External Brainstem

Which cranial nerves exit the brain stem?

CN 3- 12 -bulbar part of spinal accessory; the rest exits the spine

Which cranial nerves exit the midbrain? Where

CN3, oculomotor: Interpeduncular fossa CN4, trochlear: back of midbrain

chin tuck, head tilt is indicative of a lesion of what CN? Where can this nerve be found around the brain stem?

CN4, which runs right above the tentorial notch

Which cranial nerves exit the back of the brain stem?

CNIV

What is the path of CNXI out of the cranium?

Cell bodies for CN11 (SPINAL accessory n) come from the spine - enters the cranium through the foramen magnum and exits through the jugular foramen.

In the body to brain stem analogy, what are your fists? What other names does this structure go by?

Cerebral peduncles -aka. crus cerebri, pes pedunculi

What create the facial colliculus?

LMN of the facial n create this eminence

A stoke of the Inferior pontine sulcus (red line) occurs in which division of the brain stem? What CN may be effected?

Medulla/Pons: CNs VI (abducens), VII (facial), VIII (auditory)

A stoke of the Preolivary sulcus occurs in which division of the brain stem? What CN may be effected?

Medulla: - CN XII (Hypoglossal n.)

A stoke of the Postolivary sulcus occurs in which division of the brain stem? What CN may be effected?

Medulla: - CNs IX (glossopharyngeal n.), - X (vagus n.) - XI (bulbar part of the accessory n.)

Midbrain aka and exact anterior boundaries

Mesencephalon (Midbrain) -Superior anterior (ventral) boundary: Caudal to mamillary bodies of hypothalamus -Inferior anterior (ventral) boundary: Superior pontine sulcus at the pontomesencephalic junction

Pons aka and anterior boundaries

Metencephalon (Pons) -Superior anterior (ventral) boundary: Superior pontine sulcus at the pontomesencephalic junction -Inferior anterior (ventral) boundary: Inferior pontine sulcus at the pontomedullary junction

Medulla oblongata aka and posterior boundaries

Myelencephalon -Superior posterior (dorsal) boundary: Stria medullaris of the fourth ventricle -Inferior posterior (dorsal) boundary: Plane just rostral to C1 ventral root emergence and caudal to the decussation of the pyramids

What are the important tracts of the midbrain? What structure do they run through?

PBS: CorticoPontine tract, CorticoBulbar Tract CorticoSpinal tract -Cerebral peduncles (crus cerebri, pes pedunculi)

What is the primary blood supply of the medulla? What cranial nerves may be effected by compromise of this blood supply?

Vertebral aa run up the medulla oblongata

What is involved in a Superior (midbrain) alternating hemiplesia?

Weber syndrome: eye goes out (CNIII), lesion at cerebral peduncle of corticospinal tract; posterior cerebral a, hemiparalysis

Fasciculus cuneatus

sensory tract for trunk, neck and upper extremities proprioception, vibration, 2 pt discrimination, graphesthesia

Superior colliculus and Inferior colliculus collectively form?

the corpora quadrigemina of the tectum

brain stem blood supply

vertebral aa - medulla baislar a - pons basilar a branches into posterior cerebral aa

Myelencephalon aka and anterior boundaries

(Medulla oblongata) -Superior anterior (ventral) boundary: Inferior pontine sulcus at the pontomedullary junction -Inferior anterior (ventral) boundary: Line drawn just caudal to the decussation of the pyramids

What is involved in Midpontine base syndrome?

(mid pons on the basilar surface (anterior) [tegmentum is posterior]. CN5, lesion at basilar pons of corticospinal tract; branches of basilar a. - bilateral = locked-in syndrome.

What is the difference between a coma and sleeping? eg. What wakes you up, and how?

- the ability to wake up - which comes from the reticular activating system. ADP binds to a receptor on the recticular activating system - puts you to sleep Caffeine blocks the ADP receptor so you don't feel as sleepy.

Your patient is unable to follow an H pattern with their eyes; they have ptosis (droopy eyelid), double vision, and their pupils are non-reactive to light. What CN may be effected? What does this CN begin? Where does it exit the skull? Why would the above symptoms be associated with this CN?

-CN3, oculomotor -Begins in the oculomotor nuclei (and Edinger-Westphal for parasympathetics) of the midbrain at the *Interpeduncular fossa* -Exits through the superior orbital fissure into the orbit. -Innervates: +Parasympathetics: innervate two separate intrinsic muscles within the eye. These will constrict the pupil and cause accommodation of the lens of the eye respectively. +Motor: Superior Rectus, Inferior Rectus, Medial Rectus, Inferior Oblique, and Levator Palpabrae Superioris (elevation of the eyelid)

Which CN exits the Interpeduncular fossa? Where does this CN exit the skull?

-CN3, oculomotor -Exits through the superior orbital fissure into the orbit.

