Chapter 2: Neurophysiology
Questions
- What is the basic functional unit of the nervous system?
A. Axon
B. Neuron
C. Synapse
D. Dendrite - Which part of the neuron conducts impulses away from the cell body?
A. Dendrite
B. Soma
C. Axon
D. Nucleus - What is the name of the gap between two communicating neurons?
A. Nucleus
B. Axon hillock
C. Synapse
D. Myelin sheath - Which ion primarily moves into the neuron during depolarization?
A. Potassium (K⁺)
B. Chloride (Cl⁻)
C. Calcium (Ca²⁺)
D. Sodium (Na⁺) - What structure increases the speed of nerve impulse conduction along an axon?
A. Axon hillock
B. Myelin sheath
C. Dendrites
D. Synaptic vesicle - What is the resting membrane potential of a typical nerve cell?
A. +30 mV
B. 0 mV
C. -70 mV
D. -90 mV - During repolarization, which ion exits the neuron to restore the resting membrane potential?
A. Sodium (Na⁺)
B. Potassium (K⁺)
C. Calcium (Ca²⁺)
D. Chloride (Cl⁻) - What is the term for the minimal stimulus needed to initiate an action potential?
A. Stimulus peak
B. Membrane return
C. Threshold potential
D. Resting potential - Which fibers are responsible for transmitting dull, aching pain and are blocked later than others by local anesthetics?
A. A-alpha fibers
B. A-delta fibers
C. B fibers
D. C fibers - What effect do local anesthetics have on nerve membranes?
A. Increase permeability to sodium
B. Stimulate neurotransmitter release
C. Block sodium ion channels
D. Enhance potassium outflow - What is the term for the insulating layer that surrounds some axons?
A. Synaptic cleft
B. Axon terminal
C. Myelin sheath
D. Schwann cell - What part of the neuron receives incoming signals?
A. Axon
B. Dendrite
C. Node of Ranvier
D. Myelin - What happens when a neuron reaches threshold potential?
A. The neuron becomes permanently inactive
B. An action potential is generated
C. The neuron releases enzymes
D. Sodium exits the neuron - Which structure is responsible for transmitting signals from one neuron to the next?
A. Synaptic vesicle
B. Dendrite
C. Soma
D. Axon hillock - What ion is more concentrated inside the neuron at rest?
A. Sodium (Na⁺)
B. Calcium (Ca²⁺)
C. Potassium (K⁺)
D. Chloride (Cl⁻) - What is the name of the small gaps between segments of the myelin sheath?
A. Axon terminals
B. Ion channels
C. Nodes of Ranvier
D. Neurotransmitter junctions - What type of nerve fiber has the fastest conduction velocity?
A. C fiber
B. A-delta fiber
C. A-alpha fiber
D. B fiber - What term describes the return of the membrane potential to a negative value after depolarization?
A. Hyperpolarization
B. Action potential
C. Depolarization
D. Repolarization - What is the primary function of neurotransmitters?
A. To strengthen the myelin sheath
B. To conduct impulses directly through axons
C. To carry chemical signals across the synapse
D. To increase blood flow to neurons - Which ion channel opens during depolarization of a neuron?
A. Potassium channels
B. Sodium channels
C. Chloride channels
D. Calcium channels - Why does myelination of nerve fibers increase the speed of impulse conduction?
A. It increases the number of synapses
B. It enhances neurotransmitter production
C. It allows impulses to jump between nodes of Ranvier
D. It reduces the number of ion channels - How does a local anesthetic block pain perception at the molecular level?
A. By causing the nerve to depolarize faster
B. By permanently damaging the nerve membrane
C. By preventing sodium ions from entering the neuron
D. By increasing potassium efflux - Why are small, unmyelinated fibers more susceptible to local anesthetic action?
A. They have fewer mitochondria
B. They produce more neurotransmitters
C. They conduct impulses more slowly and have less insulation
D. They are located only in motor nerves - What is the significance of the resting membrane potential in neurophysiology?
A. It allows the neuron to store neurotransmitters
B. It ensures that neurons remain inactive
C. It creates a state ready for action potential generation
D. It blocks ion channels - How does a neuron return to its resting state after an action potential?
A. By actively pumping sodium in and potassium out
B. By opening chloride channels
C. By releasing calcium from storage vesicles
D. By potassium efflux restoring negative internal charge - Why is the threshold potential critical in nerve conduction?
A. It triggers enzyme release
B. It activates the myelin sheath
C. It initiates the all-or-nothing action potential
D. It regulates blood flow - Why does saltatory conduction result in faster signal transmission compared to continuous conduction?
