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Questions and Answers
What is the primary function of the Na+-glucose cotransporter?
What is the primary function of the Na+-glucose cotransporter?
Which type of ion channel is specifically activated by changes in membrane potential?
Which type of ion channel is specifically activated by changes in membrane potential?
Which of the following statements about sodium channels is false?
Which of the following statements about sodium channels is false?
What is the role of the Na+-Ca2+ exchanger?
What is the role of the Na+-Ca2+ exchanger?
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What class of drugs can block voltage-sensitive calcium channels?
What class of drugs can block voltage-sensitive calcium channels?
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Which type of molecules can freely diffuse across the plasma membrane?
Which type of molecules can freely diffuse across the plasma membrane?
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What primarily drives the movement of molecules across the plasma membrane?
What primarily drives the movement of molecules across the plasma membrane?
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What does the term 'selectively permeable' refer to in the context of the plasma membrane?
What does the term 'selectively permeable' refer to in the context of the plasma membrane?
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What is the basis for the electrical excitability of nerve and muscle cells?
What is the basis for the electrical excitability of nerve and muscle cells?
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What role does membrane potential play in cells?
What role does membrane potential play in cells?
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What is the primary function of the plasma membrane?
What is the primary function of the plasma membrane?
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Which type of transport mechanism does not require energy?
Which type of transport mechanism does not require energy?
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What role does the Na+-K+ pump play in cells?
What role does the Na+-K+ pump play in cells?
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Which of the following describes endocytosis?
Which of the following describes endocytosis?
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What are the components of the cell membrane's phospholipid bilayer?
What are the components of the cell membrane's phospholipid bilayer?
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Which ion is primarily pumped out of the cell by the Na+-K+ pump?
Which ion is primarily pumped out of the cell by the Na+-K+ pump?
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What types of molecules can easily diffuse across the plasma membrane?
What types of molecules can easily diffuse across the plasma membrane?
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What characteristic of membrane proteins allows them to perform their functions?
What characteristic of membrane proteins allows them to perform their functions?
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What is the primary reason for the negative resting membrane potential inside the cell?
What is the primary reason for the negative resting membrane potential inside the cell?
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How does the Na+/K+ ATPase pump contribute to the resting membrane potential?
How does the Na+/K+ ATPase pump contribute to the resting membrane potential?
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What is the main ion responsible for generating the resting membrane potential?
What is the main ion responsible for generating the resting membrane potential?
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What is the typical resting membrane potential value for a neuron?
What is the typical resting membrane potential value for a neuron?
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What effect does the selective permeability of the membrane to K+ ions have on the resting membrane potential?
What effect does the selective permeability of the membrane to K+ ions have on the resting membrane potential?
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What ions are transported by the sodium-potassium ATPase and in what direction?
What ions are transported by the sodium-potassium ATPase and in what direction?
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Which statement correctly describes depolarisation?
Which statement correctly describes depolarisation?
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What is hyperpolarisation?
What is hyperpolarisation?
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What is the major driving force for transport processes across membranes?
What is the major driving force for transport processes across membranes?
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Which of the following options indicates repolarisation?
Which of the following options indicates repolarisation?
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During which phase is the membrane potential the highest?
During which phase is the membrane potential the highest?
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What is the typical resting membrane potential of a cell?
What is the typical resting membrane potential of a cell?
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What is the effect of sodium ion influx on membrane potential?
What is the effect of sodium ion influx on membrane potential?
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What determines the direction of movement for lipid-soluble and small uncharged molecules across the plasma membrane?
What determines the direction of movement for lipid-soluble and small uncharged molecules across the plasma membrane?
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What phenomenon arises from the separation of opposite charges across the plasma membrane?
What phenomenon arises from the separation of opposite charges across the plasma membrane?
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Which of the following accurately describes cells with membrane potentials?
Which of the following accurately describes cells with membrane potentials?
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How do excitable cells utilize membrane potential?
How do excitable cells utilize membrane potential?
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What is the primary factor that prevents the free movement of charged ions and water-soluble substances across the plasma membrane?
