physio lecture 1 Flashcards
(112 cards)
1
Q
What is the charge on the outer side of the cell membrane?
A
The outer side of the cell membrane has a positive charge.
2
Q
What kind of movement occurs when charged particles move across the cell membrane?
A
When charged particles move across the cell membrane, they move toward the opposite charge, and this movement is called electro-kinetic transport.
3
Q
Why is it important to understand where molecules are located in and around the cell?
A
Understanding the location of molecules is crucial because it helps us comprehend how substances move in and out of the cell, affecting various cellular processes.
4
Q
What often influences the movement of particles within the cell more, concentration differences or charge differences?
A
Often, the movement of particles within the cell is influenced more by differences in their concentration (how many of them are present) than by differences in their charge.
5
Q
What is the Nernst equation primarily used for?
A
The Nernst equation is primarily used to calculate the inner charge of the cell membrane for different ions and can also be used to calculate osmolarity, which measures the concentration of solute particles in a solution.
6
Q
Can you provide examples of inner charges for specific ions using the Nernst equation?
A
Certainly. For example:
Inner charge for Na+ is 60 mV.
Inner charge for Ca2+ is 120 mV.
Inner charge for K+ is around -90 mV.
7
Q
How is the resting membrane potential related to the permeability of potassium ions?
A
The resting membrane potential is closer to -90 mV due to the permeability of potassium ions through potassium channels in the cell membrane. This potassium permeability contributes to the overall charge inside the cell.
8
Q
What does osmolarity measure, and why is it important?
A
Osmolarity measures the concentration of solute particles in a solution per liter of the solution. It’s important because it helps us understand how osmotic pressure works and how solvent (like water) moves across semipermeable membranes between solutions with different concentrations. Osmolarity provides information about how solvent moves to balance concentration differences.
9
Q
What is passive transport, and how does it differ from active transport?
A
Passive transport is the movement of particles along their concentration gradients and does not require ATP energy. It occurs as particles move from areas of high concentration to low concentration. In contrast, active transport requires energy (usually ATP) to move particles against their concentration gradients.
10
Q
What is diffusion, and what types of molecules does it typically apply to?
A
Diffusion is a passive transport mechanism where particles move from areas of high concentration to low concentration. It typically applies to small, non-charged, lipophilic molecules like oxygen (O2) and carbon dioxide (CO2). However, it’s not as fast as some other methods of transport.
11
Q
What is simple diffusion, and how do particles move in this process?
A
Simple diffusion is when particles move directly through the cell membrane or through protein channels like ion channels and aquaporins. They move from areas of high concentration to low concentration.
12
Q
What are channel proteins, and what do they allow to diffuse through them?
A
Channel proteins are specialized proteins that allow charged particles (ions, amino acids) to diffuse through them. They can be specific to certain types of ions.
13
Q
How does facilitated diffusion work, and what kinds of molecules does it help transport?
A
Facilitated diffusion involves larger molecules like amino acids and glucose binding to transport proteins. This binding changes the shape of the transport proteins, which helps these larger molecules pass through the cell membrane.
14
Q
What is electro-kinetic transport, and what happens when charged substances move in this process?
A
Electro-kinetic transport is the movement of charged substances. They move across the cell membrane in the direction opposite to their electric charge. Positive charges move toward negative charges, and vice versa.
15
Q
What is osmosis, and what specifically does it involve the diffusion of?
A
Osmosis is the diffusion of water.
16
Q
In the context of osmosis, what does isotonic osmosis refer to?
A
Isotonic osmosis refers to a balanced movement of water between a cell and its surroundings, where there is no net gain or loss of water by the cell.
17
Q
What is filtration, and where does it occur in the body?
A
Filtration is the movement of substances across the cell membrane due to hydrostatic pressure from the cardiovascular system. It’s important for exchanging particles in the fluid dissolved in blood circulation and occurs in places like the kidneys.
18
Q
How are ion channels classified, and what controls their opening and closing?
A
Ion channels can be classified based on their “gates” that control their opening and closing. These gates can be controlled by voltage changes (voltage-gated channels), chemical signals (ligand-gated channels), or mechanical changes (mechanically-gated channels).
19
Q
What is the primary difference between passive transport and active transport?
A
The primary difference is that passive transport moves substances along concentration gradients without using ATP energy, while active transport requires ATP energy to move substances against concentration gradients.
