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NS LM3 practice questions

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Question 1Fundamentals of the Nervous System

Which glial cell type forms myelin sheaths around axons in the central nervous system?

  1. Astrocyte
  2. Microglial cell
  3. Schwann cell
  4. Oligodendrocyte Correct answer.

Explanation

Oligodendrocytes are the myelinating cells of the central nervous system, and a single oligodendrocyte can extend processes that wrap several different axons. Schwann cells perform the equivalent role but are found only in the peripheral nervous system. Astrocytes and microglia support and defend neural tissue without producing central myelin.

Question 2Fundamentals of the Nervous System

The resting membrane potential of a typical neuron is closest to which value?

  1. -70 mV Correct answer.
  2. 0 mV
  3. -140 mV
  4. +30 mV

Explanation

A typical neuron at rest sits near -70 mV inside relative to outside, maintained largely by potassium leak conductance and the electrogenic sodium-potassium pump. This negative interior is the baseline from which depolarizing and hyperpolarizing signals are measured. Values near +30 mV describe the peak of an action potential rather than rest.

Question 3Fundamentals of the Nervous System

Which ion's permeability dominates the neuronal membrane at rest?

  1. Potassium Correct answer.
  2. Calcium
  3. Sodium
  4. Chloride

Explanation

At rest the membrane is far more permeable to potassium than to any other ion because potassium leak channels are open. The resting potential therefore sits near the potassium equilibrium potential. Sodium permeability is low at rest, although sodium leak currents contribute to the slow drift of the membrane potential.

Question 4Fundamentals of the Nervous System

During the absolute refractory period, why can a second action potential not be generated?

  1. Voltage-gated sodium channels are inactivated Correct answer.
  2. The axon has run out of ATP
  3. Potassium channels are fully closed
  4. Synaptic vesicles are depleted

Explanation

After opening, voltage-gated sodium channels enter an inactivated state from which they cannot reopen until the membrane repolarizes and the inactivation gate resets. This makes the absolute refractory period a time when no stimulus, however strong, can trigger another spike. It also enforces the one-way propagation of the action potential.

Question 5Fundamentals of the Nervous System

A myelinated axon conducts action potentials faster than an unmyelinated axon of the same diameter mainly because conduction is:

  1. Continuous along the entire membrane
  2. Saltatory, jumping between nodes Correct answer.
  3. Slower to repolarize
  4. Dependent on calcium influx

Explanation

Myelin insulates internodal membrane, so regenerating currents occur mainly at the nodes of Ranvier. The action potential therefore appears to jump from node to node, a saltatory pattern that greatly increases conduction velocity. Continuous conduction, by contrast, requires regeneration at every patch of membrane.

Question 6Fundamentals of the Nervous System

Which structure releases neurotransmitter into the synaptic cleft?

  1. Axon hillock
  2. Dendritic spine
  3. Node of Ranvier
  4. Presynaptic terminal Correct answer.

Explanation

The presynaptic terminal contains synaptic vesicles, and calcium entry there triggers vesicle fusion and transmitter release into the cleft. The postsynaptic membrane, by contrast, carries receptors that detect the transmitter. Dendrites and the axon hillock are sites of input integration and spike initiation rather than release.

Question 7Fundamentals of the Nervous System

Which division of the nervous system controls voluntary contraction of skeletal muscle?

  1. Parasympathetic division
  2. Sympathetic division
  3. Somatic motor system Correct answer.
  4. Enteric nervous system

Explanation

The somatic motor system innervates skeletal muscle and mediates voluntary movement. The sympathetic and parasympathetic divisions belong to the autonomic nervous system, which controls smooth muscle, cardiac muscle, and glands. The enteric system governs the gastrointestinal tract independently of conscious control.

Question 8Fundamentals of the Nervous System

The blood-brain barrier is formed primarily by tight junctions between which cells?

