Ch. 11 Neural Tissue Pt. 1
At which membrane potential, given the graphs shown, do a sufficient number of the voltage-gated Na+ channels start to open?
-60 mV
Assume you have a membrane with only potassium leakage channels. The RMP is -90mV. Predict the RMP if we add Na+Na+ leakage channels.The most likely RMP value of Na+Na+ is
-70 mV
What is the resting membrane potential of the neuron used in the experiment?
-80 mV
What type of channel on the postsynaptic membrane binds neurotransmitter?
A chemically gated channel
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 Transport
The concentration of ions in the chemical environment surrounding the neurons must be tightly regulated for neurons to function properly. Which of the following cells is most responsible for this?
Astrocytes
The term central nervous system refers to the ________.
Brain and Spinal Cord
Events that occur during synaptic activity are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Voltage-gated calcium channels open (b) Neurotransmitter binds to receptors (c) Action potential arrives at axon terminal (d) Neurotransmitter is removed from the synaptic cleft (e) Neurotransmitter released into synaptic cleft (f) Graded potential generated in postsynaptic cella.
C - A - E - B - F - D (c) Action potential arrives at axon terminal (a) Voltage-gated calcium channels open (e) Neurotransmitter released into synaptic cleft (b) Neurotransmitter binds to receptors (f) Graded potential generated in postsynaptic cell (d) Neurotransmitter is removed from the synaptic cleft
What does the central nervous system use to determine the strength of a stimulus?
Frequency of action potentials
Where do most action potentials originate?
Initial segment
A neuron that has as its primary function the job of connecting other neurons is called a(n)
Interneuron
In multiple sclerosis, the cells that are the target of an autoimmune attack are the
Oligodendrocytes
Schwann cells are functionally similar to
Oligodendrocytes
What characterizes repolarization, the second phase of the action potential?
Once the membrane depolarizes to a peak value of +3- mV, it repolarizes to its negative resting value of -70 mV
If a motor neuron in the body were stimulated by an electrode placed about midpoint along the length of the axon, ________.
The impulse would spread bidirectionally
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value
A second nerve impulse cannot be generated until ________.
The membrane potential has been reestablished
During the relative refractory period of an action potential, a larger than normal stimulus is needed to cause another action potential. This is due to the fact that ________.
The voltage gate potassium ion channels remain open long enough to hyper-polarize the axon membrane
Which of the following is NOT a characteristic of neurons?
They are mitotic
The depolarization phase of an action potential is punctuated by the closing of inactivation gates in the voltage gated sodium ion channels. All of the following are consequences of this inactivation except one. Choose the statement below that is not a consequence of the closing of inactivating gates
This allows for the efflux (diffusion out) of potassium ions, resulting in the repolarization of the cell
Local anesthetics block voltage-gated Na+ channels, but they do not block mechanically gated ion channels. Sensory receptors for touch (and pressure) respond to physical deformation of the receptors, resulting in the opening of specific mechanically gated ion channels. Why does injection of a local anesthetic into a finger still cause a loss of the sensation of touch from the finger?
Touch stimulation of this sensory receptor will open the mechanically gated ion channels, but action potentials are still not initiated because propagation of an action potential required the opening of voltage-gated Na+ channels
The generation of an action potential in a neuron requires the presence what type of membrane channels? Select the best answer.
Voltage-gated Channels
Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?
Voltage-gated channel
Immediately after an action potential has peaked, which of the following channels will open?
Voltage-gated potassium channels
How is an action potential propagated along an axon?
an influx of sodium ions from the current action potential depolarizes the adjacent area
Why does the action potential only move away from the cell body?
the areas that have had the action potential are refractory to a new action potential
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
What is the major role of the Na+-K+ pump in maintaining the resting membrane potential?
Maintaining the concentration gradients for Na+ and K+ across the cell membrane
Meningitis can be caused by infection of the central nervous system by bacteria. Which cells would be most responsible for removing the infection?
Microglia
Which of the following types of glial cells monitors the health of neurons, and can transform into a special type of macrophage to protect endangered neurons?
Microglia
Which of the choices below describes the ANS?
