CSGD Quiz 2 2009

1

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


  Depolarization of photoreceptors occurs because of closure of cGMP gated sodium channels.

  Photoreceptors release more of the neurotransmitter glutamate when stimulated by light.

  Closure of cGMP gated sodium channels causes photoreceptors to hyperpolarize.

  Depolarization of photoreceptors occurs because of activation of a G-protein cascade within the photoreceptor outer segment.

  Depolarization of photoreceptors occurs because of activation of mGluR6 receptors by glutamate.


A is incorrect because closure of cGMP gated sodium channels causes hyperpolarization of photoreceptors. B is incorrect because light causes hyperpolarization of photoreceptors and decrease in glutamate release. C is correct. D is incorrect because photoreceptors are depolarized in the dark. Light initiates a G-protein cascade leading to closure of sodium channels and hyperpolarization. E is incorrect because photoreceptors do not express mGluR6 receptors (ON bipolar cells are the only cells that express mGluR6).

2

Mary has suffered a stroke affecting the right lateral geniculate nucleus. Which of the following visual deficits is most likely?


  She will be unable to see a red flower with her right eye.

  She will be unable to see an object in the temporal parts of the visual field in either eye.

  For each eye, she will be unable to see an object in the right side of the visual field.

  She will be unable to perceive any visual information relating to the lower half of the visual field of her right eye.

  She will be unable to perceive information relating to motion detection from the left side of her visual field for both eyes.


A lesion affecting the right LGN will affect the nasal fibres projecting from the left retina and the temporal fibres from the right retina. This will lead to loss of vision in the left visual field for both eyes.

3

The German shepherd barks with a tone at 150 Hz. A person who has particular difficulty in localising the sound of this dog could have:


  Damage to hair cells near the base of the left cochlea.

  Damage to hair cells near the base of the left cochlea and to hair cells near the base of the right cochlea.

  A lesion in the central nervous system affecting cells sensitive to interaural intensity differences.

  A bilateral lesion in the frontal cortex.

  Damage to hair cells near the apex of the right cochlea.

4

The motor control system can be considered to be a hierarchy, with the cerebral cortex at the top and the spinal cord at the bottom. In addition, there are the modulating side loops of the basal ganglia and the cerebellum. Which one of the following statements about the connections within the motor control system is correct?


  Information travels between the spinal cord and the cerebellum via the spino-cerebellar and cerebello-spinal tracts.

  All direct inputs to the cerebellum come from the midbrain, pons or medulla.

  Basal ganglia affect motor patterns both directly (via connections with the cerebral cortex) and indirectly (by projections to the spinal cord).

  Activity of the thalamus is a crucial determinant of motor activity.

  Cerebellum pathways include projection (via the thalamus) to most regions of the cerebral cortex.

5

The maintenance of posture relies on sensory information at all levels of the motor hierarchy. Which one of the following statements about postural control is correct?


  Visual inputs relevant to postural maintenance come via cortical vision as well as the retino-tectal pathway.

  Segmental reflex functions elicited by activation of muscle spindles and Golgi tendon organs must be suppressed in order to maintain posture.

  Ultimately, all postural maintenance is due to the speed and accuracy of feedback mechanisms that correct disturbances to postural set-points.

  Visual, vestibular and proprioceptive information is integrated in brainstem nuclei, which control posture via lateral descending pathways in the spinal cord.

  Voluntary movements override (cancel out) reflex and postural control systems.


A is correct: Both higher cortical areas and more direct visual pathways to the brainstem are involved in postural maintenance. B is incorrect: These are essential to posture maintenance and work in conjunction with other postural maintenance mechanisms. C is incorrect: Anticipation and adaptation are also important in postural maintenance. D is incorrect: Postural control is effected mainly by axial muscles whose fibres run more medially. E is incorrect: Voluntary movements are coordinated with reflex and postural control systems.

6

Which one of the following statements about brain tumours is correct?


  A patient with glioblastoma multiforme has a good prognosis.

  Multiple myeloma is a neoplastic proliferation of melanocytes.

  Schwannoma is a benign tumour commonly arising from the meninges.

  For oligodendrogliomas chromosomal abnormalities are important in determining the prognosis.

  Plexiform neurofibroma is associated with neurofibromatosis type 2 (NF2).


In most oligodendrogliomas chromosome testing shows 1p/19q loss which indicates a good prognosis. Patients with glioblastoma multiforme have a bad prognosis. Multiple myeloma is a neoplastic proliferation of plasma cells (B lymphocytes). Schwannoma is a benign tumour arising from Schwann cells (peripheral nerve). Plexiform neurofibroma is associated with neurofibromatosis type 1.

7

Which one of the following statements about the diagnosis of infarctive stroke is correct?


  Skull X-ray is the preferred modality because of its ability to differentiate multiple soft tissues of subtly different densities.

  CT sensitively demonstrates infarcts as areas of increased density (whiteness) relative to normal brain parenchyma.

  MRI is a very sensitive technique in general, but gives a high dose of ionising radiation to the patient.

  The MRI technique "diffusion weighted imaging" can identify an infarct within 30 minutes of onset due to restricted diffusion of water in cells deprived of oxygen.

  MRI is preferred because it is relatively cheap and more widely available in the community.


D is correct: diffusion-weighted MRI is particularly sensitive for early CNS ischaemia. CT has much lower sensitivity and established infarcts are hypodense (darker). MRI uses non-ionising radiation.

8

When considering DNA testing for different late-onset inherited neurological disorders caused by triplet repeat expansions, which one of the following statements is the most correct?


  In these conditions a relatively young age of onset is generally associated with a shorter triplet repeat.

  A person with 34 CAG repeats in exon 1 of the HD gene would not be expected to develop Huntington disease.

  Genes involved in spinocerebellar ataxias typically have a CAG repeat in their first intron.

  In Friedreich ataxia anticipation is usually seen through the paternal line of transmission.

  In Friedreich ataxia the causative triplet repeat expansion responsible for the condition codes for glutamine.


A is incorrect: Generally a relatively young age of onset is associated with a longer triplet repeat. B is correct: 34 CAG repeats in exon 1 of the HD gene is in the normal, mutable range and the person would not be expected to develop HD. C is incorrect: These CAG repeats are in exons, i.e. in coding regions of the genes. D is incorrect: In FA anticipation is usually seen through the maternal line of transmission. E is incorrect: In FA, the repeat is GAA and is in the first intron (i.e. non-coding region) and so does not code for any amino acid.

9

Which one of the following statements about the venous sinuses is correct?


  The cavernous sinus is located in the posterior cranial fossa.

  The superior sagittal sinus is the site for CSF to enter the venous system.

  They all drain into the internal jugular vein via the foramen magnum.

  They are formed in the potential space between the dura and arachnoid mater.

  The inferior sagittal sinus contains arachnoid granulations.


CSF is resorbed via arachnoid granulations especially into the superior sagittal sinus. Dural venous sinuses are formed between the two layers of dura.

10

Which one of the following statements regarding the larynx is correct?


  The thyroid cartilage is closed posteriorly.

  The vocal ligaments are attached to the arytenoid cartilages.

  The false vocal cords are inferior to the true vocal cords.

  Arytenoid cartilages articulate with the thyroid cartilage.

  Intrinsic muscles in the larynx are innervated by the ninth cranial nerve.


This attachment is important for movements of the (true) vocal cords.