Anatomy of the cranial nerves

cranial nerves anatomy, a neurosurgical aspect, basis of neurosurgical approaches

1. Anatomy of the Cranial Nerves Dr Mukhtar Neurosurgery HMC

2. Classification Pure Sensory Function: CN I, II and VIII Pure Motor Function: CN III, IV, VI, XII Mixed (Sensorimotor): CN V, VII, IX, X, XI

3. Cranial nerves nuclei Somatic Motor and Branchiomotor nuclei: Axons of nerve cells situated within the brain Nuclei which innervate striated muscles Nerve cell with its fibres is called Lower Motor Neuron Receive impulses from cortex through corticonuclear fibres Bilateral connections except for part of facial nucleus and a part of hypoglossal nucleus

4. Cranial nerves nuclei General Visceral Motor nuclei: C ranial outflow of the parasympathetic portion of the autonomic nervous system Edinger-Westphal Nucleus of CN III Superior salivatory and lacrimal nuclei of CN VII Inferior salivatory nucleus of CN IX Dorsal motor nucleus of CN X These nuclei receive numerous afferent fibres, including descending pathways from the hypothalamus

5. Cranial nerves nuclei Sensory Nuclei of the Cranial Nerves Include visceral and somatic sensory nuclei afferent parts of a cranial nerve are the axons of nerve cells outside the brain and are situated in ganglia on the nerve trunks or the sensory organs. First, second and third order neurons

6. The Olfactory Nerves Course: Olfactory hair  Olfactory receptor cells  Central processes  Olfactory nerve fibres  Olfactory bulb  Olfactory tract  Primary Olfactory Cortex (peri-amygdaloid & prepiriform cortex)  Entorhinal area of parahippocampal gyrus (Secondary Olfactory Cortex)

7. Optic Nerve Origin : The fibres of the optic nerve are the axons of the cells in the ganglionic layer of the retina . Optic Chiasma : situated at the junction of the anterior wall and floor of the third ventricle Optic tract : The optic tract emerges from the optic chiasma and passes posterolaterally around the cerebral peduncle . fibres terminate by synapsing with nerve cells in the lateral geniculate body, while some fibres pretectal nucleus and superior colliculus

8. Optic nerve Lateral Geniculate Body : small, oval swelling projecting from the pulvinar of the thalamus. Six layers of cells . Optic Radiation : F ibres of the optic radiation are the axons of the nerve cells of the lateral geniculate body. The tract passes posteriorly through the retrolenticular part of the internal capsule . The visual association cortex (areas 18 and 19) is responsible for recognition of objects and perception of colour and terminates in the visual cortex (area 17 ).

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10. Oculomotor Nerve The Oculomotor Nuclei: Two nuclei: i) main motor nucleus: situated in the anterior part of the gray matter that surrounds the cerebral aqueduct of the midbrain Oculomotor nucleus receives corticonuclear fibres from both cerebral hemispheres receives tectobulbar fibres from the superior colliculus ii) Edinger-Westphal nucleus: situated posterior to the main oculomotor nucleus axons of the nerve cells, which are preganglionic, accompany the other oculomotor fibres to the orbit

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12. Oculomotor Nerve Course: emerges at the anterior surface of midbrain p asses between posterior cerebral and sup. Cerebellar arteries Lateral wall of cavernous sinus Divides into superior and inferior rami Enters the orbit

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14. Trochlear nerve Trochlear nucleus: It lies inferior to the oculomotor nucleus at the level of the inferior colliculus The nerve fibres, pass posteriorly around the central gray matter to reach the posterior surface of the midbrain Course: emerges from the midbrain and immediately decussates with the nerve of the opposite side lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure

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17. Trigeminal Nerve

18. Trigeminal nerve Click to add text Second line of text

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22. Abducens Nerve

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25. Facial nerve Nuclei: Main motor nucleus: lies deep in the reticular formation of the lower part of the pons The part of the nucleus that supplies the muscles of the upper part of the face receives corticonuclear fibres from both cerebral hemispheres The part of the nucleus that supplies the muscles of the lower part of the face receives only corticonuclear fibres from the opposite cerebral hemisphere .

26. Facial nerve Nuclei: Parasympathetic nuclei: Parasympathetic nuclei lie posterolateral to the main motor nucleus Superior salivatory and lacrimal nuclei Sensory nucleus upper part of the nucleus of the tractus solitarius and lies close to the motor nucleus Sensations of taste travel through the peripheral axons of nerve cells situated in the geniculate ganglion on the seventh cranial nerve

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29. Facial nerve Course: Sesory and motor components fibers of the motor root first travel posteriorly around the medial side of the abducent nucleus They then pass around the nucleus beneath the colliculus facialis in the floor of the fourth ventricle and, finally, pass anteriorly to emerge from the brainstem The sensory root ( nervus intermedius ) is formed of the central processes of the unipolar cells of the geniculate ganglion

