Biology 112, Homework Collection P3

Which statement correctly describes what causes the second voltage-gated Na+ channel to open?

After the first channel opens, the movement of many types of ions (both inside and outside the cell) alters the distribution of charges near the second channel, causing it to open.

Although blood work suggests that your patient has hypokalemia, it is important to do other tests to confirm this diagnosis. Another test for electrolyte imbalances is a simple electrocardiogram (ECG). Because contraction of cardiac muscle depends on the proper concentrations of Na+, K+, and Ca2+, hypokalemia and hyperkalemia cause very distinctive ECG changes. Examine the patient's ECG results. Does the ECG confirm your preliminary diagnosis of hypokalemia?

ECG indicates hypokalemia.

An impulse relayed along a myelinated axon "jumps" from _____ to _____.

node of Ranvier ... node of Ranvier

Researchers observed that the crows only gather and drop the largest whelks. Why might crows favor larger whelks?

Large whelks might offer more calories than small whelks.

What type of cell makes up the myelin sheath of a motor neuron?

Schwann cells

Drag the arrows onto the diagram to show the direction of Na+ (gray arrows) and K+ (red arrows) movement through each transport protein at resting potential. If no ions move through a transport protein at resting potential, leave that target blank.

a and b. blank c. Na+ up, K+ down d. K+ up e. Na+ down

How does the average number of drops required to break open a whelk depend on platform height?

The number of drops required decreases with increasing drop height.

Look at total flight height (represented by the green bars). Remember that total flight height was calculated by multiplying the drop height by the average number of drops required. How would you describe the relationship between total flight height and drop height?

Total flight height is higher at the lowest and highest drop heights than at the mid-range drop heights.

Total flight height can be considered to be a measure of the total energy required to break open a whelk. Compare the graph of total flight height for the platform drops to the drop height preferred by crows. Are the data consistent with the hypothesis of optimal foraging?

Yes, because the height preferred by crows roughly coincides with the lowest total flight height.

What part of a neuron relays signals from one neuron to another neuron or to an effector?

synaptic terminal

Neurons store neurotransmitter molecules in vesicles located within _____.

synaptic terminals

Which of these causes the release of neurotransmitter molecules?

an action potential reaching the end of the axon

A nerve impulse moves away from a neuron's cell body along _____.

axon

A nerve impulse moves toward a neuron's cell body along _____.

dendrites

Drag the labels to their appropriate locations on the diagram of the neurons below. Use only the pink labels for the pink targets (which indicate the locations of gated ion channels).

a. cell body b. myelin sheath c. synaptic terminal d. axon hillock e. nucleus f. location of voltage-gated channels g. location of ligans-gated channels h. axon i. dendrite

Which of the following statements describes an ultimate cause?

Birds have hollow bones because hollow bones increased the fitness of their ancestors by allowing them to run faster and capture prey more efficiently.

The space between an axon of one neuron and the dendrite of another neuron is called a(n) _____.

synaptic cleft

Axons insulated by a(n) _____ are able to conduct impulses faster than those not so insulated.

myelin sheath

There are two properties that affect the conduction speed of an action potential along an axon: the axon's diameter and whether or not the axon is myelinated. Rank the axons from slowest to fastest conduction speed. If two axons have the same conduction speed, place one on top of the other.

(slowest to fastest) - non-myelinated invertebrate axon, 20 um diameter - non-myelinated invertebrate axon, 30 um diameter - non-myelinated invertebrate axon, 40 um diameter - myelinated invertebrate axon, 30 um diameter

Scientists have made the following observations: - Egyptian vultures use rocks to break open ostrich eggs, which they then eat. - A vulture may search as far as 50 m away from an ostrich egg for an appropriate rock (which is generally egg-shaped) to use to break the egg. The vulture then throws the rock at the egg until the egg cracks. - This same rock-throwing behavior also occurs in young captive-hatched birds that have not been exposed to rock-throwing adults. However, these naive vultures had to learn that the ostrich eggs were a source of food. Some scientists theorize that this behavior developed from the tactic of throwing smaller eggs to break them open. Ostrich eggs, however, are too big to pick up and throw, so perhaps the rock-throwing technique evolved in the vultures. This could explain why vultures choose rocks that are egg-shaped, rather than ones that are jagged or irregular. Based on the scientists' observations and your knowledge of animal behavior, which of the following statements are true? Select all that apply.

- Examining the anatomical mechanism that enables Egyptian vultures to throw rocks relates to proximate causation. - Questioning whether the rock-throwing behavior arose from egg-throwing relates to ultimate causation. - In Egyptian vultures, eating ostrich eggs is a learned behavior. - Rock-throwing in vultures is an innate behavior.