What is the primary factor that prevents the free movement of charged ions and water-soluble substances across the plasma membrane?
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What primarily maintains the unequal distribution of K+ and Na+ in and out of the cell?
What primarily maintains the unequal distribution of K+ and Na+ in and out of the cell?
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What effect does the selective leakiness of the plasma membrane to K+ have on the resting membrane potential?
What effect does the selective leakiness of the plasma membrane to K+ have on the resting membrane potential?
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How many sodium ions are transported out of the cell for every two potassium ions transported in by the Na+/K+ ATPase pump?
How many sodium ions are transported out of the cell for every two potassium ions transported in by the Na+/K+ ATPase pump?
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What ion concentration is highest inside the cell at resting membrane potential?
What ion concentration is highest inside the cell at resting membrane potential?
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What results from the unequal transport of positive ions by the Na+/K+ ATPase pump?
What results from the unequal transport of positive ions by the Na+/K+ ATPase pump?
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What characterizes a membrane potential?
What characterizes a membrane potential?
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What is the typical resting membrane potential value for a neuron?
What is the typical resting membrane potential value for a neuron?
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What causes the cell membrane to be more negative inside compared to outside?
What causes the cell membrane to be more negative inside compared to outside?
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What indicates the presence of a membrane potential across a cell membrane?
What indicates the presence of a membrane potential across a cell membrane?
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What is the significance of the separation of charges across the plasma membrane?
What is the significance of the separation of charges across the plasma membrane?
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Which of the following is true regarding the conditions of a cell in the absence of a membrane potential?
Which of the following is true regarding the conditions of a cell in the absence of a membrane potential?
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How does charge separation across the plasma membrane influence the physiological activities of the cell?
How does charge separation across the plasma membrane influence the physiological activities of the cell?
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What term can be used to describe the interior of a neuron compared to its exterior at rest?
What term can be used to describe the interior of a neuron compared to its exterior at rest?
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What primarily causes the inside of a cell to become negatively charged at rest?
What primarily causes the inside of a cell to become negatively charged at rest?
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What is the significance of the Nernst equation in relation to K+ ions?
What is the significance of the Nernst equation in relation to K+ ions?
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What is the role of residual negative charge in a cell regarding K+ ions?
What is the role of residual negative charge in a cell regarding K+ ions?
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How does the concentration gradient for K+ ions differ between the extracellular fluid (ECF) and intracellular fluid (ICF)?
How does the concentration gradient for K+ ions differ between the extracellular fluid (ECF) and intracellular fluid (ICF)?
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What is the conventional resting membrane potential of a neuron?
What is the conventional resting membrane potential of a neuron?
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Which membrane components contribute to the negative inner membrane potential?
Which membrane components contribute to the negative inner membrane potential?
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What balances the electrical and chemical driving forces on K+ at equilibrium?
What balances the electrical and chemical driving forces on K+ at equilibrium?
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Which value is crucial for calculating the equilibrium potential for K+ using the Nernst equation?
Which value is crucial for calculating the equilibrium potential for K+ using the Nernst equation?
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Which ion cannot cross the plasma membrane freely according to the provided data?
Which ion cannot cross the plasma membrane freely according to the provided data?
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Which ions are pumped out of the cell by the sodium-potassium ATPase?
Which ions are pumped out of the cell by the sodium-potassium ATPase?
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What change in membrane potential occurs during depolarization?
What change in membrane potential occurs during depolarization?
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Which of the following best describes repolarization?
Which of the following best describes repolarization?
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During the action of the sodium-potassium ATPase, how many potassium ions are transported into the cell?
During the action of the sodium-potassium ATPase, how many potassium ions are transported into the cell?
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What is a primary effect of the sodium-potassium ATPase on cell function?
What is a primary effect of the sodium-potassium ATPase on cell function?
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What does hyperpolarization indicate concerning membrane potential?
What does hyperpolarization indicate concerning membrane potential?
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What role does sodium play in the transport processes across cell membranes?
What role does sodium play in the transport processes across cell membranes?
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What is the typical electrical state of a cell at resting membrane potential?
