Cranial nerves V, VII Flashcards
In a broad sense, what is CN V responsible for?
Main general sensory nerve for the head
What type of information does the trigeminal nerve send? (4)
Tactile
Proprioceptive
Pain
Temperature
What are the three branches/divisions of CN V and what are they responsible for?
Ophthalmic division- upper face (sensory only)
Maxillary division- middle face (sensory only)
Mandibular division- lower face (sensory and motor)
What muscles are innervated by CN V?
Muscles of mastication
Tensor timpani
Tensor veli palatini
There are 4 trigeminal nuclei. Where are they and what are they called?
- The trigeminal mesencephalic nucleus is found in the midbrain (almost to the inferior colliculus)
- The trigeminal principal sensory nucleus is found in the rostral pons (superior cerebellar peduncle)
- The trigeminal motor nucleus is found in the rostral pons, opposite the principal sensory nucleus
- The trigeminal spinal nucleus begins in the rostral pons and continues to the medulla
There are projections that come off the trigeminal spinal nucleus. Where do they go to?
It’s a contralateral projection to the VPM (ventral posteromedial nucleus) of the thalamus
There are projections that also come off the main trigeminal sensory nucleus. Where do they go?
It’s a bilateral projection to the VPM (ventral posteromedial nucleus) of the thalamus
The ascending projections of the trigeminal spinal and sensory nuclei go to where? And then where?
First to the VPM of the thalamus. Then they go from there to the post central gyrus- the somatosensory cortex.
The sensory afferent of CN V serves what areas? (4 things)
- Face
- Oral cavity
- Teeth
- Meninges
The sensory afferent pathway that terminates in the main trigeminal sensory nucleus senses what?
Descriminative touch and vibration
T/F the CN V main sensory nucleus is a homologue of the posterior column nuclei?
Truth
T/F the main sensory nucleus is responsible for discriminative tactile (face and oral cavity) and some proprioception (jaw position)
Trooth
There are two ascending pathways associated with the main sensory nucleus. Where do they go?
One is a crossed path that meets up with and joins the medial lemniscus on its way to the VPL
The other is not crossed, it is a dorsal trigeminal tract, and the inside of the mouth is represented to the VPM
The sensory afferent pathway of CN V that terminates in the trigeminal spinal nucleus senses what? (3 things)
Pain
Crude touch
Temperature
What are the three parts/divisions of the spinal trigeminal nucleus?
- Oral nucleus (from main sensory nucleus to the pontomedullary junction)
- Interpolar nucleus (from the pontomedullary junction to the obex)
- Caudal nucleus (from the obex to the spinal cord)
Concerning the spinal trigeminal nucleus, the Pars Oralis (oral nucleus) receives input from what?
Intraoral and perioral structures
What is the pars/interpolaris proper responsible for?
Activation of the trigemino-autonomic reflexes
- Is the caudalis interpolaris transition zone somatotopically organized?
- Does it respond to pain stimuli from many areas served by CN V?
- Is the Pars Caudalis somatotopically organized?
- Nope
- Yep
- Yep
The Pars Caudalis is the target of fibers mediating what three things?
Pain
Crude touch
Temperature sensation
Where do fibers that go to the Pars Caudalis originate from? (remember, this is ascending)
They deliver information from:
The superficial structures including the oral cavity and teeth
The deep structures including jaw muscles and the TMJ
The second order neurons of the spinal trigeminal tract do what?
They send axons across the midline, which ascend and join the spinothalamic tract which terminates in the VPM
The Pars caudalis is somatotopically organized. Explain how.
It has an inverted representation of the face
It has an onion peel representation- the rostral aspect is responsible for the oral cavity and the caudal aspect is responsible for the peripheral face
What does the Substantia gelatinosa contain and receive?
Contains excitatory and inhibitory interneurons
Receives raphe spinal tract fibers (seratonin)
The Pars Caudalis receives afferent from which cranial nerves?
CN VII, IX, X (all for the area near the ear)
Explain the somatotopic arrangement of the pain-temperature afferents in Pars Caudalis.
Ventral side: Ophthalamic division
Dorsal side: Mandibular division
In between those two: Maxillary division
In the Pars Caudalis, where do fibers representing the center of the face end?
Near the obex
In the Pars Caudalis, fibers representing the back of the face end where?
In the upper cervical cord
T/F- the more rostral the spinal trigeminal tract injury is the larger the area around the mouth that is spared sensory loss?
False- the more caudal the injury the less you lose feeling around your mouth.
The nerve fibers in the pulp of a tooth are 70-80% fast pain, thermal fibers and 20-30% are spindle, touch and pressure. Where do those fibers project to? (3 places)
- Trigeminal main sensory nucleus (heaviest projection- shared)
- Trigeminal spinal nucleus (pars oralis- heaviest projection; pars interpolaris- modest projection; pars caudalis- light projection)
- Upper cervical spinal cord
Where does most trigeminal neuralgia pain occur?
In the mandibular division
What is the most common trigger for trigeminal neuralgia pain?
A tactile stimulus
What would happen if you cut the nerve root or introduced a lesions in the trigeminal ganglion?
You would lose all tactile sensation, including pain.
