Module 4 Flashcards
The membrane potential is established by what two forces?
1) Electrostatic pressure (i.e., opposite charges attract; identical charges repel) and;
2) Pressure for ions to move down their concentration gradients. (Concentration gradients induce diffusion (passive movement) of ions from areas of high concentration to areas of relatively low concentration.)
The resting membrane potential is ______
a) negative
b) positive
a) negative
It’s negative (typically between -65 to -70 mV) because there is a higher concentration of cations (positively charged ions) in the extracellular fluid compared to the cytoplasm).
What is depolarization?
When there is a predominant influx of positive ions, the neuron becomes less negative, which we call depolarization (in fact, the neuron may even become positive, as during the generation of an action potential).
What is hyperpolarization?
When there is a net addition of negative charges to the inside of a neuron, it becomes more negative, an event termed hyperpolarization.
For neurons, the membrane potential changes over time, and these changes are caused by ______moving in and out of the neuron.
ions
(As ion channels in the cell membrane open and ions move in and out of the neuron according to their electrochemical gradients, the membrane potential will become more or less negative, depending on the net movement of charge. This is the process of depolarization and hyperpolarization.)
Because the phospholipid bilayer that makes up the cell membrane is an effective block against the movement of charged molecules, specialized membrane proteins are required to facilitate ion movement.
The membrane proteins responsible for facilitating ion movement are __________ and _____________.
ion channels, transporters.
What are ion channels?
What are transporters?
An ion channel is a protein that facilitates the passive movement of ions from regions of high concentration to low concentration (diffusion) through a pore.
Transporters are membrane proteins that facilitate active (energy-dependent) movement of ions and molecules in the absence of a pore.
What are the 3 main types of transporters and what do they do?
1) Pumps: move ions in or out of the neuron, against their concentration gradient, using energy derived from the breakdown of adenosine triphosphate (ATP, the main source of energy for all cells, obtained by the metabolism of glucose).
2) Co-transporters: move ions in or out of the neuron, against their concentration gradients, using energy derived from the diffusion of other ions in the same direction.
3) Exchangers: move ions in or out of the neuron, against their concentration gradients, using energy derived from the diffusion of other ions in the opposite direction.
The plasma membrane contains proteins that allow both passive and active ion movement. The ion channels facilitate the ______ movement of ions down concentration gradients.
In contrast, exchangers, co-transporters, and pumps facilitate the movement of ions ________ their concentration gradients in an energy-dependent manner.
passive
against
The pore of an ion channel is opened and closed via a gaiting mechanism, limiting ion movement and membrane permeability for certain ion species. The gaiting mechanism of most ion channels is a change in protein conformation (shape) that opens and closes the pore.
Most ion channels can be categorized into what 2 categories?
1) Voltage-gated channels - open and close in response to changes in membrane potential (depolarization or hyperpolarization)
2) Ligand-gated channels - open in response to the binding of an extracellular chemical, such as a neurotransmitter or neuromodulator to a receptor associated with the channel.
The membrane potential is maintained by concentration gradients and electrostatic pressure. The ion species that contribute most strongly to the membrane potential are ____, _____ and ______.
Na+, K+ and Cl-
Ions move in and out of neurons via ________ and __________.
ion channels and transporters.
Ion channels may open and close in response to changes in ___________ or the binding of a _______.
membrane potential
ligand
When Cl- channels open in a neuron at rest, which of the following will occur?
a) Cl- will flow out of the cell and the cell will be hyperpolarized
b) Cl- will flow out of the cell and the cell will be depolarized
c) Cl- will flow into the cell and the cell will be hyperpolarized
d) Cl- will flow into the cell and the cell will be depolarized
c) Cl- will flow into the cell and the cell will be hyperpolarized
The reason for the correct answer above is:
Cl- follows its concentration gradient.