What is the typical electrical state of a cell at resting membrane potential?
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What is the relationship between membrane potential and the distribution of ions across the plasma membrane?
What is the relationship between membrane potential and the distribution of ions across the plasma membrane?
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How do excitable cells utilize membrane potential for their function?
How do excitable cells utilize membrane potential for their function?
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What is the primary factor that enables the selective permeability of the plasma membrane?
What is the primary factor that enables the selective permeability of the plasma membrane?
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Why is the resting membrane potential typically negative in cells?
Why is the resting membrane potential typically negative in cells?
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What role does charge separation across the plasma membrane play in cellular physiology?
What role does charge separation across the plasma membrane play in cellular physiology?
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What contributes to the generation of the resting membrane potential due to the unequal distribution of ions?
What contributes to the generation of the resting membrane potential due to the unequal distribution of ions?
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What effect does the Na+/K+ ATPase pump have on the membrane potential of the cell?
What effect does the Na+/K+ ATPase pump have on the membrane potential of the cell?
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During resting membrane potential, which ion's diffusion plays the most significant role in making the inside of the neuron negatively charged?
During resting membrane potential, which ion's diffusion plays the most significant role in making the inside of the neuron negatively charged?
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What is the purpose of the Na+/K+ ATPase in regards to cellular ion balance?
What is the purpose of the Na+/K+ ATPase in regards to cellular ion balance?
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What outcome results from the K+ ions diffusing out of the cell through the leaky plasma membrane?
What outcome results from the K+ ions diffusing out of the cell through the leaky plasma membrane?
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What constitutes the primary barrier of the cell membrane which helps maintain distinct internal and external environments?
What constitutes the primary barrier of the cell membrane which helps maintain distinct internal and external environments?
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Which feature of membrane proteins allows them to function both as receptors and channels?
Which feature of membrane proteins allows them to function both as receptors and channels?
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How does the Na+-K+ pump primarily influence membrane potential?
How does the Na+-K+ pump primarily influence membrane potential?
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Which mechanism represents the process of engulfing large particles by the cell membrane?
Which mechanism represents the process of engulfing large particles by the cell membrane?
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Which type of transport mechanism does NOT involve the movement of molecules against their concentration gradient?
Which type of transport mechanism does NOT involve the movement of molecules against their concentration gradient?
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What role does the fluidity of the plasma membrane play in cellular function?
What role does the fluidity of the plasma membrane play in cellular function?
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Which statement best differentiates between active and passive transport mechanisms?
Which statement best differentiates between active and passive transport mechanisms?
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What happens to the ion concentration inside a cell at resting membrane potential?
What happens to the ion concentration inside a cell at resting membrane potential?
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What happens to the membrane potential in the presence of a membrane potential?
What happens to the membrane potential in the presence of a membrane potential?
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Which statement accurately describes the state of a cell membrane in the absence of a membrane potential?
Which statement accurately describes the state of a cell membrane in the absence of a membrane potential?
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How is the typical resting membrane potential of a neuron characterized?
How is the typical resting membrane potential of a neuron characterized?
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What primarily contributes to the resting membrane potential being negative?
What primarily contributes to the resting membrane potential being negative?
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What is indicated by the presence of separated charged ions across the plasma membrane?
What is indicated by the presence of separated charged ions across the plasma membrane?
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Which of the following best describes the concept of membrane potential?
Which of the following best describes the concept of membrane potential?
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Which consequence occurs due to the selective permeability of the plasma membrane to certain ions?
Which consequence occurs due to the selective permeability of the plasma membrane to certain ions?
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What effect does the presence of positive ions inside the cell have on the membrane potential?
What effect does the presence of positive ions inside the cell have on the membrane potential?
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Which of the following is transported by the sodium-potassium ATPase?
Which of the following is transported by the sodium-potassium ATPase?
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What effect does depolarization have on the membrane potential?
What effect does depolarization have on the membrane potential?
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How does hyperpolarization affect the state of the cell?
How does hyperpolarization affect the state of the cell?
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Which statement best describes the function of cotransporters in relation to sodium ions?
