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Questions and Answers
What is the primary characteristic that distinguishes action potentials from graded potentials?
What is the primary characteristic that distinguishes action potentials from graded potentials?
Which of the following statements is true regarding the refractory periods of action potentials?
Which of the following statements is true regarding the refractory periods of action potentials?
What determines the frequency of action potentials in response to stimulus intensity?
What determines the frequency of action potentials in response to stimulus intensity?
What is the resting membrane potential (RMP) of a nerve fiber?
What is the resting membrane potential (RMP) of a nerve fiber?
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Which ion channel primarily maintains the polarized resting membrane potential?
Which ion channel primarily maintains the polarized resting membrane potential?
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How does conduction differ between myelinated and unmyelinated fibers?
How does conduction differ between myelinated and unmyelinated fibers?
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Which of the following describes the characteristics of a graded potential?
Which of the following describes the characteristics of a graded potential?
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What occurs during the depolarized state of a cell membrane?
What occurs during the depolarized state of a cell membrane?
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Which transport mechanism is responsible for the active maintenance of resting membrane potential?
Which transport mechanism is responsible for the active maintenance of resting membrane potential?
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What triggers the generation of an action potential in a nerve fiber?
What triggers the generation of an action potential in a nerve fiber?
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What is the speed of conduction in unmyelinated fibers?
What is the speed of conduction in unmyelinated fibers?
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What happens during the hyperpolarized state of a membrane?
What happens during the hyperpolarized state of a membrane?
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Which of the following ions is primarily involved in generating the resting membrane potential?
Which of the following ions is primarily involved in generating the resting membrane potential?
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Which ion channels are primarily involved in generating action potentials?
Which ion channels are primarily involved in generating action potentials?
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What signifies the beginning of an action potential in excitable cells?
What signifies the beginning of an action potential in excitable cells?
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During which phase is the membrane considered polarized?
During which phase is the membrane considered polarized?
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What initiates the action potential in the muscle fiber?
What initiates the action potential in the muscle fiber?
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What process prevents excessive muscle stimulation following neurotransmitter release?
What process prevents excessive muscle stimulation following neurotransmitter release?
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Which component of the neuromuscular transmission is responsible for covering the binding sites, thereby stopping muscle contraction?
Which component of the neuromuscular transmission is responsible for covering the binding sites, thereby stopping muscle contraction?
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Which of the following statements is true regarding the properties of neuromuscular transmission?
Which of the following statements is true regarding the properties of neuromuscular transmission?
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What effect does the presence of excess magnesium ions have on neurotransmitter release?
What effect does the presence of excess magnesium ions have on neurotransmitter release?
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After calcium ions are released from the sarcoplasmic reticulum, what action do they facilitate?
After calcium ions are released from the sarcoplasmic reticulum, what action do they facilitate?
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Which drug inhibits the release of acetylcholine, affecting neuromuscular transmission?
Which drug inhibits the release of acetylcholine, affecting neuromuscular transmission?
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What term describes the potential that occurs at the motor end plate due to depolarization?
What term describes the potential that occurs at the motor end plate due to depolarization?
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Which type of muscle fiber is primarily characterized by high endurance and low fatigue?
Which type of muscle fiber is primarily characterized by high endurance and low fatigue?
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What is the primary ATP generation method for Type IIb muscle fibers?
What is the primary ATP generation method for Type IIb muscle fibers?
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Which statement correctly describes the energy efficiency of isometric contractions?
Which statement correctly describes the energy efficiency of isometric contractions?
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In Myasthenia Gravis, what is the effect of antibodies on nicotinic ACh receptors?
In Myasthenia Gravis, what is the effect of antibodies on nicotinic ACh receptors?
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Which type of muscle fiber is likely to have the least amount of mitochondria?
Which type of muscle fiber is likely to have the least amount of mitochondria?
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What is the role of neostigmine in the treatment of Myasthenia Gravis?
What is the role of neostigmine in the treatment of Myasthenia Gravis?
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Which type of muscle fiber is associated with fast contraction and high fatigue?
Which type of muscle fiber is associated with fast contraction and high fatigue?