If a neuron at rest becomes highly permeable to sodium (i.e., Na+ channels open), the membrane potential will become:
a) polarized
b) depolarized
c) hyperpolarized
d) repolarized
b) depolarized
Researchers often record the activity of neurons in fresh, living brain slices. Preparing brain slices without killing all of the neurons in the slice is extremely difficult. One strategy for maintaining neuron health when preparing a slice is to prevent them from firing action potentials. How might this be accomplished?
a) bathing the slices in a solution lacking K+
b) bathing the slices in a solution lacking Cl-
c) bathing the slices in a solution that contains high levels of Na+
d) bathing the slices in a solution lacking Na+
d) bathing the slices in a solution lacking Na+
While recording from a neuron in a slice of brain tissue, you identify a novel membrane protein that facilitates the movement of Na+ using energy derived from glucose. What type of membrane protein have you likely identified?
a) Na+ ion channel
b) co-transporter
c) exchanger
d) pump
d) pump
True or False?
Even small changes in voltage-gated ion channel function can have dramatic effects on neuron activity and health.
True.
Given the sensitivity of a neuron’s membrane potential to current flow through open ion channels, even small changes in voltage-gated ion channel function can have dramatic effects on neuron activity and health.
How do a number of toxins derived from plants and animals (or synthesized in a lab) disrupt nervous system function?
By altering the activity of voltage-gated ion-channels, transporters, and receptors.
These chemicals disrupt the ability of neurons to maintain ion gradients and generate action potentials. Toxins can alter ion channel activity by blocking or opening them, or by altering the amount of time that the channels remain open.
What are two kinds of naturally-occurring toxicants?
1) Tetrodotoxin - originally isolated from pufferfish found along the coast of Japan. It’s highly lethal.
Tetrodotoxin blocks voltage-gated Na+ channels, preventing neuron membranes from depolarizing and reaching the threshold for generating action potentials. Tetrodotoxin can be lethal because it prevents neurons from exciting muscles, resulting in paralysis of muscles throughout the body, including those of the respiratory tract.
2) Palytoxin - produced by marine species including certain corals. It’s highly lethal. Rather than preventing the opening of Na+ channels, palytoxin disrupts neuron activity by converting the Na+ /K+ pump into a non-selective cation channel (that is, it allows for the non-selective movement of positive
ions).
Which of the following drugs would reduce the ability of a neuron to generate an action potential?
a) tetrodotoxin, which prevents the opening of Na+ channels
b) DDT, an insecticide that opens Na+ channels
c) batrachotoxin, which results in persistent activation of Na+ channels
d) lorazepam, a drug that opens ligand-gated Cl- channels
a) tetrodotoxin, which prevents the opening of Na+ channels
Here is a list of four (hypothetical) drugs and their respective LD50 values. Which of these drugs is the safest for you to consume?
a) drug A: LD50 = 3 kg/kg body weight
b) drug B: LD50 = 4 g/kg body weight
c) drug C: LD50 = 5 mg/kg body weight
d) drug D: LD50 = 6 µg/kg body weight
a) drug A: LD50 = 3 kg/kg body weight
You are a biopsychologist investigating a newly discovered brain area (area X). Your experiment involves (a) exciting and (b) inhibiting neurons in area X and observing effects on the behavior in mice. To cause neuronal excitation and inhibition, you use drugs with the following effects on ion channels:
a). excitation: open K+ channels; inhibition: open Na+ channels
b). excitation: open Na+ channels; inhibition: open K+ channels
c). excitation: open Na+ channels; inhibition: open Cl- channels
d). excitation: open Cl- channels; inhibition: open K+ channels
e.) both (b) and (c) are correct
e.) both (b) and (c) are correct
Which of the following drugs are used clinically to alleviate chronic (neuropathic) pain by modifying the activity of Na+ channels?
a). selective serotonin reuptake inhibitors
b). tricyclic antidepressants
c). local anesthetics
d). tetrodotoxin
e). both (b) and (c) are correct
e). both (b) and (c) are correct
Hodgkin and Huxley made several important discoveries about the nature and induction of action potentials. List 3 of those discoveries.
A neuron’s membrane potential rapidly reverses during an action potential; the membrane potential is transiently positive (approximately +40 mV).
Influx of Na+ through open voltage-gated channels depolarizes the membrane, thus triggering the action potential.
