Nerves of the Head and Neck Regions PDF

Nerves of the Head and neck regions By Dr. Maher Finjan  Cranial Nerves The 12 pairs of cranial nerves are part of the peripheral nervous system (PNS) and pass through foramina or fissures in the cranial cavity. All nerves except one, the accessory n...

Nerves of the Head and neck regions By Dr. Maher Finjan  Cranial Nerves The 12 pairs of cranial nerves are part of the peripheral nervous system (PNS) and pass through foramina or fissures in the cranial cavity. All nerves except one, the accessory nerve (XI), originate from the brain.  Olfactory Nerve I The olfactory system consists of: 1- Olfactory epithelium. 2-Olfactory bulb. 3-Olfactory tract. 4-Cerebral olfactory area. Olfactory nerve carries special sense afferent fibers for the sense of smell. The smell receptors are in the roof and upper parts of the nasal cavity (The olfactory mucous membrane is present in the upper part of the nose above the superior concha), that form small bundles(they are about 20 olfactory filaments) enter the cranial cavity by passing through the cribriform plate of the ethmoid bone. They terminate by synapsing with olfactory area of the cerebral cortex (parahippocampal gyrus).  Optic Nerve II It carries sensory fibers for vision (special sense). These fibers return information to the brain from photoreceptors in the retina (rods and cons). The optic nerves enter the cranial cavity through the optic canals. Within the orbit it is surrounded by three meninges which carry with them an extension of the subarachnoid space containing CSF. Optic chiasma situated in the chiasmatic groove in the Sella tursica, then optic tract Emerges from the optic chiasma and passes posterolaterally in the base of skull to enter area of vision in the cerebral cortex (occipital lobe).  Oculomotor Nerve III It has two type of nuclei: 1-Motor nuclei (somatic efferent): It supplies all the extra- ocular muscles except superior oblique and lateral rectus. 2-The accessory parasympathetic nucleus: supply the sphincter pupillae and ciliary body (smooth muscles inside the eye ball) via ciliary ganglion. It leaves the anterior surface of the brainstem between the midbrain and the pons (The oculomotor nerve is closely related to the trochlear and abducent nerve, because they all together supply the extraocular muscles), and leaves the cranial cavity through the superior orbital fissure.  Trochlear Nerve IV It arises in the midbrain and is the only cranial nerve to exit from the posterior surface of the brainstem. It Passes (intracranially) between the posterior cerebral and superior cerebellar arteries. Then passes to the cavernous sinus to enter it then exist from the sinus to enter the orbit via the superior orbital fissure and supply superior oblique muscle.  Trigeminal nerve The largest cranial nerve. It have two component motor and sensory. 1-motor part: innervates the muscles of mastication, the tensor tympani, the tensor veli palatini, the mylohyoid, and the anterior belly of the digastric. 2-sensory part: It receives sensory input from the face, anterior one-half of the scalp, mucous membranes of the oral and nasal cavities and the paranasal sinuses, part of the tympanic membrane, the eye and conjunctiva. Intracranial course: Trigeminal nerve Emerge from the anterior surface of the pons by a large laterally situated sensory and small medially situated motor roots. It passes forward out of the posterior cranial fossa below the superior petrosal sinus and carries with it a pouch derived from the meningeal layer of dura matter. The ophthalmic, maxillary, and mandibular nerves arise from the anterior border of the trigeminal ganglion. 1-Ophthalmic nerve (ophthalmic division V1): Divides into 3 branches : lacrimal, frontal and nasocilliary nerves. They enter the orbital cavity through the superior orbital fissure. Sensory to forehead and nasal cavity. 2-Maxillary nerve (maxillary division V2): Purely sensory a pierces the dura matter and runs forward to leave the skull through the foramen rotundum and enters the pterygopalatine fossa. gives infraorbital, superior alveolar nerve sensory to the cheek upper lip and teeth and nasal cavity. 3- Mandibular nerve (mandibular division V3): have Motor and sensory parts, the large sensory root leaves the trigeminal ganglion piercing the dura matter , it passes through the foramen ovale. The small motor root passes beneath the ganglion then through the foramen ovale. Immediately after emerging they join together. Then it descend between the tensor veli palatini medially and the lateral pterygoid laterally (in infratemporal fossa) then divide into a small anterior and large posterior division, many branches arise from the main trunk, the anterior and posterior divisions. Motor to masticator muscles and anterior belly of digastric muscle, sensory to chin and tongue. ophthalmic  Abducent Nerve VI The fibers of the abducent nerve pass anteriorly through the pons and emerge in the groove between the lower border of the pons and the medulla oblongata, It passes forward with the internal carotid artery trough the cavernous sinus in the middle cranial fossa. It enters the orbit through the superior orbital fissure. The abducent nerve has the longest intracranial course and is the smallest nerve (more vulnerable to injury). It supplies the lateral rectus muscle of the eyeball.  