Clinical Considerations Fractures can tear the fibers crossing the cribiform plate, leading to loss of smell. A frontal lobe mass can cause compression of the olfactory tract and \ or bulb and this can cause IL loss of smell.
For all of the lesions refer to Dr. Archers lecture, it was the bomb.
The cranial nerve 3rd starts in the oculomotor nucleus at the level of the superior colliculus. Lower motor neurons leave and go through the red nucleus and come out of the brainstem between the level of the midbrain and the pons. This is where they combine with the fibers of the EW nucleus. After this joining they all become the Oculomotor nerve. This passes between the posterior cerebral and superior cerebellar arteries, goes through the cavernous sinus, then goes through the superior orbital fissure, enters the orbit and splits into an inferior and superior division.
1. Superior division Levator palpebrae superioris, superior rectus
2. Inferior division medial and inferior recti, and inferior oblique
The superior rectus, inferior oblique, and levator palpebrae superioris are used to perform upward gazing.
EW is dorsal to the oculomotor complex. Preganglionic axons leave this and leave the midbrain with the somatic motor axons. Then the path is middle cranial fossa, cavernous sinus, superior orbital fissure, orbit. Here the fibers leave the 3rd cranial nerve and goes into the ciliary ganglion. From here 6-10 short ciliary nerves leave ganglion and travel between the sclera and the choroid of the eye. They terminate in the ciliary body and the iris. They control the constrictor pupillae, and ciliary muscles that control the size of the muscle and shape of the lens.
Direct light reflex constricts the pupil the light is shone on; consensual light reflex is the closing of the other pupil in response to the light in the 1st pupil. If the 3rd cranial nerve is lost in one eye the direct reflex will be gone and then the other eye will still have a consensual light reflex.
Vascular problems with the Posterior cerebral and Superior cerebellar arteries can damage the 3rd CN. Inflammation of the 3rd CN (syphilis and TB meningitis localizes between the chiasm, pons, and temporal lobe). Herniation of an enlarged temporal nerve displaces the cerebral peduncle and stretches the 3rd CN. Pathological conditions in the cavernous sinus can cause problems too.
1-5 together is called oculomotor ophthalmoplegia.
Clinical comments Paralysis caused by a lesion will cause the eye to rotate outward and cause double vision. The patient will tilt their head to the unaffected side.
1. V1 goes out through the superior orbital fissure
2. V2 goes out through the foramen rotundum
3. V3 goes out through the foramen ovale
The motor root follows the V3 division.
There are UMN axons from the cortex of the brain that synapse bilaterally in the motor (masticator) nucleus, which is in the tegmentum of the pons. The LMN axons go through the pons and exit as the motor root that runs medially to the sensory root. They exit through the foramen ovale. Outside of the cranium the motor and sensory branches of V3 unite to form the mandibular nerve. It has a lot of branches:
UMN lesions show no significant change because the masticator nucleus is innervated by both cerebral hemispheres and numerous other inputs from the brainstem.
LMN lesions lead to weakness and atrophy of the muscles of mastication on the IL side.
This division carries touch, pain and temperature from the eye, forehead, frontal and ethmodial sinuses. There are three divisions:
The three above join in the superior orbital fissure to form V1.
General Sensory Component Maxillary Component (V2)
This division carries sensory information from the maxilla and overlying skin, nasal cavity, palate, nasopharynx, and meningies of the anterior and middle cranial fossa. The zygomatic nerve is made of the zygomaticofacial and zygomaticotemproal nerves, which joins the maxillary nerve. The infraorbital nerve joins with the superior alveolar nerve (anterior branches), which becomes the maxillary nerve. Then the rest of the superior alveolar nerve and the palatine nerves join the maxillary nerve, this makes the maxillary division (V2). This goes through the foramen rotundum.
General Sensory Component Mandibular Division (V3)
This carries sensory information from the buccal region, carried by the buccal nerve, which merges with the main trunk of the mandibular nerve. The auriculotemporal nerve carries information from the side of the head and scalp. This later joins the main trunk as well. Sensation from the anterior 2\3 of the tongue is carries by the lingual nerve. The inferior alveolar nerve is made up of the mental nerve and dental branches from the teeth. Then the lingual nerve and the inferior alveolar nerve join the trunk of V3. Sensation from the meningies of the anterior and middle cranial fossa is carried by the meningial branch of V3, which will also join the main trunk. V3 goes through the foramen ovale.
V1, V2, and V3 all join together to make the ganglion, where most but not all of the nerve cell bodies are. Then the central processes from the ganglion bifurcate in the pons. One of the branches goes up to the pontine trigeminal nucleus and one goes down to the spinal tract of the Trigeminal to reach the spinal tract of the trigeminal nucleus. Axons of the secondary neurons from the trigeminal nucleus go to the various parts of the brain. These parts are:
From the thalamus the tertiary neurons go through the internal capsule to the postcentral gyrus in the IL cerebral cortex.