Which statement best describes the function of cotransporters in relation to sodium ions?
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What role does the resting membrane potential play in cellular activity?
What role does the resting membrane potential play in cellular activity?
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What occurs during repolarization of the membrane potential?
What occurs during repolarization of the membrane potential?
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Which situation best describes a condition where the sodium-potassium ATPase is malfunctioning?
Which situation best describes a condition where the sodium-potassium ATPase is malfunctioning?
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What is the typical response of a neuron following a significant depolarization event?
What is the typical response of a neuron following a significant depolarization event?
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Study Notes
Cell Membrane
- Plasma membrane surrounds all cells.
- Functions: structural barrier, controls substance passage, maintains internal/external composition, contributes to cell fluidity, enables cell communication, and allows response to stimuli.
- Two main components: phospholipid bilayer and proteins.
Membrane Transport
- Diffusion: Movement of molecules from high to low concentration (e.g., oxygen, carbon dioxide, fat-soluble substances).
- Protein-mediated transport:
- Channel proteins: act as selective pores for specific molecules.
- Carrier proteins: bind to molecules and facilitate their movement across the membrane.
- Endocytosis: engulfing substances from the extracellular environment.
- Phagocytosis: engulfing solid particles.
- Pinocytosis: engulfing liquids.
- Exocytosis: releasing substances from within the cell to the extracellular environment.
Membrane Potential
- Membrane potential results from the separation of charges across the cell membrane.
- All cells have a membrane potential, which is the electrical difference across the membrane.
- Excitable cells (nerve and muscle) actively change their membrane potential, which is the basis for their electrical excitability.
- Membrane potential is also used to transport substances.
Resting Membrane Potential (RMP)
- RMP is the potential difference maintained across the cell membrane when the cell is at rest.
- RMP is usually negative inside the cell compared to the outside.
- Neurons typically have an RMP of approximately -70 mV.
- RMP is a result of two factors:
- Unequal distribution of ions: K+ ions are higher inside the cell, Na+ ions are higher outside the cell, and large protein anions are only found inside the cell.
- Selective permeability of the plasma membrane: the membrane is more permeable to K+ ions than Na+ ions.
Na+/K+ ATPase (Pump)
- This protein plays a crucial role in establishing and maintaining the concentration gradients of Na+ and K+ across the cell membrane.
- It actively transports 3 Na+ ions out of the cell for every 2 K+ ions transported into the cell.
- This process requires energy (ATP) and contributes to the negative charge inside the cell.
Factors contributing to RMP
- The Na+/K+ ATPase creates a small potential difference by transporting more positive charges out than in.
- The key factor contributing to the RMP is the diffusion of K+ ions out of the cell down their concentration gradient. This movement leaves the inside of the cell more negative compared to the outside.
Membrane Potential Changes
- Depolarization: The membrane potential becomes more positive.
- Hyperpolarization: The membrane potential becomes more negative.
- Repolarization: The membrane potential returns to its resting state.
Na+/K+ Pump and Transport Processes
- The Na+/K+ pump provides the driving force for various transport processes across the membrane.
- Cells utilize the Na+ concentration gradient created by the pump to drive other transport mechanisms.
- Cotransporters: move substances in the same direction as Na+ (e.g., glucose, amino acids).
- Exchangers: move substances in the opposite direction of Na+ (e.g., Ca2+, H+).
Classes of Ion Channels
- Leak channels: constantly open and allow ions to flow passively down their concentration gradients (e.g., K+ leak channels).
- Voltage-gated channels: open and close in response to changes in membrane potential (e.g., voltage-gated sodium channels).
- Ligand-gated channels: open and close in response to the binding of specific molecules (ligands) (e.g., acetylcholine receptor).
Drug Modification of Ion Channels
- Local anesthetics: block voltage-gated Na+ channels, leading to reduced nerve impulse transmission (e.g., Xylocaine/Lidocaine).
- Ca2+-channel blockers: inhibit Ca2+ channels, affecting smooth muscle contraction and blood vessel constriction (e.g., nifedipine).
