Cranial Nerves Flashcards
What are cranial nerves prone to? and what do the symptoms relate to?
compression due to inflammation, tumours and fractures
symptoms relate to the function of the nerves
What may cranial nerves contain?
Somatic motor fibres - supply striated muscle
Autonomic motor fibres - cranial division of the parasympathetic supply innervates smooth muscle & glands
Visceral sensory - afferent inputs from pharynx, larynx, heart, lung, gut etc - not normally conscious
General sensory - afferent inputs (eg touch, temperature, pain) from skin & mucous membranes
Special sensory – taste, smell, vision, hearing & balance
Why do cranial nerves not carry sympethetic fibres?
As sympathetic fibres arise form the thoraco-lumbar region
Name fibre type A?
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sensory (afferent) fibres
Name fibre type B?
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somatic motor (efferent) fibres
Name fibre type C?
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autonomic motor (efferent) fibres
Do nerves carry sensory or motor fibres or both?
Some are purely sensory, some purely motor but lots of them are mixed and have both sensory and motor fibres in them
What fibres does the Olfactory (CNI) carry?
sensory (smell)
What fibres does the Optic (CNII) carry?
sensory (vision)
What fibres does the Oculomotor (CNIII) carry?
motor (eye movement)
What fibres does the Trochlear (CNIV) carry?
motor (eye movement)
What fibres does the Trigeminal (CNV) carry?
mixed (sensation from face & mouth, muscles of mastication)
What fibres does the Abducent (CNVI) carry?
motor (eye movement)
What fibres does the Facial (CNVII) carry?
mixed (muscles of facial expression, parasymp, taste)
What fibres does the Vestibulocochlear (CNVIII) carry?
sensory (hearing & balance)
What fibres does the Glossopharyngeal (CNIX) carry?
mixed (swallowing, sensation from tongue, parasymp)
What fibres does the Vagus (CNX) carry?
mixed (muscles of throat, parasymp, visceral sensory)
What fibres does the Accessory (CNXI) carry?
motor (soft palate, throat & neck)
What fibres does the Hypoglossal (CNXII) carry?
motor (tongue)
What is CNI?
olfactory nerve
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What is the pathway of the olfactory nerve?
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 is the clinical application of the olfactory nerve?
fractured cribriform plate may tear olfactory nerve fibres causing anosmia (loss of sense of smell)
Whatis CN II?
optic nerve
What is the pathway of 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 is the clinical application of the optic nerve?
increase in CSF pressure can cause papilloedema (optic disc swelling that is caused by increased intracranial pressure due to any cause)
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)
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What is CN III?
oculomotor nerve
What is the pathway of the oculomotor nerve?
emerges from midbrain and exits via superior orbital fissure
What are the components of the oculomotor nerve?
somatic motor - extraocular muscles (superior, medial & inferior rectus and inferior oblique) and eyelid (levator palpebrae superioris)
autonomic motor - parasympathetic to pupil causing constriction and to ciliary muscle causing accommodation of the lens
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What is the clinical application of the oculomotor nerve?
drooping of upper eyelid (ptosis)
eyeball abducted and pointing down
no pupillary reflex
no accommodation of the lens - wont be able to focus on things close up
What is cranial nerve IV?
trochlear nerve
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)
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What is the clinical application of the trochlear nerve?
diplopia when looking down
What is diplopia?
double vision
What is CN VI?
abducent nerve
What is the pathway of the abducent nerve?
emerges between pons and medulla and exits via the superior orbital fissure
What are the components of the abducent nerve?
somatic motor - extraocular muscle (lateral rectus abducts the eye)
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What is the clinical application of the abducent nerve?
medial deviation of the affected eye causing diplopia
What is cranial nerve V?
trigeminal nerve
What is the pathway of Trigeminal (ophthalmic) CNV1?
emerges from the pons, travels through the trigeminal ganglion and exits via the superior orbital fissure
What are the components of the Trigeminal (ophthalmic) CNV1?
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) CNV2?
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) CNV3?
emerges from the pons, travels through the trigeminal ganglion and exits via the foramen ovale
What are the components of the Trigeminal (mandibular) CNV3?
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 palatini & tensor tympani
What is the clinical application of the trigeminal nerve?
paralysis of muscles of mastication
loss of corneal or sneezing reflex
loss of sensation in the face
trigeminal neuralgia
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What is CN VII?
facial nerve
What is the pathway of the facial nerve?
emerges between pons and medulla and exits via internal acoustic meatus, facial canal and stylomastoid foramen
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What are the components of the facial nerve?
somatic motor - muscles of facial expression & scalp, stapedius of middle ear, part of digastric muscle
autonomic 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 CN VIII?
Vestibulocochlear
What is the pathway of the vestibulocochlear nevre?
emerges from between pons and medulla and exits via internal acoustic meatus, dividing into vestibular & cochlear nerves
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What are the components of the vestibulocochlear nevre?
special sensory :
vestibular sensation from semicircular ducts, utricle, saccule gives sense of position & movement
hearing from spiral organ - organ of corti
What is the clinical application of the vestibulocochlear nerve?
tinnitus (ringing in the ears)
deafness (conductive vs sensorineural)
vertigo (loss of balance)
nystagmus (involuntary rapid eye movements)
WHat is CN IX?
glossopharyngeal nerve
What is the pathway of the glossopharyngeal nerve?
emerges form the medulla and exits via the jugular foramen
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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
autonomic motor - parasympathetic innervation of parotid gland
somatic motor - to stylopharyngeus, helps with swallowing
What is the clinical application 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 CN X?
vagus nerve
What is the pathway of the vagus nerve?
emerges from medulla and exits via jugular foramen, then everywhere!
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What are the components of the vagus nerve?
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
autonomic motor - parasympathetic innervation of muscle in bronchi, gut, heart
somatic motor - to pharynx, larynx, palate & oesophagus
What is the clinical application of the vagus nerve?
damage to pharyngeal branches cause difficulty in swallowing
damage to laryngeal branches causes difficulty in speaking
What is CN XI?
accessory nerve
What is the pathway of the accessory nerve?
small cranial (medulla) and large spinal roots exit via jugular foramen
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What are the components of the accessory nerve?
somatic motor - striated muscle of soft palate, pharynx & larynx, and to sternocleidomastoid & trapezius
What is the clinical application of the accessory nerve?
weakness in turning head and shrugging shoulder
What is CN XII?
hypoglossal nerve
What is the pathway of the hypoglossal nerve?
emerges form medulla and exists through hypoglossal canal
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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
Study this list
- Smell - Olfactory
- Sight - Optic
- Taste - Facial, Glossopharyngeal & Vagus
- Hearing & Balance - Vestibulocochlear
- Movement of the eyes - Oculomotor, Trochlear & Abducent
- Accomodation of the eye – Oculomotor
- Constriction of the pupil - Oculomotor
- Movement of muscles in the face - Facial
- Sensation from the face - Trigeminal
- Chewing - Trigeminal (mandibular)
- Swallowing - Glossopharyngeal & Accessory
- Movement of the tongue - Hypoglossal
- Movement of the vocal cords – Vagus
- Movement of the neck - Accessory