20
Q
What distinguishes specific facilitated diffusion from non-specific facilitated diffusion?
A
Specific facilitated diffusion requires molecules to bind to a particular transport protein to pass through the cell membrane. In contrast, non-specific facilitated diffusion doesn’t require binding to a specific transport protein and allows molecules to move through without such specificity.
21
Q
Can you provide an example of a process that exemplifies passive transport?
A
One example of passive transport is simple diffusion, where molecules move from areas of high concentration to low concentration across a cell membrane without expending energy.
22
Q
What is the key energy source involved in active transport?
A
ATP (adenosine triphosphate) is the primary energy source used in active transport processes to move substances against their concentration gradients.
23
Q
How does non-specific facilitated diffusion differ from specific facilitated diffusion in terms of the molecules involved?
A
In non-specific facilitated diffusion, molecules can move through the membrane without needing to bind to specific transport proteins, which is in contrast to specific facilitated diffusion where binding to specific transport proteins is required for passage.
24
Q
What is the primary function of ion channels in the cell membrane?
A
Ion channels in the cell membrane primarily allow ions to move through, enabling electro-kinetic transport, which is the movement of charged substances.
25
How do ligand-gated channels, also known as ionotropic receptors, open?
Ligand-gated channels open when a specific molecule, called a ligand, binds to the protein channel.
26
Can you provide an example of how a ligand-gated channel works?
Certainly, for example, when a calcium ion binds to a potassium channel, it can activate the channel, allowing the passage of potassium ions. This mechanism helps regulate the movement of ions through the cell membrane.
27
What role do ligand-gated channels play in cell membrane function?
Ligand-gated channels are crucial for regulating the movement of ions through the cell membrane. They open in response to specific signaling molecules (ligands) binding to them, allowing for controlled ion flow, which is essential for various cellular processes and signaling.
28
What triggers the opening of voltage-gated channels?
Voltage-gated channels open in response to changes in voltage (membrane potential) across the cell membrane.
29
How are voltage-gated channels different from other ion channels in terms of complexity?
Voltage-gated channels are more complex because they have two gates: an activation gate and an inactivation gate.
30
Could you explain what happens when the voltage changes for a sodium voltage-gated channel?
Certainly. When the membrane potential changes from -100 mV to 40 mV, the inactivation gate of the voltage-gated sodium channel opens, allowing sodium ions to flow into the cell.
31
What occurs after the inactivation gate of the sodium voltage-gated channel opens?
After a while, the inactivation gate of the sodium channel closes due to positive charges, and the potassium channel opens, allowing potassium ions to flow out of the cell.
32
How does the speed of sodium voltage-gated channels compare to that of potassium voltage-gated channels?
Sodium voltage-gated channels open and close more quickly than potassium voltage-gated channels.
33
What is the significance of voltage-gated channels in cells like neurons and muscle cells?
Voltage-gated channels are critical for transmitting electrical signals in excitable cells like neurons and muscle cells. They play a fundamental role in the initiation and propagation of action potentials, which are essential for communication and muscle contractions.
34
How do mechanical deformation-gated channels open, and when does it happen?
Mechanical deformation-gated channels open in response to physical changes or deformations in the cell membrane, such as stretching or pressure.
35
What triggers the opening of temperature-gated ion channels?
Temperature-gated ion channels open when there are significant changes in temperature, either requiring heating or cooling.
36
In sensory organs, what is necessary for receptors to respond to stimuli?
In sensory organs, a specific amount of receptive energy is needed for receptors to respond to stimuli effectively.
37
What distinguishes ionotropic receptors from metabotropic receptors?
Ionotropic receptors open directly when a ligand binds to them, with the ligand acting like a key to open the channel. In contrast, metabotropic receptors do not open themselves but, when a ligand binds to them, trigger the activation of secondary messengers that can lead to various cellular responses.
38
What is the role of active transport, and what does it require?
Active transport is a mechanism that moves substances against their electrochemical gradient and requires ATP energy.
39
What are the three types of active transport mechanisms, and how do they differ?
The three types of active transport mechanisms are: Uniport: Moves one substance in one direction at a time (e.g., calcium ions).
Symport: Moves multiple substances in the same direction together (e.g., sodium and glucose).
Antiport: Moves multiple substances in opposite directions (e.g., sodium and potassium).
