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Arab Board Neurosurgery Part 1 study materials
Arab Board Neurosurgery Part 1 study resources

Arab Board Neurosurgery Part 1 practice questions

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Question 1Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which structure forms the floor of the third ventricle?

  1. The fornix
  2. The corpus callosum
  3. The hypothalamus and its associated structures Correct answer.
  4. The thalamus

Explanation

The third ventricle is bounded laterally by the thalami, superiorly by the fornix and corpus callosum, and inferiorly by the hypothalamus and related diencephalic structures. The floor is thus hypothalamic rather than commissural or cortical.

Question 2Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

The middle cerebral artery most commonly arises as a terminal branch of which vessel?

  1. The vertebral artery
  2. The internal carotid artery Correct answer.
  3. The posterior communicating artery
  4. The basilar artery

Explanation

The internal carotid artery terminates by dividing into the anterior cerebral artery and the middle cerebral artery. The basilar and vertebral arteries supply the posterior circulation, while the posterior communicating artery connects the carotid and posterior systems.

Question 3Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

A lesion of the left optic tract produces which visual field defect?

  1. A left monocular visual loss
  2. A bitemporal hemianopia
  3. A left homonymous hemianopia
  4. A right homonymous hemianopia Correct answer.

Explanation

Each optic tract carries fibers from the temporal retina of the ipsilateral eye and the nasal retina of the contralateral eye, both representing the contralateral visual field. A left tract lesion therefore causes a right homonymous hemianopia. Chiasmal lesions instead produce bitemporal defects.

Question 4Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which cranial nerve provides motor innervation to the stapedius muscle?

  1. The vagus nerve
  2. The facial nerve Correct answer.
  3. The glossopharyngeal nerve
  4. The trigeminal nerve

Explanation

The facial nerve gives off the nerve to stapedius within the facial canal before exiting the stylomastoid foramen. This branch dampens ossicular movement and its loss contributes to hyperacusis in facial nerve lesions.

Question 5Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

In the spinal cord, the corticospinal tract fibers that will innervate the lower limb are located where within the lateral corticospinal tract?

  1. Laterally Correct answer.
  2. Dorsally
  3. Medially
  4. Ventrally

Explanation

The lateral corticospinal tract is somatotopically organized with sacral and lower-limb fibers situated most laterally and cervical and upper-limb fibers most medially. This lamination means that a laterally placed cord lesion can preferentially affect lower-limb function.

Question 6Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

The primary somatosensory cortex is located in which region?

  1. The precentral gyrus of the frontal lobe
  2. The superior temporal gyrus
  3. The occipital pole
  4. The postcentral gyrus of the parietal lobe Correct answer.

Explanation

The primary somatosensory cortex occupies the postcentral gyrus of the parietal lobe and receives thalamocortical input via the ventral posterolateral nucleus. The precentral gyrus, by contrast, houses the primary motor cortex.

Question 7Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which cerebellar region is chiefly responsible for the coordination of voluntary limb movement?

  1. The fastigial nucleus
  2. The vermis
  3. The cerebrocerebellum (lateral hemispheres) Correct answer.
  4. The flocculonodular lobe

Explanation

The cerebrocerebellum, comprising the lateral hemispheres, participates in planning and coordination of skilled voluntary limb movements through its connections with the cerebral cortex. The vestibulocerebellum governs balance and the spinocerebellum governs gait and posture.

Question 8Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which basal ganglia pathway directly facilitates movement by disinhibiting the thalamus?

  1. The direct pathway Correct answer.
  2. The indirect pathway
  3. The nigrostriatal dopaminergic pathway
  4. The corticospinal pathway

Explanation

In the direct striatal pathway, GABAergic projections inhibit the internal globus pallidus, reducing its tonic inhibition of the thalamus and thereby facilitating movement. The indirect pathway increases pallidal inhibition and suppresses movement.

Question 9Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which thalamic nucleus relays somatosensory information from the face?

