Cranial Nerves in the Cat
In the previous lab, you dissected out the brain from your dissection cat. We are hopeful that the cranial nerves will not have been obliterated during the extraction. In this exercise, you will be guided through identification of some of the cranial nerves (in bold) on this specimen. See Gilbert, p 83 for an illustration of the ventral view of a sheep brain. Here is an images: cranial nerves 1
I Olfactory bulbs project out of anterior-most cerebra (often truncated during dissection)
Functions: Pure sensory: smell
II Optic form chiasma (if you preserved it) just anterior to hypothalamic infundibulum. During dissection, the chiasma may be torn off leaving only the stumps of the optic tracts.
Functions: Pure sensory: vision
III Oculomotor Emerge from under medial side of cerebral peduncles just outside of Circle of Willis. Functions: Extrinsic eye muscles except for lat. Rectus & sup. oblique
IV Trochlear tiny, most easily located by looking just below the corpora quadrigemmina on the backside of the brain. It is a thin thread that circles around to the ventral side of the brain.
Functions: superior oblique extrinsic eye muscle
V Trigeminal largest cranial nerve, most anterior of the three large clustered cranial nerves, V, VII and VIII. Lateral to pons, points forward.
Functions: branches to form ophthalmic, maxillary & mandibular nerves.
VI Abducens tiny thread-like nerve, emerges somewhat near midline just below the pons.
Functions: lateral rectus extrinsic muscle of the eye
VII Facial emerges laterally between pons and medulla , in front of the vestibulocochlear (VIII)
Functions: taste in ant. tongue, glands of nose & salivation, not parotid
VIII Vestibulocochlear emerges laterally between pons and medulla, behind and larger than the facial (VII). (Also know as the auditory nerve.)
Functions: Pure sensory: hearing and balance
IX Glossopharangeal CRANIAL NERVES IX-XII ARE DIFFICULT TO DISTINGUISH IN THE CAT (for me…). emerges adjacent to and in front of the larger vagus (X)
Functions: taste in post. tongue, glands of pharynx, parotid gland
X Vagus emerges from upper side of medulla, larger than others in this area (Easily seen outside the cranium, attached to the carotid arteries.)
Functions: major parasympathetic nerve. Also detects taste at tongue base, and ennervates muscles of pharynx and larynx
XI Spinal Accessory originates below foramen magnum, collected just below X.
Functions: trapezius, sternocleidomastoid
XII Hypoglossal emerges from upper side of medulla just behind pyramids
Functions: extrinsic and intrinsic muscles of tongue
Notice on this dissected brain that the pituitary is still intact just below the optic chiasma (indicated by the probe), a rarity because it is usually torn off by the circle of dura mater which surrounds the infundibulum.
David Fankhauser 