CRANIAL NERVES ANATOMY Keele Neurology Society Aziza Mohamed

CRANIAL NERVES ANATOMY Keele Neurology Society Aziza Mohamed Aisha Saleem

Introduction • Twelve pairs of cranial nerves that originate from the forebrain, brainstem and rostral spinal cord. • Form part of the peripheral nervous system – similar properties to spinal nerves. • Responsible for sensory, motor and/or autonomic function in mainly* functional regions of head and neck. • Integral part of neurological examination. *

Cranial Nerve Function Overview • Sensory, motor, autonomic or mixed. • Can receive afferents or send impulses locally or to regions such as thoracic and abdominal viscera (e. g. CN X Vagus Nerve). • Sensory - general somatic afferent, general visceral afferent or special afferent. • Motor - general somatic efferent or branchial motor efferents. • General or special visceral efferents are also described as - Parasympathetic efferents.

Internal Cranium Base – Quick Overview

Cranial Nerve Foramina

Cranial Nerve I: Olfactory SENSORY - Special Afferent • FORAMEN - Cribriform Plate of the Ethmoid Bone • Sensory – perception of smell. Transmitted into the frontal lobe from olfactory epithelium.

Cranial Nerve II: Optic SENSORY - Special afferent • FORAMEN - Optic canal • Sensory – perception of vision; detects and transmits light input from optic disc at retina. NB: Contralateral; optic chiasm at the sphenoid wing involves decussation of the nerves into the optic tract.

Cranial Nerve III: Occulomotor MOTOR – occulomotor nerve palsy (down and out – neurogenic ptosis causes drooping of the eyelid due to damage to CN III) PARASYMPATHETIC EFFERENTS • FORAMEN - Superior Orbital Fissure • Motor - Controls four of the six extraoccular muscles ; superior rectus, inferior rectus, medial rectus and inferior oblique muscles. *Also controls levator palpebrae superioris (upper eyelid muscle) • Parasympathetic efferent – innervates sphincter pupillae for pupil constriction and ciliary muscle accommodation of lens at near vision.

Cranial Nerve IV: Trochlear MOTOR • FORAMEN - Superior Orbital Fissure • Motor - controls the movement of the superior oblique muscle of the eye. Aids internal rotation of eye. • *SO 4 – Trochlear (CN IV)

Cranial Nerve V: Trigeminal SENSORY MOTOR - • FORAMEN – Varied: – V 1 [opthalmic]- Superior Orbital Fissure – V 2 [maxillary]- Foramen Rotundum – V 3 [mandibular]- Foramen Ovale • Sensory – touch, temperature perception on different regions of face (testing with soft/crude touch and temperature). • Motor - Muscles of mastication particularly masseter and temporalis

Cranial Nerve VI: Abducens MOTOR • FORAMEN – Superior Orbital Fissure • Motor - Lateral rectus muscle of the eye. Enables abduction of the eye. • *LR 6 – Abducens (CN VI)

Cranial Nerve VII: Facial SENSORY MOTOR PARASYMPATHETIC EFFERENTS • FORAMEN – Internal Acoustic Meatus • Sensory – special sensory is anterior 2/3 taste of tongue and external acoustic meatus (including auricle) • Motor – muscles of facial expressions [5 branches] and neck muscles. • Parasympathetic – submandibular, sublingual and lacrimal salivary glands. Also innervates mucous membranes of nasal cavity. 1. Temporal 2. Zygomatic 3. Buccal 4. Maxillary 5. Cervical

Cranial Nerve VIII: Vestibulocochlear SENSORY - special afferent • FORAMEN – Internal Acoustic Meatus • Sensory – special sensory function: – Vestibular division responsible for balance – Cochlear division responsible for hearing

Cranial Nerve IX: Glossopharyngeal SENSORY MOTOR PARASYMPATHETIC EFFERENTS • FORAMEN – Jugular Foramen • Sensory – input from the carotid body and sinus (detects changes in PCO 2 and pressure). Taste in posterior 1/3 of tongue. • Motor – controls stylopharyngeal muscle for swallowing. • Parasympathetic efferent innervates parotid salivary gland

