Cranial Nerves Flashcards
Give an overview of the 12 cranial nerves
CNI = Olfactory = Sensory (smell)
CNII = Optic = Sensory (vision)
CNIII = Oculomotor = Motor (eye movement)
CNIV = Trochlear = Motor (eye movement)
CNV = Trigeminal = Mixed (sensation from face & mouth, muscles of mastication)
CNVI = Abducent = Motor (eye movement)
CNVII = Facial = Mixed (msucles of facial expression, parasymp, taste)
CNVIII = Vestibulocochlear = Sensory (hearing & balance)
CNIX = Glossopharyngeal = Mixed (swallowing, sensation from tongue, parasymp)
CNX = Vagus = Mixed (muscles of throat, parasymp, visceral sensory)
CNXI = Accessory = Motor (soft palate, throat & neck)
CNXII = Hypoglossal = Motor (tongue)
Explain the pathway, components and clinical application of the Olfactory nerve
Pathway: Receptors in Olfactory epithelium of nasal cavity - olfactory nerve fibres pass through foraminifera in cribiform plate of ethmoid bone and enter olfactory bulb in the anterior cranial fossa
Components:
Special sensory - smell
Clinical application:
Fractured cribiform plate may tear olfactory nerve fibres causing anosmia = cannot smell
Explain the pathway, components and clinical application of the Optic nerve
Pathway: Enters via the optic canal, nerves join to form the optic chiasm, fibres from the medial (nasal) half of each retina cross to form the optic tract
Components: Special sensory - vision
Clinical Applications:
- 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
Explain the pathway, components and clinical application of the Oculomotor nerve
Pathway: Emerges from midbrain and exits via superior orbital fissure
Components:
- Somatic motor: extraocular muscles (superior, inferior, medial rectus & inferior oblique) and eyelid (levator palpebrae superioris)
- Autonomic motor: parasympathetic to pupil causing constriction and to ciliary muscle causing accommodation of the lens
Clinical Application:
- Drooping of upper eyelid (ptosis)
- Eyeball abducted and pointing down
- No pupilary reflex
- Reduced accommodation of the lens
Explain the pathway, components and clinical application of the Trochlear nerve
Pathway: Emerges from the dorsal surface of the midbrain and exits via the superior orbital fissure
Components:
- Somatic motor - extraocular muscle (superior oblique turns eye downwards)
Clinical Application:
- Diplopia (double vision) when looking down
Explain the pathway, components and clinical application of the Abducent nerve
Pathway: Emerges between the pons and medulla and exits via the superior orbital fissure
Components:
- Somatic motor - extraocular muscle (lateral rectus abducts the eye)
Clinical Application:
- Medial deviation of the affected eye causing diplopia
Explain the pathway, components and clinical application of the Trigeminal (Ophthalmic division)
Pathway: Emerges from the pons, travels through the trigeminal gnaglion and exits via the superior orbital fissure
Components:
- General sensory - from cornea, forehead, scalp, eyelids, nose and mucosa of nasal cavity and sinuses
Explain the pathway, components and clinical application of the Trigeminal (Maxillary division)
Pathway: Emerges from the pons through the trigeminal ganglion and exits via the foramen rotundum
Components:
- General sensory - from face over
Explain the pathway, components and clinical application of the Trigeminal (Mandibular division)
Pathway: Emerges from the pons and travels through the trigeminal ganglion and exits through foramen ovale
Components:
- General sensory - from face over mandible, mandibular teeth (inferior mandibular nerve), TMJ, mucosa of the mouth & anterior 2/3 of tongue
- Somatic motor - muscles of mastication,part of digastric muscle, tensor veli palatini and tensor tympani
Clinical Applications:
- Paralysis of muscles of mastication
- Loss of corneal or sneezing reflex
- Loss of sensation in the face
- Trigeminal neuralgia
Explain the pathway, components and clinical application of the Facial nerve
Pathway: Emerges between the pons and medulla and exits via the internal acoustic meatus, facial canal and stylomastoid formaen
Components:
- Somatic motor - muscles of facial expression and scalp, stapedius and part of digastric muscle
- Autonomic motor - parasympathetic innervatin of submandibular and sublingual salivary glands, lacrimal glands, glands of nose and palate
Special sensory - taste from anterior 2/3 of tongue and soft palate
General sensory - from external acoustic meatus
Clinical Applications:
- Most frequently injured due to long pathway through bone
- Bell’s Palsy - cannot frown, close eyelid or bare teeth
Explain the pathway, components and clinical application of the Vestibulocochlear nerve
Pathway: Emerges from between the pons and medulla and exits via internal acoustic meatus, dividing into vestibular and cochlear nerves
Components:
- Special sensory - vestibular sensation from semicircular ducts, utricle, saccule gives sense of position and movement
- Hearing from spiral organ (cochlear)
Clinical Applications:
- Tinnitus (ringing in the ears)
- Deafness (conductive vs sensorineural)
- Vertigo (loss of balance)
- Nystagmus (involuntary rapid eye movements)
Explain the pathway, components and clinical application of the Glossopharyngeal nerve
Pathway: Emerges from medulla and exits via the jugular foramen
Components:
- 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
- Autonomic motor - parasympathetic innervation of the parotid gland
- Somatic motor - to stylopharyngous, helps with swallowing
Clinical Applications:
- Loss of gag reflex and taste from the back of the tongue
- Associated with injures to CNX and XI - jugular foramen syndrome
Explain the pathway, components and clinical application of the Vagus nerve
Pathway: Emerges from the medulla and exits via the jugular foramen then disseminates everywhere
Components:
- Special sensory - taste from epiglottis and palate
- General sensory - sensation from auricle, external acoustic meatus
Visceral sensory - from the pharynx, larynx, trachea, bronchi, heart, oesophagus, stomach and intestine
- Autonomic moor - parasympathetic innervation of muscles in bronchi, gut and heart
- Somatic motor - to pharynx, larynx, palate and oesophagus
Clinical Application:
- Damage to pharyngeal branches causes difficulty in swallowing
- Damage to laryngeal branches causes difficulty in speaking
Explain the pathway, components and clinical application of the Accessory nerve
Pathway: Emerges from small cranial (medulla) and large spinal roots + exits via the jugular foramen
Components:
- Somatic motor - striated muscle of soft palate, pharynx and larynx and to sternocleidoastoid and trapezius
Clinical applications:
- Weakness in turning head and shrugging shoulder
Explain the pathway, components and clinical application of the Hypoglossal nerve
Pathway: Emerges from the medulla and exits through the hypoglossal canal
Components:
- Somatic motor - to muscles of tongue
Clinical application:
- Vulnerable to damage during tonsillectomy
- Causes paralysis and atrophy of ipsilateral half of the tongue - top deviates towards affected side
