Cranial nerves Flashcards
What are the 12 cranial nerves?
- CN I (the olfactory nerve)
- CN II (the optic nerve)
- CN III (the oculomotor nerve)
- CN IV (the trochlear nerve)
- CN V (the trigeminal nerve)
- CN V1 (the ophthalmic nerve)
- CN V2 (the maxillary nerve)
- CN V3 (the mandibular nerve) - CN VI (the abducent nerve)
- CN VII (the facial nerve)
- CN VIII (the vestibulocochlear nerve)
- CN IX (the glossopharyngeal nerve)
- CN X (the vagus nerve)
- CN XI (the accessory nerve)
- CN XII (the hypoglossal nerve)
Describe the anatomy and function of CN I (the olfactory nerve)
• Pathway
- Receptors in the olfactory epithelium in the nasal cavity
- The olfactory nerve fibres pass through the foraminifera in the cribriform plate of the ethmoid bone
- They then enter the olfactory bulb in the anterior cranial fossa
• Components
- Special sensory: smell
Describe the anatomy and function of CN II (the optic nerve)
• Pathway - Enters via the optic canal - Nerves join to form a chiasm - Fibres from nasal part of each retina cross to form optic tract • Components - Special sensory: vision
Describe the anatomy and function of CN III (the oculomotor nerve)
• Pathway
- Emerges from the midbrain
- Exits via the superior orbital fissure
• Components
- The inferior orbital
- The superior, inferior and medial rectus
- The levator palpebrae superioris (eyelid)
- Parasympathetic to constrictor pupilae and dilator pupilae causing constriction of ciliary muscles causing accommodation of the lens
Describe the anatomy and function of CN IV (the trochlear nerve)
• Pathway
- Emerges from the dorsal surface of the midbrain
- Exits via the superior orbital fissure
• Components
- The superior orbital muscle (turns eye downwards)
Describe the anatomy and function of CN V1 (the ophthalmic nerve)
• Pathway
- Emerges from the pons
- Travels through the trigeminal ganglion
- Exits via the superior orbital fissure
• Components
- General; sensory: from cornea, forehead, scalp, eyelids, nose and mucosa of nasal cavity
Describe the anatomy and function of CN V2 (the maxillary nerve)
• Pathway
- Emerges from the pons
- Travels through the trigeminal ganglion
- Exits through the foramen rotundum
• Components
- General sensory: from face over maxilla, maxillary teeth, temporomandibular joint, mucosa of nose, maxillary sinuses and palette
Describe the anatomy and function of CN V3 (the mandibular nerve)
• Pathway
- Emerges from pons
- Travels through the trigeminal ganglion
- Exits via the foramen ovale
• Components
- General sensory: face from over mandible, mandibular teeth, temporomandibular joint, mucosa of mouth and anterior 2/3 of the tongue
Somatic motor: muscles of mastication, part of the digastric, tensor veli palatini and tensor tympani
Describe the anatomy and function of CN VI (the abducent nerve)
• Pathway
- Emerges between the pons and medulla
- Exits via the superior orbital fissure
• Components
- Lateral rectus muscle (abducts the eye)
Describe the anatomy and function of CN VII (the facial nerve)
• Pathway
- Emerges between the pons and the medulla
- Exits via the internal acoustic meatus, facial canal and stylomastoid foramen
• Components
- Somatic motor: Muscles of facial expression and scalp, stapedius of middle ear, part of the digastric muscle
- Visceral motor: Parasympathetic innervation of submandibular and sublingual salivary glands, lacrimal glands, glands of the nose and pallet
- Special sensory: Taste from anterior 2/3 of the tongue and soft pallet
- General sensory: From acoustic meatus
Describe the anatomy and function of CN VIII (the vestibulocochlear nerve)
• Pathway
- Emerges between the pons and medulla
- Exits through the internal acoustic meatus
- Divides into vestibular and cochlear nerves
• Components
- Special sensory: Vestibular sensation from semi-circular ducts, utricle, saccule gives sense of position and movement
- Hearing from cochlea
Describe the anatomy and function of CN IX (the glossopharyngeal nerve)
• Pathway
- Emerges from the medulla
- Exits via the jugular foramen
• Components
- Special sensory: taste from posterior 1/3 of the tongue
- General sensory: Cutaneious sensation from the middle ear and posterior oral cavity
- Visceral sensory: Sensation from the carotid body and carotid sinus
- Visceral motor: Parasympathetic innervation of the parotid gland
- Somatic motor: The stylopharyngeus, helps with swallowing
Describe the anatomy and function of CN X (the vagus nerve)
• Pathway
- Emerges from the medulla
- Exits via the jugular foramen
- Then goes everywhere
• Components
- Special sensory: taste from epiglottis and pallet
- General sensory: sensation from auricle, external acoustic meatus
- Visceral sensory: from pharynx, larynx, trachea, bronchi, heart, oesophagus, stomach and intestine
- Visceral motor: Parasympathetic innervation of muscle in the bronchi, gut and heart
- Somatic motor: To pharynx , larynx, pallet and oesophagus
Describe the anatomy and function of CN XI (the accessory nerve)
• Pathway - Emerges from the medulla - Exits via the jugular foramen • Components - Somatic motor: Striated muscle of the soft pallet, pharynx and larynx and to sternomastoid and trapezius
Describe the anatomy and function of CN XII (the hypoglossal nerve)
• Pathway - Emerges from the medulla - Exits via the hypoglossal canal • Components - Somatic motor: Muscles of the tongue
What happens if CN I is damaged?
- Fractured cribriform plate may tear the olfactory nerve fibres causing anosmia
What happens if CN II is damaged?
- Increase in CSF pressure can cause palpilloedema
- Section of the right optic nerve causes blindness through right eye
- Section of optic chiasm causes loss of peripheral vision (bitemporal hemianopsia)
- Section of right optic tract causes blindness in left temporal and right nasal fields (left homonymous hemianopia)
What happens if CN III is damaged?
- Drooping of upper eyelid (ptosis)
- Eyeball abducted and pointing down
- No pupillary reflex
- No accommodation of the lens
What happens if CN IV is damaged?
Diplopia when looking down
What happens if CN V is damaged?
- Paralysis of muscles of mastication
- Loss of corneal sneezing reflex
- Loss of sensation to the face
- Trigeminal neuralgia
What happens if CN VI is damaged?
Medial deviation of the affected eye causing diplopia
What happens if CN VII is damaged
- Most frequently injured due to long pathway through bone
- Bell’s palsy: cannot frown, close eyelid, or bare teeth
What happens if CN VIII is damaged
- Tinnitus (ringing in the ears)
- Deafness (conductive vs sensorineural)
- Vertigo (loss of balance)
- Nystagmus (involuntary rapid eye movements)
What happens if CN IX is damaged
- Loss of gag reflex and taste from back of tongue
- Associated with injuries to CNs X and XI- jugular foramen syndrome
What happens if CN X is damaged?
- Damage to pharyngeal branches cause difficulty swallowing
- Damage to laryngeal branches cause difficulty speaking
What happens if CN XI is damaged?
Weakness in turning head and shrugging shoulders
What happens if CN XII is damaged?
- Vulnerable to damage during tonsillectomy
- Causes paralysis and atrophy of ipsilateral half of tongue (tip deviates towards the affected side)
