Question 1

Sodium ions are single atoms.Why can't they simply diffuse through the cell membrane's lipid bilayer?

Accepted Answer

Sodium ions have a positive charge and cannot easily pass through the hydrophobic (nonpolar) center of the lipid bilayer. They require protein channels or pumps to cross the membrane.

Question 2

Since there is a larger concentration of potassium ions inside a neuron, why is the inside of the neuron negative (-70mV) relative to the outside?

Accepted Answer

While potassium ions carry a positive charge, there is a high concentration of negatively-charged proteins inside the cell that counteract the positive charge of potassium ions. This, combined with the fact that there is a higher concentration of potassium ions inside the cell, results in a negative resting potential.

Question 3

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?

Accepted Answer

Voltage-gated K+ channels open when the membrane potential reaches +50 mV during the depolarization phase. The diffusion gradient and electrical force cooperate to drive K+ ions out of the cell, leading to the repolarization of the membrane potential back to its resting state. This process is important for the proper functioning of neurons in transmitting signals. A and B are incorrect as they do not accurately describe the mechanism of ion movement during an action potential. D is incorrect as negatively charged proteins do not leave the cell during an action potential.

Question 4

What does the Nernst equation allow us to do?

Accepted Answer

The Nernst equation allows us to calculate the equilibrium potential for an ion, which is the voltage at which there is no net movement of ions across the membrane. This is important for understanding resting membrane potential and how ions contribute to the generation of action potentials.

Question 5

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

Accepted Answer

The answer of How do temporal and spatial summation improve...

Question 6

How do somatic neurons and autonomic neurons differ? (Check all that apply.)
_____ Somatic neurons innervate the body surface, while autonomic neurons innervate internal structures.__X__ Somatic neurons control skeletal muscle, while autonomic neurons control smooth and cardiac muscle._____ Somatic neurons control exocrine glands, while autonomic neurons do not.__X__

Accepted Answer

The answer of How do somatic neurons and autonomic neurons...

Question 7

What would happen if the G-protein coupled receptor in heart cells that binds to ACh had a mutation that caused it to bind more tightly to the G-protein alpha subunit?

Accepted Answer

The answer of What would happen if the G-protein coupled...

Question 8

What limits the frequency of action potentials?

Accepted Answer

The refractory period limits the frequency of action potentials because it is the period of time after an action potential when the neuron is unable to fire another one. This is due to the inactivation of voltage-gated sodium channels and activation of potassium channels, which both prevent the neuron from depolarizing and firing another action potential until they return to their resting states.

Question 9

You accidentally consume botulinum toxin by eating a contaminated can of sausages.What do you predict will be the most harmful physiological effect?

Accepted Answer

Botulinum toxin causes flaccid paralysis by blocking the release of acetylcholine at neuromuscular junctions, leading to muscle relaxation and potential respiratory failure.

Question 10

What is the likely impact of this toxin on the resting potential of a neuron?

Accepted Answer

The toxin likely disrupts the ion gradients across the neuron's membrane, which are essential for maintaining the resting potential. Without these gradients, the resting potential cannot be sustained.

Question 11

The outside of a neuron is positively charged at resting potential.Why don't negative ions exit from the cell to normalize charge across the membrane?

Accepted Answer

The negative charge inside the cell is carried by large proteins that cannot diffuse through the membrane. This creates an electrical gradient that prevents negatively charged ions from leaving the cell and balancing the charge across the membrane.

Question 12

In contrast to these toxins, strychnine acts postsynaptically, to block glycine from binding to receptors on motor neurons.Would you expect the symptoms of strychnine poisoning to be more similar to those of botulinum or tetanus toxin?

Accepted Answer

Strychnine poisoning symptoms are more similar to those of tetanus toxin because both cause increased muscle contractions and spasms due to their effects on inhibitory neurotransmission.

Question 13

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?

Accepted Answer

The negative electrical potential inside the cell creates a force that holds the K⁺ ions in. Leaky channels allow some degree of ion movement, but the net flow is still inward due to the electrical potential inside the cell. Therefore, the ions do not flow out until the concentration gradient is equilibrated.

Question 14

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?

Accepted Answer

Botulinum toxin prevents the release of acetylcholine (ACh) at the neuromuscular junction, leading to muscle relaxation and paralysis because the muscles are not activated to contract.

Question 15

A patient of yours is injured in a car accident.The surgeon reports that while there is damage to the dorsal roots, the spinal cord and nerves otherwise appear intact.What functions would you expect to be affected in the patient?

Accepted Answer

Damage to the dorsal roots can affect sensory input, which may lead to loss of some sensory perception. However, since the spinal cord and nerves otherwise appear intact, motor function should be retained, although lack of proprioceptive input may make muscle control difficult. Autonomic functions are not likely to be affected by the injury. Therefore, option C is the most appropriate choice.

Question 16

What is the likely impact of this toxin on action potentials?

Accepted Answer

Ion gradients are critical for the generation and propagation of action potentials. Without them, action potentials cannot occur. Therefore, the toxin will completely abolish action potentials rather than alter their frequency, strength or refractory period.

Question 17

K⁺ channels in the heart do not have binding sites for ACh, yet parasympathetic release of ACh causes outward flux of K⁺ from heart cells.How does this occur?

Accepted Answer

ACh binds to a G protein-coupled receptor on heart cells, which activates a G protein alpha subunit. The G protein alpha subunit then binds to a separate K⁺ channel and causes it to open, resulting in K+ efflux from the heart cells.

Question 18

Another toxin that also blocks neurotransmitter release is tetanus toxin; however, it primarily affects inhibitory interneurons of the spinal cord that negatively regulate motor neurons.Which would be symptoms of tetanus toxin poisoning?

Accepted Answer

Tetanus toxin primarily affects inhibitory interneurons, leading to unopposed activity of motor neurons and spastic paralysis. Flaccid paralysis is typically caused by botulinum toxin, which blocks the release of acetylcholine at the neuromuscular junction. Slowed action potential conduction and pupil dilation are not typically associated with tetanus toxin poisoning.

Quiz 43: The Nervous System