Cranial nerves Flashcards
What are cranial nerves?
PNS components that connect directly to the brain instead of the spinal cord
What do the numbers of cranial nerves correspond to?
The level they emerge from the brain
1. low numbers = most anterior
2. high numbers = most posterior
What is the special sensory for the olfactory nerve?
Smell
What type of fibres are in the olfactory nerves?
sensory only
What is cranial nerve I
The olfactory nerves
What is the origin of the olfactory nerves?
Receptors of the olfactory epithelium
What do the olfactory nerves pass through?
Cribiform plate of the ethmoid bone
What is the destination of the olfactory nerves?
Olfactory bulbs
What is the pathway of the olfactory nerve?
- Axons from special sensory neurons collect to form around 20 bundles that penetrate the cribiform plate
- olfactory afferents synapse in the olfactory bulb
- axon of post-synaptic neurons proceed to cerebrum as olfactory tracts, running along the underside of the frontal lobe
What happens if the olfactory nerve is damaged?
Loss of sense of smell (anosmia)
Is olfactory innervation ipsilateral or contralateral?
ipsilateral - information is processed by the olfactory bulb on the same side as the nostril detecting the stimulus
What is the clinical test for the olfactory nerve (CNI)?
Hold a strong smelling substance under each nostril
What is cranial nerve II?
The optic nerves
What is the special sensory of the optic nerve?
vision
What are the nerve fibres in the optic nerve?
sensory
What is the origin of the optic nerve?
Retina of eye
What does the optic nerve pass through?
optic canals of sphenoid bone
What is the destination of the optic nerves?
Diencephalon via the optic chiasm
Which side of the visual field hit the nasal part of the retina?
The temporal visual field
Which side of the retina field do images from the nasal visual field hit?
The temporal part of the retina
Where do the optic nerves converge?
At the anterior margin of the diencephalon at the optic chiasma
Where do axons from the temporal visual field cross?
At the chiasma
Where do axons from the nasal visual fields cross?
They remain uncrossed
Which axons diverge from the optic tract and why?
The retinotectal axons go to the midbrain for reflex activity of the eye
Where do most optic nerve axons synapse?
In the lateral geniculate nuclei of the thalamus, where they continue as optic radiation to the visual cortex
What happens if there is damage to the optic nerve before it reaches the chiasma?
Blindness in the same eye
What happens if there is damage at the optic chiama?
Bitemporal hemianopia (loss of temporal fields)
What happens if there is damage to the optic tract/ radiation?
Complex visual losses
What are the clinical tests for visual loss?
- Snellen charts
- Test visual fields in 4 quadrants of each eye
What is cranial nerve III?
The occulomotor nerve
What is cranial nerve IV?
The trochlear nerve
What is cranial nerve VI?
The abducens nerve
What do CN III, IV and VI do?
Motor nerves to the extraoccular muscles of the eye
What does cranial nerve III also do?
carries parasympathetic axons supplying pupillary constrictor muscles and ciliary muscles involved in eye reflexes
What types of nerve fibres are carried by the occulomotor nerve?
motor, and autonomic motor
What is the action of the superior rectus?
To pull the eye up and towards the nose
What is the action of the medial rectus?
Pull the eye towards the nose
What is the action of the superior oblique?
pull the eye down and away from the nose and roll it slightly out
What is the action of the inferior rectus?
To pull the eye down and towards the nose
What is the action of the lateral rectus?
To pull the eye away from the nose
What is the action of the inferior oblique?
Pulls the eye up and away from the nose and roll it slightly out
What muscles do the oculomotor nerve supply?
Superior, medial, and inferior rectus, inferior oblique, constrictor and ciliary muscles
What muscles does the trochlear nerve supply?
The superior oblique
What muscles does the abducens supply?
The lateral rectus
What occurs when there is damage to the occulomotor nerve?
- diplopia
- lateral strabismus (squint)
- dilated pupil in affected eye
What happens if there is damage to the abducens nerve?
- diplopia
- medial strabismus
These can be early signs of raised intracranial pressure, because they have the longest contact with the bone, so may become compressed
What happens if there is damage to the trochlear nerve?
- vertical diplopia
- torsional diplopia
- patient often tilts head to other side to fuse the different images
What is the clinical test for cranial nerves III,IV, and VI?
Ask a patient to follow the end of a pen or pen torch as you move it across the different visual fields
Where does the occulomotor nerve arise?
midbrain
Where does CN IV arise?
in the midbrain
Where does CN VI emerge?
junction between pons and medulla
What is the additional test for the occulomotor nerve?
Shine torch into eye to check for pupillary reflex. Pupil in affected eye won’t respond.
What type of nerve fibres does CN IV use?
motor
What type of nerve fibres does CN VI use?
motor
How can the abducens nerve become damaged?
has longest contact with bone, so can become compressed if ICP increases
What is cranial nerve V?
The trigeminal nerve
Where does the trigeminal nerve arise?
In the pons
What are the main functions of the trigeminal nerve?
sensory to face, scalp, and deep structures of the face, and motor to the muscles of mastication
What are the branches of the trigeminal nerve?
- ophthalamic - sensory
- maxillary - sensory
- mandibular - sensory and motor to muscles of mastication
Where are the cell bodies of the sensory neurons of the trigeminal branches found?