Motor fibers that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands
Complete the following sentence. The operation of the Na+−K+Na+−K+ ATPase pump __________.
Move 3 Na+ to the ECF and 2 K+ to the cytoplasm
Ependymal cells line many open cavities in the central nervous system (CNS). Ependymal cells have cilia on the side of the cell that face these openings. What is the most likely function of these ciliated cells?
Movement and circulation of cerebrospinal fluid
During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?
Na+ is entering the cell
What is happening to voltage-gated channels at this point in the action potential?
Na2+ channels are inactivating, and K+ channels are opening
The interior surface of a neuron's plasma membrane at resting membrane potential will have a ________.
Negative charge and contains less sodium than outside of the cell
Like all cells, the neurons' internal organization dictates its function. Neurons have relatively many mitochondria, an extensive network of rough endoplasmic reticulum and many clusters of ribosomes. These cellular features indicate all of the following EXCEPT ________.
Neurons have stable, relatively unchanging internal environments
What is the direct role of neurotransmitter at a chemical synapse?
Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane
Nerve impulses leading to the brain carry information about cool temperatures on the skin. The nerve fibers sending these signals will most likely belong to which division of the nervous system?
Sensory (afferent) division
What division of the nervous system is most specifically responsible for voluntary motor control?
Somatic nervous system
Which of the stimuli in this experiment would be considered a threshold stimulus?
Stimulus 2
Which of the following best describes the Na+ and K+ concentrations across a neuron's plasma membrane?
The Na+ concentration is higher outside the cell compared to inside. The K+ concentration is higher inside the cell compared to outside
Tetraethylammonium (TEA) blocks voltage-gated K+ channels such that K+ cannot pass even when the channels are open. However, TEA leaves K+ leakage channels largely unaffected. How would you expect the action potential to change if you treated a neuron with TEA?
The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time
Which mechanism allows the rabies virus to gain access to the central nervous system (CNS)?
The rabies virus uses retrograde movement along the neuronal axon
Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane?
The resting membrane potential would become less negative (more positive)
What is the electrochemical gradient of an ion?
The sum of the electrical and concentration gradients for that ion
As you start working out, you notice that your heart rate and breathing rate start to increase. Which division of your nervous system is generating this response? Be as specific as possible
The sympathetic division of the autonomic nervous system
What is the basic condition when a neuron is described as polarized?
There is a separation of positive and negative charges across a membrane
Which of the following is NOT true of graded potentials?
They increase amplitude as they move away from the stimulus point
True or False: Bundles of axons in the central nervous system are called tracts.
True
True or False: During depolarization, the inside of the neuron's membrane becomes less negative
True
True or False: If the neuron membrane becomes more permeable to Na+, Na+ will transport across the membrane, causing the cell to depolarize.
True
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gated open
What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?
inactivation gates of voltage-gates Na+ channels close, while activation gates of voltage-gated K+ channels open
Suppose a drug is developed that blocks K+ leakage channels. The drug prevents ions from passing through those channels. If this drug was applied to a neuron, what would be the most immediate effect on that neuron?
the resting membrane potential would become less negative (more positive)
Which of the following is NOT a difference between graded potentials and action potentials?
The magnitude of action potentials decrease as the impulse travels further away from the start of the impulse while graded potentials do not decrease in magnitude
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
Cl−Cl− is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl−Cl− gated channels are suddenly opened
a more negative RMP would result
What must occur for threshold to be reached?
enough excitatory potentials add up to open voltage-gated channels at the axon hillock
Which of the following correctly describes a graded potential?
It can have amplitudes of various sizes
During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?
K+ channels close. Na+ channels go from an inactivated state to a closed state
Which of the following is the clearest example of a neuronal membrane's selective permeability?
K+ ions can diffuse across the membrane more easily than Na+ ions
What type of conduction takes place in unmyelinated axons?
Continuous conduction
What is meant by an EPSP?
A localized change in the membrane potential resulting in a less negative membrane voltage
A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?
A neuron
The velocity of the action potential is fastest in which of the following axons?
