Head and Neck Anatomy Lecture Notes PDF

L13 Reem Habboub  Head and Neck Anatomy Lecture 13: Cranial nerves (I-VI) Dr. Heba Ali Assistant Professor of Anatomy and Histology [email protected]  Cranial Nerves 12 pairs of nerves. Arise directly from the brain Pass thr...

L13 Reem Habboub  Head and Neck Anatomy Lecture 13: Cranial nerves (I-VI) Dr. Heba Ali Assistant Professor of Anatomy and Histology [email protected]  Cranial Nerves 12 pairs of nerves. Arise directly from the brain Pass through skull openings (foramen, fissure, canal). All of the cranial nerves are distributed among the head and neck region, except the 10th cranial nerve (vagus X) which extends to thorax and abdomen carrying parasympathetic innervation to thoracic and abdominal viscera. Cranial nerves I-VI  Olfactory Nerve (CN I) Purely sensory. Conduct the sense of smell (olfaction). Olfactory receptor cells >>Bipolar neurons (1st order neurons). Axons of these neurons pass through perforations in cribriform plate of ethmoid bone. Those fibers are collectively known as the olfactory nerve. After passing through cribriform plate, those 1st order neurons synapse with 2nd order neurons in olfactory bulbs. Olfactory bulbs paired masses of gray matter resting over cribriform plate (extension of forebrain). Axons of 2nd order neurons extends from olfactory bulbs posteriorly forming olfactory tracts that run to primary olfactory area in temporal lobe. Remember! Does not relay in thalamus  Olfactory nerve Olfactory receptor (1st)  olfactory nerves  olfactory bulbs (synapse with 2nd order)  olfactory tracts  primary olfactory area (temporal lobe). Cribriform Plate, Olfactory Bulb & Tract Olfactory Bulb Olfactory Cribriform Tract plate  Optic Nerve (II) Special sensory. Conduct the sense of vision. Axons extend from sensory receptors in the retina to form the optic nerve, then pass through optic foramen. The two optic nerves join each other posterior to orbits to Form a cross known as optic chiasm. In optic chiasm some fibers cross to other side whereas the others continue to same side.  Optic Nerve (II) Retina is divided into: -Medial (nasal) half. Temporal Temporal -Lateral (temporal) half. Nasal Nasal Fibers coming from medial half of retina cross in chiasm to opposite side, those coming from lateral half continue to the same side ! From the chiasm optic tract. Optic tracts relay (synapse) in the thalamus. From the thalamus, the axons forms a loop known as the optic radiation that reach the visual cortex. Primary visual area around calcarine sulcus.  Oculomotor Nerve (III) Motor  to extrinsic muscles of eye. Emerge from ant. surface of midbrain. Pass in lateral wall of cavernous sinus. Divide into superior and inferior rami that pass through superior orbital fissure. Supply extrinsic muscles of the eye except: Superior oblique & lateral rectus  Muscles of The Eye Extrinsic muscles: -Originate outside eyeball (in orbit) -Inserted to eye ball. -Moves the eyeball. Intrinsic muscles: - Originate and inserted in eyeball.  Oculomotor Nerve (III) Superior branch : superior rectus, levator palpebrae superioris muscles. Inferior branch: inferior rectus, inferior oblique, medial rectus.  Trochlear Nerve (IV) Motor. The smallest C.N. Trochlear nerve emerge from midbrain posteriorly ! Pass in lateral wall of cavernous sinus. Pass through superior orbital fissure to supply: Superior Oblique muscle (SO4)  Abducent Nerve (VI) Motor. Emerges from the anterior surface of the hindbrain between the pons and the medulla oblongata Pass through cavernous sinus Pass through superior orbital fissure to supply: Lateral Rectus muscle (LR6) So called because it causes the abduction of the eye. LR6  Muscles of The Orbit (Extrinsic Eye Muscles) 7 muscles: -Levator palpebrae Superioris: Elevate upper eyelid. - 4 recti muscles: -Superior rectus. - Inferior rectus. -Medial rectus. -Lateral rectus. Recti and oblique muscles move the eyeball - 2 oblique muscles - Superior oblique. -Inferior oblique All extrinsic muscles of eye are supplied by occulomotor n.(III) EXCEPT SO4 LR6  Trigeminal Nerve (V) Latin tri = three, geminus = twins The largest cranial nerve. The sensory nerve to the greater part of the head and the motor nerve to several muscles, including the muscles of mastication. Emrges from anterior aspect of pons Mixed nerve: – Sensory face & teeth – Motor 8 muscles.  