Cranial nerves (I - XII).pdf

CRANIAL NERVES SUMMARY Summary of Function of Cranial Nerves 1. Olfactory nerve 2. Optic nerve 3. Oculomotor nerve 4. Trochlear nerve 5. Trigeminal nerve 6. Abducent nerve 7. Facial nerve 8. Vestibulocochlear nerve 9. Glossopharyngeal nerve 10. Vagus ner...

CRANIAL NERVES SUMMARY Summary of Function of Cranial Nerves 1. Olfactory nerve 2. Optic nerve 3. Oculomotor nerve 4. Trochlear nerve 5. Trigeminal nerve 6. Abducent nerve 7. Facial nerve 8. Vestibulocochlear nerve 9. Glossopharyngeal nerve 10. Vagus nerve 11. Accessory nerve 12. Hypoglossal nerve  Classification of cranial nerves Sensory cranial nerves: contain only afferent (sensory) fibers – ⅠOlfactory nerve – ⅡOptic nerve – Ⅷ Vestibulocochlear nerve Motor cranial nerves: contain only efferent (motor) fibers – Ⅲ Oculomotor nerve – Ⅳ Trochlear nerve – ⅥAbducent nerve – Ⅺ Accessory nerv – Ⅻ Hypoglossal nerve Mixed nerves: contain both sensory and motor fibers--- – ⅤTrigeminal nerve, – Ⅶ Facial nerve, – ⅨGlossopharyngeal nerve – ⅩVagus nerve  Cranial Nerve I: Olfactory Arises from the olfactory epithelium Passes through the cribriform plate of the ethmoid bone Fibers run through the olfactory bulb and terminate in the primary olfactory cortex Functions solely by carrying afferent impulses for the sense of smell Cranial Nerve I: Olfactory Figure I from Table 13.2 The olfactory nerve can be damaged through trauma eg TBI; Blunt trauma to the head can lead to laceration of the olfactory nerve as it crosses the ethmoid bone; Infections can also cause damage to the olfactory nerve. COVID-19 Damage Seen in Olfactory System  Cranial Nerve II: Optic Arises from the retina of the eye Optic nerves pass through the optic canals and converge at the optic chiasm They continue to the thalamus where they synapse From there, the optic radiation fibers run to the visual cortex Functions solely by carrying afferent impulses for vision Cranial Nerve II: Optic Figure II Table 13.2 The optic nerve is a bundle of more than 1 million nerve fibers that carry visual messages. There is a connection of the back of each eye (retina) to the brain. Damage to an optic nerve can cause vision loss. The type of vision loss and how severe it is depends on where the damage occurs. It may affect one or both eyes.  There are many different types of optic nerve disorders, including: Glaucoma is a group of diseases that are the leading cause of blindness in the United States. Glaucoma usually happens when the fluid pressure inside the eyes slowly rises and damages the optic nerve. Optic neuritis is an inflammation of the optic nerve. Causes include infections and immune-related illnesses such as multiple sclerosis. Sometimes the cause is unknown. Optic nerve atrophy is damage to the optic nerve. Causes include poor blood flow to the eye, disease, trauma, or exposure to toxic substances. Optic nerve head drusen are pockets of protein and calcium salts that build up in the optic nerve over time  Cranial Nerve III: Oculomotor Fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape The latter 2 functions are parasympathetically controlled Parasympathetic cell bodies are in the ciliary ganglia Cranial Nerve III: Oculomotor Figure III from Table 13.2 Oculomotor paralysis  Cranial Nerve IV: Trochlear Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle Primarily a motor nerve that directs the eyeball Cranial Nerve IV: Trochlear Figure IV from Table 13.2  Cranial Nerve V: Trigeminal Composed of three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3) Fibers run from the face to the pons via the superior orbital fissure (V1), the foramen rotundum (V2), and the foramen ovale (V3) Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication Cranial Nerve V: Trigeminal Figure V from Table 13.2  Ophhtalmic nerve The ophthalmic nerve supplies sensory innervation to the structures of the eye, including the cornea, ciliary body, lacrimal gland, and conjunctiva. It also supplies nerves to the part of the mucous membrane of the nasal cavity, and to the skin of the eyelids, eyebrow, forehead, and nose.  If the ophthalmic nerve is damaged, a person may experience symptoms related to sensory malfunctions. For example, infections of the trigeminal ganglion by the herpes zoster virus (shingles) causes painful sensations along the path of the trigeminal nerve, but mostly affects the areas innervated by the ophthalmic nerve. The infection may result in complete loss of sensation in the affected parts.  