Flashcards in Lesson 9: Cranial Nerves V and VII Deck (51):
What is the function of the trigeminal nerve?
THE major sensory nerve for the face, head and neck and for the muscles of mastication.
Carries general sensory information from the head and neck, at all depths from the skull to the skin.
(info from the tongue
It also conducts voluntary motor instructions to the muscles of mastication
Where does the trigeminal nerve enter/exit?
The trigeminal nerve is a mixed nerve that exits/enters at mid pons.
Where does the sensory component of the trigeminal nerve travel?
Leaves the brainstem and mid pons, enters floor of the middle cranial fossa, from which it passes through the skull, leaving the cranium via three openings and exiting the skull through numerous small openings
Which branches supply the upper, mid and lower face?
Which branch innervates the muscles of mastication?
What to they mediate?
Ophthalmic, maxillary, and mandibular branch;
Pain and temperature from the nociceptive receptors in the facial and intraoral skin
What do the first order trigeminal ganglia neurons in the medulla carry, and where do they synapse?
Which structures are mediated in this process?
First order neurons from the trigeminal ganglia carrying pain and temperature information synapse in the “spinal nucleus of the trigeminal nerve”.
- External ear, tympanic membrane, and mucosa of pharynx, larynx, esophagus, and Eustachian tube
What do the first order trigeminal ganglia neurons in the pons carry, and where do they synapse?
First order neurons from the same ganglia that carry touch and pressure will synapse in the “principal sensory nucleus or chief sensory nucleus of trigeminal nerve
Where do neurons from the trigeminal ganglia synapse in the third order/tertiary neuron?
Where do they terminate?
Neurons in both these nuclei will subsequently synapse on cell bodies of the third order/tertiary neuron in the contralateral VPM of the thalamus.
Terminates in the primary sensory cortex in the parietal lobe near the lateral fissure
Where/how does conscious proprioception occur in the trigeminal process?
Axons terminate onto the chief sensory nucleus, the second order neuron. Fibers from this neuron will then cross midline and travel to synapse on the third order neuron in the contralateral VPM of the thalamus. Subsequently, projections from the VPM terminate in the somatosensory cortex for conscious processing
Where/how does unconscious proprioception occur in the trigeminal process?
Occurs via the cerebellum, wherein the first order mesencephalic neuron will synapse onto the second order neuron in the chief sensory nucleus. The second order neuron then send projections to the ipsilateral cerebellum for processing
Which nucleus is involved in a monosynaptic reflex loop to produce the jaw-jerk reflex?
Mesencephalic nucleus - axons will synapse onto the motor nucleus of the trigeminal nerve, which emits the efferent response
Which nerve is used for the jaw reflex?
Uses the trigeminal nerve for both afferent and efferent limbs (‘in on V out on V’).
Which reflex tests the trigeminal nerve's afferent limb? How does it work?
what nerves does it check?
What does it cause in the eye?
Corneal reflex - check both CN V and CN VII together (“in on V, out on VII)
stimulus = touch the cornea/response = blink response
How does the corneal reflex work if there IS/ISN'T a response?
If there IS a response, you quickly know they are both intact. BUT if there ISN’T a response you have to test the afferent and efferent components separately.
If the jaw reflex is hyper-responsive/hypo-responsive, what type of lesion exists?
Hyper-Resopnsive: It is likely an Upper Motor Neuron Lesion and may coincide with absence of voluntary movement
Hypo-Responsive/Absent: A lower motor neuron lesion (LMNL) and coincide with voluntary muscle paralysis or paresis (partial paralysis of the voluntary muscles)
What can the jaw protrusion test indicate?
How does it work for protrusion?
Whether the trigeminal nerve pathway is involved and on which side; whether the trigeminal nerve is functioning
If the left pathway is not functioning, the left side won’t protrude, but the right side will protrude, cause the jaw to deviate towards the impaired side (left)
If a trigeminal lesion is an UMNL/LMNL is it ipsilateral or contralateral to the symptoms?
UMNL: contralateral to the symptoms
LMNL: ipsilateral to the symptoms
What is trigeminal neuralgia?
Pain from irritation along the peripheral component of the trigeminal nerve.
How many nerves are involved for peripheral nerve lesions/CNS lesions?
Peripheral nerve lesions usually involve only one nerve while CNS lesions may involve a group mixed collection of nervous tissue that is damaged at the same time
What types of fibres does the facial nerve have?
Voluntary motor, involuntary motor and special sensory fibres (anterior 2/3 of tongue)
What do the involuntary motor instructions do in the facial nerve?
The facial nerve carries involuntary motor (parasympathetic) instructions to all the glands of the face, except the parotid gland
(submandibular, sublinguial, lacrimal glands)
What do the special sensory instructions of the facial nerve do?
Facial nerve also receives taste sensation from the anterior 2/3 of the tongue and nasopharynx.
Does the facial nerve innervate the parotid gland?
No, but it runs through it
Where does the facial nerve enter/exit the brainstem?
Facial nerve exits/enters the brainstem is at the all-important ponto-medullary junction-right beside the Auditory nerve.
How is the stapedius muscle involved with the facial nerve?
Why is it clinically important?
If a lesion occurs before reaching this point (in the facial canal) then Wallerian degeneration will occur prior to the point where the branch leaves to supply stapedius.
If reinnervation occurs central to the place that the small nerve to stapedius leaves the main nerve, a growing axon originally destined for stapedius may incorrectly find its way into the wrong sheath and end up innervating a facial muscle
What is the reflex test for the facial nerve?
