A&P Lecture Exam 2

Which of the following statements about the action potential is FALSE?

*** The rapid depolarization phase is caused by the entry of potassium ions. *** TRUE: - During the depolarization phase, membrane potential becomes positive. - During the repolarization phase, sodium channels close and potassium channels open. - Repolarization occurs as potassium ions leave the axon. - In the after-hyperpolarization phase, membrane potential approaches the potassium equilibrium potential.

Functions of astrocytes include all of the following, EXCEPT:

*** conducting action potentials *** FUNCTIONS: - maintaining the blood-brain barrier - responding to neural tissue damage - forming a three-dimensional framework for the CNS - guiding neuron development

Which of the following is NOT a function of the neuroglia?

*** memory *** FUNCTION: - support - maintenance of the blood-brain barrier - secretions of cerebrospinal fluid -phagocytosis

Which of the following would NOT cause the membrane potential to change from -70mV to +30mV?

*** potassium ions leaving the cell *** WOULD CAUSE CHANGE: - phosphate ions leaving the cells - calcium ions entering the cell - sodium ions entering the cell

Which of the following is NOT true of graded potentials?

*** they increase amplitudes as they move away from the stimulus point**** TRUE: - they are short lived - they can be called postsynaptic potentials - they can form on receptor endings

which of the following is NOT a function of the nervous system?

***direct long-term functions, such as growth*** IT DOES: - integrate sensory information - sense the internal and external environments - coordinate voluntary and involuntary activities - control peripheral effectors

Which of the following is NOT a recognized structural classification for neurons?

***pseudopolar*** RECOGNIZED - bipolar ( very rare mostly in the eyes ) - unipolar (sensory neurons) - multipolar (motor neurons) - anaxonic

Any stimulus that opens a _______ ion channel will produce a graded potential.

- sodium - chemically gated - voltage-gated - mechanically gated

On which structure do most neuron to neuron communications occur?

1

Which part of the neuron can propagate an action potential?

3

The following are the main steps in the generation of an action potential. 1. Sodium channels are inactivated. 2. Voltage-gated potassium channels open and potassium moves out of the cell, initiating repolarization. 3. Sodium channels regain their normal properties. 4. A graded depolarization brings an area of an excitable membrane to threshold. 5. A temporary hyperpolarization occurs. 6. Sodium channel activation occurs. 7. Sodium ions enter the cell and depolarization occurs. The proper sequence of these events is

4, 6, 7, 1, 2, 3, 5.

Which is the correctly written Nernst equation?

61/z × log [ion]out / [ion]in

The structures labeled "1' are dendrites. Their membranes contain numerous chemically-gated ion channels.

Both statements are true and relate to synaptic transmission

What type of conduction takes place in unmyelinated axons?

Continuous conduction

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.

Where do most action potentials originate?

Initial segment

The resting membrane potential (Vm) of a neuron ___________.

Is generated by a difference of electrical charges across the plasma membrane

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

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak channels

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

Myelinated axons with the largest diameter

What prevents the Na+ and K+ gradients from dissipating?

Na+ - K+ ATPase

Clusters of RER and free ribosomes in neurons are called:

Nissl bodies

What characterizes repolarization, the second phase of the action potential?

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

If the soma of a neuron became more permeable to potassium, which statement below best describes the graded potential that would be generated in the soma?

Potassium would leave the cell, causing the membrane to hyperpolarize

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?

Resting membrane potential (RMP)

The neurilemma of axons in the peripheral nervous system is formed by:

Schwann cells

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

Which of the following best describes the Na+ and K+ concentration 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

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.

If the potassium permeability of a resting neuron increases above the resting permeability, what effect will this have on the transmembrane potential?

The inside of the membrane will become more negative.

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane is much more negatively charged than the outside

What characterizes depolarization, the first phase of the action potential?

The membrane potential changes from a negative value to a positive value.

What event triggers the generation of an action potential?

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value 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.

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

The presence of concentration gradients and leak channels

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)

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels

What is the first change to occur in response to a threshold stimulus?

Voltage-gated Na+ channels change shape, and their activation gates open.

If the axolemma becomes more permeable to potassium ion:

a stronger stimulus will be required to cause an action potential

Graded potentials can

act as signals over short distances and make an action potential more or less likely

The part of the peripheral nervous system that carries sensory information to the CNS is designated:

afferent

The all-or-none principle states that

all stimuli great enough to bring the membrane to threshold will produce identical action potentials.

