Deck 28: The Nervous System

Question 1

Which region of the CNS listed below is NOT correctly paired with its function?

A) Somatosensory cortex-receives sensory input from all parts of the body
B) Hypothalamus-regulates body temperature, appetite, thirst, and emotions
C) Cerebellum-relay station for ascending and descending tracts
D) Corpus callosum-connects the two brain hemispheres
E) Auditory cortex-interprets sound information from the ears

Answer 1

Cerebellum-relay station for ascending and descending tracts

Question 2

For your birthday, you get a robot-building kit with three parts: 1) a set of gadgets for detecting sound, touch, and light, 2) a set of motors that can move mechanical parts, and 3) a microprocessor that can be programmed to respond to inputs according to predetermined rules. You build a robot car, and find it surprisingly lifelike as it navigates around the room. The three parts of the kit are analogous which parts of the human body?

A) 1) autonomic nervous system, 2) somatic nervous system, 3) hypothalamus
B) 1) sympathetic pathways, 2) parasympathetic pathways, 3) CNS
C) 1) sensory pathways, 2) motor pathways and muscles, 3) CNS
D) 1) motor pathways and muscles, 2) sensory pathways, 3) CNS

Answer 2

1) sensory pathways, 2) motor pathways and muscles, 3) CNS

Question 3

Your roommate is on an ultra-low fat diet to try to lose weight. Given what you know about structure of the nervous system, what advice would you give him?

A) "You should drink large quantities of water, because the brain is mostly water."
B) "Good for you! Losing weight by any means necessary can only help your brain."
C) "You should eat some healthy unsaturated fats, like those found in fish, olive oil, and nuts, because your brain needs fatty acids to build the myelin sheaths around your axons."
D) "You should eat trans fats, from donuts, because 'trans' is short for neurotransmission."

Answer 3

"You should eat some healthy unsaturated fats, like those found in fish, olive oil, and nuts, because your brain needs fatty acids to build the myelin sheaths around your axons."

Question 4

"Synapses are connections between the axon of one neuron and the dendrite of another neuron, where neurotransmitters transmit a chemical signal." How would you modify this statement to make it more complete? (Check all that apply.)

A) The statement needs no modification.
B) Synapses can also form between an axon and a cell soma.
C) Neuromuscular synapses form between the axon of a neuron and a muscle.
D) Synapses often form among the parts of a single cell.
E) Synapses can be electrical as well as chemical.

Question 5

Choose the two primary factors that contribute to the resting membrane potential of a neuron.

A) K⁺ leak channels make the cell membrane more permeable to K⁺.
B) The sodium-potassium pump exports 3 K⁺ from the cell for every 2 Na⁺ it imports.
C) Na⁺ leak channels make the cell membrane more permeable to Na⁺.
D) K⁺ leak channels cause a higher concentration of K⁺ outside the cell.
E) The sodium-potassium pump exports 3 Na⁺ from the cell for every 2 K⁺ it imports.

Question 6

Palytoxin is incredibly toxic, perhaps the second most dangerous non-peptide toxin. It targets the sodium-potassium pump, locking it open and forming a channel through which the ions can passively flow. Palytoxin is produced by zoanthid cnidarians (soft coral), and there have been incidents of poisoning from zoanthids within marine aquaria tanks in people's homes. It is also thought to be the source of the legend of the Limu make o hana ("Seaweed of Death from Hana").

-A Hawaiian legend tells of a village that angered a shark god. In revenge, a "seaweed" began to grow in the tidepools that killed anyone who touched it. In fact, this "limu-make-o-Hana" -- a zoanthid cnidarian -- contains a palytoxin that locks the sodium-potassium pump open, allowing free flow of ions. If a villager suffers palytoxin poisoning, which way will the ions in his neurons flow?

A) all ions will flow out
B) potassium in, sodium out
C) chloride and sodium out, potassium in
D) sodium in, potassium out

Question 7

If K⁺ can exit the cell through leak channels, why don't they flow out until there are equal concentrations on both sides of the membrane?

A) K⁺ can act as an enzymatic cofactor, and most K⁺ ions are bound to cellular enzymes.
B) The leak channels allow a very slow leak that cannot keep pace with active import of K⁺ ions.
C) Chelator molecules trap K⁺ on the inside of the membrane.
D) The negative electrical potential inside the cell creates a force that holds the K⁺ ions in.

Question 8

The outside of a neuron is positively charged at resting potential. Why do K⁺ ions leave the cell when K⁺ channels open during an action potential?

A) The diffusion gradient is the only factor that affects ion movement.
B) K⁺ ions are actively pumped out by the sodium-potassium pump acting in reverse.
C) Voltage-gated K⁺ channels open when membrane potential reaches +50 mV during the depolarization phase. The diffusion gradient and electrical force cooperate to drive K⁺ ions out of the cell.
D) Negatively charged proteins leave the cell at the onset of the action potential.

