UBC NSCI 311 - Lecture 6 (Brainstem + CN V & VII)

Advanced Neuroanatomy, Midterm 1 Content

brainstem general function

• acts as a conduit for information passing to and from cerebrum and cerebellum

• facilitates many integrative (autonomic) functions

what cranial nerves exit/enter brainstem

all except CN I, II and XI

why is the vagus nerve called the wandering nerve

because in addition to innervating sensory and motor functions in head/face/neck like the other CN nuclei in brainstem, it innervates organs in thorax and abdomen

what do the cranial nerves that have nuclei in the brainstem do

sensory and motor functions of head/face/neck

are cranial nerves the same as spinal nerves

like spinal nerves, they carry both sensory and motor information, but they all have differenet modalities

where is pituitary stalk

superior to mamillary bodies, inferior to optic tract, ventral surface of brainstem

where is pineal gland

superior to superior colliculi

where is obex

where fourth ventricle closes on medulla

which fibers/tracts would you find in base longitudinal partition

corticospinal and corticonuclear fibers (motor pathways)

which fibers/tracts would you find in tegmentum longitudinal partition

spinal and medial lemniscus

which fibers/tracts would you find in tectum longitudinal partition

superior colliculi

longitudinal partitions from ventral to dorsal

• base

• tegmentum

• ventricular system

• tectum (“roof”)

how many cranial nerves are there

12 paired nerves

what are cranial nerves

bundles of axons in peripheral nervous system

which cranial nerves are sensory only

• CN I (olfactory)

• CN II (optic)

• CN VIII (vestibulocochlear)

which cranial nerves are motor only

• CN III (Oculomotor)

• CN IV (Trochlear)

• CN VI (Abducens)

• CN XI (Spinal Accessory)

• CN XII (Hypoglossal)

which cranial nerves are both motor and sensory

• CN V (Trigeminal)

• CN VII (Facial)

• CN IX (Glossopharyngeal)

• CN X (Vagus)

what does the tectum consist of

• superior and inferior colliculi

• superior and inferior medullary velum

which nerves emerge from midbrain

CN III and IV

which nerves emerge from pons

• CN V (basal pons)

• CN VI, VII, VIII (pontomedullary junction)

which nerves emerge from medulla

• CN VI, VII, VIII (pontomedullary junction)

• CN IX, X, XII

where does CN XI emerge

upper cervical spinal cord

special sensory cranial nerve modalities

vision, hearing and balance

somatic sensory cranial nerve modalities

somatosensation from skin and muscles (pain, touch, temperature, proprioception)

special sensory cranial nerve modalities

tase and smell (olfaction)

visceral sensory cranial nerve modalities

sensation from internal organs (especially pain)

visceral motor cranial nerve modalities

parasympathetic NS only, to smooth muscle, glands, etc.

branchial motor cranial nerve modalities

motor information to skeletal muscle derived from pharyngeal arches

somatic motor cranial nerve modalities

motor information to skeletal muscle derived from somites

pharyngeal (branchial) arches

paired outpouchings of mesoderm, each innervated by a different branchial motor cranial nerve

how does the developing neural tube divide

into basal and alar plates

where are branchial motor neurons in dividing neural tube

basal plate, between somatic and visceral motor

where are special sensory motor neurons in dividing neural tube

alar plate, lateral/dorsal to somatic sensory

secondary migration of brachial motor nuclei location at rostral medulla

just dorsal of olivary colliculi

secondary migration of somatic sensory nuclei at rostral medulla

slightly ventral to visceral and special sensory nuclei

brainstem nuclei of the same modality are oriented how

in the same vertical (rostral-caudal) column

are cranial nerves only associated with one modality

no, many carry many modalities and many nuclei

typically, how many modalities per CN nucleus?

one

trigeminal nerve roots

• motor and sensory

• both emerge from lateral pons 

trigeminal dermatomes (list, location)

