Cranial nerves Flashcards
How many pair of spinal nerves and cranial nerves are in the PNS?
Cranial Nerves: 12 pairs
Spinal Nerves: 31 pairs
What is a collection of cell bodies in the CNS vs PNS called?
What is the exception?
CNS = Nuclei PNS = Ganglia
Cranial nerves are peripheral nerves but are termed nuclei
Which cranial nerves are ‘atypical’ and why?
Typical peripheral nerves are normal spinal nerves 3-12
1-2 are atypical nerves because they are extensions of the brain. Compared to typical peripheral nerves, so it doesn’t have a cranial nerve nucleus in the brainstem like nerves 3-12
Which cranial nerves carry autonomic fibres?
3, 7, 9 and 10
(III, VII, IX, X)
What are the names of the 12 cranial nerves?
State which cranial nerves are sensory, motor or mixed
Label the select Foramina in the Skull
Cranial nerve emerge from holes 1-12 in that order from front to back
State which foramina in the skull each CN emerges from
State which region of the brainstem each CN nuclei resides
What are the 2 exceptions
3 and 4 come from the midbrain
5,6,7,8 come from the pons
9, 10, 11, 12 come from the medulla
Excepton: 1 and 2 do NOT come from the brainstem, they come directly from the brain
What is name and function of CN I
Describe its pathway
Olfactory nerve: sense of smell (sensory)
Starts at the olfactory mucosa where the olfactory receptor neurons are located (sense of smell is detected here)
The axons assemble into small bundles of olfactory nerves and assend through the cribiform plate of the ethmoid bone
Once in the cranial cavity, the fibres form the olfactory bulb which then pass into the olfactory tract.
Why are CN I and II not considered ‘true nerves’
because they do NOT come from the brainstem, they come directly from the brain
considered a ‘a brain tract’
What structure is indicated on the image?
Which bone is this structure found in?
Cribriform Plate in the Ethmoid bone
What is the clinical term for a loss of sense of smell?
Anosmia
Why might a fractured cribriform plate lead to a loss of sense of smell and a runny nose?
Loss of smell: compression of the olfactory receptor neurons ➞ can’t feedback to olfactory bulb
Runny nose: CSF leakage from nose!
Give 4 causes for a lack of smell
1) Upper resp. tract infection
2) Nasal polyps/rhinosinusitis
3) Trauma
4) Meningitis
How do you test the Olfactory Nerve?
First, the patient should be asked if they have noticed any changes in their taste or sense of smell.
Then each nostril should be tested, asking the patient to identify a certain smell (coffee, orange, vanilla).
The eyes should be closed for this part of the examination.
What is name and function of CN II
Describe its pathway
Optic nerve: innervates the eye, sight (sensory)
Complex pathway but simplified:
Nerve comes in through the back of the eye
Fibres cross over from the eye at the optic chiasm
Name 5 ways to examine the integrity of the optic nerve
1) Visual acuity: snellen chart
2) Colour vision: Ishihara test
3) Visual Fields
4) Pupillary reflexes
5) Fundoscopy
Where will visual field loss be produced if there is a lesion on the optic chiasm?
lesion on the optic chiasm will produce a visual field defect laterally on both sides
What is the pupillary reflex? (In response to light)
It is a neural pathway which has an afferent limb (from the optic nerve CN II) and two efferent limbs (from the oculomotor nerve CN III)
The afferent limb carries sensory input and when light is shone, cells of the retina project fibers through the optic nerve
The efferent limb is the pupillary motor output and controls the ciliary sphincter muscle of the iris. CN III is under PNS control and causes constriction of the pupil in response to light
What is name and function of CN III
Describe its pathway (Incl what structures are innervated)
Occulomotor nerve: moves the eyeball/eyelid and pupil constriction (motor + PNS)
Starts in the occulomotor nucleus of the midbrain
It exits the brain through the superior orbital fissue and splits into 2 branches: superior and inferior
The superior branch provides motor innervation to the superior rectus and levator palpabrae superioris.
