Chapter 11.3 Channels and the Electrical Properties of Membranes

Question 1

__ are channels that connect the cytoplasm of adjacent animal cells, while __ perform a similar function in plant cells.

Answer 1

• Gap junctions
• plasmodesmata

Question 2

Large, permissive channels found in the outer membranes of bacteria, mitochondria, and chloroplasts, allowing the passage of small molecules.

Answer 2

porins

Question 3

Why would large channels that connect the inside of a cell to the extracellular space be dangerous?

Answer 3

They could disrupt the cell’s internal environment, as some bacterial toxins form such large channels to kill cells.

Question 4

• Have narrow, highly selective pores that open and close rapidly to control the transport of specific inorganic ions like Na⁺, K⁺, Ca²⁺, and Cl⁻.
• allow specific inorganic ions to diffuse rapidly down their electrochemical gradients, facilitating passive transport across the lipid bilayer.

Answer 4

Ion channels

Question 5

How fast can ions pass through an open ion channel?

Answer 5

Up to 100 million ions can pass through an open ion channel per second, which is 100,000 times faster than the fastest transporter.

Question 6

Can ion channels be coupled to an energy source for active transport?

Answer 6

No, ion channels mediate passive transport only, allowing ions to flow down their electrochemical gradients.

Question 7

What percentage of a cell’s weight is typically water?

Answer 7

About 70%

Question 8

Produced by the difference in concentration of all solutes on either side of a semi-permeable membrane.

Answer 8

osmotic gradient

Question 9

How do cells balance the osmotic gradient caused by intracellular solutes?

Answer 9

the concentration of inorganic ions, like Na⁺ and Cl⁻, in the extracellular fluid.
- a combination of active transport, passive diffusion, the use of compatible solutes, and specialized channels,

Question 10

How long does it take for cell volume to equilibrate in response to osmotic changes?

Answer 10

in minutes or less due to the permeability of biological membranes to water.

Question 11

Why does osmosis play only a minor role in regulating cell volume in most animal cells?

Answer 11

Most of the cytoplasm in animal cells is in a gel-like state, which resists large changes in volume due to changes in osmolarity.

Question 12

Are water channels in the plasma membrane that facilitate rapid water movement across the membrane.

Answer 12

Aquaporins

Question 13

Where are aquaporins particularly abundant, and why?

Answer 13

Cells that transport large volumes of water, such as kidney epithelial cells and exocrine gland cells.

Question 14

Water flow is regulated by hormones like __, which control the concentration of aquaporins in the plasma membrane.

Answer 14

antidiuretic hormone (vasopressin),

Question 15

ADH (vasopressin) increases water reabsorption in the kidneys by promoting the insertion of __ into the plasma membranes of kidney tubule cells. This __ urine volume and helps __ the urine, especially when the body is dehydrated or blood osmolarity is high.

Answer 15

• aquaporins
• reduces
• concentrate

Question 16

Cells lining the ducts of exocrine glands secrete large volumes of fluid through a coordinated process. (1)__, such as Na⁺/K⁺ ATPase, actively transport Na⁺ (2)__ of the cell and Cl⁻ into the (3)__, creating a high concentration of these ions in the lumen. This accumulation generates an osmotic gradient that draws water into the lumen to balance the solute concentration. Water rapidly follows through (4)__, specialized water channels located in the plasma membrane of the ductal cells. The combined movement of ions and water results in the secretion of large volumes of fluid into the (5)__, which is essential for the proper functioning of exocrine glands, including the secretion of saliva, sweat, and digestive enzymes.

Answer 16

1) Ion pumps
2) out
3) ductal lumen
4) aquaporins
5) ducts

Question 17

Aquaporins form __, with each monomer containing an __.

Answer 17

• tetramers
• aqueous pore

Question 18

How many water molecules can each individual aquaporin channel pass per second?

Answer 18

about 1 billion

Question 19

The feature of aquaporin pore that aids in water transport is that the pore is lined with (1)__ that provide (2)__, helping to align and orient water molecules in a single row.

Answer 19

1) hydrophilic amino acids
2) transient (impermanent) hydrogen bonds

Question 20

In aquaporins, the (1)__ lining the hydrophilic face of the pore align water molecules, and strategically placed (2)__ a central water molecule, preventing (3)__ from passing through. (3)__ diffuses extremely rapidly by being relayed from one water molecule to the next.

Answer 20

1) carbonyl groups (C=O)
2) asparagines tether
3) H⁺

Question 21

The arrangement of water molecules in the aquaporin pore affect hydrogen bonding because the arrangement (1)__ the entire column of water molecules, allowing each water molecule to act as a (2)__ for its inner neighbor.

Answer 21

1) bipolarizes
2) hydrogen-bond acceptor

Question 22

What is the primary challenge that aquaporins face compared to ion channels?

Answer 22

Aquaporins must allow the rapid passage of water while completely blocking the passage of ions to maintain ion gradients across membranes.

Question 23

How does the three-dimensional structure of aquaporins contribute to their selectivity for water?

Answer 23

Aquaporins have a narrow pore that allows water molecules to pass in single file, guided by carbonyl oxygens lining one side of the pore.

Question 24

Why are aquaporins impermeable to hydrated ions such as K⁺, Na⁺, Ca²⁺, or Cl⁻?

Answer 24

The pore is too narrow for hydrated ions to enter, and dehydrating an ion would incur a high energy cost that cannot be compensated by interactions with the hydrophobic wall of the pore.

Question 25

Aquaporins cannot conduct H⁺ because H⁺ is mainly present as (1)__, which diffuses rapidly through water using a relay mechanism that relies on the making and breaking of hydrogen bonds, which aquaporins block.

Answer 25

1) H₃O⁺ (hydronium)

Question 26

What role do strategically placed asparagines play in aquaporins?