  1. The ventral posterolateral nucleus
  2. The ventral posteromedial nucleus Correct answer.
  3. The medial geniculate nucleus
  4. The lateral geniculate nucleus

Explanation

The ventral posteromedial nucleus receives trigeminothalamic fibers carrying facial sensation and projects to the face area of the postcentral gyrus. Body sensation instead relays through the ventral posterolateral nucleus.

Question 10Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which structure is the principal output of the hippocampus?

  1. The entorhinal cortex
  2. The fornix Correct answer.
  3. The dentate gyrus
  4. The mammillary body

Explanation

Hippocampal pyramidal cells project through the alveus and fimbria to form the fornix, which is the major efferent pathway of the hippocampus. The dentate gyrus and entorhinal cortex are primarily input-related structures, and the mammillary body is a target of the fornix.

Question 11Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

A patient has a lesion of the right abducens nerve. Which finding is expected?

  1. The right eye fails to abduct on attempted gaze to the right Correct answer.
  2. The right eye cannot adduct on attempted gaze to the left
  3. The right pupil is dilated and unreactive
  4. The right eye is deviated downward and outward at rest

Explanation

The abducens nerve supplies the ipsilateral lateral rectus, which abducts the eye. A right abducens palsy therefore impairs abduction of the right eye and typically produces a resting esotropia.

Question 12Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

The blood supply of the anterior two-thirds of the spinal cord is derived mainly from which vessel?

  1. The anterior spinal artery Correct answer.
  2. The radicular arteries alone
  3. The artery of Adamkiewicz alone
  4. The paired posterior spinal arteries

Explanation

The anterior spinal artery supplies the anterior two-thirds of the cord, including the corticospinal tracts and spinothalamic tracts. It is reinforced by radicular contributions, and the artery of Adamkiewicz is a major but segmental contributor rather than the sole supply.

Question 13Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which type of nerve fiber has the fastest conduction velocity?

  1. B fibers
  2. A-alpha fibers Correct answer.
  3. A-delta fibers
  4. C fibers

Explanation

Conduction velocity is proportional to axonal diameter and myelination. A-alpha fibers are the largest and most heavily myelinated, so they conduct fastest, whereas unmyelinated C fibers are slowest.

Question 14Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

During the rising phase of a neuronal action potential, which conductance change predominates?

  1. Increased potassium conductance
  2. Increased calcium conductance
  3. Increased chloride conductance
  4. Increased sodium conductance Correct answer.

Explanation

Depolarization of the action potential is produced by opening of voltage-gated sodium channels, causing rapid sodium influx. Repolarization is then driven by sodium inactivation and increased potassium conductance.

Question 15Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

A lesion of the left dorsal columns at the cervical level will most affect which function?

  1. Pain and temperature sensation on the left side
  2. Pain and temperature sensation on the right side
  3. Fine touch and vibration sense on the left side Correct answer.
  4. Fine touch and vibration sense on the right side

Explanation

Dorsal column fibers ascend ipsilaterally until they synapse in the medulla, so a cervical dorsal column lesion impairs fine touch, vibration, and proprioception on the same side. Pain and temperature travel in the spinothalamic tract, which crosses segmentally.

Question 16Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which reflex arc is monosynaptic?

  1. The stretch reflex Correct answer.
  2. The withdrawal reflex
  3. The flexor reflex
  4. The crossed extensor reflex

Explanation

The stretch reflex involves a single synapse between the Ia afferent and the alpha motor neuron innervating the homonymous muscle. Withdrawal, flexor, and crossed extensor reflexes are polysynaptic and involve interneurons.

Question 17Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which neurotransmitter is released by the preganglionic neurons of both sympathetic and parasympathetic divisions?

  1. Dopamine
  2. Serotonin
  3. Norepinephrine
  4. Acetylcholine Correct answer.

Explanation

All preganglionic autonomic neurons, whether sympathetic or parasympathetic, release acetylcholine acting on nicotinic receptors in the ganglion. Norepinephrine is released by most postganglionic sympathetic terminals.

Question 18Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which brainstem structure contains the cell bodies of the neurons that give rise to the nigrostriatal dopaminergic projection?

