The document summarizes key aspects of spinal cord and brainstem anatomy related to somatosensory and motor pathways. It describes: 1) Spinal cord gray matter including dorsal horn, ventral horn, and intermediate gray matter which contain sensory, motor, and autonomic nuclei respectively. 2) Brainstem organization into nuclei rather than horns. Cranial nerves originate from specific motor and sensory nuclei analogous to spinal cord regions. 3) Somatosensory and motor pathways for each cranial nerve, including ganglia, nuclei, and innervation targets. Key nuclei include trigeminal, facial, vestibulocochlear nuclei and more.

1. DORSAL HORN
IML
VENTRAL
HORN
The spinal ganglion -
location of neurons that
convey somatosensory
information to dorsal
horn. It’s peripheral
process associated
with a receptor and a
central process that
enters the CNS.
Ventral horn -
origin of
somatomotor fibers
innervating
skeletal muscles
Intermediate gray
(IML; T1-L2 and S2-4)
- location of
preganglionic
visceromotor neurons
innervating smooth and
cardiac muscles.
SPINAL
GANGLION

2. SPINAL
GANGLION Spinal cord - grey
matter deep to
white matter
Brainstem - grey
matter and white
matter intermingle
with one another
Brainstem - no
dorsal, intermediate
or ventral horns
Neuron groups are
organized into
nuclei

3. Brainstem:
1. Midbrain
2. Pons
3. Medulla
1
2
3
Most cranial nerves are associated with the brainstem (continuous with
spinal cord) except CN I and CN II.

4. Cranial nerve somatomotor nuclei are the location of neuronal cell bodies for
somatomotor fibers that innervate skeletal muscles of the face and neck.
The somatomotor cranial nerve nuclei are equivalent to the ventral horn of
the spinal cord.
Medulla

5. Cranial nerve sensory ganglia (equivalent to the spinal ganglia) are located
outside the brain (it may be a distinct ganglion or it may be many neurons
dispersed throughout a region). They have a peripheral process that is
associated with a receptor.
Its central process terminates in a cranial nerve sensory nucleus (equivalent
to the dorsal horn).

6. CN III, VII, IX and X have parasympathetic nucleus (equivalent to intermediate
gray matter of spinal cord levels S2-4). Preganglionic parasympathetic fibers
travel initially with the cranial nerve in which it is associated.
Preganglionic fibers synapse in parasympathetic ganglion located in head
(except vagus nerve’s parasympathetic component). Postganglionic
parasympathetic fibers from ganglion innervate smooth or cardiac muscles.

7. CN I, CN II and CN VIII are
purely sensory
CN IV, CN VI, CN XI, CN XII
are purely motor (not really
true)
CN III, CN V, CN VI, CN VII,
CN IX, CN X are mixed
(somatomotor,
somatosensory,
parasympathetic)

8. Sensory ganglion - dispersed
neurons located in olfactory
mucosa in roof of nasal cavity
Peripheral processes: located
at surface of olfactory mucosa
Central processes: pass
through cribriform plate to
terminate in olfactory bulb
(dorsal horn equivalent)
Olfactory bulb’s axons form
olfactory tract that terminates in
cortex.
Olfactory Nerve (Cranial Nerve I)

9. Light pass through pupil
anterior and posterior chambers
to retina. It passes through all
layers of retina until it strikes the
most posterior layer, which
contains the rods and cones.
They transduce light into a
neural signal.
bipolar cells - receive input
from rods and cones; allow for
convergence of information
from multiple receptor cells.
ganglion cells - receive input
from bipolar cells
-cell bodies of origin (sensory
ganglion) for optic nerve
-central processes of the sensory
ganglia.
-terminate in lateral geniculate
nucleus (dorsal horn equivalent)
of thalamus.
Optic Nerve (Cranial Nerve II)