Answer 26

They bind to the oxygen atom of the central water molecule in the pore, creating a bipolarity that prevents the participation of this water molecule in an H⁺ relay.

Question 27

A channel that exhibits ion selectivity, allowing certain inorganic ions to pass while excluding others.

Answer 27

Ion channel

Question 28

The narrowest part of the ion channel that forces permeating ions into close contact with the channel walls, determining which ions can pass based on size and charge.

Answer 28

selectivity filter

Question 29

When passing through ion channels, ions interact with water molecules in different ways. Some ions (1)__ most or all of their associated water molecules to pass through the channel, effectively becoming “(2)__.” In contrast, other ions can pass through as (3)__ or (3)__ ions, retaining some of their water molecules. This interaction influences the permeability and selectivity of the ion channels, as the degree of hydration can affect the ion’s ability to traverse the channel.

Answer 29

1) shed
2) dehydrated
3) hydrated or partially hydrated

Question 30

How do ion channels differ from aqueous pores in terms of their state?

Answer 30

Ion channels are gated, meaning they are not continually open and can open or close in response to specific stimuli (e.g., voltage changes, mechanical stress, or ligand binding). In contrast, aquaporins are generally constitutively open aqueous pores that facilitate the rapid movement of water based on osmotic gradients. While aquaporins can be influenced by factors like hormonal signaling, they do not undergo the same gating mechanisms as ion channels, allowing water to flow continuously when present in the membrane.

Question 31

With prolonged stimulation, ion channels may enter a __ “__” or “__” state, becoming refractory to further opening until the stimulus is removed. This state prevents the channels from responding to additional signals, allowing the cell to reset before it can respond to new stimuli.

Answer 31

• closed; desensitized; inactivated

Question 32

What are the main types of stimuli that cause ion channels to open? (3)

Answer 32

1) Change in voltage across the membrane (voltage-gated channels)
2) Mechanical stress (mechanically gated channels)
3) Binding of a ligand (ligand-gated channels)

Question 33

What are the two types of ligands that can regulate ligand-gated ion channels? (2)

Answer 33

1) Extracellular mediators, such as neurotransmitters (transmitter-gated channels)
2) Intracellular mediators, such as anions or nucleotides (ion-gated and nucleotide-gated channels)

Question 34

__, the addition of a phosphate group, can enhance or inhibit channel opening, while __, the removal of a phosphate group, can reverse these effects. This regulatory mechanism influences whether the ion channel is open or closed, impacting ion flow across the membrane and ultimately affecting cellular signaling and function.

Answer 34

• Phosphorylation
• dephosphorylation

Question 35

How many types of ion channels have been identified, and are new types still being discovered?

Answer 35

More than 200

Question 36

Ion channels are characterized by the __ they conduct, the __ by which they are gated, and their __ and __ in the cell and specific cell types.

Answer 36

• ions
• mechanism
• abundance
• localization

Question 37

Ion channels are responsible for the electrical excitability of __ and mediate most forms of electrical signaling in the __. (what type of cell in the body?; what system in the body?)

Answer 37

• muscle cells
• nervous system

Question 38

A single neuron can typically contain __ kinds of ion channels, located in different domains of its plasma membrane.

Answer 38

10 or more

Question 39

Are ion channels found only in electrically excitable cells?

Answer 39

No, ion channels are present in all animal cells, as well as in plant cells and microorganisms.

Question 40

Give an example of a plant and a microorganism that utilize ion channels.

Answer 40

The mimosa plant uses ion channels to propagate its leaf-closing response, while the single-celled motile Paramecium uses them to reverse direction after a collision.

Question 41

• A subset of K⁺ channels that open even in an unstimulated or “resting” cell.
• They make the plasma membrane much more permeable to K⁺ than to other ions, helping to maintain the membrane potential.

Answer 41

K⁺ leak channels

Question 42

• arises from a difference in electrical charge across a membrane due to a minute excess of positive ions on one side and a minute deficit on the other.
• the difference in electric potential between the interior and the exterior of a biological cell.
• principle: If two solutions of different ion concentrations are separated by a permselective membrane a potential difference between the two solutions is established.

Answer 42

membrane potential

Question 43

Passive ion movements, particularly through __, make the largest contribution to the electrical potential across the plasma membrane. It primarily contributes to the membrane potential in animal cells.

Answer 43

• K⁺ leak channels

Question 44

__ balances the charge carried by fixed anions (negatively charged organic molecules) inside the cell and is actively pumped in by the Na⁺-K⁺ pump.

Answer 44

• K⁺

Question 45

The equilibrium of K⁺ affects membrane potential because K⁺ tends to move out of the cell down its concentration gradient, leaving behind unbalanced negative charges, creating an electrical field that opposes further __.

Answer 45

K⁺ efflux

Question 46

Defined as the voltage at which the electrical driving force on K⁺ exactly balances the effect of its concentration gradient, resulting in no net flow of ions across the membrane.

Answer 46

Resting membrane potential

Question 47

Used to quantify the equilibrium condition and calculate the theoretical resting membrane potential based on internal and external ion concentrations.

Answer 47

Nernst equation

Question 48

Why is the actual resting membrane potential often not equal to the value predicted by the Nernst equation for K⁺?

Answer 48

The plasma membrane of a real cell is not exclusively permeable to K⁺; therefore, other ions also influence the actual resting membrane potential.

Question 49

The flow of inorganic ions is driven by the __ for that ion, which combines the effects of the voltage gradient and the concentration gradient.

Answer 49

electrochemical gradient

Question 50

• When the voltage gradient and concentration gradient for an ion balance each other, the electrochemical gradient for the ion is zero, resulting in no net flow of the ion through the channel. What do you call this?
• refers to the specific membrane potential at which the concentration gradient for a particular ion is balanced by the electrical gradient, resulting in no net movement of that ion across the membrane.

