Cranial Nerves Flashcards
How many cranial nerves are there?
12 pairs
Why are they prone to compression?
- Inflammation due to soft nerves pressing on hard bone
- Tumours causing compression
- Fractures of bone
What is the difference between visceral ad general sensory innervation?
- Visceral - not usually conscious; afferent inputs from pharynx, larynx, heart, lung, gut etc
- General - person is aware of it; afferent inputs (i.e. touch, temp, pain) from skin and mucous membranes
What are the three different sensory innervations?
Visceral, general and special sensory
What are the special sensory nerve important for?
Taste, smell, vision, hearing and balance
Describe where the cell body is on a sensory (afferent) fibre
Cell bodies outside on the CNS - i.e. in spinal nerve they are in dorsal root ganglions
Where is the cell body of a somatic motor (efferent) fibre?
Cell body is in the ventricle of the brain, travelling all the way out to the periphery to skeletal muscle
Where is the cell body of an autonomic motor (efferent) fibre?
Cell body in the CNS but also autonomic ganglia as there is a preganglion and postganglionic fibre
From CN I to XII, what is the order of the cranial nerves?
- Olfactory (CN I)
- Optic (CN II)
- Oculomotor (CN III)
- Trochlear (CN VI)
- Trigeminal (CN V)
- Abducent (CN VI)
- Facial (CN VII)
- Vestibulocochlear (CN VIII)
- Glossopharyngeal (CN IX)
- Vagus (CN X)
- Accessory (CN XI)
- Hypoglossal (CN XII)
What is the component and the pathway of the olfactory nerve (CN I)?
- Special sense - smell
- Receptors in olfactory epithelium of nasal cavity, olfactory nerve fibres pass through foraminifera in cribriform plate of ethmoid bone and enter olfactory bulb in the anterior cranial fossa
What can occur if the the cribriform plate fractures?
May tear the olfactory nerve passing through it causing anosmia (loss of smell)
What is the component and pathway of the optic nerve (CN II)?
- Special sensory - vision
- Enters via optic canal, nerves join to form optic chiasm, fibres from medial (nasal) half of each retina cross to form optic tract
Name some clinical applications that occur with damage to the optic nerve (CN II)
- Increase in CSF pressure can cause papilloedema
- Section of 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 hemianopsia)
What are the components of the occulomotor nerve (CN III)?
- 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 is the pathway of the oculomotor nerve (CN III)?
Emerges from midbrain and exits via superior orbital fissure
What is the clinical application of the oculomotor nerve?
- Drooping of upper eyelid (ptosis)
- Eyeball abducted and pointing down (as it doesn’t innervate LR and SO)
- No pupillary reflex
- No accommodation of the lens
What is the component and pathway of the trochlear nerve?
- Somatic motor - extraocular muscle (superior oblique depresses eye)
- Emerges from dorsal surface of the mid brain and exits via the superior orbital fissure
What can occur with damage to the trochlear nerve?
Diplopia when looking down (as SO adducts and depresses)
What is diplopia?
Double vision
What is the component and pathway of the abducent nerve (CN VI)?
- Somatic motor - extraocular muscle (lateral rectus abducts eye)
- Emerges between pons and medulla and exits exits via the superior orbital fissure
What can occur if the abducent nerve is damaged?
Medial deviation of the affected eye causing diplopia
What is the component and pathway of the ophthalmic dividision of the trigeminal nerve (CN VI)?
- General sensory - from cornea, forehead, scalp, eyelids, nose and mucosa of nasal cavity and sinuses
- Emerges from the pons, travels through the trigeminal ganglion and exits via the superior orbital fissure
What is the component and pathway of the maxillary dividision of the trigeminal nerve (CN VII)?
- General sensory - from face over maxilla, maxillary teeth, temperomandibular joint, mucosa of nose, maxillary sinuses and palate
- Emerges from the pons, travels through the trigeminal ganglion and exits via the foramen rotundum
What is the component of the mandibular dividision of the trigeminal nerve (CN VIII)?
- General sensory - from face over mandible, mandibular teeth, temperomandibular joint, mucosa of mouth and anterior 2/3rds of tongue
- Somatic motor - muscles of mastication, part of digastric, tensor veli palatinin and tensor tympani
What are clinical application that occur with damage to the trigeminal nerve (CN V)?
- Paralysis of muscles of mastication
- Loss of corneal or sneezing reflex
- Loss of sensation in the face
- Trigeminal neuralgia
What are the four different components of the facial nerve (CN VII)?
- Somatic motor - muscles of facial expression and scalp, stapedius of middle ear, part of digastric muscle
- Visceral motor - parasympathetic innervation of submandibular and sublingual salivary glands, lacrimal glands, glands of nose and palate
- Special sensory - taste from anterior 2/3rd of tongue & soft palate
- General sensory - from external acoustic meatus
What is the pathway of the facial nerve (CN VII)?
Emerges between pons and medulla and exits via internal acoustic meatus, facial canal and stylomastoid foramen
What are clinical application of the facial nerve (CN VII)?
- Most frequently injured - due to long pathway through bone
* Bell’s palsy - cannot frown, close eyelid, or bare teeth
What is the component of the vestibulocochlear nerve (CN VIII)?
Special sensory - vestibular sensation from semicircular ducts, utricle, saccule gives sense of position and movement, and hearing from spiral organ (cochlea)
What is the pathway for the vestibulocochlear nerve (CN VIII)?
Emerges from between pons and medulla and exits via internal acoustic meatus, dividing into vestibular and cochlear nerves
What is the clinical application fo the vestibulocochlear nerve (CN VIII)?
- Tinnitus (ringing in the ears)
- Deafness (conductive vs sensorineural)
- Vertigo (loss of balance)
- Nystagmus (involuntary rapid eye movements)
What the five components of the glossopharyngeal nerve (CN IX)?
- 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 and carotid sinus
- Visceral motor - parasympathetic innervation of parotid gland
- Somatic motor - to stylopharyngeus, helps with swallowing
What is the pathway of the glossopharyngeal nerve (CN IX)?
Emerges from medulla and exits via jugular foramen
What is the clinical application of the glossopharyngeal nerve (CN IX)?
- Loss of gag reflex and taste from back of tongue
* Associated with injuries to CNs X and XI - jugular foramen syndrome
What are the 5 different components of the vagus nerve (CN X)?
- Special sensory - taste from epiglottis and palate
- General sensory - sensation from auricle, 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 is the pathway of the vagus nerve (CN X)?
Emerges from medulla and exits via jugular foramen and branches off
What is the clinical application of then vagus nerve (CN X)?
- Damage to pharyngeal branches cause difficulty in swallowing
- Damage to laryngeal branches causes difficulty in speaking
What is the component, pathway and clinical application of the accessory nerve (CN XI)?
- Small cranial (medulla) and large spinal roots exit via jugular foramen
- Somatic motor - striated muscle of soft palate, pharynx and larynx, and to sternocleidomastoid and trapezius
- Weakness in turning head and shrugging shoulder
What is the component and pathway of the hypoglossal nerve (CN XII)?
- Emerges from medulla and exits through the hypoglossal canal
- Somatic motor - to muscles of tongue
What is the clinical application of the hypoglossal nerve (CN XII)?
- Vulnerable to damage during tonsillectomy
* Causes paralysis and atrophy of ipsilateral half of tongue. Tip deviates towards affected side
