Cranial nerves Flashcards
What can cranial nerve abnormalities arise from?
Lesions affecting the:
- communicating pathways to and from the cortex, cerebellum and other parts of the brainstem
- nerve nucleus
- nerve
- neuromuscular junciton disorders
- muscle
Name the cranial nerves
I- olfactory II - optic III - oculomotor IV- trochlear V - trigeminal VI - abducens VII - facial VIII - vestibulocochlear IX - glossopharyngeal X- Vagus XI -spinal accessory XII - hypoglossal
State the components of each of the cranial nerves
I-olfactoy - sensory II- optic - Sensory III - oculomotor - Motor IV- trochlear - motor V- trigeminal - both VI - Abduncens - motor VII - Facial - both VIII - Vestibulocochlear - sensory IX - Glossopharyngeal - both X- Vagus - both XI- Accessory - motor XII- hypoglossal - motor
What is the function of CN I?
Smell
What is the tract of CN I?
Olfactory cells of the nasal mucosa -> olfactory bulbs -> pyriform cortex
What is the function of the optic nerve?
Vision
What is the tract of the optic nerve?
Retinal ganglion cells -> optic chasm -> thalamus -> primary visual cortex in occipital lobe
How do you examine the optic nerve?
- Optic disc via opthalmoscopy
- Pupillary responses - consensual response
- Visual acuity (snellen)
- Visual fields and blind spot (confrontation)
Explain pupillary reflexes
- optic nerve -> optic tract -> pretectal nucleus ->posterior commissure ->edinger-wetphal nucleus
- oculomotor nucleus ->oculomotor nerve -> ciliary ganglion -> short ciliary nerve to ciliary muscle and constrictor papillae muscle
Severed optic nerve
Monocular vision loss on side of severed nerve
Lesion to optic tract
contralateral homonymous hemianopia
Lesion to optic chiasm
Bitemporal hemianopia
Where is the location of the motor nucleus of CN III?
Midbrain (oculomotor nucleus)
What is the motor function of CN III?
Movement of the eyeball and lens accommodation
•Inferior oblique
•Superior, medial and inferior recti muscles
•Levator palpebrae superioris
What is the parasympathetic function of CN III?
Pupil constriction
•Innervates ciliary muscles and pupillary constrictor muscles
Where is the location of the parasympathetic nucleus of oculomotor
Midbrain - edinger westphal
What is the result of a complete left oculomotor nerve palsy?
- Dilation of the pupil
- Eye down and out
- complete ptosis
What is the function of CN IV?
Move the eyeball (depresses the adducted eye and introrts the abducted eye) - superior oblique muscle
Where is the location of the trochlear nucleus?
Midbrain (inferior colliculus)
What is the function of CN VI?
Eyeball movement - abducts the eye on the horizontal plane, innervates the lateral rectus
Describe abducens nerve palsy
Cannot look to the side of the affected nerve
Which cranial nerve has the longest intracranial course?
Trochlear
Which of the cranial nerves decussate to the contralateral side?
II and IV
What is the sign of a 4th nerve palsy?
Failure of downgaze
What is internuclear ophthalmoplegia?
Disorder of conjugate gaze - failure of adduction of affected eye with nystagmus on lateral gaze in contralateral eye
What does internuclear ophthalmoplegia result from?
Lesion of medial longitudinal fasiculus
What are the signs of horners syndrome?
- Ptosis
- miosis
- anhydrosis
- Aoparent epothalmos
What are the causes of Horner’s syndrome?
Results for ipsilateral disruption of the cervical/thoracic sympathetic chain: •Congenital •Brainstem stroke •Cluster headache •Apical lung tumour •Multiple sclerosis •Carotid artery dissection •Cervical rib •Syringomyelia
What are the branches of the trigeminal nerve?
Ophthalmic, maxillary and mandibular
What is the sensory function of CN V?
- Sensory input from the face
- Ophthalmic, mandibular and maxillary divisions
- Anterior 2/3 of the tongue
What is the motor function of the trigeminal nerve?
- Mastication
* Masseter, temporalis, medial and lateral pterygoids (mandibular branch)
Where is the location of the sensory nucleus of the trigeminal nerve?
