 point)
• Write and bubble in your social security number in the lower left.
• If you wish to retrieve your exam score through the course web site, write and bubble in a secret code (i.e. a password) in the "Special Codes" section.  Be sure you remember it!
• Write in your name in the upper left (last name first).  (No bubbling required)
• Sign your form in the upper right.
   
1. I promise I did everything above.
2. - e.  I have better ways to spend my time.
    
2. Consider a person sitting in a bathtub of water.  Which of the following would be considered part of Claude Bernard’s “internal environment”?
   1. Fluid inside the person’s cells.
   2. The person’s blood.
   3. The water in the bathtub.
   4. Two of the above.
   5. All of the above.
       
3. The best definition of the term "homeostatic" (the adjective form of homeostasis) is
   1. warm-blooded.
   2. conforming to the environment.
   3. showing a proportional response of a physiological variable.
   4. using feed forward control of a physiological variable.
   5. showing tight regulation of a physiological variable.
       
4. In normal biological systems, positive feedback loops
   1. never occur.
   2. rarely occur and always continue indefinitely.
   3. rarely occur and are ultimately limited by a negative feedback mechanism.
   4. frequently occur and always continue indefinitely.
   5. frequently occur and are ultimately limited by a negative feedback mechanism.
      [I will accept e as well]
       
5. According to the Fick equation, for which of the following would all the changes result in a decrease in the diffusion rate?
   1. Increased area for diffusion, increased concentration gradient, decreased membrane thickness.
   2. Increased area for diffusion, increased concentration gradient, increased membrane thickness.
   3. Reduced area for diffusion, reduced concentration gradient, decreased membrane thickness.
   4. Reduced area for diffusion, increased concentration gradient, increased membrane thickness.
   5. Reduced area for diffusion, reduced concentration gradient, increased membrane thickness.
       
6. Which of the following best describes the structure of a typical cell membrane?
   1. A simple phospholipids bilayer.
   2. A phospholipid bilayer containing embedded proteins.
   3. A phospholipid bilayer containing cholesterol.
   4. A phospholipid bilayer containing embedded proteins and cholesterol.
   5. A chicken salad sandwich on rye with tomatoes but no lettuce.
       
7. At least some water is believed to cross cell membranes by which of the following routes?
   1. Simple diffusion.
   2. Permeation.
   3. Facilitated diffusion.
   4. Two of the above.
   5. All of the above.
       
8. Breathing is controlled in part by
   1. the cerebellum.
   2. the medulla.
   3. the thalamus.
   4. the spinal cord.
   5. Two of the above.
       
9. The dendrites
   1. house a neuron’s nucleus.
   2. carry signals to other cells.
   3. receive signals from other cells.
   4. provide a supporting role in the nervous system.
   5. are not associated with the nervous system.
       
10. The generation of a membrane potential requires
    1. that the membrane is permeable to at least one ion.
    2. that the membrane is permeable to more than one ion.
    3. that there be a difference in the concentration of these ions across the membrane.
       
    4. a and c.
    5. b and c.
        
11. The absolute refractory period of a neuron occurs when
    1. sodium channels cannot yet reopen.
    2. potassium channels cannot yet reopen.
    3. the sodium gradient across the membrane is reduced.
    4. the potassium gradient across the membrane is reduced.
    5. threshold potential cannot be reached.
        
12. An axon with a greater diameter exhibits faster action potential propagation relative to a smaller axon because
    1. ions can flow along the axon more quickly.
    2. it provides a greater membrane surface area, allowing more sodium ions to enter the cell during depolarization.
    3. a diameter above a threshold value leads to saltatory conduction.
    4. the membrane potential decays more slowly with distance.
    5. Axons diameter does not affect the propagation of action potentials.
        
13. In a chemical synapse, the neurotransmitter is moved across the synaptic cleft by
    1. actin filaments.
    2. G-proteins.
    3. synaptic vesicles.
    4. active transport.
    5. diffusion.
        
14. A postsynaptic neuron with two presynaptic neurons might exhibit which of the following?
    1. Excitatory postsynaptic potentials.
    2. Inhibitory postsynaptic potentials.
    3. Temporal summation.
    4. Spatial summation.
    5. All of the above.
        
15. Adrenergic receptors are activated by
    1. acetylcholine.
    2. epinephrine
    3. glycine
    4. serotonin.
    5. enkephalins.
        
16. A neuron that senses hydrostatic pressure is a called a 
    1. mechanoreceptor.
    2. baroreceptor.
    3. thermoreceptor.
    4. photoreceptor.
    5. chemoreceptor.
        
17. Extremely sensitive receptor cells may rely on signal amplification provided by
    1. positive feedback loops.
    2. feed forward mechanisms.
    3. high-amplitude action potentials.
    4. G-protein complexes.
    5. the spike-initiating zone.
        