Membrane Permeability
- Lipid soluble and small uncharged molecules (e.g. oxygen) freely diffuse across cell membranes
- Movement across the membrane is driven by the concentration gradient
- Charged ions and water-soluble molecules cannot freely move across the hydrophobic interior of the cell membrane
- Cell membranes are selectively permeable
- The cell membrane is permeable to certain substances and impermeable to others
Membrane Potential
- Opposite charges attract and the separation of these creates a membrane potential
- There is a difference in concentration of positive and negative ions across the cell membrane
- All cells have a membrane potential
- Excitation cells actively induce changes in the membrane potential
- The membrane potential is the basis for the electrical excitability of nerve and muscle cells
- Membrane potential can be harnessed for transporting substances
Absence of a Membrane Potential
- No charge difference across the membrane, resulting in no membrane potential
Presence of a Membrane Potential
- Separated charges are responsible for the presence of a membrane potential
Resting Membrane Potential (RMP)
- The cell membrane is more negative inside than outside
- The RMP of a neuron is approximately -70mV
- The unequal distribution of potassium, sodium, and protein anions (A-) between the inside and outside of the cell contributes to the RMP
- The permeability of the cell membrane to potassium plays a major role
- The cell membrane contains many leak channels, that allow potassium to diffuse out of the cell down its concentration gradient
Concentration of Ions
- The intracellular concentration of potassium is significantly higher than the extracellular concentration
- Conversely, the extracellular concentration of sodium is significantly higher than the intracellular concentration
- The concentration of protein anions (A-) is only found intracellularly
Sodium-Potassium ATPase (Na-K Pump)
- The Na-K pump is a membrane-spanning enzyme that establishes the concentration gradients of Na+ and K+
- The pump transports three sodium ions out of the cell and two potassium ions into the cell
- The pump uses ATP as an energy source
- The pump actively transports approximately 200 million ions per second
Contribution to RMP
- The Na-K pump generates a small potential due to unequal transport of positive ions across the membrane
- The inside of the cell becomes slightly negatively charged relative to the outside because of the 3Na+ out for 2K+ in ratio
- Diffusion of potassium out of the cell down its concentration gradient contributes significantly to the RMP
- Potassium leaks out of the cell down its concentration gradient, further increasing the negativity inside the cell
Additional Contributors to Negative Membrane Potential
- Phosphatidylinositol (PIP2) and Phosphatidylserine (PS) contribute to the negative inner membrane potential
- These negatively charged lipids provide a negative charge to the inner part of the plasma membrane
Nernst Equilibrium
- The chemical gradient acts as the driving force for diffusion of potassium out of the cell
- The chemical gradient is balanced by the electrical gradient which draws potassium back into the cell
- At equilibrium, the electrical force balances the chemical force, resulting in no net transport of potassium
Nernst Equation
- The Nernst equation is used to calculate the equilibrium potential for an ion
- The equilibrium potential is the membrane potential at which the electrical driving force for the ion movement is equal and opposite to the chemical driving force
Membrane Potential Changes
- Depolarization: The membrane potential becomes more positive
- Hyperpolarization: The membrane potential becomes more negative
- Repolarization: The membrane potential returns to its resting state
NA-K Pump and Transport Processes
- The cell utilizes the chemical gradient of sodium to transport substances into the cell
- Cotransporters are involved in this process
Cell Membrane
- Plasma Membrane: 3-10 nm thick membrane made of fluid lipid-protein bilayer, enclosing all cells
-
Functions:
- Structural barrier
- Controls substance passage, maintaining cell's internal environment
- Maintains cell fluidity
- Facilitates communication between cells
- Enables response to external stimuli
-
Membrane Proteins:
- Integral/transmembrane: Span the entire membrane
- Extrinsic/peripheral: Attached to the membrane surface
Transport Across Membranes
- Diffusion: Movement of substances across membrane driven by concentration gradient, applies to lipid-soluble and small uncharged molecules (e.g., O2, CO2)
-
Protein-mediated transport: Facilitated by channel or carrier proteins for charged (ions) or water-soluble molecules
- Channels: Provide specific pathways for substances to move through the membrane
- Carriers: Bind to the transported substance, change conformation, and release it on the other side of the membrane
-
Endocytosis: Process of bringing substances into the cell by engulfing them in membrane-bound vesicles:
- Phagocytosis: Ingestion of large particles, e.g., bacteria
- Pinocytosis: Ingestion of fluid and small molecules
- Exocytosis: Process of releasing substances from the cell by fusing vesicles with the plasma membrane
Movement Across Plasma Membrane
- Lipid-soluble and small uncharged molecules: Freely diffusible across the membrane, driven by concentration gradient
- Charged (ions) / water-soluble molecules: Movement is restricted due to the hydrophobic interior of the membrane
- Selectively permeable membrane: Allows for the control of ion movement across the membrane
Membrane Potential
- Separation of charges: Gives rise to "membrane potential" due to attraction between opposite charges (cations (+) and anions (-)) across the membrane.