What are the major structures that enter and exit the brain stem? What are the major ascending and descending structures in the brain stem?

-CN3-12 -tracts

What are the segments of the brain stem? (Give both names)

-Medulla oblongata or Myelencephalon -Pons (and cerebellum) or Metencephalon -Midbrain or Mesencephalon

Describe the Important Structures of the Medullary Portion of the Rhomboid Fossa

-Vagal and hypoglossal trigones -Area postrema/Chemoreceptor trigger zone (CTZ) -Vestibular area (lateral recess) -CN VIII (vestibulocochlear n.) -Lateral recess and Foramina of Luschka - how CSF gets out Stria medullaris of the IV ventricle -Inferior cerebellar peduncle (restiform body) -Obex -Fasciculus gracilis and gracile tubercle (for the lower limbs) Fasciculus cuneatus and cuneate tubercle (for the upper limbs)

Name the important structures of the midbrain

Cerebral peduncles (aka. crus cerebri, pes pedunculi) - CorticoPontine, CorticoBulbar, and CorticoSpinal Tracts Interpeduncular fossa - Oculomotor nerves (CN III) Superior colliculi (optic reflex center) and inferior colliculi (auditory reflex center) of the tectum (Corpora quadrigemina) Lateral lemniscus (auditory pathway structure to inf. colliculus) CN IV (Trochlear n.) **only n that exits the brainstem posteriorly. Brachium of the superior colliculus Brachium of the inferior colliculus Superior cerebellar peduncles (brachium conjunctivum)

What is involved in a Middle (pons) alternating hemiplesia?

Foville/Raymond: CN6; lesion at basilar pons of corticospinal tract; branches of basilar a

Name the Important Structures of the Medulla

Inferior pontine sulcus - CNs VI (abducens n.), VII (facial n.), VIII(vestibulochochlear n.) Pyramids Decussation of the pyramids Anterior median fissure Preolivary sulcus - CN XII (Hypoglossal n.) Postolivary sulcus - CNs IX (glossopharyngeal n.), X (vagus n.) XI (bulbar part of the accessory n.) Inferior olivary eminence Inferior cerebellar peduncle (restiform body) CN XI (accessory n.) Tuberculum cinereum Fasciculus cuneatus and cuneate tubercle

Which cranial nerves exit the medulla? Where?

Inferior pontine sulcus: - CNs VI (abducens n.), - VII (facial n.), - VIII(vestibulochochlear n.) Preolivary sulcus - CN XII (Hypoglossal n.) Postolivary sulcus - CNs IX (glossopharyngeal n.), - X (vagus n.) - XI (bulbar part of the accessory n.)

Which cranial nerves exit the pons? Where?

Inferior pontine sulcus: +CNs VI (abducens), VII (facial), VIII (auditory) Middle cerebellar peduncle (brachium pontis): +Motor and sensory root of CN V (trigeminal n.) +CN VII (facial n.) and Nervus intermedius of CN VII. +CN VIII (vestibulocochlear n.) CNs 5, 7, and 8 come off the middle cerebellar peduncles laterally

Name Important Structures of the Pontine Portion of the Rhomboid Fossa

Posterior median sulcus Medial eminence Facial colliculus Sulcus limitans Locus caeruleus - epi and norepinephrine containing axons...because epi and NE can't cross the BBB.

cuneate tubercle

Produced by the nucleus cuneatus where fibers from fasciculus cuneatus synapse -a nucleus that relays sensory information from the upper body

What are the important structures of the Metencephalon?

aka (Pons): -Basilar sulcus -Basal portion of the pons -Superior pontine sulcus (isthmus) -Inferior pontine sulcus: +CNs VI (abducens), VII (facial), VIII (auditory) -Middle cerebellar peduncle (brachium pontis) +Motor and sensory root of CN V (trigeminal n.) +CN VII (facial n.) and Nervus intermedius of CN VII. +CN VIII (vestibulocochlear n.)

What is involved in Inferior alternating hemiplesia?

aka Dejerines: CN12; lesion at rostral medulla of corticospinal tract; vertebral a (lesion is in the inferior brain stem (medulla) and has paralysis of half of the body [from neck down] - on the alternate ½ from the lesion)

Mesencephalon posterior boundaries and aka

aka Midbrain Need to know the jist of: -Superior posterior (dorsal) boundary Posterior commissure of diencephalon -Inferior posterior (dorsal) boundary Line drawn immediately caudal to the site of emergence of CN IV (trochlear n.)

Metencephalon aka and posterior boundaries?

aka Pons -Superior posterior (dorsal) boundary: Caudal to site of emergence of the trochlear n. (CN IV) -Inferior posterior (dorsal) boundary: Stria medullaris (blue box) on the floor of the fourth ventricle

What is the primary blood supply of the pons?

basilar a

Where are the pyramids? What is decussating at the pyramids?

medulla -Lateral corticospinal tract