The brain stem

Liu jiao

Binzhou Medical University

Department Of Anatomy

The brain

Telencephalon Diencephalon Cerebellum Brain stem

Names of cranial nerves Ⅰ Olfactory nerve Ⅱ Optic nerve Ⅲ Oculomotor nerve Ⅳ Trochlear nerve Ⅴ Trigeminal nerve Ⅵ Abducent nerve Ⅶ Facial nerve Ⅷ Vestibulocochlear nerve Ⅸ Glossopharyngeal nerve Ⅹ Vagus nerve Ⅺ Accessory nerve Ⅻ Hypoglossal nerve

The brain stem

Consists of Midbrain Pons Medulla oblongata

Medulla oblongataVentral surface Pyramid: contain pyramidal tr

act (corticospinal tract) Decussation of pyramid: form

ed by crossing fibers of corticospinal tract

Olive: produced by underlying inferior olivary nucleus

Anterolateral sulcus: rootlets of hypoglossal nerve emerge from it

Retroolivary sulcus: rootlets of glossopharyngeal, vagus and accessory nerves emerge from it

Medulla oblongata

Dorsal surface Lower portion

Gracile tubercle: produced by und

erlying gracile nucleus Cuneate tubercle: marks the site

of cuneate nucleus Inferior cerebellar peduncle Obex

Upper portion: forms the lower half of rhomboid fossa

PonsVentral surface Basilar part Basilar sulcus Bulbopontine sulcus :

from medial to lateral, the abducent, facial and vestibulocochlear nerves appear

Middle cerebellar peduncle Trigeminal nerve Pontocerebellar trigone :

the junction of medulla, pons and cerebellum

Pons

Dorsal surface Superior cerebellar pedu

ncle Superior medullary velu

m Trochlear nerve

Midbrain

Ventral surface Crus cerebri Interpeduncular fossa o

culomotor nerves emerge from medial of crus cerebri

Posterior perforated substance

MidbrainDorsal surface Superior colliculus con

stitute centers for visual reflexes

Inferior colliculus associated with auditory pathway

Brachium of superior colliculi

Brachium of inferior colliculi

Fourth ventricle

Position Situated ventral to

cerebellum, and dorsal to pons and cranial half of medulla

Central canal →fourth ventricle →mesencephalic aqueduct→third ventricle

Boundaries Inferolateral: gracile an

d cuneate tubercles, inferior cerebellar peduncle

Superolateral: superior cerebellar peduncle

Lateral recess

Features Median sulcus Sulcus limitans Vestibular area overlies vestibular nuclei

Acoustic tubercle overlying dorsal cochlear nucleus

Medial eminence Striae medullares

Facial colliculus: overlies nucleus of abducent n. an

d genu of facial nerve

Hypoglossal triangle: verlyi

ng hypoglossal nucleus Vagal triangle: overlies dorsal nucleus of vagus n

erve

Funiculus separans Area postrema Locus ceruleus

Roof Anterior part: formed by s

uperior cerebellar peduncle and superior medullary velum

Posterior part: formed by inferior medullary velum and choroid plexus of fourth ventricle

Three apertures Median aperture of fourth

ventricle Two lateral apertures of fo

urth ventricle

Internal structures

Gray matter Cranial nerve nuclei Relay nuclei

General somatic motor nuclei

Nucleus of oculomotor n. Nucleus of trochlear n. Nucleus of abducent n. Nucleus of hypoglossal n.

Nucleus Site Cranial n. Function

Nucleus of

Oculomotor n.

Midbrain Ⅲ Supreior, inferior,and medial recti, inf. obliquus, levator palpebrae superioris

Nucleus oftrochlear n.

Midbrain Ⅳ Superior obliquus

Nucleus of abducent n.

Pons Ⅵ Lateral rectus

Nucleus of hypoglossal n.

Medulla Ⅻ Muscles of tongue

General somatic motor nuclei

Special visceral motor nuclei

Motor nucleus of trigeminal n.

Nucleus of facial n. Nucleus ambiguus Accessory nucleus

Special visceral motor nuclei

Nucleus Site Cranial n. Function

Motor nucleus of trigeminal n.

Pons Ⅴ Masticatory muscles

Nucleus of facial n.

