أسئلة المحاضرة الـ 15 فسيولوجي (قبل التعديل)

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Questions and Answers

What occurs during the ascending limb of the spike potential?

The membrane remains at resting potential and does not respond to stimuli.

Gates of voltage-activated Na+ channels are already closed.

The membrane is partially repolarized allowing strong stimuli to reopen Na+ gates. (correct)

Membrane is hyperpolarized and cannot initiate another action potential.

What best describes the early part of the descending limb of spike potential?

The membrane is hyperpolarized, preventing action potential generation.

Na+ gates are closed and a sufficient period of repolarization is required. (correct)

Membrane potential is at its peak allowing for multiple action potentials.

Gates of Na+ channels are fully opened and allow repeated impulses.

What limits the number of impulses that a nerve fiber can conduct?

The presence of continuous stimuli that trigger depolarization.

The speed of neurotransmitter release at the synapse.

The overall length of the nerve fiber.

The inability of the Na+ channels to open immediately after an action potential. (correct)

Which of the following is NOT a cause of failure in nerve impulse propagation?

Electrical stimulation of the adjacent neuron. (C) Signup and view all the answers

After a second stimulus is applied during the late part of the descending limb, what is the expected outcome?

A second action potential can be generated with reduced magnitude. (D) Signup and view all the answers

During the late phase of the descending limb, how is the membrane state described?

The membrane is close to the threshold but not quite back to resting state. (B) Signup and view all the answers

What happens when a strong stimulus is applied during the ascending limb of the spike potential?

It can reopen some of the Na+ channels that are closed. (D) Signup and view all the answers

How does severe cooling affect nerve excitability?

It leads to failure in initiation and propagation of nerve impulses. (C) Signup and view all the answers

Which type of nerve conducts action potentials at a faster speed?

Myelinated nerve (B) Signup and view all the answers

What is the energy consumption difference between continuous and saltatory conduction?

Saltatory conduction uses less energy (B) Signup and view all the answers

What initiates the depolarization process in a nerve?

Stimulation of the nerve (A) Signup and view all the answers

In saltatory conduction, what does the local current flow cause?

The polarized resting node to depolarize (A) Signup and view all the answers

What is the threshold level required for an action potential to occur?

-55 mV (D) Signup and view all the answers

What is a key significance of saltatory conduction?

Increased velocity of conduction (D) Signup and view all the answers

Which mechanism is involved in continuous conduction?

Uniform depolarization along the membrane (C) Signup and view all the answers

What is the resting membrane potential typically in a polarized resting node?

-70 mV (D) Signup and view all the answers

What effect does an increase in the internal diameter of a nerve fiber have on conduction velocity?

Increases conduction velocity (D) Signup and view all the answers

Which type of nerve fibers are characterized by being thick and myelinated?

Type A fibers (D) Signup and view all the answers

What defines orthodromic conduction?

Conduction in the normal direction (D) Signup and view all the answers

Which characteristic of myelination most significantly affects conduction velocity?

Increase in myelin sheath thickness (B) Signup and view all the answers

What is the conduction speed range for Type B fibers?

3-15 m/sec (D) Signup and view all the answers

Which type of nerve fibers are most sensitive to local anesthetics?

Type C fibers (B) Signup and view all the answers

What source of energy does a nerve fiber utilize to maintain resting membrane potential (RMP)?

ATP (A) Signup and view all the answers

What is the diameter range of Type C fibers?

0.5-1 μm (D) Signup and view all the answers

What is one of the main effects of increased metabolic reactions during nerve impulses?

Increase in CO2 production (B) Signup and view all the answers

What characterizes the absolute refractory period (ARP) in nerve fibers?

Excitability is completely lost (B) Signup and view all the answers

In what phase is the excitability of nerve fibers considered supernormal?

When excitability is above normal (B) Signup and view all the answers

What happens during the delayed heat phase of nerve impulse conduction?