  1. The substantia nigra pars compacta Correct answer.
  2. The pedunculopontine nucleus
  3. The locus coeruleus
  4. The raphe nuclei

Explanation

Dopaminergic neurons of the substantia nigra pars compacta project to the striatum and degenerate in Parkinson disease. The locus coeruleus is noradrenergic and the raphe nuclei are serotonergic.

Question 19Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which of the following best describes the blood-brain barrier at the capillary level?

  1. An open perivascular space continuous with the subarachnoid space
  2. Fenestrated endothelial cells with loose junctions
  3. Continuous endothelial cells joined by tight junctions and supported by astrocytes Correct answer.
  4. A single layer of choroid plexus epithelial cells

Explanation

Brain capillaries forming the blood-brain barrier have non-fenestrated endothelium sealed by tight junctions, with astrocytic endfeet contributing to induction and maintenance. This restricts paracellular movement of large and polar solutes.

Question 20Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which pathologic process is the hallmark of an astrocytoma classified as grade 4 (glioblastoma)?

  1. Myelin loss with relative axonal preservation
  2. Uniform low cellularity with calcification
  3. Microvascular proliferation and necrosis with pseudopalisading Correct answer.
  4. Rosenthal fiber formation without necrosis

Explanation

Glioblastoma is defined by high-grade astrocytic features plus microvascular proliferation and/or necrosis, often with pseudopalisading of tumor cells around necrotic zones. These features distinguish grade 4 from lower-grade diffuse astrocytomas.

Question 21Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

A patient develops a CSF leak with clear rhinorrhea after a skull base fracture. Which complication is most directly attributable to the disrupted barrier?

  1. Cerebral infarction
  2. Hydrocephalus
  3. Meningitis Correct answer.
  4. Subdural hematoma

Explanation

A dural and bony defect allowing CSF to escape also creates a route for nasopharyngeal flora to enter the subarachnoid space, predisposing to meningitis. The other complications are not the direct consequence of the breached barrier.

Question 22Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which cell type is responsible for producing myelin in the peripheral nervous system?

  1. The microglial cell
  2. The Schwann cell Correct answer.
  3. The astrocyte
  4. The oligodendrocyte

Explanation

Schwann cells myelinate individual peripheral axons, whereas oligodendrocytes myelinate multiple central axons. This distinction underlies differences in regeneration and in the cellular origin of certain tumors.

Question 23Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

In the cerebral cortex, which layer is the principal source of corticospinal tract fibers?

  1. Layer V Correct answer.
  2. Layer III
  3. Layer I
  4. Layer VI

Explanation

Large pyramidal cells in layer V, including Betz cells in the motor cortex, give rise to descending corticospinal and corticobulbar projections. Layer VI projects back to the thalamus, and layers II and III project to other cortical areas.

Question 24Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which feature distinguishes an epidural hematoma from a subdural hematoma on imaging?

  1. A diffuse collection within the subarachnoid space
  2. A biconvex collection limited by cranial sutures Correct answer.
  3. A crescentic collection crossing suture lines
  4. A collection confined to the ventricular system

Explanation

Epidural hematomas typically arise from middle meningeal artery injury and appear biconvex because the dura is tightly attached at sutures, limiting spread. Subdural hematomas are crescentic and not limited by sutures.

Question 25Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which structure lies immediately anterior to the cerebral aqueduct and is vulnerable to compression from a posterior fossa mass?

  1. The fourth ventricle
  2. The periaqueductal gray Correct answer.
  3. The pineal gland
  4. The tectal plate

Explanation

The periaqueductal gray surrounds the cerebral aqueduct and, together with the aqueduct itself, is compressed by posterior fossa mass effect, which can cause obstructive hydrocephalus and impaired upgaze. The tectal plate and pineal gland lie posterior to the aqueduct.

Question 26Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which cranial nerve nucleus provides the parasympathetic innervation to the parotid gland?

  1. Superior salivatory nucleus
  2. Nucleus ambiguus
  3. Edinger-Westphal nucleus
  4. Inferior salivatory nucleus Correct answer.