• V1, top of head to nose

• V2, temple to side of nose and top of lip

• V3, above ear to chin

trigeminal V1 division

Ophthalmic n. (somatic sensory from head)

trigeminal V2 division

maxillary n. (upper jaw, somatic sensory from head)

trigeminal V3 division

mandibular n. (lower jaw, branchial motor signals to muscles of mastication)

sensory trigeminal nucleus divisions

• mesencephalic nucleus

• chief nucleus

• spinal nucleus

location of mesencephalic nucleus

midbrain to pons

location of chief nucleus

mid-pons

location of spinal nucleus

• pons to cervical spine

• continuous with dorsal horn

motor trigeminal nerve nucleus

motor trigeminal nucleus, mid-pons where CN V emerges (just superior to chief nucleus)

spinal nucleus modalities

pain and temperature

spinal trigeminal tract location

continuous with Lissauer’s/dorsolateral tract (important in spinothalamic pathway)

mesencephalic nucleus modalities

• proprioception from mandible

why us mesencephalic nucleus unique

contains the cell bodies of the primary sensory neurons (the only known case of primary sensory cell bodies in CNS)

chief nucleus modalities

fine/discriminative touch and vibration

pathway of CN V UMN corticonuclear fibers

• from primary motor cortex of “face area”

• through corona radiata

• through internal capsule GENU

• through cerebral peduncle

• through basal pons

• synapse bilaterally with LMN in motor trigeminal nuclei

  • LMNs emerge mid-pons

divisions of facial nerve (CN VII)

• chorda tympani

• branchial motor branches

branchial motor fibers modalities

muscles of facial expression (branches labelled TZBMC)

chorda tympani modalities

• hitchhikes onto trigeminal V3 to get into oral cavity

• visceral motor (parasympathetic) to 3 major glands

• special sensory (taste) of anterior 2/3s of tongue

sensory ganglion of CN VII

geniculate ganglion (where the branchial motor branches off)

3 major glands innervated by visceral motor components of facial nerve

submandibular, sublingual and lacrimal

autonomic ganglia of CN VII

• pterygopalatine ganglion (in upper branches of branchial motor)

• submandibular ganglion (visceral motor)

location of facial nerve

ventrolateral pontomedullary junction

list of facial nerve nuclei

• nucleus solitarius

• facial motor nucleus

• superior salivatory nucleus

nucleus solitarius

• just dorsomedial of sensory trigeminal nucleus in pons

• taste sensation from anterior 2/3s of tongue (chorda tympani)

facial motor nucleus

• fairly medial in pons, fibers go dorsally to wrap around abducens nucleus then exit ventrally

• motor innervation of facial expression (branchial motor branches)

superior salivatory nucleus

• just ventral of facial motor nucleus

• lacrimation and salivation (parasympathetic/visceral motor, chorda tympani)

pathway of CN V UMN corticonuclear fibers

• from primary motor cortex, “face area”

• through corona radiata

• through internal capsule GENU

• through cerebral peduncle

• through basal pons

• synapse in facial motor nuclei

  • bilaterally for upper face

  • contralaterally only for lower face

cause of Bell’s palsy

lesion in lower motor neuron (peripheral) associated with CN VII

Bell’s palsy

complete paralysis of ipsilateral side of face (ipsilateral to lesion)

cause of palsy in one side of lower half of face

lesion in contralateral upper motor neuron (central/supranuclear) associated with CN VII

why does the lesion of the CN VII upper motor neuron cause contralateral damage of just the lower face

lower face is only innervated contralaterally, whereas upper face is innervated bilaterally so the other side will compensate

why does the lesion of the CN VII lower motor neuron cause ipsilateral damage of the entire face

because the lesion would affect both the upper and lower face neurons

is jaw jerk reflex monosynaptic or polysynaptic

monosynaptic

jaw jerk reflex pathway

• chin tap proprioceptive stimulus of masication muscles sent via sensory CN V3

  • muscle spindles

• primary sensory neuron cell bodies in mesencephalic nucleus

• synapse with motor neuron in trigeminal motor nuclei

• motor CN V3 takes it to neuromuscular junctions

  • mouth closes, bilateral projections

corneal blink reflex stimulus

nociception (pain)

pathway of corneal blink reflex

• nociceptors in cornea of eye send sensory info via CN V1

• synapse with interneurons in spinal trigeminal nucleus

• interneurons project bilaterally (from medulla)

• synapse with LMNs in facial motor nuclei

• CN VII innervates neuromuscular junction in orbicularis oculi muscles

  • both eyes close (blink)