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What did Dr. McKhann observe in the children in Beijing and why did this observation lead him to question the original diagnosis of Guillain-Barré syndrome?
Children were not able to move but they did have sensory function
Why would the conduction velocity of a neuron be used to diagnose demyelinating diseases?
In a demyelination disease, myelin is degraded, which will decrease conduction velocity.
If the children from Beijing did in fact have a demyelinating disease, what would have been the result of Dr. McKhann's conduction velocity test?
decreased conduction velocity
Why is the diminished strength of the action potential observed by Dr. McKhann a problem with axons and not myelination?
Because the axonal membrane contains the ion channels necessary to conduct the action potential.
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)
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
Leak channels
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 surface.
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.
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
What prevents the Na+ and K+ gradients from dissipating?
Na+-K+ ATPase
Where do most action potentials originate?
Initial segment
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value.
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 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 first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gates open.
What type of conduction takes place in unmyelinated axons?
Continuous conduction
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
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 function of the myelin sheath?
The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.
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.
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
The small space between the sending neuron and the receiving neuron is the
synaptic cleft
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.
We describe the regeneration of the action potential down the membrane of the axon of the neuron as _______.
conduction or propagation
Increasing the voltage resulted in which of the following?
no change to the action potential
Which of the following occurs during depolarization?
Sodium flows into the cell.
In most cells, the concentration of ions contributing to the membrane potential is __________ in the intracellular fluid compared with the extracellular fluid, with the exception of __________ ions.
lower; potassium
The neurons of the central nervous system are also known as __________.
interneurons
Which glial cells form myelin in the central nervous system?
Oligodendrocytes
Which is a similarity between spatial summation and temporal summation?
Both allow subthreshold graded potentials to trigger an action potential.
Which of the following statements best describes the resting membrane potential? Choose the best answer.
A. an osmotic pressure difference that exists between the intracellular and extracellular fluids
B. the differences that exist between excitable cells and non-excitable cells
C. a concentration gradient that exists between the intracellular and extracellular fluids
D. an electrical gradient that exists between the intracellular and extracellular fluids
an electrical gradient that exists between the intracellular and extracellular fluids
An action potential releases neurotransmitter from a neuron by opening which of the following channels?
voltage-gated Ca2+ channels
The depolarization phase of an action potential results from the opening of which channels?
voltage-gated Na+ channels
A molecule that carries information across a synaptic cleft is a
neurotransmitter.
When calcium ions enter the synaptic terminal,
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
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.
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.
Which of the following statements about receptor potentials is FALSE?
The receptor potential is carried by neuroglia.
Which of the following is NOT a functional region of a neuron?
medullary region
The conducting region of the neuron is the _______.
axon
The typical concentration of sodium is _______.
lower than potassium intracellularly.
Which of the following describes a change from the resting membrane potential?
a receptor potential, a synaptic potential or an action potential
What effect did increasing the extracellular potassium have on the resting membrane potential?
The resting membrane potential became less negative.
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.
The channels that provide for the movement of potassium in the resting neuron are _______.
leakage
Establishing the resting membrane potential requires energy through the use of the _______.
sodium-potassium pump
A nerve is _______.
a bundle of axons
The region on the neuron where action potentials are generated is called the ______.
trigger zone
In this simulation, ___________________ will be used to stimulate the axon.
voltage
The minimum voltage that is required to generate an action potential is called the _______.
threshold voltage
An axon that is more negative than the resting membrane potential is said to be _______.
hyperpolarized
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.
An action potential requires _______.
voltage-gated sodium channels to open and sodium to flow with its electrochemical gradient
To reach threshold, the amount of sodium _______.
entering the cell must overcome the potassium exiting
Which of the following blocks voltage-gated sodium channels?
tetrodotoxin and lidocaine
Which of the following is used to block pain?
lidocaine
Which of the following occurs first in the generation of an action potential?
The membrane depolarizes.
Which of the following occurs during repolarization?
Voltage-gated potassium channels open and some voltage-gated sodium channels inactivate. Potassium flows out of the cell.