Trigeminal nuclei (1) main sensory nucleus (2) spinal nucleus (3) mesencephalic nucleus (4) motor nucleus. The motor nucleus receives corticonuclear fibers from both cerebral hemispheres  Trigeminal Nerve Course Emerges from the pons as two roots : - Large sensory root. - Small motor root. Sensory root expand to form trigeminal ganglion. From ganglion, 3 branches (or divisions) arise: 1 Ophthalmic division (V1). 2 Maxillary division (V2). 3 Mandibular division (V3). Provides Face Sensations  Ophthalmic Nerve (V1) Entirely sensory. Didive into 3 branches that pass to orbit through: superior orbital fissure. Those 3 main branches are  1 Lacrimal nerve. 2 Frontal nerve. 3. Nasociliary nerve.  Main Branches of V1 1 Frontal nerve (the middle branch) : - run above the upper surface of levator palpebrae superioris. - Terminates as supraorbital and supratrochlear nerves. 2 Lacrimal nerve (the lateral branch): -runs above the upper border of lateral rectus muscle. 3 Nasociliary nerve (the medial branch): -runs above upper border of medial rectus muscle. -Gives 2 branches to the face : infratrochlear & external nasal nerves.  Maxillary Nerve (V2) Entirely sensory that arises from trigeminal ganglion Passes through foramen rotundum. Crosses pterygopalatine fossa. Enters orbit through inferior orbital fissure. In orbit runs through infraorbital groove then infraorbital canal. Arises in the face through infraorbital foramen.  Zygomatic n Zygomaticotemporal n Zygomaticofacial n Trigeminal ganglion Foramen rotundum Maxillary Ant. Sup. Alveolar n nerve middle. Sup. Alveolar n post. Sup. Alveolar n Infraorbital n. entering infraorbital canal  Branches of Maxillary Nerve (3 x 3 x 3) Main branches:  3 branches to the upper teeth: superior alveolar nerves.  3 branches to the face.  3 branches to the palate. V2  3 Superior Alveolar Nerves  V2  3 branches arise in the face Zygomatic N. Enters the orbit through the inferior orbital fissure & divides into: zygomaticotemporal nerve that exits through its foramen. To supply skin of the non-hairy part of temple. zygomaticofacial nerve: that exits through its foramen. To supply skin of cheek. V2  Palatine Branches  Mandibular Nerve (V3) Mixed branch (both motor & sensory) : Sensory to : temporal region, tongue, lower teeth ,chin. Motor: 8 muscles. Sensory and motor roots pass through foramen ovale to enter the infratemporal fossa. Two roots (sensory & motor)> join (merge)> main trunk The trunk divides to: - Small anterior division (3M & 1S) - Large posterior division (3S & 1M)  Mandibular Nerve (V3) Branches from main trunk :  Nerve to medial pterygoid: supplies medial pterygoid muscle in addition to two tensor muscles (tensor tympani muscle & tensor veli palatini muscle)  Two tensors muscles External acoustic meatus Posterior view Medial Pterygoid Muscle  Mandibular Nerve (V3) Branches from anterior division (3 Motor, 1 Sensory) : 3 Motor branches to the remaining muscles of mastication: 1 - Nerve to temporalis (deep temporal nerves) 2 - Nerve to masseter (massetric nerve) 3 - Nerve to lateral pterygoid muscles. 1 Sensory branch to the skin and mucosa (lining) of cheek & buccal gingiva of lower posterior teeth: Buccal (long buccal) nerve. Anterior Division 3 motor & 1 sensory Branches from the anterior division Anterior division Deep temporal nerves Masseteric n Lat. Pterygoid n Buccal nerve  Mandibular Nerve (V3) Branches from the posterior division (1 Motor, 3 Sensory) 1 Motor branch: Nerve to mylohoid (motor) : to mylohoid & anterior belly of digastric muscle. 3 Sensory branches : 1 Auriculotemporal nerve (Arises by 2 roots Encircles the middle meningeal artery) Supplies sensory fibers to the auricle and temporal region and articular (sensory) fibers to the TMJ. 2 Lingual nerve Lies anterior to IAN enters the mouth between the medial pterygoid muscle and the ramus of the mandible and passes anteriorly under cover of the oral mucosa, just inferior to the 3rd molar tooth. It is sensory to the anterior 2/3rd of the tongue, the floor of the mouth, and the lingual gingivae. 3. Inferior alveolar nerve. Enters mandibular canal to supply the teeth of the lower jaw and emerges through the mental foramen (mental nerve) to supply the skin of the chin. Before entering the canal, it gives off the mylohyoid nerve  Branches from the posterior division Auriculotemporal n Lingual n Nerve to mylohyoid Inferior alveolar n V3  Posterior Division  Clinical note (Being superficial, the lingual nerve is liable to injury during extraction of lower last molar hence it is considered a dangerous site)  Innervation of tongue ?! Sensory: Ant 2/3rds: -general lingual n. (V3) -special chorda tympani (VII) post.1/3rd: All sensations glossopharyngeal (IX) Motor: hypoglossal n.(XII)