A. It prevents depolarization
B. It allows impulses to jump between myelinated segments
C. It eliminates the need for neurotransmitters
D. It increases the number of dendrites - What would happen if the sodium-potassium pump failed in a neuron?
A. The cell would generate more action potentials
B. The resting membrane potential would be lost
C. The synapse would enlarge
D. The neuron would increase neurotransmitter production - Why do C fibers take longer to block with local anesthetic?
A. They are located deeper in the brain
B. They are thicker and myelinated
C. They are unmyelinated and conduct slowly
D. They have more sodium channels - How does understanding neurophysiology support safe anesthetic delivery?
A. It ensures billing is accurate
B. It allows better handwriting on charts
C. It helps in targeting the correct nerve and minimizing complications
D. It removes the need for topical anesthetics - Why is the refractory period important in nerve conduction?
A. It allows sodium to accumulate inside the cell
B. It ensures nerve impulses travel in one direction
C. It helps speed up neurotransmitter release
D. It blocks potassium channels from closing - How does a local anesthetic alter the action potential of a nerve?
A. It increases the strength of the action potential
B. It blocks the depolarization phase by preventing sodium influx
C. It enhances the potassium efflux during repolarization
D. It accelerates the return to resting potential - What is the function of voltage-gated sodium channels in nerve conduction?
A. To release neurotransmitters into the synaptic cleft
B. To maintain resting membrane potential
C. To initiate depolarization by allowing Na⁺ influx
D. To stimulate potassium uptake - Why is understanding the structure of the nerve membrane important in dental hygiene anesthesia?
A. It helps the hygienist diagnose neural infections
B. It allows proper nerve penetration for effective anesthesia
C. It controls how the anesthetic affects bone tissue
D. It determines which instruments are used - How does depolarization affect the charge across the nerve membrane?
A. The interior becomes more negative
B. The membrane becomes impermeable to all ions
C. The interior becomes more positive
D. There is no change in charge - Why are action potentials considered “all-or-none” responses?
A. They vary depending on the strength of the stimulus
B. Once the threshold is reached, the full action potential occurs
C. They only happen in sensory neurons
D. The magnitude depends on neuron size - What role do Schwann cells play in nerve function?
A. They generate neurotransmitters
B. They destroy damaged neurons
C. They form the myelin sheath around peripheral nerves
D. They transport calcium into the axon - How does the neuron return to resting potential after an action potential?
A. By opening sodium channels
B. By allowing potassium to exit the cell
C. By closing all ion channels
D. By producing ATP - Why is knowledge of nerve fiber types important for effective local anesthesia?
A. It helps identify the correct tooth for extraction
B. It explains why certain patients respond better to sedation
C. It allows targeting of specific fibers for pain control
D. It determines which scaler to use - What is the relationship between nerve diameter and conduction velocity?
A. Smaller nerves conduct faster than larger nerves
B. Larger, myelinated nerves conduct impulses more quickly
C. Diameter has no effect on nerve conduction
D. Only unmyelinated nerves conduct signals - A patient has a known sensitivity to unmyelinated fibers, often experiencing delayed numbness. Which type of nerve fiber is most likely affected?
A. A-alpha fiber
B. A-beta fiber
C. C fiber
D. B fiber - You are administering local anesthesia and want to achieve rapid onset. What type of nerve fiber would facilitate the fastest response to the drug?
A. C fiber
B. A-delta fiber
C. A-alpha fiber
D. Unmyelinated sensory fiber - A patient begins to experience muscle twitching and mild tremors shortly after a high dose of anesthetic is administered. What neurophysiological process might be affected?
A. Increased potassium influx
B. Blocked sodium channels in the brain
C. CNS excitation from overdose disrupting inhibitory pathways
D. Decreased neurotransmitter synthesis - During a nerve block, you aim to anesthetize a bundle containing mixed nerve fibers. Which fiber will likely be affected first by the anesthetic?
A. A-alpha fiber
B. A-delta fiber
C. C fiber
D. B fiber - You need to anesthetize a patient for a long-duration, low-pain procedure. Which nerve fiber would you prioritize in blocking for sustained dull pain relief?
A. A-alpha fiber
B. A-delta fiber
C. C fiber
D. B fiber - After injection, the patient still perceives sharp, localized pain. Which fiber has likely not yet been effectively blocked?
A. C fiber
B. A-delta fiber
C. B fiber
D. A-alpha fiber - A patient with liver dysfunction requires local anesthesia. You must select an agent that minimizes hepatic metabolism. Which neurophysiological principle guides this decision?
