Cranial Nerves PDF

0  Cranial Nerves I 12 pairs of nerves. Nerves that pass through skull (cranial) openings. The 1st and 2nd cranial nerves are continuous with the forebrain. The 3rd and 4th cranial nerves arise from the midbrain. The 5th - 8th cranial nerves arise fr...

0  Cranial Nerves I 12 pairs of nerves. Nerves that pass through skull (cranial) openings. The 1st and 2nd cranial nerves are continuous with the forebrain. The 3rd and 4th cranial nerves arise from the midbrain. The 5th - 8th cranial nerves arise from the pons. o The 5th cranial nerves arise directly from the pons. o 6th-8th cranial nerves arise from the pontomedullary junction. The 9th - 12th cranial nerves arise from the medulla oblongata. Cranial nerves can be divided according to their function to: o Pure sensory, pure motor, or mixed (both). Oh, Once One Takes The ▪ CN I, II, VIII are pure sensory. Anatomy Final- Very Good ▪ CN III, IV, VI, XI, XII are pure motor. Vacations Are Heavenly! ▪ CN V, VII, IX, X are mixed (both sensory and motor). The sensory components of cranial nerves originate from collections of neurons located outside the brain. o These collections of pseudounipolar neurons are called sensory ganglia. ▪ They are the same functionally and anatomically as the Dorsal Root Ganglia in spinal cord. o Pseudounipolar neurons in sensory ganglia send out a branch that divides into two branches: ▪ Central branch that enters the brain and peripheral branch that is connected to a sensory organ. - Bipolar neurons are concerned with special senses. - Pseudounipolar neurons are concerned with general sensations Olfactory Nerve (I) Pure sensory (special sensory). o Conduct the sense of smell (olfaction). Olfactory receptor cells are Bipolar neurons. o 1st order neurons. o They’re located in the olfactory mucosa. ▪ In the roof of the nasal cavity. o Axons (central processes) pass through perforations in cribriform plate of ethmoid bone. ▪ Those axons form the olfactory nerve. After passing the cribriform plate, 1st order neurons synapse with 2nd order neurons in olfactory bulbs. o Olfactory bulbs are paired masses of gray matter. ▪ Extensions of forebrain. o Axons of 2nd order neurons extends from olfactory bulbs posteriorly forming olfactory tracts that run to primary olfactory area. Testing Integrity of Olfactory nerve (I) Test each nostril with essence )‫ (مستخلَص مركز لرائحة‬bottles of coffee, vanilla, peppermint. o Remember COVID-19 Cause Loss of sense of smell. Optic Nerve (II) Pure sensory (special sensory). o Conduct the sense of vision. Pass through optic canal to reach the orbit. The optic nerve was discussed in detail in LECTURE 1 1 Testing Integrity of Optic nerve (II) Test the vision by eye chart. Examine Visual Fields by wiggling fingers 1 foot from patient's eyes, asking which fingers they see move. Use a fundoscopy. Oculomotor Nerve (III) Pure motor. o Motor supply to extrinsic muscles of eye. Emerge from anterior surface of midbrain. Originates from motor neurons in: o Oculomotor nucleus (somatomotor). o Edinger-Westphal nucleus (parasympathetic [visceral] Motor). Pass through superior orbital fissure to reach the orbit. Divide into superior and inferior divisions. o Superior division innervates superior rectus, levator palpebrae superioris muscles. o Inferior division innervates inferior rectus, inferior oblique, medial rectus muscles. ▪ Inferior division sends branches that enter the ciliary ganglion. ▪ Where they synapse with the ganglion cells, which sends the short ciliary nerve (postganglionic fibers). ▪ Short ciliary nerve innervate ciliary muscle & constrictor (sphincter) pupillae muscle. Levator palpebrae Superioris muscle ▪ It’s attached to the upper eyelid (not the eyeball). ▪ It elevates upper eyelid. Testing Integrity of oculomotor nerve (III) Test pupillary reflexes (pupil’s Light Reaction) by shining a light from the side. o Look for failure of movement, nystagmus. o Look at pupils: Shape, Relative Size, Ptosis. Test Convergence by