Facial Nerve VII Has three nuclei : The main motor nucleus, the parasympathetic nuclei and The sensory nucleus. The sensory root called nervus intermedius (parasympathetic and special sense), Because it lies between the motor root and the vestibulocochlear nerve. The facial nerve leaves the anterior surface of the brain in the groove between the lower border of the pons and the medulla oblongata. Passes laterally in the posterior cranial fossa with the vestibulocochlear nerve and enter the internal acoustic meatus in the petrous part of the temporal bone. At the bottom of the meatus the nerve enters the facial canal that runs laterally through the inner ear. It becomes related to the middle ear and the aditus to the tympanic antrum. Then It emerges from the canal through the stylomastoid foramen, Now it passes forward through the parotid gland to its distribution. 1-The facial nerve (motor root): supply the muscles of the face, the cheek, and the scalp , the stylohyoid , and the posterior belly of digastric muscles , and the stapedius muscle of middle ear. 2-The sensory root: carries nerve fibers from the: a-anterior two thirds of the tongue ( special sensation) (chorda tympani) the floor of the mouth and the palate. b-The parasympathetic secretomotor fibers (chorda tympani) supply the submandibular and sublingual salivary glands through submandibular ganglion via lingual nerve. c- The parasympathetic secretomotor fibers (greater superficial petrosal nerve) supply the lacrimal gland , and the glands of the nose and palate through sphenopalatine ganglion via maxillary nerve..  Facial nerve and nervous intermedius Chorda tympani  Vestibulocochlear Nerve VIII It carries sensory fibers (special sense) for hearing and balance, and consists of two divisions: 1-Vestibular component for balance, and 2-Cochlear component for hearing. 1-vestibular fiber: Its fibers are the central processes of nerve cells located in the vestibular ganglion in the internal acoustic meatus. They enter the anterior surface of the brainstem in a groove between the lower border of the pons and the upper part of the medulla oblongata. 2-cochlear nerve: Its fibers are the central processes of nerve cells located in the spiral ganglion of the cochlea. They enter the anterior surface of the brain stem at the lower border of the pons on the lateral side of the emerging facial nerve and are separated from it by the vestibular nerve.  Vestibulocochlear nerve Spiral ganglion of cochlear nerve  GLASSOPHARYNGEAL NERVE IX Three nuclei (motor, sensory, parasympathetic) 1-Intracranial course: glossopharyngeal nerve leaves anterolateral surface of the upper part of the medulla oblongata as a series of rootlets in a groove between the olive and the inferior cerebellar peduncle.It passes laterally in the posterior cranial fossa and leaves skull by passing through the jugular foramen. 2-Extracranial course it descends through upper part of the neck to the back of tongue where it supplies stylopharyngeus muscle , parotid gland , posterior third of the tongue and the pharynx , carotid sinus and body.  BRANCHES & DISTRIBUTION 1-Tympanic nerve : forms tympanic plexus & supply middle Ear, Eustachian Tube, mastoid antrum & air cells. Lesser petrosal nerve – preganglionic secretomotor fibers to otic ganglion to parotid gland. 2-Carotid branch : to Internal Carotid Artery & supply carotid sinus & carotid body 3-Pharyngeal branch : forms pharyngeal plexus along with vagus & sympathetic , distributed over mucosa of pharynx 4-Muscular branch : to stylopharyngeus 5-Tonsillar branch : to tonsil , join to lesser palatine nerve to form plexus from which fibers are distributed to soft palate & to palatoglossal arches. 6-Lingual branch : taste & general sensation posterior one third of tongue including circumvallate papillae.  The vagus nerve X It is the largest cranial nerve. It innervates structures in the head , neck, chest , abdomen and pelvis. 1-As motor: Innervates one muscle of the tongue (palatoglossus muscle), the muscles of the soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), and larynx. 2-As parasympathetic: It innervates the smooth muscles of the bronchial passages and lining of the gut, also smooth muscles and glands in much of the respiratory and gastrointestinal tract, It can slowdown the heart rate. 3-Sensory part of the vagus: supply the mucosa of the epiglottis, larynx, tracheobronchial tree and gastrointestinal tract as far as the mid transverse colon, and some axons to the outer surface of the tympanic membrane and floor of the external auditory meatus. 