Lecture 16: Sensory Cranial Nerves Flashcards
What are the three sensory nuclei for the trigeminal nerve and what are their locations?
- Chief Sensory (pons)
- Mesencephalic (mesencephalon)
- Spinal Nucleus (extends as a column from the mesencephalon to the spinal cord where it continues as the substantia gelatinosa.
What does the vestibular nuclei control and where is it located?
body position; pons; associated with CNVIII
What does the cochlear nuclei control and where is it located?
hearing; pons; associated with CNVIII
What is the rostral part of the nucleus solitarius concerned with?
taste
What is the caudal part of the nucleus solitarius concerned with?
cardiorespiratory inputs
Describe CNI (Olfatory)
- Purely sensory and serves olfaction.
- Sensory receptors lie in the nasal epithelium and they send axons through the cribriform plate to synapse in the olfactory bulb. They travel in the olfactory tract to synapse in the olfactory cortex, amygdala and related forebrain structures.
Anosmia
Loss of the sense of smell
Describe CNII (Optic Nerve)
- Purely sensory and transmits visual input into the brain
- Receptors are located in the retina at the rear of the eye.
What is the optic nerve made of?
axons of retinal ganglion cells
Describe the path of the optic nerves.
They converge just outside the mesencephalon where 50% of the fibers from each eye cross to the opposite side of the body via the optic chiasm.
**Central to the chiasm, the fibers run as the optic tract.
Describe the path of the optic tract.
It runs along the outside of the mesencephalon to the lateral geniculate body (visual thalamus) which in turn projects to the primary visual cortex on the banks of the calcarine fissure.
What is the alternative path for fibers of the optic tract?
Some fibers bypass the LGN and instead travel in the brachium of the superior colliculus to synapse in the superior colluculus.
**This is important for startle reflexes.
Describe CNV
- Mixed nerve that serves as the primary one for somesthesis of the face.
- Carries nerves for fine touch, proprioception, and pain and temperature afferents from the skin of the face region.
What provides innervation to the back of the head?
primarily spinal nerves from C2
What provides innervation to the external ear?
multiple cranial nerves
Where do all fine touch afferents (even those not running with CNV) form the face synapse?
In the Chief Sensory Nucleus
What are the sensory functions of CNVII?
- Taste sensation to the anterior 2/3 of the tongue.
- Somesthetic afferents (fine touch, vibration, pain and temperature) for a small area around the external auditory meatus.
Where are cell bodies for the somesthetic afferents located?
geniculate ganglion
Where do the central processes of the somesthetic afferents project to?
chief sensory nucleus of V (epicritic) or the spinal nucleus of V (pain and temperature
Describe the gustatory nucleus.
- Located in the rostral parts of the nucleus solitarius (runs as a column through the pons and the medulla)
- Concerned with taste sensation.
- Receives input from CNVII, IX and X.
Where does sensory taste input come from?
CNVII= anterior 2/3 of tongue CNIX= posterior 1/3 of the tongue CNX= pharynx and epiglottis
What is contained in the caudal part to the solitary nucleus?
Cadriorespiratory nucleus
What is the function of the cardiorespiratory nucleus and where does it receive input from?
It receives visceral sensory input (glands, chemoreceptors and baroreceptors) carried by CNVII, IX and X.
Describe the component of CNVIII
It has one function component (sensory) and two divisions:
- Vestibular-> balance and acceleration
- Auditory-> hearing
Where are the sensory afferents for hearing and vestibular sense located?
In the inner ear
Describe the auditory receptors.
- “Hair Cells”
- Located in the organ of corti in the cochlea.
- Sensitive to airborne pressure waves, as transducer into fluid waves in the cochlea.
- Depending on the location in the cochlea, these receptors are tuned to different frequencies of sound.
- Auditory afferents travel in CNVIII
Describe the vestibular receptors.
- “Hair Cells”
- Located in the saccule, utricle, and three semicircular canals.
- Afferents also travel in CNVIII
Where are the cell bodies of the auditory afferents located?
spiral ganglion
Where do axons of the auditory afferents synapse?
dorsal and ventral cochlear nuclei
Describe the path of the auditory afferent signal transmission.
- Hair cells and from the organ of corti located in the cochlea synapse on cells in the spiral ganglion.
- Spiral ganglion cells send their axons in the cochlear division via CNVIII.
- The cochlear nerve fibers synapse in the ipsilateral dorsal and ventral cochlear nuclei (at the pontomedullary junction).
- From here, they ascend bilaterally to the inferior colliculus.
- Inferior colliculus neurons project to the medial geniculate body (auditory thalamus).
- The medial geniculate projects to the auditory cortex (Heschel’s gyrus: transverse gyri in the superior temporal lobe)
Describe the path of the vestibular afferent signal transmission.
- Vestibular hair cells synapse on cells in the vestibular ganglion (Scarpa’s Ganglion).
- These cells send their axons in the vestibular division of CNVIII.
- The axons of these cells synapse on the vestibular nuclei, located in the pons and rostral medulla, near the floor of the fourth ventricle.
What are the four vestibular nuclei?
- Lateral Vestibular Nuclei
- Medial Vestibular Nuclei
- Inferior Vestibular Nuclei
- Superior Vestibular Nuclei
What is the function of the lateral vestibular nuclei?
gives rise to the lateral vestibulospinal tract, which is a descending motor pathway for balance and extensor tone
Where does the medial vestibulospinal tract originate from and what is its function?
It comes from the medial and inferior vestibular nuclei and only extends to cervical levels of the spinal cord to help control head and neck position.
Which vestibular nuclei contribute to the MLF and what is its purpose?
Medial and Superior Vestibular nuclei.
Coordinates eye movements.
Describe CNIX.
- Mediates taste from the posterior 1/3 of the tongue.
- Somatic sensation from the pharynx and posterior 1/3 of the tongue
- Chemo and baro reception from the carotid sinus and carotid bodies.
- Fine touch, pain and temperature from the middle ear and portion o the external ear.
Where do the afferents of CNIX that carry taste terminate?
rostral solitary tract (gustatory nucleus)
Where do the afferents of CNIX that carry baro and chemoreception project to?
Caudal part of the solitary nucleus and tract.
Where do the motor neurons from CNIX project to?
nucelus ambiguous
Where do the pain and temp afferents of CNIX project to?
spinal tract and nucleus of V
Where do the afferents for epicritic touch of CNIX project to?
Chief sensory nucleus of V
What are the sensory components of CNX?
- Taste from the pharynx and epiglottis
- Visceral info from the aortic arch bro and chemo receptors.
- Somatic information from the pharynx and larynx.
- Touch, pain and temp from a small portion of the external ear.
Where do the afferents of taste from cNX project?
Rostral solitary nucleus and tract (gustatory)
Where do the afferents of CNX carrying chemo and baroreceptor information project?
Caudal solitary nucleus and tract
Where do the afferents of CNX that carry somatic info from the pharynx, posterior larynx, and meninges, and touch, pain and temp from a small portion of the external ear project?
Spinal tract and nucleus of CNV
Describe the gag reflex.
- The afferent limb is carried by afferents of CNIX projecting to the caudal solitary nucleus.
- An interneuron is interposed between the afferent and efferent in the nucleus ambiguous.
- The efferent response is mediated by motor neurons in the nucleus ambiguous whose axons travel with CNX.