Maxillary nerve Branches Zygomatic nerve (zygomaticotemporal nerve, zygomaticofacial nerve), through the inferior orbital fissure. Nasopalatine nerve, through the sphenopalatine foramen. Posterior superior alveolar nerve. Greater and lesser palatine nerves. Pharyngeal nerve. This nerve branch is responsible for sensations in the middle part of the face. Maxillary refers to the upper jaw. The maxillary nerves extend to the cheeks, nose, lower eyelids and upper lip and gums.  What happens if the maxillary nerve is damaged? As a branch of the trigeminal nerve, the maxillary nerve is often implicated in trigeminal neuralgia, a rare condition characterized by severe pain in the face and jaw. In addition, lesions of this nerve can cause intense hot and cold sensations in the teeth.  Mandibular nerve It the only branch of the trigeminal nerve that contains a motor root. In the infratemporal fossa, near the skull base, the main trunk immediately gives off the sensory meningeal branch and motor muscular branches to the medial pterygoid, tensor tympani, and tensor veli palatini muscles.  The sensory root of the mandibular nerve originates from the trigeminal ganglion. It has a short course across the middle cranial fossa, after which it exits the skull via the foramen ovale, and enters the intratemporal fossa. The motor root originates from the motor nucleus of trigeminal nerve. It passes below the trigeminal ganglion without synapsing with it, and then through the foramen ovale. After traversing the foramen, it joins the sensory root of the nerve. The mandibular division then passes between the medial pterygoid and tensor veli palatyni muscles. Here it gives off the meningeal branch and the nerve to medial pterygoid muscle. Soon after, it bifurcates into its two divisions: a smaller anterior division and a larger posterior division. The anterior division ramifies and produces motor branches for the masticatory muscles, as well as one sensory branch, the buccal nerve, which innervates the cheek. The posterior division divides into three sensory branches: the auriculotemporal, lingual and inferior alveolar nerves. Moreover, it gives off a motor branch which innervates the anterior belly of the digastric muscle and the mylohyoid muscle.  What happens if mandibular nerve is damaged? The pain typically involves the lower face and jaw, although sometimes it affects the area around the nose and above the eye. This intense, stabbing, electric shock-like pain is caused by irritation of the trigeminal nerve, which sends branches to the forehead, cheek and lower jaw.  Cranial Nerve VI: Abducens Fibers leave the inferior pons and enter the orbit via the superior orbital fissure Primarily a motor nerve innervating the lateral rectus muscle (abducts the eye; thus the name abducens) Figure VI from Table 13.2 Abducens nerve injury  Cranial Nerve VII: Facial Fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands Sensory function is taste from the anterior two-thirds of the tongue Cranial Nerve VII: Facial Figure VII from Table 13.2  The facial nerve is associated with the derivatives of the second pharyngeal arch: Motor – muscles of facial expression, posterior belly of the digastric, stylohyoid and stapedius muscles. Sensory – a small area around the concha of the external ear. Special Sensory – provides special taste sensation to the anterior 2/3 of the tongue via the chorda tympani Parasympathetic – supplies many of the glands of the head and neck, including: – Submandibular and sublingual salivary glands. – Nasal, palatine and pharyngeal mucous glands. – Lacrimal glands.  The course of the facial nerve is very complex. There are many branches, which transmit a combination of sensory, motor and parasympathetic fibres. Anatomically, the course of the facial nerve can be divided into two parts: Intracranial – the course of the nerve through the cranial cavity, and the cranium itself. Extracranial – the course of the nerve outside the cranium, through the face and neck. Intracranial course The nerve arises in the pons, an area of the brainstem. It begins as two roots; a large motor root, and a small sensory root (the part of the facial nerve that arises from the sensory root is sometimes known as the intermediate nerve). The two roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of the temporal bone. Here, they are in very close proximity to the inner ear. Still within the temporal bone, the roots leave the internal acoustic meatus, and enter into the facial canal. The canal is a ‘Z’ shaped structure. Within the facial canal, three important events occur: Firstly the two roots fuse to form the facial nerve. Next, the nerve forms the geniculate ganglion (a ganglion is a collection of nerve cell bodies). Lastly, the nerve gives rise to: – Greater petrosal nerve – parasympathetic fibres to mucous glands and lacrimal gland. – Nerve to stapedius – motor fibres to stapedius muscle of the middle ear. – Chorda tympani – special sensory fibres to the anterior 2/3 tongue and parasympathetic fibres to the submandibular and sublingual glands. The facial nerve then exits the facial canal (and the cranium) via the stylomastoid foramen. This is an exit located just posterior to the styloid process of the temporal bone. Extracranial After exiting the skull, the facial nerve turns superiorly to run just anterior to the outer ear. The first extracranial branch to arise is the posterior auricular nerve. It provides motor innervation to the some of the muscles around the ear. Immediately distal to this, motor branches are sent to the posterior belly of the digastric muscle and to the stylohyoid muscle. The main trunk of the nerve, now termed the motor root of the facial nerve, continues anteriorly and inferiorly into the parotid gland (note – the facial nerve does not contribute towards the innervation of the parotid gland, which is innervated by the glossopharyngeal nerve). Within the parotid gland, the nerve terminates by splitting into five branches: Temporal branch Zygomatic branch Buccal branch Marginal mandibular branch Cervical branch These branches are responsible for innervating the muscles of facial expression.  Intracranial Lesions Intracranial lesions occur during the intracranial course of the facial nerve (proximal to the stylomastoid foramen). The muscles of facial expression will be paralysed or severely weakened. The other symptoms produced depend on the location of the lesion, and the branches that are affected: Chorda tympani – reduced salivation and loss of taste on the ipsilateral 2/3 of the tongue. Nerve to stapedius – ipsilateral hyperacusis (hypersensitive to sound). Greater petrosal nerve – ipsilateral reduced lacrimal fluid production. The most common cause of an intracranial lesion of the facial nerve is infection related to the external or middle ear. If no definitive cause can be found, the disease is termed Bell’s palsy. Facial nerve injury +/- Bells Palsy  Extracranial Lesions Extracranial lesions occur during the extracranial course of the facial nerve (distal to the stylomastoid foramen). Only the motor function of the facial nerve is affected, therefore resulting in paralysis or severe weakness of the muscles of facial expression. There are various causes of extracranial lesions of the facial nerve: Parotid gland pathology – e.g a tumour, parotitis, surgery. Infection of the nerve – particularly by the herpes virus. Compression during forceps delivery – the neonatal mastoid process is not fully developed and does not provide complete protection of the nerve. Idiopathic – If no definitive cause can be found then the disease is termed Bell’s palsy.  Cranial Nerve VIII: Vestibulocochlear Fibers arise from the hearing and equilibrium apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border Two divisions – cochlear (hearing) and vestibular (balance) Functions are solely sensory – equilibrium and hearing Cranial Nerve VIII: Vestibulocochlear Figure VIII from Table 13.2  Vestibular component – arises from the vestibular nuclei complex in the pons and medulla. Cochlear component – arises from the ventral and dorsal cochlear nuclei, situated in the inferior cerebellar peduncle. Both sets of fibres combine in the pons to form the vestibulocochlear nerve. The nerve emerges from the brain at the cerebellopontine angle and exits the cranium via the internal acoustic meatus of the temporal bone. Within the distal aspect of the internal acoustic meatus, the vestibulocochlear nerve splits, forming the vestibular nerve and the cochlear nerve. The vestibular nerve innervates the vestibular system of the inner ear, which is responsible for detecting balance. The cochlear nerve travels to cochlea of the inner ear, forming the spiral ganglia which serve the sense of hearing.  