Central Nervous System: MRCEM Primary questions with answers

Central Nervous System anatomy sits in the anatomy section of MRCEM Primary, which carries 60 of the 180 questions. This topic covers the cerebrum, cerebellum, brainstem and pons, medulla, ventricles, basal ganglia and thalamus, together with spinal cord tracts, spinal cord syndromes and the blood supply of the CNS. Emergency physicians localise lesions from the examination every day, whether the problem is a stroke, a head injury or cord compression.

5 free questions below, each with the answer and the full explanation · 114 in the full bank · Last updated after the 27 October 2026 MRCEM Primary sitting.

1. Question 1 · Spinal Cord Syndrome

   A man aged 43 years underwent surgery of the posterior part of the neck, after which he lost sensation around the clavicle. Which of the following dermatome is best localized on the supraclavicular region?

   1. AC4
   2. BC5
   3. CT2
   4. DC3
   5. EC2
   Show answer and explanation

   Answer: D. The supraclavicular region is supplied by C3 in this question.

   • A: Supplies the shoulder top, below the supraclavicular zone here.
   • B: Supplies the lateral upper arm.
   • C: Supplies the axilla, far below.
   • E: Supplies the occiput and upper neck.

   Full explanation: Spinal Cord Syndrome

   Spinal cord syndrome: 

   High yield: 

   Anterior cord syndrome	Direct anterior cord compression Flexion of cervical spine Thrombosis of anterior spinal artery	Corticospinal, spinothalamic and spinocerebellar tracts	Bilateral motor loss Bilateral loss of crude touch, pain and temperature sensation
   Posterior cord syndrome	hyperextension injury associated with vertebral arch fractures or penetrating trauma to the back	Dorsal column	Bilateral loss of proprioception, vibration and light touch sensation

2. Question 2 · Central Nervous System

   While carrying out a neurological examination, you ask medical students for the sensory level of Umbilicus.

   1. AT8
   2. BT10
   3. CT9
   4. DT11
   5. ET7
   Show answer and explanation

   Answer: B. The umbilicus lies at the T10 dermatome.

   • A: Lies near the lower costal margin.
   • C: Lies above the umbilicus.
   • D: Lies midway between the umbilicus and inguinal ligament.
   • E: Lies near the xiphisternum.

   Full explanation

   T1= medial antecubital fossa

   T2= Apex of axilla

   T3= third intercostal space

   T4= level of nipples

   T5= 5th intercostal space

   T6= level of xiphisternum

   T10= level of Umbilicus

   T11= midway between Umbilicus and inguinal ligament

   T12= midpoint of inguinal ligament

3. Question 3 · Thalamus

   A woman aged 54 presents with acute back pain and complains of numbness around her rectum. Which dermatome best describes this area of numbness?

   1. AS3
   2. BS2
   3. CL5
   4. DS1
   5. ES5
   Show answer and explanation

   Answer: E. Perianal skin is supplied by S5 in this question.

   • A: Higher sacral level; perianal dermatome here is S5.
   • B: Supplies the posterior thigh.
   • C: Supplies the dorsum of the foot.
   • D: Supplies the lateral foot and sole.

   Full explanation: Thalamus

   Thalamus:

   Paired grey matter structure located around the third ventricle made up of at least 50 thalamic nuclei 

    

    

   Thalamus function:

   • Sensory integration and relay station for all the sensory pathways except Olfactory
   • Recognition of crude pain, temperature & touch
   • Influences voluntary movements by receiving impulses from basal ganglia & cerebellum & relaying them to motor cortex, influence LMN
   • Participates in maintenance of state of wakefulness & alertness through RAS
   • Role in emotions & recent memory

4. Question 4 · The Ventricles

   A female aged 24 presents with severe headache, photophobia, and stiffness of her back. Physical examination reveals positive signs for meningitis. The attending physician decides to perform a lumbar puncture to determine whether a pathogen is in the CSF. What is the last structure the needle will penetrate before reaching the CSF?

   1. APosterior longitudinal ligament
   2. BPia mater
   3. CDura mater
   4. DLigamentum flavum
   5. EArachnoid mater
   Show answer and explanation

   Answer: E. The arachnoid mater is the final layer penetrated before reaching CSF in the subarachnoid space.

   • A: Lies anterior to the dural sac; not crossed.
   • B: Adheres to the cord; not crossed by the needle.
   • C: Pierced before the arachnoid.
   • D: Pierced earlier, before the epidural space.

   Full explanation: The Ventricles

   The Ventricles:

   • The ventricles are a set of communicating cavities within the brain that are responsible for the production, transport and removal of cerebrospinal fluid (CSF), which bathes the central nervous system. There are four ventricles; right and left lateral ventricles, the third ventricle and the fourth ventricle. 
   • Lateral Ventricles:The lateral ventricles are C-shaped cavities located within their respective hemispheres of the cerebrum.  The lateral ventricles are connected to the third ventricle by the interventricular foramen of Monro. 
   • Third Ventricle: The third ventricle is a slit-like space in the sagittal plane, situated between the right and left thalamus and superior to the hypothalamus. The third ventricle is connected to the fourth ventricle by the cerebral aqueduct. 
   • Fourth Ventricle: The fourth ventricle lies within the brainstem, at the junction between the pons and the medulla oblongata. 

   Cerebrospinal fluid:

   CSF is secreted by the ependymal cells of the ventricular choroid plexus. The majority of CSF arises from the plexuses of the lateral ventricles. 

