Brain stem

The brain stem

Consists of Midbrain Pons Medulla oblongata

1

2

3

Medulla oblongata

Ventral surface Pyramid: contains pyramida

l tract (corticospinal tract) Decussation of pyramid: f

ormed 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

1

2

3

45

XIIIX

XXI

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

12

3

45

Pons

Ventral surface Basilar part (1)

Basilar sulcus (2)

Bulbopontine sulcus (3): from medial to lateral, the abducent, facial and vestibulocochlear nerves appear

Middle cerebellar peduncle (4)

Trigeminal nerve (5)

1

2

34

5VVI

VIIVIII

Pons

Dorsal surface Superior cerebellar pedu

ncle (1) Superior medullary velu

m (2) Forms the upper half of r

homboid fossa

1

2

Midbrain

Ventral surface Crus cerebri (1)

Interpeduncular fossa (2) oculomotor nerves emerge from medial of crus cerebri

Posterior perforated substance (3)

Oculomotor nerve

123III

VI

Midbrain

Dorsal surface Superior colliculus (1) consti

tute centers for visual reflexes Inferior colliculus (2) associ

ated with auditory pathway Brachium of superior colliculi Brachium of inferior colliculi Trochlear nerve (IV) Medial geniculate body (3) Lateral geniculate body (4)

1

2IV

34

Fourth ventricle

Position Situated ventral to

cerebellum, and dorsal to pons and cranial half of medulla

Central canal →fourth ventricle →mesencephalic aqueduct→third ventricle

Fourth ventricle

Boundaries Inferolateral: gracile an

d cuneate tubercles, inferior cerebellar peduncle

Superolateral: superior cerebellar peduncle

Lateral recess

Fourth ventricle

FloorUpper pontine and lower medullary se

parated by Striae medullares (1) Median sulcus divided it into right and

left halves (2 Medial eminences) (2)

Upper part: Facial colliculus (3): overlies nucleus

of abducent n. and fibers of facial nerve

Upper Vestibular area (4): overlies vestibular nuclei

Superior fovea (5)

1

2

3

4 5Sulcus Limitans

Fourth ventricle

Lower part: Hypoglossal triangle (1): overlying h

ypoglossal nucleus Lower Vestibular area (2) Vagal triangle (3): overlies dorsal nu

cleus of vagus nerve Inferior Fovea ( Inverted Y ). 22 12

3

Roof Upper part: formed by superio

r cerebellar peduncle and superior medullary velum

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

Three apertures Median aperture of fourth ve

ntricle Two lateral apertures of fourt

h ventricle

Fourth ventricle

Internal structures

Gray matter Cranial nerve nuclei Relay nuclei

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

Functional components General somatic afferent fibers (GSA): transmit exteroceptive an

d proprioceptive impulses from head and face to somatic sensory nuclei

Special somatic afferent fibers (SSA): transmit sensory impulses from special sense organs of vision, equilibrium and hearing to the brain

General visceral afferent fibers (GVA): transmit interoceptive impulses from the viscera to the visceral sensory nuclei

Special visceral afferent fibers (SVA): transmit sensory impulses from special sense organs of smell and taste to the brain

General somatic efferent fibers (GSE): innervate skeletal muscles of eye and tongue

Special visceral efferent fibers (SVE): transmit motor impulses from the brain to skeletal muscles derived from brachial (gill) arches of embryo. These include the muscles of mastication, facial expression and swallowing

General visceral efferent fibers (GVE): transmit motor impulses from the general visceral motor nuclei and relayed in parasympathetic ganglions. The postganglionic fibers supply cardiac muscles ， smooth muscles and glands

Classification of cranial nerves Sensory cranial nerves: contain only afferent (sensory) fibers

ⅠOlfactory nerve ⅡOptic nerve Ⅷ Vestibulocochlear nerve

Motor cranial nerves: contain only efferent (motor) fibers Ⅲ Oculomotor nerve Ⅳ Trochlear nerve ⅥAbducent nerve Ⅺ Accessory nerv Ⅻ Hypoglossal nerve

Mixed nerves: contain both sensory and motor fibers--- ⅤTrigeminal nerve, Ⅶ Facial nerve, ⅨGlossopharyngeal nerve ⅩVagus nerve

Sensory cranial nervesN. Location of cell

body and axon categories

Cranial exit

Terminal nuclei

Main action

Ⅰ Olfactory cells (SVA)

Cribrifomforamina

Olfactory bulb

Smell

Ⅱ Ganglion cells (SSA)

Optic canal

Lateral geniculate body

Vision

Ⅷ Vestibular ganglion(SSA)

Internal acoustic meatus

Vestibular nuclei

Equilibrium

Cochlear ganglion (SSA)

Cochlear nuclei

Hearing

Motor cranial nervesN. Nucleus of origin and

axon categoriesCranial exit Main action

Ⅲ Nucleus of oculomotor (GSE)

Superior orbital fissure

Motor to superior, inferior and medial recti; inferior oblique; levator palpebrae superioris

Accessory nucleus of oculomotor (GVE)

Parasympathetic to sphincter pupillea and ciliary muscles

Ⅳ Nucleus of trochlear nerve (GSE)

Superior orbital fissure

Motor to superior oblique

Ⅵ Nucleus of abducent nerve (GSE)

Superior orbital fissure

Motor to lateral rectus

Ⅺ Nucleus of accessory nerve (SVE)

Jugular foramen Motor to sternocleidomastoid and trapezius

Ⅻ Nucleus of hypoglossal nerve( GSE)

Hypoglossal canal Motor to muscles of tongue except palatoglossus

General somatic efferent nuclei

Nucleus of oculomotor n.

Nucleus of trochlear n.

Nucleus of abducent n.

Nucleus of hypoglossal n.

Special visceral motor nuclei

Motor nucleus of trigeminal n.

Nucleus of facial n.

Nucleus ambiguous

Accessory nucleus

Special visceral efferent nuclei

Nucleus Site Cranial n. Function

Motor nucleus of trigeminal n.

Pons Ⅴ Masticatory muscles, tensor palati & t. tympani

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.

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 afferent nuclei Mesencephalic

nucleus of trigeminal n.

Main sensory nucleus of trigeminal n.

Spinal nucleus of

trigeminal n.

General somatic sensory nucleiNucleus Site Cranial

n.Function

Mesencephalic nucleus of trigeminal n.

Midbrain Ⅴ Proprioception of head

Main sensory nucleus of trigeminal n.

Pons Ⅴ Tactile sensation of face

Spinal nucleus of trigeminal n.

Medulla upto 2nd cx. seg.

Ⅴ Pain and temperature sense of face

Special somatic afferent nuclei Cochlear nuclei 2

- Dorsal

- Ventral Vestibular nuclei 4

- Superior

- Inferior

- Medial

- Lateral

Special somatic afferent nuclei

Nucleus Site Cranial n. Function

Cochlear nuclei

Pons and medulla

Ⅷ Sense of hearing

Vestibular nuclei

Pons and medulla

Ⅷ Sense of equilibrium

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