The Inferior branch provides motor innervation to middle rectus, inferior rectus, inferior oblique, sphincter of the iris (PNS to constrict) and ciliary muscle of the eye
What are the 4/6 extraocular eye muscles innervated by CN III
State the movement each allows
Superior Rectus Muscle (upwards movement)
Medial Rectus Muscle (inward movement)
Inferior Rectus (downwards movement)
Inferior Oblique (upwards and outwards movement)
What nerve innvertates the other 2/6 extraocular eyes that are not innervated by CN III
LR6: Lateral rectus innervated by CN VI
- Outward movement
SO4: Superior oblique innervated by CN IV
- depresses, internally rotates and abducts the eye
- ability to move eye downward and out
What is the function of Levator Palpebrae Superioris?
Lifts the upper eyelid (CN III)
Label the image of the eye
What other nerves are tested along with the Oculomotor Nerve?
How can these be tested
CN IV and CN VI are examined together by drawing an H to test if all eye movements are working
Also test Pupillary Light Reflex and Accommodation reflex (absent in paralysis of ciliary muscle)
What are the typical features of a complete third cranial nerve palsy?
Explain why each occurs
‘Down and Out eye’ (while other eye is looking straight ahead): No innervation by CN III muscles, hence only CN IV and VI are working which pull the eye down and out
Closed eyelid: CN III supplies levator palpabrae superioris which lifts the eyelid
Enlarged pupil: normally PNS fibers go to sphincter of the eye which constrict pupil
List 3 reasons why autonomic damage to CN III may occur
1) Aneurysm
2) Increased intracranial pressure
3) Mydriasis or ‘Blown’ pupil
What is name and function of CN IV
Describe its pathway
Trochlear nerve: eye movements ‘down and ‘in’ (motor)
Starts at the Trochlear nucleus and passes dorsal to Midbrain through the superior orbital fissure to Superior Oblique Eye Muscle
List 3 nerves and 1 artery that travel through the cavernous sinus with CN IV
Occulomotor nerve (CN III)
Abducens nerve (CN VI)
Trigeminal nerve (V1 and V2)
Internal Carotid Artery
Which CN travels the longest intracranial length?
Trochlear Nerve (CN IV)
How may the Trochlear nerve be damaged?
Give 3 signs/symptoms of CN IV palsy
Cavernous sinus thrombosis: CN IV passes through CS with other nerves so palsy doesn’t tend to occur on its own, if it does it is very subtle.
Signs/symptoms of CN IV palsy:
- Hypertropia on affected side (one eye higher than fixating eye)
- Vertical and horizontal diplopia (double vision) ➞ worse on downgaze (walking downstairs) or reading
- subtle head tilt away from side of problem
What is the name and function of CN VI
Describe its pathway
Abducens nerve: lateral, eye movement (motor)
From the Abducens nucleus (pons) to the lateral rectus of the eye
How may the Abducens nerve be damaged?
What would be seen on examination?
What is meant by a ‘False Localising Sign’?
Cavernous Sinus Thrombosis
Ask patient to draw an H, they cannot ABDUCT affected eye
False localising signs: as this is a very long nerve, signs may reflect dysfunction that are distant from the site of the pathology. (difficult to localise lesion)
What is the name and function of CN V?
Describe its pathway
Trigeminal nerve: general face sensation and muscles of mastication (both)
From the Trigeminal sensory nuclei to the Trigeminal ganglion to branch into V1, V2 and V3
What are the 3 branches of the Trigeminal nerve? (incl sensory and motor)
What does each supply?
Ophthalmic (V1) branch: sensory innervation to the eye
Maxillary branch (V2): sensation to the sinuses, nose, skin of the cheek
Mandibular branch (V3): supplies mandible area, teeth of the bottom jaw, muscles of mastication (motor)
Where do V1, V2, and V3 all exit the skull?
Ophthalmic (V1) through Superior Orbital Fissure
Maxillary (V2) through Foramen Rotundum
Mandibular (V3) through Foramen Ovale
What is Trigeminal Neuralgia?
Extremely painful (sharp pain), can be triggered by brushing side of face
What is an Inferior Alveolar Nerve Block?
The Inferior Alveolar Nerve is a branch of V3 and thus a block to this nerve can anaesthetise the lower teeth
How can we test the sensory and motor branch of the Trigeminal nerve?