Explanation

Preganglionic parasympathetic fibers to the parotid gland arise from the inferior salivatory nucleus, travel with the glossopharyngeal nerve, and synapse in the otic ganglion. The superior salivatory nucleus supplies the submandibular and sublingual glands via the facial nerve.

Question 27Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

A lesion at the level of the lateral medulla classically spares which of the following functions?

  1. Ipsilateral facial pain and temperature sensation
  2. Ipsilateral Horner syndrome
  3. Contralateral voluntary limb movement Correct answer.
  4. Contralateral pain and temperature sensation of the body

Explanation

The lateral medullary syndrome results from occlusion of the posterior inferior cerebellar artery or vertebral artery and damages the spinothalamic tract, spinal trigeminal nucleus, and descending sympathetic fibers. The corticospinal tract lies in the medial medulla and is therefore spared, so limb strength remains intact.

Question 28Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

The cell bodies of second-order neurons for conscious proprioception from the lower limb are located in which structure?

  1. Dorsal root ganglion
  2. Ventral posterolateral thalamic nucleus
  3. Nucleus cuneatus
  4. Nucleus gracilis Correct answer.

Explanation

Primary afferents from the lower limb ascend in the fasciculus gracilis and synapse on second-order neurons in the nucleus gracilis of the lower medulla. The nucleus cuneatus serves the upper limb, and thalamic neurons are third-order.

Question 29Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which structure forms the lateral wall of the third ventricle?

  1. Septum pellucidum
  2. Fornix
  3. Thalamus Correct answer.
  4. Corpus callosum

Explanation

The lateral walls of the third ventricle are formed by the medial surfaces of the two thalami and hypothalamus. The roof is formed by the fornix and tela choroidea, while the septum pellucidum separates the lateral ventricles.

Question 30Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

In a neuron at resting membrane potential, which ion has the largest driving force when its channels open?

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

Explanation

At rest the membrane is far from the sodium equilibrium potential, so opening sodium channels produces a very large inward driving force. Potassium is close to its equilibrium potential at rest and therefore has a small net driving force.

Question 31Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which process describes the increase in synaptic strength that follows high-frequency stimulation of a presynaptic pathway?

  1. Habituation
  2. Presynaptic inhibition
  3. Long-term depression
  4. Long-term potentiation Correct answer.

Explanation

Long-term potentiation is a persistent activity-dependent increase in synaptic efficacy, classically requiring postsynaptic NMDA receptor activation and calcium influx. It is widely studied as a cellular substrate of learning and memory.

Question 32Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which electroencephalographic rhythm is normally most prominent over the occipital region of an awake adult with eyes closed?

  1. Beta
  2. Theta
  3. Alpha Correct answer.
  4. Delta

Explanation

The alpha rhythm (8 to 13 Hz) is maximal over the posterior head regions when the subject is relaxed with eyes closed and attenuates on eye opening. Beta activity is faster and frontally predominant, while theta and delta are slower and abnormal in awake adults.

Question 33Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which type of receptor mediates the fast excitatory synaptic current at the neuromuscular junction?

  1. Metabotropic glutamate receptor
  2. GABA-A receptor
  3. Muscarinic acetylcholine receptor
  4. Nicotinic acetylcholine receptor Correct answer.

Explanation

Acetylcholine released at the motor end plate binds nicotinic receptors, which are ligand-gated cation channels producing a rapid depolarizing end-plate potential. Muscarinic receptors are G-protein coupled and slower.

Question 34Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which structure is the main relay for visual information en route to the primary visual cortex?

  1. Lateral geniculate body Correct answer.
  2. Medial geniculate body
  3. Superior colliculus
  4. Pulvinar

Explanation

Retinal ganglion cell axons synapse in the lateral geniculate body, whose neurons project via the optic radiations to the primary visual cortex. The medial geniculate body relays audition.

Question 35Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

A patient has a lesion of the medial longitudinal fasciculus on the right side. Which finding is expected on attempted leftward gaze?

