Lect 8 Cranial Nerves Flashcards
CN originating in telecephalon
I
CN originating in Diencephalon
II
CN originating in the midbrain
III,IV
CN originating in the pons
V,VI,VII,VIII
CN originating in the pons
IX,X,XI,XII
What is carried in a cranial nerve
several different types of fibers
- cutaneous sensory fibers from the skin
- fibers from special senses (taste)
- motor fibers to skeletal muscles
- motor fibers to blands
fiber types within cranial nerves are considered the functional components of these nerves and are commonly referred to as neural modalites
Cranial nerve modalities initials
1st initial: Special vs General
2nd initial: Visceral vs somatic
3rd initial: Afferent vs Efferent
Special vs General modality CN
Special: function found only in a cranial nerve
General: function may be found in a cranial or spinal nerve
CN modality Visceral vs somatic
2nd initial
Visceral: target is part of the visceral system (organ, gland, smooth muscle) OR a structure derived from the specialized embryonic precursors called pharyngeal arches
Somatic: the somatic motor system is under voluntary motor control; somatic sensory fibers carry information from body areas such as skin, muscles, joints
CN modality Afferent vs Efferent
Afferent: axon is relaying sensory info to CNS
Efferent: the axon is relaying motor info away from the CNS
Afferent Fiber Types/Neural modalities
General somatic afferent (GSA)
General visceral Afferent
Special Afferent
GSA
general somatic afferent - convey sensations from skin, muscles, joints
GVA
general visceral afferent - convey sensations from internal organs
SA
special afferent - serve special senses of vision, hearing, balanc, taste, smell
Efferent fiber types
GSE
SVE
GVE
GSE
general somatic eff.
innervated striated muscle NOT derived from embryonix pharyngeal arches
SVE
innervated striated muscle with embryological origin from the pharyngeal arches (facial expression, mastication muscles)
GVE
general visceral efferent
autonomic fibers that innervates smooth muscle and glands (parotid gland, submandibular gland)
SA only CNs
I,II,VIII
SVE only CNs
XI
GSE only CNs
IV,VI,XII
GSE,GVE only
CN III
GSA, SVE only CNs
CN V
SVE, GVE, GSA, GVA, SA Cranial nerves
CN VII, IX, X
Trigeminal Nerve
CN V GSA, SVE 3 divisions emerge from the trigeminal ganglion V1- opthalmic nerve V2 - Maxillary Nerve V3- Mandibular Nerve
All carry sensory info, V3 also has a motor component
four brainstem nuclei receive (3) sensory info or project (1) axons - form trigeminal nerve
other terms for trigeminal ganglion
semilunar ganglion
gasserian ganglion
GSA of CN V
3 divisions of sensory nuclei
- Spinal trigeminal nucleus
- Main sensory nucleus
- Mesencephalic nucleus
Spinal trigeminal nucleus
GSA
receives pain, temperature and non discriminitive/crude touch sensations from the face
Main sensory nucleus
GSA: receives light touch and pressure info from the face, also proprioceptive info
Mesencephalic nucleus
GSA
associated with proprioceptive afferents from the face (displaced ganglion)
SVE of CN V
motor nucleus
projects axons to the muscles of mastication (temporalis, masseter, medial, pterygoid, lateral pterygoid) and others
Course of trigeminal nerve
emerges from the brainstem, courses anteriorly through middle cranial fossa
- from trigeminal ganglion located on the flood of the middle cranial fossa, emerge V1,2,3
- these leave the cranial cavity via openings in the middle cranial fossa
V1 travels through…
the superior orbital fissure
V2 travels through…
the foramen rotundum
V3 travels through
the foramen ovale
Sensory distribution of V1
Supraorbital Supratrochlear Infratrochlear External nasal Lacrimal
Supraorbital distribution to the skin
mucosa of frontal sinus
skin and conjuctiva of middle superior eyelid
skin and pericranium of anterolateral forehead and scalp to vertex
Supratrochlear distribution to the skin
Skin and conjunctive of medial aspect of superior eyelid
skin and pericranium of anteromedial forehead
Lacrimal distribution to the skin
lacrimal gland (secretomotor fibers) -small area of skin and conjunctiva of lateral part of superior eyelid
Infratrochlear distribution to the skin
Skin lateral to root of nos
-skin and conjunctiva of eyelids adjacent to medial canthus, lacrimal sac and lacrimal caruncle
External nasal distribution to skin
skin of nasal ala, vestibule and dorsum of nose, including apex
V2 terminal branches
infraorbital
zygomaticofacial
zygomaticotemporal
infraorbital distribution to skin
mucosa of maxillary sinus
- premolar canine and incisor teeth