Answer 50

Equilibrium potential or Nernst potential

Question 51

How is the equilibrium potential for an ion calculated?

Answer 51

Nernst equation

Question 52

the primary contributor to the resting potential of a cell

Answer 52

K⁺ equilibrium mechanism

Question 53

When the Na⁺-K⁺ pump is suddenly inactivated, there is an immediate slight __ in the membrane potential due to the pump’s electrogenic nature, as it normally contributes to the maintenance of the resting membrane potential by moving more Na⁺ out of the cell than K⁺ in. However, the major resting potential can persist for several minutes due to the presence of other ion channels and the overall ionic balance in the cell. Over time, without the pump’s activity, the resting potential will eventually decline further.

Answer 53

drop

Question 54

After stopping the Na⁺-K⁺ pump, the ion gradients established by the pump will gradually __. This allows __ to enter the cell, leading to a new resting state where the concentrations of Na⁺, K⁺, and Cl⁻ reach equilibrium. As a result, the membrane potential __, ultimately leading to a lower resting potential than what was maintained during active pumping.

Answer 54

• diminish
• Na⁺
• decreases

Question 55

What is the typical range of resting potential in animal cells?

Answer 55

-20 mV and -120 mV

Question 56

What was the first ion channel to be crystallized and studied by x-ray diffraction?

Answer 56

bacterial K⁺ channel

Question 57

K⁺ channels conduct K⁺ ions much faster than Na⁺ despite similar sizes due to specific structural features, including the arrangement of __ in the __.

Answer 57

• carbonyl oxygens
• selectivity filter

Question 58

What is the effect of a single amino acid substitution in the pore of a K⁺ channel?

Answer 58

loss of ion selectivity and result in cell death

Question 59

The bacterial K⁺ channel consists of __ identical transmembrane subunits that form a __ through the membrane, with each subunit contributing two transmembrane __.

Answer 59

• four
• central pore
• α-helices

Question 60

In the bacterial K⁺ channels, this part from the four subunits forms a narrow pore lined with carbonyl oxygen atoms, which allows K⁺ ions to enter while excluding Na⁺ ions.

Answer 60

selectivity loops

Question 61

selectivity filter in K+ channel function:
A K⁺ ion must (1)__ almost all of its bound water molecules to enter the filter, where it interacts with (2)__ that are spaced to accommodate K⁺, while Na⁺ cannot enter due to insufficient proximity of the (2)__.

Answer 61

1) lose
2) carbonyl oxygens

Question 62

When K⁺ channel structure closes, the inner helices of the K⁺ channel __ to constrict the pore at the cytosolic end, blocking ion entry with bulky hydrophobic side chains.

Answer 62

tilt

Question 63

Other ion channels also use similar gating principles, where the channel’s pore helices are __ __ to sensor domains that induce conformational changes in response to stimuli, opening or closing the ion-conducting pathway.

Answer 63

• allosterically coupled

Question 64

• Protein channels that respond to mechanical forces in their environment, allowing cells to sense and react to changes such as pressure, shear forces, and osmotic pressure.
• rare, often embedded in complex structures, and their gating mechanisms require attachment to the extracellular matrix or cytoskeleton, making them challenging to isolate and study.

Answer 64

Mechanosensitive channels

Question 65

Why is it difficult to study mechanosensitive channels?

Answer 65

Mechanosensitive channels are rare, often embedded in complex structures, and their gating mechanisms require attachment to the extracellular matrix or cytoskeleton, making them challenging to isolate and study.

Question 66

• It is a mechanosensitive ion channels located in the cell membrane and function as key cellular mechanotransducers for converting mechanical stimuli into electrochemical signals.
• essential for touch sensation, detecting bladder fullness, and play a crucial role in developmental processes and blood pressure regulation.
• formed from three identical subunits, each containing 36 transmembrane helices that create a dome-like structure, with a central hub that forms the ion-conducting pore.

Answer 66

Piezo ion channels

Question 67

Researchers were able to identify Piezo ion channels by using __ __ to find cell lines that opened an ion channel in response to mechanical pressure and systematically disrupted genes encoding proteins with membrane-spanning helices.
definition: a versatile electrophysiological tool for understanding ion channel behavior.

Answer 67

• patch clamping

Question 68

Piezo channels are formed from __ identical subunits, each containing __ transmembrane helices that create a __-__ structure, with a central hub that forms the __-__ __.

Answer 68

• three
• 36
• dome-like
• ion-conducting pore

Question 69

Bacteria open __ in hypotonic environments to leak small molecules when osmotic pressure becomes dangerous, allowing them to maintain essential macromolecules while quickly losing smaller ones.

Answer 69

mechanosensitive channels

Question 70

What are the two types of mechanosensitive channels found in bacteria? (2) What are their pore sizes?

Answer 70

1) MscS channel (small conductance, opening at low to moderate pressures) - 1.3 nm in diameter
2) MscL channel (large conductance, opening at high pressures). - 3 nm in diameter

Question 71

What is the fundamental task of a neuron?

Answer 71

to receive, integrate, conduct, and transmit signals.

Question 72

A human neuron can be as long as __, such as a neuron extending from the spinal cord to a muscle in the foot.

Answer 72

1 meter

Question 73

A neuron consists of a __(containing the nucleus), one long __ (which conducts signals away), and multiple __(which receive signals from other neurons).

Answer 73

• cell body
• axon
• dendrites

Question 74

provide an enlarged surface area to receive signals from the axons of other neurons, and they can receive as many as 100,000 inputs on a single neuron.

Answer 74

Dendrites

Question 75

Neuron signals consist of changes in the __ __ across the plasma membrane.

