Anatomy of cranial nerves ani

1. By Dr. Anilesh pratap singh 1st yr PGRD

2. Names of cranial nerves Olfactory nerve Optic nerve Oculomotor nerve Trochlear nerve Trigeminal nerve Abducent nerve Facial nerve Vestibulocochlear nerve Glossopharyngeal nerve Vagus nerve Accessory nerve Hypoglossal nerve

3. INTRODUCTION:- 12 in number. Are part of the peripheral nervous system All exit the cranial cavity through foramina or fissures All originate from the brain except cranial nerve 11( Accessory nerve) Contain sensory, motor or both components

4. ORIGIN:- The first and second cranial nerves derive from the telencephalon and diencephalon respectively. olfactory nerve (CN I) optic nerve (CN II) The third and fourth cranial nerves originate from the midbrain. oculomotor nerve (CN III) trochlear nerve (CN IV) The middle four cranial nerves originate from the pons trigeminal nerve (CNV) abducens nerve (CNVI) facial nerve (CNVII) vestibulocochlear nerve (CNVIII)

5. The final four cranial nerves originate from the medulla oblongata glossopharyngeal nerve (CN IX) vagus nerve (CN X) accessory nerve (CN XI) hypoglossal nerve (CN XII) In utero, 6 pharyngeal arches are designated but the 5th never develops. Each pharyngeal arch is associated with a developing cranial nerve or one of its branches. 1st arch-Trigeminal nerve(V3) 2nd arch- Facial nerve 3rd arch- Glossopharyngeal nerve 4th arch- Superior Laryngeal Branch ofVagus nerve 6th arch- Recurrent Laryngeal Branch ofVagus nerve

6. Classification of cranial nerves Sensory cranial nerves: contain only afferent (sensory) fibers Olfactory nerve Optic nerve Vestibulocochlear nerve Motor cranial nerves: contain only efferent (motor) fibers Oculomotor nerve Trochlear nerve Abducent nerve Accessory nerv Hypoglossal nerve Mixed nerves: contain both sensory and motor fibers--- Trigeminal nerve, Facial nerve, Glossopharyngeal nerve Vagus nerve

7. Olfactory nerve-CN I Carries special afferents (SA) for smell Peripheral processes act as receptors in the nasal mucosa Receptors are located in the roof and upper parts of the nasal cavity Central processes return information to the brain Central processes enter cranial cavity through the Cribiform plate of the ethmoid Terminate by synapsing with neurons in the olfactory bulb Lesions result in ANOSMIA

8. Olfactory nerve Olfactory mucosa (SVA) Cribriform foramina Olfactory bulb

9. Olfactory nerve. Axial (a) and coronal (b) 0.8-mm-thick SSFP MR images show the olfactory nerve (white arrow) within the CSF-filled olfactory groove . .

10. Olfactory nerve. Coronal 1.0-mm-thick SSFP MR image shows the cisternal segment of the olfactory nerve (arrow), which is located inferior to and between the gyrus rectus (r) and the medial orbital gyrus (o).

11. Optic nerve-CN II Special afferents for vision Returns information from photoreceptors in the retina to the brain Optic nerve enter the cranial cavity through the optic canals Lesion leads to blindness,visual field abnormalties and loss of light reflex

12. Optic nerve. Axial oblique 0.8-mm-thick SSFP MR image shows three of four segments of the optic nerve: the retinal (black arrow), orbital (black arrowheads), and canalicular (white arrowhead) segments. The infundibulum of the pituitary gland (white arrow) also is seen

13. Oculomotor nerve- CN III Moves the eyeball in all directions Adduction is the most important action Constricts pupil (sphincter pupillae) Accomodates (ciliary muscle) Raises eyelids (LPS) Carries 2 types of fibers GSE innervating most of the extra ocular muscles (LPS,SR,IR,MR,IO) GVE part of the parasympathetic part of Autonomic Nervous System -synapse in the ciliary ganglion (pupillary constriction and accommodation) Exits the cranial cavity via the lateral wall of the cavernous sinus through the superior orbital fissure Lesion involves ptosis, external strabismus etc

14. Oculomotor nerve. Axial oblique 0.8-mm-thick SSFP MR image shows the nerve (small arrows) where it emerges from the interpeduncular cistern (large arrow), which lies medial to the cerebellar peduncle (p).