- skin and conjunctiva of inferior eyelid, skin of cheek, lateral nose and anterioinferior nasal septum, skin and oral mucosa of superior lip
zygomaticofacial distribution to skin
prominence of cheek
zygomaticotemporal distribution to skin
hairless skin anterior part of temporal fossa
V3 terminal branches
auriculotemporal
buccal
mental
auriculotemporal distribution to skin
skin anterior to auricle and posterior two thirds of temporal region
- skin of tragus and adjacent helix of auricle
- skin of roof of external acoustic meatus
- skin of superior tympanic membrane
buccal distribution to skin
skin and oral mucosa of cheek
buccal gingivae
adjacent second and third molars
mental distribution to skin
chin and skin
oral mucosa of inferior lip
Spinal trigeminal system pathway
Trigeminal nerve and ganglia receive face pain, temp and crude touch from A delta and c fibers
Passes through spinal trigeminal tract to spinal trigeminal nucleus
-both tract and nucleus extend from mid pons into the rostral spinal cord (C3) where they are continuous with the substantia gelatinosa and Lissauer’s tract
2nd order fibers cross to join spinothalamic tract - called trigeminothlamic tract - synapse on VPM/ILN
Organization of spinal trigeminal nucleus
(rostral to caudal)
Pars oralis - extends from main sensory nucleus to pontomedullary junction
Pars interpolaris - extends from pontomedullary junction to level of obex
Pars caudalis - nucleus extends from obex to spinal cord (C2-C3)
obex
marks caudal end of fourth ventricle
Pars caudalis function and organization
Thought to be major synaptic site for pain, temp and crude touch from the face
- represents onion pattern for facial distribution
- more rostrally located nerve endings come from intraoral zones
- further down the caudalis moves more caudal on the head
responsible for organization
Spinal trigeminal tract and spinal trigeminal nucles organization
have a ventral to dorsal organization
V1 - located ventrally
V2- located in middle
V3- located dorsally
Main sensory and mesencephalic nucleus pathway
GSA
no synapse in Mesencephalic nucleus, cell body of pseudounpolar neuron
-A-beta fibers synapse from both tracts on the main sensory nucleus
- 2nd order fibers join the medial lemniscus in the mid-pons - called trigeminal lemniscus
2nd order neurons that reveive A-beta info from oral cavity
remain uncrossed
travel in dorsal trigeminal tract, located in the dorsomedial brainstem tegmentum (not in the medial lemniscus)
travel ipsilaterally
3 regions of the main sensory nucleus of CN V
Ventral: receives V1 - to contralateral VPM
mid region: receives V2 - Contralateral VPM
Dorsal: receives V3 - to ipsilateral VPN and contralateral VPM (intraoral regions)***
Wallenberg’s syndrome
aka lateral medullary syndrome
caused by ischemia in the territory of the vertebral artery or PICA
involves spinal trigeminal nucleus and tract, spinothalamic tract, descending sympathetic fibers
Clinical features of Wallenberg’s syndrome
issues w/ trigeminal nucleus and tract - ipsilateral facial decreased pain and temp sense
issues w/ spinothalamic tract- contralateral body decreased pain and temp sense
A lesion in the left lateral medulla will cause..
decrease pain and temp sensation of
- ipsilateral face (left) (2nd order damage of spinal trigeminal nucleus/tract)
- contralateral (right) UE, LE and trunk 2nd order damage of the spinothalamic tract
Horners syndrome
includes the absence of sympathetically stimulated functions on the ipsilateral side of the head includes: ptosis: drooping superior eyelid miosis: constriction of pupil anhydrosis: absence of sweating Redness of skin
Sensory information from the trigeminal nerve travels…
through the posterior limb of internal capsule to reach postcentral gyrus (laterally) this region (perioral region) has highest density of innervation, largest section
Mesencephalic pathway projections
Central projections include
- Main sensory Nucleus V, follows S-1 pathway
- Spinal trigeminal nucleus - > cerebellum; used to modulate motor output (mastication)
- Reticular formation mediates reflexes
- Motor nucleus V - mediates jaw jerk reflex
most proprioceptive infor from the face is carried by primary afferent axons with the soma in the mesencephalic nucleus
CN V motor nerves of V3
Soma of alpha beta fibers in mesencephalic nucleus, synapses on motor nucleus
this synapses in the mouth
jaw jerk reflex - tap to middle of chin with the mouth slightly open
also receives input from precentral gyrus -motor nucleus receives bilateral input from corticobulbar tract fibers
will a unilateral lesion of corticobulbar tract fibers produce dramitic weakness of mastication?