  1. Ependymal cells
  2. Astrocyte cell bodies
  3. Capillary endothelial cells Correct answer.
  4. Neuronal cell bodies

Explanation

Tight junctions linking capillary endothelial cells create the physical barrier that restricts paracellular movement of solutes into brain tissue. Astrocyte endfeet and pericytes provide supporting signals that induce and maintain this barrier property. Ependymal cells line the ventricles rather than forming the vascular barrier.

Question 9Fundamentals of the Nervous System

A drug that opens potassium channels on a resting neuron would most likely produce which immediate change?

  1. An immediate action potential
  2. Depolarization toward threshold
  3. No change in membrane potential
  4. Hyperpolarization away from threshold Correct answer.

Explanation

Increasing potassium conductance pulls the membrane potential toward the potassium equilibrium potential, which is more negative than rest. The cell therefore hyperpolarizes and moves farther from threshold, making firing less likely. Depolarization would require opening channels permeable to sodium or calcium.

Question 10Fundamentals of the Nervous System

In a chemical synapse, what immediate effect does calcium entry into the presynaptic terminal have?

  1. It reverses the action potential
  2. It degrades transmitter in the cleft
  3. It triggers fusion of vesicles with the membrane Correct answer.
  4. It opens postsynaptic chloride channels

Explanation

Depolarization of the terminal opens voltage-gated calcium channels, and the resulting calcium influx acts on vesicle-associated proteins to trigger exocytosis. Transmitter then diffuses across the cleft to bind postsynaptic receptors. Postsynaptic channel opening and transmitter degradation are downstream or separate events.

Question 11Fundamentals of the Nervous System

A neuron has an axon that branches to contact many postsynaptic targets. This arrangement most directly supports which function?

  1. Saltatory conduction
  2. Myelination of the axon
  3. Convergence of many inputs onto one cell
  4. Divergence of a signal to multiple targets Correct answer.

Explanation

When one neuron branches to contact many postsynaptic cells, a single signal spreads to multiple targets, which is divergence. Convergence is the reverse pattern, in which many inputs funnel onto one neuron. Conduction speed and myelination are properties of the axon itself, not of its branching pattern.

Question 12Fundamentals of the Nervous System

An excitatory postsynaptic potential is produced when a transmitter opens channels that are mainly permeable to which ion?

  1. Potassium
  2. Sodium Correct answer.
  3. Chloride
  4. Hydrogen

Explanation

Opening channels permeable to sodium lets positive charge enter the cell, depolarizing it toward threshold and producing an excitatory postsynaptic potential. Chloride and potassium conductances generally push the membrane toward or below rest, favoring inhibition. The amplitude of the potential depends on how far the membrane potential lies from the relevant ion equilibrium potential.

Question 13Fundamentals of the Nervous System

A ligand-gated channel lets both sodium and potassium pass. What happens when it opens at a resting potential of -70 mV?

  1. The cell stays exactly at -70 mV
  2. The cell hyperpolarizes
  3. The cell depolarizes toward a value between the two equilibrium potentials Correct answer.
  4. The cell fires without reaching threshold

Explanation

With both ions permeable, the membrane potential moves toward the combined reversal potential, which lies between the sodium and potassium equilibrium potentials and is usually positive to rest. Because that value is above -70 mV, the net effect is depolarization. The outcome is not a fixed value like the resting potential or an automatic spike.

Question 14Fundamentals of the Nervous System

Why does an action potential propagate in only one direction along an axon?

  1. Because sodium channels are absent behind the spike
  2. Because myelin blocks reverse current
  3. Because vesicles are only at the terminal
  4. Because the refractory period prevents backward re-excitation Correct answer.

Explanation

The region just behind a traveling spike is refractory, so the depolarizing current cannot re-excite it and the spike advances forward. This refractory tail enforces unidirectional travel. Myelin, vesicle location, and channel distribution modulate conduction but do not by themselves set the direction.

Question 15Fundamentals of the Nervous System

Which statement best describes the relationship between a graded potential and an action potential?