Pons Ⅶ Facial m., platysma, posterior belly of digastric, stylohyoid, stapedius

Nucleus ambiguus Medulla Ⅸ, .Ⅹ Ⅺ Skeletal m. of pharynx, larynx and upper part of esophagus

Accessory nucleus Medulla-cervical cord

Ⅺ Sternocleidomastoid, trapezius

General visceral motor nuclei

Accessory oculomotor nucleus

Superior salivatory nucleus

Inferior salivertory nucleus

Dorsal nucleus of vagus n.

General visceral motor nuclei

Nucleus Site Cranial n.

Function

Accessory oculomotor nucleus

Midbrain Ⅲ Sphincter pupillae and ciliary m.

Superior salivatory nucleus

Pons Ⅶ Submandibular, sublingual and lacrimal glands

Inferior salivertory nucleus

Medulla Ⅸ Parotid gland

Dorsal nucleus of vagus n.

medulla Ⅹ Many cervical, thoracic and abdominal viscera

Visceral sensory nuclei ( general and special ) Nucleus of solitary tract

Visceral sensory nuclei ( general and special )

Nucleus Site Cranial n. Function

Nucleus of solitary tract

Medulla Ⅶ, ,Ⅸ Ⅹ Taste and visceral sensation

General somatic sensory nuclei

Mesencephalic nucleus of trigeminal n.

Pontine nucleus of trigeminal n.

Spinal nucleus of trigeminal n.

General somatic sensory nuclei

Nucleus Site Cranial n. Function

Mesencephalic nucleus of trigeminal n.

Midbrain Ⅴ Proprioception of head

Pontine nucleus of trigeminal n.

Pons Ⅴ Tactile sensation of head

Spinal nucleus of trigeminal n.

Medulla Ⅴ Pain and temperature sense of head

Special somatic sensory nuclei

Cochlear nuclei

Vestibular nuclei

Special somatic sensory nuclei

Nucleus Site Cranial n. Function

Cochlear nuclei

Pons and medulla

Ⅷ Sense of hearing

Vestibular nuclei

Pons and medulla

Ⅷ Sense of equilibrium

Gracile nucleus Cuneate nucleus Inferior olivary nucleus Superior olivery nucleus Pontine nucleus Nucleus of inferior colliculus Gray matter layers of superi

or colliculus Red nucleus Substantia nigra Pretectal area

Relay nuclei

Non-cranial nerve nuclei Nucleus Site

Gracile nucleus Medulla (underneath gracile tubercle)

Cuneate nucleus Medulla (underneath cuneate tubercle)

Superior olivery nucleus Pons

Pontine nucleus pons

Nucleus of inferior colliculus Midbrain

Gray matter layers of superior colliculus

Midbrain

Red nucleus Midbrain

Substantia nigra Midbrain

Pretectal area Midbrain

White matter

Ascending tracts Medial lemniscus Spinal lemniscus Trigeminal lemniscus Lateral lemniscus

Medial lemniscus

Spinal lemniscus

Trigeminal lemniscus

Descending tracts

Corticospinal tract Rubrospinal tract Tectospinal tract Vestibulospinal tract Reticulospinal tract

Lateral lemniscus

Reticular formation of brain stem Ascending reticular a

ctivating system (ARAS)

Motor central and vital centres Reticulospinal tract Cardiovascular center an

d respiratory center Serotonergic rapheal

nuclei

The characters of internal structure of

brain stem

Medulla oblongataLower part (closed part) Two decussations–

Decussations of medial lemniscus Decussations of pyramid

Medulla oblongata

Upper part (open part) Appearance of inferior oliv

ary nuculeus and inferior cerebellar peduncle

Enlargement of central canal to form the fourth ventricle floor

Pons Tegmentum of pons directed upward continuation of me

dulla oblongata Basilar part contain both longitudinal and transv

erse fibers intermixed with pontine nuclei

Midbrain Rectum of midbrain: includ

es superior and inferior colliculi Cerebral peduncle

Tegmentum :

contain ascending tracts, central gray matter, recticular formation and so on Substentia nigra Crus cerebri :

Pyramidal tract middle three-fifths of the crus: Frontopontine tract medial one-fifth: pariatotempopontine tract lateral one-fifth