15. Oculomotor nerve. Coronal 0.8-mm-thick SSFP MR image shows the oculomotor nerve (white arrow) in cross section between the posterior cerebral artery (white arrowhead) and the superior cerebellar artery (black arrowhead), which are distal branches of the basilar artery (black arrow).

16. OCCULOMOTOR NERVE PALSY

17. Trochlear nerve CN IV GSE to Superior Oblique muscle Enters the orbit via the lateral wall of the cavernous sinus Only cranial nerve to exit from the posterior surface of the brainstem. Inability to look inferiorly when the eye is adducted. Trochlear nerve. Axial 0.8-mm-thick SSFP MR image shows both trochlear nerves (arrows) where they emerge from the dorsal midbrain to cross the ambient cisterns.The characteristic course of the trochlear nerves allows their differentiation from the nearby superior cerebellar artery (arrowheads).

18. Trigeminal nerve CNV Major general sensory nerve of the head, motor innervation to muscles that move the lower jaw GSA-sensory input from the face, the scalp, mucous membrane of oral and nasal cavity ,PNS, part of theTM, eye and conjunctiva, dura mater in the anterior and middle cranial fossa 2 roots- Large sensory - small motor In middle cranial fossa sensory root expands into theTrigeminal ganglion.(trigeminal depression) 3 divisions:- V1- ophthalmic nerve V2- maxillary nerve V3- mandibular nerve

19. Trigeminal nerve. Axial 0.8-mm-thick SSFP MR image shows the sensory (arrowhead) and motor (large arrow) roots of the trigeminal nerve where they cross the prepontine cistern and enter the Meckel cave (small arrows).

20. Ophthalmic nerve (V1) exits the cranial cavity into the orbit via the lateral wall of the cavernous sinus and superior orbital fissure Sensory from the eyes, conjunctiva and orbital contents including the lacrimal gland Maxillary nerve(V2) Exits the cranial through foramen rotundum Sensory branches from anterior and middle cranial fossa, nasopharynx, palate, nasal cavity, teeth of the upper jaw, maxillary sinus, skin of the side of the nose, lower eyelid, cheek, upper lip Mandibular nerve(V3) Exits skull through foramen ovale Motor root of CNS also exits through foramen ovale and unites with the sensory component of V3 outside the skull Only division that contains a motor component Motor fibers innervate muscles of mastication, tensor tympani, anterior belly of digastric

21. Sensory fibres from the skin of the lower face, cheek lower lip, ear, external auditory meatus and temporal region, anterior two thirds of the tongue, teeth of the lower jaw, mastoid air cells, mucus membrane and dura in the middle cranial fossa Lesion involves loss of sensation, weakness in chewing, Jaw deviation towards the affected side, Trigeminal neuralgia Trigeminal nerve. Coronal 0.8-mm-thick SSFP MR image at the level of the Meckel cave shows the complex web of trigeminal nerve branches (arrows), which coalesce anteriorly to form the gasserian ganglion.The temporal horn of the lateral ventricle (arrowhead) is also shown.

22. Abducent nerve-CN VI GSE Lateral Rectus in orbit Crosses the cavernous sinus as it enters the orbit through the superior orbital fissure Lesion-internal strabismus

23. Abducens nerve. Axial 0.8-mm-thick SSFP MR image at the level of the pontomedullary junction shows both abducens nerves (arrows) where they traverse the prepontine cistern.The bottom of the pons (p) and the top of the medulla (m) are visible in this section, and the cerebellopontine angle (CPA) and basilar artery (arrowhead) are important anatomic landmarks.

24. Abducens nerve. Axial 0.8-mm-thick SSFP MR image shows the abducens nerve where it enters the Dorello canal (arrow) along the posterior aspect of the clivus.Vascular landmarks include the basilar artery (black arrowhead) and the anterior inferior cerebellar artery (white arrowhead).