  1. Both are all-or-none events
  2. Graded potentials require voltage-gated sodium channels
  3. Graded potentials decay with distance while action potentials regenerate Correct answer.
  4. Both propagate without decrement

Explanation

Graded potentials spread passively and lose amplitude as current leaks across the membrane with distance. Action potentials are regenerated by voltage-gated channels at each patch of membrane, so they maintain amplitude. This distinction underlies the role of graded potentials in local integration and action potentials in long-distance signaling.

Question 16Fundamentals of the Nervous System

A patient loses the myelin sheath on peripheral motor axons while the axons themselves remain intact. Which consequence is most expected?

  1. Immediate loss of muscle fibers
  2. Loss of neurotransmitter synthesis
  3. Reversal of the resting potential
  4. Slower conduction and possible conduction block Correct answer.

Explanation

Demyelination raises membrane capacitance and reduces insulation, slowing conduction and sometimes halting it at sites of severe loss. The axon remains capable of generating spikes where the membrane is intact, but the safety factor for propagation falls. Transmitter synthesis and muscle survival depend on other factors such as the cell body and innervation.

Question 17Fundamentals of the Nervous System

Which sequence correctly describes the main events of chemical synaptic transmission?

  1. Calcium entry, receptor binding, action potential, vesicle fusion
  2. Receptor binding, vesicle fusion, calcium entry, action potential
  3. Action potential, calcium entry, vesicle fusion, receptor binding Correct answer.
  4. Vesicle fusion, calcium entry, receptor binding, action potential

Explanation

The presynaptic action potential depolarizes the terminal, opening calcium channels; calcium then triggers vesicle fusion and release, and transmitter binds postsynaptic receptors. This ordering places calcium entry before exocytosis and receptor activation. Reversing the steps would break the causal chain that links electrical to chemical signaling.

Question 18Fundamentals of the Nervous System

Inhibitory synapses often open chloride channels. When this happens near rest, the usual result is that the membrane potential:

  1. Moves toward the chloride equilibrium potential and resists depolarization Correct answer.
  2. Becomes more positive than threshold
  3. Moves toward the sodium equilibrium potential
  4. Oscillates rapidly

Explanation

Opening chloride channels pulls the membrane potential toward the chloride equilibrium potential, which is usually near or below rest. The resulting increase in conductance shunts excitatory current and makes it harder for the cell to reach threshold. This shunting inhibition is distinct from simply producing a large hyperpolarization.

Question 19Fundamentals of the Nervous System

Which feature of the axon hillock makes it the usual site of action potential initiation?

  1. It has the highest density of voltage-gated sodium channels Correct answer.
  2. It is farthest from the synaptic inputs
  3. It lacks myelin entirely
  4. It contains the nucleus

Explanation

The axon initial segment carries a high density of voltage-gated sodium channels, which lowers the threshold for spike initiation. Because it lies just downstream of the integrating dendrites and soma, it converts summed graded potentials into all-or-none output. The nucleus is in the soma, and being distant from inputs would not favor initiation.

Question 20Fundamentals of the Nervous System

A neuron's membrane is suddenly made freely permeable to potassium only. The membrane potential will settle near which value?

  1. Zero millivolts
  2. The sodium equilibrium potential
  3. The potassium equilibrium potential Correct answer.
  4. The chloride equilibrium potential

Explanation

When permeability to a single ion dominates, the membrane potential approaches that ion's equilibrium potential as described by the Nernst relation. For potassium this is a negative value determined by the concentration gradient. The sodium and chloride equilibrium potentials govern the membrane only when those conductances dominate.

Question 21Fundamentals of the Nervous System

Two axons have the same diameter, but one is myelinated and one is not. Which comparison of their conduction velocities is expected?

  1. The myelinated axon conducts faster because it has more sodium channels per unit length
  2. The unmyelinated axon conducts faster because its membrane is fully excitable
  3. Both conduct at the same speed because diameter is equal
  4. The myelinated axon conducts faster because capacitance and current leak are reduced Correct answer.

Explanation

Myelin lowers membrane capacitance and increases membrane resistance, so less current is lost and less charge is needed to depolarize the internode. Current therefore spreads farther and faster to the next node, raising conduction velocity. Diameter matters as well, but at equal diameter myelination still confers a large speed advantage.