A small myelinated axon
Which of the following mechanisms is most significant in returning the ion concentrations to the resting state (from point D to point E)?
Active transport by the Na+ - K+ pump
During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)?
At the end of the depolarization phase, as the membrane potential approaches its peak value
What is the role of calcium in synaptic activity?
Calcium influx into the synaptic terminal causes vesicle fusion
What kinds of gated channels are typically found in high concentrations at the dendrites?
Chemically Gated
During an action potential, the rapid decrease in sodium permeability and simultaneous increase in potassium permeability is responsible for __________.
During repolarization phase
During the action potential, when does sodium permeability initially DECREASE?
During the peak of depolarization
During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.
K+ ions diffusing through voltage-gated channels
The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by
K+ ions leaving the cell through voltage-gated channels
Which of the following would increase the membrane permeability to K+?
More K+ leakage channels
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
Which of the following does NOT describe conditions that occur during an action potential?
Na+ is used to repolarize the membrane
In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?
Reuptake and Degradation
Which of the following statements is correct regarding the polarization of a neuronal membrane and the formation of a resting membrane potential?
Sodium - potassium pumps maintain concentration gradients; sodium and potassium move down their concentration gradients through leakage channels
Nerve impulses leading to the skeletal muscle carry information to direct movement. The nerve fibers sending these signals will most likely belong to which division of the nervous system?
Somatic nervous system
Imagine that the cell membrane from the previous problem becomes more permeable to Na+Na+. Predict how this will affect the RMP.
The RMP will be more positive
Which is the main receptive portion of the neuron?
The dendrite
Which choice best characterizes K+K+ leakage channels?
transmembrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy
Which component has a role in the postsynaptic cell during synaptic activity?
Chemically gated channels
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
These cells in the CNS have cilia that move in order to circulate cerebrospinal fluid
Ependymal Cells
Neurotransmitter is released from presynaptic neurons through what mechanism?
Exocytosis
Collections of nerve cell bodies outside the central nervous system are called ________.
Ganglia
Which of the following is NOT a function of dendrites?
Generate nerve impulses and transmit them away from the cell body
Which description best fits graded potentials?
Graded potentials can result in either depolarization or hyper-polarization of the membrane and vary in strength
Nerve impulses are sent to slow the heart's rate of contraction. The nerve fibers sending these signals will most likely belong to which division of the nervous system?
Parasympathetic division
1. You are working on a new medication to selectively kill cancer cells. You test the drug on a culture of normal neurons to check for any side effects. Despite the presence of the drug, a normal resting membrane potential of −−70 mVmV is maintained. Look at each of the figures below to analyze how the drug might be affecting the neuron. Figure A shows neuron activity under normal, or control, conditions (without the drug). Figure B shows neuron activity that has been altered due to exposure to the drug. Based on these results, the drug is most likely __________.
Preventing Na+ - gated channel from opening
Which of the following is NOT one of the basic functions of the nervous system?
Release hormones into the bloodstream that travel around the systemic blood circulation to communicate with cells in multiple locations within the body
Name the glial cell at F.
Schwann cell
Some nerve fibers of the peripheral nervous system have the ability to regenerate after damage has occurred. Which of the following cells is most responsible for aiding in this regulation?
Schwann cells
Cranial nerve II, the optic nerve, sends nerve impulses to the brain carrying information about the things we see. These nerve fibers most likely belong to which division of the nervous system?
Sensory (afferent) division
Many neurons have many short, branching extensions called dendrites. What is the benefit of these structures for a neuron?
The dendrites provide a large surface area for connections from other neurons
Which criterion is used to functionally classify neurons?
The direction in which the nerve impulse travels relative to the central nervous system
Imagine you changed the concentration of K+ outside a neuron such that the resting membrane potential changed to -80 mV (from the normal resting value of -70 mV). What have you changed?
The electrical gradient for K+ and the concentration gradient for K+
What event triggers the generation of an action potential?
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold of -55 mV
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
You discover that a new chemical compound interacts with K+ voltage-dependent channels. What would be the effect on a neuron if the chemical came into contact with the axonal membrane?
The neuron would be unable to repolarize
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+Na+ and K+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
