Brainstem and CNs

what are the regions of the brainstem?

1. tegmentum

2. basilar

3. tectum

what is the tegmentum continuous with?

the spinal cord past the foramen magnum

What is the tegmentum?

a major area for ascending tracts (sensory) and CN nuclei (III-XII)

What does ascending tract mean?

sensory; towards the CNS

Where are majority of CNs originating?

from the tegmentum

Which cranial nerves are in the tegmentum?

3-12

what is the reticular formation?

large network of nuclei located in the core of the tegmentum

what does the basilar region of the brainstem contain?

major tracts and nuclei involved with motor circuits; descending tracts

What does descending tract mean?

away from the CNS

Where is the tectum of the brainstem?

ONLY in midbrain

what are the 2 parts of the tectum?

1. superior colliculus: non-conscious visual processing

2. inferior colliculus: non-conscious auditory processing

what is the blood supply to the midbrain?

• PCA (posterior cerebral artery)

• basilar artery

Pooh Bah

what is the blood supply to the pons

• basilar artery

• anterior inferior cerebral artery

AB

what is the blood supply to the medulla?

• vertebral artery

• anterior spinal artery

• posterior inferior cerebral artery

VAP

blood supply to midbrain, pons, medulla

what is the most common cause of brainstem damage?

stroke (both kinds)

What are the symptoms of a stroke dependent on?

vessel (s) effected

what are brainstem functions?

1. breathing

2. Heartbeat

3. BP

4. origins of CN 3-12

5. consciousness, sleep, alertness

What does the brainstem serve as?

a conduit for many ascending and descending pathways

Where does the reticular formation extend through?

throughout the brainstem tegmentum (acts like a net)

reticular formation

what is the reticular formation loosely defined as?

“functional” system

What does the reticular formation contain?

networks of local-circuit interneurons that interact with ascending (sensory) and descending (motor) pathways

What does the reticular formation generate?

motor and autonomic patterns

what does the reticular formation coordinate?

reflexes and simple behaviors:

• crying

• swallowing

• breathing

• HR

• BP

what is the ascending reticular activating system (ARAS)?

• arousal, consciousness, and sleep (thalamus/cortex)

• pain modulation (spinoreticular formation)

startles you awake when you feel pain

What does reticular mean?

net-like

Does the sympathetic pathway descend or ascend?

descend

Where do sympathetic nerves originate?

hypothalamus and pass through the brainstem and SC

What does the sympathetic pathway instigate?

fight or flight

What does injury to the sympathetics result in?

ipsilateral horner’s syndrome

what are the symptoms of horner’s syndrome?

• ptosis - drooping eyelid

• miosis - constricted pupil

• anhidrosis - loss of sweating

where is the midbrain?

superior most region of brainstem

What CN comes from the dorsal side of the midbrain?

CN 4 trochlear

midbrain (rostral view); ignore STT/ML

what are dopaminergic nuclei found?

in substantia nigra

where do the dopaminergic nuclei project?

to basal ganglia

what is the function of dopaminergic nuceli?

modulate movement

What do the dopaminergic nuclei play a major role in?

parkinson’s

which NT is found in the substantia nigra’s nuclei?

dopamin

dark is the substantia nigra and dopaminergic nuclei are found there

what part of the brainstem is the pons?

intermediate part

what is the pons covered by dorsally?

cerebellum

what is the rhomboid fossa?

back of the pons and medulla that is the floor of the 4th ventricle

know that this is an image of the pons, and the small holes at the bottom are the locus coeruleus

what does the locus coeruleus produce?

norepi

what is the function of the Locus Coeruleus?

arousal, modulation of stress responses

what is the Locus Coeruleus linked to?

depression, anxiety, PTSD

what the Locus Coeruleus account for?

psychiatric symptoms of PD

what does the Raphe Nuclei produce?

serotonin

what is locked in syndrome?

stroke in the pons

what is locked syndrome most often caused by?

basilar artery thrombosis

where is the damage occuring for locked in syndrome?

bilateral damage to ventral pons

what does locked-in syndrome result in?

complete paralysis of all voluntary muscles (corticospinal and corticobulbar tracts are damaged/descending tracts)

What is spared in locked in syndrome?

CN 3 bc midbrain is not affected

where is the medulla?

inferior most region of brain → blends into spinal cord at foramen magnum

what is the area postrema?

“vomiting center” d/t incomplete BBB → area has to sample blood for toxins

What is the area postrema the floor of?

the 4th ventricle

what are the Big four pathways in the brainstem?

1. corticospinal tract - descending motor

2. spinothalamic tract - ascending pain/temp

3. dorsal columns/medial lemniscus - ascending somatosensory/proprioception

4. spinocerebellar tracts - ascending unconscious proprioception

red part are pyramids

most CN are associated with what?

position of the CN EXCEPT CN 5 and CN 11

what does CN and nuclei damage cause?

ipsilateral deficits EXCEPT CN 4

• midline = motor

• lateral = sensory

What may CNs have multiple of?

nuclei → may be motor, sensory, or autonomic

know this

CN 5 is everywhere and CN 1 is in the nose

Why are CNs called CNs?

they emerge through the foramina or fissures in the cranium

How many pairs of CNs are there?

12

how many CNs are in the brainstem?

9

how many CNs are in the telencephalon?

1 - CN 1 olfactory

how many CNs are in the diencephalon?

1 - CN 2 optic

how many CNs are in the cervical spine?

1 - CN 11 accessory

what are the fiber types that cranial nerves carry?

1. motor (efferent) fibers

2. sensory (afferent) fibers

what are the parasympathetic CNs?

• CN 3 - oculomotor

• CN 7 - facial

• CN 9 glossopharyngeal

• CN 10 - vagus

What does CN 3 innervate?

oculomotor

1. pupil constriction

2. accommodation of lens

Where is the synapse for CN 3?

ciliary ganglion

What does CN 7 innervate?

1. lacrimal glands - tears

2. mucosal glands of nose/palate

3. submandibular and sublingual glands - salivary

where are the synapses for CN 7?

Pterygopalatine ganglion and Submandibular ganglion

What does CN 9 innervate?

parotid gland

where is the synapse for CN 9?

otic ganglion

What does CN 10 innervate?

viscera as far as proximal colon; cardiac, pulmonary, and esophageal plexus

How many you describe the parasympathetic CNs?

rest and digest

what is the corticobulbar tract the counterpart to?

the corticospinal tract

do CNs 1 & 2 have nuclei in the brainstem?

NO! (above midbrain)

Where is the nuclei for CNs 3 and 4?

midbrain - dorsal exit

Where is the nuclei for CNs 5, 6 (motor), and 7?

pons

where is nuclei for CNs 9-12?

medulla

Not all CNs have …

nuclei

Some nuclei receive info from more than one …

cranial nerve

What is CN 1?

olfactory

where is CN 1 from?

olfactory mucosa in nasal cavity

what type of neuron is CN 1?

special sensory

where doesn’t the olfactory system stop?

the thalamus

is CN 2 sensory or motor?

special sensory

where is CN 2 from?

the retina

is CN 2 a true peripheral nerve?

no, apart of CNS tract

What kind of layers does CN 2 have?

dural layers - myelinated by oligodendrocytes

what does CN 2 cross?

the optic chiasm

what does CN 2 pass through?

the optic canal

what does a pituitary tumor compress?

optic chiasm

damage to the optic chiasm causes what?

loss of vision laterally in both visual fields → called bitemporal hemianopia

what is CN 3?

oculomotor nerve