Cranial Nerve columns and tracts

Question 1

Somatic motor column

Answer 1

Includes nuclei for Oculomotor, trochlear, abducens, hypoglossal

Located closest to the midline and anterior to the ventricular space

Contains Lower motor neurons of these nuclei innervate skeletal muscle that originates from paraxial mesoderm

is SE/GSE

Question 2

Parasympathetic motor column

Answer 2

Includes the following specific nuclei:

• dorsal motor vagal nucleus (CN10)
• inferior salivatory nucleus (CN9)
• superior salivatory nucleus (CN7)
• edinger westphal nucleus (CN3)
• ALL carry parasympathetics*

Found slightly lateral to the somatic motor column

Gives rise to preganglionic axons

Is VE/GVE

Question 3

Branchial motor column

Answer 3

Includes the following nuclei

• nucleus ambiguus (CN10/9)
• CN 7 motor nucleus
• CN 5 motor nucleus

More lateral to the parasympathetic column and is found in the lateral medulla and pons tegmentum

Muscles innervated by these lower motor neurons originate from the paraxial mesoderm

is SE

Question 4

Solitary tract

Answer 4

Visceral sensory column + the nucleus.

Located just laterally to the parasympathetic motor tract (almost superimposed)

Cranial nerves 7/9 and 10 convey taste fibers and visceral sensations from salivary glands (rostral portion) as well as thoracic viscera/abdominal viscera for cardiorespiratory muscles (caudal portion)

Is found throughout the pedulla into the medulla-pons junction

Is SVA/GVA

Question 5

Special somatic sensory column

Answer 5

Contains the following:

• medial and spinal vestibular nuclei
• anterior and posterior cochlear nuclei
• superior and lateral vestibular nuclei

Immediately posteriorly adjacent to the solitary tract and nucleus

Receives sensory input form CN 8 only

Question 6

General somatic sensory column (trigeminal sensory system)

Answer 6

is found throughout the entire length of the brainstem

Contains the following nuclei

• spinal trigeminal nucleus (located in lateral medulla -> caudal pons)
• principal sensory nucleus (located at the midpontine level)
• mesencephalic nucleus (located at rostral pons to lateral aspect of PAG)

All are components of CN5

Question 7

Hypoglossal nerve tract

Answer 7

Originates from the hypoglossal trigone internally and leaves the medulla via the preolivary sulcus

Supplies intrinsic tongue muscles, genioglossus, hyoglossus and geniohyoid muscles

Blood supply to nucleus = anterior spinal artery

Question 8

Accessory nerve tract

Answer 8

Originates from cervical spinal segments C1-6

Axons from individual segments exit lateral aspect of cord and coalesce to form the nerve

The tracts course = ascends through foramen magnum -> posterior cranial fossa -> exits out jugular foramen

Supplies the SCM and traps

Question 9

Vagus nerve (motor component) tract

Answer 9

Originates from 2 places

1) the dorsal motor vagal nuclei in the medulla
- contains visceral motor fibers to the intramural ganglia in the walls of the viscera

2) the nucleus ambiguus in the medulla
- contains somatic efferent fibers to the skeletal muscles in the pharynx/larynx and upper esophagus

Question 10

Vagus nerve (sensory component) tracts

Answer 10

Originates from

1) the nuclei in the superior vagal ganglion
- processes enter spinal trigeminal tract where they meet up with additional nuclei
- picks up somatic sensations of the ear, external auditory meatus and dura of the posterior cranial fossa

2) the nuceli in the inferior vagal ganglion
- processes enter the solitary tract where they meet up with solitary nuclei
- picks up visceral sensations from he neck/throat and abdiomen areas.

• taste sensations are the same except as #2 except the secondary nuclei (where they meet up) is in the gustatory nuclei of the solitary nucleus*

Question 11

Glossopharyngeal nerve (motor components) tracts

Answer 11

Originates from:

1) Inferior salivatory nucleus
- contains visceral motor fibers that send fibers to the otic ganglion and innervate parotid gland

2) nucleus ambiguus
- contains somatic motor fibers that innervate the stylopharyngeus

Both exit from the post-olivary sulcis to go to their respective targets

Question 12

Glossopharyngeal nerve (sensory components) tracts

Answer 12

Originate form

1) superior glossopharyngeal ganglion. Central processes from this ganglion join the spinal trigeminal tract, where the secondary nuclei are located
- contains fibers that pick up somatic sensations from the pinna/external auditory meatus and posterior 1/3 of tongue

2) inferior glossopharyngeal carotid body. Central processes join the solitary tract, where the secondary nuclei are located.
- contains fibers that pick up visceral sensations from the parotid gland/oropharynx and carotid bodies

taste sensation from the posterior 1/3 of tongue is similar to #2, except the central processes join the gustatory nucleus, where the secondary nuclei are located

Question 13

Vestibulocochlear nerve tracts

Answer 13

Cochlear division

• originates from spiral ganglion in the cochlea
• projects to brainstem and conveys auditory information -> medial geniculate nucleus -> auditory cortex
• functions to bring hearing impulses

Vestibular division

• originates from the vestibular ganglion medially to the semicircular canals.
• projects to cerebellum and other brainstem centers.
• functions to bring balance and equilibrium impulses

Question 14

Facial nerve (motor component) tracts

Answer 14

Facial motor nucleus is located at the pons-medulla junction

Sends somatic motor neurons posteromedial around the abducens nucleus and then anterolateral out the brainstem

Innervates muscles of facial expression and posterior belly of the diagastric

these motor fibers are joined by visceral motor axons from neurons of the superior salivatory nucleus.
- they either synapse at the submandibular ganglion or the pterygopalatine ganglion to innervate glands below the oral fissure or above the oral fissure respectively.