Answer 75

electrical potential

Question 76

The electrical disturbance as it travels along a neuron __ with increasing distance unless the neuron expends energy to __ the signal.

Answer 76

• weakens
• amplify

Question 77

Can conduct signals passively, without amplification, over short distances.

Answer 77

Small neurons

Question 78

Larger neurons use an active signaling mechanism that amplifies the signal as it travels, generating an __ __ (__ __) that propagates rapidly without attenuation.

Answer 78

action potential (nerve impulse)

Question 79

An action potential is triggered when an electrical stimulus exceeds a certain __ strength, leading to rapid electrical activity.

Answer 79

• threshold

Question 80

• A channel responsible for the generation and propagation of action potentials in neurons.
• generate action potentials in electrically excitable cells, including neurons, muscle, endocrine, and egg cells.

Answer 80

Voltage-gated cation channel

Question 81

In nerve and skeletal muscle cells, action potential is triggered by the __ of the plasma membrane, where the membrane potential shifts to a __ __ value inside.

Answer 81

• depolarization
• less negative

Question 82

When voltage-gated Na+ channels open during depolarization, __ ions enter the cell, further depolarizing the membrane and opening more Na+ channels, creating a __ feedback loop.

Answer 82

• Na+
• positive

Question 83

What stops the depolarization process in a neuron during an action potential? (2)

Answer 83

(1) Na+ channels automatically inactivate
(2) voltage-gated K+ channels open to restore the membrane potential to a negative value.

Question 84

The __ __ consists of a single polypeptide chain with four similar domains, each contributing to the central channel and containing a voltage sensor (S4 helix) with positively charged amino acids. During __, the S4 helices experience electrostatic forces that cause them to twist, exposing their charges to the opposite side of the membrane, which opens the channel.

Answer 84

• Na+ channel
• depolarization

Question 85

__ __ automatically inactivate after opening, even though the membrane remains depolarized, and they cannot reopen until the membrane potential returns to its initial negative value.

Answer 85

Na+ channels

Question 86

Delayed K+ channels open during the __ __ of the action potential, allowing K+ to __ the cell and __ the membrane.

Answer 86

• falling phase/repolarization
• exit
• repolarize/hyperpolarize

Question 87

The time needed for Na+ channels to recover from inactivation, limiting the neuron’s repetitive firing rate and ensuring unidirectional action potential propagation.

Answer 87

refractory period

Question 88

Along neurons membrane, action potential propagates as a __, with the depolarization of one patch of membrane triggering depolarization in neighboring regions, sweeping across the membrane.

Answer 88

wave

Question 89

The __-__ __ speeds up ion pumping to restore electrochemical gradients during rapid firing, and neurons with high energy consumption preferentially take up radioactive glucose, which is imaged in a Positron Emission Tomography (PET) scan.

Answer 89

• Na+-K+ pump

Question 90

The (1)__ insulates axons, increasing the speed of action potential conduction by preventing current leakage and allowing the action potential to jump between (2)__ in a process called (3)__.

Answer 90

1) myelin sheath
2) nodes of Ranvier
3) saltatory conduction

Question 91

__ is a demyelinating disease where the immune system attacks the myelin sheaths in some areas of the central nervous system. This slows or halts the propagation of nerve impulses, often leading to severe neurological damage.

Answer 91

Multiple sclerosis

Question 92

What cells form the myelin sheath in the peripheral and central nervous systems? (2)

Answer 92

1) Schwann cells form the myelin sheath in the peripheral nervous system.
2) Oligodendrocytes form the myelin sheath in the central nervous system.

Question 93

1) Schwann cells form the myelin sheath in the __nervous system.
2) Oligodendrocytes form the myelin sheath in the __ nervous system.

Answer 93

1) peripheral
2) central

Question 94

(1)__ and (2)__ wrap multiple layers of their plasma membrane tightly around the axon, creating a myelin sheath that insulates the axon, preventing current leakage.

Answer 94

1) Schwann cells
2) oligodendrocytes

Question 95

(1)__ are gaps in the myelin sheath where Na+ channels are concentrated. Action potentials jump from one node to the next in (2)__, speeding up signal transmission and conserving metabolic energy.

Answer 95

1) Nodes of Ranvier
2) saltatory conduction

Question 96

What are the two main advantages of saltatory conduction? (2)

Answer 96

1) Faster transmission
2) Energy conservation

Question 97

(1)__, developed in the 1970s and 1980s, allows the study of individual ion channels by recording (2)__ flowing through a small patch of membrane. It has enabled detailed examination of ion channels in various cell types, even in small cells like yeast, which cannot be studied using traditional electrophysiology methods.

Answer 97

1) Patch-clamp recording
2) currents

Question 98

Patch-clamp recording shows that ion channels, such as voltage-gated Na+ channels, open in an (1)__ fashion. They open (2)__, with a voltage-dependent probability, but when open, they always allow the same amount of ions to pass through.

Answer 98

1) all-or-nothing
2) stochastically/randomly

Question 99

Conductance of a voltage-gated Na+ channel: when a voltage-gated Na+ channel is open, it allows more than __ ions to pass through per millisecond, maintaining a consistent conductance level.

Answer 99

1000

Question 100

The __ __ recorded across a membrane reflects the total number of open ion channels at any given time, rather than the degree to which individual channels are open.

Answer 100

aggregate current

Question 101

The interior of a resting neuron or muscle cell has an electrical potential of about 40-100 mV __ negative than the external environment, creating a strong voltage gradient across the plasma membrane.

Answer 101

more

Question 102

Changes in __ __ alter the stability of the open, closed, and inactivated conformations of ion channels. These channels can “flip” between conformations when influenced by the strong electrical field across the plasma membrane.

Answer 102

membrane potential

Question 103

The __ __ across the plasma membrane can reach 100,000 V/cm, which significantly influences the behavior of charged proteins like Na+ channels, affecting their conformation and gating properties.

