CSGD Quiz 2 2006

1

Joan is a 45 year old woman who has been experiencing headaches. Her visual acuity is normal as is her colour vision. Her visual fields are shown below. The MOST LIKELY cause of her problem is:




  Vascular disease in the right thalamus.

  A disease of the retina.

  A vascular insult that has affected the optic chiasm.

  A tumour in the right temporal lobe.

  A tumour within the left parietal lobe.


A is incorrect: A lesion of the right thalamus (i.e. right lateral geniculate nucleus) would result in left hemianopia. B is incorrect: This is not impossible, although the symmetry of the deficit makes C more likely. C is correct: The pattern of deficit is consistent with a lesion affecting the superior nasal fibres of both eyes. The ideal place for a single lesion to cause this is in the optic chiasm. D is incorrect: A tumour in the right temporal lobe would result in superior left quadrantanopia. E is incorrect: A tumour in the left parietal lobe would result in inferior right quadrantanopia.

2

A spot of light is shone into the centre of a ganglion cell receptive field causing the cell to increase the number of action potentials it fires. Which ONE of the following statements is CORRECT?


  This ganglion cell is an ON centre ganglion cell and receives synaptic input directly from ON bipolar cells.

  This ganglion cell is an OFF centre ganglion cell and receives synaptic input from OFF bipolar cells.

  This ganglion cell depolarise to a spot of light because it expresses mGluR6 receptors.

  This ganglion cell depolarises to light because of negative feedback from horizontal cells.

  This ganglion cell depolarizes to light because of synaptic connectivity with a variety of amacrine cells.


A is correct: ON ganglion cells always receive input from ON bipolar cells, and are excited when light is shone on the centre of their RFs. B is incorrect: OFF ganglion cells are excited when light is shone on the SURROUND of their RF. C is incorrect: Only bipolar cells express the mGluR6 (metabotropic) receptor. D is incorrect: Horizontal cells are responsible for (indirectly) modulating the centre-surround antagonism of ganglion RFs. E is incorrect: Similar reasoning to D, although the function of amacrine cells is less certain.

3

Following a viral infection, a patient's inner and outer hairs at the apical end of the right cochlear are damaged. The result will be:


  Complete deafness for high frequency sounds.

  Difficulty hearing high frequency sounds on the right side of the head.

  Difficulty hearing high frequency sounds on the left side of the head.

  Difficulty locating high frequency sounds.

  Difficulty locating low frequency sounds.


The apical end of the cochlear is responsible for low frequency sound detection. Damage will therefore have little effect on high frequency hearing.

4

Which ONE of the following statements is CORRECT?


  CT is the best method of imaging the brain, because it does not involve ionising radiation.

  Skull x-rays are very efficient methods of examining the brain, because subtle differences in density, such as those between grey and white matter can easily be distinguished.

  PET (Positron Emission Tomography) and SPECT (Single Photon Emission Computed Tomography) have in common that they use high energy ultrasound to obtain images.

  MRI, CT and DSA (Digital Subtraction Angiography) can all be used to obtain images of intracerebral arteries, but only DSA has the complication that 0.5% of patients will suffer a stroke as a result of undergoing the procedure.

  MRI is better than CT in imaging acute head trauma, because imaging time for MRI is far less than for CT.


A is incorrect: CT uses x-rays and therefore ionising radiation. B is incorrect: Skull x-rays are not good for imaging the brain for a variety of reasons (e.g. too much bone in the way). C is incorrect: Both these techniques use gamma rays. D is correct: DSA is the best technique for intracerebral angiography, but carries significant risks. Extra note: This is due to catheterisation of the veins in question. E is incorrect: Depending on who you talk to, imaging time for MRI is either about the same or slightly longer than for CT. In any case, CT is better for trauma because it can image bone fractures.

5

A 46 year old woman presents with twitches of the face and upper limbs and personality changes. After molecular testing she is diagnosed with Huntington disease. Which ONE of the following statements is CORRECT?


  The CAG repeat number in both of her HD alleles will be in the range 27 to 35 repeats.

  The CAG repeat is found in intron 1 of the HD gene.

  Her CAG repeat number is very likely to increase in her children.

  The neurons in the caudate nucleus will be affected by the toxic action of the huntingtin protein.

  Her children have a 1 in 4 chance of inheriting Huntington disease from her.


A is incorrect: This is in the "unaffected" range. B is incorrect: The CAG repeat is in exon 1 (the coding region). C is incorrect: Anticipation in Huntington's is usually paternal. D is correct. E is incorrect: Huntington's disease is autosomal dominant, so her children will have a 50% chance of inheritance.