Question 22Fundamentals of the Nervous System

A toxin blocks voltage-gated potassium channels in an axon. What is the most likely effect on a single action potential?

  1. Repolarization is slowed and the spike is prolonged Correct answer.
  2. The upstroke fails to occur
  3. The resting potential becomes positive
  4. The threshold becomes unreachable

Explanation

Voltage-gated potassium channels open during the falling phase and help return the membrane toward rest. Blocking them slows repolarization and broadens the action potential, and it can also delay the afterhyperpolarization. The rising phase depends on sodium channels, so the upstroke itself is largely unaffected.

Question 23Fundamentals of the Nervous System

A synapse shows facilitation: the second postsynaptic response is larger than the first when two presynaptic spikes occur close together. Which mechanism best explains this?

  1. Residual calcium in the terminal increases release probability Correct answer.
  2. The cleft widens between stimuli
  3. Transmitter reuptake is accelerated
  4. Postsynaptic receptors are permanently saturated

Explanation

After a spike, calcium is cleared from the terminal relatively slowly, so a second spike arriving soon after adds to residual calcium and triggers more vesicle fusion. This short-term enhancement is a presynaptic phenomenon. Receptor saturation, cleft geometry, and faster reuptake would tend to reduce rather than enhance the second response.

Question 24Fundamentals of the Nervous System

Why does increasing extracellular potassium concentration depolarize a neuron?

  1. It reverses the sodium gradient
  2. It increases sodium permeability directly
  3. It closes all leak channels
  4. It raises the potassium equilibrium potential toward less negative values Correct answer.

Explanation

The potassium equilibrium potential depends on the ratio of internal to external potassium, so raising external potassium shrinks the gradient and shifts that equilibrium potential toward less negative values. The resting potential follows, becoming less negative. Sodium permeability and the sodium gradient are not directly altered by this maneuver.

Question 25Fundamentals of the Nervous System

A drug prevents synaptic vesicles from fusing with the presynaptic membrane. What is the most direct consequence at that synapse?

  1. The resting potential of the postsynaptic cell inverts
  2. Action potentials fail to reach the terminal
  3. Transmitter release is abolished while axonal conduction continues Correct answer.
  4. Postsynaptic receptors become supersensitive immediately

Explanation

Blocking vesicle fusion removes the release step, so the presynaptic action potential still invades the terminal but no transmitter is liberated. Postsynaptic responses therefore fail even though conduction along the axon is intact. Any change in receptor sensitivity would develop over time through compensatory regulation, not immediately.

Question 26Fundamentals of the Nervous System

Which glial cell type forms the myelin sheath around axons in the peripheral nervous system?

  1. Schwann cell Correct answer.
  2. Oligodendrocyte
  3. Ependymal cell
  4. Astrocyte

Explanation

In the peripheral nervous system each Schwann cell wraps a single axon segment to build myelin, and Schwann cells also assist peripheral axon regeneration. Oligodendrocytes perform the myelinating role centrally, while astrocytes and ependymal cells serve other support functions.

Question 27Fundamentals of the Nervous System

Which part of a neuron contains the nucleus and most of the organelles needed for protein synthesis?

  1. The axon terminal
  2. The cell body (soma) Correct answer.
  3. The axon hillock
  4. The node of Ranvier

Explanation

The soma houses the nucleus, rough endoplasmic reticulum, and other organelles that manufacture proteins and maintain the cell. Dendrites and axons are extensions that receive and transmit signals but lack this full biosynthetic machinery.

Question 28Fundamentals of the Nervous System

During the rising phase of an action potential, voltage-gated sodium channels open and sodium enters the axon. Which change in membrane potential does this produce?

  1. Hyperpolarization toward the potassium equilibrium potential
  2. Rapid depolarization toward the sodium equilibrium potential Correct answer.
  3. No change, because sodium and potassium fluxes cancel
  4. A graded depolarization that decays with distance

Explanation

Sodium has a positive equilibrium potential, so opening sodium channels drives the membrane rapidly toward that value, producing the steep depolarizing upstroke. The subsequent inactivation of sodium channels and delayed opening of potassium channels then repolarize the membrane.