Answer 103

voltage gradient

Question 104

Patch-clamp recording is a technique that measures the ionic current passing through individual ion channels in a __ __ of membrane using a micropipette. The membrane potential is maintained at a set value using an __ __, allowing detailed study of ion channel behavior.

Answer 104

• small patch
• electronic clamp

Question 105

In patch-clamp recording, the __ forms an extremely tight seal with the membrane, ensuring that current can only pass through the ion channels in the membrane covering its tip, allowing precise measurement of ionic flow.

Answer 105

micropipette

Question 106

Two configurations used in patch-clamp recording:
1) __: The micropipette remains connected to the rest of the cell, allowing the study of ion channels in their natural environment.
2)__: The membrane is isolated, making it easier to manipulate the solution on either side of the membrane to test the effects of different solutes. It can also be used to change the orientation of the membrane, exposing the cytoplasmic surface inside the pipette.

Answer 106

1) Attached Patch
2) Detached Patch

Question 107

are ion channels that open in response to changes in membrane potential, allowing the flow of cations (such as Na+, K+, or Ca2+). These channels can generate action potentials in various cell types, including neurons, muscle cells, and endocrine cells.

Answer 107

Voltage-gated cation channels

Question 108

The diversity of voltage-gated cation channels is caused by __ __ and the __ __ of RNA transcripts, resulting in a variety of channel types with different structural and functional properties.

Answer 108

• multiple genes
• alternative splicing

Question 109

How many voltage-gated K+ channel genes are found in different organisms? (Give two organisms)

Answer 109

1) Saccharomyces cerevisiae (yeast) has 1 gene encoding a voltage-gated K+ channel.
2) Caenorhabditis elegans (worm) has 68 genes encoding different but related K+ channels.

This indicates a large diversity in ion channel genes even in simple organisms.

Question 110

Mutations in ion channel genes can lead to various diseases, depending on the cells affected. Examples include (2):

Answer 110

1) Myotonia: Delayed muscle relaxation due to faulty Na+ channels in skeletal muscle.
2) Epilepsy: Caused by mutations in Na+ or K+ channels in the brain, leading to excessive synchronized neuronal firing and seizures.

Question 111

A disease caused by mutations in Na+ or K+ channels in the brain, leading to excessive synchronized neuronal firing and seizures.

Answer 111

Epilepsy

Question 112

A disease that causes delayed muscle relaxation due to faulty Na+ channels in skeletal muscle.

Answer 112

Myotonia

Question 113

How do neurons differ in firing action potentials? (1-3)
The combination of (4)__, (5)__, and (6)__ channels expressed in a neuron determines its firing pattern.

Answer 113

1) Some fire up to 300 times per second.
2) Others fire in short bursts separated by silence.
3) Some fire only once at a time.
Threshold for Action Potential Initiation: Varies among neurons, affecting how easily they can fire.
Refractory Periods: Variation in the duration of refractory periods influences firing frequency and responsiveness.
Frequency of Action Potentials: Different firing rates can encode the intensity of stimuli.

4-6) Na+, K+, and Ca2+

Question 114

In some cells, such as muscle, egg, and endocrine cells, (1)__ generate action potentials instead of Na+ channels, playing a key role in cellular signaling and function.

Answer 114

voltage-gated Ca2+ channels

Question 115

How many neurons and synaptic connections are estimated to be in the human brain?

Answer 115

approximately 10¹¹ neurons and 10¹⁴ synaptic connections

Question 116

What allows the brain to remain stable despite changes over time? One theory suggests that neurons are (1)__. They constantly adjust the expression of ion channels and neurotransmitter receptors to maintain stable function, even as neural circuitry is modified by experience, learning, memory, and aging.

Answer 116

1) self-tuning devices

Question 117

The firing properties of neurons are largely determined by the ion channels they express. The number of __ (Na+ and Ca²⁺) and __ (K⁺) channels can be adjusted to maintain the neuron’s characteristic firing behavior.

Answer 117

• depolarizing
• hyperpolarizing

Question 118

Neurons can _______________ in their membranes as conditions change. This adjustment helps them maintain stable firing behavior, a process that reflects homeostatic control

Answer 118

modify the number of ion channels

Question 119

Understanding how neurons self-regulate ion channels to maintain stable firing properties is crucial because it reveals insights into (1)__, (2)__, and (3)__.

Answer 119

1) homeostatic control
2) neural plasticity - (or neuroplasticity) refers to the brain’s ability to change, adapt, and reorganize itself in response to experiences, learning, and environmental factors.
3) potential interventions in neurological disorders

Question 120

When an action potential reaches the nerve terminal of a presynaptic cell:

1) It stimulates the release of __ from synaptic vesicles.
2) The (1) bind to ___ in the postsynaptic cell membrane.
3) This opens the ion channels, causing ion flow that alters the __ of the postsynaptic cell, transmitting the signal.

Answer 120

1) neurotransmitters
2) transmitter-gated ion channels
3) membrane potential

Question 121

__ __ contain neurotransmitter molecules and are released when they fuse with the plasma membrane of the nerve terminal, allowing neurotransmitters to enter the synapse and bind to the postsynaptic receptors.

Answer 121

Synaptic vesicles

Question 122

When an action potential reaches the presynaptic cell, it causes the __ of the membrane, which opens voltage-gated Ca²⁺ channels. The influx of Ca²⁺ triggers the release of __ stored in synaptic vesicles through __.

Answer 122

• depolarization
• neurotransmitters
• exocytosis

Question 123

Neurotransmitters are removed from the synaptic vesicle are either:

1) __ by specific enzymes in the synaptic cleft.
2) __ by being taken up by the presynaptic cell or surrounding glial cells via Na⁺-dependent neurotransmitter symporters.