6

A subdural haematoma is caused by:


  Rupture of an aneurysm.

  Haemorrhage in the brain.

  Rupture of a vein.

  Obstruction of the cerebrospinal fluid.

  Abnormal meninges.


Veins are the prominent vascular structures beneath the dura.
Extra note: subdural haemorrhage is often associated with trauma.

7

Which ONE of the following is associated with the middle meatus of the nasal cavity?


  Sphenoethmoidal recess.

  Superior concha.

  Opening of the frontonasal duct.

  Opening of the posterior ethmoid air cells.

  Tubal elevation.


A, B and D are all associated with the superior meatus. E is a feature of the auditory tube opening, which is in the pharynx.

8

In the course of a neurological examination it is noticed that the tendon reflex (monosynaptic stretch reflex) is abnormally strong and brisk when elicited from the left patella and left achilles tendon. The tendon reflexes from the right leg are normal. Which ONE of the following statements about this symptom is CORRECT?


  It may be caused by a loss of descending input due to a lesion in the territory of the left anterior cerebral artery.

  There may be an ipsilateral loss of the direct projection from the cerebellum to the spinal cord.

  With time, there may be a wasting of the extensor muscles of the right leg.

  It may be associated with right leg apraxia (loss of motor coordination).

  This may be associated with a positive Babinski sign (dorso-flexion of the foot and splaying of the toes in response to noxious planter stimuli) on the left but not the right.


A is incorrect: A vascular insult to the left side of the cortex would result in right-sided symptoms. B is incorrect: The cerebellum is responsible for FINE motor movements, not reflex modulation. C is incorrect: The right lower limbs show no weakness and will therefore not waste. D is incorrect: The symptoms appear to be restricted to the left side. E is correct: The Babinski sign is another UMN sign that one would expect to be present along with exaggerated reflexes in the rest of the lower limb.

9

During the maintenance of standing posture, the monosynaptic ("stretch") reflex activation of gastrocnemius muscle due to ankle flexion can be facilitated or diminished depending on whether gastrocnemius contraction helps to correct the postural challenge. The BEST description of the neural basis of this adaptive modulation of spinal reflexes is:


  The visual system detects motion relative to the environment and acts to pre-empt the action of the spinal reflex before any "stretch" signal is generated at the ankle joint.

  Proprioceptive, visual and vestibular information is integrated in brainstem and cerebellum; descending pathways from the brainstem adaptively control activity of the segmental stretch reflex.

  Anticipation of postural destabilization by pre-frontal and posterior parietal cortex is sent to pre- motor and motor cortex, which sends their output to spinal neurons via the corticospinal tract.

  When postural stability is disturbed, the semicircular canals of the vestibular system detects this and pre-emptively inhibits or excites spinal motoneurons.

  Postural disturbance increases activity of the Golgi tendon organs which strongly inhibits the relevant spinal motoneurons.


A is incorrect: while this statement is true, it describes only feed-forward mechanisms - it does not take into account the role of feedback and adaptive correction described B is correct: this is true and would also account for the capacity to detect postural stability and correct motor reflexes C is incorrect: modulation of postural refexes is not conscious or goal directed voluntary movement, as involvement of cortical areas implies (esp. pfc) D is incorrect: vestibular mechanisms are crucial for head / eye position reflexes but of minor importance in ongoing postural maintenance or modulation - and in any case it would operate by feedback rather than pre-emptively (feed-forward) E is incorrect: even if falling activated tendon organs (unlikely since falling would be associated with unloading muscle) it wouldn't have any effect on the process by which postural reflexes are modulated

10

Which ONE of the following statements about the forebrain is CORRECT?


  In humans there is no evidence of sexual dimorphism in any nuclei in the diencephalon.

  The limbic association cortex is mainly concerned with cognition and motor planning.

  In a right-handed person the region of cerebral cortex responsible for language expression is most likely to be located medially in the left frontal lobe.

  A patient with reduced blood flow in the territory of the right middle cerebral artery is likely to exhibit weakness of the lower part of the left side of the face.

  The anterior limb of the internal capsule is located laterally to the putamen and globus pallidus.


A is incorrect: The diencephalon includes the hypothalamus, some of whose nuclei show clear differences in both structure and function between males and females. B is incorrect: The limbic system, of which the limbic association cortex is a part, is mainly concerned with emotion and memory. C is incorrect: Language "expression" is ambiguous, but both Broca's and Wernicke's areas are located laterally making this statement unequivocally false. D is correct: The right middle cerebral artery will supply the facial area of the right primary motor cortex, and if this is hypoperfused one would expect contralateral facial weakness. E is incorrect: The internal capsule lies medially to the basal ganglia.