Question 29Fundamentals of the Nervous System

A neuron is at rest with an internal potential of about -70 mV. A stimulus opens a channel permeable only to chloride, and chloride's equilibrium potential is about -70 mV. What happens to the membrane potential?

  1. It oscillates between threshold and rest
  2. It shifts little, because the driving force on chloride is near zero Correct answer.
  3. It hyperpolarizes strongly below -80 mV
  4. It depolarizes strongly toward threshold

Explanation

The direction and size of an ion's flow depend on the difference between membrane potential and that ion's equilibrium potential. Because chloride's equilibrium potential already matches the resting potential, opening these channels adds conductance with almost no net driving force, so the voltage barely changes.

Question 30Fundamentals of the Nervous System

A neuron's plasma membrane is at rest. Which combination of ion gradients and permeabilities best explains why the resting potential is close to but not equal to the potassium equilibrium potential?

  1. Complete impermeability to all ions except during action potentials
  2. Slight resting sodium permeability plus a small chloride leak added to dominant potassium permeability Correct answer.
  3. High sodium permeability with low potassium permeability
  4. Equal permeability to sodium and potassium with no other conductances

Explanation

The resting membrane is dominated by potassium leak conductance, which pulls the potential near the potassium equilibrium value. A small sodium leak and a modest chloride conductance add inward and outward currents, shifting the potential a few millivolts positive of the potassium equilibrium potential.

Question 31Neuroanatomy and Neurophysiology

Which structure produces cerebrospinal fluid within the ventricular system?

  1. Choroid plexus Correct answer.
  2. Substantia nigra
  3. Pineal gland
  4. Corpus callosum

Explanation

The choroid plexus is a vascularized epithelial tissue located in the walls of the lateral ventricles and the roof of the third and fourth ventricles. It secretes most of the cerebrospinal fluid that fills the ventricles and subarachnoid space, providing buoyancy and chemical stability for the brain.

Question 32Neuroanatomy and Neurophysiology

Which lobe of the cerebral cortex contains the primary motor cortex?

  1. Frontal lobe Correct answer.
  2. Temporal lobe
  3. Parietal lobe
  4. Occipital lobe

Explanation

The primary motor cortex lies in the precentral gyrus of the frontal lobe, just anterior to the central sulcus. Its corticospinal output drives voluntary movement of the contralateral body, with a somatotopic organization often called the motor homunculus.

Question 33Neuroanatomy and Neurophysiology

The blood-brain barrier is formed primarily by which feature of cerebral capillaries?

  1. Open perivascular spaces
  2. Tight junctions between endothelial cells Correct answer.
  3. Absence of basement membrane
  4. Fenestrated endothelial pores

Explanation

Cerebral capillary endothelial cells are joined by continuous tight junctions that restrict paracellular diffusion of water-soluble molecules. Surrounding astrocyte end-feet and pericytes reinforce this barrier, giving the brain a highly selective interface with the blood.

Question 34Neuroanatomy and Neurophysiology

Which neurotransmitter is released at the neuromuscular junction to trigger skeletal muscle contraction?

  1. Dopamine
  2. GABA
  3. Glutamate
  4. Acetylcholine Correct answer.

Explanation

Motor neurons release acetylcholine onto nicotinic receptors of the muscle end plate, producing a large depolarizing end-plate potential. This depolarization opens voltage-gated sodium channels and initiates the muscle action potential that leads to contraction.

Question 35Neuroanatomy and Neurophysiology

Which brainstem structure regulates breathing rhythm and is often called the respiratory pacemaker region?

  1. Thalamus
  2. Cerebellar vermis
  3. Medulla oblongata Correct answer.
  4. Midbrain tectum

Explanation

Rhythmic respiratory drive arises from neuronal networks in the medulla oblongata, including the pre-Botzinger complex and related groups. These neurons generate the basic breathing rhythm and relay it to spinal motor neurons controlling the diaphragm and intercostal muscles.