10. Optic nerve - central processes of ganglion cell
that pass through the optic canal in posterior
wall of orbit to enter middle cranial fossa.
Optic chiasm - crossing of nasal (medial) half
of the optic nerve to the contralateral side;
-temporal (lateral) half remains uncrossed.
Optic tracts - caudal continuation of optic fibers
to the thalamus
Optic Nerve (Cranial Nerve II)

11. Oculomotor nucleus (ventral
horn equivalent) - cell
bodies of origin for nerves
innervating five extraocular
muscles.
Oculomotor nerve splits into:
- superior division innervates:
Superior Rectus
Levator Palpebra Superioris
-inferior division innervates:
Medial Rectus
Inferior Rectus
Inferior Oblique
Accessory oculomotor nucleus
(Edinger-Westphal nucleus)-
first cell body of two neuron
chain responsible for
parasympathetic innervation of
two smooth muscles
Oculomotor Nerve (Cranial Nerve III)

12. SUPERIOR ORBITAL FISSURE
Oculomotor fibers (both the somatomotor and preganglionic parasympathetic
fibers) leave the cranial cavity through the superior orbital fissure to enter the
orbit.

13. Trochlear Nerve
(Cranial Nerve IV)
Trochlear nucleus
(ventral horn
equivalent) is the
location of the cell
bodies of origin
- only cranial nerve
to leave from
brainstem’s dorsal
(posterior) side.
- innervates one
extraocular skeletal
muscle, superior
oblique
- Leaves cranial
cavity through
superior orbital
fissure

14. Trigeminal Nerve (Cranial
Nerve V): principal sensory
nerve of the head.
Trigeminal ganglion – cell
bodies of origin for sensory
fibers (spinal ganglion
equivalent located on petrous
ridge of temporal bone)
- Peripheral processes:
convey somatosensory
information from the face
- Central processes:
terminate in spinal
trigeminal nucleus of
brainstem.
Sensory component is
divided into:
Ophthalmic (V1)
Maxillary (V2)
Mandibular (V3)
Trigeminal motor nucleus-
(ventral horn equivalent)
neuronal cell bodies of origin
for fibers innervating eight
skeletal muscles.

15. Ophthalmic Division-area of forehead to the lateral corners of the eyes and onto the bridge of the nose
Maxillary Division-area between lateral corners of eyes to corners of the mouth
Mandibular Division-area of the mandible (only division to contain motor fibers)
SOMATOSENSORY INNERVATION PATTERN FOR THE FACE

16. Ophthalmic Division-area of
forehead to the lateral corners
of the eyes and onto the bridge
of the nose.
- Leaves cranial cavity through
superior orbital fissure to
enter orbit.
- peripheral processes divides
into:
frontal nerve
supraorbital nerve
supratrochlear nerve
lacrimal nerve
nasociliary nerve

17. Maxillary Division-area between lateral
corners of eyes to corners of mouth
- Leaves cranial cavity by passing
through foramen rotundum to enter
pterygopalatine fossa.
Its peripheral processes divides into:
1.infraorbital n.
2.greater and lesser palatine nn.
(descending palatine nerves)
3. zygomatic n. (cheek)
4.posterior superior alveolar n.
5.sphenopalatine n.(nasal cavity)

18. Mandibular Division-innervates the area of mandible; only division to contain motor fibers.
- Leaves cranial cavity by passing through foramen ovale to enter infratemporal fossa.
Its peripheral sensory
processes branch into :
1. inferior alveolar n.
2. lingual n.
3. buccal n.
4. auriculotemporal n.
5. motor nerves to
skeletal muscles.

19. Trigeminal motor nucleus: location of
somatomotor neuronal cell bodies of
origin for fibers innervating eight
muscles: muscles of mastication
(masseter, temporalis, medial pterygoid,
lateral pterygoid), mylohyoid, anterior
belly of digastric, tensor tympani and
tensor veli palatini.

20. Abducens Nerve
(Cranial Nerve VI)
Abducens nucleus
(ventral horn
equivalent)- cell bodies
of origin
- responsible for
innervating one
extraocular muscle,
lateral rectus.
- Exits cranial cavity by
passing through the
superior orbital fissure
to enter the orbit.