25. Facial nerve- CN VII Carries GSA,SA,GVE and BE GSA-sensory input from external auditory meatus and small skin posterior to the ear. SA-taste from anterior two thirds of the tongue GVE-parasympathetic part of Autonomic Nervous System -stimulate secretomotor activity in the lacrimal gland, submandibular and sublingual glands, mucus membranes of the nasal cavity, hard and soft palates BE-muscles of the face, scalp, stapedius, posterior belly of the digastric and stylohyoid muscles 2 roots- Large motor - Smaller sensory (the intermediate nerve)

26. Intermediate nerve contains SA (taste), GVE (parasympathetic) and GSA Large motor root contains the BE fibres Both roots exit the posterior cranial fossa through the internal auditory meatus and fuse within the facial canal (petrous part of the temporal bone) facial nerve Expands into the geniculate ganglion Greater petrosal nerve preganglionic parasympathetic Nerve to stapedius and chorda tympani in the facial canal Exits the skulls through the stylomastoid foramen Chorda tympani carries taste (SA) fibres from the anterior two thirds of the tongue and preganglionic parasympathetic (GVE) to the submandibular ganglion.

27. Axial 0.8-mm-thick SSFP MR image shows the parallel courses of the facial (black arrowheads) and superior vestibular (white arrowheads) nerves as they cross the cerebellopontine angle to enter the internal auditory canal through the porus acusticus (double arrow).

28. Vestibulocochlear nerve-CNVIII SA for hearing and balance 2 divisions -vestibular component for balance -cochlear component for hearing

29. Glossopharyngeal nerve CN (IX) carries GVA, SA, GVE, and BE fibers: GVA fibers provide sensory input from the carotid body and sinus, posterior one-third of the tongue, palatine tonsils, upper pharynx, and mucosa of the middle ear and pharyngotympanic tube; SA fibers are for taste from the posterior one-third of the tongue; GVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate secretomotor activity in the parotid salivary gland BE fibers innervate the muscle derived from the third pharyngeal arch (the stylopharyngeus muscle)

30. Coronal oblique 0.8-mm-thick SSFP MR image through the cerebellopontine angle shows the glossopharyngeal nerve (arrow) just beneath the flocculus (f) of the cerebellum.The two roots of the vagus nerve (arrowheads) are visible in the same plane, and the superior and inferior vestibular nerves canbe seen above the flocculus. Tympanic nerve: branch from CN IX within the jugular foramen Forms part of the tympanic plexus within the middle ear cavity Contributes GVE which leaves tympanic plexus in the lesser petrosal nerve carrying preganlionic parasympathetic fibres to the otic ganglion parotid

31. Vagus nerve- CN X carries GSA, GVA, SA, GVE, and BE fibers: GSA fibers provide sensory input from the skin posterior to the ear and the external acoustic meatus; GVA fibers provide sensory input from the aortic body chemoreceptors and aortic arch baroreceptors, and the mucous membranes of the pharynx, larynx, esophagus, bronchi, lungs, heart, and abdominal viscera in the foregut and midgut; SA fibers are for taste around the epiglottisGVE fibers are part of the parasympathetic part of the autonomic division of the PNS and stimulate smooth muscle and glands in the pharynx, larynx, thoracic viscera, and abdominal viscera of the foregut and midgut;

32. BE fibers innervate one muscle of the tongue (palatoglossus), the muscles of the soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), and larynx. Lesion- dysphagia, hoarseness, uvula points away from the affected side, loss of gag and cough reflex, Horner's syndrome Axial oblique 0.8-mm-thick SSFP MR image shows the vagus nerve (arrow) where it crosses the lateral cerebellomedullary cistern (LCM) and approaches the jugular foramen.The vagus and glossopharyngeal nerves, which are difficult to distinguish in this plane, are clearly distinguishable in the coronal oblique plane

33. Accessory nerve-CN XI BE fibres to the sternocleidomastoid and trapezius muscles Roots arise from the motor neurons in the upper 5 segments of the cervical spinal cord Turns head to opposite side/elevates and rotates scapula Lesion- shoulder droop, weakness turning head to opposite side Axial 0.8 mm-thick SSFP MR image at the level of the cervicomedullary junction (CMJ) shows the cranial rootlets (arrowheads) of the accessory nerve

34. Hypoglossal nerve- CN XII GSE- Intrinsic and most extrinsic muscles of the tongue Exits the cranial cavity through the hypoglossal canal Supplies the hyoglossus, styloglossus, genioglossus and all the extrinsic muscles of the tongue Lesion causes tongue to point towards affected side Coronal oblique 0.8-mm-thick SSFP MR image shows multiple hypoglossal nerve roots (arrows) converging toward the hypoglossal foramen (arrowhead).The nerve roots are immediately posterior to the vertebral artery (V).

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