Cranial Nerves Flashcards
How many pairs of cranial nerves are there?
12
What types of fibres may cranial nerves contain?
- SOMATIC MOTOR FIBRES (supply striated muscle; efferent)
- VISCERAL MOTOR FIBRES (smooth muscle and glands
- VISCERAL SENSORY (afferent; from pharynx, larynx, heart, lung, gut etc; not normally conscious)
- GENERAL SENSORY – (afferent inputs e.g. touch, temperature, pain; from skin & mucous membranes
- SPECIAL SENSORY (taste, smell, vision, hearing & balance)
Difference in structure between the different nerve fibres?
- Sensory (afferent) fibres = signals from periphery to CNS; ganglion along axon
- Somatic motor (efferent) = signals from CNS to periphery; ganglion in CNS
- Autonomic motor (efferent) fibres = signal from CNS; signals synapse between pre and post ganglionic fibres before heading to periphery
Order of cranial nerves I to XII?
OOOTTAFVGVAH
(olfactory, optic, oculomotor, trochlear, trigeminal, abducent, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal)
CNI
Olfactory
Pathway of olfactory CNI?
Receptors in olfactory epithelium of nasal cavity, olfactory nerve fibres pass through foraminifera in cribriform plate of ethmoid bone and enter olfactory bulb in anterior cranial fossa
Components of olfactory CNI?
Special sensory = smell
Clinical application for olfactory CNI?
• Fractured cribriform plate may tear olfactory nerve fibres = anosmia
CNII
Optic
Pathway of optic CNII?
Enters via optic canal, nerves join to form optic chiasm, fibres from medial (nasal) half of each retina cross to form optic tract
Components of optic CNII?
Special sensory = vision
Clinical application of optic CNII?
- Increased CSF pressure = papilloedema
- Section of right optic nerve = right eye blindness
- Section of optic chiasm = loss of peripheral vision (bitemporal hemianopsia)
- Section of right optic tract = blindness in left temporal and right nasal fields (left homonymous hemianopsia)
CNIII
Oculomotor
Pathway of oculomotor CNIII?
Emerges from midbrain and exits via superior orbital fissure
Components of oculomotor CNIII?
- Somatic motor - extraocular muscles (superior, medial & inferior rectus and inferior oblique) and eyelid (levator palpebrae)
- Visceral motor - parasympathetic to pupil causing constriction & to ciliary muscle causing accomodation of lens
Clinical application of oculomotor CNIII?
- Drooping of upper eyelid (ptosis)
- Eyeball abducted & pointed down
- No pupillary reflex
- No accomodation of the lens
CNIV
Trochlear
Pathway of trochlear CNIV?
Emerges from dorsal surface of the mid brain and exits via the superior orbital fissure; goes through pulley and innervates superior oblique
Components of trochelar CNIV?
Somatic motor - extraocular muscle (superior oblique turns eye downwards)
Clinical application of trochlear CNIV?
Diplopia (double vision) when looking down
CNVI
Abducent
Pathway of abducent CNVI?
Emerges between pons and medulla and exits via the superior orbital fissure
Components of abducent CNVI?
Somatic motor - extraocular muscle (lateral rectus)
Clinical application of abducent CNVI?
Medial deviation of the affected eye causing diplopia
CNV
Trigeminal:
- CNV1 = opthalmic
- CNV2 = maxillary
CNV3 = mandibular
Pathway of opthalmic CNV1?
Emerges from pons, travels through the trigeminal ganglion and exits via the superior orbital fissure
Components of opthalmic CNV1?
General sensory = from cornea, forehead, scalp, eyelids, nose & mucosa of nasal cavity and sinuses
Pathway of maxillary CNV2?
Emerges from the pons, travels through the trigeminal ganglion and exits via foramen rotundum
Components of maxillary CNV2?
General sensory - from face over maxilla, maxillary teeth, temporomandibular joint, mucosa of nose, maxillary sinuses and palate
Pathway of mandibular CNV3?