Answer 123

1) Destroyed
2) Recycled

Question 124

__-__ __ __ (__ __) convert chemical signals into electrical signals by opening in response to neurotransmitter binding. They allow ions to flow through the membrane, changing the membrane potential at the postsynaptic site.

Answer 124

• Transmitter-gated ion channels
• ionotropic receptors

Question 125

Significance of rapid neurotransmitter removal from the synapse:

1) __ of signaling.
2) Decreased chances of influencing __.
3) Clears the cleft before the next neurotransmitter release, ensuring __ of repeated signals.

Answer 125

1) Temporal precision
2) neighboring cells
3) accurate timing

Question 126

(1)__ respond to neurotransmitters and are relatively insensitive to membrane potential. In contrast, (2)__ respond to changes in membrane potential and are responsible for the self-amplifying excitation of action potentials.

Answer 126

1) Transmitter-gated ion channels
2) voltage-gated ion channels

Question 127

1) __ open nonselective cation channels (Na⁺, Ca²⁺, and K⁺), causing depolarization of the postsynaptic membrane, moving it closer to the action potential threshold.
2) __ open Cl⁻ channels, making the postsynaptic membrane more negative (hyperpolarization) and suppressing action potential firing.

Answer 127

1) Excitatory neurotransmitters
2) Inhibitory neurotransmitters

Question 128

__ __ open in response to inhibitory neurotransmitters, allowing Cl⁻ to enter the cell. This buffers the membrane potential by counteracting depolarization, making it harder for excitatory signals to reach the action potential threshold.

Answer 128

Cl⁻ channels

Question 129

Which neurotransmitters are generally excitatory or inhibitory? Give two examples each.

Answer 129

1) Excitatory: Acetylcholine, Glutamate.
2) Inhibitory: GABA, Glycine.
(Note: Some neurotransmitters, like acetylcholine, can be either excitatory or inhibitory depending on the receptor and location.)

Question 130

1) Opening K⁺ channels causes __ because K⁺ ions flow out of the cell, moving the membrane potential closer to the equilibrium potential for K⁺, which is typically more negative (around -90 mV in most cells). This makes the inside of the cell more negative relative to the outside, causing hyperpolarization.

2) Opening Cl⁻ channels can __ membrane potential by allowing Cl⁻ ions to flow into the cell (or out, depending on the intracellular Cl⁻ concentration). This generally makes the membrane potential more negative (if Cl⁻ enters) or stabilizes it, preventing excessive __. However, the specific effect depends on the cell’s resting Cl⁻ equilibrium potential, which varies by cell type.

Answer 130

1) hyperpolarization
2) buffer; depolarization

Question 131

Major class of neurotransmitter receptors: Fast-acting ion channels that respond to neurotransmitters like acetylcholine, glutamate, glycine, and GABA, mediating immediate and brief excitatory or inhibitory signals.

Answer 131

Ionotropic receptors

Question 132

Major class of neurotransmitter receptors: G-protein-coupled receptors that indirectly regulate ion channels via intracellular signaling, providing slower, more complex, and longer-lasting effects.

Answer 132

Metabotropic receptors

Question 133

Major class of neurotransmitter receptors (2)

Answer 133

1) Ionotropic receptors
2) Metabotropic receptors

Question 134

Toxins like __ block the action of inhibitory neurotransmitters (such as glycine) by binding to their receptors, preventing inhibitory action, leading to symptoms like muscle spasms, convulsions, and potentially death.

Answer 134

strychnine

Question 135

A __ __ is the specialized chemical synapse between a motor neuron and a skeletal muscle cell, where acetylcholine is released from the nerve terminal, triggering muscle contraction.

Answer 135

neuromuscular junction

Question 136

__ __ are densely packed at the neuromuscular junction, with about 20,000 receptors per square micrometer in the muscle-cell plasma membrane. It opens when two acetylcholine molecules bind to its pentameric complex, inducing a conformational change that allows the channel to flicker open.

Answer 136

Acetylcholine receptors

Question 137

After acetylcholine binds to the receptor at the neuromuscular junction, the channel flickers between open and closed states with a higher probability of being __. Once acetylcholinesterase hydrolyzes acetylcholine, the concentration __, and the receptor returns to its (3)__ __. The channel typically closes within about 1 millisecond after acetylcholine is hydrolyzed, well before (3)__occurs.

Answer 137

• open
• lowers
• resting state; desensitization

Question 138

The acetylcholine receptor allows the passage of (1-3)__,__, and __. Clusters of negatively charged amino acids near the pore exclude negative ions and encourage the passage of cations, especially (4)__.

Answer 138

1-3) Na⁺, K⁺, and Ca²⁺
4) Na⁺

Question 139

At resting potential, the voltage gradient and concentration gradient for Na⁺ both act to drive Na⁺ __ (into/ouside) the cell, causing a large net __ (influx/eflux) of Na⁺ through the acetylcholine receptor and membrane depolarization, which signals __ __ (what mechanism in the body).

Answer 139

• into
• influx
• muscle contraction

Question 140

__ regulate acetylcholine signaling at the neuromuscular junction. It rapidly hydrolyzes acetylcholine in the synaptic cleft, lowering its concentration and allowing the acetylcholine receptor to return to its resting state within about 1 millisecond.

Answer 140

Acetylcholinesterase

Question 141

What types of neurotransmitters activate transmitter-gated ion channels similar to acetylcholine receptors? (4)

Answer 141

1) Acetylcholine
2) serotonin
3) GABA
4) glycine

Question 142

Unlike other transmitter-gated ion channels, __-__ __ __ are constructed from a distinct family of subunits that form tetramers, resembling the structure of K⁺ channels.