40
How are protein pumps and protein channels/transporters different in terms of their involvement in transport?
A protein pump is involved in active transport, moving substances against their gradients. In contrast, a protein channel or transporter is involved in passive transport, allowing substances to move along their gradients.
These mechanisms, along with endocytosis and exocytosis, are crucial for maintaining the cell's internal environment and its interactions with the external world.
41
What is the primary source of energy for primary active transport, and what does it enable?
The primary source of energy for primary active transport is ATP hydrolysis (breaking down ATP), and it enables the movement of substances against their electrochemical gradient.
42
Can you provide an example of primary active transport involving a pump?
Certainly, the sodium-potassium pump (Na+/K+ pump) is a prime example of primary active transport. It moves sodium ions out of the cell and potassium ions into the cell, both against their respective gradients, using ATP energy. This is an example of antiport transport, where two substances move in opposite directions.
43
How does the calcium pump function, and what type of transport mechanism is it?
The calcium pump moves calcium ions from inside the cell to the outside. This is a uniport transport mechanism.
44
Why is primary active transport important for cells?
Primary active transport is essential for maintaining the proper ion concentrations within cells, which is crucial for their normal functioning. These mechanisms help cells maintain the right ion balance and enable various cellular processes to occur.
45
How does secondary active transport differ from primary active transport in terms of energy usage?
Secondary active transport relies indirectly on ATP by using the energy generated through primary active transport. In contrast, primary active transport directly uses ATP energy. Secondary active transport occurs when primary active transport decreases the concentration of a specific ion within a cell, creating a concentration gradient that is then used to move another substance against its gradient.
46
What establishes the conditions for secondary active transport, and how does it work?
Secondary active transport relies on the electrochemical gradient established by primary active transport. For example, in the case of antiport sodium and potassium active transport, the accumulation of sodium in the extracellular space establishes a concentration gradient. This higher extracellular sodium concentration causes sodium to diffuse back into the cell. Simultaneously, substances like glucose are transported from inside the cell to the extracellular space without using ATP directly, utilizing the energy from the ion's movement.
47
Can you provide examples of secondary active transport processes?
Examples of secondary active transport processes include sodium/glucose transport, sodium/amino acid transport, and sodium/hydrogen transport. These processes use the electrochemical gradient established by primary active transport to move other substances against their gradients.
48
What is the primary distinction between primary active transport and secondary active transport?
Primary active transport establishes concentration gradients by directly using ATP energy, while secondary active transport uses these gradients to move other molecules, with or against their gradients, indirectly relying on the energy generated through primary active transport.
49
What is the role of sodium in secondary active transport, and how does it carry other molecules?
In secondary active transport, sodium is transported back into the cell, and it carries along other molecules using ATP indirectly. For instance, glucose moves inward against its gradient by utilizing the energy derived from the restoration of sodium concentration.
50
What are the three different types of endocytosis, and how do they differ?
The three types of endocytosis are:
Phagocytosis: Ingesting large particles, often part of the immune response.
Pinocytosis: Taking up small particles by surrounding droplets of fluid containing dissolved substances.
Receptor-Mediated Endocytosis: Involving specific molecules binding to receptor proteins on the cell surface, triggering the formation of coated vesicles for processing.
51
What is exocytosis, and how does it function?
Exocytosis is a process involving the release of materials from a vesicle into the extracellular space. It includes steps like vesicle formation, transport to the cell membrane, vesicle fusion with the membrane, and material release.
52
How does exocytosis play a crucial role in neurons?
In neurons, exocytosis is vital for releasing neurotransmitters. Neurotransmitter-containing vesicles fuse with the neuron's cell membrane, allowing the release of neurotransmitters into the synapse to transmit signals to other neurons or cells.
53
What are second messengers, and what is their role in cellular signaling?
Second messengers are molecules that relay signals from the cell surface to the cell's interior, amplifying and transmitting the signal. They play a crucial role in various cellular processes, including gene expression, metabolism, and cell growth.
54
How do ionotropic signaling and metabotropic signaling differ in terms of receptor mechanisms and speed of action?
Ionotropic signaling involves ligand-gated ion channels and acts quickly. In contrast, metabotropic signaling involves G-protein-linked receptors, which activate second messengers to initiate a broader range of responses over a longer period.
