5. Introduction to Cranial Nerves - Tagged.pdf

Introduction to Cranial Nerves Naida Jakirlic, OD, FAAO Head & Neck Anatomy Fall 2024  Learning Objectives ▪ Identify the major divisions of the nervous system ▪ Define afferent and efferent fibers ▪ Identify major principles of the somatic and autonomic nervous system ▪ Identify the 12 pairs...

Introduction to Cranial Nerves Naida Jakirlic, OD, FAAO Head & Neck Anatomy Fall 2024  Learning Objectives ▪ Identify the major divisions of the nervous system ▪ Define afferent and efferent fibers ▪ Identify major principles of the somatic and autonomic nervous system ▪ Identify the 12 pairs of cranial nerves ▪ Locate the origin and point of exit of the 12 pairs of cranial nerves 2 Required Reading Illustrated Anatomy of the Head and Neck Pages 134-143 Clinical Anatomy and Physiology of the Visual System Pages 208-226 Note: you only need to know the names and details that are covered in lecture and lab; any additional details provided in the textbook that are not covered in lecture or lab will not be on quizzes or exams. 3 Divisions of the Nervous System Central Nervous System (CNS) Peripheral Nervous System (PNS) ▪ Brain ▪ Cranial nerves ▪ Brainstem: midbrain, pons, medulla ▪ Spinal nerves ▪ Cerebellum ▪ Ganglia ▪ Spinal cord Central Nervous System ▪ Brain: master organ of the CNS ▪ Cerebrum: frontal, temporal, parietal, occipital lobes ▪ Thalamus & hypothalamus ▪ Brainstem ▪ Cerebellum ▪ Spinal Cord: ▪ Lies within vertebral canal deep to meninges ▪ Runs from foramen magnum to L1-L2 ▪ Gives off 31 pairs of spinal nerves Cerebrum The cerebrum is composed of four major divisions (lobes) Frontal Lobe Parietal Lobe ▪ Main area of inhibition of impulsive behaviors ▪ Primary sensory cortex ▪ Primary motor cortex Occipital Lobe ▪ Broca's Area: formation of words. ▪ Primary visual cortex Temporal Lobe ▪ Wernicke’s area: interpretation of speech Peripheral Nervous System Somatic: innervation distributed to structures in the body wall for voluntary control of body movements ▪ skin ▪ skeletal muscle Visceral/autonomic: innervation distributed to visceral structures in body wall and cavity for (mostly) involuntary control of body functions ▪ smooth muscles ▪ cardiac muscle ▪ glands ▪ striated muscle from branchial arch origin (special embryologic origin) Peripheral Nervous System Both somatic and visceral divisions of the PNS contain two types of nerve fibers ▪ Afferent: carry information back to CNS from target organ (sensory) ▪ Efferent: carry information away from CNS to target organ (motor)  Peripheral Nervous System Afferent fibers: carry information back to CNS Efferent fibers: carry information away from CNS ▪ General Afferent (GA): conscious sensation ▪ General Efferent (GE): innervation of striated muscle from skin, skeletal mucosa, and gland mucosa ▪ general somatic efferent: all skeletal muscle except for branchial arch muscles of head and neck ▪ Visceral Afferent (VA): unconscious sensation from viscera and blood vessels ▪ special visceral efferent: branchial arch muscles of head and neck that are striated ▪ Special Afferent (SA): vision, hearing, balance, ▪ Visceral Efferent (VE): innervation of smooth muscle taste, smell (special senses) and glands  Sympathetic & Parasympathetic Nervous System The efferent fibers of the visceral/autonomic nervous system can be further subdivided into sympathetic and parasympathetic fibers, which are part of the autonomic nervous system Sympathetic Parasympathetic  ​control the body's response during perceived  ​control the body's response while at rest threat  responsible for "rest and digest" response  responsible for "fight or flight" response  body slows down (decreased heart rate,  body speeds up, tenses up (increased heart increased secretion from glands, rate, decreased secretion from glands, dilated constricted pupils) pupils) Sympathetic & Parasympathetic Nervous System Sympathetic fibers originate in the spinal cord Exit spinal cord and synapse in sympathetic ganglia Postganglionic fibers hitchhike along different nerves to reach target organs Parasympathetic fibers originate in nuclei of specific cranial nerves Synapse in ganglia located within the head (for head structures) Postganglionic fibers hitchhike along different nerves to reach target organs Ganglion: collection of cell bodies outside the CNS Sympathetic ganglia Parasympathetic Ganglia Questions? 