21. FACIAL NERVE (CN VII)
- contains somatomotor, somatosensory & preganglionic parasympathetic fibers.
- Location of cell bodies for components of facial nerve:
1.Facial nucleus-somatomotor nucleus (ventral horn equivalent) innervating: muscles of facial
expression & stylohyoid, posterior belly of the digastric and stapedius.
2. Superior salivary nucleus- visceral motor nucleus (intermediate gray equivalent) containing
first parasympathetic cell bodies of two neuron chain innervating lacrimal gland, submandibular
gland, sublingual gland, nasal mucous glands and oral mucous glands.
3. Geniculate ganglion,
somatosensory ganglion (spinal
ganglion equivalent) located in
bend of facial canal in temporal
bone posterior to middle ear.
Peripheral processes innervate
portions of the external ear and
taste receptors on the anterior 2/3
of the tongue; central processes
terminate in nucleus solitarius
(taste) and spinal trigeminal
nucleus (external ear).

22. FACIAL NERVE (CN VII)
Internal auditory meatus: exit/entrance of facial nerve from cranial cavity. Internal opening
of facial canal (posterior to the middle ear) in temporal bone.
Facial canal has an initial horizontal course and then a vertical course through the temporal
bone. In the horizontal part that the geniculate ganglion is located.
Stylomastoid foramen -
inferior opening of facial
canal; exit point of
somatomotor and
somatosensory fibers
leaving the skull.
★ Two additional
openings in the facial
canal before the
stylomastoid foramen
that serve as the exit
points for other parts of
the facial nerve.

23. INTERNAL AUDITORY MEATUS
The internal auditory meatus, which is on the posterior
edge of the petrous ridge of the temporal bone, is the
opening for the entrance/exit of the facial nerve.
Once it passes through the internal auditory meatus, the
facial nerve takes a complicated course in the facial canal,
which is inside the temporal bone.
Internal View
External View

24. In facial canal different components split off:
1)greater petrosal nerve (preganglionic parasympathetic fibers from the superior salivary
nucleus for lacrimal, nasal and oral mucosa glands) leaves the facial nerve at the geniculate
ganglion to move rostrally.
2)chorda tympani (preganglionic parasympathetic fibers for submandibular and sublingual
glands [superior salivary nucleus] and taste fibers [geniculate ganglion] for anterior 2/3
of tongue) leave the facial
nerve distal to geniculate
ganglion and enter the
middle ear cavity to move
rostrally.
3)somatomotor
fibers (facial nucleus)
to skeletal muscles &
somatosensory fibers
to external ear exit
the temporal bone at
the stylomastoid
foramen.

25. The greater petrosal nerve leaves the facial nerve at the geniculate ganglion to move
rostrally.
The chorda tympani leaves the facial nerve at the midpoint of the facial canal and takes a
rostral course through the middle ear cavity.
The remainder of the facial nerve continues through the facial canal until it exits on the
anterior side of the skull at the stylomastoid foramen.

26. Somatic motor component of facial nerve branches in parotid gland into:
1. temporal
2. zygomatic
3. buccal
4. mandibular
5. cervical

27. Vestibulocochlear Nerve (Cranial
Nerve VIII)
The two ganglia,
vestibular ganglion (associated
with the semicircular canals) &
dispersed neurons that comprise the
spiral ganglion (associated with the
cochlea) in the inner ear These are
the neuronal cell bodies of origin
for CN VIII.
Vestibular ganglion cells: convey
balance and orientation
Spiral ganglion cells: convey
auditory sense
Peripheral processes of the
vestibular ganglia are associated
with receptors in the semicircular
canals and the central processes end
in vestibular nuclei of the brainstem.
Peripheral processes of the spiral
ganglia are associated with
receptors in the cochlea and the
central processes end in cochlear
nuclei of the brainstem.
Central processes pass
through the internal
auditory meatus to
enter the cranial cavity.

