Cranial nerves Flashcards
How do cranial nerves exit in relation to their corresponding vertebra? Which cervical nerve is somewhat of an exception and why?
Cervical spinal nerves emerge above their corresponding vertebral body EXCEPT C8 which emerges below the C7 vertebra (between C7 and T1) as there is no C8 vertebra
Where are the cell bodies of cranial nerves and where are the nerves themselves located? kind of nerves are the cranial nerves?
Cell bodies in the brain but actual nerves are peripheral nerves (not part of CNS)
What are the collections of cell bodies called in the CNS and PNS?
CNS: Nuclei
PNS: Ganglia
Which cranial nerves are atypical and why?
CN I and II which are part of the brain tract, so they are an extension of the brain
Which cranial nerves are autonomic?
Autonomic: CN III, VII, IX, X
Why is the accessory nerve sometimes called the spinal accessory nerve?
As it has a cranial portion/root which joins VAGUS and provides part of its motor component
Which general location do all (non atypical) cranial nerves originate from? Which specific cranial nerves originate from where?
The brain stem (midbrain, pons and medulla)
Midbrain: III and IV
Pons: V, VI, VII, VIII
Medulla: IX, X, XI, XII
What is the function of CN I and where is it located?
Sensory: detects sense of smell
Starts at the olfactory mucosa (superior portion of nasal cavity) where the olfactory receptors neurones are
Ascends through cribriform plate of ethmoid bone
Forms the olfactory bulb (swelling of olfactory nerve) -> Olfactory tract
What is the term given for a sense of bad smell not related to a specific odour?
Kakosmia
Name four things that can damage CN I
- Trauma (i.e fractures to cribriform plate)
- Meningitis
- Upper resp tract infection
- Nasal polyps/rhinosinusitis
Define rhinosinusitis
Inflammation of nasal cavity and sinuses
What three things could you use to test one’s sense of smell?
Vanilla, coffee and orange
*test each nostril separetely!
Which of the cranial nerves are purely sensory?
CN I, II, VIII
What is the function of CN II? Briefly describe its course
Sight
Retina -> optic canal -> optic chiasma -> optic tract -> primary visual cortex (occipital lobe)
What structure is the optic chiasma directly superior to? Which major blood vessel runs below and lateral to it?
The pituitary gland is immediately below
The ICA is below and lateral
Name five ways to examine the integrity of the optic nerve, what specific tools might be used to test them if any?
- Visual acuity: snellen chart
- Color vision
- Visual fields
- Papillary reflexes
- Fundoscopy: looking in back of eye at optic disc (i.e for swelling/papilloedema)
Which cranial nerves are involved in papillary reflex?
CN II: afferent nerve sensing sensory info from retina-> brain
CN III: efferent nerve
Which cranial nerves are purely motor?
CN III, IV, VI, XII
What does CN III originate from and which foramen does it pass through to exit the skull? Which muscles does it provide somatic and visceral motor innervation?
Goes from the oculomotor nucleus (in the midbrain) -> superior orbital fissure ->
Somatic: 4/6 Oculomotor muscles
a) Moving the upper eyelid: levator palpabrae superioris
b) Moving the eyeballs: Superior, inferior, medial rectus. Inferior oblique
Visceral/Parasympathetic: sphincter pupillae (constricts during PS stimulation) and ciliary muscle of the eye (changes the lens)
Name the extra ocular muscles and work out how each muscles will move the eye if moving individually. Which cranial nerve supplies the majority of them?
Superior rectus: up
Medial rectus: medial
Inferior rectus: down
Lateral rectus: lateral
Inferior oblique: up, out and external rotation
Superior oblique: down (depression), in (ABduction) and internal rotation
Levator Palpebrae superioris: lifts the upper eyelid
Majority supplied by CN III
Which extraocular muscles does CN III NOT supply? Which cranial nerves do supply these muscles?
Superior oblique (CN IV) and the lateral rectus (CN VI)
What is the classical presentation of a damaged oculomotor nerve?
- Eye is down and out
- Ptosis: droopy eyelid
- Mydriasis: Lone dilated pupil
How can the function of CN III be tested and which reflexes would be absent in a lesion?
- By testing the eye motor movements: ask patient to follow ‘H’ drawn with finger
- Absent pupillary light reflex (paralysis of constrictor muscles)
- Absent accommodation reflex (paralysis of ciliary muscles)
What might cause damage to CN III
- Aneurysm
2. Increased intracranial pressure
What does CN IV supply and what is its course?
Just supplies superior oblique muscle; helps eye look down (and in) on its own
Extends from the trochlear nucleus -> dorsal midbrain -> cavernous sinus -> enters orbit of eye through superior orbital fissure -> superior oblique muscle
Which CN is the only one to emerge from the brain dorsally?
Trochlear: CN IV
Which structures travel through the cavernous sinus?
Therefore, name one pathology that can affect any one of these structures
Cavernous sinus thrombosis can affect any of these structures
IT OAT Trochlear nerve CN IV Abducens nerve CN VI Oculomotor nerve CN III Trigeminal V1 and V2 Internal carotid artery