Flashcards in Lesson 10: Cranial Nerves IX-XII Deck (48):
What classes of innervation does the glossopharyngeal nerve carry?
1. General Sensory – from posterior 1/3 of tongue, palate, naso-pharynx to larynx
2. Special Sensory – taste from posterior 1/3 of tongue, carotid bodies
3. Voluntary – stylopharyngeus
4. Involuntary Motor – parotid gland – a little of everything
In the sensory portion of the glossopharyngeal nerve tract, where does general and special sensory information enter the cranium?
All general sensory information from the pharynx as far down as the larynx and the special sensory information enter the cranium through the same opening in the skull as the venous blood is leaving (jugular foramen).
Where does sensory information of the glossopharyngeal nerve tract enter, synapse?
-It then enters the medulla posterior to the olive to synapse in the nucleus solitarius for taste and lower part of the spinal nucleus of the trigeminal nerve for general sensory.
Once synapsed in the nucleus solitarius, where does the sensory info synapse and terminate for the glossopharyngeal nerve?
From there, the information crosses to ascend to the thalamus, synapses in the VPM of the thalamus on the tertiary neuron that terminates in the parietal lobe.
Where does the superior salivary nucleus carry information from?
Lacrimal, submandibular and sublingual glands
What is motor innervation for the glossopharyngeal nerve?
The involuntary motor (parasympathetic) innervation is to the parotid gland
What is the reflex that can be tested for the glossopharyngeal nerve?
What can happen in a glossopharyngeal nerve lesion?
What would a discrete lesion cause?
Central component is often involved in a stroke (either at cerebral cortex, in the internal capsule or in the brainstem) and therefore included in the assessment of swallowing (UMNL).
Rarely sustains peripheral nerve lesion (LMNL)
Partial paresis of the unilateral stylopharyngeal muscles, impairing ipsilateral pharyngeal elevation in deglutition. Loss of general and taste sensation from the ipsilateral posterior third of tongue.
How do you test the glossopharyngeal nerve?
Touching the back of the throat, stimulates general sensory receptors at the back of the throat carried by the glossopharyngeal nerve. In the brainstem, this stimulates the efferent component of the gag reflex, carried by the vagus nerve, causing a gag.
What does the vagus nerve do?
- Sensory supply of the larynx and voluntary motor innervation of the muscles of pharynx for swallowing and larynx for sound production.
- Main branch (parasympathetic) travels throughout the thorax and abdomen, innervating virtually all of the thoracic (heart and lungs) and abdominal viscera.
- General sensory role provides info from all viscera
- Involuntary motor: regulates critical organs such as lungs, heart and almost the entire digestive tract
In the vagus nerve, where do the voluntary and involuntary motor fibres come from?
The voluntary motor fibres come from the nucleus ambiguus
The involuntary motor fibres (parasympathetic) come from the “dorsal motor nucleus of the vagus”.
Where do the general sensory fibres come from in the vagus nerve?
What does this structure carry?
Come from nucleus solitarius; usually said to carry only special sensation, i.e., taste fibres.
What are the special sensory innervations carried by in the vagus nerve?
Nucleus solitarius caries these (minor) taste fibres.
Where do the voluntary motor innervations come from in the vagus nerve?
Voluntary motor innervation to striated muscles of speech and swallowing are indicated as coming from nucleus ambiguus
What is the process of the sensory neurons in the vagus nerve?
First neuron: synapses in nucleus solitarius (or spinal nucleus of the trigeminal nerve)
Second neuron: crosses immediately and travels to the VPM of the thalamus
Third neuron: then terminates in the sensory cortex in the parietal lobe. It will then synapse on many other neurons to start new pathways to distribute the information to other association areas or the motor cortex for a response
What reflexes is the vagus nerve involved in?
Coughing, vomiting, gagging, cardiac pacing, and swallowing.
Provides the efferent component of the gag reflex due to its innervation of the muscles of the pharynx
“In on IX, out on X”
How is the tympanic membrane associated with the trigeminal and vagus nerve, and glossopharyngeal nerve?
Outer surface supplied by trigeminal and vagus nerves and inner surface by glossopharyngeal nerve.
- Sensory stimulation of the eardrum associated with an ear infection can cause vomiting by stimulating the vagus through its sensory innervation to the eardrum resulting in a reflex contraction of involuntary muscles of the stomach
Pain in the eardrum stimulates the vagus nerve
Vagus nerve lesions: What happens if the left branch is pulled down by the aortic arch?
Left branch is pulled down by aortic arch during development and if heart becomes enlarged, the stretching causes loss of innervation to the larynx and hoarse voice.
What is the best testing for the vagus nerve?
What is the easiest voluntary motor test? How do you tell which side is intact vs. paralyzed?
Gag reflex is the easiest to test. It is elicited by touching the back of the throat and the response is a gag. Probably the easiest voluntary motor test is asking the patient to say “AH” and watch for the equal rising of the palate at the back of the throat. Because the intact side actively raises the palate, it pulls the uvula. This means that the uvula is pulled away from the paralyzed side and toward the intact side
In a vagus nerve lesion, what is the difference between an UMNL and a LMNL?
If it is a LMNL: ipsilateral to the lesion
UMNL: the paralysis is contralateral to the lesion.
What type of innervation is the spinal accessory nerve?
Voluntary motor only
What is the input to the nucleus ambiguus of the spinal accessory nerve tract?
The central input to nucleus ambiguous is primarily crossed
Where dos the spinal accessory nerve tract travel?
What does it innervate?