  1. The right eye fails to adduct Correct answer.
  2. Both eyes fail to converge
  3. The left eye fails to abduct
  4. The right eye fails to abduct

Explanation

The medial longitudinal fasciculus carries internuclear fibers from the contralateral abducens nucleus to the ipsilateral medial rectus subnucleus. A right-sided lesion therefore impairs adduction of the right eye on leftward gaze while the left eye abducts with nystagmus.

Question 36Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which finding best localizes a lesion to the left optic tract?

  1. Left homonymous hemianopia
  2. Right homonymous hemianopia Correct answer.
  3. Bitemporal hemianopia
  4. Binasal hemianopia

Explanation

The optic tract carries fibers from the ipsilateral temporal retina and contralateral nasal retina, representing the contralateral visual field. A left optic tract lesion therefore produces a right homonymous hemianopia.

Question 37Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which vascular territory infarction most commonly produces a contralateral homonymous hemianopia with macular sparing?

  1. Posterior cerebral artery Correct answer.
  2. Middle cerebral artery superior division
  3. Anterior choroidal artery
  4. Anterior cerebral artery

Explanation

The occipital pole, which represents the macula, receives dual supply from the posterior and middle cerebral arteries, so posterior cerebral artery infarction often spares central vision. The resulting defect is a contralateral homonymous hemianopia with macular sparing.

Question 38Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which statement best describes the growth pattern of a diffuse astrocytoma compared with a pilocytic astrocytoma?

  1. Diffuse astrocytomas arise exclusively within the cerebellum
  2. Diffuse astrocytomas are always confined to the ventricular lining
  3. Diffuse astrocytomas infiltrate surrounding brain parenchyma Correct answer.
  4. Diffuse astrocytomas are well circumscribed and non-infiltrative

Explanation

Diffuse astrocytomas are infiltrative tumors that spread through the surrounding brain without a clear border, which limits complete surgical resection. Pilocytic astrocytomas, by contrast, are typically well circumscribed.

Question 39Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which molecular alteration is most characteristic of oligodendroglioma?

  1. MYCN amplification
  2. SMARCB1 loss
  3. H3 K27M mutation
  4. IDH mutation with 1p/19q codeletion Correct answer.

Explanation

Oligodendrogliomas are defined by the combination of an IDH mutation and whole-arm codeletion of chromosomes 1p and 19q, which also predicts chemosensitivity. This molecular signature distinguishes them from other diffuse gliomas.

Question 40Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which cell of the central nervous system is derived from the monocyte lineage rather than the neuroectoderm?

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

Explanation

Microglia arise from yolk-sac primitive myeloid progenitors and populate the CNS as resident macrophages. Astrocytes, oligodendrocytes, and ependymal cells are all neuroectodermal derivatives.

Question 41Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which feature best distinguishes a schwannoma from a neurofibroma on histology?

  1. Abundant myxoid stroma with axons embedded in the tumor
  2. Presence of Antoni A and B areas Correct answer.
  3. Nuclear palisading with Verocay bodies
  4. Whorled meningothelial cells

Explanation

Schwannomas show alternating compact Antoni A areas and loose Antoni B areas, reflecting their origin from Schwann cells alone. Neurofibromas contain a mixture of Schwann cells, fibroblasts, and embedded axons in a myxoid matrix.

Question 42Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which type of cerebral edema results from increased permeability of the capillary endothelium after a focal ischemic insult?

  1. Osmotic edema
  2. Interstitial edema
  3. Cytotoxic edema
  4. Vasogenic edema Correct answer.

Explanation

Vasogenic edema follows breakdown of the blood-brain barrier, allowing protein-rich fluid to accumulate in the extracellular space, chiefly in white matter. Cytotoxic edema is intracellular swelling from failure of ion pumps.

Question 43Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which mechanism best explains the selective vulnerability of hippocampal CA1 neurons to global ischemia?

  1. Lack of mitochondrial enzymes
  2. High density of voltage-gated sodium channels
  3. Absence of local capillary supply
  4. Excessive glutamate release with calcium influx Correct answer.