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What contraction type is described as having fixed tension with no change in muscle length?
What contraction type is described as having fixed tension with no change in muscle length?
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What is the primary function of the myelin sheath in nerve fibers?
What is the primary function of the myelin sheath in nerve fibers?
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Which part of the neuron is responsible for receiving signals?
Which part of the neuron is responsible for receiving signals?
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What distinguishes gated ion channels from leakage channels?
What distinguishes gated ion channels from leakage channels?
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How do ion channels contribute to membrane potential?
How do ion channels contribute to membrane potential?
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What is the role of chemically-gated channels in neurons?
What is the role of chemically-gated channels in neurons?
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What describes the composition of the cell membrane?
What describes the composition of the cell membrane?
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Which ionic movement causes the membrane potential in cells?
Which ionic movement causes the membrane potential in cells?
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What is NOT a characteristic of leakage channels?
What is NOT a characteristic of leakage channels?
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What is the effect of curare on neuromuscular transmission?
What is the effect of curare on neuromuscular transmission?
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What occurs during the cross bridge cycle when myoplasmic calcium levels are elevated?
What occurs during the cross bridge cycle when myoplasmic calcium levels are elevated?
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Which statement is true regarding the hydrolysis of ATP in the cross bridge cycle?
Which statement is true regarding the hydrolysis of ATP in the cross bridge cycle?
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What is the primary mechanism behind the sliding filament theory of muscle contraction?
What is the primary mechanism behind the sliding filament theory of muscle contraction?
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What is the result of low levels of myoplasmic calcium during muscle contraction?
What is the result of low levels of myoplasmic calcium during muscle contraction?
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Which of the following drugs can produce persistent depolarization at the neuromuscular junction?
Which of the following drugs can produce persistent depolarization at the neuromuscular junction?
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What does the term 'length-tension relationship' refer to in muscle contraction?
What does the term 'length-tension relationship' refer to in muscle contraction?
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Which type of cholineesterase inhibitor is characterized as irreversible?
Which type of cholineesterase inhibitor is characterized as irreversible?
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Study Notes
Excitable Tissues
- Nerves and muscles are excitable tissues, responding to environmental changes (stimuli) by altering electrical properties and generating impulses. These impulses transmit signals.
Nerve Cells (Neurons)
- Neurons are the structural and functional units of the nervous system.
- They have four main parts:
- Cell Body
- Dendrites (receive signals)
- Axon (transmits signals)
- Axonal Terminals (transmit signals to other cells)
- Myelin sheath covers many nerve fibers, insulating fibers and increasing impulse speed.
Physiology of Cell Membrane
- Extracellular fluid (ECF) and intracellular fluid (ICF) have different compositions.
- Cell membranes are lipid bilayers with proteins, acting as barriers for water and water-soluble substances.
- Membrane potential is created by ion concentration differences across the membrane, due to ion diffusion from high concentration areas to low concentration areas.
Ion Channels
- Plasma membranes have various ion channels, made from membrane proteins:
- Leakage channels (passive): always open, permitting ion/molecule movement
- Gated channels (active): open/close in response to signals
- Chemically-gated channels (ligand): open when a neurotransmitter binds
- Voltage-gated channels: respond to changes in electrical potential across the membrane
Membrane Potentials
- Polarized state (resting membrane potential): difference in potential between the outer and inner surfaces of the membrane in a resting state.
- Depolarized state: the reduction of membrane potential negativity
- Hyperpolarized state: increase in membrane potential negativity.
Factors Determining RMP
- Selective permeability of the membrane to potassium ions plays a significant role. Potassium leak channels are more permeable to K+ than Na+.
Active Transport
- Sodium-Potassium Pump (Na+-K+ pump): actively transports 3 sodium ions out of the cell and 2 potassium ions into the cell, maintaining the negative potential inside the membrane. ATP provides the energy.
Action Potential
- Definition: a transient reversal in the membrane polarity of an excitable cell.
- Phases:
- Resting phase: membrane is polarized (e.g., -70 mV).
- Local excitatory state: depolarization from -70 mV to -55 mV.
- Depolarization phase: membrane potential changes from -55 mV to +35 mV.
