11. Nervous Tissue and Nervous System

Casey is taking a new medication that blocks potassium channels. What stage of an action potential would be MOST affected by this drug?

330

When an action potential is at its peak, the electrical gradient forces potassium ____________.

308

What happens when the neuron reaches threshold (-55 mV)?

299

Which of the following electrical events occurs when a certain threshold is reached?

Which of the following is characteristic of an action potential?

An action potential is a phenomenon that either happens completely or doesn't happen at all.

Which part of the action potential occurs when the voltage-gated Na⁺ channels are inactivating and voltage-gated K⁺ channels open?

The CNS can discriminate between strong and weak stimuli as strong stimuli __________.

During which phase of an action potential are voltage-gated K⁺ channels open, while voltage-gated Na⁺ channels are closed?

1022

The anatomical region of a multipolar neuron where the AP is initiated is the a. soma, b. dendrites, c. axon's initial segment, d. axon terminals.

193

Since all APs generated by a given nerve fiber have the same magnitude, how does the CNS 'know' whether a stimulus is strong or weak?

159

What is the polarized membrane state? How is it maintained? (Note the relative roles of both passive and active mechanisms.)

165

Describe the events that must occur to generate an AP. Relate the sequence of changes in permeability to changes in the ion channels, and explain why the AP is an all-or-none phenomenon.

169

When admitted to the emergency room, Sean was holding his right hand, which had a deep puncture hole in its palm. He explained that he had fallen on a nail while exploring a barn. Sean was given an antitetanus shot to prevent neural complications. Tetanus bacteria fester in deep, dark wounds, but how do their toxins travel in neural tissue?

181

Rochelle developed multiple sclerosis when she was 27. After eight years she had lost a good portion of her ability to control her skeletal muscles. How did this happen?

162

Describe the three components of the neuromuscular junction.

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

c. The Na+/K+ pumps and gated channels maintain the Na+ and K+ gradients necessary for action potentials to occur.

Sequence the following list of events of a neuronal action potential by placing 1 next to the first event, 2 next to the second event, and so on.

a. ____The activation gates of voltage-gated Na+ channels open, Na+ flood the cytoplasm, and depolarization occurs.

b. ____K+ continue to flow out of the axon until the membrane is hyperpolarized.

c. ____Local potentials depolarize the membrane to threshold.

d. ____The inactivation gates of voltage-gated Na+ channels close as voltage-gated K+ channels open, K+ begin to exit the axon, and repolarization begins.

e. ____Repolarization continues and Na+ channels return to resting.

The drug neostigmine blocks the actions of acetylcholinesterase in the synaptic cleft. What effect would this have on synaptic transmission? What effects might you expect to see as a result of this drug?

During a surgical procedure, an anesthesiologist administers to the patient an inhaled anesthetic agent that opens Cl− channels in the postsynaptic membranes of neurons in the brain. Explain why this would put the patient 'to sleep' for the duration of the surgical procedure.

Albert accidentally ingests the poison tetrodotoxin from the pufferfish, which you know blocks voltage-gated Na+ channels. Predict the symptoms Albert will experience from this poisoning.

Albert, the patient in question 3, takes the drug lithium, which reduces the permeability of the neuronal axolemma to Na+ (that is, it allows fewer Na+ to enter the axon). Predict the effect this would normally have on his neuronal action potentials. Do you think this drug would be beneficial or harmful, considering his condition?

Predict the effect that tetrodotoxin would have on Albert's muscle fiber action potentials (see question 3). Would it affect end-plate potentials at the motor end plate? Why or why not? (Connects to Chapter 10)

Explain what would happen if depolarization of the trigger zone led to a negative feedback loop instead of a positive one. (Connects to Chapter 1)