Explanation

CA1 pyramidal cells carry a high density of glutamate receptors, so ischemic depolarization triggers excessive excitatory transmitter release and calcium entry, which activates proteases and endonucleases. This excitotoxic cascade underlies delayed neuronal death in these neurons.

Question 44Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

A patient develops a rapidly expanding supratentorial mass with transtentorial herniation. Which finding indicates compression of the oculomotor nerve?

  1. An ipsilateral ptosis with preserved light reflex
  2. A fixed constricted ipsilateral pupil
  3. A fixed dilated ipsilateral pupil Correct answer.
  4. Bilateral miosis

Explanation

The parasympathetic fibers on the surface of the oculomotor nerve are compressed first, removing pupillary constriction and producing a dilated, unreactive pupil on the side of the herniation. This is an early warning sign of transtentorial herniation.

Question 45Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which structure is most likely to be compressed by a posterior fossa mass causing obstructive hydrocephalus?

  1. Foramen of Monro
  2. Cerebral aqueduct Correct answer.
  3. Arachnoid granulation
  4. Interventricular foramen

Explanation

A posterior fossa mass obstructs the cerebral aqueduct, which connects the third and fourth ventricles, producing enlargement of the lateral and third ventricles. The foramina of Monro connect the lateral ventricles to the third.

Question 46Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which feature of the cerebral cortex is most characteristic of the primary motor area compared with the primary somatosensory area?

  1. Presence of a prominent granular layer IV
  2. Thickened layer V with large Betz cells Correct answer.
  3. Dominance of layer II stellate cells
  4. Absence of pyramidal cells

Explanation

The primary motor cortex is agranular, with a poorly developed layer IV and a prominent layer V containing large Betz cells that give rise to corticospinal fibers. The primary sensory cortex is granular, with a thick layer IV.

Question 47Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which neurotransmitter is the principal inhibitory transmitter of the basal ganglia output nuclei?

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

Explanation

The output nuclei of the basal ganglia, the globus pallidus internus and substantia nigra pars reticulata, project to the thalamus using GABA as their inhibitory transmitter. Loss of this inhibition underlies the hyperkinetic features of movement disorders.

Question 48Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which sequence correctly describes the route of cerebrospinal fluid from its site of production to absorption?

  1. Fourth ventricle, third ventricle, lateral ventricle, subarachnoid space
  2. Lateral ventricle, third ventricle, fourth ventricle, subarachnoid space Correct answer.
  3. Third ventricle, lateral ventricle, fourth ventricle, subarachnoid space
  4. Lateral ventricle, fourth ventricle, third ventricle, subarachnoid space

Explanation

CSF formed by the choroid plexus flows from the lateral ventricles through the foramina of Monro into the third ventricle, then through the aqueduct into the fourth ventricle and out into the subarachnoid space. Absorption occurs at the arachnoid granulations.

Question 49Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

A lesion of the right cerebellar hemisphere is most likely to produce which finding?

  1. Left-sided spastic weakness
  2. Resting tremor of the right arm
  3. Loss of vibration sense in the right leg
  4. Intention tremor of the right arm Correct answer.

Explanation

The cerebellar hemispheres control the ipsilateral limbs, so a right hemispheric lesion causes intention tremor and dysmetria of the right arm. Resting tremor and spasticity point to basal ganglia and corticospinal lesions, respectively.

Question 50Basic Neurosciences (Neuroanatomy, Neurophysiology, Neuropathology)

Which mechanism best explains the hyperkalemia-related depolarizing block at the neuromuscular junction?

  1. Reduced calcium entry into the presynaptic terminal
  2. Increased acetylcholinesterase activity
  3. Persistent depolarization inactivates voltage-gated sodium channels Correct answer.
  4. Competitive blockade of acetylcholine receptors

Explanation

Sustained depolarization of the end plate inactivates voltage-gated sodium channels, so further action potentials cannot be generated despite receptor activation. This produces a depolarizing block rather than a competitive one.