Can some cases of trigeminal neuralgia be caused by vascular decompression?
Yes.
Where is the trigeminal mesencephalic nucleus located?
Just caudal to the inferior colliculus
The trigeminal mesencephalic nucleus has centrally directed processes that terminate where? (2 places)
Trigeminal motor nucleus- for the jaw jerk reflex
Supratrigeminal nucleus- for chewing movements
What does the trigeminal mesencephalic nucleus sense? (3 things)
proprioception
spindles in the muscles of mastication
mechanoreceptors in the gums, teeth, and hard palate
Does the mesencephalic nucleus have proprioceptive capabilities? If not, why, if so, what are they?
Yep. Neuromuscular spindles of mastication muscles; pressure/tension receptors in the periodontal ligaments; controls the distance between the mandible and maxilla
GREAT SUMMARY SLIDE
For each of the following tell me about the myelination of the fibers, its homologue and what its responsible for:
Mesencephalic nucleus
Main sensory nucleus
Spinal nucleus
Mesencephalic nucleus: heavily myelinated fibers; posterior column homologue- medial lemniscal system; proprioception
Main sensory nucleus: heavily myelinated fibers; posterior column homologue- medial lemniscal system; discriminative touch
Spinal nucleus: lightly myelinated fibers; homologue of the anterolateral system; pain crude touch temperature
Where does the trigeminal motor nucleus terminate?
In the muscles of mastication
What is the function of the trigeminal motor nucleus?
To close the jaw
What happens if there is a trigeminal motor lesion?
Jaw closure is weakened.
The opened jaw will deviate toward the side of the lesion
What nucleus is the pattern generator for masticatory rhythm
The supratrigeminal nucleus
What muscles is the branchial motor nucleus responsible for?
1st pharyngeal arch muscles
The jaw-jerk reflex is a _____synaptic reflex.
Monosynaptic
What are the afferent and efferent limbs for the jaw-jerk reflex?
Afferent: trigeminal mesencephalic neuron innervating masseter spindle
Efferent: trigeminal motor nucleus
What is the clinical significance of the jaw-jerk reflex?
Well, like other reflexes, it is enhanced with upper motor neuron damage, so it is used to determine the level of injury
What does the stapedius muscle do?
It modulates sound volume
CN VII is responsible for taste to how much of the tongue?
The anterior 2/3
Concerning CN VII,
- Where do somatic sensory fibers come from?
- Where do visceral sensory fibers come from?
- Where do branchial motor fibers go to?
- Where do visceral motor fibers go to?
- from the outer ear- geniculate ganglion
- from the tastebuds on the anterior 2/3 of tongue
- to the muscles of facial expression + the stapedius
- to all the glands in the face
Somatic sensory fibers of CN VII transmit information concerning what?
the skin of the outer ear
T/F does the peripheral distribution of the facial nerve reach both orbicularis oculi and oris as well as the parotid gland?
Yep. That is a truth.
What is the difference in how upper and lower facial muscles are innervated?
The upper facial muscles are innervated bilaterally.
The lower facial muscles are innervated by the contralateral cortex.
T/F Are the facial motor nucleus and the corticobulbar pathway connected?
Yep. In fact, it appears they share some real estate
What happens with unilateral damage to the corticobulbar pathway concerning upper and lower facial muscles?
There is an inability to to smile or bare one’s teeth symmetrically. However, the ability to wrinkle one’s forehead is unaffected. (see a previous slide for an explanation)
T/F Bell’s palsy is generally bilateral?
False- unilateral
Bell’s palsy is due to what?
Dysfunction in CN VII
What is a crucial thing to be aware of with the eyeball of someone who is affected with bells palsy?
The cornea can dry out- permanent corneal damage can result!
The corneal blink reflex- what happens if you touch the cornea?
Blink with both eyes
What are the afferent and efferent limbs of the corneal blink reflex?
Afferent: trigeminal to spinal trigeminal tract
Efferent: CN VII elicited by bilateral projection from the spinal trigeminal nucleus
What is the jaw closing reflex?
When food comes in contact with oral membranes
What is the jaw opening reflex?
When the periodontal afferents are activated by dental occlusion or
the pain afferents are activated from the mucosal membranes
The jaw opening and closing reflexes receive input from what?
The jaw muscles (proprioception from trigeminal mesencephalic nucleus) Tactile information (food in the mouth- from trigeminal main nucleus) Pain information (from trigeminal spinal nucleus)
What is the output of the jaw opening and closing reflexes?
from CN VII to the muscles of mastication
How does the perception of flavor work?
Chemical stimulation of taste buds
Olfactory receptors respond to food vapors
Chemosensitive and somatosensory free nerve endings of CN V, IX, X in mucus membranes of oral cavity repsond to temperature, spiciness (pain), texture of food
The nervus intermedius is located where?
it is between CN VII and VIII
What do second order nerve fibers do? (2 things)
- Reflex activities IE swallowing, salivation
2. Project uncrossed to the thalamus (VPM), then to the gustatory cortex (insula, medial surface of frontal operculum)
Where does the gustatory cortex project?
To the orbitofrontal cortex where it is integrate with olfactory information. Then it reaches the amygdala and then to the limbic system and the hypothalamus