It travels from nucleus ambiguous, exits the brainstem in the cervical cord, enters the foramen magnum, then again exits the skull, innervates sternomastoid right away and then pass between neck muscles to reach trapezius. After it innervates sternomastoid it passes between the neck muscles traveling through the major neck lymph nodes, then innervating trapezius (raises and stabilizes the shoulder)
What kind of testing is done for spinal accessory nerve reflexes?
Voluntary testing is used
Spinal Accessory Nerve Lesions: Peripheral Nerve Injury Causing LMNL
What is the nerve vulnerable to?
Vulnerable during “radical neck dissection” surgery to remove lymph nodes to prevent metastasis in cancers of the head and neck including tongue and face
If the spinal accessory nerve is not cut, how fast can it recover?
If it is not “cut”, it can recover and will grow at 1mm/day taking about 1 year for re-innervation.
Spinal Accessory Nerve Lesions: Peripheral Nerve Injury Causing LMNL
What is the result of paralysis of the trapezius?
Results in poor stabilization of the shoulder in all arm movements therefor is not trivial. Not all nerve fibres get to the target and the shoulder remains weak
Spinal Accessory Nerve Lesions: Central Nervous System Damage causing UMNL
What type of injury?
What is the result of an UMNL?
Stroke or damage to the cervical cord, paralysis is not as profound as with a LMNL.
Partial paralysis is often called “paresis”. It is not exactly the same as “weakness”
Spinal Nerve Testing: How does the sternocleidomastoid muscle get tested?
What is the result of injury to the sternocleidomastoid?
Ask patient to direct chin downward to side opposite to muscle being tested, giving some resistance
- Damage to the sternocleidomastoid restricts head turning to the side away from the lesion.
Spinal Nerve Testing: How doe the trapezius muscle get tested?
What is the function of the trapezius?
(Stabilizes the scapula during all movement of the arm and shrugging of the shoulders) A quick test is to ask the patient to shrug his shoulder against some resistance. Compare with the opposite side
Hypoglossal Nerve: what type of innervation is the nerve?
What does the nerve do?
Has only voluntary motor function.
Supply the muscles of the tongue; are very important to swallowing and speech.
Where does the hypoglossal nerve leave the brainstem?
It leaves the brainstem just medial to CNs IX, X and XI
What does the hypoglossal nerve receive central input from? Is it crossed or uncrossed?
Hypoglossal nerve receives central input to the hypoglossal nucleus that is primarily crossed, it has some uncrossed input as backup.
How is the tongue tested?
Do neurons in the hypoglossal receive crossed or uncross innervation from the motor cortex?
What is shown if there is damage to one side of the tongue?
(protrusion of the tongue) is done by genioglossus. Neurons in the hypoglossal nucleus that are going to genioglossus muscle receive ONLY crossed innervation from the cerebral cortex.
The tongue will not protrude on that side, and instead of pointing directly forward, will point toward the involved side.
What is the hypoglossal nerve tract?
From the hypoglossal nucleus, the peripheral nerve leaves the brainstem on the medial side of the olive (bump caused by inferior olivary nucleus) and exits the skull (through a hole of its own) to supply the tongue, ipsilateral to its nucleus.
What are the hypoglossal nerve reflex tests?
No useful reflex used clinically
In a hypoglossal nerve lesion, what are the symptoms of a peripheral nerve lesion?
LMN symptoms: there will be profound wasting and wrinkling of the side of the tongue ipsilateral to the lesion.
On protrusion, the tongue deviates to the side of the lesion because of the unopposed protrusion of the normal half (genioglossal muscle) of the tongue.
In a hypoglossal nerve lesion, what are the resulting sypmtoms of a UMNL - stroke?
Some central backup to the hypoglossal nucleus and increased tone. Therefore, although primarily crossed, there will be backup from the non-injured side. This means that the tongue will not be as wrinkled and atrophied (wasted) looking as seen in the peripheral nerve lesion nor will the patient’s swallowing and speech be as impaired
What does the vagus nerve consist of?
Dorsal motor nucleus, nucleus ambiguous, and nucleus solitarius
Where does the vagus nerve exit from the brainstem?
What happens after it passes through the jugular foramen?
Exits the brainstem from the lateral medulla between the inferior olivary nucleus and the inferior cerebellar peduncle
After passing through the jugular foramen, it distributes its sensorimotor branches peripherally
Lesions in the vagus nerve: what happens if there is a unilateral lesion of the nerve fibres and/or nucleus of the nucleus ambiguus?
Likely to result in ipsilateral paresis or paralysis of the soft palate, pharynx, and larynx
Lesions in the vagus nerve: What happens if there is injury to the pharyngeal branch of the vagus nerve?
Causes paralysis of the pharynx and the soft palate, leading to swallowing difficulty.
Lesions in the vagus nerve: what happens if there is unilateral paralysis of the levator muscle of the soft palate
Lowers on the affected side, and the uvula is pulled to the unaffected side
Lesions in the vagus nerve: what do bilateral central (UMN) lesions produce?
Produce profound phonatory and swallowing problems.
In the hypoglossal nerve, what is the result of bilateral LMN damage to the nucleus/nerve?
Likely to cause severe difficulty in swallowing, eating and speaking.
What is the function of the soft palate?
Soft palate seals the nasopharynx to prevent the entrance of food during swallowing. It also regulates speech nasality.
What is the function of the muscles of the pharynx?
The circular constrictor muscles of the pharynx perform squeezing actions on the bolus, and vertical muscles elevate the larynx during swallowing.