It is caused by ATP reforming after the action potential (A) Signup and view all the answers

During which phase are stronger stimuli needed to excite a nerve?

Relative refractory period (A) Signup and view all the answers

What is the primary reason for the increase in heat production during nerve impulse activity?

Generation and propagation of nerve impulses (B) Signup and view all the answers

During which phase does the nerve cell experience partial recovery of excitability?

Relative refractory period (A) Signup and view all the answers

What generally follows the temporal rise of excitability in nerve fibers?

Absolute refractory period (D) Signup and view all the answers

What is the maximum speed of action potential propagation in myelinated nerves?

120 m/sec (C) Signup and view all the answers

How does energy consumption differ between continuous and saltatory conduction?

Saltatory conduction uses approximately 1% of the energy of continuous conduction (B) Signup and view all the answers

Which node plays a critical role in saltatory conduction after the depolarization of an adjacent node?

Node of Ranvier (A) Signup and view all the answers

What is the lower threshold level required for action potential initiation?

-55 mV (C) Signup and view all the answers

Which type of nerve conduction consumes more energy?

Continuous conduction (B) Signup and view all the answers

In saltatory conduction, what happens at the nearest node of Ranvier during stimulation?

The node undergoes depolarization (A) Signup and view all the answers

What mechanism occurs in continuous conduction at the site of stimulation?

Local current flows between depolarized and resting areas (B) Signup and view all the answers

What occurs after a second stimulus is applied during the late part of the descending limb of the action potential?

Depolarization occurs without producing an action potential (C) Signup and view all the answers

What is a characteristic of the early part of the descending limb of the action potential?

Gates of Na+ channels are just closing (D) Signup and view all the answers

How does local anesthetic, such as lidocaine, affect nerve impulse propagation?

It prevents initiation and propagation of nerve impulses (A) Signup and view all the answers

During the ascending limb of the spike potential, what happens to the Na+ channels?

Most gates are in an open state but can be reopened by new stimuli (D) Signup and view all the answers

Which of the following accurately reflects the state of the membrane during the late part of the descending limb?

The membrane is still partially repolarized (D) Signup and view all the answers

What is a significant result of a second stimulus applied during the ascending limb?

No further action potential can be initiated (D) Signup and view all the answers

What defines the mechanism of excitability in relation to nerve impulses?

Capacity to depolarize and generate action potentials (C) Signup and view all the answers

What can severely hinder the ability of a nerve to conduct impulses?

Deep pressure or local anesthetics (B) Signup and view all the answers

What effect does the thickness of the myelin sheath have on nerve conduction velocity?

Thicker myelin increases membrane resistance to current (C) Signup and view all the answers

Which type of nerve fiber exhibits the highest conduction speed?

Type A fibers (A) Signup and view all the answers

What is the diameter range for Type B nerve fibers?

1-3 μm (B) Signup and view all the answers

What defines antidromic conduction in the context of nerve signaling?

Conduction occurring in the opposite direction of impulse (B) Signup and view all the answers

Which factor primarily decreases internal resistance in nerve fibers, thereby increasing conduction velocity?

Increased internal diameter (A) Signup and view all the answers

What is a significant characteristic of Type C fibers?

Thin unmyelinated structure (D) Signup and view all the answers

What happens to the conduction velocity as the internal diameter of nerve fibers decreases?

Conduction velocity decreases (D) Signup and view all the answers

Which of the following factors does NOT affect the conduction speed of action potentials in nerve fibers?

Purity of the nerve fiber (D) Signup and view all the answers

What occurs during the absolute refractory period (ARP) of nerve fibers?

Nerve fibers exhibit complete loss of excitability. (D) Signup and view all the answers

Which phase indicates that the excitability of nerve fibers is considered to be below normal?

Subnormal phase of excitability (D) Signup and view all the answers

During which phase do nerve fibers require stronger than threshold stimuli to be excited?