55
What is the significance of signal amplification through secondary messengers?
Signal amplification through secondary messengers enhances the responsiveness of cells to external signals. It ensures that even a small extracellular signal can lead to significant cellular responses, playing a vital role in orchestrating various cellular activities.
56
How does metabotropic signaling using G-protein coupling start?
Metabotropic signaling begins when a message molecule from outside the cell attaches to a receptor on the cell's surface.
57
What are the two ways by which metabotropic signaling creates a second message inside the cell?
Metabotropic signaling creates a second message inside the cell by either opening special doors for certain particles (ions) to come in, like calcium, or by waking up a special worker enzyme on the cell's outer surface, such as IP3, DAG, cAMP, or cGMP.
58
What happens when the message molecule attaches to a metabotropic receptor?
When the message molecule attaches to a metabotropic receptor, it activates the receptor, which is like a key fitting into a lock. This receptor is friends with a G-protein.
59
What role does the G-protein play in metabotropic signaling?
The G-protein is involved in metabotropic signaling and helps transmit the message inside the cell. It can be turned off by certain proteins called RGS proteins, which act like the G-protein's snooze button.
60
How do IP3 and DAG work as common second messengers?
IP3 and DAG are common second messengers in metabotropic signaling. They are produced when a messenger molecule activates a special G-protein called G-Q. IP3 is like an alarm that triggers the release of calcium ions from storage, which can have effects like muscle contraction and cell secretions. DAG wakes up protein kinase C, which acts like a supervisor, altering how other proteins work in the cell and potentially opening calcium channels in the cell's outer surface.
61
What is cAMP, and what role does it play in cellular signaling?
cAMP stands for cyclic adenosine monophosphate, and it acts as a helper molecule in cellular signaling.
62
How does cAMP signaling start, and what is the first message?
The process begins with a first message that comes from molecules like epinephrine or norepinephrine.
63
What is the role of the G-protein in cAMP signaling?
A G-protein is involved in cAMP signaling, and it serves as a special worker that wakes up another worker called adenylyl cyclase.
64
What does adenylyl cyclase do in cAMP signaling?
Adenylyl cyclase takes energy molecules (ATP) and breaks them down into cAMP, which acts as a messenger in the signaling process.
65
What role does protein kinase A play in cAMP signaling?
Protein kinase A is like a supervisor in cAMP signaling. It changes how the cell works by opening certain doors (channels), sending messages to the cell's control center (nucleus), and activating other workers.
66
How do "beta" receptors and "alpha" receptors in the heart respond to cAMP signaling?
In the heart, "beta" receptors, when they receive the first message, speed up the heart rate as a response to cAMP signaling. On the other hand, "alpha" receptors act like brakes for the adenylyl cyclase worker, slowing down heart rate and heart function.
67
How does the process of tyrosine binding affect a cell?
Tyrosine binding to a special part of a cell acts like flicking a switch and activates a special enzyme inside the cell.
68
What does the activated enzyme do within the cell?
The activated enzyme makes the cell add little tags (phosphate groups) to itself.
69
How are these tags (phosphate groups) used within the cell?
These tags can be moved to other parts inside the cell, where they can either enhance the activity of those parts or slow them down, acting like switches that control cellular processes.
70
How does the addition or removal of these tags affect the cell's behavior?
By adding or removing these tags, the cell can control its actions and behavior, similar to turning things on or off. For instance, the insulin receptor can communicate with other parts of the cell and modify their functions.
71
What are voltage-gated calcium channels, and how do they function?
Voltage-gated calcium channels are like gates that can open when there's a voltage change or when something outside the cell attaches (ligand-gated). This allows calcium ions to flow into the cell, increasing their concentration inside the cell.
72
What happens when calcium ions increase in the cell's cytosol?
When calcium ions increase in the cell's cytosol, they can bind with calmodulin, a helper protein, to facilitate smooth muscle contractions. Calcium can also bind with other proteins like tagmin, triggering processes such as exocytosis (releasing substances) and various movements within the cell.
73
How do enzymes and secondary messengers play a role in calcium signaling?
Enzymes like cyclases (adenyl cyclase, guanylyl cyclase) activate secondary messengers such as cAMP and cGMP. These messengers, in turn, activate protein kinases like protein kinase A and G. There's also the enzyme kinase (phospholipase C) that leads to the production of IP3 and DAG, which activate protein kinase C.