4-As special taste: It also provides some taste sensation to the epiglottis. The vagus nerve has three nuclei : The main motor nucleus, parasympathetic nucleus , & sensory nucleus. 1-Intracranial course: It leaves the medulla as a series of rootlets in a groove between the olive and the inferior cerebral peduncle. It leaves the skull through the jugular foramen together with the accessory nerve and the glossopharyngeal nerve 2- Extracranial course It passes down the neck in the carotid sheath. It enter the thorax. 1-In the thorax: the right and left vagus nerves lie on the posterior surface of the root of the lung and passing through the esophageal opening of the diaphragm , they enter the abdomen. 2-In the neck: the vagus nerve gives of the recurrent laryngeal nerves. Right recurrent laryngeal arise at the root of the neck. beneath the subclavian artery and pass upward Left recurrent laryngeal nerve arise as the vagus crosses the aortic arch and pass beneath the arch of the aorta upward.  The accessory nerve XI The 11th cranial nerve has 2 roots: a cranial root arising from the medulla oblongata and a spinal root arising from upper five cervical segments of spinal cord. The nerve fibers pass through the white column and emerge to form a nerve trunk that ascends into the skull through the foramen magnum then joins the cranial root and pass through the jugular foramen. Extracranial course: The cranial part join the vagus nerve intracranially then the Spinal portion pass through the jugular foramen with glossopharyngeal and vagus nerves, then enters the neck, runs downward and laterally and crosses the internal jugular vein, Then enter the deep surface of the sternomastoid ( which it supplies), Then it crosses posterior triangle of the neck on the levator scapulae to supply trapezius.  hypoglossal nerve (xii) Supplies all the intrinsic muscles of the tongue ,the styloglossus ,hyoglossus and the genioglossus muscles. It is a pure motor nerve with no sensory innervations. Nucleus of hypoglossal nerve is situated in medulla oblongata Intracranial course Hypoglossal nerve forms from a series of rootlets emerging from the ventrolateral medulla (between the pyramid and the olive ). It exits the skull base through the hypoglossal canal in the occipital bone. Extracranial course It descends between the internal carotid artery and internal jugular vein until it reaches the lower border of the posterior belly of digastric muscle where it turns forward and medially. Extracranial course As it descends in the carotid sheath , it is joined by the descending cervical nerve ( C2 , C3 ) from the cervical plexus to form a loop called ansa cervicalis , branches from the loop supplies the omohyoid , sternohyoid , and the sternothyroid muscles Cervical plexus There are 8 cervical spinal nerves: the first of them is sometimes called the suboccipital nerve (because it leaves the vertebral canal below the occipital bone). The first cervical nerve does not give cutaneous branches. Each one of the 8 cervical nerves receives a grey ramus from the sympathetic chain. Each cervical nerve divides into a posterior and an anterior primary ramus. The posterior rami pass backwards to reach the muscles of the back of the neck. The anterior rami run laterally to form plexuses: 1-upper four cervical nerves form the cervical plexus. 2-lower four cervical nerves form the brachial plexus (with the first thoracic nerve). So the cervical plexus is formed by the anterior primary rami of the upper four cervical nerves and is placed opposite the upper four cervical vertebrae on the scalenus medius, behind the prevertebral fascia. It is covered by the upper part of sternocleidomastoid, and does not lie in the posterior triangle. The branches of cervical plexus: 1-meningeal branches: The upper three cervical nerves have meningeal branches for the posterior cranial fossa. C1 fibers ascend with the hypoglossal nerve, C1 and 2 fibers ascend with the vagus nerve and C2 and 3 fibers ascend through the foramen magnum. 2-Muscular branches: a-are given off segmentally to the prevertebral muscles (longus capitis, longus colli and the scalenes). Other muscular branches are: b-A branch from Cl to the hypoglossal nerve: By which the fibers are carried to the superior root of the ansa cervicalis and the nerves from it to thyrohyoid and geniohyoid and upper part of omohyoid, sternothyroid and sternohyoid muscles (As the hypoglossal nerve descends and passes forward across the internal and external carotid arteries, some of the cervical nerve fibers leave it and descend between the internal jugular vein and the internal, and then common carotid arteries). C-Branches from C2 and 3 to sternocleidomastoid. d- and from C3 and 4 to trapezius, these fibers are mainly proprioceptive, but occasionally the whole of trapezius is not paralyzed when the accessory nerve is damaged, some of the cervical fibers