A stimulus that changes a postsynaptic neuron's membrane from resting potential to -85 mV is:

an inhibitory stimulus

Neurons that are rare, small, and lack features that distinguish dendrites from axons are called:

anaxonic

The neuroglial cells that participate in maintaining the blood-brain barrier are the

astrocytes

Action potentials are mainly associated with the membranes of

axons only

Neurons that have one axon and one dendrite, with the soma in between, are called:

bipolar

Raising the potassium ion concentration in the extracellular fluid surrounding a nerve cell will have which effect?

both hyperpolarize it and decrease the magnitude of the potassium equilibrium potential

The _____________ nervous system is composed of the brain and spinal cord

central

If acetylcholine (ACh) causes inhibition of a postsynaptic neuron, to what type of membrane channel did the ACh bind?

chemically-regulated potassium channel

Branches that may occur along an axon are called:

collaterals

Which of the following is the correct term for the movement of an electrical charge across a membrane?

current

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

____________ line the brain ventricles and spinal cord

ependymal cells

Damage to ependymal cells would most likely affect the

formation of cerebrospinal fluid

A(n) _____________ is a subthreshold change in membrane potential within the cell body that decays as it travels away from its point of origin

graded potential

Loss of positive charges (or gain of negative charges) makes the inside of the cell more negative.

hyperpolarization

The boxed region represents what?

hyperpolarization

Which of the following correctly describes a graded potential?

it can have amplitudes of various sizes

What would happen to a patient's cellular Ek+ if a nurse accidentally administered a potassium solution that caused the patient's extracellular potassium ion concentration to rise to 6.01 mM? Assume a body temperature of 37C.

it would become less negative, -85mV

What would happen to the membrane potential if a resting cell suddenly becomes more permeable to Na+?

it would depolarize

Which of the following ion channels located in the plasma membrane of the neuron are always open and are largely responsible for the resting membrane potential?

leak channels

Which of the following is the primary factor in the maintenance of a cell's negative charge during resting membrane potential?

leak channels

Extensive damage to oligodendrocytes in the CNS could result in

loss of sensation and motor control

In most cells, the concentration of ions contributing to the membrane potential are ____________ in the intracellular fluid compared to the extracellular fluid, with the exception of _____________ ions.

lower; potassium

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

Small, wandering cells that engulf cell debris and pathogens in the CNS are called

microglia

Which of the following would increase the membrane permeability to K+?

more K+ leakage channels

Neurons that have several dendrites and a single axon are called

multipolar

The most abundant class of neuron in the central nervous system is:

multipolar

How would a chemical that prevents the opening of voltage-regulated Na+ channels affect the function of a neuron?

neuron will only be capable of producing graded potentials

What is contained inside the structure labeled "5:?

neurotransmitter molecules

The same ________ can have different effects depending on the properties of the ________.

neurotransmitter; receptor

The myelin sheath that covers many CNS axons is formed by

oligodendrocytes

During repolarization of a neuron

potassium ions move out of the cell.

At the resting membrane potential, the membrane is most permeable to ________, which moves __________ the cell due to its electrochemical gradient.

potassium: out of

The rabies virus travels to the CNS via

retrograde axoplasmic transport

Glial cells that surround the neurons in ganglia are

satellite cells

The structure labeled "2" is a

soma (cell body)

The ____________ nervous system controls the skeletal muscles

somatic

identify the structure labeled "5"

synaptic terminals

Axons terminate in a series of fine extensions known as:

telodendria

Identify the structure labeled "4"

telodendria

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+

Many medications introduced into the bloodstream cannot directly affect the neurons of the CNS because

the endothelium of the CNS capillaries forms a blood-brain barrier

Which of the following best describes the electrochemcial forces acting on sodium and potassium ions at the resting membrane potential?

the force on sodium ions is to move into the cell, and the force on potassium ions is to move out of the cell

The Nernst equation can be used to predict

the membrane potential resulting from permeability to a single ion

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 determines the strength of a graded potential?

the size of the stimulus

What is the electrochemical gradient of an ion?

the sum of the electrical and concentration gradients for that ion

What is the basic condition when a neuron is described as polarized?

there is a separation of positive and negative charges across a membrane

Neurotransmitters ready for release are stored in synaptic _______________

vesicles

Most CNS neurons lack centrioles. This observation explains:

why CNS neurons cannot divide to regenerate damaged tissue