- Repolarization phase: return to resting potential.
- Hyperpolarization: temporary overshooting of resting potential.
- Excitability changes:
- Absolute refractory period (ARP): nerve has no response to stimulus.
- Relative refractory period (RRP): stronger stimulus required to trigger response.
Local Potential
- A partial, non-propagated change in membrane potential, a response to sub-threshold stimuli.
- Has characteristics differing from action potentials:
- Smaller amplitude
- Graded/proportional to stimulus strength
- Non-propagated
- Summation possible
All or None Law
- A stimulus must reach a threshold to trigger an action potential—no change in amplitude, with stimuli exceeding threshold causing the same response magnitude.
Propagation
- Conduction in unmyelinated fibers: continuous depolarization, slow.
- Conduction in myelinated fibers: jumps between nodes of Ranvier, fast.
Factors Affecting Conduction Velocity
- Nerve fiber type: type A (fastest), B, and C (slowest).
- Fiber diameter: thicker fibers, faster conduction.
- Myelin sheath: thicker sheath, faster conduction.
- Temperature: higher temperatures, faster conduction.
Muscular Tissue
- Types of muscle tissue: skeletal, cardiac, and smooth muscles.
- Characteristics of each:
- Skeletal: striated, voluntary, multinucleated.
- Cardiac: striated, involuntary, uninucleated.
- Smooth: unstriated, involuntary, uninucleated
Myofibril
- Contains thick (myosin) and thin (actin) filaments. Ordered arrangement of filaments produces striations.
- Myosin heads bind to actin, causing the thin filaments to slide over the thick filaments.
Myofibril Structure
- Thick filaments (myosin): tail and head regions, with heads containing binding sites for actin and ATP.
- Thin filaments (actin), tropomyosin, troponin
Sarcomere
- The functional unit of muscle contraction, consisting of overlapping thick and thin filaments.
Transverse T-tubules (T-tubules)
- Invaginations of the sarcolemma (muscle cell membrane) carrying the action potential into the muscle fiber interior.
Sarcoplasmic Reticulum (SR)
- A network of tubules and cisternae within muscle cells, storing calcium ions, and releasing them upon stimulation to initiate contraction.
Neuromuscular Junction
- The connection between a motor neuron and a muscle fiber.
- Structures involved: axon terminal, motor end plate, synaptic cleft
- Neurotransmitter: Acetylcholine (ACh).
Steps of Neuromuscular Transmission
- Action potential travels to axon terminal.
- Calcium channels open, releasing ACh into the synaptic cleft.
- ACh binds to receptors triggering muscle action potential.
- Acetylcholinesterase breaks down ACh.
- Calcium ions are actively pumped back into the SR.
- Myosin heads detach from actin filaments.
Properties of Neuromuscular Transmission
- Unidirectional
- Time delay
- Fatigue: exhaustion of Ach vesicles during repeated stimulation.
- Ion effect: excess Mg+ ions decrease Ach release, while Ca++ increase it.
Drugs Affecting Neuromuscular Junction
- Some drugs inhibit transmission (e.g., botulinum toxin, curare).
- Others enhance transmission (e.g., nicotine, cholinesterase inhibitors).
Cross Bridge Cycle
- A cyclical series of steps involved in muscle contraction, where myosin heads bind to actin, rotate, and detach causing the sliding movement of filaments.
Factors Affecting Muscle Fiber Length
- Initial length of sarcomere affects the amount of tension a muscle can generate. Maximum tension occurs when there's optimal overlap between actin and myosin filaments.
Types of Muscle Fibers and Mechanical Changes
-
Fast and slow twitch muscle fibers differ in their ATP source (oxidative or glycolytic), contraction time, mitochondria quantity, and fatigue resistance.
-
Isotonic contractions: muscle shortens, doing work.
-
Iso-metric contractions: no muscle shortening, maintaining tension.
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Description
This quiz covers the fundamentals of excitable tissues, focusing on nervous system structures and functions. Explore the roles of neurons, the physiology of cell membranes, and the significance of ion channels in generating impulses. Test your knowledge on how these components interact to facilitate communication within the body.