may be motor. The inferior root of the ansa cervicalis is formed by union of a branch each from C2 and C3 (supply inferior belly of omohyoid, lower part of sternothyroid and sternohyoid muscles). The inferior root spirals around the lateral side of the internal jugular vein and descends to join the superior root (Cl) at the ansa. e-The phrenic nerve is formed mainly from C4 with contribution from C3 and C5 and runs down vertically over the obliquity of the scalenus anterior muscle, passing from lateral to medial borders, beneath the prevertebral fascia, lateral to the ascending cervical branch of the inferior thyroid artery. It passes behind the subclavian vein into the mediastinum. It may be joined below the subclavian vein by a branch (the accessory phrenic nerve) from the nerve to subclavius; this branch may descend in front of the subclavian vein. The phrenic nerve is one of the most important in the body, being the sole motor supply to its own half of the diaphragm, and it also has an extensive afferent distribution, not only to the diaphragm but to the pericardium, pleura and peritoneum. f-Also the cervical plexus supplies the following muscles: rectus capitis anterior, rectus capitis lateralis, and levator scapulae muscles. 3-Cutaneous branches: supply the front and sides of the neck and contribute to the supply of the scalp, face and chest. a-The lesser occipital nerve (C2) is a slender branch that hooks around the accessory nerve and runs up along the posterior border of sternocleidomastoid to supply the posterior part of the upper neck and adjacent scalp behind the auricle. It may contribute to the supply of the auricle. b-The great auricular nerve (C2, 3, mostly 2) is a large trunk passing almost vertically upwards over sternocleidomastoid; it is distributed to an area of skin on the face over the angle of the mandible and the parotid gland and to the parotid fascia. It also supplies the skin of the auricle over the whole of its cranial surface and on the lower part of its lateral surface below the external acoustic meatus, and skin over the mastoid region. Branches passing deep to the parotid gland supply the deep layer of the parotid fascia. c-The transverse cervical nerve (C2, 3) curves round the posterior border of sternocleidomastoid, perforates the investing fascia and divides into ascending and descending branches that innervate the skin of the front of the neck from chin to sternum. The ascending branch communicates with the cervical branch of the facial nerve. d-The supraclavicular nerve (C3, 4, but mostly 4) emerges with the other three nerves at the posterior border of sternomastoid and soon divides into several branches. They are distributed in three main groups. The medial group supply the skin as far down as the sternal angle. The intermediate group proper pass anterior to the clavicle and supply skin as far down as the second rib. The lateral group cross the acromion to supply skin halfway down the deltoid muscle, and pass posteriorly to supply skin as far down as the spine of the scapula. Parasympathetic Ganglia of the Head & neck Each parasympathetic ganglion have three roots entering the ganglion and a variable number of exiting branches: 1-The parasympathetic root carries presynaptic parasympathetic nerve fibers 2-The sympathetic root carries postsynaptic sympathetic fibers 3-The sensory root carries general sensory fibers, the fibers pass in a direction opposite to the direction of the fibers in parasympathetic and sympathetic roots. As a general rule each parasympathetic ganglion in the head and neck is suspended from a branch of the trigeminal nerve as follows: 1-ciliary ganglion is suspended from the nasocilliary nerve. 2-sphenopalatine ganglion is suspended from the maxillary nerve. 3-submandibular ganglion is suspended from the lingual nerve. 4-otic ganglion is suspended from the mandibular nerve. Parasympathetic part of oculomotor nerve: arises from Edinger-Westphal nucleus in midbrain. Leaves the mid brain as preganglionic fibers in the oculomotor nerve, then to inferior division of oculomotor, then to nerve to inferior oblique muscle, which gives parasympathetic root to ciliary ganglion. The fibers synapse (relay) in the ganglion which has the size of the head of pin and is flattened against the optic nerve by the lateral rectus muscle. postganglionic fibers pass as short ciliary nerves to supply two muscles: 1-sphincter pupillae (for light reflex). 