Relative refractory period (D) Signup and view all the answers

Which of the following best describes the increased metabolic reactions during nerve impulse conduction?

They result in an increased production of CO2 and heat. (C) Signup and view all the answers

What is the significance of the temporal rise of excitability in nerve fibers?

It is associated with local depolarization before reaching the firing level. (B) Signup and view all the answers

What primarily drives the increase in heat production during nerve impulse conduction?

The generation and propagation of the nerve impulse. (B) Signup and view all the answers

What characterizes the delayed heat phase of nerve conduction?

It results from metabolic reactions that reform ATP used during the action potential. (A) Signup and view all the answers

What is indicated by the numerical values of the stimuli during the relative refractory period (RRP)?

Stimuli strength can vary from 0 to 100%. (B) Signup and view all the answers

What is the main difference in speed between continuous and saltatory conduction?

Saltatory conduction is significantly faster, reaching up to 120 m/sec, while continuous conduction typically ranges from 0.5 to 2 m/sec. Signup and view all the answers

In what way does saltatory conduction conserve energy compared to continuous conduction?

Saltatory conduction requires only 1% of the energy that continuous conduction consumes due to fewer depolarization events. Signup and view all the answers

What causes the initial heat production during the conduction of a nerve impulse?

The initial heat production is due to the generation and propagation of the nerve impulse. Signup and view all the answers

Describe the role of the node of Ranvier in saltatory conduction.

The node of Ranvier serves as the site where action potentials are generated and allows ions to flow in and out, facilitating rapid conduction. Signup and view all the answers

Explain the difference in excitability during the absolute refractory period compared to the relative refractory period.

During the absolute refractory period, excitability is completely lost, while in the relative refractory period, excitability is partially recovered. Signup and view all the answers

What occurs at the site of stimulation during continuous conduction?

At the site of stimulation, the membrane becomes depolarized to +35 mV, triggering a local current that depolarizes adjacent resting areas. Signup and view all the answers

How does the excitability of nerve fibers change during the supernormal phase?

In the supernormal phase, the excitability of the nerve fibers is above normal. Signup and view all the answers

What threshold must be reached for an action potential to be initiated in both types of conduction?

The threshold for action potential initiation is typically -55 mV, which must be reached during the depolarization process. Signup and view all the answers

What metabolic changes occur during nerve impulse transmission?

There is an increase in CO2 production, glucose utilization, and heat production. Signup and view all the answers

Explain how potential difference is established during saltatory conduction.

A potential difference is established between the active node (depolarized to +35 mV) and the adjacent resting node (-70 mV), generating local currents. Signup and view all the answers

What is the role of ATP reform during the delayed heat phase in nerve impulses?

ATP reform is necessary to replenish energy used during the action potential. Signup and view all the answers

What is the effect of myelination on conduction velocity?

Myelination increases conduction velocity by allowing faster transmission of action potentials through saltatory conduction. Signup and view all the answers

Describe the consequence of weak stimuli during the subnormal phase of excitability.

In the subnormal phase, weak stimuli can still excite the nerve but require stronger stimuli than normal. Signup and view all the answers

What significant advantages does saltatory conduction provide to the nervous system?

Saltatory conduction enhances conduction velocity and conserves energy, which is crucial for efficient nerve function. Signup and view all the answers

Discuss the importance of local depolarization in the temporal rise of excitability.

Local depolarization triggers the initial increase in excitability leading to action potential firing. Signup and view all the answers

What is the significance of a strong stimulus during the relative refractory period?

A strong stimulus is required to evoke an action potential during the relative refractory period. Signup and view all the answers

Describe the effect of strong stimuli on Na+ channels during the ascending limb of the spike potential.

Strong stimuli can reopen some of the previously activated Na+ channels, but not all of them during the ascending limb. Signup and view all the answers

What occurs in the nerve membrane during the early part of the descending limb of the action potential?