30. Facial nerve Course: It also contains the efferent preganglionic parasympathetic fibers from the parasympathetic nuclei They pass laterally in the posterior cranial fossa with the vestibulocochlear nerve and enter the internal acoustic meatus in the petrous part of the temporal bone At the bottom of the meatus, the nerve enters the facial canal and runs laterally through the inner ear On reaching the medial wall of the tympanic cavity, the nerve expands to form the sensory geniculate ganglion and turns sharply backwards. At the posterior wall of the tympanic cavity, the facial nerve turns downward on the medial side of the aditus of the mastoid antrum , descends behind the pyramid, and emerges from the stylomastoid foramen

31. Facial nerve Distribution: The motor nucleus supplies the muscles of facial expression, the auricular muscles, the stapedius , the posterior belly of the digastric, and the stylohyoid muscles The superior salivatory nucleus supplies the submandibular and sublingual salivary glands and the nasal and palatine glands. The lacrimal nucleus supplies the lacrimal gland The sensory nucleus receives taste fibers from the anterior two-thirds of the tongue, the floor of the mouth, and the palate

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34. Vestibulocochlear Nerve C onsists of two distinct parts, the vestibular nerve and the cochlear nerve Vestibular Nerve conducts nerve impulses from the utricle and saccule that provide information concerning the position of the head central processes of nerve cells located in the vestibular ganglion, which is situated in the internal acoustic meatus They enter the anterior surface of the brainstem in a groove between the lower border of the pons and the upper part of the medulla oblongata When they enter the vestibular nuclear complex, the fibres divide into short ascending and long descending fibres; some fibres pass directly to the cerebellum through the inferior cerebellar peduncle, bypassing the vestibular nuclei

35. Vestibulocochlear nerve The Vestibular Nuclear Complex Four nuclei may be recognized: the lateral vestibular nucleus, the medial vestibular nucleus the superior vestibular nucleus, the inferior vestibular nucleus Efferent fibers from the nuclei pass to the cerebellum through the inferior cerebellar peduncle

36. Vestibulocochlear nerve Efferent fibers also descend uncrossed to the spinal cord from the lateral vestibular nucleus and form the vestibulospinal tract In addition, efferent fibers pass to the nuclei of the oculomotor, trochlear, and abducent nerves through the medial longitudinal fasciculus Ascending fibers also pass upward from the vestibular nuclei to the cerebral cortex, to the vestibular area in the postcentral gyrus just above the lateral fissure

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41. Vestibulo cochlear nerve Cochlear Nerve The cochlear nerve conducts nerve impulses concerned with sound from the organ of Corti in the cochlea The fibres of the cochlear nerve are the central processes of nerve cells located in the spiral ganglion of the cochlea Entering pons at the level of the facial nerve Nerve fibres are distributed to anterior and posterior cochlear nuclei Efferent fibers are relayed through various nuclei to the auditory cortex

42. Glossopharyngeal Nerve Nuclei: The glossopharyngeal nerve has three nuclei: the main motor nucleus, the parasympathetic nucleus, and the sensory nucleus Course: The glossopharyngeal nerve leaves the anterolateral surface of the upper part of the medulla oblongata as a series of rootlets in a groove between the olive and the inferior cerebellar peduncle leaves the skull through the jugular foramen Descends along internal jugular vein and artery and supplies the stylopharyngeus, the upper two constrictor oesophageal muscles, posterior 3 rd of the tongue and pharynx.

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44. Vagus nerve Nuclei: Main motor Sensory Parasympathetic Course: Leaves anterolateral surface of medulla Leaves the skull through jugular foramen Superior and Inferior sensory ganglia

45. Vagus Nerve Descends down in the neck inside the carotid sheath In the thorax, it contribute to the pulmonary plexus, cardiac plexus and nerves of the larynx. In the upper abdomen it forms anterior and posterior gastric nerves

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49. Accesory nerve The accessory nerve is a motor nerve that is formed by the union of a cranial and a spinal root . Cranial Root formed from the axons of nerve cells of the nucleus ambiguus The nucleus receives corticonuclear fibers from both cerebral hemispheres The efferent fibers of the nucleus emerge from the anterior surface of the medulla oblongata between the olive and the inferior cerebellar peduncle

50. Accessory nerve Course of the cranial part: The nerve runs laterally in the posterior cranial fossa and joins the spinal root Exits through the jugular foramen The roots then separate, and the cranial root joins the vagus nerve and is distributed in its pharyngeal and recurrent laryngeal branches

51. Accessory nerve Course of the spinal part: Formed by the spinal nucleus in the upper part of the spinal cord Receives corticospinal fibres from cerebral cortex The spinal root emerges from the cervical spinal cord and ascends into the skull to join the cranial part. Descending down it supplies the sternocleidomastoid and trapezius muscles

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53. Hypoglossal nerve The hypoglossal nerve is a motor nerve that supplies all the intrinsic muscles of the tongue as well as the styloglossus , the hyoglossus , and the genioglossus muscles The hypoglossal nucleus is situated close to the midline immediately beneath the floor of the lower part of the fourth ventricle Exits the skull through the hypoglossal canal Passes between the internal carotid artery and internal jugular vein Posterior belly of the digastric is supplied Passes deep to the mylohyoid muscle lying on the lateral aspect of hypoglossus muscle Joined by fibers of the C1 spinal nerve

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