CSGD Quiz 2 2004

1

A 47 year old woman presents with the visual field defect shown below. Which one of the following COULD NOT be the cause?




  Defect in the visual pathway posterior to the optic chiasm.

  A defect in the visual pathway at the chiasm.

  A defect in the optic radiations.

  A defect in the left lateral geniculate nucleus.

  A defect in the left visual cortex on the lower bank of calcarine sulcus.


To produce this deficit at the optic chiasm, a lesion would have to affect both the inferior temporal fibres of the left eye and the inferior nasal fibres of the right eye (without affecting anything else), which is highly unlikely. This deficit is right superior quadrantanopia, characateristic of a left temporal lobe lesion (affecting the Meyer's loop part of the left optic radiations). Partial lesions at the left LGN and left lower visual cortex could also cause this.

2

Which of the following statements about the retina is NOT CORRECT?


  The density of rods is higher than cones except in the fovea.

  Horizontal cell bodies are found in the inner nuclear layer and they are inhibitory neurons.

  In the fovea, the bipolar, horizontal, amacrine, and ganglion cells are displaced to the side so that light has a direct pathway to the photoreceptors.

  The cell bodies of amacrine cells and bipolar cells are found in the inner nuclear layer and both cell types have processes in both the inner and outer plexiform layers.

  Amacrine cells are neurons that have inhibitory synapses on bipolar cells.


D is incorrect because amacrine cells do not have processes in the outer plexiform layer.

3

Which one of the following statements is NOT CORRECT?


  Magnetic Resonance Imaging (MRI) is a technique which uses magnetic fields, radiofrequency pulses and no ionising radiation.

  Haemorrhages are hyperdense and ischaemic infarcts hypodense on Computed Tomography (CT) scans.

  Digital Subtraction Angiography (DSA) is the best technique for demonstrating intracranial vessels because it is non-invasive.

  The spinal cord is best imaged by MRI.

  Duplex Doppler ultrasound can be used to evaluate the carotid arteries in the neck.


C is incorrect because it is invasive and has a complication rate of 0.5% strokes and 0.1% mortality.

4

Which one of the following is NOT CORRECT?


  Anticipation of certain genetic conditions is usually associated with earlier onset and/or greater severity of symptoms.

  In Huntington disease, the IT15 allele with more than 40 CAG repeats is fully penetrant.

  In Huntington disease, the triplet repeat gene mutation results in a dominant-negative effect.

  Inheritance of spinocerebellar ataxias is usually autosomal dominant.

  In Friedreich ataxia, the triplet repeat expansion in the frataxin gene is found in the first intron.


The triplet repeat mutation in Huntington disease results in a novel gain of function, not a dominant-negative effect.

5

Which one of the following statements regarding a lesion of the 3rd cranial nerve is NOT CORRECT? A lesion of the 3rd cranial nerve will:


  Result in ptosis on the affected side.

  Result in lateral deviation of the eyeball on the affected side.

  Result in a dilated pupil on the affected side.

  Affect pupillary reflexes.

  Affect the corneal reflex.


The afferent arc of the corneal reflex is the ophthalmic division of the trigeminal nerve (innervating the cornea) and the efferent arc is the facial nerve (innervating the orbicularis oculi muscles... leading to a tight closure of the eyes bilaterally). Ptosis can result from occulomotor nerve palsy because it innervates the levator palpebrae superioris muscle.

6

Which of the following statements is INCORRECT? Saccular (berry) aneurysms occuring in intracranial subarachnoid arteries are:


  The commonest cause of spontaneous subarachnoid haemorrhage in adult patients.

  Amenable to surgical treatment by clipping.

  Incidental findings in 2-3% of routine autopsies.

  Caused by vessel wall weakening due to deposition of amyloid.

  More frequent in the anterior than the posterior circulation.


Saccular aneurysms develop as a consequence of both congenital and acquired factors at arterial branch points. Although vessel wall degeneration occurs, amyloid deposition is not a factor.
Extra note: Congenital amyloid angiopathy is cause of intracerebral haemorrhage, but not associated with SAH.

7

Which one of the following statements about a 9KHz sound source located 25 degrees to the right of the midline is NOT CORRECT?


  It can be located in space because the amplitude of vibration of the right tympanic membrane is greater than that of the left tympanic membrane.

  It will result in a wave travelling from the base of the basilar membrane to its apex.

  It will increase the firing rate in auditory nerve fibres with a characteristic frequency of 10KHz but will not affect fibres with a characteristic frequency of 2KHz.

  It will result in movement of the basilar membrane that is greater at the apical end than at the base end.

  There will be a delay in time of arrival of sound at the two ears.


High frequencies have the peak of their travelling wave envelope at the base end of the basilar membrane. 9KHz is a high frequency for the human with a peak close to the base.

8

Which of the following statements is NOT CORRECT?


  A positive Babinski sign (dorsiflexion of the foot and splaying of the toes in response to a mildly noxious plantar stimulus) indicates a loss of the brain's influence over spinal reflex pathways.

  The semicircular canals are the main detectors of postural instability in the maintenance of a standing position.

  Extrafusal muscle fibres and the muscle spindle stretch receptors of the gastrocnemius and tibialis muscles are crucial to maintenance of standing posture.

  If a patient with brain damage exhibits rigidity of the limbs such that the legs are extended but the arms are flexed, this indicates that the damage is located above (rostral) to the level of the red nucleus of the brain.

  Pre-motor cortex and primary motor cortex both contribute fibres to the lateral corticospinal tract.


The incorrect statement is B; they are sensitive to angular acceleration of the head, not slow movement of the head due to body sway.

9

Which ONE of the following statements is NOT CORRECT?


  "Split-brain" patients have difficulty naming an object presented to their left visual field if their language centres are located in the right hemisphere.

  The anterior association cortex plays an important role in executive function, foward planning and cognition.

  The region V5 (medial temporal) in the cortex is involved with processing of information about motion.

  The hemineglect syndrome usually arises from a lesion in the posterior association cortex of the non-dominant hemisphere.

  Most of the non-pyramidal (granule, stellate) cells use GABA as their neurotransmitter.


Split-brain patients have difficulty naming objects present to their left visual field if their language centres are located in the left hemisphere.

10

Which of the following statements about Parkinson's disease is NOT CORRECT?


  It is a motor disorder of the basal ganglia.

  It is characterized by hyperkinetic movements of the limbs.

  It is associated with a decrease in dopamine levels in the striatum.

  It response to pharmacological treatment with L-DOPA + carbidopa.

  It repsonse to treatments which reduce the actions of acetylcholine.


Parkinson's is a HYPOkinetic disorder. It is associated with a decrease in dopamine, which disrupts the balance of dopamine and acetylcholine in the brain.