The nerve membrane is partially repolarized, and not all Na+ gates are open, leading to a reduced magnitude of the action potential. Signup and view all the answers

Explain the significance of the negative afterpotential in nerve impulse conduction.

The negative afterpotential occurs as the membrane hyperpolarizes, making it less likely to fire another action potential immediately. Signup and view all the answers

What characterizes the absolute refractory period in terms of nerve excitability?

During the absolute refractory period, the nerve fiber cannot be excited to generate a second action potential, regardless of the strength of a stimulus. Signup and view all the answers

Identify the relationship between local anesthetic drugs like lidocaine and nerve excitability.

Local anesthetics such as lidocaine inhibit the initiation and propagation of nerve impulses, reducing excitability. Signup and view all the answers

How does hyperpolarization of the nerve membrane affect subsequent action potential generation?

Hyperpolarization increases the threshold for depolarization, requiring a stronger stimulus to generate another action potential. Signup and view all the answers

Discuss the impact of thermal cooling on nerve impulse behavior.

Severe cooling leads to a failure in the initiation and propagation of nerve impulses, resulting in decreased nerve excitability. Signup and view all the answers

What role does sufficient repolarization play in action potential conduction?

Sufficient repolarization is necessary to reopen Na+ channels, allowing a second action potential to be generated. Signup and view all the answers

How does the diameter of nerve fibers influence conduction velocity in action potentials?

A larger diameter decreases internal resistance, which increases conduction velocity. Signup and view all the answers

What is the role of myelination in the conduction of action potentials?

Myelination increases membrane resistance, allowing charge to jump between nodes and speeding up conduction. Signup and view all the answers

Distinguish between orthodromic and antidromic conduction.

Orthodromic conduction travels in the normal direction, while antidromic conduction occurs in the opposite direction. Signup and view all the answers

How does the speed of conduction vary among Type A, B, and C fibers?

Type A fibers conduct at 10-120 m/sec, Type B at 3-15 m/sec, and Type C at 0.5-2 m/sec. Signup and view all the answers

What types of fibers are most sensitive to local anesthetics and why?

Type C fibers are most sensitive to local anesthetics due to their thin, unmyelinated structure. Signup and view all the answers

What is the significance of the resting membrane potential (RMP) in nerve fibers?

The RMP allows nerve fibers to respond to stimuli and maintain excitability for action potentials. Signup and view all the answers

Explain the influence of energy consumption in continuous versus saltatory conduction.

Saltatory conduction consumes less energy than continuous conduction due to fewer action potentials being generated. Signup and view all the answers

What types of physical stressors influence the sensitivity of nerve fibers, particularly Type A?

Type A fibers are sensitive to prolonged deep pressure and oxygen lack (hypoxia). Signup and view all the answers

How does the internal diameter of a nerve fiber influence conduction velocity?

A larger internal diameter decreases internal resistance, which increases conduction velocity. Signup and view all the answers

What role does the myelin sheath play in action potential conduction?

The myelin sheath increases membrane resistance, allowing the charge to jump between nodes, which speeds up conduction. Signup and view all the answers

Differentiate between orthodromic and antidromic conduction.

Orthodromic conduction occurs in the normal direction, while antidromic conduction occurs in the opposite direction. Signup and view all the answers

What is the speed range for Type A nerve fibers?

Type A fibers conduct action potentials at speeds ranging from 10 to 120 m/sec. Signup and view all the answers

What types of stimuli are Type C fibers most sensitive to?

Type C fibers are most sensitive to prolonged deep pressure and oxygen lack (hypoxia). Signup and view all the answers

Compare the speed of action potential conduction in continuous versus saltatory conduction.

Continuous conduction is slow, ranging from 0.5 to 2 m/sec, while saltatory conduction can reach speeds of up to 120 m/sec. Signup and view all the answers

Describe the energy source utilized by nerve fibers to maintain resting membrane potential (RMP).