Sensory:
Ask the patient to close their eyes and introduce a cotton wisp to areas of the face supplied by the 3 divisions to detect tactile sensory competence.
Motor:
Ask the patient to clench their jaw as you palpate superior to the zygomatic arch to feel for contraction of the temporalis and then repeat palpating inferiorly for the masseter.
Ask the patient to open their mouth and deviate their mandible to the right and left to check for competence of the medial and lateral pterygoid muscles
Explain the corneal reflex and state what nerves are being tested?
This is the involuntary blinking of the eyelids stimulated by tactile, thermal or painful stimulation of the cornea
The ophthalmic nerve (V1 branch of CN V) acts as the afferent limb, detecting the stimuli.
The facial nerve (temporal & zygomatic branches) act as the efferent limb, causing contraction of the orbicularis oculi muscle.
If the corneal reflex is absent, it is a sign of damage to the trigeminal/ophthalmic nerve, or the facial nerve.
Explain the Jaw Jerk reflex and state which nerve is being tested
This can help to indicate an upper motor neuron lesion.
The patient is told to let their mouth fall open slightly. The examiner places his finger on the patient’s chin and taps his finger lightly with a tendon hammer.
An exaggerated closure of the mouth can indicate an upper motor neurone lesion, e.g. pseudobulbar palsy of the fifth cranial nerve.
What is the name and function of CN VII
Describe its pathway
Facial nerve: facial movements (expression), taste (ant. 2/3rds tongue), salivation and lacrimation (both + PNS)
From the Pons to the IAM → Facial Canal → Stylomastoid foramen → Distal Branches (5)
What are the 5 Motor branches of the facial nerve that control facial expression?
(To zanzibar by motor car)
Temporal
Zygomatic
Buccal
Mandibular
Cervical
What is the sensory, motor, special sensory and PNS innervation of the facial nerve?
Sensory: small area around the concha of the auricle
Motor
- nerve to stapedius in middle ear
- digastric (post belly), and stylohyoid muscles
- temporal, zygomatic, buccal, mandibular, cervical
PNS:
- submandibular and sublingual salivary glands
- lacrimal Glands
Special sensory: chorda tympani → taste to ant 2/3rds tongue
What are the 3 PNS (autonomic) innervations by the facial nerve?
Sectetomotor to many of glands of the head and neck: including:
- Submandibular and sublingual salivary glands.
- Lacrimal glands.
- Nasal, palatine and pharyngeal mucous glands.
What is Bell’s Palsy?
Why is it considered a diagnosis of exclusion?
Idiopathic one-sided facial paralysis (on the ipsilateral side)
Bell’s Palsy is most common cause of facial palsy BUT as this is Idiopathic we must first rule out potential causes before we can conclude it is this
eg. we must first assess the ear to check there isn’t pathology there causing the facial nerve palsy (such as an ear infection)
Bells Palsy indicates lower motor neuron problem
List 4 things that must be considered before a diagnosis of Bells’ Palsy is concluded
Surgery, Tumors, Fracture, Infection
How would we examine the facial nerve?
Assess movements and taste
Movements: raised eyebrows, blown out cheeks, closed eyes, smiling, pursed lips
Taste: ask the patient if they have noticed any recent changes in their sense of taste
What is the name and function of CN VIII
What are the 2 branches of this nerve and what does each branch do?
Vestibulocochlear Nerve: hearing and balance (sensory)
Vestibular branch: balance
Cochlear branch: hearing
How may the vestibulocochlear nerve get damaged?
Vestibular Schwannoma: a swelling on the nerve, which put pressure and compresses it. This results in a sensorineural hearing loss
How would we test the vestibulocochlear nerve?
1) Whisper in each ear
2) Rinne’s & Weber’s Tuning Fork Test (compares R and L ear and air vs bone conduction)
Explain Webers test
State what would be expected:
1) normally
2) if there was a sensorineural hearing loss
3) If it is a problem in the external/middle ear (eg. fluid in ear)
Webers test: put fork in the middle of ear and ring
This test compares where the patient hears the sound when the fork is rung (which ear)
1) Normally: it would be in both ears (all around).
