Morphology Mechanism Of Cranial Nerves In Yak Adapts To Ecological Environment Of Qinghai-Tibetan Plateau

The origin, distribution, branch, shape and location of the cranial nerves in the head and neck of the yak were studied with gross anatomy method to explore the morphology mechanism of the cranial nerves of the yak to adapt to the ecological environment of the Qinghai-Tibetan plateau, which can provide the basic data for furthermore molecular and gene levels' research. The results are as followed:1. The olfactory nerves arises from the mucous membrane of the caudal portions on the nasal septum and superior nasal meatus, and terminates in the rostroventral aspect of the olfactory bulb. The terminal nerve arises from the mucosa of the retro-superior part of the superior nasal meatus and blood vessel and glandular organ in the olfactory area epithelium of the retro-superior part of the nasal septum, and terminates in the medial surface of the olfactory trigon and subcallosal area. The vomeronasal nerve arises from the vomeronasal organ in the medial of the proximal wall of the anterior part of the nasal cavity and mucosa of the close together area and nasal septum, and ends in the olfactory gyrus of the anterio-medial margin of the olfactory triangle.2. The optic nerve arises from the optic nerve disc of the retina of the eye bulb, enters the cranial cavity through the optic canal, runs retro-medially about 2～3 cm in the cranial cavity and terminates in the optic chiasm. It is circular cylinder shape and its diameter ranges from 4.60 mm to 5.50mm. The diameter of the optic nerve ranges from the optic chiasm to the eyeball about 0.50 mm. It runs like S-shape in the orbit, and receives one to two twigs from the ciliary ganglion during its course.3. The oculomotor nerve origins from the intercrural fossa of the posterior part of the ventral aspect of the mesencephalic cerebral peduncle. Immediately, it divides into dorsal and ventral branches after leaving the cranial cavity through the foramen orbitorotundum. The two branches supply all bulbal muscles except the lateral rectus and dorsal oblique muscles. The ciliary nerv is from the ventral branch to associate with the ciliary ganglion. 4. The trochlear nerve comes from the canal between the colliculus caudalis of the quadrigeminal bodies (corpora quadrigemina) and rostral medullary velum, goes to the fossa orbitalis through the foramen orbitorotundum, and supplies the obliquus dorsalis muscle. It was connected the ophthalmic nerve with the communicating branches.5. The trigeminal nerve arises from the dorsolateral side of the pons, and divides into the ophthalmic, maxillary and mandibular nerves.The ophthalmic nerve gives off the zygomaticotemporal branch, lacrimal, frontal, frontal sinus nerves, muscular branches and nasociliary nerve. The nasociliary nerve divides into the infratrochlear and ethmoidal nerves. The ethmoidal nerve divides into the internal nasal and external nasal branches. There is a communicating branch in the nasociliary nerve and the ciliary ganglion.The maxillary nerve gives off the zygomaticofacial, accessory zygomaticofacial branches, zygomatic bone, caudal nasal, greater palatine, lesser palatine and caudal superior alveolar nerves. The infraorbital nerve is the continuation of the maxillary nerve. The maxillary nerve is connected with the ophthalmic and buccal nerves by the major communicating branches. The caudal nasal nerve gives off some slender branches to the pterygopalatine plexus in the pterygopalatine fossa. The greater palatine nerve gives off accessory palatine nerve and collateral branches to enter the proximal wall of the nasal cavity.The mandibular nerve gives off the deep temporal, masseteric, buccal, lingual, inferior alveolar, mylohyoid, medial peterygoid, later peterygoid and auriculotemporal nerves. The buccal nerve is connected with the maxillary, greater palatin nerves and dorsal buccal branch of the facial nerve by means of the communicating branches. The medial pterygoid muscle is also innervated by a branch of the buccal nerve. Two large accessory mental nerves arise from the inferior alveolar nerve.6. The abducent nerve is originated from the posterior margin of the trapezoid body of the antero-ventral surface of the medulla oblongata and bilateral anterior extremity of the pyramid. The nerve branches supply to the rectus lateral and retractor bulbi muscles.7. The facial nerve arises from the antero-lateral aspect of the trapezoid body of the medulla oblongata. Before its emergence through the stylomastiod foramen, the nerve gives off the greater petrosal, stapedial nerves, chorda tymapanic and communicating branches with the lesser petrosal nerve. It receives a communicating branch of the vestibulocochlear nerve and a auricular branch of the vagus nerve. After its emergence through the stylomastiod foramen, the nerve gives off the posterior auricular, auriculopalpebral nerves, internal auricular, parotid, digastric, cervical, dorsal buccal and ventral buccal branches. The caudal auricular nerve and the internal auricular branch give off wigs to the parotid gland and parotid auricularis muscle. The dorsal buccal branch divides into branches and forms a plexus with the branches of the infraorbital nerve under the canius muscle. The ventral buccal branch is connected with the accessory mental nerve on the lateral aspect of the mandible.8. The vestibulocochlear nerve connects with the dorsolateral side of the trapezoid body of the medulla oblongata. In the internal acoustic