Nerve fibers use ATP generated from metabolic processes as the energy source to maintain RMP. Signup and view all the answers

What role does the node of Ranvier play in saltatory conduction?

The node of Ranvier facilitates the rapid depolarization of the nerve membrane, allowing the action potential to jump from one node to the next. Signup and view all the answers

How does the thickness of the myelin sheath relate to conduction velocity?

Increased myelin sheath thickness enhances conduction velocity by increasing membrane resistance to current. Signup and view all the answers

Explain the energy consumption difference between continuous and saltatory conduction.

Continuous conduction consumes more energy, whereas saltatory conduction uses only about 1% of the energy required for continuous conduction. Signup and view all the answers

What diameter range do Type B nerve fibers typically have?

Type B nerve fibers generally have a diameter range of 1 to 3 μm. Signup and view all the answers

Describe the mechanism by which an action potential is generated at a polarized resting node.

Depolarization occurs when a stimulation causes a local current to flow, transforming the resting potential from -70 mV to the threshold level of -55 mV. Signup and view all the answers

What is the primary significance of saltatory conduction in nervous system function?

The primary significance is an increased velocity of conduction and conservation of energy during impulse transmission. Signup and view all the answers

Identify the resting membrane potential typically found at a polarized resting node.

The resting membrane potential at a polarized resting node is typically around -70 mV. Signup and view all the answers

How does the metabolic energy requirement of continuous conduction compare to that of saltatory conduction?

Continuous conduction requires a higher metabolic energy output compared to saltatory conduction, which is more energy-efficient. Signup and view all the answers

What happens to the neuronal membrane potential after it reaches +35 mV during action potential propagation?

After reaching +35 mV, the neuronal membrane repolarizes, transitioning back toward the resting membrane potential. Signup and view all the answers

What occurs in the membrane state during the early part of the descending limb after an action potential?

The membrane is partially repolarized and not all Na+ channels are opened. Signup and view all the answers

How does a second stimulus affect the membrane during the late part of the descending limb?

It can lead to depolarization and the production of a second action potential if the membrane is sufficiently repolarized. Signup and view all the answers

What physiological mechanisms underlie the excitability of nerve fibers?

Excitability relates to the opening and closing of voltage-gated Na+ channels following depolarization and repolarization phases. Signup and view all the answers

What happens during the hyperpolarization phase of a nerve fiber's action potential?

The membrane potential moves away from the threshold, making it less likely for a new action potential to occur. Signup and view all the answers

Describe the impact of mechanical stimuli, such as deep pressure, on nerve excitability.

Mechanical stimuli can alter the excitability of nerve fibers by affecting the permeability of the membrane to ions. Signup and view all the answers

What is the role of cooling in nerve impulse conduction?

Severe cooling can impede nerve excitability and conductivity, potentially leading to failure in impulse propagation. Signup and view all the answers

What characterizes the condition of a nerve fiber during the absolute refractory period?

During this period, the nerve fiber cannot be activated to generate another action potential, regardless of the stimulus strength. Signup and view all the answers

How does the repolarization process affect the conduction capabilities of nerve fibers?

Repolarization resets the membrane potential, establishing conditions for future action potentials but temporarily limits the number of impulses that can be conducted. Signup and view all the answers

What are the two phases of heat production associated with nerve impulse conduction?

The two phases are initial heat, which occurs during the generation and propagation of the nerve impulse, and delayed heat, which results from metabolic reactions to reform ATP. Signup and view all the answers

Explain the absolute refractory period (ARP) in terms of nerve excitability.

During the ARP, the excitability of the nerve fiber is completely lost, meaning no stimuli can excite the nerve regardless of strength. Signup and view all the answers

What governs the excitability of nerve fibers during the relative refractory period (RRP)?

During the RRP, the nerve fiber's excitability is partially recovered, requiring stronger stimuli than usual to evoke an action potential. Signup and view all the answers

Describe the significance of the supernormal phase of excitability.