Question 36Neuroanatomy and Neurophysiology

Damage to the right optic tract produces which visual field deficit?

  1. Bitemporal hemianopia
  2. Left homonymous hemianopia Correct answer.
  3. Right homonymous hemianopia
  4. Complete blindness of the right eye

Explanation

Each optic tract carries axons from the temporal retina of the ipsilateral eye and the nasal retina of the contralateral eye, both representing the contralateral visual field. A right tract lesion therefore removes input from the left hemifield of both eyes, causing a left homonymous hemianopia.

Question 37Neuroanatomy and Neurophysiology

Which cranial nerve carries taste sensation from the anterior two-thirds of the tongue?

  1. Vagus nerve
  2. Glossopharyngeal nerve
  3. Facial nerve Correct answer.
  4. Trigeminal nerve

Explanation

Taste buds of the anterior two-thirds of the tongue are innervated by the chorda tympani branch of the facial nerve. The glossopharyngeal nerve supplies taste to the posterior third, while general sensation from the anterior tongue travels in the trigeminal nerve.

Question 38Neuroanatomy and Neurophysiology

Which type of glial cell myelinates axons in the central nervous system?

  1. Oligodendrocyte Correct answer.
  2. Microglia
  3. Ependymal cell
  4. Schwann cell

Explanation

Oligodendrocytes extend multiple processes that wrap around central axons to form myelin sheaths, enabling saltatory conduction. A single oligodendrocyte can myelinate segments of several different axons, unlike Schwann cells in the periphery.

Question 39Neuroanatomy and Neurophysiology

A patient cannot abduct the right eye and has horizontal diplopia that worsens when looking right. Which cranial nerve is most likely affected?

  1. Right oculomotor nerve
  2. Right abducens nerve Correct answer.
  3. Right trochlear nerve
  4. Left abducens nerve

Explanation

The abducens nerve supplies the lateral rectus, which abducts the eye. A right abducens palsy prevents abduction of the right eye and causes horizontal diplopia maximal in rightward gaze because the weak muscle fails to keep the eyes aligned.

Question 40Neuroanatomy and Neurophysiology

Which descending pathway primarily carries voluntary fine motor commands from cortex to distal limb muscles?

  1. Lateral corticospinal tract Correct answer.
  2. Ventral spinothalamic tract
  3. Spinocerebellar tract
  4. Dorsal columns

Explanation

The lateral corticospinal tract arises from cortical motor neurons, decussates in the medullary pyramids, and synapses on spinal motor neurons controlling distal muscles. It supports skilled, fractionated voluntary movements, especially of the hands and fingers.

Question 41Neuroanatomy and Neurophysiology

A lesion of the left internal capsule posterior limb most likely produces which finding?

  1. Right-sided spastic hemiparesis Correct answer.
  2. Left-sided flaccid paralysis of the arm only
  3. Bilateral cerebellar ataxia
  4. Loss of pain sensation confined to the face

Explanation

The posterior limb of the internal capsule carries the corticospinal fibers from the motor cortex before they descend to the brainstem and spinal cord. Because these fibers cross below the lesion, a left-sided lesion produces contralateral right hemiparesis, initially flaccid and later spastic.

Question 42Neuroanatomy and Neurophysiology

Which receptor type mediates the fast excitatory synaptic current at most central glutamatergic synapses?

  1. Nicotinic receptor
  2. AMPA receptor Correct answer.
  3. Muscarinic receptor
  4. GABA-B receptor

Explanation

AMPA receptors are ligand-gated cation channels that open rapidly when glutamate binds, generating the fast excitatory postsynaptic potential. NMDA receptors contribute a slower, calcium-permeable component that depends on membrane depolarization to relieve magnesium block.

Question 43Neuroanatomy and Neurophysiology

A lesion of the right cerebellar hemisphere most likely causes which motor abnormality?