Question 15

Facial nerve (sensory component) tracts

Answer 15

Possess 3 routes

1) anterior 2/3 of the tongue taste.
- Nuclei are located in the geniculate ganglion.
- nerve fibers leave the geniculate ganglion and travel to the gustatory nucleus to synapse onto secondary cell bodies (located at rostral end of the solitary sulcus)

2) visceral sensation from submandibular and sublingual glands and the mucous membranes
- nuclei are located within geniculate ganglion
- nerve fibers travel to the cardiorespiratory nucleus (located at the caudal end of the solitary nucleus)

3) somatic sensations from regions of the external ear and auditory meatus
- nuclei are located within geniculate ganglion
- nerve fibers travel to the spinal trigeminal tract and join

Question 16

Abducens nerve tract

Answer 16

is the most medial nerve emerging from the pons-medulla junction

Nuclei is located internal to the facial colliculus
- contains lower motor neurons and exits from the pons medulla junction to form the abducens nerve and provide motor to the lateral rectus

• also contains interneurons which exit at the same point as above, but goes back into the contralateral pons-midbrain junction to synapse onto the contralateral medial longitudinal fasciculus
• these interneurons go to the ocular motor nucleus on the contralateral side and form excitatory synapses on CN 3 neurons that innervate the medial rectus*

Question 17

Trigeminal nerve tracts

Answer 17

Has multiple nuclei all located in the dorsal part of the pons w/ exception of spinal trigeminal nucleus
- all fibers exit laterally to the pons and either forms a large sensory root attached to the trigeminal ganglion or a small motor root which bypasses the ganglion all together

Motor component:

• consists of the trigeminal motor nucleus, forms small motor root (portio minor) and innervates mastication muscles
• only the mandibular division (V3) possesses motor components*

Question 18

Trigeminal sensory-nuclei tracts

Answer 18

There are 3 sensory nuceli

1) spinal trigeminal nucleus
- nuclei is located in lateral caudal medulla and runs into the caudal pons
- receives of fibers from trigeminal ganglion conveying pain/thermal sense and non discriminatory touch

2) principal (pontine) sensory nucleus
- nuclei is located in the lateral part of the mid-level pontine tegmentum
- receives fibers from trigeminal ganglion conveying discriminative touch

3) mesencephalic nucleus
- nuclei is located in the principal sensory nucleus but travels to the PAG in the midbrain (unlike the principal sensory nuclei)
- actually possess primary cell nuclei for proprioceptive infromation from masticatory/extraocular/ and periodontal muscles ( these fibers then move to the trigeminal motor nucleus and go from there)

Question 19

Which is the only sensory component of CN5 to NOT have primary cell bodies (nuclei) in the trigeminal ganglion?

Answer 19

Proprioceptive information for masticatory/extraocular/periodontal muscles

The primary cell bodies are located with the mesencephalic nuclei and use the mensecphalic tract to move to the trigeminal motor nucleus.

Question 20

Jaw-jerk reflex

Answer 20

Mandibular fueled that is tested by tapping the middle of the chin with the reflex hammer with the patients mouth slightly open
- if intact, the jaw will suddenly but slightly close the jaw

Afferent limb brings infromation to the mesencephalic nuclei, where it then uses the mesencephalic tract to get the information to the trigeminal motor nucleus

Efferent limb from the trigeminal motor nucleus then sends information to masticatory muscles to close mouth

Question 21

Trochlear nerve tract

Answer 21

Nucleus is found in the dorsal midbrain just ventral to the PAG
- exits out the dorsal side of the midbrain AFTER DECUSSATING and then moves to the superior oblique directly and synapses

Question 22

Oculomotor nerve tract

Answer 22

2 Nuclei and both are located in the ventral portion of the PAG of the midbrain (only in midbrain)

1) E-W nuclei
- projects to brainstem and spinal centers responsible for regulating behavioral aspects of stress/eating/drinking
- also projects parasympathetic fibers to the ciliary ganglion

2) oculomotor nuclei
- is directly controlled by the frontal field cortex and projects to the superior colliculus and riMLF

Question 23

Optic nerve tract

Answer 23

Is a false cranial nerve so not really a tract

Optic nerve -> optic chiasm -> optic tract -> lateral geniculate nucleus of thalamus -> optic radiations to the cortex of the occipital lobe for processing

• note that the medial 1/2 of vision of both eyes decussate at the chiasm, the lateral 1/2 of the eye fields do not decussate*

Question 24

Olfactory nerve tract

Answer 24

False cranial nerve so not really a tract

Olfactory axons -> olfactory bulb -> olfactory tract -> primary olfactory cortex (includes piriform cortex/amygdala and uncus) -> entorhinal cortex