Pons and medulla
Where is the location of the motor nucleus of the trigeminal nerve?
Pons
What is herpes zoster ophthalmicus?
Herpes in the distribution of one of the branches of the trigeminal nerve (normally V1)
What is the motor function of the facial nerve?
Muscles of facial expression
Where is the motor nucleus of the facial nerve?
Pons
Where is the sensory nucleus of the facial nerve?
Medulla
What is the sensory function of the facial nerve?
Taste - anterior 2/3 of tongue
What is the parasympathetic function of the facial nerve?
Salivation and lacrimation
Where is the parasympathetic nucleus of the facial nerve?
Medulla
What is bells palsy
Weakness of superior and inferior facial muscles
Describe the difference in an upper and lower motor neurone facial weakness
Lower: upper and Lower muscle of the face
Upper: just weakness of the lower muscles of the face
What nerves are involved in the corneal reflex?
Afferent - V
Efferent - VII (orbicularis oculi)
(tests pontine function)
What is the function of CN VIII?
- Balance - nerve endings within semi-circular canals -> cerebellum and spinal cord
- Hearing - cochlear -> auditory cortex in the temporal lobes
Where is the nucleus of the vestibulocochlear nerve?
Pons and medulla
What is the sensory component of the CN IX?
- Taste - innervates the posterior 1/3 of the tongue
* Proprioception for swelling and blood pressure receptors - innervated pharyngeal wall and carotid sinuses
What is the motor component of CN IX?
- Swallow and gag reflex - innervates the pharyngeal muscles
- lacrimation - lacrimal gland
What is the parasympathetic function of CN IX?
- saliva production
* Innervates the parotid gland
What is the presentation of a glossopharyngeal palsy?
Deviation of the uvula away from the side of the lesion
What is the location of the nucleus of the glossopharyngeal nerve?
Medulla
What is the location of the nucleus of the vagus nerve?
Medulla
What is the sensory function of the vagus?
- Chemoreceptors -innervates the carotid bodies monitoring blood oxygen concentration
- Pain receptors in the dura - respiratory and digestive tracts
- Sensation: external ear, larynx and pharynx
What is the parasympathetic function of the vagus
Smooth muscle and glands of the same areas innervated by the motor component as well as thoracic and abdominal areas
What is the motor function of the vagus?
- Heart rate and stroke volume: pacemaker and ventricular muscles
- Peristalsis: smooth muscles of the digestive tract
- Air flow: Smooth muscles in the bronchial tubes
- Speech and swallowing: muscles of the larynx and pharynx
What is the function of CN XI?
- Head rotation and shoulder shrugging
* Innervates sternocleidomastoid and trapezius
What is the function of CN XII?
Speech and swallowing, motor innervation to the tongue
What is the presentation of a hypoglossal palsy?
Tongue deviates to the side of the lesion
If there is a lesion in the cavernous sinus, which cranial nerves are likely to be affected?
- III - oculomotor - dilated eye, looking down and out, ptosis
- IV - trochlear - failure of downgaze
- V - trigeminal (V1 and V2) -sensory face, muscles of mastication
- VI - Abducens - diplopia, can’t abduct eye on the horizontal plane
- Horner’s syndrome
What nerves can be affected if there is a lesion in the superior orbital fissure?
- III - oculomotor - eye down and out
- IV- trochlear - failure of downgaze
- V1 - trigeminal, ophthalmic branch - sensory to face
- VI - abducens - can’t abduct eye on horizontal plane
What nerves can be affected if there is a lesion at the cerebellopontine angle?
- V - Trigeminal - sensory, muscles of mastication
- VII - Facial - facial expression, taste anterior 2/3 tongue, salivation
- VIII - Vestibulocochlear - balance and hearing
- Corneal reflex affected: afferent - V, efferent VII
What nerves can be affected if there is a lesion at the jugular foramen?
- IX - glossopharyngeal - swallowing proprioception, taste post 1/3, swallowing and gag reflex, saliva, BP receptors
- X - vagus
- XI - accessory - head rotation and shoulder shrugging
What cranial nerves can be affected in a bulbar/pseudobulbar palsy?
- IX - Glossopharyngeal
- X - Vagus
- XI - Accessory
- XII - hypoglossal