A. Local anesthetics must bind directly to neurotransmitters
B. Anesthetic metabolism should involve non-hepatic pathways
C. Potassium channels should be upregulated
D. Myelination status affects drug excretion - The patient experiences a tingling sensation in their lips after a mandibular block. What does this suggest about nerve fiber involvement?
A. The motor neurons are overstimulated
B. A-delta and C fibers are being affected
C. Only the muscle fibers are anesthetized
D. Sodium-potassium pump activity has increased - You notice that the anesthesia takes effect unevenly across different areas of the oral cavity. What is a likely neurophysiological explanation?
A. Varying density of nerve fiber types and myelination in the target area
B. Poor anesthetic concentration in the solution
C. Inadequate topical anesthetic application
D. Overactive potassium channel response - A patient with multiple sclerosis, a disease involving myelin degradation, exhibits slower nerve responses. What explains this altered conduction?
A. Reduced neurotransmitter production
B. Enhanced sodium channel activity
C. Loss of saltatory conduction due to myelin damage
D. Increased ion channel density
Answers and Explanation
- Answer: B. Neuron
Explanation: The neuron is the fundamental unit of the nervous system responsible for receiving and transmitting nerve impulses. - Answer: C. Axon
Explanation: The axon carries nerve impulses away from the cell body to other neurons or effectors. - Answer: C. Synapse
Explanation: The synapse is the junction between two neurons where communication occurs through neurotransmitter release. - Answer: D. Sodium (Na⁺)
Explanation: During depolarization, sodium ions flow into the neuron, making the inside more positive and initiating the action potential. - Answer: B. Myelin sheath
Explanation: The myelin sheath acts as an insulator and increases the speed of nerve impulse conduction by allowing saltatory conduction. - Answer: C. -70 mV
Explanation: The typical resting membrane potential of a neuron is -70 millivolts, indicating a polarized state. - Answer: B. Potassium (K⁺)
Explanation: Potassium exits the cell during repolarization, helping to return the membrane potential to its resting state. - Answer: C. Threshold potential
Explanation: The threshold potential is the minimum level of depolarization required to trigger an action potential. - Answer: D. C fibers
Explanation: C fibers are unmyelinated and transmit dull, aching pain. They are typically the last to be blocked by local anesthetics. - Answer: C. Block sodium ion channels
Explanation: Local anesthetics prevent nerve impulse conduction by blocking sodium ion channels, which are essential for depolarization. - Answer: C. Myelin sheath
Explanation: The myelin sheath is a fatty insulating layer that surrounds some axons and helps speed up nerve impulse conduction. - Answer: B. Dendrite
Explanation: Dendrites are extensions from the neuron’s cell body that receive electrical messages from other neurons. - Answer: B. An action potential is generated
Explanation: When threshold potential is reached, voltage-gated sodium channels open, triggering an action potential. - Answer: A. Synaptic vesicle
Explanation: Synaptic vesicles store neurotransmitters that are released into the synaptic cleft to transmit signals between neurons. - Answer: C. Potassium (K⁺)
Explanation: At rest, potassium is found in higher concentrations inside the neuron, while sodium is more concentrated outside. - Answer: C. Nodes of Ranvier
Explanation: These are the unmyelinated gaps between segments of the myelin sheath where ion exchange occurs, allowing saltatory conduction. - Answer: C. A-alpha fiber
Explanation: A-alpha fibers are large, myelinated nerve fibers that conduct impulses rapidly, making them the fastest in the nervous system. - Answer: D. Repolarization
Explanation: Repolarization is the process where the neuron restores its resting membrane potential, usually by the efflux of potassium ions. - Answer: C. To carry chemical signals across the synapse
Explanation: Neurotransmitters are chemical messengers that transmit signals from one neuron to another across the synaptic gap. - Answer: B. Sodium channels
Explanation: During depolarization, sodium channels open, allowing Na⁺ to enter the neuron and initiate an action potential. - Answer: C. It allows impulses to jump between nodes of Ranvier
Explanation: Myelinated fibers conduct impulses via saltatory conduction, where impulses leap from one node of Ranvier to the next, speeding up transmission. - Answer: C. By preventing sodium ions from entering the neuron
Explanation: Local anesthetics block sodium channels, stopping the influx of Na⁺ necessary for depolarization and nerve signal transmission. - Answer: C. They conduct impulses more slowly and have less insulation
Explanation: Unmyelinated fibers like C fibers are more susceptible because the anesthetic can more easily disrupt their conduction due to the lack of myelin. - Answer: C. It creates a state ready for action potential generation
Explanation: The resting membrane potential maintains a voltage difference that prepares the neuron to respond rapidly when stimulated. - Answer: D. By potassium efflux restoring negative internal charge