A basilar skull fracture is a fracture of the skull base, usually resulting from major trauma. The vestibulocochlear nerve can be damaged within the internal acoustic meatus, producing symptoms of vestibular and cochlear nerve damage. Patients may also exhibit signs related to the other cranial nerves, bleeding from the ears and nose, and cerebrospinal fluid leaking from the ears (CSF otorrhoea) and nose (CSF rhinorrhoea).  Cranial Nerve IX: Glossopharyngeal Fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat Nerve IX is a mixed nerve with motor and sensory functions Motor – innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland Sensory – fibers conduct taste and general sensory impulses from the tongue and pharynx Cranial Nerve IX: Glossopharyngeal Figure IX from Table 13.2  Branches of the glosopharyngeal nerve and area of innervation Thympanic nerve Tympanic cavity Auditive tube - which goes via tympanic canaliculus to tympaic cavity, in which takes part in creation of the tympanic plexus. Nest it is continuated in the minor petrosal nerve. Minor petrosal nerve goes to otic ganglion Parotid salivatory gland Buccales glands Carotic branch Carotic sinus Carotic body Muscular branch to the stylopharyngeal muscle Stylopharyngeal muscle and the neighbouring membrane of the pharynx Pharyngeal branches with tonsilares branches Mainly the superior constrictor of the pharynx muscle and the mucouse membrane at the same level (pharyngeal plexus- Muscles of the pharynx except stylopharyngeal muscle) Muscles of the soft palatine except tensor veli palatini muscle Palantine tonsils Lingual- Mucous membrane of the posterior (base) third of the tongue - sensory and taste fibers Innervation by glossopharyngeal n. Palsy of IX nerve Loss of taste on the posterior 1/3 of the tongue Loss of the sensation of the soft palate  Cranial Nerve X: Vagus The only cranial nerve that extends beyond the head and neck Fibers emerge from the medulla via the jugular foramen The vagus is a mixed nerve Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs Its sensory function is in taste Cranial Nerve X: Vagus Figure X from Table 13.2 leaves the skull by lateral part of the jugular foramen( in common sheath with XI ) forms the superior ganglion- in the jugular foramen Palsy of X nerve Soft palate deviation with deviation of the uvula to the normal side Vocal cord paralysis  Vagus nerve lessions palatal and pharyngeal paralysis; laryngeal paralysis; abnormalities of esophageal motility, gastric acid secretion, gallbladder emptying, heart rate and other autonomic dysfunction.  Cranial Nerve XI: Accessory Formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord The spinal root passes upward into the cranium via the foramen magnum The accessory nerve leaves the cranium via the jugular foramen  Cranial Nerve XI: Accessory Primarily a motor nerve – Supplies fibers to the larynx, pharynx, and soft palate – Innervates the trapezius and sternocleidomastoid, which move the head and neck Cranial Nerve XI: Accessory Figure XI from Table 13.2  XI cranial nerve The accesory nerve: the cranial root separates from the spinal root and joints the vagus nerve at its inferior ganglion. It is distributed mainly in the pharyngeal and recurrent laryngeal branches of vagus nerve the spinal root runs downward, crosses the internal jugular vein enters the deep surface of the sternocleidomastoid m. and supplies it. runs by the posterior triangle of the neck on the levator scapulae to the trapezius muscle. It is accompanied by branches from the anterior rami of the 3- rd and 4-th cervical nerves. Supplies the sternocleidomastoid m. and trapezius m.  XI cranial nerve The accesory nerve: Palsy of XI nerve Asymmetry of the shoulder- winged scapula  Cranial Nerve XII: Hypoglossal Fibers arise from the medulla and exit the skull via the hypoglossal canal Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech Cranial Nerve XII: Hypoglossal Figure XII from Table 13.2  XII cranial nerve The hypoglosal nerve: Branches: Meningeal branch- innervates the occipital sinus Descending Muscular branches to the intrinsic and extrinsic muscles of the tongue Palsy of XII nerve Atrophy of ipsilateral muscles of the tongue and deviation toward the effected side Speech disturbances