The cranial nerves

1. The cranial nerves

2. The cranial nerves • These are twelve pairs and numbered from before backward. • All the nerves are distributed in the head and neck except the tenth which supply structures in the thorax and abdomen. • Sensory: • 1st, 2nd and 8Th. • Motor: • 3rd, 4th, 6th, 11th and 12th. • Mixed: • 5th, 7th, 9th and 10th.

3. Cr I Olfactory Cr II Optic Cr III Oculomotor Cr IV Trochlear Cr V Trigeminal Cr VI Abducent Cr VII Facial Cr VIII Vestibulocochlear Cr XI Glossopharyngeal Cr X Vagus Cr XI Accessory Cr XII Hypoglossal The cranial nerves Overview

4. The cranial nerves • The first two are merely an outdrawn part of the CNS rather than nerves. • Olfactory: (Sensory) Cr I • Optic: (sensory) Cr II

5. Olfactory:(Sensory) Cr I • Fibers originate in the upper part of the nose. • They are unique in being the central processes not peripheral ones • Clinically: • Bilateral anosmia & CSF leak • are common signs of head • injuries with anterior cranial • fossa fracture.

6. Optic:(sensory) Cr II • Leaves the orbital cavity through the optic canal They join each other to form the chiasma. • Clinically: • Section through the optic nerve • causes epsilateral blindness. • Lesions behind the optic chiasma • (pituitary gland tumors) lead to • contro-lateral blindness.

7. Oculomotor nerve:(motor) Cr III • Oculo: Eye + Motor: mover • Somatic nerve to four of the six muscles of that moves the eye and the muscle that raises the eyelids • Enter the orbit through superior orbital fissure

8. Oculomotor nerve:(motor) Cr III • Clinically: • Inability to look up, down or medially. • Dilatation of the pupil. • Ptosis (drooping of the eyelid paralysis • of LPS) • Supply all the orbital muscles, except the superior oblique,lateral rectus and levator palpebrae superioris • Supply parasympathic fibers to the constrictors of the pupil.

9. Trochlear nerve: (motor) Cr IV • Enter through the superior orbital fissure • supply the superior oblique muscle • Clinically: • Unable to look downward and • inward. • Difficulty in walking downstairs

10. Trigeminal Nerve: (mixed) Cr V • Motor nucleus (branchial) in the upper pons, for the muscles of the first branchial arch. • Sensory nucleus (somatic) divided into three • Mesencephalic • Main • Spinal

11. Trigeminal Nerve: (mixed) Cr V • Mesencephalic: • extend through the midbrain • First order neurons • mediate proprioceptive impulses • Main sensory: • upper pons lateral to the motor • second order neurons • mediate touch • Spinal: • extend from lower pons, medulla to spinal cord • second order neurons • mediate pain & temperature

12. Trigeminal Nerve: (mixed) Cr V • Ophthalmic division: • It is the nerve for the frontonasal process • emerging through the superior orbital fissure • divide into three branches: 1-Lacrimal nerve. 2-Frontal nerve. 3-Nasociliary nerve.

13. Trigeminal Nerve:(mixed) Cr V • Maxillary division: • It is the nerve to the maxillary process, leaves the skull through foramen rotundum and have a very short course. • Ganglionic branches • zygomatic nerve • posterior superior alveolar nerve • Infraorbital nerve

14. Trigeminal Nerve: (mixed) Cr V • Mandibular division: • It is the nerve for the first pharyngeal arch, very short and emerges through foramen ovale • Accompanied by the motor root of the trigeminal nerve • divide into: • Anterior division • all motor except one • Posterior division • all sensory except one

15. Trigeminal Nerve: (mixed) Cr V • Nerve to medial pterygoid muscle • Anterior branches: • nerves to lateral pterygoid, masseter and two deep temporal • the long buccal nerve “S”. • Posterior branches: • Auriculotemporal • inferior alveolar (nerve to mylohoid “M”) • the lingual nerves

16. Trigeminal Nerve: (mixed) Cr V • Clinically • Fracture midface, zygoma or mandible might lead • to anaesthesia to light touch and other modalities. • Lesions of the entire nerve leads to • anaesthesia and paralysis and atrophy • of the muscles of mastication. • Trigeminal neuralgia • Herpes zoster

17. Abducent :(motor) Cr VI • Somatic, leave the brain through the superior orbital fissure • Supply the lateral rectus muscle. • Clinically: • Strabismus and diplopia • on lateral gaze

18. Facial:(mixed) Cr VII • Joined by the nervus intermedius, sensory root, in the facial canal in the temporal bone before it emerges through the stylomastoid foramen. • Passes into the parotid gland and divides into five motor • Branchial motor branches: • supply the muscles of the facial expression (from second pharyngeal arch)

19. Facial:(mixed) Cr VII • Visceral efferent: • Secretomotor to submandibular & sublingual salivary gland • Sensory fibers: • Visceral afferent • Taste buds anterior two third of tongue & soft palate • Somatic afferent • skin of external auditory meatus and tympanic membrane • Clinically: • Bell’s Palsy • Loud sound, • paralysis of stapidus muscle

20. Vestibulocochlear:(sensory) CrVIII • A special sensory nerve, consist of two kinds of fibers, the vestibular and the cochlear • Mediate sound reception and balance. • Clinically: • Deafness • vertigo

21. Glossopharyngeal Nerve:(mixed) Cr IX • Sensory: • Special: • taste from the posterior 1/3 of tongue. • General sensation: • from the back of the tongue wall of the pharynx and the middle ear. • Chemoreceptor & pressure: • Carotid sinus concerned with regulation of respiration and circulation

22. Glossopharyngeal Nerve:(mixed) Cr IX • Motor: • To the stylopharyngeus muscle of the pharynx. • Parasympathetic fibres: • to the otic ganglion, the postganglionic fibres travel with the auriculo-temporalnerve to the parotid • Clinically: • Neuralgia. • Loss of gagging reflex

23. Vagus nerve:mixed Cr X • Has the most extensive distribution of all the cranial nerves, supply the heart and the major part of the respiratory and alimentary tract. • Has one sensory and two motor nuclei in the medulla. • Leave the cranial cavity through the jugular foramen. • passes vertically down the neck within the carotid sheath.

24. Vagus nerve:mixed Cr X • Have 4 types of fibres: • Motor fibres to the striated muscles of larynx and pharynx. • Paralysis of soft palate, dysphagia and aphonia • Visceral-motor fibres carry impulses to thoracic and abdominal viscera • Sensory fibres • for pain from external auditory meatus • Visceral fibres: • Taste buds in the epiglottis • Stretch receptors in the heart, aorta and common carotid bifurcation (Blood Pressure and heart rate) • Stretch receptors in the lung and upper G-T I (rate and depth of respiration

25. Accessory nerve:(Motor) Cr XI • A small cranial root which is distributed to the muscles of the palate, pharynx and larynx. • A large spinal root to the sternocleidomastoid and trapezius muscles.

26. Accessory nerve:(Motor) Cr XI • Clinically: • Paresis of the laryngeal and pharyngeal muscles leading to dysphonia and dysphagia. • Paresis of the trapezius and sternocleidomastoid muscle following neck dissection for tumour surgery.

27. Hypoglossalnerve:(Motor) Cr XII • Leave the posterior cranial fossa via the hypoglossal canal in the occipital bone. • Supply the intrinsic and the extrinsic muscles of the tongue with the exception of the palatoglossus • Clinically: • Unilateral lingual paresis • hemiatrophy of the tongue • Dysarthia.