74
Why is calcium important in cellular processes?
Calcium acts as a crucial message carrier in cells. It responds to external signals by changing its concentration inside cells. Calcium serves as a messenger in two ways: by directly binding to other molecules or by binding to a helper protein called calmodulin. It plays a vital role in muscle contraction, the release of substances (e.g., neurotransmitters), and the docking of neurotransmitter vesicles.
75
What is membrane potential, and how is it established?
Membrane potential is the difference in electric charge across a cell's membrane. It is established due to the uneven distribution of ions, with membranes preferring potassium ions over sodium and chloride ions. Potassium ions tend to move out of the cell, making the outside positive and accumulating negative charges inside, resulting in the creation of membrane potential. This potential arises from the differing concentrations of ions inside and outside the cell.
76
How is membrane potential measured using electrophysiology?
Electrophysiology involves using a tiny electrode inserted both inside and outside the cell to measure the difference in charge across the cell's membrane. This measurement provides information about the membrane potential.
77
What is the resting membrane potential, and what does it indicate?
The resting membrane potential is the electrical charge of a cell when it is at rest, typically ranging from -70 mV to -90 mV. This negative number signifies that the inside of the cell is more negatively charged compared to the outside.
78
What are the three phases of an action potential, and what happens during each phase?
An action potential has three phases:
Depolarization: The cell becomes more positive.
Repolarization: The cell returns to a negative charge.
Hyperpolarization: The cell becomes even more negative than usual.
79
Explain the "All-or-Nothing Principle" in the context of action potentials.
The "All-or-Nothing Principle" means that an action potential either occurs fully or not at all. If the triggering stimulus is strong enough, the action potential will happen; otherwise, it won't.
80
How does the Na+/K+-ATPase contribute to the resting membrane potential?
The Na+/K+-ATPase, acting like a pump, moves sodium (Na+) and potassium (K+) ions across the cell's membrane selectively. It helps maintain the right balance of these ions by pumping out 3 Na+ ions and bringing in 2 K+ ions, utilizing 1 molecule of ATP. This contributes to the cell's resting membrane potential, ensuring it is ready for action when needed.
81
What are leak channels for Na+ and K+, and how do they contribute to balancing the resting membrane potential?
Leak channels for sodium (Na+) and potassium (K+) ions are like gates that are always slightly open. They allow these ions to move, even against their usual direction, helping to balance the cell's charge. This movement helps maintain the stability of the resting membrane potential, ensuring the cell is prepared and balanced for its next activity.
82
How do special potassium (K+) channels contribute to maintaining the resting membrane potential?
Special K+ channels are more conductive for potassium ions (K+). They create "background K+ currents" that help maintain the cell's negative resting membrane potential and prevent it from becoming too positive (depolarized). These channels act as guardians, ensuring the cell remains in its resting state and ready for action.
83
What happens at the K+ equilibrium potential during normal resting?
At the K+ equilibrium potential during normal resting, there is no net movement of ions across the cell's membrane. The chemical gradients for K+ and other ions are balanced but going in opposite directions. The membrane is more permeable to K+ than Na+, and the voltage at this equilibrium is around -98.81 mV. This equilibrium represents a balanced state where forces are in equilibrium, creating the resting potential the cell maintains when not actively engaged in other activities.
84
How is the resting membrane potential measured, and what does it represent?
The resting membrane potential is measured by considering the permeability of sodium (Na+) and potassium (K+) ions through the cell membrane. Since Na+ permeability is much lower than K+ permeability, only about 5% of the difference between the equilibrium potential for Na+ (E(Na+)) and K+ (E(K+)) contributes to the resting membrane potential. For example, if E(K+) is -80 mV and 5% of the difference between E(Na+) and E(K+) is 7 mV, then the resting membrane potential is around -73 mV. This measurement reflects the cell's state when it is not actively sending signals or responding to external influences.
85
How would you simplify depolarization?
Depolarization can be simplified as a change in the cell's charge. Normally, the cell's interior is more negative than the exterior (resting potential). Depolarization occurs when the interior becomes more positive than usual. This can happen because positive ions rush into the cell or negative ions rush out. Essentially, depolarization reduces the difference in charge between the inside and outside of the cell, moving it closer to a neutral state.
