CSGD Quiz 1 2004

1

With regard to the action potential, which one of the following statements is not correct?


  Current flow from the site of the action potential depolarises the adjacent axonal membrane.

  In the depolarising stage of the action potential, the magnitudes of the potassium and sodium currents are approximately equal.

  In the repolarising stage of the action potential, the magnitude of the potassium current is greater than that of the sodium current.

  Compared to unmyelinated axons, myelinated axons allow less trans-membrane current per unit length of axon, and have a greater length constant (lambda).

  The rate of action potential propagation is limited by the action potential rise-time (time interval from threshold to peak voltage) and by the value of lambda, where lambda reflects the extent of passive spread of depolarisation.


The magnitude of the sodium current exceeds the magnitude of the potassium current.

2

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


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

  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 cerebral cortex is formed in an “outside-in” order with layer 2 forming before layer 6.

  The growth cone at the tip of an axon can respond to guidance cues on cell surfaces, on the extracellular matrix or in a soluble (diffusible) form.

  Synapses are initially formed without neural activity but activation is then required to refine connectivity.


Answer C is incorrect – the cerebral cortex forms in an “inside-out” order, layer 6 forms before layer 2.

3

Which one of the following statements is not correct?


  The superior colliculi are major nuclei in the auditory system and are located on the ventral surface of the midbrain.

  The lateral horns are present in the grey matter of the thoracic and upper lumbar spinal cord and contain the preganglionic neurons that project to sympathetic ganglia.

  Compact bone and cerebrospinal fluid are typically dark in T1 weighted MRI.

  The cerebrospinal fluid is secreted in the lateral ventricles mainly by the choroid plexus and is turned over about three times per day.

  At the circle of Willis, the two anterior cerebral arteries are connected by the anterior communicating artery and the posterior cerebral arteries are connected to the internal carotid by the posterior communicating arteries.


Answer A is incorrect – The superior colliculi are concerned with vision and are located on the dorsal surface of the midbrain.

4

Which of the following statements in relation to cranial nerves is incorrect?


  Special sensory nerves include cranial nerves I, II and VIII.

  Branchial arch nerves convey motor fibres.

  Parasympathetic supply to the sphincter pupillae and ciliary muscle of the eye is via the oculomotor nerve.

  Skin of the face is supplied by somatic sensory branches of the facial nerve.

  The glossopharyngeal nerve conveys sensation from the pharynx and back of the tongue.

5

A person is stabbed with a stiletto between the sixth and seventh cervical vertebrae. The lesion is confined to the dorsal part of the spinal cord. Which one of the following symptoms is the patient unlikely to have:


  Impaired position sense in the right leg.

  Impaired position sense in the left leg.

  Impaired tactile texture perception in the left hand.

  Impaired tactile texture perception in the right hand.

  Impaired temperature sensation in both legs.


A lesion confined to the dorsal part of the spinal cord is likely to affect the dorsal columns, probably bilaterally, and hence affect touch and position sense for all dermatomes below C7/C8. Pain and temperature sensation travels in the anterolateral tract which is unlikely to be damaged in this case.

6

Which one of the following lesions will not result in an absent or reduced patella (knee-jerk) reflex:


  A tumour impinging on the spinal cord at the L3 level.

  A neurological disease affecting only alpha motor neurons.

  A neurological disease affecting only gamma motor neurons.

  A neurological disease causing demyelination of A alpha motor axons.

  A neurological disease causing demyelination of large fibre (A beta) sensory axons.


The afferent arm of the reflex arises from the muscle spindles innervated by A beta sensory axons and the efferent arm arises from the alpha motor neurons innervated by A alpha axons. Gamma motor neurons are not in the reflex loop.

7

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


  Peptides released by terminals of nociceptors (at the receptor end) may result in hyperalgesia.

  Peptides released by synaptic terminals (in the spinal cord) of nociceptive afferents may result in pain sensation from areas of the body where tissue is not damaged.

  Glutamate released by synaptic terminals (in the spinal cord) of nociceptive afferents may result in hyperalgesia.

  Opiates are “doubly effective” because they inhibit neurons both in the periaqueductal grey region and in the dorsal horn.

  Enkaphalin released by synaptic terminals of interneurons in the dorsal horn results in both presynaptic inhibition and postsynaptic inhibition.


The double action of opiates is due to their excitation of cells in the periaqueductal grey region and inhibition of cells in the dorsal horn.

8

Which one of the following statements about the control of bladder function is not correct?


  Activation of the parasympathetic pathways from the sacral spinal cord constricts the body of the bladder and relaxes the smooth muscle of the sphincter.

  Activation of sympathetic pathways originating from the S1-2 spinal cord relax the smooth muscle of the body of the bladder to aid filling.

  Somatic ventral horn motor neurons contribute to continence by contracting striated muscle of the pelvic floor around the base of the bladder.

  Conscious control over micturition includes pathways originating from the frontal cortex.

  Spontaneous switching between filling and emptying of the bladder is under the control of a pontine micturition centre.


The sympathetic supply to the bladder originates from the L1-2 spinal cord.

9

A section through the medulla in the mid-olivary level would not contain which one of the following structures?


  Hypoglossal nucleus.

  Pyramid.

  Lateral reticular nucleus.

  Nucleus ambiguous.

  Red nucleus.


Red nucleus is in the midbrain (level of superior colliculi).

10

Which of the following statements regarding analgesics is incorrect?


  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.

  Morphine and paracetamol both inhibit cyclooxygenase activity.

  Morphine impairs respiratory reflexes.

  Aspirin and paracetamol both inhibit prostaglandin synthesis in the central nervous system.


Morphine inhibits neurotransmission by activation of presynaptic opioid receptors and does not have any effect on cyclooxygenase activity or prostaglandin synthesis. Paracetamol inhibits prostaglandin synthesis in the spinal cord where prostaglandins enhance neurotransmission of the pain signal.