A&P I Lecture Chapter 11 HW

Assume you have a membrane with only potassium leak channels. The RMP is -90mV. Predict the RMP if we add Na+ leak channels. The most likely RMP value of Na+ is __________.

-70 mV

A resting neuron is an unstimulated neuron that is not presently generating an action potential. The resting membrane potential is the separation of the relative positive and negative charges across the membrane of a cell at rest. What is the charge in and outside of the neuron?

A resting neuron has a negative (-) charge inside the neuron and a positive (+) outside the neuron. The separation of charges creates a voltage (electrical potential difference), which can be measured using a voltmeter. The resting membrane potential of a neuron averages -70mV (millivolts). All neural activities begin with a change in the resting membrane potential of a neuron.

In a resting neuron the concentration of which ion is higher inside than outside the cell?

K+ Potassium

How do neurofibrils differ from nerve fibers?

Neurofibrils are cytoskeletal intermediate filaments maintaining cell shape, but they do not conduct impulses.

Imagine that the cell membrane from the previous problem becomes more permeable to Na+. Predict how this will affect the RMP.

The RMP will be more positive.

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,

ion channels in the plasma membrane of the receiving neuron open.

A molecule that carries information across a synaptic cleft is a

neurotransmitter. Neurotransmitter molecules carry information across a synaptic cleft.

If a signal from a sending neuron makes the receiving neuron more negative inside,

the receiving neuron is less likely to generate an action potential.

When calcium ions enter the synaptic terminal,

they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.

The generation of an action potential in a neuron requires the presence what type of membrane channels?

voltage-gated channels

events involved in generation of an action potential in the correct order of occurrence

1-Threshold stimulus Na+ channels open. 2-Na+ influx Depolarization. 3-Na+ channels close K+ channels open. 4-K+ efflux Repolarization. 5-Hyperpolarization K+ channels close. Action potentials are all-or-nothing events. Once an action potential is generated at the initial segment, it will continue to propagate (move) along the entire length of the axon.

Cl− is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl− gated channels are suddenly opened.

A more negative RMP would result. Correct! Cl− is negatively charged and has a higher concentration in the ECF. The opening of Cl− channels would allow more negative charge to attempt to enter the cytoplasm. If the cell's normal RMP were -70mV, it would now become more negative. The farther away the RMP is from zero, either in the positive or in the negative direction, the greater the separation of charges is. This is called hyperpolarization. When the RMP moves closer to 0 mV, depolarization occurs. Congratulations! You've successfully examined the construction of the resting membrane potential, an important concept in any human cell.

Which choice best characterizes K+ leak channels? A. chemically gated K+ channels that open and close according to the binding of other molecules. B. common transmembrane channels that are always open for any ion to move through in the presence of K+. C. transmembrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy. D. transmembrane channels that use energy to allow the movement of K+ across the membrane.

C. transmembrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy.

What type of conduction takes place in unmyelinated axons?

Continuous conduction An action potential is conducted continuously along an unmyelinated axon from its initial segment to the axon terminals. The term continuous refers to the fact that the action potential is regenerated when voltage-gated Na+‎ channels open in every consecutive segment of the axon, not at nodes of Ranvier.

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open. Closing of voltage-gated channels is time dependent. Typically, the inactivation gates of voltage-gated Na+‎ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+‎ channels open.

In a resting neuron the membrane is more permeable to?

K+ Potassium

In which type of axon will velocity of action potential conduction be the fastest?

Myelinated axons with the largest diameter The large diameter facilitates the flow of depolarizing current through the cytoplasm. The myelin sheath insulates the axons and prevents current from leaking across the plasma membrane.

In a resting neuron the concentration of what ion is higher outside than inside the cell?

Na+ Sodium

The resting membrane potential is maintained by Na+-K+ pumps that actively transport what ions into and out of the cell?

Na+ sodium and K+ potassium

In multiple sclerosis, the cells that are the target of an autoimmune attack are the _________.

Oligodendrocytes are a type of neuroglial cell that function to form the myelin sheath around the axons of neurons within the central nervous system.

You are going to record RMP from a cell using an electrode. You place your electrode and record a resting membrane potential every millisecond. You record an initial value of -70mV; however, over time you notice that your recordings become more and more positive until the RMP reaches 0mV. Assuming that Na+ and K+ are the major determinants of RMP in this cell, which of the following could best explain your results?

The cell's Na+-K+ ATPase pumps have stopped functioning. Since the RMP eventually becomes zero, the concentration of ions on either side of the membrane would be roughly equal. Without active processes to maintain concentration gradients, we would expect the concentration of ions on either side of the membrane to equilibrate.

Why does regeneration of the action potential occur in one direction, rather than in two directions?

The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential. At the peak of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+‎ channels become absolutely refractory to another depolarizing stimulus.

What is the function of the myelin sheath?

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals. The myelin sheath increases the velocity of conduction by two mechanisms. First, myelin insulates the axon, reducing the loss of depolarizing current across the plasma membrane. Second, the myelin insulation allows the voltage across the membrane to change much faster. Because of these two mechanisms, regeneration only needs to happen at the widely spaced nodes of Ranvier, so the action potential appears to jump.

Cold sores on the skin of the mouth occur when herpes simplex viruses that are dormant in neural ganglia become active and travel to the skin of the mouth. Which of the following is the mechanism by which these viruses travel from the ganglia (located within the head) to the skin of the mouth?

anterograde axonal transport

An action potential is self-regenerating because __________.

depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment The Na+‎ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold.

Complete the following sentence. The operation of the Na+−K+ ATPase pump __________.

moves 3 Na+ to the ECF and 2 K+ to the cytoplasm. The pumps move more Na+ than K+, which counteracts the effect of the membrane's being more permeable to K+ (more K+ leak channels than Na+).

The small space between the sending neuron and the receiving neuron is the

synaptic cleft. The synaptic cleft is the small space between the sending neuron and the receiving neuron.