CSGD Quiz 1 2008

1

With regard to a neuropraxia injury to the ulnar nerve, which one of the following statements is INCORRECT?


  There may be temporary loss of fine control of the fingers

  A claw hand will develop and continue to grow worse with time

  Conduction block is attributed mainly to myelin ischaemia and localised demyelination

  The epineurium is intact

  The axons are not severed

2

Which one of the following is correct? The ventral portion of the neural tube:


  is derived from the lateral regions of the neural plate

  contains nuclei which are exclusively in the S-phase of the cell cycle

  gives rise to neural crest cells

  contains progenitor cells whose progeny differentiate into motorneurons

  is induced by the release of BMP4 from the overlying ectoderm


A is incorrect as the lateral regions of the neural plate give rise to the dorsal portion of the neural tube during neurulation. B is incorrect because nuclei of dividing cells move from the ventricular to the pial side of the neural tube, not from the dorsal to the ventral portion. Nuclei in the S-phase are found close to the pial side of the neural tube. C is incorrect because the neural crest is derived from the dorsal-most part of the neural tube. D is correct. Motorneurons are produced by asymmetric divisions of progenitor cells that are found in the ventral part of the neural tube. E is incorrect because BMP4 released from the ectoderm induces cell fates in the dorsal part of the neural tube. Sonic hedgehog released from the notochord is responsible for the induction of cell fates in the ventral half of the neural tube.

3

All of the following drugs are opioid analgesics, EXCEPT:


  Morphine

  Alfentanil

  Ketamine

  Pethidine

  Buprenorphine


All the others are from the opiod class of drugs. Ketamine is an older anaesthetic with potent analgesic properties at subanaesthetic concentration. Acts via the antagonism at the NMDA receptors.

4

Neuroimaging is likely to be a key investigation if demyelination in the CNS is suspected. In regard to the preferred imaging method, which one of the following is CORRECT?


  It is usually easier to see if a lesion is confined to white matter with CT than it is with MRI.

  CT is preferred because in this situation MRI has a higher rate of false negatives.

  MRI is preferred because it is reliable for diagnosing Multiple Sclerosis.

  MRI provides better spatial resolution, especially for brainstem or spinal cord.

  MRI is preferred for the spinal cord, but for the brain CT provides better structural detail.


Generally MRI provides better spatial resolution than CT for all clinical soft-tissue imaging. This is important for detecting small lesions. CT is not so good for visualizing the brainstem or spinal cord. A is incorrect: it is easier to see if a lesion is confined to white matter with MRI because it is better at differentiating white from grey. B is incorrect: for demyelination, MRI is highly sensitive whereas CT has a higher rate of false negatives. C is incorrect: Finding multiple white matter lesions with MRI is not specific for Multiple Sclerosis. Not all white matter lesions are demyelination, and there are causes of demyelination other than MS. E is incorrect: MRI provides better structural detail for all regions of CNS.

5

Which on of the following statements regarding a lesion of cranial nerve VII is incorrect?


  a lesion of cranial nerve VII may produce impaired taste sensation on part of the tongue.

  A lesion of cranial nerve VII may result in loss of corneal sensation.

  A lesion in cranial nerve VII may reduce the ability to blink.

  A lesion in cranial nerve VII may cause paralysis in some of the muscles of facial expression.

  A lesion in cranial nerve VII may cause greater sensitivity to sounds.


The Facial nerve does not supply the cornea with somatic sensory fibres, the 5th cranial nerve (trigeminal nerve) provides this.

6

A section through the rostral midbrain would not contain which of the following?


  Red nucleus

  Oculomotor nucleus

  Edinger-Westfal nucleus

  Nucleus ambiguuus

  Medial lemniscus.


The nucleus ambiguus is found in the medulla.

7

The pterion is formed at the junction of the


  frontal, parietal, sphenoid and occipital bones

  frontal, parietal, temporal and occipital bones

  frontal, parietal, sphenoid and temporal bones

  parietal, sphenoid, temporal and occipital bones

  none of the above

8

Which one of the following questions about the meninges and cerebrospinal fluid (CSF) is correct?


  CSF circulates between the arachnoid and the pia in the subarachnoid space.

  The thickest and strongest connective tissue layer of the meninges is the dura

  CSF is formed in the fourth ventricle and flows forward into the lateral ventricles through the aqueduct

  CSF is an ultrafiltrate of plasma formed by the thinnest of the meninges, the pia.

  The meninges are made up of three layers, the closest to the brain being the dura, the middle the arachnoid and the outermost being the pia.

9

The following scenario applies to both Q9 and Q10.

A patient presents at casualty and the registrar established the following: (1) Position sense is absent for the left ankle. (2) Light touch sensation is absent for the left foot. (3) Reflexes are exaggerated for the left biceps. (4) Temperature sensation is normal for both feet.

The patient is likely to have a lesion:


  In the medial and anterior part of the medulla on the right side.

  In the medial and anterior part of the pons on the left side.

  In the postcentral gyrus on the right side.

  In the left side of the spinal cord at the C5-C6 level.

  In the right side of the spinal cord at the C5-C6 level.


The medial lemniscus on the right side of the brainstem has been affected and therefore light touch and position sense on the left side of the body are affected. Also, the corticospinal tract (upper motor neurons) on the right side has been affected and therefore the left biceps shows upper motor neuron signs. B is incorrect because a left-sided lesion of the pons would result in signs on the right side of the body. C is incorrect because biceps reflexes would not be affected. D is incorrect because the biceps would show lower motor neuron signs (decreased or absent reflex). E is incorrect because light touch would be affected on the right side of the body and the right biceps would be affected.

10

In this patient, absent light touch sensation in the left foot:


  Results from a lesion of unmyelinated fibres.

  Is likely to be accompanied by absent pain sensation in the left foot.

  Is likely to be accompanied by lack of pain sensation from the left shoulder.

  Is mediated by a pathway in which all the primary afferent fibres are large myelinated fibres.

  Is mediated by a pathway in which there are only two synapses between the receptors and neurons in the somatosensory cortex.


Light touch sensation is conveyed by the dorsal column-medial lemniscal system, which comprises large myelinated fibres from the low threshold mechanoreceptors (principally cutaneous, also joint, muscle spindles, Golgi tendon organ). A is incorrect because dorsal column-medial lemniscal fibres are myelinated. B is incorrect because pain sensation from the left foot is conveyed by the anterolateral system which is not affected by the lesion (because temperature sensation is normal for both feet). C is incorrect because pain sensation from the left shoulder is conveyed by the anterolateral system which is not affected by the lesion (because temperature sensation is normal for both feet). E is incorrect because there are three synapses in the pathway; first in the gracile nucleus, second in the ventral posterior lateral nucleus of the thalamus, third onto the neurons in the somatosensory cortex)