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Cranial nerves overview 2013

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  • 1. DORSAL HORN IML VENTRAL HORN The spinal ganglion - location of neurons that convey somatosensory information to dorsal horn. It’s peripheral process associated with a receptor and a central process that enters the CNS. Ventral horn - origin of somatomotor fibers innervating skeletal muscles Intermediate gray (IML; T1-L2 and S2-4) - location of preganglionic visceromotor neurons innervating smooth and cardiac muscles. SPINAL GANGLION
  • 2. SPINAL GANGLION Spinal cord - grey matter deep to white matter Brainstem - grey matter and white matter intermingle with one another Brainstem - no dorsal, intermediate or ventral horns Neuron groups are organized into nuclei
  • 3. Brainstem: 1. Midbrain 2. Pons 3. Medulla 1 2 3 Most cranial nerves are associated with the brainstem (continuous with spinal cord) except CN I and CN II.
  • 4. Cranial nerve somatomotor nuclei are the location of neuronal cell bodies for somatomotor fibers that innervate skeletal muscles of the face and neck. The somatomotor cranial nerve nuclei are equivalent to the ventral horn of the spinal cord. Medulla
  • 5. Cranial nerve sensory ganglia (equivalent to the spinal ganglia) are located outside the brain (it may be a distinct ganglion or it may be many neurons dispersed throughout a region). They have a peripheral process that is associated with a receptor. Its central process terminates in a cranial nerve sensory nucleus (equivalent to the dorsal horn).
  • 6. CN III, VII, IX and X have parasympathetic nucleus (equivalent to intermediate gray matter of spinal cord levels S2-4). Preganglionic parasympathetic fibers travel initially with the cranial nerve in which it is associated. Preganglionic fibers synapse in parasympathetic ganglion located in head (except vagus nerve’s parasympathetic component). Postganglionic parasympathetic fibers from ganglion innervate smooth or cardiac muscles.
  • 7. CN I, CN II and CN VIII are purely sensory CN IV, CN VI, CN XI, CN XII are purely motor (not really true) CN III, CN V, CN VI, CN VII, CN IX, CN X are mixed (somatomotor, somatosensory, parasympathetic)
  • 8. Sensory ganglion - dispersed neurons located in olfactory mucosa in roof of nasal cavity Peripheral processes: located at surface of olfactory mucosa Central processes: pass through cribriform plate to terminate in olfactory bulb (dorsal horn equivalent) Olfactory bulb’s axons form olfactory tract that terminates in cortex. Olfactory Nerve (Cranial Nerve I)
  • 9. Light pass through pupil anterior and posterior chambers to retina. It passes through all layers of retina until it strikes the most posterior layer, which contains the rods and cones. They transduce light into a neural signal. bipolar cells - receive input from rods and cones; allow for convergence of information from multiple receptor cells. ganglion cells - receive input from bipolar cells -cell bodies of origin (sensory ganglion) for optic nerve -central processes of the sensory ganglia. -terminate in lateral geniculate nucleus (dorsal horn equivalent) of thalamus. Optic Nerve (Cranial Nerve II)
  • 10. Optic nerve - central processes of ganglion cell that pass through the optic canal in posterior wall of orbit to enter middle cranial fossa. Optic chiasm - crossing of nasal (medial) half of the optic nerve to the contralateral side; -temporal (lateral) half remains uncrossed. Optic tracts - caudal continuation of optic fibers to the thalamus Optic Nerve (Cranial Nerve II)
  • 11. Oculomotor nucleus (ventral horn equivalent) - cell bodies of origin for nerves innervating five extraocular muscles. Oculomotor nerve splits into: - superior division innervates: Superior Rectus Levator Palpebra Superioris -inferior division innervates: Medial Rectus Inferior Rectus Inferior Oblique Accessory oculomotor nucleus (Edinger-Westphal nucleus)- first cell body of two neuron chain responsible for parasympathetic innervation of two smooth muscles Oculomotor Nerve (Cranial Nerve III)
  • 12. SUPERIOR ORBITAL FISSURE Oculomotor fibers (both the somatomotor and preganglionic parasympathetic fibers) leave the cranial cavity through the superior orbital fissure to enter the orbit.
