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Download Physiology and function of the cranial nerves - Wk 1-2
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Physiology and function of the cranial nerves 1. Describe in basic detail, the origin and course of the cranial nerves. 2. Identify the component fibres, structures innervated and functions of each cranial nerve. Like spinal nerves, cranial nerves are bundles of sensory or motor fibres that innervate muscles or glands; carry impulses from sensory receptors, or show a combination of these fibre types. They are called cranial nerves because they emerge through foramina or fissures in the cranium and are covered by tubular sheaths derived from the cranial meninges. There are twelve pairs of cranial nerves, which are numbered I to XII, from rostral to caudal, according to their attachment to the brain and penetration of the cranial dura. Their names reflect their general distribution or function. Nerve Component s Location of Nerve Cell Bodies Cranial Exit Main Actions I Olfactory Special sensory II Optic III Oculomotor Special sensory Somatic motor Olfactory epithelium (olfactory cells) Retina (ganglion cells) Midbrain Foramina in cribriform plate of ethmoid bone Optic canal Superior orbital fissure Smell from nasal mucosa of roof of each nasal cavity and superior sides of nasal septum and superior concha Vision from retina Motor to superior rectus, inferior rectus, medial rectus, inferior oblique, and levator palpebrae superioris muscles; raises superior eyelid; turns eyeball superiorly, inferiorly and medially (Not inferiorly or laterally) Parasympathetic innervation to sphincter of pupil and ciliary muscle; constricts pupil and accommodates lens of eye Superior orbital fissure Motor to superior oblique that assists in turning eye inferolaterally (or laterally when adducted) Superior orbital fissure Sensation from cornea, skin of forehead, scalp, eyelids, nose and mucosa naval cavity and paranasal sinuses Visceral motor IV Trochlear Somatic motor Presynaptic: midbrain Postsynaptic: ciliary ganglion Midbrain V Trigeminal V1 Opthalmic General sensory Trigeminal ganglion V2 Maxillary Foramen rotundum V3 Mandibular Foramen ovale VI Abducent VII Facial VIII Vestibulocochlear Vestibular Cochlear IX Glossopharyngeal Brachial motor Pons Somatic motor Brachial motor Pons Pons Special sensory Visceral motor Geniculate ganglion Presynaptic: pons Postsynaptic: pterygopalatine ganglion; submandibular ganglion Special sensory Vestibular ganglion Special sensory Brachial motor Visceral motor Spiral ganglion Medulla Presynaptic; medulla Postsynaptic; otic ganglion Superior ganglion Visceral sensory Special sensory General sensory Brachial motor X Vagus Visceral motor Visceral sensory XI Spinal Accessory XII Hypoglossal Inferior ganglion Inferior ganglion Medulla Superior orbital fissure Internal acoustic meatus; facial canal; stylomastoid foramen Internal acoustic meatus Jugular foramen Jugular foramen Presynaptic; medulla Postsynaptic; neurons in, on or near viscera Superior ganglion Special sensory General sensory Inferior ganglion Superior ganglion Somatic motor Spinal cord Jugular foramen Somatic motor Medulla Hypoglossal canal Sensation from skin of face over maxilla, including upper lip, maxillary teeth, mucosa of nose, maxillary sinuses and palate Sensation from skin and over side of head mandible including lower lip, mandibular teeth, temporomandibular joint, mucosa of mouth and anterior two thirds of tongue Motor to muscles of mastication, mylohyoid, anterior belly of digastric, tensor veli palatini, and tensor tympani Motor to lateral rectus that turns eye laterally Motor to muscles of facial expression and scalp; also supplies stapedius of middle ear, stylohyoid, and posterior belly of digastric Taste from anterior two thirds of tongue and the palate Parasympathetic innervation to submandibular and sublingual salivary glands, lacrimal gland, and glands of nose and palate Vestibular sensation from semicircular ducts, utricle, and saccule related to position and movement of head Hearing from spiral organ Motor to stylopharyngeus to assist with swallowing Parasympathetic innervation to parotid gland Visceral sensation from parotid gland, carotid body and sinus, pharynx, and middle ear Taste from posterior third of tongue Cutaneous sensation from external ear Motor to constrictor muscles of pharynx (except stylopharyngeus), intrinsic muscles of larynx, muscles of palate (except tensor veli palatini), and striated muscle in superior two thirds of esophagus Parasympathetic innervation to smooth muscle of trachea, bronchi, digestive tract, and cardiac muscle of heart Visceral sensation from base of tongue, pharynx, larynx, trachea, bronchi, heart, esophagus, stomach, and intestine to left colic flexure Taste from epiglottis and palate Sensation from auricle, external acoustic meatus, and dura mater of posterior cranial fossa Motor to sternocleidomastoid and trapezius Motor to intrinsic and extrinsic muscles of tongue (except palatoglossus) 3. Describe the anatomy of the skull with particular reference to the cranial nerves. 4. Identify the eye muscles and describe how they function to maintain binocular vision (conjugate gaze). Remember what Katie said “3, 4 and 6, think of them together” CRANIAL NERVE III Oculomotor MUSCLE INNERVATED Superior Rectus Inferior Rectus Medial Rectus Inferior Oblique IV Trochlear VI Abducens Levator Palpebrae Superioris Superior Oblique Lateral Rectus The general modes of action of the six extraocular muscles have been described in connection with their anatomy: rotation of the eye toward the nose is carried out by the medial rectus; outward movement is by the lateral rectus. Upward movements are carried out by the combined actions of the superior rectus and the inferior oblique muscles, and downward movements by the inferior rectus and the superior oblique. Intermediate directions of gaze are achieved by combined actions of several muscles. When the two eyes act together, as they normally do, and change their direction of gaze to the left, for example, the left eye rotates away from the nose by means of its lateral rectus, while the right eye turns toward the nose by means of its medial rectus. These muscles may be considered as a linked pair contributing to binocular vision. The binocular movements (the movements of the two eyes) fall into two classes, the conjugate movements, when both eyes move in the same direction, as in a change in the direction of gaze, and disjunctive movements, when the eyes move in opposite directions. Thus, during convergence onto a near object both eyes move toward the nose; the movement is horizontal, but disjunctive, by contrast with the conjugate movement when both eyes move, say, to the right. The disjunctive movement of convergence can be carried out voluntarily, but the act is usually brought about reflexly in response to the changed optical situation—i.e., the nearness of the object of gaze. 5. Present an elementary analysis of causes of diplopia. When movements of the external muscles of the two eyes are not perfectly coordinated, a person cannot properly focus the images of the same area of the visual field from each eye and so sees two images instead of one. This condition is called diplopia, or double vision. It can result from paralysis or weakness of certain extrinsic muscles. Diplopia on lateral gaze is associated with VI Abducent nerve paralysis. Diplopia when looking down is associated with IV Trochlear nerve paralysis. However, often diplopia may present as a temporary consequence of acute alcohol intoxication.