Question 9

Botulinum toxin-- A toxin produced by the bacterium Clostridium botulinum. Known for sometimes lethal poisoning from infected meat products. In modern controlled medical or cosmetic use, the very same toxin is known as Botox.
Tetanus toxin-- Another very potent neurotoxin produced by Clostridium tetani.
Strichnine-- A highly poisonous alkaloid produced by the Strychnos nux-vomica tree, historically used to kill rats and other pests.

-Botulinum toxin, or "botox", has become popular for cosmetic surgery. The toxin prevents neurosecretory vesicles from docking at the plasma membrane and releasing neurotransmitter. How would this toxin affect the neuromuscular junction?

A) Since ACh is not released, the muscles stay in a state of repeated contraction.
B) Since ACh is not released, the muscles are not activated to contract and remain relaxed.
C) Buildup of ACh causes promiscuous activation of all nearby sensory neurons.
D) Buildup of ACh leaks back into the brain, creating a calming effect.

Question 10

How do temporal and spatial summation improve the processing power of the brain?

A) Temporal summation allows circadian rhythms to regulate neuronal activity. Spatial summation allows latitude to regulate neuronal activity.
B) Temporal summation allows a neuron to fire prolonged action potentials, and spatial summation allows a neuron to synapse onto new targets.
C) Temporal and spatial summation both make the neuron more likely to fire action potentials.
D) Temporal summation allows a neuron to recognize a persistent signal from a single presynaptic cell, and spatial summation allows a neuron to recognize a broad signal from multiple presynaptic cells.

Question 11

What sequence of events leads to the perception of a visual scene?
I. In response to light, retinal dissociates from rod and cone photopigments, hyperpolarizing the photoreceptor cells and leading to activation of bipolar neurons.
II. Action potentials are propagated through ganglion cells, whose axons project to the occipital lobe of the brain.
III. In response to light, rod and cone photoreceptors depolarize, causing increased release of neurotransmitter and activation of bipolar neurons.

A) I then III
B) III then II
C) III then I then II
D) I then II then III
E) I then II

Question 12

In what order will you encounter the following structures if you examine the human ear from the outside inward?

A) tympanic membrane $\rightarrow$ malleus $\rightarrow$ incus $\rightarrow$ stapes $\rightarrow$ oval window $\rightarrow$ cochlea
B) tympanic membrane $\rightarrow$ incus $\rightarrow$ malleus $\rightarrow$ stapes $\rightarrow$ oval window $\rightarrow$ cochlea
C) tympanic membrane $\rightarrow$ stapes $\rightarrow$ malleus $\rightarrow$ incus $\rightarrow$ oval window $\rightarrow$ cochlea
D) tympanic membrane $\rightarrow$ malleus $\rightarrow$ incus $\rightarrow$ stapes $\rightarrow$ cochlea $\rightarrow$ oval window
E) tympanic membrane $\rightarrow$ oval window $\rightarrow$ malleus $\rightarrow$ incus $\rightarrow$ stapes $\rightarrow$ cochlea

Question 13

Which of the following are tactile receptors? (Check all that apply.)

A) Merkle cell
B) node of Ranvier
C) Meissner corpuscle
D) Ruffini corpuscle
E) rod cell
F) Pacinian corpuscle
G) free nerve ending
H) ganglion cell
I) cone cell

Question 14

Put the steps in the correct order for a birder hearing the call of a whip-poor-will.

A) basilar membrane vibrates in different regions for each note
B) cilia of hair cells bend in different regions for each note
C) sound waves travel to the birder's pinna and enter the canal
D) action potentials travel down axons that represent different frequencies
E) auditory cortex interprets the pattern
F) bird sings "whip-poor-will"
G) malleus, incus, and stapes vibrate
H) tympanic membrane vibrates
I) pressure waves travel through fluid in the cochlea
J) oval window vibrates

Question 15

How is the lateral line of a fish similar to the ears of a human? (Check all that apply.)

A) cilia embedded in a gelatinous matrix
B) cochlea
C) hair cells
D) large external structures for capturing pressure waves
E) line of cells extends along length of the body
F) organ of Corti
G) pressure waves
H) sensory neurons
I) several kinocilia and one stereocilium
J) several stereocilia and one kinocilium

Question 16

Mutations in the DFNA20/26 locus, which codes for the actin gamma 1 protein, are associated with congenital deafness. An irate senator complains that government money is being wasted on studies of this mutant gene -- in yeast! "I am no biologist," says the senator, "but I am pretty sure yeast don't have ears." How do you respond?

