CSGD Quiz 1 2003

1

Which one of the following statements is not correct?


  The pyramidal decussation (visible on the ventral surface of the brainstem) demarcates the border between the medulla and the spinal cord.

  All sensory pathways, with the exception of the olfactory pathway, synapse in the diencephalon before projecting to the cerebral cortex.

  Compact bone is typically bright in T1-weighted MR images

  The telencephalon includes the cerebral cortex, underlying white matter, basal ganglia, hippocampus and amygdala.

  The cerebrospinal fluid flows through the foramina in the roof of the fourth ventricle into the subarachnoid space and returns to the venous circulation via the superior sagittal sinus.


C is incorrect. Compact bone is typically dark in T1-weighted MRI.

2

Which one of the statements about the formation of the nervous system is not correct?


  At the time of closure, the neural tube consists of a single layer of columnar epithelial cells.

  Reelin, an extracellular matrix molecule, is secreted by Cajal-Retzius cells and arrests the progress of neurons along radial glial fibres in the cerebral cortex.

  The programmed death of about 50% of neurons is a major and widespread feature of normal development of the nervous system.

  The refining of connections from the lateral geniculate nucleus to layer 4 of the cerebral cortex to form ocular dominance columns occurs prenatally.

  The space in the hindbrain vesicle gives rise to the fourth ventricle.


D is incorrect. This process occurs in the period of neonatal plasticity after birth. Prenatally, the connections are refined from the retinal ganglion cells to the lateral geniculate nucleus.

3

With regard to neuropraxic injury of several hours duration, to the ulnar nerve, which one of the following statements is not correct?


  There may be temporary loss of fine control of the fingers

  A claw hand will develop and continue to grow worse over the course of several weeks

  Conduction block is attributed mainly to myelin ischaemia and localised demyelination

  The epineurium is intact

  The axon is not severed


B is incorrect. A claw hand will develop but it will improve with time.

4

Which one of the following statements about myelin is not correct?


  Myelin decreases axonal capacitance

  Myelin increases the electrical resistance between intra-axonal fluid and extracellular fluid

  Myelin increases the electrical length constant of the axon

  Myelin increases the speed of action potential propagation

  Pain-sensitive nerve fibres are always myelinated


E is incorrect. Both unmyelinated C fibres and myelinated A fibres carry nociceptive information to the CNS.

5

Which one of the following statements about the spinal cord is not correct?


  Co-activation ensures that muscle spindles are able to signal unplanned changes in muscle length during voluntary movements.

  Fibres carrying fine touch information from the toes will occupy the medial part of the dorsal columns.

  The enhanced tendon reflexes that occur with upper motor neuron lesions are mediated by spinal connections of the muscle spindle afferents.

  A cross-section of the spinal cord from the lumbar region (lumbar enlargement) will have more white matter than a section from the thoracic region.

  Propriospinal neurons mediate coordination of posture and movement across multiple spinal cord segments.


D is incorrect. The amount of white matter in the spinal cord increases progressively in the rostral direction because of the addition of sensory input and motor output at each level.

6

Which one of the following statements about pain and temperature sensation is not correct?


  A lesion in the left lateral medulla is likely to disrupt temperature sensation from the left leg.

  The temperature of objects warmer than the skin surface is conveyed to the CNS by unmyelinated C fibres.

  Primary afferent fibres from nociceptors in the foot synapse in the dorsal horn at sacral or lumbar levels.

  Glutamate released by nociceptor terminals in the dorsal horn activates both AMPA and NMDA type receptors.

  Hyperalgesia and allodynia can be evoked from undamaged parts of the body.


A is incorrect because the pathway conveying pain and temperature sensation from the left leg decussates at the lumbar and sacral levels of the spinal cord and is thus on the right side at the level of the medulla.

7

Which one of the following statements about the oculomotor nerve (C.N. III) is not correct?


  It carries parasympathetic nerve fibres,

  It passes through the superior orbital fissure,

  It supplies the orbicularis oculi muscle,

  It exits through the interpeduncular fossa of the midbrain,

  It supplies the muscle which elevates the upper eye lid.


C is incorrect. Orbicularis oculi muscle is part of the facial expression musculature, hence it is innervated by the facial nerve.

8

Which one of the following statements concerning the medial lemniscus is not correct?


  In the medulla it is located close to the midline and immediately dorsal (posterior) to the corticospinal tract,

  It contains uncrossed ascending (sensory) fibres,

  On its way to the thalamus, it occupies the lateral aspect of the midbrain tegmentum,

  It contains fibres originating from neurons located in the gracile and cuneate nuclei,

  It contains fibres from second-order neurons in this tract.


B is incorrect. Fibres which form the medial lemniscus originate in the contralateral dorsal column nuclei and cross-over at the caudal medulla forming internal arcuate fibres.

9

Which one of the following statements regarding analgesics is not correct?


  Morphine inhibits neurotransmission of pain signals in the dorsal horn of the spinal cord.

  Paracetamol inhibits neurotransmission of pain signals in the dorsal horn of the spinal cord.

  With repeated use, tolerance develops to the analgesic actions of morphine due to the induction of metabolising enzymes

  Combined use of paracetamol and codeine increases the level of analgesia without increasing the level of adverse effects.

  Aspirin and paracetamol are antipyretic as well as analgesic


C is incorrect. Tolerance to morphine occurs due to a downregulation of receptor expression and a reduction in the coupling between receptors and second messengers. There is no change in the pharmacokinetics. Codeine and paracetamol are additive. Therefore their combined use increases the analgesic action without increasing adverse effects. Aspirin and paracetamol are antipyretic by inhibiting prostaglandin synthesis in the hypothalamus.

10

Which one of the following statements about the organisation of the higher centres of the autonomic nervous system is not correct?


  The nucleus of the solitary tract integrates and relays sensory inputs from cranial nerves, such as the vagus.

  The hypothalamus contains a number of nuclei that integrate autonomic reflexes with endocrine and behavioural responses during many homeostatic responses.

  The micturition centre in the pons controls switching between continence and micturition, under the influence of higher centres, such as the frontal cortex.

  The amygdala contributes to homeostasis by directly detecting changes in temperature, blood gas and electrolyte level and hormone concentration and organising responses by the autonomic nervous system.

  All motor output of the autonomic nervous system generated by centres in the brain must pass though either sympathetic or parasympathetic preganglionic neurons before affecting smooth muscle or glands in the periphery.


D is incorrect. The functions listed are carried out by the hypothalamus, not the amygdala.