Exam 2: Answer key
1) State TRUE or FALSE for the following. If FALSE, write a sentence with the correct
answer (5 points)
a) The layer of photoreceptors, bipolar cells and ganglion cells is uniform throughout the
retina, even in areas of high visual acuity. False, in the fovea
light hits photoreceptors directly because the layer of bipolar and ganglion cells is
b) Photoreceptors are absent from the optic disk, but are abundant in the fovea
c) Glutamate activates ON bipolar cells by binding to AMPA receptors in the light
False. Photoreceptors release GLU in the dark and ON bipolar cells are activated in
the light when GLU does not bind to mGLU keeping K+ channels closed.
d) A one-to-one connection exists between photoreceptors and bipolar cells in all areas
except the fovea
False: One to one connections are only present in the fovea
e) The mechanism of dark adaptation is produced by pupil dilation and increased
concentration of Ca.
2) Complete the following table comparing Rods and Cones using the following terms:
High, Low (8 points)
Total number High Low
Total number in fovea Low High
Ability to distinguish two Low High
Photoreceptor/Ganglion ratio High Low 3) Determine the appropriate response for each of the following scenarios (6 points):
a. Which cells synapse on layer one of the left LGN
i. P ganglion cells of the right eye
ii. P ganglion cells of the left eye
iii. NonM-NonP cells of the left eye
iv. M ganglion cells of the right eye
v. M ganglion cells of the left eye
b. Which of the following statements is correct about blob cells in V1? Select all that
i. The cells are binocular
ii. The cells are monocular
iii. The cells are direction and orientation selective
iv. The cells display color opponency
v. Blob cells have circular (center/surround) receptive fields
4) For the following cases, describe which component of the visual system is likely to be
damaged (9 points)
a) An elderly woman complains of headaches, nausea, and worsening peripheral vision
in both of her eyes. Her neurologist suspects a brain tumor compressing which region of
the visual system? Explain your reasoning with a sentence.
Optic chiasm...this is the point where the crossing fibers from the nasal retina of each
eye could be damaged, leading to loss of peripheral vision.
b) Upon careful examination of the patient, the neurologist finds out that her peripheral
vision is ONLY poor in her left eye. The ophthalmologist also suspects that her problem
is happening at the level of the retina? What eye and portion of the retina may have
been damaged in this patient?
Nasal retina, left eye (ipsilateral)
c) After checking the retina the ophtalmologist concludes that he was wrong because
the cells in the eye are healthy. What might be his next suspicion to explain the woman’s
lack of peripheral vision in the left eye?
Left optic nerve is damaged causing the loss of the peripheral vision on the left side.
5) Which of the following stimuli will show A) the greatest and B) the lowest response in a G+/R- P-type ganglion cell? Explain your answer in EACH case. (7 points)
i. completely green circle
ii. a completely red circle
iii. a green center and red surround
iv. a red center and white surround
v. a green center and white surround
A) Greatest Response:________________
(v) Since green and red have significant overlap in their wavelengths, any green in the
surround will negatively activate the surround (R-) and inhibit the center from firing.
B) Lowest Response__________________
(ii) Although there is some green in the red center, this is not the optimal stimulus for the
center and, in addition, it will be inhibited by the red surround.
6) In your rush to get to your BBB109 lecture the other day you banged your elbow
against your bedroom door. (8 points, 2 points each)
a. You feel an initial sharp pain right after you hit the door, then a longer lasting
dull ache as you walk down the hall. What nerve fibers carry each feeling (sharp
pain vs. long lasting ache)?
Sharp = A gamma fibers & Long = C fibers
b. You find that a larger portion of your arm hurts than the small part of your
elbow that hit the door. What is the name of this phenomenon and what produces
it? (in your answer include at least 2 chemicals that lead to this process)
Hyperalgesia. This is produced by the swelling of neighboring tissue and
hyperexcitability of nocicetors due to the diffusion of chemicals such as
bradykinin, Substance P and prostaglandins
c. Which of the following ions or chemicals activate nociceptors? Circle ALL that
vi. blood accumulation
d. You realize you’re gently rubbing your elbow and it’s helping to ease the
pain. What is happening in the afferent axon to regulate your elbow pain?
The activation of touch mechanoreceptors by your rubbing sends an
additional signal along the afferent axon that activates an interneuron in
the dorsal horn. The interneuron inhibits the firing of a projection neuron
that was activated by pain signals. This reduces the sensation of pain.
7) The plot below shows how the membrane potential of a hair cell changes in the
presence of a sound stimulus. (8 points) i.Point to where receptor ion channels are i) opened, ii) closed and iii) at rest
^Stimulus Onset Time
( i. peak, ii. trough, iii. dotted line)
ii. The peak of the receptor depolarization coincides with which of the
a. Trough of the sound wave and trough of the basilar
b. Peak of the sound wave and trough of the basilar
c. Trough of the sound wave and peak of the basilar
d. Peak of sound wave and peak of the basilar membrane
iii. In one sentence, describe the ionic conditions that enable hair cells
depolarization through this channel.
The endolymph bathing stereocilia has a higher K+ concentration