Corneal reflex - requires an intact facial nerve for the efferent response of a blink. No response seen, then you need to test the afferent and efferent components separately. This is done by testing the jaw reflex to rule out a lesion in the afferent trigeminal component
Facial nerve lesion: what is facial palsy?
How does it happen and what parts of the face are affected?
It is a LMNL to the muscles of facial expression - compression along the course of the nerve through the skull and involves the entire side of the face, ipsilateral to the lesion. It will undergo Wallerian degeneration and then regeneration
Usually results from inflammation within facial canal, just before the exit at the stylomastoid foramen
Facial nerve lesion: How does a stroke affect the facial muscles? Why? What is the backup?
Weakness is ONLY on the lower face - because the facial nucleus in the brainstem receives bilateral (although predominantly crossed) input to the area for the upper face
Damage to this input is backed up from the contralateral cortex - The part of the nucleus for the lower face is exclusively from the contralateral cortex resulting in weakness for the lower face
Facial Nerve Testing: what would you ask a patient to do?
Ask the patient to “show me your teeth” or “raise the corners of your mouth”. This is usually more active and bilateral. You can assess if there is a normal response. THEN ask the patient to “squeeze your eyes tightly closed”.
Facial Nerve Testing: If an individual can close their eye, but not show their teeth, what lesion is it?
May be an UMNL
Facial Nerve Testing: What would be affected if there was an UMNL/LMNL?
UMNL: is likely to have other associated weakness, such as of the tongue and palate
LMNL: likely be confined to the distribution of the facial nerve
Is it possible to have a LMNL in the facial nerve, just confined to the motor component?
Which structures are spared?
Yes, it is not uncommon
Parasympathetic innervation to the lacrimal gland, the chorda tympani branch to the glands of the mouth, special sensory of the mouth, and the branch to stapedius
How do you tell if facial nerve paralysis is due to an UMNL?***
Primary motor neuron synapsing on the motor nucleus of the facial nerve provides primarily crossed but also uncrossed input for the upper face only. If a stroke involving facial muscles, the upper face will be only partially paralyzed due to contralateral innervation AND back up information from the ipsilateral cerebral cortex to the motor nucleus for the facial nerve but only for the neurons going to the upper face. Information from the cerebral cortex going to the motor nucleus for the facial nerve for neurons going to the lower face is crossed ONLY. That means that, following a stroke, only the contralateral lower face will be paralyzed.
How do you tell if facial nerve paralysis is due to a LMNL?***
LMNL such as compression of the facial nerve as it passes through the skull, will involve the entire upper and lower side of the face ipsilateral to the lesion.
What does the motor component of the facial nerve stimulate?
Supplies the stapedius and then exits the stylomastoid foramen to supply all the muscles of the face
Where does the facial canal extend?
The facial canal extends from the internal auditory meatus to the sylomastoid foramen
What would be the result of a tumour in the middle cranial fossa?
What would be more spared if it was distal along the facial nerve? What would happen if it was further into the canal?
A tumour in the middle cranial fossa could compress all branches, as well as the auditory nerve.
A lesion more distal along the facial canal may spare the lacrimal gland
Further into the canal may spare the functions carried by chorda tympani and the branch to the stapedius leaving only a facial palsy of the entire ipsilateral side of the face.
What structures do the trigeminal branches mediate?
Skin of the face, forehead, anterior half of the scalp, and most of the dura mater, orbital cavities, and mucosal membrane in the nasal and oral cavities
What is the role of the VPM nucleus of the thalamus?
Ipsilateral VPM nucleus?
VPM nucleus of the thalamus relays sensation from the head and face
Reticular cortical arousal
What do the first-order trigeminal fibres mediate?
Mediate fine discriminative sensation from the head, intraoral structures, and face.
What is trigeminal neuralgia?
(Tic douloureux) is characterized by episode of intense pain that is paroxysmal (sudden and stabbing); usually in the territory of the ophthalmic or mandibular branch
What happens if there is damage to the fibres in the secondary ascending tract?
The ability to sense pain in the contralateral half of the face is affected
What happens is there is damage to the trigeminal ascending tract?
Causes partial to complete anesthesia in the face and head
What would be the result of damage to peripheral branches in the trigeminal nerve?
Ipsilateral loss of sensation in the face, rostral tongue, teeth, and gingiva, and the cavities of the nose, orbit and mouth
What happens in a motor assessment of the trigeminal nerve?
Ask patients to bite down on a tongue depressor, move the jaw laterally against resistance, or open the jaw against resistance
What 3 components are in the facial nuclear complex?
Facial motor nucleus, superior salivatory nucleus, and nucleus solitarious
Injury in the facial nerve near the pons would affect which functions of the facial nerve?
1) paralysis of the ipsilateral facial muscles
2) excessive secretion from the glands
3) loss of taste from the anterior two-thirds of the tongue
Injury in the facial nerve at or beyond the stylomastoid foramen would affect which functions of the facial nerve?
Paralysis of the ipsilateral half of the facial muscles, sparing glandular secretion and taste sensation
Injury in the facial nerve at the chorda tympani fibres before they merge with facial motor root would affect which functions of the facial nerve?
Affect only taste sensation from the anterior two-thirds of the tongue and secretion from sublingual and submandibular glands.
What is the result of dysfunction in the unilateral motor cortex (UMN)?
Affects muscles in the contralateral lower half of the face. Upper facial muscles are spared in the case of a contralateral cortical lesion. Patient can wrinkle the forehead and close the eye – partial projections from the ipsilateral motor cortex
What do bilateral corticonuclear (UMN) lesions produce?
Produce bilateral facial palsy and result in profound impairments of motor speech, discrete motor control, muscles become paralyzed