Emerges from pons, travels through trigeminal ganglion and exits via the foramen ovale
Components of mandibular CNV3?
- General sensory - from face over mandible, mandibular teeth, temporomandibular joint, mucosa of mouth & anterior 2/3rds of tongue
- Somatic motor - muscles of mastication, part of digastric, tensor veli palatinin & tensor tympani
Clinical application of trigeminal CNV?
- Paralysis of muscle of mastication
- Loss of corneal or sneezing reflex
- Loss of sensation in the face
- Trigeminal neuralgia
CNVII
Facial
Pathway of facial CNVII?
Emerges between pons and medulla and exits via internal acoustic meatus, facial canal and stylomastoid foramen
Components of facial CNVII?
- Somatic motor - muscles of facial expression & scalp, stapedius of middle ear, part of digastric muscle
- Visceral motor - parasympathetic innervation of submandibular & sublingual salivary glands, lacrimal glands of nose and palate
- Special sensory - taste from anterior 2/3rds of tongue & soft palate
General sensory - from external acoustic meatus
Clinical application of facial CNVII?
- Long pathway to bone so most frequently injured
- Bell’s palsy (cannot frown, close eyelid or bare teeth)
- Main motor nerve of face; trigeminal is main sensory
CNVIII
Vestibulocochlear
Pathway of vestibulocochlear CNVIII?
Emerges from between pons and medulla and exits via internal acoustic meatus, dividing into vestibular & cochlear meatus
Components of vestibulocochlear CNVIII?
- Special sensory - vestibular sensation from semi-circular ducts, utricle, saccule gives sense of position & movement
- Hearing from Organ of Corti
Clinical application of vestibulocochlear CNVIII?
- Tinnitus
- Deafness
- Vertigo
- Nystagmus
CNIX
Glossopharyngeal
Pathway of glossopharyngeal CNIX?
Emerges from medulla and exits via jugular foramen
Components of glossopharyngeal CNIX?
- Special sensory - taste from posterior 3rd of tongue
- General sensory - cutaneous sensations from middle ear & posterior oral cavity
- Visceral sensory - sensation from carotid body & carotid sinus
- Visceral motor - parasympathetic innervation of parotid gland
- Somatic motor - to stylopharyngeus, helps with swallowing
Clinical application of glossopharyngeal CNIX?
- Loss of gag reflex and taste from pack of tongue
- Associated with injuries to CNX and CNXI = jugular foramen syndrome
CNX
Vagus
Pathway of vagus CNX?
Emerges from medulla and exits via jugular foramen, then goes everywhere
Components of vagus CNX?
- Special sensory – taste from epiglottis and palate
- General sensory – sensation from auricle, external acoustic meatus
- Visceral sensory – from pharynx, larynx, trachea, bronchi, heart, oesophagus, stomach, intestine
- Visceral motor – parasympathetic innervation muscle in bronchi, gut, heart
- Somatic motor – to pharynx, larynx, palate & oesophagus
Clinical application of vagus CNX?
- Damage to pharyngeal branches = difficulty swallowing
- Damage to laryngeal branches = difficulty speaking
CNXI
Accessory
Pathway of accessory CNXI?
Small cranial (medulla) and large spinal roots exit via jugular foramen
Components of accessory CNXI?
Somatic motor – striated muscle of soft palate, pharynx & larynx, and to sternocleidomastoid & trapezius
Clinical application of accessory CNXI?
Weakness in turning head and shrugging shoulder
CNXII
Hypoglossal
Pathway of hypoglossal CNXII?
Emerges from medulla and exits through the hypoglossal canal
Components of hypoglossal CNXII?
Somatic motor - to muscles of tongue
Clinical application of hypoglossal CNXII?
- Vulnerable to damage during tonsillectomy
- Causes paralysis & atrophy of ipsilateral half of tongue; tip deviates to affected side