18 Olfactory Nerve – CN I Exits cranial cavity via perforation in the cribriform plate of the ethmoid bone Contains only special afferent (SA) fibers for smell Optic Nerve – CN II ▪ Exits cranial cavity via optic canal ▪ Composed of axons of ganglion cells that are located in the retina ▪ At the optic chiasm, the nasal fibers from each nerve cross over into the opposite optic tract ▪ Contains only special afferent (SA) fibers for vision Oculomotor Nerve – CN III ▪ Originates from nuclei located in the midbrain ▪ Exits cranial cavity via the superior orbital fissure ▪ Mixed cranial nerve ▪ General Efferent (GE) fibers: motor innervation to striated extraocular muscles ▪ Superior rectus ▪ Medial rectus ▪ Levator palpebrae superioris ▪ Inferior rectus ▪ Inferior oblique ▪ Visceral Efferent (VE) fibers: motor innervation to smooth muscles of the eye ▪ Parasympathetic innervation to iris sphincter and ciliary muscle Trochlear Nerve – CN IV ▪ Contains only General Efferent (GE) fibers to the superior oblique muscle ▪ Nucleus located in the dorsal midbrain at the level of the inferior colliculi ▪ Exits midbrain from its dorsal aspect ▪ Only cranial nerve to cross over completely ▪ Exits cranial cavity via superior orbital fissure ▪ Highly vulnerable to trauma due to its long intracranial course Trigeminal Nerve – CN V ▪ Provides sensory information to the CNS from most head and neck structures ▪ Three divisions ▪ Ophthalmic (V1): exits cranial cavity via superior orbital fissure ▪ Maxillary (V2): exits cranial cavity via foramen rotundum ▪ Mandibular (V3): exits cranial cavity via foramen ovale ▪ Complicated cranial nerve ▪ General Afferent (GA): sensation for head & neck structures ▪ General Efferent (GE): motor innervation to muscles of mastication and tensor tympani muscle of the middle ear Trigeminal Nerve – CN V Large sensory nucleus spans length of brainstem; motor nucleus located in the pons Emerges from brainstem at the lateral aspect of the pons Suspends four parasympathetic ganglia within the head – its branches will carry hitchhiking post- ganglionic parasympathetic fibers to their target organs ▪ Ciliary ganglion ▪ Pterygopalatine ganglion ▪ Otic ganglion ▪ Submandibular ganglion Abducens Nerve – CN VI ▪ Contains only General Efferent (GE) fibers ▪ Innervates lateral rectus muscle ▪ Nucleus is in dorsal pons ▪ Emerges from brainstem at junction of pons and medulla (aka pontomedullary junction) ▪ Exits cranial cavity via superior orbital fissure Facial Nerve - CN VII ▪ Emerges from brainstem at the pontomedullary junction, lateral to CN VI ▪ Has multiple nuclei that are in the caudal pons ▪ Exits cranial cavity via internal acoustic meatus, travels within the facial canal of the petrous part of the temporal bone Facial Nerve – CN VII ▪ Complicated cranial nerve ▪ General Efferent (GE): muscles of facial expression and scalp, stapedius muscle ▪ Visceral Efferent (VE): lacrimal gland, submandibular gland, sublingual gland, glands of nose and palate ▪ Special Afferent (SA): taste from anterior 2/3 of tongue ▪ General Afferent (GA): general sensation from the skin of the auricle and small area behind the ear Vestibulocochlear Nerve – CN VIII ▪ Nuclei located in caudal pons and superior medulla ▪ Exits brainstem at pontomedullary junction inferior to CN VII ▪ Contains only Special Afferent (SA) fibers for hearing and balance ▪ Exits cranial cavity via internal acoustic meatus and stays within petrous portion of temporal bone (it does not leave the skull) ▪ Innervates inner ear structures ▪ Cochlea: hearing ▪ Semicircular canals: balance Glossopharyngeal Nerve – CN IX ▪ Emerges from brainstem from the lateral aspect of the rostral medulla ▪ Exits cranial cavity via the jugular foramen ▪ Complicated nerve ▪ Visceral Efferent (VE): parotid gland secretion ▪ Visceral Afferent (VA): sensation from carotid body and sinus ▪ General Afferent (GA): general sensory information from tonsils, pharynx, middle ear, eustachian tube, mastoid air cells, posterior 1/3 of tongue ▪ Special Afferent (SA): taste from posterior 1/3 of tongue ▪ General Efferent (GE): stylopharyngeus muscle for swallowing and speech Vagus Nerve – CN X ▪ Emerges from brainstem inferior to CN IX in the upper medulla ▪ Exits cranial cavity via jugular foramen (with CN IX) ▪ Provides VE innervation to many visceral organs below the neck Vagus Nerve – CN X Complicated nerve: ▪ General Efferent (GE): motor muscles of pharynx, larynx, uvula, soft palate, superior esophagus ▪ Visceral Efferent (VE): parasympathetic innervation to smooth muscles of trachea, bronchi, digestive tract, cardiac muscle ▪ Visceral Afferent: unconscious sensation from pharynx, larynx, trachea, bronchi, heart, esophagus, stomach, intestines ▪ Special Afferent (GA): taste from epiglottis and palate ▪ General Afferent (GA): sensation from auricle, external acoustic meatus, dura of posterior cranial fossa Spinal Accessory Nerve – CN XI ▪ Contains General Efferent (GE) fibers only for motor innervation of trapezius and sternocleidomastoid muscles ▪ Originates both within cranium and outside of skull in upper spinal cord (C1-C5) ▪ Enters skull via foramen magnum ▪ Exits skull via jugular foramen (along with CN IX and CN X) ▪ Only partly a true cranial nerve as it does not entirely originate in the cranial cavity Hypoglossal Nerve – CN XII ▪ Contains only General Efferent (GE) fibers for motor innervation of the tongue ▪ Emerges from brainstem on the lateral aspect of the medulla ▪ Exits cranial cavity via hypoglossal canal Questions?