9-cranial nerves.pdf

Cranial nerves Anatomy Cranial nerves are the 12 nerves of the peripheral nervous system that emerge from the foramina and fissures of the cranium. Their numerical order (1-12) is determined by their skull exit location (rostral to caudal). All cranial nerves originate from nuclei in the brain. Two...

Cranial nerves Anatomy Cranial nerves are the 12 nerves of the peripheral nervous system that emerge from the foramina and fissures of the cranium. Their numerical order (1-12) is determined by their skull exit location (rostral to caudal). All cranial nerves originate from nuclei in the brain. Two originate from the forebrain (Olfactory and Optic), one has a nucleus in the spinal cord (Accessory) while the remainder originate from the brainstem. The function of a nerve is to carry sensory and/or motor information between the body and the brain. If the information goes from the brain to the periphery, then it is an efferent (motor) nerve. If it travels from the periphery to the brain, then it is an afferent (sensory) nerve. Nerves that do both are mixed nerves. Unlike spinal nerves which are always mixed, cranial nerves can be purely motor, purely sensory or mixed. Somatic and visceral The information is classified as special if it travels from our special senses (vision, smell, taste, hearing and balance), while general describes information to/from everywhere else. The information carried by a nerve is called somatic if it goes to/from the skin and skeletal muscles, or visceral if it travels to/from our internal organs. Combining these categories allows us to define the functional components of a nerve. For example, if the nerve fibers exclusively carry special sensory information, it is called a special afferent nerve. If it carries other types of sensory information, like touch, pressure, pain, temperature, then it is a general afferent nerve. If the nerve carries information to smooth muscle, cardiac muscle or glands, then it is a visceral efferent nerve. If it carries information to skin or skeletal muscle, then it is a somatic efferent nerve. As the term visceral is often a synonym for autonomic (nervous system), note that general visceral nerves carry autonomic nerve fibers to/from the target organs. The exception to this are the special visceral efferent nerves, sometime described as branchial efferent (BE). These are motor nerves, named for the embryological origin of the fibres. Information of movement and position (proprioception) from somatic structures like muscles, tendons, and joints is carried by general somatic afferent nerves. Lastly, be aware that there is no special somatic efferent classification. So to conclude, considering the possible directions and modalities, cranial nerves can be:  General somatic afferent (GSA)  General somatic efferent (GSE)  General visceral afferent (GVA)  General visceral efferent (GVE)  Special somatic afferent (SSA)  Special visceral afferent (SVA)  Special visceral efferent (SVE) Cranial nerves list Cranial nerve 1 Olfactory nerve (CN I) - sensory Cranial nerve 2 Optic nerve (CN II) - sensory Cranial nerve 3 Oculomotor nerve (CN III) - motor Cranial nerve 4 Trochlear nerve (CN IV) - motor Cranial nerve 5 Trigeminal nerve (CN V) - mixed Cranial nerve 6 Abducens nerve (CN VI) - motor Cranial nerve 7 Facial nerve (CN VII) - mixed Cranial nerve 8 Vestibulocochlear nerve (CN VIII) - sensory Cranial nerve 9 Glossopharyngeal nerve (CN IX) - mixed Cranial nerve 10 Vagus nerve (CN X) - mixed Cranial nerve 11 (Spinal) Accessory nerve (CN XI) - motor Cranial nerve 12 Hypoglossal nerve (CN XII) - motor  1- Olfactory nerve (CN I) Cranial nerve 1 is a special somatic afferent nerve which innervates the olfactory mucosa within the nasal cavity. It carries information about smell to the brain. The many branches of the olfactory nerve, called fila olfactoria, pass from the nasal cavity through the cribriform plate of the ethmoid bone. They terminate in the olfactory bulb, which continues as the olfactory tract. Within the brain, the fibers of the olfactory tract disperse and end within the olfactory cortex. The olfactory nerve doesn’t have a specific nucleus of its own. Instead its cell bodies are found in the olfactory area-the nasal mucosa that covers the roof of the nasal cavity. 