86
Can you simplify repolarization for better understanding?
Repolarization is like the cell's way of returning to its usual resting charge after depolarization. In response to depolarization, inactivation gates close (similar to doors) to prevent positive sodium (Na+) ions from entering. Simultaneously, potassium (K+) channels open, allowing more K+ ions to exit the cell. This process restores the cell's negative interior charge, bringing it back to its calm state after the excitement of depolarization.
87
How can hyperpolarization be simplified?
Hyperpolarization occurs when the cell's interior becomes even more negative than usual compared to the outside (resting potential). This can happen because negative ions rush into the cell or positive ions rush out. Think of hyperpolarization as making the cell extra "charged," creating a greater difference in charge between the inside and outside of the cell.
88
How would you simplify the concept of an action potential?
An action potential is like a sudden change in the cell's charge. It occurs when a strong stimulus, equal to or above a certain level called the threshold, is applied to the cell. In neurons, it generates a nerve impulse for signal transmission, and in muscle cells, it triggers contraction for movement. Think of an action potential as a quick electrical signal that gets the cell active and ready to perform an important task.
89
Can you explain the all-or-nothing principle in simpler terms?
The all-or-nothing principle is like a simple switch. It means that either the action potential happens completely, or it doesn't happen at all. If the stimulus is strong enough and reaches the threshold, the action potential occurs fully. If the stimulus is weak or doesn't reach the threshold, there's no action potential. It's like the cell makes a straightforward decision – either it responds with a full action potential or it remains quiet, without any halfway responses.
90
How does the change in ion movement relate to nerve or muscle action potentials?
During a nerve or muscle action potential, the cell's membrane experiences a sudden change in charge. This change occurs in distinct phases, much like different steps in a dance. Initially, sodium (Na+) channels open, allowing Na+ ions to rush into the cell. This causes the cell's interior to become more positive, known as the depolarization phase. Subsequently, potassium (K+) channels open, permitting K+ ions to flow out of the cell, leading to repolarization. The cell goes from a negative resting state to a positive action potential and then returns to a negative resting state due to the movement of sodium and potassium ions. This ion movement dance enables the cell to send signals and perform its functions.
91
What is the resting membrane potential (RMP) and what happens at the molecular level during this state?
The resting membrane potential (RMP) is the electrical charge difference across a cell's membrane when it's not actively transmitting signals. During RMP:
The activation gates of voltage-gated sodium ion channels are closed, and the inactivation gates are open, preventing sodium ions from entering the cell.
Voltage-gated potassium channels are also closed, preventing potassium ions from leaving the cell.
This state maintains a negative charge inside the cell compared to the outside.
92
How does depolarization occur and what triggers it?
Depolarization is the process of changing the cell's membrane potential from a negative resting state to a more positive one. It is triggered when a nerve or muscle is stimulated, causing voltage-gated sodium channels to open. This allows sodium ions (Na+) to flow into the cell, creating a local change in charge (depolarization). The specific ion channels that open during depolarization depend on the type of stimulus, such as mechanical stimuli, neurotransmitters, or temperature changes.
93
What happens during repolarization and why is it necessary?
Repolarization is the process of returning the cell's membrane potential from a positive state back to a negative resting state. After sodium channels have reached their equilibrium, voltage-gated potassium (K+) channels open. This allows potassium ions (K+) to exit the cell, contributing to repolarization. Repolarization is essential because it restores the cell's membrane potential to its resting level after depolarization.
94
Could you explain hyperpolarization and its role in the process?
Hyperpolarization occurs as the continued outflux of potassium ions (K+) makes the cell's membrane even more negative than its resting state. After voltage-gated potassium channels close, the active transport of sodium (Na+) and potassium (K+) ions helps return the membrane potential to its resting level. This process involves the sodium-potassium pump, which pumps out 3 sodium ions (Na+) and pumps in 2 potassium ions (K+). Hyperpolarization is a crucial step in re-establishing the proper ion concentration levels on each side of the membrane, ultimately preparing the cell for the next cycle of depolarization and repolarization.
95
What is the role of activation gates in ion channels, and how do they respond to stimulation?
Activation gates, located on the outside of ion channels, play a crucial role in ion channel function. They are sensitive to stimulation and are initially closed when the cell is at rest. When a stimulus is applied and depolarization occurs, activation gates open, allowing ions to flow through the channel.