During the action potential, voltage-gated K+ channels open and K+ flows out of the neuron, eventually returning the membrane potential to the resting membrane potential.
Regarding the video in module 4.3……
What are three different changes in ion channel conductance induced by the drug that would have an effect to depolarize the neuron and increase firing rate?
1) INCREASED FLOW OF NA+ INTO THE NEURON
2) DECREASED FLOW OF CL- INTO THE NEURON
3) DECREASED FLOW OF K+ OUT OF THE NEURON
What are field potentials?
Potentials generated by the summed activity of a relatively large “field of neurons”, as opposed to potentials in a single neuron, as discussed so far.
These field potentials are sufficiently large that they can be recorded by electrodes attached to the scalp. This is the basis for electroencephalography (EEG).
EEG signals, often referred to as “brain waves”, have high _______ resolution, meaning that changes in neuronal activity are very quickly reflected by changes in EEG signals.
temporal
EEG signals can be categorized on the basis of their _____________.
frequencies (i.e., how fast the signal oscillates).
EEG signals are often associated with specific behavioral states (e.g., low-frequency “slow waves” are readily observed during deep sleep, whereas higher frequency signals occur more frequently during active waking).
Given that action potentials are all-or-none, what measure might a researcher use to determine whether a drug is excitatory or inhibitory while recording from a single neuron?
a) The amplitude of action potentials
b) The frequency of action potentials
c) The shape of action potentials
d) None of the above measures are informative in this case
b) The frequency of action potentials
How might a researcher induce the generation of action potentials when recording from a neuron?
a). Injecting positive (depolarizing) current into the neuron
b). Injecting negative (hyperpolarizing) current into the neuron
c). Applying an excitatory drug to the neuron
d). Both A and C
d). Both A and C
The EEG can be recorded with varying numbers of electrodes attached to the skull, ranging from as few as two electrodes to hundreds. The more electrodes are used, the more time-consuming the procedure will be. Assume that you are a very busy neurologist who sees 20-30 patient a day. Today, one of your patients is suspected of having a tumor, which interferes with their auditory processing. What would you suggest to do for the EEG assessment?
a) Use a smaller number of electrodes, since it will save valuable time
b) Use many electrodes, spaced out over the entire brain (i.e., all four lobes of the cortex)
c) Use an intermediate number of electrodes, all spaced out over the occipital cortex
d) Use an intermediate number of electrodes, all spaced out over the temporal cortex
d) Use an intermediate number of electrodes, all spaced out over the temporal cortex
Which of the following is NOT an example of a neuroprosthetic?
a) Deep brain stimulation
b) A retinal implant that bypasses retinal neurons to transmit visual signals to the brain
c) A device that electrically stimulates the spinal cord to restoring movement
d) An EEG cap that records brain activity to detect seizures
d) An EEG cap that records brain activity to detect seizures
Which of the following is NOT involved in deep-brain stimulation?
a) Stereotactic surgery to implant leads and electrodes into the brain
b) Surgical implantation of a pulse generator to control brain stimulation
c) Programming of electrical pulse parameters to optimize brain stimulation
d) Anticonvulsant medications to enhance the effects of brain stimulation
d) Anticonvulsant medications to enhance the effects of brain stimulation
A neurologist and neurosurgeon implant deep-brain stimulation electrodes into a patient diagnosed with short-term memory deficits to enhance brain signals in a relevant brain area. Which brain area should they target?
a) hippocampus
b) neocortex
c) prefrontal cortex
d) basal ganglia
c) prefrontal cortex
Based on your understanding of neuroanatomy (Module 3), where in Gertrude’s brain was the Neuralink most likely implanted?
a) the motor cortex
b) the somatosensory cortex
c) the auditory cortex
d) the olfactory cortex
b) the somatosensory cortex
How does one record a neuron’s membrane potential?
Position the tip of one electrode inside the neuron and the tip of another electrode outside the neuron in the extra- cellular fluid. Although the size of the extracellular electrode is not critical, the tip of the intracellular electrode must be fine enough to pierce the neural membrane without damaging it. The intracellular electrodes are called microelectrodes.