Cranial Nerve X: Vagus SENSORY MOTOR - dysphagia (often ( seen in patients who’ve suffered from stroke) PARASYMPATHETIC EFFERENTS • FORAMEN – Jugular Foramen • Sensory – varied: – Sensation in larynx, laryngopharynx, including parts of the external acoustic meatus. – Sensory from the aortic body and aortic sinus, thoracic and abdominal viscera. – Taste in the epiglottis and upper pharynx • Motor – innervates only one tongue muscle, varied muscles in pharynx and larynx. – Aid in speech and swallowing • Parasympathetic efferents – innervates smooth muscles and glands in throat region, thoracic viscera and abdominal viscera upto the midgut. (2/3 of Transverse Colon)

Cranial Nerve XI: Accessory MOTOR - • FORAMEN - Jugular Foramen • Motor – innervates sternocleidomastoid muscle and trapezius muscles of neck and shoulder region. Aids rotation and flexion of head and neck; shrugging move scapula and support arm.

Cranial Nerve XII: Hypoglossal MOTOR - “the tongue licks the wound” (damage to the hypoglossal nerve leads to deviation of tongue to ipsilateral side where injury occurred) • FORAMEN - Hypoglossal Canal (lateral to Foramen Magnum) • Motor – control of tongue muscles; including pharynx and larynx (muscles of speech and swallowing).

Origin of Cranial Nerves • • • CN I – Olfactory Bulb (inf. surface of Frontal Lobe) CN – Retina CN III – Midbrain CN IV – Midbrain Majority of cranial nerves CN V – PONS originate from the CN VI – PONS brainstem (CN III – CN XII [excluding CN XI]) CN VII – PONS CN VIII – PONS CN IX – Medulla CN XI – Spinal Cord* CN XII – Medulla

Cranial Nerve Nuclei* Nuclei *Spinal Accessory Nerve XI – Originates from spinal cord directly

Mnemonics • Oh Once One Takes The Anatomy Finals Very Good Vacations Are Heavenly. • Some Say Marry Money, But My Brother Says Big Business Makes Money. • Carl Only Swims South. Silly Roger Only Swims In Infiniti Jacuzzis. Jane Just Hitchhikes. • To Zanzibar By Motor Car* [5 Branches of Facial Nerve]

Useful Websites & Resources • Yale University: http: //www. yale. edu/cnerves/ • fastbleep: http: //www. fastbleep. com/medical-notes/neuroand-psych/2/95/610 • UBC (University of British Colombia): http: //www. neuroanatomy. ca/ • Teach. Me. Anatomy: www. teachmeanatomy. co. uk • Mnemonics: file: ///S: /Downloads/List%20 of%20 mnemonics%20 for%20 the %20 cranial%20 nerves. pdf

References • • • Mike Mahon – Cranial Nerve Neuroanatomy Lecture Neuroanatomy Illustrated Gray’s Anatomy for Students Bear’s Neuroscience Cranial Nerve Neuroanatomy Image 1 http: //d 7 c 2 b 0 wpljtwf. cloudfront. net/var/ezwebin_site/storage/images/media/im ages/e-anatomy/cranial-nerves-anatomy-diagrams/skull-cranial-base-foramencranial-nerves-anatomy-en/2571278 -1 -eng-GB/skull-cranial-base-foramen-cranialnerves-anatomy-en_imagelarge. jpg "Brain human normal inferior view with labels en-2" by Brain_human_normal_inferior_view_with_labels_en. svg: *Brain_human_normal_inferior_view. svg: Patrick J. Lynch, medical illustratorderivative work: Beaoderivative work: Dwstultz (talk) Brain_human_normal_inferior_view_with_labels_en. svg. Licensed under CC BY 2. 5 via Wikimedia Commons http: //commons. wikimedia. org/wiki/File: Brain_human_normal_inferior_view_wit h_labels_en 2. svg#mediaviewer/File: Brain_human_normal_inferior_view_with_labels_en-2. svg