Clinical considerations sensory test should only be done medially, b\c the demarcations are more clear-cut.
The Abducens nerve controls the lateral rectus muscle. The nerve starts in the Abducens nucleus in the pons, close to the midline like the other somatic motor nucleus. The axons of CN 7 arch around the nucleus of CN 6 and this forms the facial colliculus. The nucleus for CN 6 is ventral of the 4th ventricle. The nerve travels through the cavernous sinus (along with III, IV, and V1 & V2). Then it goes directly into the lateral rectus muscle.
Coordination of later vision when looking to one side the lateral rectus and the medial rectus have to work together. Eyes left the right frontal lobe starts it, the signal travels to the paramedian reticular formation (PPRF), then on the IL it goes to the Abducens nucleus and then the lateral rectus. Also, from the PPRF the impulse goes to the MLF, which sends a fiber CL to the oculomotor nucleus, which then goes to the medial rectus.
Lesions Strabismus is an inability to direct their eyes to the same direction. A person with this condition has diplopia (double vision). People with this condition will turn their head to the unaffected side. This can happen because of:
Nystagmus is where the eyes have jerky movements.
Motor impulses start in the cortical areas and go to the facial motor nucleus in the pontine tegmentum. They get there by going through the corticobulbar tract. The axons of the corticobulbar tract synapse on the IL and CL facial motor neurons. The part of the axons that innervate the upper face muscles project bilaterally. The axons that innervate the lower face muscles project contralaterally.
After the axons synapse in the motor nucleus the fibers move dorsally and loop around the nucleus of the Abducens nerve. This loop is called the internal genu. Then the fibers turn ventrally and emerge at the caudal border of the pons, between the 6th and 8th cranial nerves. The fibers then join up with CN VIII and go into the internal acoustic meatus and go into the temporal bone. Inside the bone the nerve to stapedius is given off. The rest of the fibers exit the facial canal at the stylomastoid foramen and then enters the parotid gland where branches are given off to all the different facial muscles.
VI and VII dont work then the lesion is in the brain stem, VII and VIII dont work then the problem is in the internal acoustic meatus. UMN Voluntary muscle control of the lower muscles of facial expressions are lost CL to the lesion. Upper still works because the upper muscles are innervated bilaterally. LMN happens when the nucleus is damaged or any axon coming out of the nucleus. Everything IL is paralyzed, upper and lower face. A Bells palsy is a form of this.
Controls the secretions of the head, these are parasympathetic fibers. The cell bodies are in the pontine tegmentum in an area called the superior salivaotry nucleus. The superior salivatory nucleus is influenced by the hypothalamus and the spinal trigeminal nucleus. The efferent fibers from the superior salivatory nucleus travel in the nervus intermedius, which divides into two nerves: the greater petrosal nerve and the chorda tympani.
The greater petrosal nerve leaves the temporal bone via the greater petrosal foramen. Then it enters the pterygoid canal and joins with the deep petrosal nerve to become the nerve of the pterygoid canal, which runs to the pterygopalatine ganglion, which is suspended, from V2. The postganglionic fibers continue via the branches of V2 to reach the lacrimal and mucous glands of the nasal and oral cavities.
The chorda tympani joins the lingual branch of the mandibular nerve V3. The fibers of the 7th CN run in V3 and then synapse in the submandibular ganglion, which is suspended from the lingual nerve. The postganglionic fibers continue to the submandibular and sublingual glands.
Nerve endings are found behind the concha of the ear and a small area behind the ear. The nerve cell bodies are in the geniculate ganglion, impulses from the geniculate ganglion go through the nervus intermedius and then descend into the spinal tract of the Trigeminal nerve that synapses in the spinal portion of the Trigeminal nucleus in the upper medulla. From here the next fibers are sent to the CL ventral posterior nucleus of the thalamus. Tertiary sensory neurons project to the postcentral gyrus or sensory cortex.
Information from taste buds on anterior 2\3 of tongue. From the tongue it runs with the lingual nerve, and then branches off to become the chorda tympani. This then synapses in the geniculate ganglion. Secondary fibers run with the nervus intermedius and then enter the tractus solitarius and synapse in the nucleus solitarius (gustatory nucleus). Fibers leave this nucleus bilaterally and go through the central trigeminal tract and reach the IL and CL ventral posterior nucleus. From there axons travel to the cortical area of taste in the postcentral gyrus.