meatus, it splites into the vestibular and cochlear parts, exchanging 2～3 twigs with the facial nerve.9. The glossopharyngeal nerve arises from the lateral aspect of the medulla oblongata. It gives off the tympanic nerve, carotid sinus, stylopharyngeal, lingual, pharyngeal branch, a communiacating branch to join the auricular branch of the vagus and a communiacating branch to the facial nerve.10. The vagus nerve arises from the lateral aspect of the medulla oblongata. It leaves the cranial cavity in company with the glossophoryngeal and accessory nerves through the jugular foramen. At the oranial end of the neck, the vagus nerve gives off the auricular branch, laryngis cranial nerve, the common trunk for the pharynx, larynx, oesophagus and trachea and some communicating branches which connect with the glossopharyngeal, hypoglossal nerves and cranial cervical ganglion.11. The accessory nerve arises from the cranial spinal spinal roots of the central nervous system. The cranial root arises from the dorsolateral aspect of the medulla oblongata. The spinal root arises from the lateral aspect of fifth cervical segment of the spinal cord. When the nerve reaches to the ventral margin of the tympanic bulla, it gives off a thin internal branch, which joined to the vagus. And then, when the nerve crosses the ventral branch of the first cervical nerve, it divides into dorsal and ventral branches. The dorsal branch finally ramifies in the medial surface of the trapezius muscle, and it gives off some twigs to supply brachium cephalic and shoulder-blade processus transversus muscles. The vental branch gives off some branches to supply the cleido-occipitalis, sternomandibularis and sternomastoideus muscles. 12. The hypoglossal neve arises from the ventrolateral aspect of the medulla oblongata. The rootlets course laterally, perforate the dura mater and then unite in a single trunk. The trunk leaves the cranial cavity through the hypoglossal canal. When the hypoglossal nerve courses on the hypoglossal and digastricus muscles, it gives off several twigs to supply cervicum lingual, hyoglossus, geniohyoid and genioglossus muscles. And then, the trunk divides into several branches to supply hyoglossus, geniohyoid, genioglossus and lingua intrinsic muscles. At the coursing, some communicating branches connects with the vagus, accessory nerves, cranial cervical ganglion and the ventral branch of the first cervical nerve.13. The sympathetic nerve in the headThe the cranial cervical ganglion is a greyish fusiform structure, which is located on the rostrolateral surface of the m. longus capitis. Roughly anterior 25% of the ganglion is covered by the tympanic bulla, the remainder by the m. stylohyoideus. The caudodorsal border of the ganglion is parallel to the internal carotid artery. Five or six internal carotid nerve branches arise from the rostrodorsal end of the cranial cervical ganglion and coursed rostrally parallel to each other about 3-3.5 cm along the rostrolateral surface of the m. longus capitis, following the internal carotid artery. Around the internal carotid artery, these branches forms the internal carotid plexus, which passed rostrally and dorsally through the tympano-occipital and petrooccipital fissures to gain the rostral border of the petrous temporal bone. There, the internal carotid plexus gives off four branches, deep petrosal, caroticotympanic, cavernous sinus and jugular nerves. The caudodorsal border of the cranial cervical ganglion gives off external carotid nerve and sympathetic trunk, together with some branches connecting the ganglion to the glossopharyngeal, vagus and hypoglossal nerves.14. The parasympathetic nerve in the head14.1 The ciliary ganglion is like a german millet, lies on the retrodorsal part of the ventral rectus of the eye and the ventrolateral part of the optic nerve and joins to the ventral branch of oculomotor nerve ( In the 3/15 specimens, the ciliary ganglion is hided in the ventral branch of oculomotor nerve) . It is connected with nasociliary nerves by communicative branches. The short ciliary nerve arises from the ciliary ganglion and enters the eyeball. But the yaks do have not the accessory ciliary ganglion.14.2 The auricular ganglion is a triangle structure of the basilar part upward. It locates on the lateral aspect of the retro-superior part of the tensor veli palatini muscle. Its retro-superior extremity connects with the lesser petrosal nerve. The ventro-superior extremity give off a large branch to connect with the buccal nerve. The medialateral aspect is smooth and glossy. The large part of the lateral aspect is covered by the maxillary nerve and give off several twigs to join the maxillary nerve. The ganglioin give off several branches to supply tensor tympani, tensor veli palatini muscle and levator muscle of velum palatine.14.3 The mandibular ganglion is a large fusiform ganglion, or is a lot of (five to six) small grayish structures. In the lateral aspect of the sublingual gland, it is located between the mylohyoid and cervicum lingual muscles. The ganglia are joined by a communicating branch from the lingual nerves and give off some branches to supply the mandibular and sublingual glands.14.4 The pterygopalatine ganglia are a lot of different size and form ganglions, and frequently are fused or connected to one another by strands of the nerve fibers. In the lateral surface of the medial pterygoid muscle, they are located in the pterygopalatine nerve plexus. The ganglia send off several twigs to the caudal nasal and greater palatine nerves.