Most typically, humans are considered to have twelve pairs of<unk>  (I–XII), with the terminal<unk> (0) more recently canonized. The<unk>  are: the olfactory<unk> (I), the optic<unk> (II), oculomotor<unk> (III), trochlear<unk> (IV), trigeminal<unk> (V), abducens<unk> (VI), facial<unk> (VII), vestibulocochlear<unk> (VIII), glossopharyngeal<unk> (IX), vagus<unk> (X), accessory<unk> (XI), and the hypoglossal<unk> (XII). Terminology<unk>  are generally named according to their structure or function. For example, the olfactory<unk> (I) supplies smell, and the facial<unk> (VII) supplies the muscles of the face. Because Latin was the lingua franca of the study of anatomy when the<unk>  were first documented, recorded, and discussed, many<unk>  maintain Latin or Greek names, including the trochlear<unk> (IV), named according to its structure, as it supplies a muscle that attaches to a pulley (). The trigeminal<unk> (V) is named in accordance with its three components ( meaning triplets), and the vagus<unk> (X) is named for its wandering course ().<unk>  are numbered based on their position from front to back (rostral-caudal) of their position on the brain, as, when viewing the forebrain and brainstem from below, they are often visible in their numeric order. For example, the olfactory<unk>  (I) and optic<unk>  (II) arise from the base of the forebrain, and the other<unk> , III to XII, arise from the brainstem.<unk>  have paths within and outside the skull. The paths within the skull are called "intracranial" and the paths outside the skull are called "extracranial". There are many holes in the skull called "foramina" by which the<unk>  can exit the skull. All<unk>  are paired, which means they occur on both the right and left sides of the body. The muscle, skin, or additional function supplied by a<unk>  on the same side of the body as the side it originates from, is an ipsilateral function. If the function is on the opposite side to the origin of the<unk>  this is known as a contralateral function. Intracranial course Nuclei Grossly, all<unk>  have a Nucleus. With the exception of the olfactory<unk> (I) and optic<unk> (II), all the nuclei are present in the brainstem. The midbrain of the brainstem has the nuclei of the oculomotor<unk> (III) and trochlear<unk> (IV); the pons has the nuclei of the trigeminal<unk> (V), abducens<unk> (VI), facial<unk> (VII) and vestibulocochlear<unk> (VIII); and the medulla has the nuclei of the glossopharyngeal<unk> (IX), vagus<unk> (X), accessory<unk> (XI) and hypoglossal<unk> (XII). The olfactory<unk> (I) emerges from the olfactory bulb, and depending slightly on division the optic<unk> (II) is considered to emerge from the lateral geniculate nuclei. Because each<unk> may have several functions, the<unk> fibres that make up the<unk> may collect in more than one nucleus. For example, the trigeminal<unk> (V), which has a sensory and a motor role, has at least four nuclei. Exiting the brainstem With the exception of the olfactory<unk> (I) and optic<unk> (II), the<unk>  emerge from the brainstem. The oculomotor<unk> (III) and trochlear<unk> (IV) emerge from the midbrain, the trigeminal (V), abducens (VI), facial (VII) and vestibulocochlea (VIII) from the pons, and the glossopharyngeal (IX), vagus (X), accessory (XI) and hypoglossal (XII) emerge from the medulla. The olfactory<unk> (I) and optic<unk> (II) emerge separately. The olfactory<unk>  emerge from the olfactory bulbs on either side of the crista galli, a bony projection below the frontal lobe, and the optic<unk>  (II) emerge from the lateral colliculus, swellings on either side of the temporal lobes of the brain. Ganglia The<unk>  give rise to a number of ganglia, collections of the cell bodies of neurons in the<unk>  that are outside of the brain. These ganglia are both parasympathetic and sensory ganglia. The sensory ganglia of the<unk> , directly correspond to the dorsal root ganglia of spinal<unk>  and are known as<unk> ganglia. Sensory ganglia exist for<unk>  with sensory function: V, VII, VIII, IX, X. There are also a number of