Which of the following allow the movement of potassium through the neuronal membrane?
leakage channels and voltage-gated potassium channels
Why does the threshold increase when the interval between the stimuli decreases?
Some sodium channels have been inactivated and cannot be reopened immediately.
During the relative refractory period, _______.
another action potential can be generated provided the stimulus is large enough
When the interval between the stimuli decreases, _______.
a second action potential is generated until the interval reaches the absolute refractory period
When the stimulus voltage is increased, _______.
a greater-than-threshold depolarization results and sodium permeability into the cell increases to overcome the potassium exiting.
Which of the following is described correctly?
A. Schwann cells provide the myelination in the peripheral nervous system.
B. Oligodendrocytes provide the myelination in the peripheral nervous system.
C. Schwann cells provide the myelination in the central nervous system.
D. Astrocytes provide the myelination in the central nervous system.
Schwann cells provide the myelination in the peripheral nervous system.
The rate with which an action potential travels along an axon _______.
is called the conduction velocity and is measured in meters/sec
Which of the following describes a B fiber?
medium diameter, lightly myelinated
The nodes of Ranvier are _______.
locations on the axon where the myelin sheath is absent
Which fibers generate the smallest value for conduction velocity?
C fibers
The time interval for conduction would be shortest with
the largest and most heavily myelinated axons
Increasing the amount of myelination _______.
decreases the time between action potentials
In this activity, the stimulus voltage used was _______.
the same for all of the axons and suprathreshold for all of the axons
When the stimulus intensity increases, _______.
the number of action potentials increases
In this activity, which of the following will increase the stimulus intensity?
increasing the duration of the stimulus
At threshold, axons will _______.
Likely generate an action potential if refractory periods have elapsed.
Longer stimuli will allow for _______.
more action potentials to occur, the absolute refractory period to finish and the relative refractory period to finish
The time interval between action potentials is called the _______.
interspike interval
Increase in stimulus intensity _______.
increases the frequency of action potentials
The frequency of action potentials is _______.
the reciprocal of the interspike interval, and measured in hertz
During the relative refractory period, _______.
the stimulus must be above threshold to generate an action potential
A synaptic cleft, or synaptic gap, can be found between a neuron and ______.
A. a gland.
B. another neuron.
C. a muscle cell.
D. All of these.
All of these
The membrane potential that occurs when neurotransmitters bind to their receptors is called _______.
a postsynaptic potential
The release of neurotransmitter occurs _______.
at the axon terminal
Which of the following occurs first?
An action potential arrives at the axon terminal.
At a chemical synapse, the intensity of the stimulus is coded by _______.
the amount of neurotransmitter released and the amount of calcium that enters the axon terminal
When the calcium was removed from the extracellular solution, _______.
no neurotransmitter was released
When magnesium was added to the extracellular solution, _______.
the amount of neurotransmitter released decreased
Calcium and magnesium are both _______.
divalent cations
A single action potential is described as _______.
not graded
A suprathreshold stimulus results in _______.
more action potentials
A depolarizing synaptic potential is also known as _______.
an excitatory postsynaptic potential
The stimulus for graded potentials includes _______.
sensory stimuli and neurotransmitter
A weak, subthreshold stimulus will result in _______.
a small depolarization at the receiving end of the neuron
Which stimulus was at or above threshold?
the moderate and strong stimuli
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
An excitatory postsynaptic potential occurs _______.
at the receiving end of the interneuron
Excitatory neurotransmitters of the CNS usually act by opening ________ channels.
Na+
Neurotransmitters are usually released into synapses by __________.
exocytosis
Which of the following would NOT cause the membrane potential to change from -70 mV to +30 mV?
Potassium ions leaving the cell
Which of the following would have the fastest action potentials?
A. An unmyelinated axon with a large diameter
B. A myelinated axon with a small diameter
C. An unmyelinated axon with a small diameter
D. A myelinated axon with a large diameter
A myelinated axon with a large diameter