  • 13. Trochlear Nerve (Cranial Nerve IV) Trochlear nucleus (ventral horn equivalent) is the location of the cell bodies of origin - only cranial nerve to leave from brainstem’s dorsal (posterior) side. - innervates one extraocular skeletal muscle, superior oblique - Leaves cranial cavity through superior orbital fissure
  • 14. Trigeminal Nerve (Cranial Nerve V): principal sensory nerve of the head. Trigeminal ganglion – cell bodies of origin for sensory fibers (spinal ganglion equivalent located on petrous ridge of temporal bone) - Peripheral processes: convey somatosensory information from the face - Central processes: terminate in spinal trigeminal nucleus of brainstem. Sensory component is divided into: Ophthalmic (V1) Maxillary (V2) Mandibular (V3) Trigeminal motor nucleus- (ventral horn equivalent) neuronal cell bodies of origin for fibers innervating eight skeletal muscles.
  • 15. Ophthalmic Division-area of forehead to the lateral corners of the eyes and onto the bridge of the nose Maxillary Division-area between lateral corners of eyes to corners of the mouth Mandibular Division-area of the mandible (only division to contain motor fibers) SOMATOSENSORY INNERVATION PATTERN FOR THE FACE
  • 16. Ophthalmic Division-area of forehead to the lateral corners of the eyes and onto the bridge of the nose. - Leaves cranial cavity through superior orbital fissure to enter orbit. - peripheral processes divides into: frontal nerve supraorbital nerve supratrochlear nerve lacrimal nerve nasociliary nerve
  • 17. Maxillary Division-area between lateral corners of eyes to corners of mouth - Leaves cranial cavity by passing through foramen rotundum to enter pterygopalatine fossa. Its peripheral processes divides into: 1.infraorbital n. 2.greater and lesser palatine nn. (descending palatine nerves) 3. zygomatic n. (cheek) 4.posterior superior alveolar n. 5.sphenopalatine n.(nasal cavity)
  • 18. Mandibular Division-innervates the area of mandible; only division to contain motor fibers. - Leaves cranial cavity by passing through foramen ovale to enter infratemporal fossa. Its peripheral sensory processes branch into : 1. inferior alveolar n. 2. lingual n. 3. buccal n. 4. auriculotemporal n. 5. motor nerves to skeletal muscles.
  • 19. Trigeminal motor nucleus: location of somatomotor neuronal cell bodies of origin for fibers innervating eight muscles: muscles of mastication (masseter, temporalis, medial pterygoid, lateral pterygoid), mylohyoid, anterior belly of digastric, tensor tympani and tensor veli palatini.
  • 20. Abducens Nerve (Cranial Nerve VI) Abducens nucleus (ventral horn equivalent)- cell bodies of origin - responsible for innervating one extraocular muscle, lateral rectus. - Exits cranial cavity by passing through the superior orbital fissure to enter the orbit.
  • 21. FACIAL NERVE (CN VII) - contains somatomotor, somatosensory & preganglionic parasympathetic fibers. - Location of cell bodies for components of facial nerve: 1.Facial nucleus-somatomotor nucleus (ventral horn equivalent) innervating: muscles of facial expression & stylohyoid, posterior belly of the digastric and stapedius. 2. Superior salivary nucleus- visceral motor nucleus (intermediate gray equivalent) containing first parasympathetic cell bodies of two neuron chain innervating lacrimal gland, submandibular gland, sublingual gland, nasal mucous glands and oral mucous glands. 3. Geniculate ganglion, somatosensory ganglion (spinal ganglion equivalent) located in bend of facial canal in temporal bone posterior to middle ear. Peripheral processes innervate portions of the external ear and taste receptors on the anterior 2/3 of the tongue; central processes terminate in nucleus solitarius (taste) and spinal trigeminal nucleus (external ear).
  • 22. FACIAL NERVE (CN VII) Internal auditory meatus: exit/entrance of facial nerve from cranial cavity. Internal opening of facial canal (posterior to the middle ear) in temporal bone. Facial canal has an initial horizontal course and then a vertical course through the temporal bone. In the horizontal part that the geniculate ganglion is located. Stylomastoid foramen - inferior opening of facial canal; exit point of somatomotor and somatosensory fibers leaving the skull. ★ Two additional openings in the facial canal before the stylomastoid foramen that serve as the exit points for other parts of the facial nerve.
  • 23. INTERNAL AUDITORY MEATUS The internal auditory meatus, which is on the posterior edge of the petrous ridge of the temporal bone, is the opening for the entrance/exit of the facial nerve. Once it passes through the internal auditory meatus, the facial nerve takes a complicated course in the facial canal, which is inside the temporal bone. Internal View External View
  • 24. In facial canal different components split off: 1)greater petrosal nerve (preganglionic parasympathetic fibers from the superior salivary nucleus for lacrimal, nasal and oral mucosa glands) leaves the facial nerve at the geniculate ganglion to move rostrally. 2)chorda tympani (preganglionic parasympathetic fibers for submandibular and sublingual glands [superior salivary nucleus] and taste fibers [geniculate ganglion] for anterior 2/3 of tongue) leave the facial nerve distal to geniculate ganglion and enter the middle ear cavity to move rostrally. 3)somatomotor fibers (facial nucleus) to skeletal muscles & somatosensory fibers to external ear exit the temporal bone at the stylomastoid foramen.