The sensory receptors for this part of the nerve are the hair cells. These hair cells synapse with the peripheral processes of the primary sensory neurons. The hair cells and the primary neurons together are called the Organ of Corti. When the hair cells move the deformation is transformed into electrical impulses. The cell bodies of the primary sensory neurons compose the spiral ganglion. This makes the auditory component of the Vestibulocochlear nerve.
Fibers leave the spiral ganglion and join with vestibular fibers and enter the internal acoustic meatus. The primary axons synapse with the dorsal (high frequency) and ventral (low frequency) cochlear nuclei. The secondary axons then go out and go to A LOT of places. Two important ones are:
1. Most of the fibers decussate and then run in the CL lateral lamniscus (some
synapse in the CL olivary nucleus before they go to the Lateral Lamniscus).
2. Some fibers stay IL and synapse in the superior olivary nucleus and then go into the lateral lamniscus in the same side.
The fibers from the lateral lamniscus ascend in the tegmentum of the pons and medulla and terminate into the inferior colliculus. From there to the medial geniculate body of the thalamus. From there the fibers go through the internal capsule to the transverse temporal gyrus. There are efferent fibers that are there to block out unwanted noise. If there is a lesion in the lateral lamniscus then hearing is still present on the effected side because the fibers are both IL and CL.
Review otoliths, macula, and all of those microanatomy structures. Movements of the head cause the gel with otoliths to move the hair cells changing deformation of the hair cells into electrical charges. These hair cells have peripheral processes that synapse with primary sensory neurons. The primary sensory neurons form the vestibular ganglion. The axons leave these bodies and then travel with the cochlear division. These axons go through the internal auditory meatus and terminate in the vestibular nuclear complex (in the floor of the 4th ventricle).
The secondary axons then leave there and go to the cerebellum and LMN in the brain stem and spinal cord. The lateral vestibular nucleus sends axons IL down the spinal cord to make the lateral vestibulospinal tract. The medial and inferior nuclei go back to the cerebellum. All of the nuclei give fibers to the Medial Longitudinal Fasciculus (MLF). The MLF controls orientation in space and eye movements.
Lesions of the vestibular component cause dizziness, falling, abnormal eye movements, nausea, and vomiting. There can also be an acoustic neuroma that is a tumor of the Schwann Cells. This will interfere with three functions of the 8th CN and 7th CN (hearing and balance by the 8th and facial movements by the 7th).
Blood Supply - is by the watershed regions.
UMN - The primary neuron starts in the premotor association cortex & other cortical areas. The fibers travel through the internal capsule and then synapse bilaterally on the ROSTRAL nucleus ambiguus.
Nucleus the rostral part of the nucleus ambiguus, which lies in the lateral gray matter.
LMN - leave the nucleus and then go into the rest of CN IX. From there the nerve leaves medulla between the olive and inferior cerebellar peduncle as 3-4 rootlets. The nerve then leaves through the jugular foramen and then to the stylopharyngeus muscle.
Function Special visceral efferent to the stylopharyngeus muscle.
Preganglionic parasympathetic fibers start in the inferior salivatory nucleus in the medulla (somewhat above the nucleus ambiguus). Then the fibers join the rest of CN IX and leave through the jugular foramen. It also sends off the Tympanic nerve (from the inferior ganglion) to the middle ear to do sensory stuff there. There the fibers form the lesser petrosal nerve, which goes through the temporal bone and then into the middle cranial fossa and then down through the foramen ovale. From there it synapses in the otic ganglion. From here postganglionic fibers join the auriculotemporal nerve and innervate the parotid gland.
Carotid body and sinus send information up the carotid nerve to the inferior ganglion. The secondary nerves go to the tractus solitarius and nucleus tractus solitarius (NTS). From there the next fibers go to the reticular formation and the hypothalamus. The function is to regulate the heart, blood pressure, etc. It is General Visceral Afferent.
Pain and temperature axons from external ear, inner tympanic membrane, posterior 1\3 of the tongue and upper pharynx have cell bodies in the superior or inferior Glossopharyngeal ganglia. Pain processes go to the spinal trigeminal tract and synapse on the caudal part of the nucleus. From here the next axons cross the midline in the medulla and go to the contralateral VPL of the thalamus. From the VPL the tertiary neurons go to the postcentral gyrus. It is General Somatic Afferent.
Lesions Lesions in the 9th CN can lead to an absence of a gag reflex, also lesions can lead to sudden pain that is brief and severe. This pain goes down the throat and goes down the side of the neck and can be caused by swallowing and protruding the tongue.
Taste from the posterior 1/3 of the tongue goes to the inferior glosspharyngeal ganglion. From there the axons go through the jugular foramen and enter the medulla and ascend through the tractus solitarius and synapse in the NTS. From there the axons go through the central tegmental tracts to the IL and CL thalamus. From there axons are sent to the internal capsule and then to the postcentral gyrus. This one is considered special afferent.