2-ciliary muscle (for accommodation). Parasympathetic branches of fascial nerve: parasympathetic nucleus of fascial nerve is called superior salivary nucleus and is found in the reticular formation of the pons. Branches of facial nerve inside petrous temporal bone (parasympathetic branches): a-greater superficial petrosal nerve leaves facial nerve in petrous bone then leaves middle cranial fossa by descending in foramen lacerum until reaches opening of pterygoid canal (vidian canal). At this place joined by a sympathetic nerve called deep petrosal nerve (from plexus of sympathetic nerves around the wall of internal carotid artery) these greater petrosal and deep petrosal together called nerve to pterygoid canal (vidian canal), this nerve then passes to pterygopalatine fossa where its parasympathetic fibers end in sphenopalatine ganglion and synapse and the postganglionic fibers join maxillary nerve and distributed to supply glands in nose, orbit, palate, pharynx, and lacrimal gland. b-chorda tympani nerve is small nerve arises from facial nerve as it lies in posterior wall of middle ear. Traverses middle ear on upper part of inner surface of ear drum. At anterior border of ear drum the chorda tympani enters minute canal which leads it out the skull at petro-tympanic fissure. It then turs downwards and forwards (deep to middle meningeal artery) to reach infratemporal fossa and join the lingual nerve by which its fibers carried to anterior two third of tongue and (taste fibers special sense) and to submandibular and sublingual glands (parasympathetic motor fibers through postganglionic fibers after synapsing with submandibular ganglion). Parasympathetic branch of glossopharyngeal nerve: Glossopharyngeal nerve give tympanic branch (called Jacobson nerve) contributes to tympanic plexus in the middle ear. From this plexus the tympanic branch of glossopharyngeal nerve passes through a hiatus in the petrous part of the temporal bone which transmits the lesser superficial petrosal nerve. Lesser superficial petrosal nerve is located posterior to the groove for the superior petrosal sinus and posterolateral to the jugular foramen. The lesser superficial petrosal nerve passes medially to mandibular foramen (foramen ovale), where it descends to end in otic ganglion that found at medial side of mandibular nerve. Postganglionic fibers from this otic ganglion join the mandibular nerve and distributed with its auriculotemporal branch to the parotid gland.  Cervical Sympathetic Trunk There are two sympathetic chains, one on each side of vertebral column. Each chain extends from the level of atlas vertebra above to the front of coccyx below where the two chains unite to form a single coccygeal ganglion called the ganglion impar. There are 3 pairs cervical ganglion, 10-12 pairs thoracic, 4 pairs lumber, sacral 3-4 pairs and 1 coccygeal. Cervical part of sympathetic chain lies almost vertically in the neck between the prevertebral fascia and carotid sheath. It lies behind the common and internal carotid arteries, outside the carotid sheath, medial to vagus nerve and opposite the roots of transverse processes of cervical vertebrae. The origin of preganglionic fibers of cervical part of sympathetic chain: The preganglionic fibers from the upper thoracic segments run mainly upwards in the sympathetic chain to synapse with three cervical sympathetic ganglia. Postganglionic fibers leave these ganglia, as grey rami, to the cervical nerves (and also to the lower cranial nerves). a-The upper four ganglia become fused to form superior cervical ganglion that gives grey rami to the upper four cervical nerves. b-The 5 and 6 ganglia become fused to form the middle cervical ganglion that gives grey rami to 5 and 6 cervical nerves. c-the 7 and 8 ganglia become fused to form the inferior cervical ganglion that gives grey rami to the 7 and 8 cervical nerves. 1-Superior cervical ganglion: Very large lies in front of C2,3 and lies behind internal carotid artery immediately below the skull, its continuation upwards inside the skull is called the internal carotid nerve, give branches to the internal carotid and external carotid arteries, forming plexuses around these vessels, grey rami to the cervical spinal nerves C1 to C4, gives branches to the pharynx and the heart as superior cardiac nerve. 2-Middle cervical ganglion: It is a very small ganglion which lies on the inferior thyroid artery, behind the common carotid artery at the level of cricoid cartilage (C6 vertebra), give grey rami to cervical spinal nerves C5 and C6 and the heart as middle cardiac nerves, and thyroid branches run with the inferior thyroid artery to the thyroid gland. 3-Inferior cervical ganglion: Is between the neck of rib 1 and the transverse process of C7, lies usually behind the common carotid artery and the lower part of the vertebral artery. It give branches to spinal nerves C7 to T1, the vertebral artery, forming a plexus associated with it, and the heart as inferior cardiac nerves. It may becomes very large when it combines with the first thoracic ganglion and forms the cervicothoracic ganglion (stellate ganglion). Ansa subclavian: Some of the fibers which pass between the middle and the inferior ganglia form a slender cord which passes in front of the subclavian artery and then turns upwards behind it. the ansa subclavia and some filaments from the inferior ganglion form a subclavian (sympathetic) plexus around the subclavian artery.