Answer 142

glutamate-gated ion channels

Question 143

How are the many subtypes of transmitter-gated ion channels generated? (2)

Answer 143

1) different subunit combinations, which are produced either by distinct genes
2) alternative RNA splicing from a single gene product.

Question 144

What factors contribute to the diversity of transmitter-gated ion channels in neurons? (4)

Answer 144

1) ligand affinities
2) channel conductances
3) rates of opening and closing
4) sensitivities to drugs and toxins

Question 145

It is possible to design drugs that target __ __ of transmitter-gated ion channels, allowing for precise influence over particular __ __ by focusing on neurons expressing different subunit combinations.

Answer 145

• specific subtypes
• brain functions

Question 146

__ __ target synapses primarily by binding to transmitter-gated ion channels, affecting neurotransmitter actions and altering synaptic transmission.

Answer 146

Psychoactive drugs

Question 147

__ is a plant-derived drug that blocks acetylcholine receptors on skeletal muscle cells, allowing surgeons to relax muscles during operations.

Answer 147

Curare

Question 148

What types of disorders are treated with drugs that act on chemical synapses?

Answer 148

1) insomnia
2) anxiety
3) depression
4) schizophrenia

Question 149

__ and __ bind to GABA receptors, enhancing the inhibitory action of GABA and allowing lower concentrations of GABA to open Cl⁻ channels more effectively.

Answer 149

1) Barbiturates
2) benzodiazepines

Question 150

a neurotransmitter, a chemical messenger in your brain. It slows down your brain by blocking specific signals in your central nervous system (your brain and spinal cord). It is known for producing a calming effect.

Answer 150

Gamma-aminobutyric acid (GABA)

Question 151

__ mechanisms in synaptic signaling, mediated by Na⁺-driven symports, clear neurotransmitters from the synaptic cleft, and inhibiting these transporters prolongs the effect of the neurotransmitter, thereby strengthening synaptic transmission.

Answer 151

Reuptake

Question 152

Prozac and similar antidepressants inhibit the reuptake of __, and some also inhibit the reuptake of __, increasing their availability in the synaptic cleft.

Answer 152

• serotonin
• norepinephrine

Question 153

Advancements in understanding the molecular biology of ion channels may lead to the design of more __ __ drugs aimed at alleviating mental illness while minimizing side effects.

Answer 153

selective psychoactive

Question 154

Neuromuscular transmission is initiated when a __ __ reaches the nerve terminal, causing __ of the presynaptic membrane and opening voltage-gated __ channels.

Answer 154

• nerve impulse
• depolarization
• Ca²⁺

Question 155

In neuromuscular junction, the influx of __ into the nerve terminal, due to its high extracellular concentration, triggers the local release of acetylcholine by exocytosis into the synaptic cleft.

Answer 155

Ca²⁺

Question 156

Acetylcholine binds to its receptors on the muscle cell membrane (sarcolemma), causing cation channels to open, leading to an influx of __ and a local __ of the muscle membrane.

Answer 156

• Na⁺
• depolarization

Question 157

These cations in the neuromuscular junction are essential, with __ primarily involved in neurotransmitter release and __ in generating and propagating action potentials.

Answer 157

• Ca²⁺
• Na⁺

Question 158

After the local depolarization of the muscle cell membrane, it opens voltage-gated Na⁺ channels and allows more Na⁺ to enter. It results in a self-propagating depolarization that generates an __ __ across the entire muscle plasma membrane.

Answer 158

action potential

Question 159

The generalized depolarization of the muscle cell membrane activates voltage-gated Ca²⁺ channels in the __ __ (_-__), which are essential for muscle contraction.

Answer 159

transverse tubules (T-tubules)

Question 160

During muscle contraction, activation of (1)__ in the (2)__ causes a mechanical change that opens Ca²⁺-release channels in the adjacent sarcoplasmic reticulum, allowing Ca²⁺ to flow from the SR into the cytoplasm. The sudden increase in cytosolic Ca²⁺ concentration leads to the contraction of the (3)__ in the muscle cell.

Answer 160

1) voltage-gated Ca²⁺ channels
2) T-tubules
3) myofibrils

Question 161

A single neuron can receive inputs from __ of other neurons and form synapses with many more, integrating information from various sources before reacting.

Answer 161

thousands

Question 162

Motor neurons receive both (1) __ __, which cause depolarization (__ postsynaptic potentials, EPSPs), and (2)__ __, which cause hyperpolarization (__ postsynaptic potentials, IPSPs). (What type of signal?)

Answer 162

1) excitatory signals; excitatory
2) inhibitory signals; inhibitory

Question 163

(1)__ is a small depolarization in the postsynaptic membrane caused by neurotransmitter release at an excitatory synapse.

Answer 163

Excitatory postsynaptic potential (EPSP)

Question 164

(1)__ is a small hyperpolarization in the postsynaptic membrane caused by neurotransmitter release at an inhibitory synapse.

Answer 164

Inhibitory postsynaptic potential (IPSP)

Question 165

Individual EPSP is generally insufficient to trigger an action potential. The plasma membrane of most neurons contains a relatively low density of (1)__ channels, making an individual EPSP too small to trigger an action potential.

Answer 165

1) voltage-gated Na⁺

Question 166

If multiple signals arrive simultaneously at several synapses, the total PSP in that area will be the sum of the (1)__, with IPSPs contributing negatively to the total.

Answer 166

individual postsynaptic potential or PSPs

Question 167

Postsynaptic potentials or PSPs are transmitted over long distances within a neuron by spreading (1)__ and converge on the cell body, where the combined magnitude is encoded into the (2)__ : stronger stimulation leads to higher firing rates.

Answer 167

1) passively
2) frequency of action potentials

Question 168

The __ __ encodes the intensity of stimulation into action potential frequency for long-distance transmission, rich in voltage-gated Na⁺ channels and various K⁺ channels.