no - CN V motor nucleus receives bilateral input from corticobulbar tract fibers
Facial nerve
CN VII
Emerges from the brainstem at the ventrolateral aspect of the caudal pons, near the pontomedullary junction
at this point, it has a large motor root (SVE) and smaller root called the nervus intermedius
nervus intermedius
GSA, SA, GVE, GVA
lies between the motor root of CN VII and CN VIII
Facial nerve (CN VII) path
emerges from brainstem and into the posterior cranial fossa
It leave the posterior cranial fossa via the internal acoustic meatus
-it then courses through the temporal bone for a distance, an exits the cranium via the styolmastoid foramen
internal acoustic meatus
where the CN VII leaves the posterior cranial fossa
CN VIII also courses through this
styolmastoid foramen
where the facial nerve leaves the cranium
Functional components of Facial nerve
SVE GVE GSA SA GVA
SVE of facial nerve
muscles of facial expression
GVE of facial nerve
Parasympathetic innervation to the following glands: lacrimal, nasal, palantine, upper pharynx, submandibular and sublingual
GSA of facial nerve
sensory from a portion of the external ear
SA of facial nerve
taste from the anterior 2/3 of the tongue and palate
GVA of the facial nerve
Recurrent fiber path that follows the GVE fibers
Facial CN VII SVE pathway
Draw - corticobulbar fibers from motor cortex descend to facial motor nucleus in the pons, ipsilaterally to rostral pons and contralaterally to mid & caudal pons
Right corticobulbar damage to upper motor neurons of CN VII
Selective weakness of LEFT lower facial muscles
would not be able to lift left lip but could raise eyebrows symmetrically
lesion to left corticobulbar fiber would be vice versa
lesion to right Facial nerve
will result in right upper and lower facial muscle weakness
orbicularis oculi
closes the eye
connections involved in the blink reflex
CN V (GSA) - comprise afferent component; carry pain info from cornea into CNS (spinal trigeminal nucleus)
CN VII (SVE) - efferent component of reflex and responsible for closing the eyes
bilateral. spinal trigeminal fibers relay through the reticular formation to bilateral facial motor nuclei
CN III, IV, VII
oculomoter, trochlear, abducens (respectively)
innervate skeletal muscle that controls eye movements
CN III, IV, VII process
emerge from the cranial cavity via the superior orbial fissure in the following order: III, IV, VI…then CN V1
Innervation of the extraocular eye muscles
6 extraocular eye muscles responsible for movement of the globe/eyeball
- CN III innervates 4 extraocular eye muscles
- CN IV innervates 1
- CN VI innervates 1
Extraocular eye muscles innervated by CN III
Superior rectus
inferior rectus
medial rectus
inferior oblique
also innervates muscle that elevates the eyelid - ;levator palpebrae superioris
Extraocular eye muscles innervated by CN IV
superior oblique
Extraocular eye muscles innervated by CN VI
Lateral rectus
Abduction of eyeball
away from midline
adduction of eyeball
toward the midline
internal/medial rotation/intorsion
12 oclock position moves toward the nose
external/lateral rotation/extorsion
12 oclock position moves away from the nose
relative orientation of eyeball
visual axis is set off from the orbital axis by about 23 degrees
attachment of extraocular muscles and their relationship to the visual axis impacts the motion each muscle has on eye movement
Direction of pull of the extraocular eye muscles if they were to contract in isolation…superior oblique
abducts, depresses and medially rotates the eye
attaches posterior and superior to horizontal axis, passes medial to vertical axis and attaches to posterior superior aspect
Direction of pull of the extraocular eye muscles …
if they were to contract in isolation inferior oblique
abducts, elevates and laterally rotates eye
attaches posterior and inferior to the horizontal axis
passes medial to vertical axis and attaches to posterior inferior aspect of globe
Direction of pull of the extraocular eye muscles if they were to contract in isolation superior rectus
elevates, adducts and rotates eyeball medially
attaches anterior and superior to horizontal axis
passes medial to vertical axis and attaches to the anterior aspect of globe
