Chapter 7
In the peripheral nervous system, ________ neurons carry sensory and visceral information to the central nervous system, and ________ neurons leave the central nervous system and innervate organs, which are usually muscles or glands.
afferent : efferent
What portion of the peripheral nervous system transmits information from sensory receptors to the central nervous system?
afferent nervous system
The movement of synaptic vesicles to the end of the axon terminal involves what type of transport?
anterograde
What portion of the efferent branch of the nervous system communicates to glands and cardiac muscle?
autonomic nervous system
On what portion of the neuron do action potentials propagate?
axon
If the graded potential remains above threshold once it reaches the ________, an action potential will be generated.
axon hillock
In a neuron, where is the greatest concentration of voltage-gated sodium and voltage-gated potassium channels?
axon hillock
An action potential originates at the ________ and travels along the axon until it reaches the ________.
axon hillock : axon terminal
In a neuron, where are voltage-gated calcium channels located?
axon terminal
What percentage of people with diabetes develop peripheral neuropathy?
30 percent
________ branch from the cell body and receive input from other neurons at specialized junctions called ________.
Dendrites : synapses
________ is the mechanism by which action potentials are propagated in unmyelinated axons.
Electrotonic conduction
What equation is used to calculate the membrane potential based on ion concentration gradients and permeabilities?
GHK equation
In Figure 7.1, if the direction of event "C" was reversed (hyperpolarization), how would this affect the ability of the postsynaptic membrane to generate an action potential?
Hyperpolarization will reduce the likelihood that an action potential will be generated.
Saxitoxin (STX) is the most well-known paralytic shellfish toxin caused by the phenomenon known as "red tide." Which statement below best describes why this neurotoxin causes paralysis?
It acts by blocking voltage-gated sodium channels which are needed to generate an action potential.
Which statement best describes the event indicated by the letter "C" in Figure 7.1 and how that event is initiated?
It is a subthreshold graded potential resulting from the opening of sodium channels, closure of potassium channels, or opening of ion channels for sodium and potassium.
The ________ maintains the resting membrane potential.
Na+/K+pump
In the peripheral nervous system, myelin is formed by ________. In the central nervous system, myelin is formed by ________.
Schwann cells : oligodendrocytes
Why do the distributions of sodium and potassium ions across the plasma membrane of neurons not change appreciably, even following hundreds of action potentials?
The movement of sodium and potassium ions that occurs during an action potential is countered by the active transport of these ions by the Na+/K+pump.
As an action potential is propagated away from the axon hillock, why does propagation continue in one direction?
The region just behind the action potential is in the absolute refractory period.
A group of nerve cell bodies in the peripheral nervous system are referred to as
ganglia
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
Which of the following potentials can sum?
graded potentials
Which of the following potentials dissipate in size as the potential moves away from the site of initiation?
graded potentials
The all-or-none principle, associated with the action potential, states that
once membrane potential reaches threshold, an action potential will be generated and that action potential will always be the same magnitude.
The depolarization phase of the action potential is generated by a rapid
opening of sodium channels.
In order to generate an action potential, the magnitude of the inward sodium current must be large enough to overcome which of the following?
outward potassium current
What two divisions of the autonomic nervous system have opposite effects on the organs they innervate?
parasympathetic and sympathetic
What portion of the nervous system provides communication between peripheral organs and the brain and spinal cord?
peripheral nervous system
The fact that a cell has an electrical potential difference across its membrane makes that cell
polarized.
The depolarization of the membrane due to a stimulus is a regenerative mechanism meaning that, once sodium gates begin to open, even more sodium gates will be activated leading to a larger inflow of sodium ions and more depolarization until it is terminated when sodium gates close. This is an example of
positive feedback.
At rest, the plasma membrane is more permeable to which of the following ions?
potassium (K+)
Increased permeability to what ion is responsible for the relative refractory period?
potassium (K+)
Movement of what ion is responsible for event "D" in Figure 7.1?
potassium (K+)
The resting membrane potential is close to the equilibrium potential of which of the following ions?
potassium (K+)
At the resting membrane potential, the membrane is most permeable to ________, which moves ________ the cell due to its electrochemical gradient.
potassium : out of
The repolarization phase of action potentials in neurons is due primarily to
potassium flow out of the cell.
Which of the following best describes the function of the myelin sheath?
reduce a membrane's ion permeability
The fact that the opening of some sodium channels can induce several other sodium channels to open describes the ________ property of these channels.
regenerative
The jumping of an action potential from node-to-node is called
saltatory conduction.
1) The central nervous system, which is composed of the brain and spinal cord, receives and processes information from both the external environment, known as ________ information and, the internal environment, which refers to ________ information.
sensory : visceral
During the rapid depolarization phase of an action potential, the plasma membrane is more permeable to which of the following ions?
sodium (Na+)
What portion of the efferent nervous system communicates with skeletal muscle?
somatic nervous system
In Figure 7.1, if S2 indicated a stimulus from a different source, and S1 occurred coincident with S2, what type of summation has been generated?
spatial
Identify the type of summation that is occurring in Figure 7.1 where "S" refers to a stimulus from one source measured in the postsynaptic membrane.
temporal
When a weak stimulus is applied in rapid succession, it will often reach threshold due to
temporal summation.