In the supernormal phase, the excitability of the nerve fiber is above normal, allowing weaker stimuli to excite the nerve. Signup and view all the answers

What effect does increased metabolic activity have on CO2 production during nerve impulses?

Increased metabolic activity leads to heightened CO2 production as a byproduct of enhanced metabolic reactions during nerve impulse conduction. Signup and view all the answers

Identify how glucose utilization is affected during nerve impulse conduction.

There is an increase in glucose utilization when nerve impulses are conducted, reflecting the heightened energy demands of the active nerve fibers. Signup and view all the answers

What role does local response play during the temporal rise of excitability?

The local response is associated with local depolarization in the nerve fiber, which leads to a temporary increase in excitability before reaching the firing level. Signup and view all the answers

How does the delayed heat phase relate to ATP reform during nerve impulse activity?

The delayed heat phase is attributed to the metabolic reactions needed to reform ATP that was consumed during the action potential. Signup and view all the answers

Study Notes

Propagation of Action Potentials

Action potentials can be propagated continuously or saltatorily
Continuous propagation: Unmyelinated axons. Slow (0.5-2 m/sec). More energy consumption. Stimulation depolarizes the membrane at the site, then the depolarized area stimulates the adjacent area, generating local current flows. This creates a domino effect, causing the polarized area to reach the threshold level (-55 mV) and generate an action potential sequentially along the axon.
Saltatory propagation: Myelinated axons. Fast (up to 120 m/sec). Lower energy consumption (1% of continuous). Stimulation depolarizes the membrane at the nodes of Ranvier. The depolarized node creates a local current that jumps to the next node, skipping the myelin-coated segments. This rapid jumping of the action potential allows for faster conduction.

Factors Affecting Conduction Speed

Internal diameter of nerve fibers: Larger diameter fibers have lower internal resistance, leading to faster conduction.
Degree of myelination: Greater myelination increases membrane resistance, speeding up action potential propagation.

Types of Nerve Fibers

Type A fibers: Thick myelinated. Somatic motor and sensory nerves. High speed (10-120 m/sec). Sensitive to pressure, alpha, beta, delta, and gamma.
Type B fibers: Thin myelinated. Autonomic preganglionic nerves. Moderate speed (3-15 m/sec). Sensitive to O2 lack and hypoxia.
Type C fibers: Thin unmyelinated. Somatic sensory (slow pain) and autonomic postganglionic. Slowest speed (0.5-1 m/sec). Sensitive to local anesthetics

Changes in Nerve During Conduction

Electrical changes: Spike potentials and after-potentials.
Metabolic changes: Increased energy use (ATP), increased CO2 production, and glucose utilization. Increase in heat production during nerve impulse.
Thermal changes: Heat production during impulse generation and propagation, initial and delayed heat phases.

Excitability Changes

Temporal rise in excitability: Associated with local responses in nerve fibers, before reaching firing level.
Absolute refractory period (ARP): Complete loss of excitability in nerve fibers.
Relative refractory period (RRP): Partial recovery of excitability, but still below normal.
Supernormal phase: Excitability is above normal.
Subnormal phase: Excitability below normal

Nerve Block

Definition: Failure of initiation and propagation of nerve impulses.
Causes:
- Thermal: Severe cooling
- Mechanical: Deep pressure
- Chemical: Local anesthetics (e.g., lidocaine), membrane stabilizers (changes in Ca, Na, K concentrations).

Multiple Sclerosis (MS)

Definition: Autoimmune disease attacking myelin.
Cause: Inflammation and injury to myelin sheath, surrounding nerve fibers.
Incidence: Women more than men, usually diagnosed 20-50 years old
Clinical picture: Muscle weakness, fatigue, sensory issues, blurred vision, slurred speech, bladder dysfunction.
Treatment: Steroids (suppress immune system), Decrease antibodies formation.

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