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Questions and Answers
What initiates the opening of a voltage-gated sodium channel?
What initiates the opening of a voltage-gated sodium channel?
Which of the following best describes primary active transport?
Which of the following best describes primary active transport?
In secondary active transport, what is the source of the energy used for transport?
In secondary active transport, what is the source of the energy used for transport?
Which transport process primarily moves three sodium ions outward while bringing two potassium ions inward?
Which transport process primarily moves three sodium ions outward while bringing two potassium ions inward?
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What type of gating mechanism uses the binding of a ligand to open the channel?
What type of gating mechanism uses the binding of a ligand to open the channel?
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What is the main distinction between primary and secondary active transport?
What is the main distinction between primary and secondary active transport?
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Which ions are commonly transported through active transport mechanisms?
Which ions are commonly transported through active transport mechanisms?
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What occurs during the activation of acetylcholine-gated sodium channels?
What occurs during the activation of acetylcholine-gated sodium channels?
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What is the primary function of the sodium-potassium pump in cells?
What is the primary function of the sodium-potassium pump in cells?
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How does the sodium-potassium pump establish a negative voltage inside the cell?
How does the sodium-potassium pump establish a negative voltage inside the cell?
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Where are the calcium pumps located in a cell?
Where are the calcium pumps located in a cell?
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What is the primary role of hydrogen pumps in the body?
What is the primary role of hydrogen pumps in the body?
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Which transport method is utilized for the co-transport of glucose with sodium ions?
Which transport method is utilized for the co-transport of glucose with sodium ions?
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What is the value of the resting membrane potential in large nerve fibers?
What is the value of the resting membrane potential in large nerve fibers?
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In the counter-transport mechanism, which ions are primarily involved with sodium?
In the counter-transport mechanism, which ions are primarily involved with sodium?
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What physiological process is dependent on the sodium-potassium pump's ability to function properly?
What physiological process is dependent on the sodium-potassium pump's ability to function properly?
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What is the minimum change in membrane potential required to initiate an action potential?
What is the minimum change in membrane potential required to initiate an action potential?
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What is the threshold membrane potential for the initiation of an action potential?
What is the threshold membrane potential for the initiation of an action potential?
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What happens to sodium and potassium ions during the depolarization stage of an action potential?
What happens to sodium and potassium ions during the depolarization stage of an action potential?
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Which mechanism is responsible for restoring the ionic gradients of sodium and potassium after an action potential?
Which mechanism is responsible for restoring the ionic gradients of sodium and potassium after an action potential?
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What characterizes the plateau phase of an action potential in heart muscle fibers?
What characterizes the plateau phase of an action potential in heart muscle fibers?
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Which channels are involved in producing the plateau phase of the action potential in heart muscle?
Which channels are involved in producing the plateau phase of the action potential in heart muscle?
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How does the action potential propagate along a nerve fiber?
How does the action potential propagate along a nerve fiber?
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During the action potential, which event occurs immediately after depolarization?
During the action potential, which event occurs immediately after depolarization?
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What role does the sarcoplasmic reticulum play in muscle contraction?
What role does the sarcoplasmic reticulum play in muscle contraction?
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Which statement best describes the composition of a muscle fiber?
Which statement best describes the composition of a muscle fiber?
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What initiates the contraction of skeletal muscle fibers?
What initiates the contraction of skeletal muscle fibers?
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What occurs to the sarcomere during muscle contraction?
What occurs to the sarcomere during muscle contraction?
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What is the function of cross-bridges in muscle fibers?
What is the function of cross-bridges in muscle fibers?
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What mechanism contributes to the cessation of muscle contraction?
What mechanism contributes to the cessation of muscle contraction?
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Which of these features is characteristic of skeletal muscle fibers?
Which of these features is characteristic of skeletal muscle fibers?
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What is the function of acetylcholine in muscle contraction?
What is the function of acetylcholine in muscle contraction?
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What role does acetylcholinesterase play in the neuromuscular junction?
What role does acetylcholinesterase play in the neuromuscular junction?
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Which structure is responsible for transmitting the action potential to the deeper regions of the muscle fiber?
Which structure is responsible for transmitting the action potential to the deeper regions of the muscle fiber?
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What initiates the release of calcium ions within the muscle fiber during muscle contraction?
What initiates the release of calcium ions within the muscle fiber during muscle contraction?
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How long can phosphocreatine provide energy for maximal muscle contraction?