2- Optic nerve (CN II) Cranial nerve 2 is a special somatic afferent nerve which innervates the retina of the eye and brings visual information to the brain. Neural fibers originate from the photoreceptors of the retina. They converge at the optic disc, forming the optic nerve. The optic nerve leaves the orbit through the optic canal. On the floor of the middle cranial fossa, the nasal parts of each nerve cross to the opposite side forming the optic chiasm. The nerve fibers then continue as the two optic pathways. CN II also doesn’t have its own nuclei, but instead its cell bodies are found in the retina. The optic nerve synapses with the visual relay centers of the brain. 3- Oculomotor nerve (CN III) Cranial nerve 3 is both a somatic and visceral efferent motor nerve. This means it has two nuclei and carries two types of efferent fibers. As the name suggests, the oculomotor nerve is the chief motor nerve supplying the eye. It originates from the midbrain and leaves the skull through the superior orbital fissure to enter the orbit where it enables eye movement, constriction of the pupil (miosis) and lens accommodation. 4- Trochlear nerve (CN IV) Cranial nerve 4 is a general somatic motor nerve. The trochlear nerve originates from the midbrain and enters the orbit through the superior orbital fissure, supplying one extraocular muscle thus playing a role in eye movement.  5- Trigeminal nerve (CN V) Cranial nerve 5 is a mixed nerve, containing both special visceral and general somatic fibers. The fibers originate from the brainstem, forming the trigeminal ganglion near the apex of the petrous part of the temporal bone. The trigeminal nerve divides into three divisions; ophthalmic nerve (CN V1), maxillary nerve (CN V2) and mandibular nerve (CN V3). Each of them leaves the skull through a different opening. Ophthalmic leaves through the superior orbital fissure, maxillary through the foramen rotundum and the mandibular nerve exits via the foramen ovale. All three branches of the trigeminal nerve supply sensation to the facial skin. The areas of cutaneous innervation (dermatomes) are as follows; Ophthalmic nerve (CN V1 dermatome) supplies the forehead, orbit and nose, maxillary nerve (CN V2 dermatome) the zygomatic region and upper lip, while the mandibular nerve (CN V3 dermatome) innervates the buccal skin, lower lip and skin of the mandibular region. 6- Abducens nerve (CN VI) Cranial nerve 6 is a general somatic efferent nerve which innervates the lateral rectus muscle (extraocular). The abducens nerve originates from the brainstem and exits the skull via the superior orbital fissure. Although it may seem the least relevant, the abducens nerve plays a very important role in eye movement 7- Facial nerve (CN VII) Cranial nerve 7 is a multimodal nerve, carrying both general and special fibers. It originates from the brainstem as two separate divisions; a larger primary root carrying motor fibers and a smaller intermediate nerve carrying sensory and parasympathetic fibers. The two divisions leave the cranial cavity through the internal acoustic meatus and then travel through the facial canal. Here they join forming the facial nerve proper and leave the cranium together through the stylomastoid foramen. Once the facial nerve reaches the face it enables many functions, such as facial expression, secretion of glands and taste sensation 8- Vestibulocochlear nerve (CN VIII) Cranial nerve 8 is a special somatic afferent nerve. It is comprised of two parts: the vestibular nerve and the cochlear nerve. The cochlear component enables hearing, while the vestibular part mediates balance and motion. At the fundus of internal acoustic meatus, both parts unite to form the vestibulocochlear nerve and enter the cranium through the internal acoustic meatus. The two components synapse with their respective nuclei in the brainstem.  9- Glossopharyngeal nerve (CN IX) Cranial nerve 9 is another multimodal nerve. It originates from the brainstem and leaves the skull through the jugular foramen. It enables swallowing, salivation, and taste sensation, as well as visceral and general sensation in the oral cavity. 