CSGD Quiz 2 2007

1

A person has their visual field tested, and the result is shown below. Which ONE of the following statements about the pathological changes to the visual pathway is the most likely explanation?




  Vascular disease affecting the right thalamus.

  A retinal disease affecting ganglion cells in the right eye.

  A tumour that has affected the optic chiasm.

  Vascular disease affecting the optic radiations on the left side.

  A tumour within the left parietal lobe.


A is incorrect: A disease affecting the right thalamus (i.e. the right lateral geniculate nucleus) would show bilateral deficits. B is correct: A disease in the superior retinal ganglion cells in the right eye could produce this effect. C is incorrect: A tumour affecting the optic chiasm is also likely to show bilateral deficits. D is incorrect: Disruptions to the optic radiation typically have bilateral deficits (especially quadrantanopia, if incomplete). E is incorrect: A lesion of the left parietal lobe would probably cause right lower quadrantanopia.

2

Which ONE of the following statements about ganglion cell function is CORRECT?


  ON ganglion cells receive input from OFF bipolar cells.

  A spot of light shown into the peripheral part of an ON ganglion cell's receptive field will hyperpolarize that cell.

  The central response of a ganglion cell is mediated by the action of horizontal cells.

  A spot of red light shown onto the central part of the receptive field of an R+/G- ON ganglion cell will cause that cell to be hyperpolarised.

  ON ganglion cells depolarize when a spot of light is shone on the centre of their receptive field because they express mGluR6 type glutamate receptors.


A is incorrect: ON ganglion cells only receive input from ON bipolar cells (and vice versa). B is correct: ON ganglion cells are excited when a light is shone on the centre of their RF, and hyperpolarise when a light is shone on the periphery. C is incorrect: Horizontal cells modulate centre-surround antagonism, and are more closely associated with photoreceptor responses. This option is ambiguous, however. D is incorrect: This would could depolarisation/excitation (increased rate of APs). E is incorrect: Only bipolar cells express mGluR6 (metabotropic) glutamate receptors, all other cells in vertical pathway use glutamate as a neurotransmitter, but express the more conventional AMPA/Kainate/NMDA ionotropic receptors.

3

Which ONE of the following statements about eye movements is CORRECT?


  A patient with a complete lesion of the left trochlear nerve will be unable to abduct the left eye.

  In the absence of a moving target, most people can make voluntary saccadic eye movements but cannot make voluntary smooth pursuit eye movements.

  To initiate a saccade, omnipause neurons must be excited.

  Burst neurons are silent during a saccade.

  Patients with a lesion in the pontine reticular formation will have deficits of vertical eye movements.

4

A 43 year old woman presents with sudden onset of severe headache and a plain Computed Tomographic (CT) brain scan shows haemorrhage in the subarachnoid space. Which ONE of the following investigations is the most accurate method of diagnosing a suspected underlying aneurysm?


  Duplex Doppler Ultrasound.

  Computed Tomographic Angiography (CTA).

  Magnetic Resonance Angiography (MRA).

  3D Digital Subtraction Angiography (DSA).

  Positron Emission Tomography (PET).

5

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

  An HD allele with 40 or more CAG repeats shows incomplete penetrance.

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

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

6

Which ONE of the following statements about infarction in the territory of the middle cerebral artery is CORRECT?


  Such infarcts are unlikely to be embolic in origin.

  Such infarcts are often associated with visual disturbances.

  Such infarcts are not at risk of undergoing haemorrhagic transformation.

  Such infarcts may involve neurons of the cerebral cortex as well as of the basal ganglia.

  Patients with atrial fibrillation are not at increased risk of developing such infarcts.

7

Which ONE of the following statements is CORRECT?


  A complete lesion of the right cochlear nucleus will reduce the loudness of a sound located on the patient's left side.

  A complete lesion of the right medial geniculate nucleus will impair the patient's ability to locate sounds on the left side.