What limits the maximum number of action potentials on an axon?
the absolute refractory period
A subthreshold stimulus will not generate an action potential whereas a suprathreshold stimulus does generate an action potential. This is an example of
the all-or-none principle.
The direction of change in membrane potential, in response to a stimulus that initiates a graded potential, is dependent upon
the ion channels that are opened or closed.
Which statement best describes the events responsible for the phase represented by the letter "A" in Figure 7.1?
the opening of sodium channel
Which statement best describes the events responsible for the phase represented by the letter "B" in Figure 7.1?
the opening of sodium channels
What determines the strength of a graded potential?
the size of the stimulus
The magnitude of depolarization at the peak of an action potential is dependent on what factor?
the strength of the electrochemical gradient for sodium and potassium ions relative to their permeability to these ions
What is the level of membrane depolarization required to induce the sodium channel's positive feedback loop called?
threshold
Information gathered about our internal environment (i.e., fullness of the stomach, blood pressure, etc.) is called ________ information.
visceral
What type of ion channels is located along the axon?
voltage-gated channels
Which statement best describes how graded potentials determine whether an action potential will be generated or not?
when an excitatory depolarization reaches threshold
What nervous system is found in the intestinal tract?
enteric nervous system
In myelinated axons, sodium and potassium channels would be concentrated in what area?
nodes of Ranvier
In myelinated nerve fibers, where do action potentials occur?
nodes of Ranvier
Which of the following are common symptoms of peripheral neuropathy?
numbness, tingling sensation, or pain in the hands and feet
What type of cell enhances the velocity of electrical transmission of an action potential along an axon in the central nervous system?
oligodendrocyte
Which type of glial cell provides the myelin sheath for many axons in the central nervous system?
oligodendrocytes
What is the only glial cell found outside of the central nervous system?
Schwann cell
Most neurons have a resting membrane potential of
-70 mV.
Which of the following is an example of spatial summation?
Two stimuli from two sources produce graded potentials on the same neuron at the same time such that the two potentials sum.
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.
Which of the following best describes the electrochemical 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.
Which statement below best describes why action potentials travel in only one direction?
They have a refractory period.
Which of the following accurately describes afferent neurons?
They transmit information from the periphery to the CNS.
How can action potentials relay information about the intensity of a stimulus, such as distinguishing between a loud and soft sound?
due to the frequency of action potentials
Which of the following potentials are affected by refractory periods?
action potentials
Which of the following potentials has an all-or-none response?
action potentials
During which of the following states are the majority of voltage-gated sodium channels closed and incapable of opening?
during the absolute refractory period
Which of the following potentials is a result of opening or closing of ion channels?
both graded potentials and action potentials
Which statement best describes how local anesthetics such as Novocaine work in numbing neurons?
by blocking voltage-gated sodium channels
What portion of the peripheral nervous system communicates to effector organs?
efferent nervous system
The brain and spinal cord are part of which of the following branches of the nervous system?
central nervous system
The repolarization phase of the action potential in a neuron is driven by the
closure of sodium channels and opening of potassium channels.
What is the inverse of resistance?
conductance
Which of the following is the correct term for the movement of an electrical charge across a membrane?
current
Once a membrane potential has been developed, the force that drives a particular ion across the membrane is its
electrochemical gradient.
What is the passive spread of current along a membrane called?
electrotonic conduction
Toward the end of the relative refractory period, the continued decrease in stimulus intensity required to initiate an action potential is caused by
decreased potassium permeability.
A change in a cell's membrane potential, such that the inside of the cell becomes more positive, is referred to as a ________ whereas if it becomes more negative it is referred to as ________.
depolarization : hyperpolarization
Which of the following changes in membrane potential is considered excitatory?
depolarization only
Which of the following axons would have the fastest conduction velocity?
diameter = 20 microns, myelinated
For an unmyelinated axon, conduction velocity is primarily determined by the
diameter of the axon.
The opening of sodium channels causes a rapid ________ of sodium that ________ the neuron's membrane.
influx : depolarizes
What is the most common neuronal cell type?
interneuron
What functional class of neurons accounts for 99 percent of the neurons in the body processing sensory information and carrying out complex functions?
interneurons
At the resting membrane potential, the electrochemical gradient for sodium across the membrane is such that the net flux for sodium movement is directed ________, thereby causing the cell's membrane potential to become more ________.
inward : positive
Which of the following determines the resistance to an ion's movement across a membrane?
ion channels within the membrane
What type of ion channels in the membrane of neurons allows ions to move across the membrane at rest and thereby contribute to resting membrane potential?
leak channels
What type of ion channels in the membrane of neurons open or close in response to a neurotransmitter binding to its receptor?
ligand-gated channels
What is the structural classification of a neuron composed of a single axon and a number of dendritic projections from the nerve cell body?
multipolar
Which of the following potentials can reach or exceed the sodium equilibrium potential?
neither graded potentials nor action potentials
What is the functional unit of the nervous system?
neurons