   CSF Flow:

   • From the lateral ventricles, CSF passes through the interventricular foramina to the third ventricle 
   • From 3rd ventricle CSF passes through the cerebral aqueduct to the fourth ventricle. 
   • From fourth ventricle, the CSF drains via foramina into the central spinal canal (bathing the spinal cord) and the subarachnoid cisterns in the subarachnoid space located between the arachnoid mater and pia mater (bathing the brain). 

   CSF Reabsorption:

   From the subarachnoid cisterns, CSF is reabsorbed by arachnoid granulations, which protrude into the dura mater, into the Dural venous sinuses and from here back into the circulation.

    

5. Question 5 · Vasculature of the Cns

   A patient attends reporting visual loss. On examination you find a contralateral homonymous hemianopia. Where is the most likely site of the lesion:

   1. AOptic tract
   2. BOptic nerve
   3. CLower optic radiation
   4. DUpper optic radiation
   5. EOptic chiasm
   Show answer and explanation

   Answer: A. An optic tract lesion causes contralateral homonymous hemianopia, as it carries ipsilateral temporal and contralateral nasal fibres.

   • B: Causes ipsilateral monocular visual loss.
   • C: Causes contralateral superior quadrantanopia.
   • D: Causes contralateral inferior quadrantanopia.
   • E: Causes bitemporal hemianopia.

   Full explanation: Visual Pathway

   Visual Pathway

   RETINAL BIPOLAR AND GANGLION CELLS:

   There are two types of photoreceptors in the human retina, rods and cones. Rods and cones are the first-order receptor cells that respond directly to light stimulation. Bipolar neurons are the second-order neurons that relay stimuli from the rods and cones to the retinal ganglion cells.

   OPTIC NERVE:

   The optic nerve is formed by the convergence of axons from the retinal ganglion cells. The optic nerve leaves the bony orbit via the optic canal, a passageway through the sphenoid bone. It enters the cranial cavity, running along the surface of the middle cranial fossa (in close proximity to the pituitary gland).

   OPTIC CHIASM:

   Within the middle cranial fossa, the optic nerves from each eye unite to form the optic chiasm.

   OPTIC TRACTS:

   At the optic chiasm, fibres from the medial (nasal) half of each retina crossover, forming the right and left optic tracts.

   • The left optic tract contains fibres from the left lateral (temporal) retina and the right medial retina.
   • The right optic tract contains fibres from the right lateral retina and the left medial retina.

   Each optic tract travels to its corresponding cerebral hemisphere to reach its lateral geniculate nucleus (LGN) located in the thalamus where the fibres synapse.

   OPTIC RADIATION:

   Axons from the lateral geniculate nucleus (LGN) then carry visual information, via the upper and lower optic radiations, to the visual cortex in the occipital lobe:

   • The upper optic radiation carries fibres from the superior retinal quadrants (corresponding to the inferior visual field quadrants) and travels through the parietal lobe to reach the visual cortex.
   • The lower optic radiation carries fibres from the inferior retinal quadrants (corresponding to the superior visual field quadrants) and travels through the temporal lobe to reach the visual cortex of the occipital lobe.

   VISUAL CORTEX:

   At the visual cortex, the brain processes the sensory information and responds appropriately.

   Visual Pathway. (Image by Miquel Perello Nieto (Own work) [CC BY-SA 4.0 , via Wikimedia Commons)

   Blood Supply

   Table: Blood Supply of the Visual Pathway

   Structure	Blood Supply
   Optic nerve (retinal and orbital part)	Central retinal artery (branch of the ophthalmic artery)
   Optic nerve (intracranial part) and optic chiasm	Ophthalmic artery, anterior cerebral and anterior communicating arteries
   Optic tract	Posterior communicating artery and anterior choroidal artery
   Lateral geniculate nucleus	Posterior cerebral artery and anterior choroidal artery
   Optic radiations	Middle and posterior cerebral arteries, anterior choroidal artery
   Visual cortex	Posterior cerebral artery (macular dually supplied by middle cerebral artery)

   Likely Causes of Disease or Injury

   Damage to the optic nerve may be caused by:

   • optic neuritis in multiple sclerosis or secondary to measles or mumps
   • optic nerve compression secondary to orbital cellulitis, glaucoma or ocular tumours
   • optic nerve toxicity secondary to ethambutol, methanol and ethylene glycol
   • optic nerve damage secondary to orbital fracture or penetrating injury to the eye
   • optic nerve ischaemia

   Compression at the optic chiasm may occur due to:

   • pituitary tumour
   • craniopharyngioma
   • meningioma
   • optic glioma
   • aneurysm of the internal carotid artery

   Damage to the visual tract central to the optic chiasm may be caused by:

   • cerebrovascular event
   • brain abscess
   • brain tumours

   Common Clinical Effects

   Table: Clinical Effects of Lesions of the Visual Pathway

   Site of Lesion	Visual Defect
   Optic nerve	Ipsilateral visual loss
   Optic chiasm	Bitemporal hemianopia
   Optic tract	Contralateral homonymous hemianopia
   Parietal upper optic radiation	Contralateral homonymous inferior quadrantanopia
   Temporal lower optic radiation	Contralateral homonymous superior quadrantanopia
   Occipital visual cortex	Contralateral homonymous hemianopia with macular sparing

   Clinical Effects of Lesions of the Visual Pathway. (Image modified by FRCEM Success. Original by KDS444 [Public domain], via Wikimedia Commons)