How long can phosphocreatine provide energy for maximal muscle contraction?
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What is the primary source of energy for sustained, long-term muscle contraction?
What is the primary source of energy for sustained, long-term muscle contraction?
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In response to an action potential, what happens to calcium ions in the muscle fiber?
In response to an action potential, what happens to calcium ions in the muscle fiber?
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What is the motor end plate?
What is the motor end plate?
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What happens after acetylcholine is released into the synaptic space?
What happens after acetylcholine is released into the synaptic space?
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Which characteristic distinguishes multi-unit smooth muscle from single-unit smooth muscle?
Which characteristic distinguishes multi-unit smooth muscle from single-unit smooth muscle?
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What is the main function of gap junctions in single-unit smooth muscle?
What is the main function of gap junctions in single-unit smooth muscle?
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How does the energy requirement for sustaining contraction in smooth muscle compare to that of skeletal muscle?
How does the energy requirement for sustaining contraction in smooth muscle compare to that of skeletal muscle?
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What is the primary structural difference between the contraction mechanisms of smooth and skeletal muscle?
What is the primary structural difference between the contraction mechanisms of smooth and skeletal muscle?
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What role do dense bodies play in smooth muscle contraction?
What role do dense bodies play in smooth muscle contraction?
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Which statement accurately describes the onset of contraction in smooth muscle?
Which statement accurately describes the onset of contraction in smooth muscle?
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What is the characteristic arrangement of actin filaments in smooth muscle?
What is the characteristic arrangement of actin filaments in smooth muscle?
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What type of muscle is commonly found in the walls of internal organs?
What type of muscle is commonly found in the walls of internal organs?
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Study Notes
Membrane Physiology
-
Extracellular Fluid Composition:
- Na+: 142 mEq/L
- K+: 4 mEq/L
- Ca²⁺: 2.4 mEq/L
- Mg²⁺: 1.2 mEq/L
- HCO₃⁻: 103 mEq/L
- Phosphates: 28 mEq/L
- Glucose: 90 mg/dL
- Amino acids: 30 mg/dL
- Cholesterol: 0.5 g/dL
- Phospholipids: 2-95 g/dl
- Neutral fat: variable
- PO₂: 46 mm Hg
- PCO₂: 40 mm Hg
- pH: 7.4
- Proteins: 2 g/dL
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Intracellular Fluid Composition:
- Na+: 10 mEq/L
- K+: 140 mEq/L
- Ca²⁺: 0.0001 mEq/L
- Mg²⁺: 58 mEq/L
- HCO₃⁻: 4 mEq/L
- Phosphates: 10 mEq/L
- Glucose: 0-20 mg/dL
- Amino acids: variable
- Others: variable
- PO₂: 20 mm Hg
- PCO₂: 50 mm Hg
- pH: 7.0 -Proteins: 16 g/dL
Diffusion
- Molecules and ions in bodily fluids are constantly moving.
- This movement is called "heat."
- Motion never ceases except at absolute zero.
Transport Through Cell Membranes
- Transport through cell membranes occurs via diffusion and active transport.
- In diffusion, substances move across membranes either through intermolecular spaces or with a carrier protein.
- The energy for diffusion comes from the kinetic motion of the substance itself.
Simple Diffusion
- Molecules or ions move through membrane openings or intermolecular spaces without interacting with carrier proteins.
- Rate depends on substance availability, kinetic motion velocity, and membrane opening number/size.
Facilitated Diffusion
- Carrier proteins aid molecule/ion passage by binding chemically with them.
- Diffusion rate approaches a maximum as the concentration of the diffusing substance increases.
- Glucose and amino acids are commonly transported via facilitated diffusion.
Diffusion Through Protein Pores and Channels
- Protein channels are selectively permeable to certain substances (e.g., Na+, K+).
- Channels open and close via gates.
- Voltage-gated channels open in response to electrical potential changes. Examples include sodium channels.
- Chemical (ligand)-gated channels open with chemical substance binding. Examples include acetylcholine-gated sodium channels.
Active Transport
- Movement of ions or substances across membranes against an energy gradient (uphill).
- This process utilizes carrier proteins.
- Energy required beside kinetic energy.
Types of Active Transport
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Primary Active Transport:
- Energy derived directly from ATP breakdown. Often used to establish concentration gradients against a gradient.
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Sodium-Potassium Pump:
- Pumps 3 Na+ ions out of the cell and 2 K+ ions in.