A) "You are right, Senator -- yeast do not have ears. We should revoke the funding immediately."
B) "We can learn valuable information about the structure of the mutant protein by expressing it in yeast. It is difficult to collect large amounts of actin from tiny hair cells, and unethical to collect it from human patients."
C) "We can learn valuable information about the transcription of the mutant gene in yeast. It is much more difficult to study transcription in human cells."
D) "We can learn valuable information about sound transmission through the mutant yeast. By placing a speaker against a yeast vial and recording sound from the other side, we can infer how the mutant actin affects sound waves."

Question 17

Beta-N-Methylamino-L-Alanine, or BMAA, is a glutamate receptor agonist produced by cyanobacteria. Since Glu is an excitatory neurotransmitter, it is not surprising that BMAA is associated with neurological damage. Buildup of BMAA in fruit bats was hypothesized to cause neurodegenerative disease in islanders that fed on the bats. A recent study found high levels of BMAA in sharks, suggesting that consumption of shark fin soup is also dangerous. The researchers suggested that a secondary effect of BMAA may actually make these hazardous foods surprisingly desirable. What might this be?

A) Since BMAA is a Glu receptor agonist, it promotes incorporation of Glu into proteins, and has health-promoting effects.
B) Since BMAA is derived from cyanobacteria, it provides unique nutrients not found in the animal or plant kingdom.
C) Since BMAA is a Glu receptor agonist, it imparts a strong umami flavor that makes food more delicious.
D) Since BMAA contains alanine, it improves protein synthesis by providing this rare nutrient.

Question 18

Unlike sweet, salty, sour, or umami, the "bitter" category of tastants includes wide structural variety of detected molecules. Multiple receptors are required to sense the different bitter tastants. What do they have in common? Bitter taste is thought to have evolved as a warning system for toxic compounds.

-The bitter receptor hTAS2R38 is activated by glucosinolates found in plants such as turnips and broccoli. Glucosinolates can block synthesis and transport of iodine. Before the advent of iodized salt, this was a particular problem in areas of the world that are naturally low in iodine. Why might the human population include different variants of the hTAS2R38 gene?

A) Areas of high iodine are generally coastal, and turnips and broccoli are not easily grown there.
B) Iodine created mutations in the hTAS2R38 gene.
C) Where iodine was low, eating plants rich in glucosinolates helped people metabolize iodine, but where iodine was high they avoided such foods.
D) Where iodine was low, it was important to avoid foods with glucosinolates, but where iodine was plentiful, palatability of a wider range of plants was beneficial.

Question 19

Researchers studying olfactory and taste receptors have stumbled upon an unusual phenomenon. These receptor proteins are sometimes expressed in other animal tissues in addition to the nose or tongue. For example, the sweet taste receptor T1R2 is expressed in the pancreas. Suggest the best possible explanation for these findings.

A) Damaged receptors are recycled by the body and end up in waste-disposal organs.
B) Control of protein expression is imperfect. As long as a receptor doesn't interfere with organ function, expression will not be selected against.
C) Chemoreceptors bind molecules that help the body sense and respond to internal phenomena, such as sugar levels in the blood.
D) Techniques used to visualize protein expression are imperfect and may lead to false positive results.

Question 20

Pax6 is a transcription factor noted for its unique role in specifying eye development across the animal kingdom. A homologous gene known as eyeless specifies eyes in Drosophila, and misexpression of mouse Pax6 can cause ectopic eyes in flies! This creates a quandary -- how can we explain the universality of the master regulatory gene for eye development, with the striking variability of eye anatomy in different phyla?

-Misexpression of the Pax6 gene was shown to promote eye development in both vertebrates and invertebrates. The authors of this study suggested that this was evidence that eyes evolved only once. What other evidence contradicts this view?

A) Invertebrates normally have only simple eyespots.
B) Many different transcription factors can initiate eye development when misexpressed.
C) While the anatomy of all animal eyes is the same, lens proteins vary greatly.
D) The anatomical structure of insect, mollusk, and vertebrate eyes are quite different.

Question 21

A research strain of mice has a mutation that causes voltage-gated sodium channels to take longer to return to the active state after a spike. What is the likely consequence for transduction of sensory stimuli?

A) There will be no effect on sensory perception, because sensory information relies on stimulus-gated ion channels and not voltage-gated ion channels.
B) Sensory information will be incorrectly perceived as high intensity stimuli, due to the increased frequency of action potentials.
C) The mutation will interfere with the ability of stimuli to create receptor potentials, and thus the neuron will fire with slow, broad action potentials, giving the animal enhanced sensory perception.
D) Due to a longer refractory period, the neuron will be unable to conduct high frequency action potentials, and thus will not effectively transmit information about strong stimuli.