parasympathetic<unk> ganglia. Sympathetic ganglia supplying the head and neck reside in the upper regions of the sympathetic trunk, and do not belong to the<unk> . The ganglion of the sensory<unk> , which are similar in structure to the dorsal root ganglion of the spinal cord, include: * The trigeminal ganglia of the trigeminal<unk> (V), which occupies a space in the dura mater called Meckel's cave. This ganglion contains only the sensory fibres of the trigeminal<unk>  * The geniculate ganglion of the facial<unk> (VII), which occurs just after the<unk> enters the facial canal. * A superior and inferior ganglia of the glossopharyngeal<unk> (IX), which occurs just after it passes through the jugular foramen. Additional ganglia for<unk>  with parasympathetic function exist, and include the ciliary ganglion of the oculomotor<unk> (III), the pterygopalatine ganglion of the maxillary<unk> (V2), the submandibular ganglion of the lingual<unk>  a branch of the facial<unk> (VII), and the otic ganglion of the glossopharyngeal<unk> (IX). Exiting the skull and extracranial course + Exits of<unk>  from the skull. Location<unk> cribriform plate Terminal<unk> (0) cribriform plate Olfactory<unk> (I) optic foramen Optic<unk> (II) superior orbital fissure Oculomotor (III)Trochlear (IV)Abducens (VI)Trigeminal V1 (ophthalmic) foramen rotundum Trigeminal V2 (maxillary) foramen ovale Trigeminal V3 (mandibular) stylomastoid foramen Facial<unk> (VII) internal auditory canal Vestibulocochlear (VIII) jugular foramen Glossopharyngeal (IX) Vagus (X)Accessory (XI) hypoglossal canal Hypoglossal (XII) After emerging from the brain, the<unk>  travel within the skull, and some must leave it in order to reach their destinations. Often the<unk>  pass through holes in the skull, called foramina, as they travel to their destinations. Other<unk>  pass through bony canals, longer pathways enclosed by bone. These foramina and canals may contain more than one<unk> and may also contain blood vessels. *The terminal<unk> (0), is a thin network of fibers associated with the dura and lamina terminalis running rostral to the olfactory<unk>  with projections through the cribriform plate. * The olfactory<unk> (I), passes through perforations in the cribriform plate part of the ethmoid bone. The<unk> fibres end in the upper nasal cavity. * The optic<unk> (II) passes through the optic foramen in the sphenoid bone as it travels to the eye. * The oculomotor<unk> (III), trochlear<unk> (IV), abducens<unk> (VI) and the ophthalmic branch of the trigeminal<unk> (V1) travel through the cavernous sinus into the superior orbital fissure, passing out of the skull into the orbit. * The maxillary division of the trigeminal<unk> (V2) passes through foramen rotundum in the sphenoid bone. * The mandibular division of the trigeminal<unk> (V3) passes through foramen ovale of the sphenoid bone. * The facial<unk> (VII) and vestibulocochlear<unk> (VIII) both enter the internal auditory canal in the temporal bone. The facial<unk> then reaches the side of the face by using the stylomastoid foramen, also in the temporal bone. Its fibers then spread out to reach and control all of the muscles of facial expression. The vestibulocochlear<unk> reaches the organs that control balance and hearing in the temporal bone and therefore does not reach the external surface of the skull. * The glossopharyngeal (IX), vagus (X) and accessory<unk> (XI) all leave the skull via the jugular foramen to enter the neck. The glossopharyngeal<unk> provides sensation to the upper throat and the back of the tongue, the vagus supplies the muscles in the larynx and continues downward to supply parasympathetic supply to the chest and abdomen. The accessory<unk> controls the trapezius and sternocleidomastoid muscles in the neck and shoulder. *Schematic 3D model of the<unk> The hypoglossal<unk> (XII) exits the skull using the hypoglossal canal in the occipital bone.
Cranial nerves
Peripheral nervous system
Nervous system
Central nervous system
Autonomic nervous system
Integumentary system
Enteric nervous system
Somatosensory system