Part A - Identifying possible diagnoses using MedlinePlus The first step in the diagnostic process is to develop a list of "candidate" conditions that might explain the patient's symptoms. Your attending physician mentions a few possible causes of muscle weakness and paralysis: - myasthenia gravis - botulism - hypokalemia - hyperkalemia She orders some initial blood work and turns the patient over to you. From talking to the patient, you get the following information about his general health and family medical history. Patient History *He has no significant medical history and is not taking any medication. *There is no family history of heart disease, stroke, diabetes or cancer. *He does not smoke. *He drinks moderately but denies use of illegal substances. *His diet is exclusively fresh vegetables and organically raised meats. *He does not eat pre-packaged foods. *He works out four times a week at his local gym. *He does not report having been sick recently. *He has had repeated episodes of muscle weakness and paralysis over the last three months. You decide to refresh your memory about each of the disorders mentioned by your attending. A good source of medical information is MedlinePlus. Enter the name of each disorder into the Search MedlinePlus field at the top of the page. Use the information you find to match each disorder to its definition.

- botulism is caused by a bacterial infection. Bacterial toxin prevents the fusion of vesicles to the membrane, stopping neurotransmitter release. - Hyperkalemia is a condition in which the level of potassium (K+) in the blood rises above normal. - Myasthenia gravis is an autoimmune disorder. Antibodies block acetylcholine receptors, preventing the opening of ion channels to depolarize the muscle cell. Patients first exhibit eyelid and eye muscle weakness or paralysis. - Hypokalemia is a condition in which the level of potassium (K+) in the blood drops below normal.

In testing the optimal foraging model, it was assumed that changing the height of the drop only changed the total energy required. What factors--other than the total energy required--could be affected by drop height? Select all that apply.

-Winds that alter drop angle might vary with height. -A crow using a very high drop height might not be able to guard as effectively against scavengers that try to seize the broken whelk. -A higher drop height might make it harder to see where an unbroken whelk ends up after bouncing off the rocks.

Under most circumstances, once an axon's membrane potential reaches threshold (about -55 mV in mammals), an action potential is automatically triggered. The graph below shows the changes in membrane potential that occur in an axon membrane that is initially at resting potential. In response to a stimulus, the membrane slowly depolarizes until the membrane potential reaches a particular value, called threshold. At threshold, a rapid depolarization of the membrane occurs and an action potential is initiated. Drag the labels onto the flowchart to show the sequence of events that occurs once the membrane potential reaches threshold. You may use a label once or not at all.

1. membrane potential reaches threshold 2. many voltage-gated Na+ channels open 3. Na+ ions rush into the cell 4. membrane potential rises (depolarizes) quickly

Suppose that an artificial non-gated K+ channel could be inserted into the plasma membrane of an axon at resting potential (membrane potential = -70 mV). Assume that the axon has not recently produced an action potential. What would happen when an artificial K+ channel is inserted into an axon membrane at resting potential? Answer questions 1-4 by selecting only from the three answer choices to the left of each question. Drag the correct answer to the right of each question.

1. out of the cell 2. promote 3. impede 4. causes a hyperpolarization

In order to explain how low blood potassium leads to muscle weakness and paralysis, you have to think about the neuromuscular junction, where a motor neuron and a muscle cell meet. Click on the figure shown here to help you fill in the flowchart below. (ACh stands for acetylcholine, a neurotransmitter released from the motor neuron.) If you need to review the roles of Na+ and K+ in the generation of action potentials, see Hint 1. Drag the labels to fill in the flowchart, explaining how hypokalemia leads to muscle weakness.

1. when potassium level outside the nerve cell are lower than normal, there is a stronger driving force for K+ to flow ___out of the cell.________.(because of high K+ inside cell, K+ can flow towards lower gradient, i.e. outside of cell). 2.As a result of K+flowing down its concentration gradient, the nerve cell becomes ____hyperpolarised______.(inside of cell will lose K+ and become more negative than usual, note that resting membrane potential is -70mV.). 3. Therefore, the patients resting membrane potential has a more ____negative___ value than normal. 4. This makes it ___harder____ for the nerve cell to reach the threshold for an action potential.(threshold is -55mV). 5. As a result, the nerve cell release ____less___ neurotransmitter into the synaptic cleft, 6. As a result, it is____harder__ for the muscle cell to become _____depolarised___ and trigger muscle contraction, explaining the patients paralysis.

Match the letter of each location along the axon with the correct description of what is occurring at that position.

Action potential start to finish steps: 5. At location g, the axon membrane is at resting potential. 2. At location f , the axon membrane reaches threshold and the voltage-gated Na+ channels open. 7. At location e, the membrane potential changes sign (from a negative value to a positive value) and the voltage-gated Na+ channels are open. 4. At location d, the voltage-gated Na+ channels are inactivating and the voltage-gated K+ channels are opening. 1. At location c , the membrane potential changes sign (from a positive value to a negative value) and the voltage-gated K+ channels are open. 6. At location b, the voltage-gated K+ channels are closing. 3. At location a, the voltage-gated Na+ channels reactivate.

