CN I: Olfactory Nerve
The olfactory nerves are short connections that project from the olfactory mucosa within the nose and the olfactory bulb within the cranial cavity. There are 9 to 15 of these nerves on each side of the brain. The olfactory bulb lies just superior to the cribriform plate and below the frontal lobe. Axons from the olfactory bulb run within the olfactory stalk, synapse in the anterior olfactory nucleus, and terminate in the primary olfactory cortex (pyriform cortex) as well as the entorhinal cortex and amygdala.
CN II: Optic Nerve
The optic nerve contains myelinated axons that come from the ganglion cells in the retina. It passes through the optic papilla to the orbit, where it is contained within the meningeal sheaths. The nerve changes its name to optic tract when the fibers have passed through the optic chiasm. Optic tract axons project to the superior colliculus and to the lateral geniculate nucleus within the thalamus, which relays visual information to the cortex.
CN III: Oculomotor Nerve
The oculomotor nerve contains axons that arise in the oculomotor nucleus (which innervates all of the oculomotor muscles except the superior oblique and lateral rectus) . The oculomotor nerve leaves the brain on the medial side of the cerebral peduncle, behind the posterior cerebral artery and in front of the superior cerebellar artery. It then passes anteriorly, parallel to the internal carotid artery in the lateral wall of the cavernous sinus, leaving the cranial cavity by way of the superior orbital fissure.
The somatic efferent portion of the nerve innervates the levator palpebrae superioris muscle; the superior, medial, and inferior rectus muscles; and the inferior oblique muscle. The visceral efferent portion innervates two smooth intraocular muscles: the ciliary and the constrictor pupillae.
CN IV: Trochlear Nerve
The trochlear nerve is the only crossed cranial nerve. It originates from the trochlear nucleus, which is a group of specialized motor neurons located just caudal to the oculomotor nucleus within the lower midbrain. Trochlear nerve axons arise from these neurons, cross within the midbrain, and then emerge contralaterally on the dorsal surface of the brain stem. The trochlear nerve then curves ventrally between the posterior cerebral and superior cerebellar arteries. It continues anteriorly in the lateral wall of the cavernous sinus and enters the orbit via the superior orbital fissure. It innervates the superior oblique muscle.
CN V: Trigeminal Nerve
The trigeminal nerve contains a large sensory root, which carries sensation from the skin and mucosa of most of the head and face, and a smaller motor root, which innervates most of the chewing muscles (masseter, temporalis, pterygoids, mylohyoid), and the tensor tympani muscle of the middle ear.
CN VI: Abducens Nerve
The abducens nerve arises from neurons of the abducens nucleus located within the dorsomedial tegmentum within the caudal pons. These axons project through the body of the pons and leave it as the abducens nerve. This nerve emerges from the pontomedullary fissure, passes through the cavernous sinus close to the internal carotid, and exits from the cranial cavity via the superior orbital fissure. Its long intracranial course makes it vulnerable to pathologic processes in the posterior and middle cranial fossae. The nerve innervates the lateral rectus muscle.
CN VII: Facial Nerve
Both parts of the facial nerve pass through the internal auditory meatus, where the geniculate ganglion for the taste component lies. The facial nerve contains axons that arise in the facial nucleus. The nerve exits through the stylomastoid foramen; it innervates the muscles of facial expression, the platysma muscle, and the stapedius muscle in the inner ear.
CN VIII: Vestibulocochlear Nerve
Cranial nerve VIII passes into the cranial cavity via the internal acoustic meatus and enters the brain stem behind the posterior edge of the middle cerebellar peduncle in the pontocerebellar angle. The cochlear nerve is concerned with hearing; the vestibular nerve is part of the system of equilibrium.
CN IX: Glossopharyngeal Nerve
Cranial nerve IX contains several types of fibers. Branchial efferent fibers from the ambiguus nucleus pass to the stylopharyngeal muscle.
CN X: Vagus Nerve
Efferent fibers from the ambiguus nucleus contribute rootlets to the vagus nerve and the cranial component of the accessory nerve (XI). Those of the vagus nerve pass to the muscles of the soft palate and pharynx. Those of the accessory nerve join the vagus outside the skull and pass, via the recurrent laryngeal nerve, to the intrinsic muscles of the larynx.
CN XI: Accessory Nerve
The accessory nerve consists of two separate components: the cranial component and the spinal component. In the cranial component, branchial efferent fibers (from the ambiguus nucleus to the intrinsic muscles of the larynx) join the accessory nerve inside the skull but are part of the vagus outside the skull. In the spinal component, the branchial efferent fibers from the lateral part of the anterior horns of the first five or six cervical cord segments ascend as the spinal root of the accessory nerve through the foramen magnum and leave the cranial cavity through the jugular foramen. These fibers supply the sternocleidomastoid muscle and partly supply the trapezius muscle.
CN XII: Hypoglossal Nerve
Somatic efferent fibers from the hypoglossal nucleus in the ventromedian portion of the gray matter of the medulla emerge between the pyramid and the olive to form the hypoglossal nerve . The nerve leaves the skull through the hypoglossal canal and passes to the muscles of the tongue. A few proprioceptive fibers from the tongue course in the hypoglossal nerve and end in the trigeminal nuclei of the brain stem. The hypoglossal nerve distributes motor branches to the geniohyoid and infrahyoid muscles with fibers derived from communicating branches of the first cervical nerve. A sensory recurrent meningeal branch of nerve XII innervates the dura of the posterior fossa of the skull.
The table below gives a great summary of the CN's.
Informative and interesting Blog! Beautifully written, as usual, I like the post.
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