  Loss of hair cells at the base end of the basilar membrane will result in hearing loss for low frequency sounds.

  High frequency sounds cause maximum vibration at the apical end of the basilar membrane.

  Stretching tip-links in cochlear hair cells opens mechanically-gated sodium channels.


A is incorrect: The cochlear nuclei receive ipsilateral input. B is correct: The medial geniculate nuclei receive bilateral input, so I imagine this would result in difficulty localising sounds on both sides (the question does not say EXCLUSIVELY the left side) C is incorrect: Cells at the base end are more sensitive to HIGH frequencies. D is incorrect: High frequencies cause maximum vibration at the basal end of the basilar membrane. E is incorrect: Stretching tip-links opens mechanically-gated potassium channels - this is why the endolymph in the scala media is high in K+ (unlike the perilymph).

8

Which ONE of the following regarding the middle ear is CORRECT?


  The tensor tympani muscle attaches to the incus and is activated by a reflex to dampen loud sounds.

  The stapes transmits sound vibrations to the inner ear via the round window.

  The chorda tympani nerve passes through the middle ear and innervates the posterior third of the tongue.

  The auditory tube opens on the anterior wall of the middle ear and is important because it allows equalization of pressure between the middle ear and the atmosphere.

  The epitympanic recess extends from the floor of the middle ear and is a route for infection to reach the mastoid air cells.


A is incorrect: The tensor tympani is attached to the malleus bone. B is incorrect: Transmission here is via the oval window. C is incorrect: The chorda tympani is a branch of the facial nerve and supplies the taste buds of the ANTERIOR tongue. D is correct: The auditory tube is also known as the Eustacian tube. E is incorrect: The epitympanic recess opens into the superior middle ear, above the tympanic cavity proper.

9

Which ONE of the following statements about the cerebral hemispheres is CORRECT?


  The region V4 in the cerebral cortex is concerned with the processing of information about motion.

  "Split brain" patients have difficulty naming an object presented to their right visual field if their language centres are located in the left hemisphere.

  In the primary motor cortex cells in layer 4 give rise to the corticospinal tract.

  The amygdala is a nucleus which is mainly involved with learning and memory processing.

  The posterior association cortex in the non-dominant hemisphere is involved with interpreting the emotional content of speech.


You've got to do a little bit of searching for this one: see the 6.1 synopsis. A is incorrect: This is the role of V5. B is incorrect: The right visual field is processed in the left hemisphere, so information does not have to cross the corpus collosum. C is incorrect: Layer 4 is primarily AFFERENT (thalamocortical). The efferent corticospinal tract arises from layer 5. D is incorrect: The amygdala is associated with emotional memory and processing; it has efferents projecting into the PFC and other cortical regions (providing an emotional influence on motor planning). E is correct.

10

Which ONE of the following statements about locomotion is CORRECT?


  Because gait pattern is a function of centres in the brainstem and spinal cord, and proprioceptive sensory input, lesions of the motor cortex typically have little effect on gait (other than difficulty initiating locomotion).

  Disorders of the basal ganglia do not significantly affect gait because there are no direct connections between the basal ganglia and the spinal cord.

  During locomotion the Golgi tendon organs limit the amount of force generated by a muscle because when they are stretched they excite inhibitory interneurons which decrease motoneuron activity.

  During locomotion the segmental pathways mediating withdrawal reflexes are cyclically inhibited in phase with the step cycle.

  When the locomotion rate increase involves a new gait pattern (for example, running versus walking), the new gait pattern is produced in midbrain locomotor region (and other brainstem nuclei) which replaces the spinal pattern generators.


A is incorrect: Gait pattern is almost entirely a function of spinal cord pattern generators. B is incorrect: Disorders of the basal ganglia can significantly affect gait (e.g. Huntington's chorea). C is incorrect: Golgi tendon organ stretch excites extensor motoneurons. D is correct. E is incorrect: As for A, all gait patterns are generated in the spinal cord.