- Essential for maintaining sodium/potassium concentration differences and voltage across membranes in nerve cells.
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Ca²⁺ Pumps:
- Pumps calcium ions out of the cell or into intracellular vesicles.
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Hydrogen Pump:
- Important in gastric glands and kidney tubules (active transport of hydrogen ions).
Co-transport
- Example: transport of glucose with Na⁺ or amino acids with Na⁺.
Counter-transport
- Example: Na⁺ counter-transport of Ca²⁺ and H⁺.
Membrane Potentials and Action Potentials
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Resting Membrane Potential:
- The potential across the membrane of a neuron when not transmitting a signal. Typically -70 mV, inside being more negative.
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Action Potentials:
- Rapid changes in membrane potential that propagate along nerve fibers.
- Begin with a sudden change from negative to positive, then back towards the negative.
Stages of Action Potential
- Resting Stage: The membrane has a -70 mV potential.
- Depolarization Stage: The membrane becomes permeable to sodium ions, positively charged sodium rushes in, and the potential becomes more positive.
- Repolarization Stage: The sodium channels close and potassium channels open, allowing potassium ions to exit the cell, restoring the more negative potential.
Initiation of the Action Potential
- A stimulus that creates enough initial rise in transmembrane voltage opens voltage-gated sodium channels.
- The following positive feedback causes further rise in voltage to trigger action potential.
Threshold for Action Potential
- A sudden membrane voltage rise of 15 to 30 mV is usually necessary to initiate an action potential in a nerve fiber. This is often around -55 mV.
Propagation of the Action Potential
- An action potential elicited at one point on an excitable membrane often excites adjacent areas, causing propagation along the membrane.
- This propagation occurs in both directions.
Re-establishing Sodium and Potassium Ionic Gradients
- After an action potential, sodium that entered and potassium that exited must be transported back to create the original concentration gradients.
Plateau in Some Action Potentials
- Some membranes do not repolarize immediately after depolarization, instead entering a plateau phase.
- This prolonged depolarization duration is important for functions like heart muscle contraction.
Skeletal and Smooth Muscle Contraction
-
Skeletal Muscle Fibers:
- Comprised of numerous myofibrils that are responsible for skeletal muscle contraction.
- Actin and myosin filaments interdigitate, resulting in striated appearance.
- Contain the sarcolemma, a cell membrane; sarcoplasm, the cell's cytoplasm, and sarcoplasmic reticulum, an endoplasmic reticulum important for contraction.
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Smooth Muscle:
- Composed of shorter and smaller fibers.
- Multi-unit and single-unit smooth muscle are two types.
- Multi-unit fibers contract independently of each other; often innervated by one nerve ending
- Single-unit fibers contract together as one unit—are connected by gap junctions.
- Have actin and myosin filaments but lack striated appearance
- Intercellular proteins transmit contraction force between cells.
Sources of Energy for Muscle Contraction
- Glycolysis of Glycogen: Quick energy source, but limited.
- Phosphocreatine: Storage molecule providing energy for quick contraction.
- Oxidative Metabolism: The primary long-term energy source.
Excitation of Skeletal Muscle Fibers
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Neuromuscular Junction: Area where nerve and muscle tissue meet.
- Acetylcholine (neurotransmitter) released from nerve to excite muscle cells.
- Stimulation initiated when nerve terminal releases acetylcholine into the synaptic cleft, leading to contraction.
- The signaling is halted as acetylcholine breaks down.
Excitation-Contraction Coupling
- Transfer of action potential from the sarcolemma into deeper regions of the muscle fiber through transverse tubules.
- T-tubule action potentials cause calcium release.
Smooth Muscle Contraction Regulation
- Different factors (nerve stimulation, hormones, stretch, and chemical environment) stimulate contraction.
- Smooth muscle fibers are often controlled by many signaling pathways unlike skeletal muscle.
- Calcium enters from extracellular space triggering smooth muscle contraction.
Smooth Muscle Contraction Factors
- Lack of oxygen (causes relaxation).
- Excess CO₂ (causes relaxation).
- Increased hydrogen ions (causes relaxation).
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Description
Test your knowledge on the composition of extracellular and intracellular fluids, as well as the mechanisms of diffusion and transport through cell membranes. This quiz will cover essential concepts in membrane physiology, including the roles of various ions and molecules in bodily fluids.