2) Sensorineural problem: sound will be heard in the good ear (uneffected ear).
3) Problem in the external/middle ear: sound will be heard in the bad ear (eg ear with fluid in it)
What is the Rinnies test and what should normally be heard?
Rinne’s tets: hold tuning fork against ear and compare it to holding it behind ear and holding it against bone.
This asses the air vs bone conduction.
Normally air conduction is better than bone conduction
What is the name and function of CN IX
Describe its pathway
Glossopharyngeal Nerve (both + PNS)
From the medulla oblongata, through the jugular foramen to the tongue- parotid gland, carotid body and sinus and stylopharyngeus
What is the motor innervation by the Glossopharyngeal nerve?
Stylopharyngeus muscle (only a small branch)
Actions: elevate the larynx, elevate the pharynx, swallowing
What is the sensory branch of the Glossopharyngeal nerve?
Oropharynx, the posterior 1/3 of the tongue and the carotid body and sinus
What is the PNS innervation of the glossopharyngeal nerve?
Supplies the parotid gland
If a patient has problems with the Glossopharyngeal nerve what may they present with?
Dysphagia: difficulty in swallowing (b/c of stylopharyngeus muscle)
Patient may say they notice a change in taste
What nerves does the ‘Gag’ or pharyngeal reflex assess?
What is considered a normal vs abnormal reflex and what may this indicate?
The affernt (sensory) limb is mediated by CN IX (glossopharyngeal nerve)
The efferent (motor) limb by CN X (vagus nerve).
Normally palate should rise when patient opens mouth and says ahhhh. With a CN IX and X Palsy the palate away from the lesion.
What nerves do a ‘Carotid Sinus massage’ involve?
The affernt (sensory) limb is mediated by CN IX (glossopharyngeal nerve)
The efferent (motor) limb by CN X (vagus nerve).
What nerve is termed the ‘wandering nerve’ and why?
CN X: The Vagus nerve, because it innervated structures outside of the head and neck region
What the name of CN X
Describe its pathway
Vagus nerve (both + PNS)
Medulla, through Jugular formaen and beyond
The Vagus nerve gives of the left and right RLN, what does this stand for?
Describe what is meant by the asymmetry of this nerve?
Recurrent Laryngeal Nerves
Asymmetry:
- Left RLN loops under the arch of aorta
- Right RLN loops under the right subclavian artery
What is the sensory innervation by the Vagus nerve
Laryngopharynx and ear
What is the motor innervation of the Vagus nerve
Muscles of the pharynx and larynx
What is the PNS innervation of the Vagus nerve
Heart, lungs and GIT
Give 2 things that may indicate Vagus nerve damage?
Hoarse Voice: RLN damage
Bovine cough: ‘coughing like a cow’ occurs because larynx isnt move properly, so vocal cords dont close.
What is the name and function of CN XI
Describe its course and Incl state 2 parts of this nerve
Accessory nerve: SCM and Trapezius (motor)
1) The spinal portion (main part)
2) The cranial portion (short)
The spinal portion is the main part and its cell bodies are located in the spinal cord roots C1-C5
They enter the skull through the Foramen magnum
Then exit the skull through the Jugular Foramen with CN IX and X, along the internal carotid artery to reach the Trapezius and SCM
What would look for and how would you test CN XI damage?
Look for: Wasting of the SCM and Trapezius
Ask patient to rotate head against resistance to test SCM
Ask patient to shrug shoulders against resistance to test Trapezius
What is the name and function of CN XII
Describe its pathway
Hypoglossal nerve (motor)
From the hypoglossal nucleus in the medulla, through the hypoglossal canal to the tongue
What would indicate damage to the Hypoglossal nerve?
Fasciculations and atrophy of the Tongue
Tongue would deviates TOWARDS side of lesion (opposite to CN IX and X)
Why do we do a carotid sinus massage for SVT?
Massaging the carotid sinus will stimulate barorecpetors
Signals from here will be transmitted via CN IX (afferent limb) to midbrain centers, mainly the CN X nucleus.
This will stimulate CN X (efferent limb) PNS inntervation to the AV node of the heart. Thus slowing HR
