CSGD Quiz 2 2008

1

Which one of the following relating to Glioblastoma multiforme is correct?


  Is a benign tumour of the brain

  Arises from meningeal cells

  Commonly metastasizes to the lungs

  Most commonly arises from astrocytes in the white matter of the brain

  Is more comon in children than adults


Glioblastoma multiforme is the most malignant of brain tumours and arises from astrocytes in the white matter of the cerebral hemispheres. It occurs most commonly in aduts after the age of 55 years and is extremely uncommon in children. It does not metastasize outside the cranio-spinal compartment.

2

Which one of the following statements about the retina is correct?


  When glutamate binds to mGluR6 receptors expressed by an ON bipolar cells, the cell is hyperpolarized.

  When glutamate binds to mGluR6 receptors expressed by an ON bipolar cell, the cell is depolarized.

  When glutamate binds to AMPA receptors expressed by an OFF bipolar cell, the cell is hyperpolarized.

  When glutamate binds to AMPA receptors expressed by a ganglion cell the cell is hyperpolarized.

  When glutamate binds to mGluR6 receptors expressed by a ganglion cells, the cell is hyperpolarized.


The binding of glutamate to mGluR6 receptors causes hyperpolarization of the ON bipolar cell. This is the situation when the retina is operating in the dark.

3

Which one of the following statements is the most likely explanation for the following visual field defect?




  This person has a lesion pressing on the posterior part of their optic chiasm.

  This person has a lesion affecting the left optic radiations.

  This person has a lesion affecting the upper and lower banks of the right calcarine sulcus.

  This person has damaged their left optic nerve.

  This person has a lesion in the right lateral geniculate nucleus.


The most likely explanation for this visual field defect is a lesion that affects the optic radiations on the left hand side. The lesion has most likely damaged those axons in Meyer's loop (temporal lobe) and partially affected those extending into the partietal lobe.

4

Which one of the following statements about hearing is correct?


  Transduction in hair cells occurs via mechanically gated sodium channels connected by tip links.

  A major function of the middle ear is to match impedances. This is achieved mainly by the contact area between the stapes and the oval window being less than the contact area between the malleus and the tympanic membrane.

  The basilar membrane travelling wave has an amplitude envelope that peaks at the base end (closest to the pillar of the bony spiral) for low frequency sounds.

  A complete lesions of the left superior olivary nucleus will result in deafness in the left ear.

  A complete lesions of the left superior olivary nucleus will result in deafness in the right ear.


B is correct: To match impedances between air (outer ear) and water (inner ear) a pressure GAIN across the middle ear is required. Most of this results from the contact area between the malleus and the tympanic membrane being greater than the contact area between the stapes and the oval window. A is incorrect because, counter-intuitively, they are mechanically gated potassium channels. Note the high potassium concentration in the scala media. C is incorrect because, for low frequency sounds the travelling wave amplitude envelope peaks at the apical end (closest to the helicotrema). D is incorrect because at the level of the superior olivary nuclei the pathway is binaural; both superior olivary nuclei have input from both ears. E is incorrect because at the level of the superior olivary nuclei the pathway is binaural; both superior olivary nuclei have input from both ears.

5

Which 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

6

Which one of the following is correct


  The anterior cerebral artery supplies blood to the face areas of the primary motor and sensory cortices

  Lenticulostriate arteries are branches of the posterior cerebral artery

  The middle cerebral arteries are direct branches of the vertebro-basilar system

  Occlusion of the posterior inferior cerebellar arteries may result in lateral medullary syndrome

  Anterior spinal arteries do not supply blood to medulla

7

The difficulty in generating voluntary movement in Parkinson's disease can be significantly overcome by the treatment with L-dopa, a drug that is converted to dopamine upon entry into the CNS.

Question: The most likely basis of L-dopa's efficacy is:


  Dopamine acts as a central muscle relaxant to attenuate the tremors and thereby permit the normal execution of voluntary and complex reflex movements.

  The vast majority of neurons in the striatum (caudate and putamen) that degenerate in Parkinson's disease are dopaminergic and the provision of exogenous dopamine counteracts this loss.

  Dopamine excites glutamatergic neurons (which are excitatory) and inhibits GABAeric neurons (which are inhibitory), the net result is an increase in the activity of the motor thalamus.

  Dopamine excites the remaining dopaminergic neurons in the substantia nigra which then increases dopamine release in the striatum, which increases activity of the motor thalamus.

  Dopamine excites neurons in the striatum that project in the direct pathway to the motor thalamus, and inhibits striatal neurons that project in the indirect pathway to the motor thalamus.


A is incorrect: Dopamine is not a muscle relaxant (its central action is to promote movement) B is incorrect: the degenerating dopaminergic neurons are in the SNpc, not the striatum C is incorrect: dopamine's action in the striatum is on GABAergic neurons (not glutamatergic) where it excites some and inhibits others D is incorrect: dopamine's action is on the striatum, not on the SN E is correct: Dopamine excites neurons in the striatum that project in the direct pathway to the motor thalamus, and inhibits striatal neurons that project in the indirect pathway to the motor thalamus. that's just so correct

8

The monosynaptic stretch reflex ("tendon jerk") reflex is crucial to the maintenance of posture. The reflex activation of gastrocnemius muscle due to ankle flexion can be facilitated or diminished depending on whether contraction of the gastrocnemius helps to correct the postural challenge.

Question: 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.

  Information about body position from proprioceptive, visual and vestibular systems is integrated in brainstem and cerebellar motor regions which ultimately control spinal interneurons.

  Anticipation of postural destabilization by pre-frontal cortex is sent to pre-motor and motor cortex, which sends their output to spinal neurons.

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

  As postural disturbance increases (when falling) the Golgi tendon organs would become activated and this would strongly inhibit 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

9

Which one of the following statements relating to acute cerebral haemorrhage due to hypertensive vascular disease is correct?


  Generally multifocal and superficial in the cerebral hemispheres.

  Never fatal.

  Related to mural degenerative changes in relatively deeply placed small cerebral blood vessels.

  Due to amyloid deposition in vessels.

  More common in patients with well-controlled hypertension.

10

A 53 year old man presents with personality changes and twitches of the face and upper limbs. After molecular testing he is diagnosed with Huntington disease. Which of the following statements is correct?


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

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

  His CAG repeat number is very likely to decrease in his children.

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

  His children have a 1 in 4 chance of inheriting Huntington disease from him.


A is incorrect: One of his alleles will have 40 repeats or more if he has been diagnosed with HD. The range 27 to 35 is in the normal, mutable range. B is incorrect: The CAG repeat is in exon 1. C is incorrect: The CAG repeat is likely to increase, rather than decrease, through the paternal line of transmission. D is correct. E is incorrect: His children have a 1 in 2 chance of inheriting HD as it is autosomal dominant.