  • 25. The greater petrosal nerve leaves the facial nerve at the geniculate ganglion to move rostrally. The chorda tympani leaves the facial nerve at the midpoint of the facial canal and takes a rostral course through the middle ear cavity. The remainder of the facial nerve continues through the facial canal until it exits on the anterior side of the skull at the stylomastoid foramen.
  • 26. Somatic motor component of facial nerve branches in parotid gland into: 1. temporal 2. zygomatic 3. buccal 4. mandibular 5. cervical
  • 27. Vestibulocochlear Nerve (Cranial Nerve VIII) The two ganglia, vestibular ganglion (associated with the semicircular canals) & dispersed neurons that comprise the spiral ganglion (associated with the cochlea) in the inner ear These are the neuronal cell bodies of origin for CN VIII. Vestibular ganglion cells: convey balance and orientation Spiral ganglion cells: convey auditory sense Peripheral processes of the vestibular ganglia are associated with receptors in the semicircular canals and the central processes end in vestibular nuclei of the brainstem. Peripheral processes of the spiral ganglia are associated with receptors in the cochlea and the central processes end in cochlear nuclei of the brainstem. Central processes pass through the internal auditory meatus to enter the cranial cavity.
  • 28. GLOSSOPHARYNGEAL NERVE (CN IX) - Primarily a sensory nerve, although it has a small somatomotor & visceromotor components. -Sensory information from posterior third of tongue, mucosa of pharynx, middle ear, auditory tube, and blood pressure & chemoreceptors associated with common carotid artery. - Somatomotor innervation: stylopharyngeus of pharynx -Visceromotor (parasympathetic) innervation: parotid gland. -Leaves cranial cavity thru jugular foramen
  • 29. Location of cell bodies: 1) Nucleus Ambiguus: cell bodies of origin for somatomotor fibers that innervate stylopharyngeus 2) Inferior Salivary Nucleus: cell bodies of origin for visceromotor fibers that are involved in innervation of the parotid gland
  • 30. 3) Inferior Ganglion of the Glossopharyngeal nerve (at the jugular foramen). Peripheral processes carry: 1) special sense (taste) & somatosensory information from the posterior 1/3 of tongue 2) Somatosensory information from the pharynx 3) Somatosensory information from the middle ear, auditory tube & mastoid air cells 4) General viscerosensory information from the carotid body (chemoreception) & carotid sinus (baroreception). Central processes from the inferior ganglion of CN IX terminate in: Nucleus solitarius – taste fibers from posterior third of tongue, carotid body and carotid sinus. Spinal trigeminal nucleus – general sensory from posterior third of tongue, pharynx, middle ear, auditory tube & mastoid air cells Spina l
  • 31. VAGUS NERVE (CN X) - contains somatomotor, visceromotor and somatosensory components - somatomotor innervates skeletal muscles of larynx, pharynx and accessory muscles of pharynx and soft palate - visceromotor component innervates smooth and cardiac muscles of thoracic cavity and smooth muscle of the abdomen up to splenic flexure - sensory component innervates laryngeal mucosa, meninges of posterior cranial fossa, external ear and comparable regions innervated by visceromotor innervation - Leaves cranial cavity through jugular foramen
  • 32. Nucleus Ambiguus: neuronal cell bodies that innervate skeletal muscles including: pharyngeal constrictor muscles, intrinsic muscles of larynx (external laryngeal & recurrent laryngeal nn.), levator veli palatini (soft palate) and palatoglossus, palatopharyngeus, salpingopharyngeus Dorsal Motor Nucleus of the Vagus: first neuronal cell bodies responsible for parasympathetic innervation of smooth muscle of digestive system (to splenic flexure), respiratory system and heart. Spinal trigeminal nucleus
  • 33. Inferior Ganglion of the vagus nerve (nodose ganglion): innervate mucosa of larynx, respiratory system, heart and digestive system. Its central processes (axons) terminate in the nucleus solitarius of brainstem. Superior Ganglion: innervate external auditory meatus, meninges of the posterior cranial fossa and external surface of tympanic membrane. Its central fibers terminate in spinal trigeminal nucleus of brainstem. Spinal trigeminal nucleus
  • 34. (Spinal) Accessory Nerve (CN XI) Location: C1-C5 of spinal cord is in the posterior portion of the anterior (ventral) horn. - fibers leave spinal cord between the posterior (dorsal) and anterior (ventral) roots to enter cranial cavity through foramen magnum. - fibers then exit cranial cavity through the jugular foramen. - innervates the sternocleidomastoid and trapezius.