28. GLOSSOPHARYNGEAL NERVE (CN IX)
- Primarily a sensory nerve, although it has a
small somatomotor & visceromotor
components.
-Sensory information from posterior third of
tongue, mucosa of pharynx, middle
ear, auditory tube, and blood pressure &
chemoreceptors associated with common
carotid artery.
- Somatomotor innervation: stylopharyngeus
of pharynx
-Visceromotor (parasympathetic) innervation:
parotid gland.
-Leaves cranial cavity thru jugular foramen

29. Location of cell bodies:
1) Nucleus Ambiguus: cell bodies of origin for somatomotor fibers that innervate stylopharyngeus
2) Inferior Salivary Nucleus: cell bodies of origin for visceromotor fibers that are involved in
innervation of the parotid gland

30. 3) Inferior Ganglion of the
Glossopharyngeal nerve
(at the jugular foramen).
Peripheral processes carry:
1) special sense (taste) & somatosensory
information from the posterior 1/3 of tongue
2) Somatosensory information from the
pharynx
3) Somatosensory information from the
middle ear, auditory tube & mastoid air cells
4) General viscerosensory information from
the carotid body (chemoreception) & carotid
sinus (baroreception).
Central processes from the inferior
ganglion of CN IX terminate in:
Nucleus solitarius – taste fibers from
posterior third of tongue, carotid body
and carotid sinus.
Spinal trigeminal nucleus – general
sensory from posterior third of tongue,
pharynx, middle ear, auditory tube &
mastoid air cells
Spina
l

31. VAGUS NERVE (CN X)
- contains somatomotor, visceromotor
and somatosensory components
- somatomotor innervates skeletal
muscles of larynx, pharynx and
accessory muscles of pharynx and soft
palate
- visceromotor component innervates
smooth and cardiac muscles of thoracic
cavity and smooth muscle of the
abdomen up to splenic flexure
- sensory component innervates laryngeal
mucosa, meninges of posterior cranial
fossa, external ear and comparable
regions innervated by visceromotor
innervation
- Leaves cranial cavity through jugular
foramen

32. Nucleus Ambiguus: neuronal cell bodies that innervate skeletal muscles including: pharyngeal constrictor
muscles, intrinsic muscles of larynx (external laryngeal & recurrent laryngeal nn.), levator veli palatini
(soft palate) and palatoglossus, palatopharyngeus, salpingopharyngeus
Dorsal Motor Nucleus of the Vagus: first neuronal cell bodies responsible for parasympathetic innervation
of smooth muscle of digestive system (to splenic flexure), respiratory system and heart.
Spinal trigeminal
nucleus

33. Inferior Ganglion of the vagus nerve (nodose ganglion): innervate mucosa of larynx, respiratory system,
heart and digestive system.
Its central processes (axons) terminate in the nucleus solitarius of brainstem.
Superior Ganglion: innervate external auditory meatus, meninges of the posterior cranial fossa and
external surface of tympanic membrane. Its central fibers terminate in spinal trigeminal nucleus of
brainstem.
Spinal trigeminal
nucleus

34. (Spinal) Accessory Nerve (CN XI)
Location: C1-C5 of spinal cord is
in the posterior portion of the
anterior (ventral) horn.
- fibers leave spinal cord between
the posterior (dorsal) and anterior
(ventral) roots to enter cranial cavity
through foramen magnum.
- fibers then exit cranial cavity
through the jugular foramen.
- innervates the
sternocleidomastoid and trapezius.