18. Which of the following pairs represents the best example of range fractionation?
    1. Ruffini’s capsules and Pacinian corpuscles.
    2. Olfactory receptors and taste buds.
    3. Rod cells and cone cells.
    4. Mechanical and chemical nociceptors.
    5. Otoliths and semicircular canals.
        
19. Cells that sense sour taste are thought to be triggered by
    1. an influx of H⁺ ions.
    2. the blockage of K⁺ channels by H⁺ ions.
    3. the activation of Na⁺ channels by H⁺ ions.
    4. the actions of G-protein complexes.
    5. Two of the above.
        
20. Hair cells are not involved in which of the following sensory systems?
    1. Orientation
    2. Acceleration
    3. Audition
    4. Olfaction
    5. Hair cells are involved in all of the above.
        
21. The actual generation of action potentials in the ear occurs in
    1. the ossicles.
    2. the tympanic membrane.
    3. the organ of Corti.
    4. the scala vestibuli.
    5. Reissner’s membrane.
        
22. Hormones
    1. travel to their target organs or tissues only.
    2. travel to all organs and tissues, but may not affect all of them.
    3. travel to and affect all organs and tissues.
    4. are released through ducts.
    5. travel only by diffusion.
        
23. Most hormones can be classified as
    1. peptide hormones.
    2. steroid hormones.
    3. amines.
    4. catecholamines.
    5. prostaglandins.
        
24. Which of the following statements is true?
    1. The anterior and posterior pituitary both release glandular hormones.
    2. The anterior and posterior pituitary both release neurohormones.
    3. The anterior pituitary releases glandular hormones, while the posterior pituitary releases neurohormones.
    4. The anterior pituitary releases neurohormones, while the posterior pituitary releases glandular hormones.
    5. The pituitary does not release hormones; it is a parasitic flatworm.
        
25. Excessive levels of growth hormone in adults tend to cause which of the following conditions?
    1. Additional growth in overall size.
    2. Growth in limited areas, such as the face.
    3. Hyperactivity.
    4. Inhibition of the immune response.
    5. Two of the above.
        
26. Which of the following is least likely to cause increased activity by the thyroid gland?
    1. Increased levels of TRH
    2. Increased levels of TSH
    3. Low body temperature
    4. Iodine deficiency
    5. Injection of T₃ and T₄ into the blood by a mad scientist.
        

Short answer:   Write a concise answer to each of the following questions.  Your answers should fit in the spaces provided.  Each question is worth 4 points.

27. Two solutions (A and B) are introduced into alternate sides of a container separated by a membrane of unknown permeability.  Solution A consists of one liter of a 500 mOsm solution of substance X, while B consists of one liter of a 500 mOsm solution of substance Y.  After an hour, the volume of B is greater than one liter, while the volume of A is less.  What must have happened in this system?  (Hint: what is the membrane permeable to?)

The membrane must be permeable to water (obviously) and also to X, which must have diffused across the membrane, increasing the osmolarity on side B, so that water was then drawn into B by osmosis.  Side B (in its initial state) can therefore be considered hypertonic to side A.

28. Provide the Nerntz equation, either in the complete form or in the simplified form (typically for 37°C).  You do not need to identify the variables except to indicate what z represents.

    or

    z is the charge or valance of the ion.

29. During an action potential
    1. What causes the sodium channels to open?

       The sodium channels involved in an AP are voltage-gated and open when the membrane is depolarized above the threshold voltage.

    2. What causes the sodium channels to close?

       The closing of sodium channels is also triggered by depolarization above threshold.  This process is slower, however, and so is slightly delayed.

30. What is the difference between a tonic and phasic receptor?

    Tonic receptors produce action potentials at a rate proportional to the current state or value of the stimulus.

    Phasic receptors produce APs at a rate proportional to the rate of change of the stimulus.

31. Briefly describe the process by which a photon changes the membrane potential of a rod or cone cell.  You can include a diagram, but be provide a written explanation of what is happening in each step.  Standard abbreviations can be used in place of complete molecular names.

    Photons strike rhodopsin molecules in the lamellar membrane, causing the retinal to change from a cis to a trans form and break away from the opsin.  In this state, the opsin activates transducin, a G-protein complex, which in turn activates PDE [phosphodiesterase] molecules.  PDE converts cyclic GMP into 5’-GMP.  Sodium channels that are held open by cGMP close as a result.  The closure of many Na⁺ channels causes the membrane to go from a depolarized state (in the dark) to a re- or hyperpolarized state.

32. Fill in the following table for the hypothalamic-pituitary system with the appropriate hormones.  (Note that this is not a complete table.)  Be sure to use the full names of each hormone, not the abbreviations.

    Hypothalamus		Anterior Pituitary		Target Organ  or Tissue
    Thyrotropin releasing hormone		Thyroid-stimulating hormone		Thyroid gland
    		Prolactin		Breasts
    Growth hormone releasing hormone		Growth Hormone		Liver (IGF-I release)
    Corticotropin releasing hormone		Adrenocorticotropic hormone		Adrenal cortex