  • 35. Hypoglossal nucleus: neuronal cell bodies for the hypoglossal nerve. - Exits cranial cavity through hypoglossal canal of occipital bone - In neck it loops around occipital artery to enter lateral side of the tongue - innervates: Intrinsic and extrinsic muscles (hyoglossus, styloglossus & genioglossus) of tongue HYPOGLOSSAL NERVE (CN XII)
  • 36. LEARNING OBJECTIVES FOR CRANIAL NERVES By the end of this unit you must have mastered for each cranial nerve (where appropriate): 1) all nuclei or ganglia of origin for its fibers 2) specific region of the brain or spinal cord its fibers are associated 3) complete pathway, any bony openings it passes through, and all its terminal targets 4) identify as motor only, sensory only, both motor and sensory and autonomic component if any 5) for sensory fibers: brain nuclei for termination of central fibers 6) for autonomic component, the nucleus of origin, bony openings, path of its preganglionic fibers, parasympathetic ganglion, path of its postganglionic fibers, terminal targets. 7) for the sympathetic fibers, cell bodies of origin, path of its fibers, sympathetic ganglion, pathway of its postganglionic fibers to the target structures. 8) Describe the functional deficits that will be manifested if any cranial nerve is lesioned at any point along its course. Specific objective for the 12 Cranial nerves: 1) Olfactory nerves-cell bodies of origin, bony openings and its path to its termination in olfactory bulb termination of olfactory tract axons 2) Optic nerve-cell bodies of origin, path of its fibers, bony opening and thalamic nucleus for termination of its central fibers location and consequences of optic chiasm 3) Oculomotor nerve-cell bodies of origin, path of its fibers cell bodies of origin and path to striated muscles for its superior and inferior divisions autonomic cell bodies of origin and complete path of its autonomic fibers location of ciliary ganglion; its contribution to short ciliary nerves and target structures for its postganglionic fibers know the location that its parasympathetic fibers join and leave specific parts of the nerve 4) Trochlear nerve-cell bodies of origin, its path, bony opening, muscle it innervates
  • 37. 5) Trigeminal nerve-cell bodies of origin, paths and bony openings of its subdivisions ophthalmic division area of innervation major branches branches of the frontal nerve associated autonomic ganglia components and cell bodies of origin for long ciliary nerves components and cell bodies of origin for short ciliary nerves maxillary division area of innervation branches in the pterygopalatine fossa, oral cavity, maxillary sinus and nasal cavity associated autonomic ganglion mandibular division area of innervation sensory branches and muscles innervated associated autonomic ganglia Know the location that autonomic fibers “hitch a ride” on specific parts of the nerve and when they leave the nerve to innervate a structure 6) Abducens nerve-cell bodies of origin, its bony opening and path to the muscle it innervates 7) Facial nerve-cell bodies of origin, bony openings, path of its fibers to its terminal targets sensory targets and somatic muscles innervated by the facial nerve autonomic cell bodies of origin and complete path of fibers to target structures components and cell bodies of origin of the chorda tympani components and cell bodies of origin for the nerve of the pterygoid canal 8) Vestibulocochlear nerve-cell bodies of origin, its path, bony openings and structures innervated
  • 38. 9) Glossopharyngeal nerve-cell bodies of origin, its path, bony openings and structures innervated. cell bodies of origin for innervation of striated muscles autonomic cell bodies of origin, path of its fibers and target structures cell bodies of origin and sensory regions innervated components and cell bodies of origin for tympanic nerve components and cell bodies of origin for lesser petrosal nerve contribution to pharyngeal plexus 10) Vagus nerve-cell bodies of origin, bony opening, path of its fibers and structures innervated. cell bodies of origin and striated muscles innervated cell bodies of origin and smooth muscle structures innervated cell bodies of origin and sensory regions innervated contribution to pharyngeal plexus 11) Accessory nerve-cell bodies of origin, its path, bony openings and terminal structures innervated 12) Hypoglossal nerve-cell bodies of origin, its path, bony openings and terminal structures innervated 13) Sympathetic innervation-cell bodies of origin for preganglionic and postganglionic fibers, most common pathways to terminal target sites. location and types of fibers in carotid plexus path and terminal targets of sympathetic components of long and short ciliary nerves components, path and terminal targets of deep petrosal nerve sympathetic path for innervation of submandibular, sublingual and parotid glands