Direction of pull of the extraocular eye muscles if they were to contract in isolation inferior rectus
depresses, adducts and rotates eyeball laterally
attaches anterior and inferior to horizontal axis
passes medial to vertical axis and attaches to the anterior aspect of the globe
Direction of pull of the extraocular eye muscles if they were to contract in isolation medial rectus
adducts eyeball
Direction of pull of the extraocular eye muscles if they were to contract in isolation lateral rectus
abducts eyeball
Intorsion of the globe
muscles with a medial pull above the visual axis mediall rotate (intort) – superior oblique and rectus
Extorsion of globe
muscles with a medial pull below the visiual axis extort/laterally rotate the globe (inferior oblique and rectus)
CN III overview of innervation
GSE - superior rectus, inferior rectus, medial rectus, inferior oblique
palpebrae superioris muscle (superior eyelid)
contains parasympathetic fibers GVE that pass to the constrictor muscle of the pupil
cranial nerve III nucleus location and path
lies in the rostral midbrain at the level of superior colliculus (SC)
oculomotor nerve traverses the superior orbital fissure
neurons in the left oculomotor nucleus project axons that cross midline in the midbrain and contribute fibers to the right oculomotor nerve, and innervate the right superior rectus muscle
the oculomotor nerve traverses the
superior orbital fissure
the levator palpebrae superioris muscle is innervated by…
both the right and left axons from the oculomotor nuclei
Parasympathetic GVE fibers of CN III
Preganglionic para fibers originate in the Edinger-Westphal nucleus
- axons trabel to ciliary ganglion and synapse on
- postganglionic para fibers that pass to the ciliary muscles and sphincter pupillae
travel in same tract as other fibers
Note about cN III GSE and GVE
innervated by the sympathetic nervous system, the preGG cell are located in the lateral horn of the spinal cord and the postGG cell bodies are located in the sympathetic chaing (superior cervical ganglion)
Trochlear Nerve
CN IV
lies in the caudal midbrain at the level of inferior colliculus (IC)
cell bodies that give rise to the trochlear nerve are located in the contralateral trochlear nucleus, fibers decussate and exit the midbrain dorsally
-traverses the superior orbital fissure
axons from the left trochlear nucleus cross in…
the midbrain and form the right trochlear nerve, innervating the right superior oblique muscle
Cranial nerve VI
abducens nerve
innervates only one muscle, the lateral rectus
GSE
abducens nucleus is located in the caudal pons
transverses the superior orbital fissure
Motor nuclei of CN III, IV, VI
do not receive direct input from the motor cortices
Rapid eye movements
aka saccades
-mediated via projections from cortical eye fields (frontal, supplementary and parietal eye fields) to the reticular formation (midbrain and pons)
-reticular formation projects to the motor nuclei of III, IV, and VI which innervate the extraocular eye muscles
What tracks visual stimuli that are moving?
smooth pursuit
smooth pursuit movements/tracking
requires continuous feedback from the visual cortex, cortical eye fields, vestibular system and cerebellum to the motor nuclei of CN-III,IV and VI
these CNS regions are critical for maintaining the moving visual stimulus on the fovea
Abducens nerve lesion
Ipsilateral eye exhibits medial strabismus (medial deviation/adduction of the eyeball)
medial strabismus occurs in the eye ipsilateral to the lesion because lack of innervation to the lateral rectus
-Medial rectus is unopposed
medial strabismus
abnormal alignment of the eyes
Oculomotor nerve lesion
ipsilateral eye is deviated laterally and slightly downward
- lateral deviation - bc unopposed action of the lateral rectus
- downward position- bc of unopposed action of the superior oblique
- impaired vertical movements - bc loss of innervation to superior rectus, inferior rectus and inferior oblique
diplopia
double vision - due to inability to direct both eyes toward the same object
ptosis
drooping of eyelid because of deficient innervation to the levator palpebrae superiors muscle
dilated/non reactive pupil
because of lack of parasympathetic innervation to pupillary constrictor muscle
