Cranial Nerves November 1 2013 Chapter 13 521

Cranial Nerves November 1, 2013 Chapter 13: 521 - 529 Dr. Diane M. Jaworski 138

Each Cranial Nerve is Unique 139

4 Classifications of Cranial Nerves 1. Sensory nerves – carry somatic sensory information: touch, pressure, vibration, temperature, and pain 2. Motor nerves – axons of somatic and autonomic motor neurons 3. Mixed nerves – have both motor and sensory fibers 4. Special sensory nerves – carry sensations: smell, taste, sight, hearing, balance 140

Olfactory Nerve (CN I) Special Sensory - Smell CN I located in cribiform plate of ethmoid bone 141

Olfactory Nerve (CN I) CN I from nasal cavity synapses here Cells synapse in olfactory bulb Projection neurons form the olfactory tract Synapse in thalamus (what smell is) & limbic system (emotion of smell) The only sense that doesn’t need to relay through the thalamus!!! 142 © Mc. Kinley et al. A & P 2013

Optic Nerve (CN II) Special sensory - Vision The optic nerve is a CNS nerve myelinated by oligodendrocytes and can’t regenerate 143

Optic Nerve (CN II) Two visual pathways: Optic Nerve - Chiasm - Tract - Thalamus - Occipital Lobe = object recognition 144 Optic Nerve - Chiasm - Tract - Superior Colliculus = tracking objects

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Eye movements involve 6 eye muscles innervated by 3 cranial nerves: III, IV, & VI 146 © Mc. Kinley et al. A & P 2013

Eye Movements are COMPLEX!!! To look right: -the right medial rectus must RELAX -the left medial rectus must CONTRACT -the right lateral rectus must CONTRACT -the left lateral rectus must RELAX Yet, both muscles are innervated by the same cranial nerve? ? ? Does that mean that both cerebral hemispheres control eye movement? No, the left cortex sends the command to look right. The brainstem sorts out the “mixed” signals to each eye appropriately. 147

Oculomotor Nerve (CN III) CN III – Somatic Motor • eye movement (4 of 6 eye muscles) • muscle that keeps eyelid up • damage results in droopy eyelid (ptosis) – Visceral Motor/Autonomic parasympathetic innervation • pupil constriction & lens focusing 148

Trochlear Nerve (CN IV) (only CN that exits from the dorsal side of brainstem) CN IV Somatic Motor for eye movement: Rolls eye down and out 149

Abducens Nerve (CN VI) CN VI Somatic Motor for eye movement: Horizontal eye movements 150

CN III CN IV CN VI Object tracking Smooth pursuits Saccade - rapid tracking 151

Trigeminal Nerve (CN V) Mixed - sensory and motor CN V Largest cranial nerve 3 major branches - General sensations of face - Muscles of mastication (chewing) 152 © Mc. Kinley et al. A & P 2013

Facial Nerve (CN VII) CN VII 153 © Mc. Kinley et al. A & P 2013

Facial Nerve (CN VII) Somatic Motor: muscles for facial expression Special sensory: taste from anterior 2/3 rds of tongue Visceral motor: Autonomic parasympathetic fibers to tear and nasal mucous glands salivary glands 154

CN VII Facial Muscles 155

Corneal blink reflex CN V feels the pain CN VII closes the eyelid 156

Vestibulocochlear Nerve (CN VIII) Special sensory - balance & hearing • Special Sensory: - vestibular branch balance and equilibrium - cochlear branch hearing • Destination - vestibular and cochlear nuclei in pons and medulla oblongata 157

CN VIII Vestibulocochlear Nerve (CN VIII) 158 © Mc. Kinley et al. A & P 2013

Acoustic Neuroma A tumor of CN VIII that compresses CN VII giving symptoms similar to Bell’s Palsy (except also have hearing loss). 159

Bell’s Palsy Bell's Palsy video http: //www. youtube. com/watch? v=rxl 4 Koi. BTEc 160

Glossopharyngeal Nerve (CN IX) Mixed - sensory and motor CN IX © Mc. Kinley et al. A & P 2013 Two cranial nerves regulate blood pressure CN IX and CN X regulate cerebral and body (peripheral) blood pressure, respectively. Why are two cranial nerves needed? If brain blood pressure drops (detected by receptors in the carotid artery via CN IX), peripheral blood vessels constrict (via CN X) to send more blood 161 to the brain – saving the brain!!!

Glossopharyngeal Nerve (CN IX) – Sensory • taste: posterior 1/3 of tongue • taste: part of pharynx & palate • carotid arteries (blood pressure) – Somatic Motor • motor neurons in medulla to innervate swallowing muscles in pharynx - Visceral Motor • Autonomic parasympathetic to parotid gland for salivation 162

Vagus Nerve (CN X) CN X Autonomics: Slows heart rate Blood pressure (see slide 163) Major parasympathetic innervation to thoracic & abdominal viscera 163 Mosby's Medical Dictionary, 2009. © Elsevier.

Vagus Nerve (X) mixed (sensory and motor) - Sensory • taste from part of pharynx • visceral organs - Somatic Motor: swallowing - Visceral Motor • palate, pharynx • digestive, respiratory, and cardiovascular systems 164 © Mc. Kinley et al. A & P 2013

Accessory Nerve (CN XI) Motor: Throat (larynx, pharynx) Swallowing Neck Muscles (Sternocleidomastoid, trapezius) maintain position of head CN XI 165

Hypoglossal Nerve (CN XII) 166

Hypoglossal Nerve (CN XII) Somatic Motor - tongue movements CN XII 167

CN XII Tongue Muscle Tongue atrophies and deviates toward side of defect 168

Summary of Cranial Nerves 169

Cranial Nerve Midbrain CN III - Oculomotor CN IV - Trochlear Pons CN V - Trigeminal (general sensation) CN VI - Abducens CN VII - Facial CN VIII - Vestibulocochlear (part) Medulla CN V - Trigeminal (pain & temp) CN VIII - Vestibulocochlear (part) CN IX - Glossopharyngeal CN X - Vagus CN XI - Accessory CN XII - Hypoglossal 170 © Tottora & Grabowski Principles of Anatomy & Physiology 1996

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Helpful Hints • • Oh, oh, to touch and feel very green vegetables…. Ah, Heaven Some Say Marry Money, But My Brother Says Big Brains Matter More O O O T T A F V G V A H Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulocochlear Glossopharyngeal Vagus Accessory Hypoglossal Sensory Motor Both Sensory Both Motor 175

How are the functions of cranial nerves tested clinically? CN III CNs III, IV, VI CN V CNs V & VII CN VIII CN IX CN XII 176