35. Hypoglossal nucleus:
neuronal cell bodies for the
hypoglossal nerve.
- Exits cranial cavity through
hypoglossal canal of
occipital bone
- In neck it loops around
occipital artery to enter lateral
side of the tongue
- innervates:
Intrinsic and extrinsic
muscles (hyoglossus,
styloglossus & genioglossus)
of tongue
HYPOGLOSSAL NERVE (CN XII)

36. LEARNING OBJECTIVES FOR CRANIAL NERVES
By the end of this unit you must have mastered for each cranial nerve (where appropriate):
1) all nuclei or ganglia of origin for its fibers
2) specific region of the brain or spinal cord its fibers are associated
3) complete pathway, any bony openings it passes through, and all its terminal targets
4) identify as motor only, sensory only, both motor and sensory and autonomic component if any
5) for sensory fibers: brain nuclei for termination of central fibers
6) for autonomic component, the nucleus of origin, bony openings, path of its preganglionic fibers, parasympathetic ganglion,
path of its postganglionic fibers, terminal targets.
7) for the sympathetic fibers, cell bodies of origin, path of its fibers, sympathetic ganglion, pathway of its postganglionic fibers to
the target structures.
8) Describe the functional deficits that will be manifested if any cranial nerve is lesioned at any point along its course.
Specific objective for the 12 Cranial nerves:
1) Olfactory nerves-cell bodies of origin, bony openings and its path to its termination in olfactory bulb
termination of olfactory tract axons
2) Optic nerve-cell bodies of origin, path of its fibers, bony opening and thalamic nucleus for termination of its central fibers
location and consequences of optic chiasm
3) Oculomotor nerve-cell bodies of origin, path of its fibers
cell bodies of origin and path to striated muscles for its superior and inferior divisions
autonomic cell bodies of origin and complete path of its autonomic fibers
location of ciliary ganglion; its contribution to short ciliary nerves and target structures for its postganglionic fibers
know the location that its parasympathetic fibers join and leave specific parts of the nerve
4) Trochlear nerve-cell bodies of origin, its path, bony opening, muscle it innervates

37. 5) Trigeminal nerve-cell bodies of origin, paths and bony openings of its subdivisions
ophthalmic division area of innervation
major branches
branches of the frontal nerve
associated autonomic ganglia
components and cell bodies of origin for long ciliary nerves
components and cell bodies of origin for short ciliary nerves
maxillary division area of innervation
branches in the pterygopalatine fossa, oral cavity, maxillary sinus and nasal cavity
associated autonomic ganglion
mandibular division area of innervation
sensory branches and muscles innervated
associated autonomic ganglia
Know the location that autonomic fibers “hitch a ride” on specific parts of the nerve and when they leave the nerve to innervate
a structure
6) Abducens nerve-cell bodies of origin, its bony opening and path to the muscle it innervates
7) Facial nerve-cell bodies of origin, bony openings, path of its fibers to its terminal targets
sensory targets and somatic muscles innervated by the facial nerve
autonomic cell bodies of origin and complete path of fibers to target structures
components and cell bodies of origin of the chorda tympani
components and cell bodies of origin for the nerve of the pterygoid canal
8) Vestibulocochlear nerve-cell bodies of origin, its path, bony openings and structures innervated

38. 9) Glossopharyngeal nerve-cell bodies of origin, its path, bony openings and structures innervated.
cell bodies of origin for innervation of striated muscles
autonomic cell bodies of origin, path of its fibers and target structures
cell bodies of origin and sensory regions innervated
components and cell bodies of origin for tympanic nerve
components and cell bodies of origin for lesser petrosal nerve
contribution to pharyngeal plexus
10) Vagus nerve-cell bodies of origin, bony opening, path of its fibers and structures innervated.
cell bodies of origin and striated muscles innervated
cell bodies of origin and smooth muscle structures innervated
cell bodies of origin and sensory regions innervated
contribution to pharyngeal plexus
11) Accessory nerve-cell bodies of origin, its path, bony openings and terminal structures innervated
12) Hypoglossal nerve-cell bodies of origin, its path, bony openings and terminal structures innervated
13) Sympathetic innervation-cell bodies of origin for preganglionic and postganglionic fibers, most common pathways to
terminal target sites.
location and types of fibers in carotid plexus
path and terminal targets of sympathetic components of long and short ciliary nerves
components, path and terminal targets of deep petrosal nerve
sympathetic path for innervation of submandibular, sublingual and parotid glands