Midterm 1 Key

Multiple choice:

1. In a negative feedback loop the effector

a. changes a regulated variable in a direction opposite to its deviation from the setpoint.

2. The “internal environment” of the body consists of

d. Two of the above.

3. The use of sensory information to anticipate a change in a regulated variable before it happens is called a

c. feed forward system.

4. Consider two compartments, A and B, divided by a membrane permeable only to chloride ions. In compartment A we put 2.0 M NaCl, and in B we put 1.0 M NaCl. Which choice below best describes the pattern of ion diffusion?

b. Some net movement of Cl^- from A into B; no change in Na⁺ concentrations from the initial state.

5. Consider two compartments, A and B, divided by a membrane. In A we put 500 mOsm NaCl, and in B we put 500 mOsm urea. Over time, water moves from compartment B into compartment A. Relative to compartment A, compartment B was initially

c. isosmotic but hypotonic.

6. Which of the following involves channel proteins?

c. Permeation

7. Which of the following synapses with skeletal muscles?

d. Somatic nervous system

8. The concentration of potassium in the extracellular fluid around a cell is changed while all other ion concentrations remain the same. The best equation to predict the new resting potential of the membrane would be

c. the Goldman equation.

9. The hyperpolarization at the end of a normal action potential results from

c. the opening of voltage-gated K⁺ channels.

10. Action potentials are propagated along an axon because

a. the action potential depolarizes adjacent regions of the neuron beyond the threshold voltage.

11. The fusing of synaptic vesicles with the membrane of the presynaptic cell is triggered most directly by

b. an influx of Ca²⁺.

12. Which of the following would not be true of slow chemical synaptic transmission?

a. Released neurotransmitters take as long as 2 ms to affect the post-synaptic neuron.

13. A neurotransmitter associated with the inhibition of pain signals is

d. Endorphin

14. Sensory neurons can send information about stimulus strength to the central nervous system via

b. the frequency of action potentials generated.

15. An interoceptive receptor

c. senses the body’s internal environment.

16. Which of the following is not true concerning the olfactory system of mammals?

e. Each olfactory neuron is sensitive to only one chemical.

17. An example of a tonic receptor is

a. Ruffini’s capsule.

18. A person who lacked otoliths would probably have trouble

d. sensing her body’s orientation.

19. The sensory neurons of the auditory system respond

c. to mechanical disturbances of the organ of Corti.

20. Which of the following statements concerning vertebrate rod cells is true?

d. The G-protein system involving transducin, phosphodiesterase and GMP amplifies the response to light in rod cells.

21. Which type of secretion is not a chemical messenger?

c. Exocrine

22. Hormones that stimulate intracellular receptors include

b. Steroid hormones

23. The release of hormones is controlled by

e. All three of these mechanisms control the release of hormones.

24. Growth hormone release is greatest.

a. Shortly after going to sleep.

25. Which of the following glands can most directly control body temperature?

b. Thyroid gland

Short answer:

26. Identify and briefly explain an example of a positive feedback loop. (3 points)

Possible examples include the depolarization phase of the action potential, uterine contractions during labor, or phases of the reproductive cycle in human females. Your explanation should indicate in some way that, once the positive feedback loop is started, the effector(s) serve to move the variable in question further from some starting or threshold value. The greater the deviation from this starting value, the more greater the response in the effector. Ultimately the positive feedback loop must be interrupted in some way.

27. Provide the Fick equation (in some form), and indicate what each variable stands for. (You do not need to provide any units.) (4 points)

J = DA {delta}C/{delta}x

J = net diffusion flux (or rate of diffusion)
A = area for diffusion
{delta}C = difference in concentration
{delta}x = distance of diffusion – (or membrane thickness)
D = permeability constant

28. Name two ways that the speed of propagation of action potentials along an axon can be increased. (2 points)

Two we discussed in class are:

• Increasing axon diameter
• Myelination of the axon

29. Briefly describe what is meant by neuronal integration, and explain the difference between temporal summation and spatial summation of post-synaptic potentials. (4 points)

Neuronal integration means that, in a postsynaptic neauron, the effects of multiple small changes in membrane potential (epsp’s and ipsp’s) caused by single AP’s in single presynaptic neurons can sum up to have a potentially greater effect than they do individually. In temporal summation, we are usually referring to the epsp’s (or ipsp’s) from a single neuron summing over time. In spatial summation, multiple presynaptic neurons contribute epsp’s and ipsp’s; the effects of all these neurons are summed to determine the final effect on membrane potential.

30. The sensory system can often provide information on the intensity of a particular kind of stimulus over ranges of several magnitudes. In other words, both a very weak and a very strong stimulus are accurately reported to the central nervous system. Briefly describe two mechanisms or strategies that allow the sensory system to do this. (You may include graphs in your response if you desire.) (4 points)

This question refers to dynamic range without using that term. The two major mechanisms we discussed that the sensory system uses to deal with a very large range in stimulus intensity are:

• Producing an AP frequency that is proportional to the log of stimulus strength, rather than directly to stimulus strength. This allows the receptors to provide accurate information on stimulus strength at both the low and high end of a large range.
• Another approach is to use range fractionation – use different receptors for different stimulus intensities. (E.g. the rods and cones of the vertebrate eye.)

31. Label the parts of the eye on the diagram. (3 points)

32. Fill in the following table for the hypothalamic-pituitary system with the appropriate hormones. (Note that this is not a complete table.) At the bottom of the table, list the two inhibitory hormones released by the hypothalamus and indicate which pituitary hormones they inhibit. Be sure to use the full names of each hormone, not the abbreviations. (5 pts.)

Hypothalamus		Anterior Pituitary		Target Organ or Tissue
Corticotropin releasing hormone		Adenocorticotropic hormone		Adrenal cortex
Gonadotropin releasing hormone		Follicle stimulating hormone		Gonads
		Luteinizing hormone
Inhibitory hormones:		Hormone(s) inhibited:
Somatostatin		Growth hormone, Thyroid stimulating hormone
Dopamine		Prolactin