Identify the function of the anatomical structure indicated by the blue arrow in the image below.
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Options:
explanation: The image shows a prosection of the basal view of the brain, with the brainstem in the centre, the cerebellum posterior to it and the inferior temporal poles to the sides. This answer describes the fibres of the left optic nerve (CN II). However, the blue arrow indicates the oculomotor nerve (CN III) as it emerges from the interpeduncular fossa at the level of the midbrain.
name: Provides fibres formed by the axons of the ganglion cells of the left retina
label: e
answer: no
explanation: The image shows a prosection of the basal view of the brain, with the brainstem in the centre, the cerebellum posterior to it and the inferior temporal poles to the sides. The blue arrow indicates the oculomotor nerve (CN III) as it emerges from the interpeduncular fossa at the level of the midbrain. This nerve provides motor innervation to some of the extrinsic eye muscles, so its compression results in the ‘down and out’ position of the eyeball, due to the unopposed action of the lateral rectus muscle (innervated by CN VI) and the superior oblique muscle (innervated by CN IV).
name: Provides motor fibres which if compressed result in a “down and out” position of the eyeball
label: a
answer: yes
explanation: The image shows a prosection of the basal view of the brain, with the brainstem in the centre, the cerebellum posterior to it and the inferior temporal poles to the sides. The blue arrow indicates the oculomotor nerve (CN III) as it emerges from the interpeduncular fossa at the level of the midbrain. This nerve provides parasympathetic fibres to the muscle that constricts the pupil, contributing to the efferent limb of the pupillary light reflex. The muscle that dilates the pupil is innervated by sympathetic fibres arising from the superior cervical ganglion.
name: Provides parasympathetic fibres to a muscle that dilates the pupil
label: b
answer: no
explanation: The image shows a prosection of the basal view of the brain, with the brainstem in the centre, the cerebellum posterior to it and the inferior temporal poles to the sides. The blue arrow indicates the oculomotor nerve (CN III) as it emerges from the interpeduncular fossa at the level of the midbrain. This nerve provides parasympathetic fibres to muscles that constrict to cause the lens to become more, rather than less, spherical by relaxing the suspensory ligaments, contributing to the efferent limb of the accommodation reflex.
name: Provides parasympathetic fibres to muscles that cause the lens to become less spherical
label: c
answer: no
explanation: The image shows a prosection of the basal view of the brain, with the brainstem in the centre, the cerebellum posterior to it and the inferior temporal poles to the sides. The blue arrow indicates the oculomotor nerve (CN III) as it emerges from the interpeduncular fossa at the level of the midbrain. This nerve provides motor fibres to a muscle of the eyelid, the levator palpebrae superioris. However, the function of this muscle is to elevate, rather than to lower the upper eyelid. The muscle contributing to eyelid closure is the orbicularis oculi muscle which is innervated by the facial nerve (CN VII).
name: Provides motor fibres to a muscle that lowers the upper eyelid
label: d
answer: no

Correct answer: a