moving finger towards bridge of patient’s nose. Test Accommodation by patient looking into Distance, then a pen 30 cm from nose. Test Extraocular movements - follow fingers. Trochlear nerve (IV) Pure Motor. The smallest cranial nerve. Trochlear nucleus in the midbrain. Trochlear nerve emerge from midbrain posteriorly. o The ONLY CN to leave posteriorly (dorsally). o The ONLY CN to decussate inside the brainstem. ▪ Left superior oblique supplied by right trochlear nerve. Pass through superior orbital fissure to reach the orbit. Supply the Superior Oblique muscle (SO4). Abducent Nerve (VI) Pure Motor. Abducent nucleus is in the pons. Abducent nerve emerge from pontomedullary junction. Pass through superior orbital fissure to reach the orbit. Called abducent nerve because it Supply the Lateral Rectus muscle (LR6). causes the abduction of the eye. 2 Testing Integrity of trochlear (IV) and abducent (VI) nerves Test Extraocular movements - follow fingers. o Problem with trochlear nerve if eye can’t go down and out. o Problem with abducent nerve if eye can’t rotate lateral. Trigeminal Nerve (V) The largest cranial nerve. Mixed nerve. Trigeminal nerve emerges from the midlateral surface of pons as two roots: o Small motor root. ▪ Originates from masticator motor nucleus of trigeminal nerve in pons. o Large sensory root. ▪ Sensory root joins the trigeminal (semilunar) ganglion. ▪ Sensory root terminates in the sensory nuclei of trigeminal. Extends from the pons? all the way down to the C2 segment of spinal cord. 3 divisions arise from trigeminal nerve: 1. Ophthalmic division (V 1) 2. Maxillary division (V 2) 3. Mandibular division (V 3) Ophthalmic and Maxillary are pure sensory nerves. Mandibular is a mixed nerve. o Sensory root of mandibular nerve and motor root of trigeminal nerve connect together to emerge as a mixed nerve. In the middle cranial fossa, trigeminal ganglion lies in a pouch of dura mater, called trigeminal cave (Meckel's cave). Ophthalmic Nerve (V1) Pure sensory. Pass through superior orbital fissure to reach the orbit. Provide sensory innervation to: o Forehead, upper eyelid, cornea of the eye, part of the nose, and tip of the nose. Maxillary Nerve (V2) Pure sensory. Exit the skull through foramen rotundum. Provide sensory innervation by sensory branches: o Branches via inferior orbital fissure provide sensation from Face, cheek, upper lip, and upper teeth. o Branches via pterygopalatine canal provide sensation from soft and hard palate, nasal cavity & pharynx. o Meningeal branch provide sensation from meninges. 3 Mandibular Nerve (V3) Exit the skull through foramen ovale. Mixed nerve: o Sensory: supplies general sensations from the mucous membranes of the mouth and cheek, anterior two-thirds of the tongue, lower teeth, lower lip, skin of the lower jaw, side of the head and scalp and meninges of the anterior and middle cranial fossae. o Motor: supplies 8 muscles. ▪ The Muscles Of Mastication: Temporalis, Masseter, Medial pterygoid, and Lateral pterygoid muscles. ▪ Mylohyoid ▪ Anterior Belly Of The Digastric. ▪ Tensor Veli Palatini (present in soft palate, helps in swallowing of food) ▪ Tensor Tympani Testing Integrity of trigeminal nerve (V) Corneal Reflex: patient looks up and away. o Touch Cotton Wool to other side. o Look For Blink In Both Eyes Facial Sensation: sterile sharp item on forehead, cheek, jaw. o Repeat with dull object. ▪ Ask to report sharp or dull. o If abnormal, then Temperature [Heated/ Water-cooled Tuning Fork] and Light Touch [Cotton]. Motor: patient opens mouth, clenches Teeth (action of mastication muscles). o Palpate temporalis, masseter muscles as they clench. Test Jaw Jerk: o Doctor’s finger on tip of jaw. o Grip patellar hammer halfway up shaft and tap Doctor’s finger lightly. o Usually nothing happens, or just a slight closure. Relation between Cavernous Sinus and Cranial Nerves In lateral wall of cavernous sinus: o III o IV o V1 o V2 Through the cavernous sinus: o VI o Internal carotid artery (ICA) 4