Cranial Nerves Flashcards
Central Nervous System
Brain and spinal cord
Carry sensory/ motor/ autonomic info between the brain and the head and neck
Collections of cell bodies = nuclei
What are collections of cell bodies in the PNS called?
Ganglia
Mnemonic to remember whether the cranial nerves are sensory, motor or both
Some Say Marry Money But My Brother Says Big Brains Matter Most
Which cranial nerves also carry parasympathetic signals?
III (oculomotor)
VII (facial)
IX (glossopharyngeal)
X (vagus)
3,7,9 and 10
Where are the cranial nerve nuclei for nerves III-XII?
In the brainstem (midbrain, pons and medulla oblongata)
Cells whose axons convey motor / efferent signals to periphery.
Some nerves share nuclei.
Some nerves with both motor and sensory components have a motor nucleus and a sensory nucleus
Parasympathetic fibres arise from specific nuclei in the brainstem
(beware this is v complicated!)
CN I
Olfactory nerve
Axons travel through cribriform plate
(olfactory bulb, tracts, temporal lobe)
Connection with limbic system
CN II
Optic nerve
Attached to brain not brainstem
(retina, primary visual cortex, calcarine sulcus, medial aspect of occipital lobe)
Optic chiasm
Nasal retinae decussates but info from temporal retinae remains ipsilateral.
Each optic tract contains fibres carrying info about the contralateral visual field
Testing CN II
Visual acuity (Swellen chart)
Visual fields
Pupillary light reflex
Fundoscopy (to see image at back of your retina)
Pupillary light reflex
Normally: both pupils constrict when light shone into either eye (direct and consensual)
Involves CN II (optic) and parasympathetic fibres in CN III (oculomotor)
CN III
Oculomotor nerve
Innervates MR, SR, IR, IO and LPS (extraocular muscles)
Parasympathetic nerves constrict pupil
Nuclei = midbrain
Nerves exit at junction between midbrain and pons
Close to PCA
Testing CN III
Test eye movements
Test pupillary light reflex
Test LPS
Bell’s Palsy
Lesion symptoms:
Ptosis
Lateral deviation of eye
Dilated pupil that doesn’t constrict
CN IV
Trochlear nerve
Innervates superior oblique
Lesions causes diplopia (double vision) on looking down
How to test CN IV
Ask to move eye medially and down
CN VI
Abducens nerve
Innervates lateral rectus
Nuclei in pons
Paralysis means not able to abduct eye on examination.
CN V
Trigeminal
Attached to pons
3 branches
ophthalmic, maxillary and mandibular
Mandibular is only one to carry motor fibres for mastication
CN V sensory functions
Dra, face and scalp, cornea, nose and mouth.
Anterior 2/3 of tongue general sensation.
Carries proprioception from TMJ and mastication muscles
Testing CN V
General sensation of face
Corneal reflex (both sensation of CN V and muscles of facial expression CN VII)
Gently touching cornea should result in blinking
CN VII
Facial nerve
Sensory, motor and parasympathetic fibres
Attached to brainstem at pontomedullary junction
2 roots - medial (motor fibres) and lateral (sensory and parasympathetic fibres, the nervus intermedius)
Facial nerve fibre types
Special sensory - anterior 2/3 of tongue
Motor - muscles of facial expression
Parasympathetic - lacrimal gland, submandibular and sublingual salivary glands
In parotid, facial nerve divides into 5 branches to innervate muscles in face
Testing CN VII
Special sensory:
Ask about taste
Is the eye dry?
Motor:
Any sagging or asymmetry in face
Frown and raise eyebrows
Screw up eyes
Puff out cheeks
Smile
CN VII Pathology
Bell’s Palsy - inflammation or nerve, related to viral infection
Tumours, inflammation of parotid gland, middle ear infection, fractures of temporal bone
Damage to facial nerve
Stroke = affects primary cortex can cause facial weakness
Cell bodies of UMNs in motor cortex.
Axons travel to facial motor nuclei in pons. Cross midline and travel to contralateral facial motor nucleus in pons to synapse to LMN.
Lower part of face is only innervated by contralateral nucleus whereas upper part of face goes to both sides, both facial motor nuclei.
This means if UMNs injured on one side the the lower contralateral face is weak but the upper contralateral face is not weak as muscles are also innervated by unaffected side as both sides of motor cortex innervate one side of upper face.
Therefore, the forehead muscles are preserved.
However, if the facial nerve (LMN) is injured on one side, all the ipsilateral facial muscles are weak.
CN VIII
Vestibulocochlear
Sensory nerve
Vestibular afferents:
Connections to spinal cord, cerebellum, nuclei of CN III, IV and VI, cerebral cortex.
Posture, balance, eye movements, conscious perception of position of head.
Cochlear afferents:
Primary auditory cortex (superior temporal gyrus)
Auditory association cortex (Wernicke’s area)
Testing CN VIII
Testing cochlear component:
Covering each ear and whispering into opposite one
Rinne and Weber’s tests
Audiometry
Testing vestibular component:
Observing balance and gait
Caloric testing (uses temperature)
Pathology of CN VIII
Acoustic neuroma (vestibular schwannoma)
Tumour, benign, compresses nerve, progresses to compress facial nerve
Hearing loss, dizziness, facial paralysis, facial pain.
CN IX
Glossopharyngeal
Sensory, motor, parasympathetic
Attached to medulla via small rootlets
Taste - posterior 1/3 of tongue, general sensation of this area + pharynx, Eustachian tube
Afferents from carotid sinus (baroreceptors) and carotid body (chemoreceptors)
Parasympathetic –> parotid gland
CN X
Vagus
Sensory, motor, parasympathetic
Attached to medulla via small rootlets
General sensation (pharynx, larynx, oesophagus, EAM, tympanic membrane)
Visceral afferents - thoracic and abdominal, parasympathetic
Afferents from aortic bodies and arch
Motor fibres = soft palate, pharynx, larynx
Testing CN X
Hoarseness - sign of vocal cord paralysis
Nasal sound - sign of soft palate paralysis
Elicit gag reflex (afferent fibres are CN IX and efferent fibres are CN X)
Look for reflex contraction of the palate
Ask patient to say “ahhh” and look for elevation of palate
Unilateral lesion of CN X causes palate and uvula to deviate away from side of lesion .
CN XI
Accessory nerve
Innervates sternocleidomastoid and trapezius
Cranial part: Rootlets from medulla, leaves via jugular foramen by joining vagus
Spinal part: from ventral horn, C1-C5.
Patient turns head against resistance
Look for symmetry, ask patients to shrug shoulders.
Cn XII
Hypoglossal
Motor nerve for muscles of tongue
Arises from medulla, through hypoglossal canal
Testing and Pathology of CN XII
Look for atrophy on tongue
Is there deviation of tongue to one side?
Nerve lesion means ipsilateral tongue muscles are paralysed.
Tongue deviates towards affected side.