Answer 168

axon hillock

Question 169

What types of K⁺ channels are present at the axon hillock? (3)

Answer 169

1) delayed
2) rapidly inactivating
3) Ca²⁺-activated K⁺ channels
, each contributing to action potential firing and response modulation.

Question 170

Delayed K⁺ channels open after an action potential, allowing K⁺ __(influx/efflux), which repolarizes the membrane and prepares it for the next action potential.

Answer 170

efflux

Question 171

Ca²⁺ channels allow Ca²⁺ __(influx/efflux) during action potentials, while Ca²⁺-activated K⁺ channels open in response to increased __(what ion), making the neuron __ responsive to prolonged stimulation (adaptation).

Answer 171

• influx
• Ca²⁺
• less

Question 172

__ __ is the decreased responsiveness to constant stimulation, allowing neurons to react sensitively to changes, which is crucial for sensory processing (e.g., feeling light touch while ignoring clothing pressure).

Answer 172

Neuronal adaptation

Question 173

The diversity of ion channels contribute to neuronal function. Hundreds of genes encode various ion channels, allowing neurons to have unique combinations of channels that tailor their electrical behavior to specific tasks, enabling __ __ and __.

Answer 173

• complex computations
• responses

Question 174

__ __ is the ability of individual synapses to strengthen or weaken based on their use, playing a crucial role in learning and memory.

Answer 174

Synaptic plasticity

Question 175

__-__ __ (__) is a persistent increase in synaptic strength following high-frequency stimulation of a synapse, crucial for learning and memory. The hippocampus plays a key role in forming new memories. It is triggered when a presynaptic neuron fires while the postsynaptic membrane is strongly depolarized, often due to repetitive stimulation. This allows glutamate to bind to (2)__ receptors.

Answer 175

long-term potentiation (LTP)
2) N-methyl-D-aspartate (NMDA)

Question 176

__ receptors mediate most excitatory postsynaptic currents, while __ receptors are crucial for LTP because they allow Ca²⁺ entry when glutamate binds and the membrane is depolarized.

Answer 176

• AMPA
• NMDA

Question 177

__ receptors are permeable to Ca²⁺, which acts as a signaling molecule in the postsynaptic cell, initiating a cascade of changes that lead to LTP.

Answer 177

NMDA

Question 178

During long-term potentiation (LTP), the number of __ receptors in the postsynaptic membrane increases, enhancing the cell’s sensitivity to glutamate.

Answer 178

AMPA

Question 179

(1)__ is a long-lasting decrease in synaptic strength that reduces AMPA receptors in the postsynaptic membrane. Unlike LTP, it involves lower levels of Ca²⁺ and activates protein phosphatases.

Answer 179

long-term depression (LTD)

Question 180

High Ca²⁺ levels activate protein kinases leading to (1)__, while moderate Ca²⁺ levels activate protein phosphatases leading to (2)__, demonstrating bidirectional control of synaptic strength.

Answer 180

1) Long-term potentiation (LTP)
2) Long-term depression (LTD)

Question 181

__ receptors are involved in synaptic plasticity and learning beyond the hippocampus and are crucial for adjusting synaptic connections during nervous system development.

Answer 181

NMDA

Question 182

A key feature of neurotransmitter effects beyond signal transmission is it can alter __ __ __, leading to lasting changes in synaptic transmission efficacy, which contribute to learning and memory.

Answer 182

intracellular mediator concentrations

Question 183

The signaling events in long-term potentiation:
1) (1.1)__ (what molecule?) binds to (1.2)__ receptors on the postsynaptic membrane, opening their channels and allowing (1.3)__ (what ion?) influx, which begins to depolarize the postsynaptic membrane.
2) Partial depolarization removes the (2.1)__ (what ion?) block from (2.2)__-__ channels, allowing them to open when (1.1)__ is bound, which permits (2.3)__(what ion?) entry into the postsynaptic cell.
3) Increased (2.3)__ concentration induces the postsynaptic cell to insert new (1.2)__ receptors into the plasma membrane, enhancing the cell’s sensitivity to (1.1)__.

Answer 183

1.1) Glutamate
1.2) AMPA
1.3)Na⁺

2.1) Mg²⁺
2.2) NMDA-receptor
2.3) Ca²⁺

Question 184

Photosensitive ion channels that open in response to light, originally evolved as sensory receptors in green algae. They contain a covalently bound retinal group that absorbs light, triggering a conformational change that opens an ion channel.

Answer 184

channelrhodopsins

Question 185

__are light-activated cation channels, while __ is a light-driven proton pump.

Answer 185

• Channelrhodopsins
• bacteriorhodopsin

Question 186

What technique is used to express channelrhodopsin in specific cell types?

Answer 186

Genetic engineering techniques

Question 187

Researchers control neuronal firing using channelrhodopsins by __ __ at specific frequencies, researchers can activate channelrhodopsin and induce neurons to fire action potentials.

Answer 187

• flashing light

Question 188

A technique that allows researchers to activate or inhibit specific neurons in living animals with spatial and temporal precision using light. It allows analysis of neurons and circuits underlying complex behaviors, including aggression and social interactions.

Answer 188

optogenetics

Question 189

Give an example of how channelrhodopsins have been used in research

Answer 189

In a study, channelrhodopsin was expressed in aggression-related neurons in mice; activating these neurons with light caused aggressive behavior.

Question 190

What are some other types of light-responsive ion channels and transporters developed after channelrhodopsins? (1)

Answer 190

channels that can rapidly inactivate specific neurons

Question 191

Optogenetics considered revolutionary in neurobiology because it enables __ __ of neuronal activity, providing insights into the neural basis of __ and neurological __.

Answer 191

• precise manipulation-
• behavior
• functions