Blood Supply Vertebral Artery & goes through PICA area
UMN Axon Fibers from the premotor, motor and other cortical areas go through the internal capsule and then synapse in the nucleus ambiguus.
Nucleus the nucleus ambiguus lies in the rostral and caudal medulla in the lateral gray matter.
LMN Axon 8-10 rootlets leave the nucleus and emerge between the olive and pyramid. Here is where the caudal fibers run with CN XI. The fibers then exit through the jugular foramen. There are three branches: pharyngeal (muscles of the palate), superior laryngeal and recurrent laryngeal (striated muscles of the tongue, and larynx).
Functions special visceral efferent to the striated muscles of the pharynx, larynx, tongue
Lesions LMN lesion causes trouble swallowing, hoarseness, drooped palate (IL) and deviated uvula (points to UNAFFECTED side).
Blood Supply Watershed: PICA, Vertebral, Anterior Spinal Artery
UMN Axon Not really UMN, but preganglionic parasympathetic. The primary nerves have cell bodies in the dorsal motor nucleus of the vagus, go through the spinal Trigeminal tract and nucleus, leave the lateral medulla and from there the fibers join the trunk of the vagus nerve and distribute to their respective organs.
Nucleus Dorsal motor nucleus of the Vagus. It is located in the caudal medulla dorsolateral to the hypoglossal nucleus.
LMN Axon Not really LMN, the fibers from the preganglionic parasympathetic nerves synapse in or around the respective structures that they innervate.
Function General visceral efferent to the smooth muscle and glands of pharynx and larynx and thoracic and abdominal viscera.
Lesions cutting the nerve can affect certain organs innervated. For example, if the stomach is producing too much acid the gastric nerve can be cut and the problem is fixed.
Visceral sensory information comes from nerve plexuses around the various organs and then converges into the right and left vagus nerves. The cell bodies of these nerves are located in the inferior vagal ganglion. The axons of these neurons travel to the medulla, then through the tractus solitarius and into the NTS (reflex control of cardio, respiratory and GI functions). The information is then carried into the hypothalamus.
Pain, touch and temperature are carried from the larynx, pharynx, external ear, external tympanic membrane and external auditory canal. Sensory fibers go up to the inferior and superior vagal ganglion, where the nerve cell bodies are. The ganglion then send out central processes that go through the jugular foramen and then join other vagal sensory fibers (from meningies). All of these go to the spinal trigeminal tract and synapse in the nucleus of the spinal trigeminal tract. From there the secondary fibers go to the contralateral Ventral Posterior nucleus of the thalamus.
Blood Supply Anterior Spinal
UMN Axon Premotor association cortex and other cortical areas send out fibers to the corticospinal tract through the internal capsule. They decussate in the pyramidal decussation then they go into the lateral corticospinal tract to the anterior lateral gray in the upper cervical spinal cord (C1-C5), after it goes down through the foramen magnum (the 1st time)
Nucleus In the anterior lateral gray horn of the upper 5 cervical vertebrae. Lies directly under the Nucleus Ambiguus that is in the caudal medulla.
LMN Axon the axon leaves through the lateral white matter of the spinal cord. The fibers emerge between the dorsal and ventral roots, they are behind the denticulate ligaments. The axons form a trunk and move up through the foramen magnum (2nd time), they then join with the caudal fibers of the vagus nerve and go down through the jugular foramen (3rd time through a hole).
Function Special Visceral Efferent to the SCM and trapezius.
Lesions LMN lesions will lead to a shoulder drop (trapezius) and the person will not be able to shrug shoulders against resistance. Weakness of the SCM will lead to inability to turn the head against resistance.
Blood Supply Anterior Spinal
UMN axon Corticobulbar tract all the way down to the Hypoglossal Nucleus. These axons decussate somewhere in the brain.
Nucleus Hypoglossal Nucleus, located between the Dorsal Motor Nucleus of the Vagus (dorsally) and the medial lamniscus (anteriorly). It is located almost right in the middle of the medulla, both caudal and rostral parts.
LMN axon can been seen in the rostral medulla. It comes out of the nucleus and moves anteriorly and lateral to the medial lamniscus. The fibers of this emerge from the anterior part of the medulla between the olive and the pyramid on each side. Leaves the skull through the hypoglossal canal.
Function General Somatic Efferent to the intrinsic musculature of the tongue.
Lesions - UMN lesion will cause contralateral deviation of the tongue, no atrophy, and fasciculations. LMN lesions will be ipsilateral deviation of the tongue, atrophy and flaccid paralysis.