Cranial Nerves Flashcards
What are the reason nerves can be compressed?
Due to inflammation, tumours and fractures
What are all the classifications of fibres that cranial nerves can contain?
Somatic motor fibres
Visceral motor fibres
Visceral sensory
General sensory
Special sensory
What do somatic motor fibres do?
Supply striated muscle
What do visceral motor fibres of the cranial nerves do?
They are parasympathetic fibres and innervate smooth muscle and glands
What are the visceral sensory parts of the cranial nerves?
•- afferent inputs from pharynx, larynx, heart, lung, gut etc - not normally conscious
What are the general sensory cranial nerves responsible for?
•General sensory - afferent inputs (eg touch, temperature, pain) from skin & mucous membranes
What are the special sensory cranial nerves responsible for?
•Special sensory – taste, smell, vision, hearing & balance
What type of cranial nerve are the following?
- Afferent sensory
- Somatic motor (efferent)
- Autonomic motor (efferent)
Where are the olfactory receptors?
Receptors in olfactory epithelium of nasal cavity
Where do olfactory nerve fibres pass?
Olfactory nerve fibres pass through foraminifera in cribriform plate of ethmoid bone and enter olfactory bulb in the anterior cranial fossa
What are the components of the olfactory nerve?
–special sensory - smell
What does a fractured cribiform plate result in?
–fractured cribriform plate may tear olfactory nerve fibres causing anosmia
What is the pathway for the optic nerve?
Enters via optic canal, nerves join to form optic chiasm, fibres from medial (nasal) half of each retina cross to form optic tract
What are the components of the optic nerve?
–special sensory - vision
What is the effect of increase in CSF pressure?
Papilloedema
What is the pathway of the occulomotor nerve?
–emerges from midbrain and exits via superior orbital fissure
What are the components of the occulomotor nerve?
–somatic motor - extraocular muscles (superior, medial & inferior rectus and inferior oblique) and eyelid (levator palpebrae superioris)
–visceral motor - parasympathetic to pupil causing constriction and to ciliary muscle causing accommodation of the lens
What are the clinical applications of the occulomotor nerve?
–drooping of upper eyelid (ptosis)
–eyeball abducted and pointing down
–no pupillary reflex
–no accommodation of the lens
What is the pathway of the trochlear nerve?
–emerges from dorsal surface of the mid brain and exits via the superior orbital fissure
What are the components of the trochlear nerve?
–somatic motor - extraocular muscle (superior oblique turns eye downwards)
What are the clinical applications of trochlear nerve?
Diploplia when looking down
What is the pathway of the abducent nerve?
–emerges between pons and medulla and exits exits via the superior orbital fissure
What is the pathway of the abducent nerve?
Emerges between the pons and the medulla - exits via the superior orbital fissure
What are the components of the abducent nerve?
Somatic motor - extraocular muscle (lateral rectus)
What is the clinical application of the abducent nerve?
Medial deviation of the affected eye causig diplopia
What is the pathway of the trigeminal nerve (ophthalmic)?
–emerges from the pons, travels through the trigeminal ganglion and exits via the superior orbital fissure
What are the components of the trigeminal (ophthamic)?
–General sensory - from cornea, forehead, scalp, eyelids, nose and mucosa of nasal cavity and sinuses
What is the pathway of the trigeminal (maxillary) CNV2?
–Emerges from the pons, travels through the trigeminal ganglion and exits via the foramen rotundum
What are the components of the trigeminal (maxillary)?
–General sensory - from face over maxilla, maxillary teeth, temperomandibular joint, mucosa of nose, maxillary sinuses and palate
What is the pathway of the trigeminal (mandibular)?
–emerges from the pons, travels through the trigeminal ganglion and exits via the foramen ovale
What are the components of the trigeminal mandibular division?
–General sensory - from face over mandible, mandibular teeth, temperomandibular joint, mucosa of mouth & anterior 2/3rds of tongue
–Somatic motor - muscles of mastication, part of digastric, tensor veli palatinin & tensor tympani
What is the clinical application of the trigeminal (mandibular)?
–paralysis of muscles of mastication
–loss of corneal or sneezing reflex
–loss of sensation in the face
–trigeminal neuralgia
What is the pathway of the facial nerve?
–emerges between pons and medulla and exits via internal acoustic meatus, facial canal and stylomastoid foramen
What are the components of the facial nerve?
–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, glands of nose & palate
–special sensory - taste from anterior 2/3rd of tongue & soft palate
–general sensory - from external acoustic meatus
What is the clinical application of the facial nerve?
–most frequently injured - due to long pathway through bone
–Bell’s palsy - cannot frown, close eyelid, or bare teeth
What is the pathway of the vestibulocochlear nerve?
Emerges from between the pons and the medulla and exits via the internal acoustic meatus, dividing into vestibular and cochlear nerves
What are the components of the vestibulocochlear nerve?
–special sensory - vestibular sensation from semicircular ducts, utricle, saccule gives sense of position & movement
- hearing from spiral organ (cochlea)
What are the clinical applications of the vestibulocochlear nerve?
–tinnitus (ringing in the ears)
–deafness (conductive vs sensorineural)
–vertigo (loss of balance)
–nystagmus (involuntary rapid eye movements)
What is the pathway of the glossopharyngeal nerve?
–emerges from medulla and exits via jugular foramen
What are the components of the glossopharyngeal nerve?
–special sensory - taste from posterior 3rd of tongue
–general sensory - cutaneous sensations from middle ear and 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
What are the clinical applications of the glossopharyngeal nerve?
–loss of gag reflex and taste from back of tongue
–associated with injuries to CNs X and XI - jugular foramen syndrome
What is the pathway of the vagus nerve?
–emerges from medulla and exits via jugular foramen, then everywhere!
What are the components of the vagus nerve?
–special sensory - taste from epiglottis and palate
–general sensory - sensation from auricle, external acoustic meatus (facial nerve also supplies general sensory to the external acoustic meatus)
–visceral sensory - from pharnyx, larynx, trachea, bronchi, heart, oesophagus, stomach, intestine
–visceral motor - parasympathetic innervation muscle in bronchi, gut, heart
–somatic motor - to pharynx, larynx, palate & oesophagus
What are the clinical applications of the vagus nerve?
–damage to pharyngeal branches cause difficulty in swallowing
–damage to laryngeal branches causes difficulty in speaking
What is the pathway of the accessory nerve?
–small cranial (medulla) and large spinal roots exit via jugular foramen
What are the components of the accessory nerve?
–somatic motor - striated muscle of soft palate, pharynx & larynx, and to sternocleidomastoid & trapezius
The vagus nerve also supplies somatic motor to the pharynx, larynx palate and oesophagus
What is the clinical application of the accessory nerve?
Weakness in turning the head and shrugging the shoulder
What is the pathway of the hypoglossal nerve?
–emerges from medulla and exits through the hypoglossal canal
What are the components of the hypoglossal nerve?
–somatic motor - to muscles of tongue
What is the clinical application of the hypoglossal nerve?
–vulnerable to damage during tonsillectomy
–causes paralysis & atrophy of ipsilateral half of tongue. Tip deviates towards affected side