- Role in all cells: Cells possess a membrane potential, representing an electrical difference across the membrane
- Excitable cells: Nerve and muscle cells actively change their membrane potential, forming the basis for their electrical excitability
- Transport: Used for active transport of substances
- Mechanism: The membrane acts as a barrier, establishing concentration gradients of key ions across the membrane. The magnitude of the potential depends on the degree of charge separation
Absence of Membrane Potential
- Electrically neutral: When there is no charge difference across the membrane, despite the membrane barrier, there is no membrane potential
Presence of Membrane Potential
- Separated charges: A charge difference across the membrane, due to the presence of separated charges (cations (+) and anions (-))
- Remainder of fluid: The remainder of the intracellular and extracellular fluids remain electrically neutral
Resting Membrane Potential (RMP)
- Negative inside: The inside of the cell membrane is more negative than the outside.
- Neuron: Typically -70mV
-
Factors contributing to RMP:
- Unequal distribution of ions: Differing concentrations of K+, Na+, and large protein anions (A-) inside and outside the cell
- Selective permeability: The cell membrane is more permeable to K+ than other ions, allowing K+ to leak out of the cell down its concentration gradient
Distribution of ions responsible for RMP
- High concentration of K+ inside the cell: 150 mM
- High concentration of Na+ outside the cell: 150 mM
- High concentration of A- inside the cell: 65 mM
Na+/K+ ATPase (Pump)
- Role: Maintains concentration gradients of K+ and Na+ across the membrane
- Mechanism: Transports 3 Na+ ions out of the cell and 2 K+ ions into the cell, using energy from ATP (ATP Hydrolysis, creating a "pump")
-
Importance:
- Establishes concentration gradients for Na+ and K+
- Contributes to the negative charge inside the cell
Resting Membrane Potential - Factors Contributing to it
- Na+/K+ ATPase pump: Transports ions unequally, resulting in slight negative charge inside the cell due to 3Na+ out for 2K+ in
- Diffusion of K+: Most significant factor; the diffusion of K+ out of the cell down its concentration gradient established by the pump makes the inside more negative
PM is "Leaky" to K+
- Ion movement: K+ is constantly moving across the membrane, but cannot fully leak out because of the Na+/K+ ATPase pump constantly working to maintain ion gradients
Membrane Potential Changes
- Depolarization: Increase in positivity of the membrane potential (becomes less negative)
- Hyperpolarization: Increase in negativity of the membrane potential (becomes more negative)
- Repolarization: Return of the membrane potential to its resting state following depolarization
Na+-K+ Pump is the Major Driving Force for Transport
- Coupled Transport: Utilizes the concentration gradient of Na+ (high outside the cell) to drive the transport of other substances into the cell
- Cotransporters: Proteins that simultaneously move two or more substances in the same direction across the membrane
- Example: The sodium-glucose cotransporter uses the energy from the movement of Na+ down its concentration gradient to bring glucose into the cell.
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Test your understanding of the cell membrane's structure and functions, including membrane transport mechanisms such as diffusion, endocytosis, and exocytosis. Dive into concepts like membrane potential and how cells interact with their environment.