Chapter 8 Mastering

Which membrane potential opens a sufficient number of the voltage-gated Na+ channels to cause a significant change in the membrane potential (making it much less negative).

-60 mV

What is the resting membrane potential of the neuron used in the experiment?

-80 mV

A chemical synapse ALWAYS includes which of the following? 1. axon terminal 2. presynaptic cell 3. synaptic cleft 4. postsynaptic cell 5. dendrite

1, 2, 3, 4

1. Chemically gated ion channels on the postsynaptic membrane are opened. 2. Calcium ions enter the axon terminal. 3. An action potential depolarizes the axon terminal at the presynaptic membrane. 4. Acetylcholine is released from storage vesicles by exocytosis. 5. Acetylcholine binds to receptors on the postsynaptic membrane. The correct sequence for these events is

3, 2, 4, 5, 1

Arrange the following events in the proper sequence: 1. Efferent neuron graded potential reaches threshold and fires an action potential. 2. Afferent neuron graded potential reaches threshold and fires an action potential. 3. Target organ responds. 4. CNS reaches decision about response. 5. Sensory receptor detects change in the environment

5, 2, 4, 1, 3

Most neurons have at least two processes extending from the soma, or cell body. Which type of neuron only has one process extending from the cell body?

A pseudounipolar neuron

When two or more graded potentials arrive at the trigger zone, which of the following could happen?

An excitatory and inhibitory signal can cancel each other out; two excitatory stimuli may be additive, and summation could occur; and two inhibitory stimuli may be additive, resulting in lower excitability.

Once a stimulus binds a receptor on the cell's membrane, what could happen next?

Any of these actions could happen next

Which two properties determine how fast neurons conduct action potentials?

Axon diameter and the leak resistance of the membrane

Which is the main inhibitory neurotransmitter in the brain?

GABA

Where do most action potentials originate?

Initial segment

During an action potential, activation of voltage-gated sodium and potassium channels occurs at different rates. What is the effect of this difference on ion flow across an axon membrane?

Initially, Na+ flows into the cell and then K+ flows out of the cell

If an increase in extracellular potassium hyperpolarizes a neuron, which of the following would be correct?

It would change the membrane potential to a more negative value.

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

It would depolarize.

The major determinant of the resting potential of all cells is

K+ gradient between the blood and interstitial fluid

When voltage-gated Na+ channels of a resting neuron open

Na+ enters the neuron and the neuron depolarizes.

The rising phase of the action potential is due to

Na+ flow into the cell only.

Which type of receptor would bind acetylcholine and be found in skeletal muscle?

Nicotinic cholinergic

If a hyperpolarizing graded potential and a depolarizing graded potential of similar magnitudes arrive at the trigger zone at the same time, what is most likely to occur?

Nothing. They will cancel each other out

Which glial cells form myelin in the central nervous system?

Oligodendrocytes

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

What effect did decreasing the extracellular sodium have on the resting membrane potential?

Only a small change occurred because the resting neuron is not very permeable to sodium.

Myelin is formed by

Schwann cells and oligodendrocytes.

In this experiment, which stimulus causes the membrane potential to reach the threshold value?

Stimulus 3

The sympathetic and parasympathetic nervous systems are divisions of which system?

The autonomic nervous system

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 effect did increasing the extracellular potassium have on the resting membrane potential?

The resting membrane potential became less negative.

Why are Na+, K+, and Cl- the only ions considered in the GHK equation when calculating resting membrane potential (Vm)?

These are the ions to which cell membranes are permeable at rest.

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.

A weak, subthreshold stimulus will result in _______.

a small depolarization at the receiving end of the neuron

originate(s) at the trigger zone

action potential

require(s) a minimum stimulus to occur

action potential

Information coming into the central nervous system is transmitted along ________ neurons.

afferent and sensory

The all-or-none principle states that

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

A depolarizing synaptic potential is also known as _______.

an excitatory postsynaptic potential

highly branched cells that transfer nutrients between blood vessels and neurons

astrocytes

An excitatory postsynaptic potential occurs _______.

at the receiving end of the interneuron

location of voltage-gated ion channels

axon

Neurotransmitter is stored and released from

axon terminals and axon varicosities

A damaged neuron has a better chance of survival and repair if the ________ is/are undamaged.

cell body

make(s) proteins necessary for repair of damaged neuron

cell body

supported by satellite cells

cell body

ependymal cells

central nervous system

microglia

central nervous system

Which type of synapse is most common in the nervous system?

chemical

The multiple thin, branched structures on some neurons whose main function is to receive incoming signals are the

dendrites

receive(s) most of the incoming synapses

dendrites

An excitatory postsynaptic potential (EPSP)

depolarizes a neuron, increasing the likelihood of an action potential

The absolute refractory period of an action potential

ensures one-way travel down an axon, allows a neuron to ignore a second signal sent that closely follows the first, and prevents summation of action potentials

cells that are a source of neural stem cells

ependymal cells

Anterograde and retrograde axonal transport are forms of ________ transport

fast

An axon that is more negative than the resting membrane potential is said to be _______.

hyperpolarized

Interneurons are found

in the CNS

The inactivation gate

is coupled to the movement of the activation gate, but is much slower

The channels that provide for the movement of potassium in the resting neuron are _______.

leakage

A suprathreshold stimulus results in _______.

more action potentials

Spatial summation refers to

multiple graded potentials arriving at one location

Increasing the voltage resulted in which of the following?

no change to the action potential

A single action potential is described as _______.

not graded

cells in the CNS that form myelin

oligodendrocytes

The inhibitory neurotransmitters of the CNS act by opening ________ channels

only Cl-

Glial cells

only help maintain homeostasis of the brain's extracellular fluid. only guide neurons during growth and repair. only provide structural and metabolic support. provide structural and metabolic support and help maintain homeostasis of the brain's extracellular fluid. All of the answers are correct.

The point during an action potential when the inside of the cell has become more positive than the outside is known as the

overshoot.

Schwann cells

peripheral nervous system

The afferent and efferent neurons together form the

peripheral nervous system.

Which ion(s) is/are higher in concentration inside the cell compared to outside?

potassium

When sodium channels open during an action potential, the opening is caused by

presence of positive charge.

The sodium-potassium exchange pump

requires ATP to function.

cells that form supportive capsules around cell bodies

satellite cells

cells that myelinate only one axon each; multiple cells per axon

schwann cells

To increase the amount of neurotransmitter released onto a postsynaptic cell, the presynaptic cell would have to

send action potentials with higher frequency

The stimulus for graded potentials includes _______.

sensory stimuli and neurotransmitter

Calcium is important in the synapse because it

signals the exocytosis of the neurotransmitter.

Establishing the resting membrane potential requires energy through the use of the _______.

sodium-potassium pump

Autonomic motor neurons are subdivided into the

sympathetic and parasympathetic branches

When a second EPSP arrives at a single synapse before the effects of the first have disappeared, what occurs?

temporal summation

Increasing the strength of the stimulus applied to the sensory receptor increased _______.

the frequency of action potentials in the sensory neuron, the amount of neurotransmitter released at the axon terminal of the sensory neuron and the frequency of action potentials in the interneuron

The Nernst equation can be used to predict

the membrane potential resulting from permeability to a single ion

Which stimulus was at or above threshold?

the moderate and strong stimuli

What does the Goldman-Hodgkin-Katz equation take into account that the Nernst equation does NOT?

the permeabilities of the ions

The minimum voltage that is required to generate an action potential is called the _______.

threshold voltage

The resting membrane potential results from

uneven distribution of ions across the cell membrane and differences in membrane permeability to ions.