Now that you know how hypokalemia can cause your patient's muscle weakness, you have to figure out what is causing his hypokalemia. Dehydration from vomiting or diarrhea is a major cause of hypokalemia, but your patient has not reported being sick. This leaves two possible causes: kidney problems or a genetic mutation in ion channels. *The kidneys are important for regulating the levels of potassium released in urine. A patient with malfunctioning kidneys may be releasing too much potassium in urine, causing the level of potassium in the blood to drop. *Abnormal ion channels can allow large amounts of potassium to be shifted from the blood into cells under certain conditions, causing the level of potassium in the blood to drop. A quick way to tell the difference between these two diagnoses is to calculate the transtubular potassium gradient (TTKG). The TTKG is a measurement of the amount of K+ kept in the collecting ducts of the kidneys. If the patient's kidneys are working properly, low blood potassium should trigger the kidney to severely reduce the amount of K+ being released into urine in order to attempt to raise blood K+ levels. However, if the hypokalemia is caused by malfunctioning kidneys, K+ levels in the urine will be high. TTKG is calculated using the following equation. In patients with hypokalemia, a value greater than 7 indicates a kidney dysfunction, and a value less than 3 indicates an ion channel disorder.

Ans 1) 1.86 units Formula used- TTKO=([K+]urine × Plasma osmolarity) ÷ ([K+] Plasma × urine osmolarity) =(8×279) ÷ (2×598) =2232 ÷ 1196 =1.86 Ans2) No And 3) Yes

In the diagram, (a), (b), and (c) represent three points along a vertebrate axon where electrodes were implanted to detect action potentials. Under normal conditions, when this neuron produces an action potential, the action potential passes through point (a) first, followed by point (b), and then point (c). Suppose, however, that an action potential is artificially triggered at the point indicated by the red arrow. In what sequence would the action potential pass through points (a), (b), and (c)? Enter the sequence in which the action potential would pass through the points. Enter the letters in the correct order separated by commas. For example if the order is point (c), then (b), then (a), enter c, b, a. If the action potential would not pass though a point, do not include that point in your answer.

B, A, C

Based on your analysis, what is your final diagnosis of the patient?

Patient has hyperthyroidism caused by a pituitary tumor. He has thyrotoxic periodic paralysis (TPP).

Which of the following statements describes a proximate cause?

People sleep at night because a molecule that accumulates during the day has an effect on the sleep centers of the brain.

In the digger wasp experiment, it was shown that the wasp used the arrangement of a ring of pinecones to navigate back to the nest. Which experiment would test if the wasp can use any arrangement of objects in the environment to find her nest, rather than only a "ring" shape?

Place a triangle of pinecones around the nest while the wasp is inside. After she leaves the nest, move the triangle to the side of the nest and see if she returns to the arrangement of pinecones instead of the nest. Repeat for other shapes.

It turns out that the probability of a whelk breaking is the same for a whelk dropped for the first time as for an unbroken whelk dropped several times previously. If the probability of breaking instead increased with each additional drop, what change might you predict in the crows' behavior?

The crows would fly to lower heights in subsequent drops.

The fixed pattern of changes in membrane potential during an action potential is coordinated by the sequential opening and closing of voltage-gated ion channels. Can you identify the status (open/closed) of the voltage-gated Na+ and K+ channels during each phase of an action potential? Drag the appropriate labels onto the graph to indicate the status (open or closed) of the voltage-gated Na+ and K+ channels during each phase of an action potential. Labels may be used once, more than once, or not at all.

a. closed, closed b. open, closed c. closed, open d. closed, open e. closed, closed

A neuron's nucleus is located in its _____.

cell body

The strength of a stimulus (for example, whether you feel a slight pain versus an intense pain) determines the number of action potentials sent along an axon. As the graphs show, a strong stimulus produces more action potentials spaced more closely together than a weak stimulus. The time between when a first action potential ends and a second action potential can be triggered is determined by the axon's refractory period. A second action potential cannot be triggered until the end of the refractory period. Which of the following characteristics determines when the refractory period ends?

how long it takes for the voltage-gated Na+ channels to reactivate at the end of an action potential

In order to focus your diagnosis, you do a brief physical examination and look over the results of blood work ordered by your attending physician. *Physical Examination *Breathing, swallowing, and speech are normal. *He has no weakness in his facial muscles, no drooping eyelids, and no vision impairments. *Patient does not report any headaches, dizziness, or confusion. *He has no cough or shortness of breath; lungs sound clear on examination. *His skin appears normal and intact with no open wounds. Based on this information, which condition is most likely?

hypokalemia Why? The patient's bloodwork indicates that the potassium level in the blood is lower than normal, suggesting that the patient is hypokalemic, not hyperkalemic. Botulism is caused by a bacterial infection. The bacteria enter the body either through eating contaminated food, usually improperly canned food, or through open wounds. The patient's diet suggests that he does not eat canned foods, and he has no open wounds through which the bacteria could enter. His white blood cell level is in normal range, and his temperature is normal. Therefore, botulism is unlikely. Myasthenia gravis usually first presents as weakness or paralysis of the muscles for eye and eyelid movement. The patient reports only lower limb weakness and does not exhibit any paralysis of his facial muscles. He also has no family history of autoimmunity, making it unlikely that he has myasthenia gravis.

In the waggle dance, distance to a food source is indicated by the speed of the dance and by the _____.

number of waggles