  1. Spastic weakness of the right leg
  2. Intention tremor of the right limbs Correct answer.
  3. Loss of vibration sense in the feet
  4. Resting tremor of the left limbs

Explanation

The cerebellar hemispheres coordinate the ipsilateral limbs through pathways that decussate twice, so a right hemisphere lesion produces ipsilateral right-sided incoordination. Typical signs include intention tremor, dysmetria, and dysdiadochokinesia on the same side.

Question 44Neuroanatomy and Neurophysiology

Which basal ganglia pathway directly inhibits the internal segment of the globus pallidus?

  1. Corticostriatal glutamatergic pathway
  2. Direct striatopallidal pathway Correct answer.
  3. Indirect striatopallidal pathway
  4. Nigrostriatal dopaminergic pathway

Explanation

Medium spiny neurons of the direct pathway project to the internal globus pallidus and substantia nigra pars reticulata, releasing GABA and inhibiting these output nuclei. Reduced inhibition of the thalamus follows, which facilitates movement initiation.

Question 45Neuroanatomy and Neurophysiology

Which thalamic nucleus relays somatosensory information from the body to the primary somatosensory cortex?

  1. Ventral posterolateral nucleus Correct answer.
  2. Medial geniculate nucleus
  3. Anterior nucleus
  4. Lateral geniculate nucleus

Explanation

The ventral posterolateral nucleus receives the medial lemniscus and spinothalamic fibers carrying body sensation and projects to the postcentral gyrus. The ventral posteromedial nucleus performs the analogous relay for facial sensation.

Question 46Neuroanatomy and Neurophysiology

A patient has loss of pain and temperature sensation on the left side of the body with preserved touch and proprioception. Which spinal cord region is most likely damaged?

  1. Right spinothalamic tract Correct answer.
  2. Right dorsal root ganglion
  3. Left dorsal columns
  4. Left lateral corticospinal tract

Explanation

Pain and temperature fibers cross within the spinal cord and ascend in the contralateral spinothalamic tract. A right-sided cord lesion therefore interrupts left body pain and temperature sensation, while the dorsal columns carrying touch and proprioception remain intact.

Question 47Neuroanatomy and Neurophysiology

Which structure connects the third ventricle with the fourth ventricle?

  1. Interventricular foramen
  2. Central canal
  3. Cerebral aqueduct Correct answer.
  4. Foramen of Luschka

Explanation

The cerebral aqueduct is a narrow channel running through the midbrain that carries cerebrospinal fluid from the third ventricle to the fourth. Its obstruction causes noncommunicating hydrocephalus with dilation of the lateral and third ventricles.

Question 48Neuroanatomy and Neurophysiology

Stimulation of the sympathetic nervous system most likely produces which response?

  1. Bronchial constriction
  2. Increased salivation
  3. Pupillary constriction
  4. Increased heart rate Correct answer.

Explanation

Sympathetic activation releases norepinephrine onto cardiac beta-1 receptors, raising heart rate and contractility as part of the fight-or-flight response. Parasympathetic activity conversely slows the heart and promotes digestion and secretion.

Question 49Neuroanatomy and Neurophysiology

Which cortical area is most closely associated with language comprehension?

  1. Wernicke area Correct answer.
  2. Primary visual cortex
  3. Primary auditory cortex
  4. Broca area

Explanation

Wernicke area, located in the posterior superior temporal gyrus of the dominant hemisphere, supports the comprehension of spoken and written language. Damage produces fluent but meaningless speech with poor comprehension, unlike the nonfluent output of Broca aphasia.

Question 50Neuroanatomy and Neurophysiology

A patient develops sudden ptosis, a dilated pupil, and an eye that rests in a downward and outward position. Which nerve is affected?

  1. Trochlear nerve
  2. Optic nerve
  3. Abducens nerve
  4. Oculomotor nerve Correct answer.

Explanation

The oculomotor nerve supplies the levator palpebrae, most extraocular muscles, and parasympathetic fibers to the pupil. Its palsy therefore causes ptosis, a fixed dilated pupil, and an eye deviated down and out because the lateral rectus and superior oblique remain unopposed.