Explanation: After depolarization, potassium exits the neuron, helping the membrane return to its resting (negative) potential. - Answer: C. It initiates the all-or-nothing action potential
Explanation: When the threshold is reached, it triggers the full action potential, leading to nerve signal propagation. - Answer: B. It allows impulses to jump between myelinated segments
Explanation: Saltatory conduction is faster because it skips over myelinated areas, depolarizing only at the nodes of Ranvier. - Answer: B. The resting membrane potential would be lost
Explanation: The sodium-potassium pump maintains ion gradients; without it, the neuron could not maintain its resting potential or respond to stimuli. - Answer: C. They are unmyelinated and conduct slowly
Explanation: C fibers lack myelin, making them slower to block with anesthetics, which tend to affect faster, smaller fibers first. - Answer: C. It helps in targeting the correct nerve and minimizing complications
Explanation: A solid understanding of neurophysiology allows for precise administration and reduces the risk of nerve damage or ineffective anesthesia. - Answer: B. It ensures nerve impulses travel in one direction
Explanation: The refractory period prevents a second action potential from occurring too soon and ensures that signals move forward along the nerve. - Answer: B. It blocks the depolarization phase by preventing sodium influx
Explanation: Local anesthetics bind to sodium channels and prevent Na⁺ from entering the neuron, thereby stopping depolarization and signal conduction. - Answer: C. To initiate depolarization by allowing Na⁺ influx
Explanation: Voltage-gated sodium channels open when threshold is reached, allowing sodium ions to enter and trigger an action potential. - Answer: B. It allows proper nerve penetration for effective anesthesia
Explanation: Understanding the nerve membrane’s structure helps in predicting how and where the anesthetic will work to block nerve transmission. - Answer: C. The interior becomes more positive
Explanation: During depolarization, sodium enters the neuron, making the inside less negative and eventually more positive. - Answer: B. Once the threshold is reached, the full action potential occurs
Explanation: Action potentials are not graded; they either happen fully once the threshold is hit or not at all. - Answer: C. They form the myelin sheath around peripheral nerves
Explanation: Schwann cells insulate nerve fibers in the peripheral nervous system by producing the myelin sheath, enhancing conduction speed. - Answer: B. By allowing potassium to exit the cell
Explanation: Repolarization is achieved by the efflux of K⁺ ions, which restores the negative internal environment of the neuron. - Answer: C. It allows targeting of specific fibers for pain control
Explanation: Knowing the characteristics of different nerve fibers helps in selecting appropriate anesthetic techniques to block pain effectively. - Answer: B. Larger, myelinated nerves conduct impulses more quickly
Explanation: Myelination and greater diameter both enhance the speed of electrical signal transmission along nerve fibers. - Answer: C. C fiber
Explanation: C fibers are small, unmyelinated, and conduct impulses slowly. They are responsible for dull, aching pain and are often affected last, explaining delayed numbness in some patients. - Answer: C. A-alpha fiber
Explanation: A-alpha fibers are large and heavily myelinated, allowing them to conduct impulses very quickly, leading to a faster onset of anesthetic effect in those fibers. - Answer: C. CNS excitation from overdose disrupting inhibitory pathways
Explanation: Local anesthetic overdose initially causes central nervous system excitation by blocking inhibitory neurons, resulting in symptoms like muscle twitching or tremors. - Answer: C. C fiber
Explanation: Smaller, unmyelinated fibers such as C fibers are generally blocked first by local anesthetics, even though they conduct more slowly. - Answer: C. C fiber
Explanation: C fibers are responsible for dull, lingering pain and are important targets when the goal is long-term, low-level pain control during procedures. - Answer: B. A-delta fiber
Explanation: A-delta fibers are thin, myelinated sensory fibers responsible for transmitting sharp pain; persistent sharp pain suggests they are not yet blocked. - Answer: B. Anesthetic metabolism should involve non-hepatic pathways
Explanation: For patients with liver impairment, anesthetics like articaine that are metabolized primarily in the plasma (via ester hydrolysis) are preferred to reduce hepatic load. - Answer: B. A-delta and C fibers are being affected
Explanation: Tingling or numbness typically results from sensory fiber blockade, particularly A-delta and C fibers, which transmit pain and temperature sensations. - Answer: A. Varying density of nerve fiber types and myelination in the target area
Explanation: Differences in nerve fiber composition, diameter, and myelination across regions can lead to uneven anesthetic effects in the oral cavity. - Answer: C. Loss of saltatory conduction due to myelin damage
Explanation: In multiple sclerosis, myelin sheath degradation disrupts saltatory conduction, slowing nerve impulse transmission and altering sensory response.