96
What about inactivation gates in ion channels, and how do they behave in response to changes in membrane potential?
Inactivation gates, situated on the inside of ion channels, are not influenced by external stimulation. Instead, they respond to changes in membrane potential (MP). These gates close when the MP becomes higher than -40 mV and open when the MP drops below -40 mV.
97
At what membrane potential (MP) are the activation and inactivation gates positioned when the cell is at its resting membrane potential (RMP)?
At the resting membrane potential (RMP), which is typically around -70 mV to -90 mV, the activation gate is closed, but the inactivation gate is open. This means that a stimulus can open the activation gate, potentially leading to the initiation of an action potential.
98
What happens to the gates during depolarization, and how does it affect the cell's excitability?
During depolarization, after the threshold is reached, the activation gate opens, but the inactivation gate remains closed. This state makes the cell non-excitable, even in the presence of a strong stimulus, because the gates are already open, and further stimulation cannot trigger additional action potentials.
99
How do the gates behave during repolarization and hyperpolarization, and what impact does this have on the cell's excitability?
During repolarization, the inactivation gate is closed, and the activation gate progressively closes as the membrane potential becomes higher than -40 mV. This makes the cell non-excitable because the inactivation gate is shut, and the activation gate is closing. However, during hyperpolarization, the inactivation gate starts to open as the membrane potential falls below -40 mV. This gradual opening of the inactivation gate increases the cell's excitability, potentially allowing a strong suprathreshold stimulus to trigger an action potential once again.
100
What is the main result of an action potential in neurons?
An action potential in neurons leads to the generation of a nerve impulse. This impulse is essentially an electrical signal that allows neurons to communicate and transmit information to other neurons or target cells.
101
What is the primary role of action potentials in neurons?
The primary role of action potentials in neurons is to contribute to the transmission of signals along nerves. When an action potential occurs in a neuron, it initiates the process of transmitting information from one part of the nervous system to another. This transmission is crucial for various functions, including sensory perception, motor control, and cognitive processes.
102
How long does the action potential in neurons typically last?
The duration of an action potential in neurons is relatively short, lasting around 1 millisecond (ms). This brief but intense electrical event allows for rapid and precise signaling in the nervous system.
103
What is the primary outcome of an action potential in muscle cells?
In muscle cells, an action potential primarily leads to muscle contraction. When an action potential occurs in a muscle cell, it triggers a series of biochemical events that ultimately result in the contraction of muscle fibers. This contraction is essential for generating movement and facilitating various bodily functions.
104
Why are action potentials in muscle cells essential?
Action potentials in muscle cells are essential because they are the fundamental electrical events that initiate muscle contractions. Without action potentials, muscles would not be able to contract, and movement, including vital functions like breathing and locomotion, would be compromised. Therefore, these action potentials are crucial for generating the force required for muscle function.
105
How does the duration of action potentials in muscle cells compare to those in neurons?
Unlike action potentials in neurons, which are relatively short-lived (around 1 ms), action potentials in muscle cells have a longer duration. They typically last between 2 to 5 milliseconds (ms). This longer duration is necessary to coordinate and sustain muscle contractions, ensuring that muscles contract and relax effectively to perform various movements and functions in the body.
106
What is the relative refractory period in a cell?
It's a phase during recovery when some cells can respond to strong signals, but not all, as they are still resetting.
107
What happens during the refractory period?
Cells can't repeat the same action, and they prepare for another stimulus after returning to their resting state.
108
What is the absolute refractory period?
It's the first part of the refractory period where a cell can't be triggered again, regardless of signal strength.
109
What is the role of sodium-gated channels in the cell's membrane?
Sodium-gated channels are crucial because they allow sodium ions to flow into the cell, initiating depolarization and influencing the cell's excitability.
110
What happens to the activation gate of sodium-gated channels during resting membrane potential?
At rest, the activation gate is closed, but the inactivation gate is open, indicating the cell is waiting for a signal.
111
When does the absolute refractory period occur in relation to sodium-gated channels?
The absolute refractory period occurs during depolarization and repolarization when the sodium-gated channels can't be excited or stimulated.
112
What characterizes the relative refractory period in terms of sodium-gated channels?
During hyperpolarization, in the relative refractory period, the cell's excitability is extremely low, and the inactivation gate starts to open.