In the trigeminal ganglion
What does the ophthalamic branch supply?
Sensory innervation to the eye and upper parts of the nasal cavity
What are the major branches of the ophthalamic branch?
- frontal - skin of forehead
- lacrimal - lateral skin of eyelid and conjunctiva (blinking)
- nasociliary - medial upper eyelid, conjunctiva, globe, and upper part of nasal cavity
What does the maxillary branch (V2) of the trigeminal nerve supply?
Sensory innervation to the skin from lower eyes to upper lip, maxillary teeth, palate, most of nasal cavity
What does the mandibular branch (V3) of the trigeminal nerve supply?
- Sensory innervation to skin of lower lip and chin, lower teeth, anterior 2/3 tongue, floor of mouth
- motor to muscles of mastication
What are the clinical function tests for the trigeminal nerve?
- Sharp-blunt test over all divisions
- Clench teeth and feel muscles
- Protrude jaw - will deviate to injured side
Which nerve in cranial nerve VII?
The facial nerve
Where does the facial nerve emerge?
between the pons and medulla
What types of nerve fibres does the facial nerve use?
motor, sensory, autonomic
What is the autonomic innervation of the facial nerve to?
salivary, lacrimal, and nasal glands
What does the facial nerve supply?
- motor innervation to all muscles of facial expression
- taste to anterior of tongue (chorda tympani)
- parasympathetic secretomotor nerves to lacrimal glands
- submandibular and sublingual salivary glands
What are the muscles of facial expression?
- frontalis
- orbicularis oculi
- lip elevator
- zygomaticus
- orbicularis oris
- buccinator
- lip depressors
What are the branches of the facial nerve?
- temporal
- zygomatic
- buccal
- mandibular
- cervical
What are the clinical tests of function for the facial nerve?
- ask patient to make exaggerated facial expressions
- facial droop
- wrinkle forehead
- puff out cheeks
- stimulate taste on anterior 2/3 tongue
What happens if there is damage to cranial nerve VII between brainstem and middle ear?
All branches and function are lost
What happens if there is damage to the facial nerve after the middle ear?
taste and lacrimation intact, but facial expression is lost on that side
What happens if there is damage to the facial nerve on the face?
Individual muscle groups are lost depending on the branches damaged
What is cranial nerve VIII?
The vestibulocochlear nerve
What part of the brainstem does the vestibulocochlear nerve arise from?
the medulla and the pons
What types of nerve fibres are carried by the vestibulocochlear nerve
sensory only
What is the special sensory of the vestibulocochlear nerve?
hearing and balance
What is conductive hearing loss caused by?
blockage of or damage to the outer or middle ear
What is sensorineural hearing loss caused by?
damage to cochlear or vestibulocochlear nerve
What are the clinical tests for function for the vestibulocochlear nerve?
- strike high frequency tuning fork and hold 2cm from patient’s ear
- if cannot hear, place it on mastoid process - sensorineural if not
What is cranial nerve IX?
the glossopharyngeal nerve
What part of the brain does the glossopharyngeal nerve arise from?
medulla
What types of nerve fibres does the glossopharyngeal nerve use?
motor, sensory, and autonomic
What does the glossopharyngeal nerve innervate?
- sensory to mucosa of pharynx, posterior 1/3 tongue
- visceral sensation from carotid sinuses and bodies
- parasympathetic secretomotor to parotid salivary glands
- motor to stylopharyngeus muscle
What happens if there is damage to glosspharyngeal nerve?
Swallowing and gag reflexes are damaged
What is the clinical test for the glossopharyngeal nerve?
touch the pharyngeal wall to test gag reflex
What is cranial nerve X?
The vagus nerve
What part of the brain does the vagus nerve emerge from?
medulla
What autonomic innervation does the vagus nerve supply?
afferent to aortic arch, efferent to thorax and abdomen
What does the vagus nerve do?
- motor to muscles of pharynx, larynx, and soft palate
- sensory to mucosa of larynx
- parasympathetic to viscera of thorax and abdomen
What can occur if there is damage to the vagus nerve?
dysarthria, dysphagia, dysphonia
What are the clinical tests for function for the vagus nerve?
- ask patient to say ahhhh - soft palate should raise symmetrically
- ask patient to cough
What is cranial nerve XI?
The accessory nerves
What is unusual about the accessory nerves?
arises from C1-4 of the spinal cord
What does the accessory nerve supply?
Motor to sternocleidomastoid and trapezius muscles
What types of fibres are the accessory nerve?
motor only
What is the clinical test for the accessory nerves?
Ask a patient to shrug or turn their head against resistance
What are the effects of damage to the accessory nerve?
- weakness or paralysis
- head and neck movement issues
- shoulder girdle dysfunction
- shoulder droop
- muscle atrophy
What is cranial nerve XII?
hypoglossal nerve
Where does the hypoglossal nerve emerge?
medulla
What does the hypoglossal nerve supply?
motor to muscles of tongue, voluntary over tongue movements
What nerve fibres does the hypoglossal nerve use?
motor
What is the clinical test for the hypoglossal nerve?
Ask patient to protrude tongue, will deviate to injured side