10- Vagus nerve (CN X) Cranial nerve 10 is also a multimodal nerve, it originates from multiple nuclei in the brainstem, and exits the skull through the jugular foramen. It is the longest cranial nerve and the only one to leave the head and neck region. The vagus nerve travels into the thoracic and abdominal cavities, providing parasympathetic supply to visceral organs. CN 10 has two ganglia, called the superior ganglion of the vagus nerve and the inferior ganglion of the vagus nerve (nodose ganglion). The former provides fibers for general sensory function, while the latter gives special sensory and visceral output. The vagus nerve controls a large number of functions, including gland secretion, peristalsis, phonation, taste, visceral and general sensation of the head, thorax and abdomen. 11- Accessory nerve (CN XI) Cranial nerve 11 is an efferent nerve originating from the brainstem and spinal cord. It exits the skull through the jugular foramen, acting to enable phonation and movements of the head and shoulders. Sensory fibers of the cervical plexus join the accessory nerve enabling general sensation for its target muscles. 12- Hypoglossal nerve (CN XII) Cranial nerve 12 is a general somatic efferent nerve originating from the brainstem. It leaves the skull through the hypoglossal foramen. Its function is to enable tongue movements. The hypoglossal nerve is extremely important for smooth daily functioning of every person, as it plays a significant role in important mouth functions such as speech and swallowing. Similar to CN XI, the hypoglossal nerve also interacts with the cervical plexus. It receives GSE fibers from C1 and C2 spinal nerves, and GSA fibers from the spinal ganglion of C2 spinal nerve. Nerve name Type Nucleus Field innervation Division olfactory SVA/S None Sensory: Nasal mucosa nerve (CN I) SA* optic nerve SSA None Sensory: Retina (CN II) Oculomotor GSE, nerve (CN III) GVE Nucleus of oculomotor nerve Motor: all extraocular muscles (parasy (GSE) except for the lateral rectus and mpathe Accessory nuclei of superior oblique (GSE); ciliary tic) oculomotor nerve (Edinger- muscle, sphincter pupillae Westphal) (GVE) muscle (GVE) Trochlear GSE Nucleus of trochlear nerve Motor: Superior oblique nerve (CN IV) muscle Trigeminal SVE, Motor nucleus of trigeminal Ophthalmi nerve (CN V) GSA nerve (SVE) Motor: Muscles of mastication, c nerve Principal sensory nucleus of mylohyoid, anterior belly of (CN V1) trigeminal nerve (GSA) digastric, tensor tympani Maxillary Spinal nucleus of trigeminal muscles (SVE) nerve (CN nerve (GSA) Sensory: Scalp, face, orbit, V2) Mesencephalic nucleus of paranasal sinuses, anterior two- Mandibula trigeminal nerve (GSA) thirds of the tongue (GSA) r nerve (CN V3) Abducens GSE Nucleus of abducens nerve Motor: Lateral rectus muscle nerve (CN VI) Facial nerve GVE Superior salivatory nucleus (CN VII) (parasy (GVE) Sensory: middle ear, nasal mpathe Motor nucleus of facial nerve cavity, soft palate (GVA); tic), (SVE) anterior two-thirds of the SVE, Nuclei of solitary tract (GVA, tongue (SVA); external GVA, SVA) auditory meatus (GSA) SVA, Spinal nucleus of trigeminal Motor: lacrimal, GSA nerve (GSA) submandibular, sublingual, basal, palatine glands (GVE); muscles of facial expression (SVE) Vestibulococh SSA Sensory: Spiral organ (of lear nerve Vestibular nuclei Corti), macula of utricle, (CN VIII) Dorsal and ventral cochlear macula of saccule, ampullae of nuclei the semicircular canals (SSA) Glossopharyn SVE, Nucleus ambiguus (SVE, geal nerve GVE GVA) Motor: stylopharyngeus and (CN IX) (parasy Inferior salivatory nucleus pharyngeal constrictors (SVE); mpathe (GVE) parotid gland (GVE) tic), Nuclei of solitary tract (SVA, Sensory: posterior one-third of SVA, GVA) the tongue (SVA); middle ear,  GVA, Spinal nucleus of trigeminal pharynx, epiglottis, carotid GSA nerve (GSA) body, carotid sinus (GVA); posterior one-third of the tongue, soft palate (GSA) Vagus nerve GVE Posterior nucleus of vagus Motor: thoracic and abdominal (CN X) (parasy nerve (dorsal motor nucleus) viscera (GVE); laryngeal and mpathe (GVE) pharyngeal muscles (SVE) tic), Nucleus ambiguus (SVE) Sensory: epiglottis (SVA); SVE, Nuclei of solitary tract (SVA, thoracic and abdominal SVA, GVA) viscera, carotid body (GVA); GVA, Spinal nucleus of trigeminal external acoustic meatus, GSA nerve (GSA) retroauricular skin, posterior part of meninges (GSA) Accessory Ambiguus Motor: Laryngeal muscles, nerve (CN XI) GSE/S Nucleus of the accessory sternocleidomastoid, trapezius VE* nerve (C1-C5) Hypoglossal GSE Motor: Intrinsic tongue nerve (CN Nucleus of hypoglossal nerve muscles, extrinsic tongue XII) muscles (except for the palatoglossus)