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Definition

  • Brain stem – the “stem” of the brain, from the medulla to the diencephalon, excluding the cerebellum
  • Connects nerves of�the peripheral �nervous system to�the brain
  • Important for basic�functions of life

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The brain stem �

Consists of

  • Midbrain.
  • Pons .
  • Medulla oblongata

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The Brainstem: Medulla oblongata

Most inferior portion, functions as a conduction pathway (descending motor neuron pathways decussate here)

Reflex centers for:

regulating heart rate

blood vessel diameter

coughing, sneezing

breathing

swallowing

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Medulla oblongata

Ventral surface

  • Pyramid contain pyramidal tract (corticospinal tract)
  • Decussation of pyramid: formed 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

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Medulla oblongata

Dorsal surface

  • Lower portion
    • Gracile tubercle produced by underlying gracile nucleus
    • Cuneate tuberclemarks the site of cuneate nucleus
    • Inferior cerebellar peduncle
    • Obex
  • Upper portion: forms the lower half of rhomboid fossa

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Boundaries

  • Inferolateral: gracile and cuneate tubercles, inferior cerebellar peduncle
  • Superolateral: superior cerebellar peduncle
  • Lateral recess

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Features

  • Median sulcus
  • Sulcus limitans
  • Vestibular area overlies vestibular nuclei
  • Acoustic tubercle overlying dorsal cochlear nucleus
  • Medial eminence
  • Striae medullares

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  • Facial colliculus overlies nucleus of abducent n. and genu of facial nerve
  • Hypoglossal triangle : verlying hypoglossal nucleus
  • Vagal triangle overlies dorsal nucleus of vagus nerve
  • Funiculus separans
  • Area postrema
  • Locus ceruleus

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Position

  • Situated ventral to cerebellum, and dorsal to pons and cranial half of medulla

​

Central canal →fourth ventricle →mesencephalic aqueduct→third ventricle

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Roof

  • Anterior part: formed by superior 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 fourth ventricle

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INTERNAL STRUCTURE

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Medulla oblongata�

Lower part (closed part)

  • Two decussations–
    • Decussations of medial lemniscus
    • Decussations of pyramid

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T.S AT LEVEL OF PYRAMIDAL DECUSSATION.

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Descending tracts

  • Corticospinal tract
  • Rubrospinal tract
  • Tectospinal tract
  • Vestibulospinal tract
  • Reticulospinal tract

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T.S AT LEVEL OF SENSORY DECUSSATION.

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SENSORY DECUSSATION

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Medial lemniscus

�

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T.S AT MID OLIVE

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White matter

Ascending tracts

  • Medial lemniscus
  • Spinal lemniscus
  • Trigeminal lemniscus
  • Lateral lemniscus

​

​

​

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Spinal lemniscus

​

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Trigeminal lemniscus

​

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Medial medullary syndrome

  • Hypoglossal nerve-paralysis of tongue muscle (ipsilateral lower motor neuron).
  • Contralateral upper motor neuron paralysis due cortical –spinal tract.
  • Medial lemniscus- contralateral loss of discriminative sense of body.

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Wallenberg’s Syndrome

Thrombosis of PICA

Lateral

medullary

syndrome

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Wallenberg’s Syndrome(lateral medullary syndrome)

  • Structures involved:
    • Inf. Cerebellar peduncle (ipsilateral ataxia)
    • Spinal lemniscus - (contra-lateral loss pain & temperature from body)
    • Spinal nucleus & it’s tract of 5th nerve (ipsilateral loss of pain & temperature from face & forehead)
    • N. ambiguus (dysphagia & dysphonia) due to paralysis of muscles of pharynx & larynx& soft palate.
    • Vestibular n. (nystagmus and postural instability)

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Pons

Ventral 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

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Pons

Dorsal surface

  • Superior cerebellar peduncle
  • Superior medullary velum
  • Trochlear nerve 滑车神经

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The Brainstem: Pons

Superior to Medulla oblongata.

Contains more ascending and descending pathways.

Relays information from cerebrum to cerebellum.

Also includes sleep and respiratory centers.

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Pons �

  • Tegmentum of pons directed upward continuation of medulla oblongata
  • Basilar part

contain both longitudinal and transverse fibers intermixed with pontine nuclei

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CLINICAL ANATOMY

  • Millard –gubler syndrome.
  • 1)ipsilateral medial squint due to involvement of abducent nerve.
  • 2)ipsilateral facial palsy due to involvement of facial nerve fibres.
  • 3)contralateral hemiplegia due to involvement of corticospinal tract.

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Midbrain

  • A.K.A. mesencephalon
  • Has 2 Primary Parts
    • Tectum – the dorsal part of the midbrain
      • Superior Colliculi
      • Inferior Colliculi
    • Tegmentum – ventral part of the midbrain
      • Reticular Formation
      • Periaqueductal Gray Matter
      • Red Nucleus
      • Substantia Nigra

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Pontocerebellar angle syndrome

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Midbrain 中脑

Ventral surface

  • Crus cerebri
  • Interpeduncular fossa oculomotor nerves emerge from medial of crus cerebri
  • Posterior perforated substance

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Midbrain中脑

Dorsal surface

  • Superior colliculus 上丘constitute centers for visual reflexes
  • Inferior colliculus 下丘associated with auditory pathway
  • Brachium of superior colliculi 上丘臂
  • Brachium of inferior colliculi 下丘臂

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The Brainstem: Midbrain

Small section superior to the pons.

Part of the auditory pathways and visual reflexes

Also involved in regulating muscle tone/activity and coordination

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Midbrain

Slide 7.39

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

  • Mostly composed of tracts of nerve fibers
    • Reflex centers for vision and hearing
    • Cerebral aquaduct – 3rd-4th ventricles

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Midbrain

  • Rectum of midbrain中脑顶盖: includes superior and inferior colliculi
  • Cerebral peduncle 大脑脚
    • Tegmentum 被盖:

contain ascending tracts, central gray matter, recticular formation and so on

    • Substentia nigra 黑质
    • Crus cerebri 大脑脚底:
      • Pyramidal tract锥体束－ middle three-fifths of the crus:
      • Frontopontine tract额桥束 medial one-fifth:
      • pariatotempopontine tract 顶颞桥束lateral one-fifth

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The Brain: Reticular formation

2 types of nuclei:�Cranial nerves III-XII�and�Reticular Formation nuclei which are scattered throughout brainstem

Many pathways from RF project directly to cerebrum to modulate activity

Habituation (repetitive stimuli)

Reticular Activating System

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Tela choroidea and choroid plexus�脉络丛和脉络组织

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Internal structures �

Gray matter

  • Cranial nerve nuclei
  • Relay nuclei

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General somatic motor nuclei 一般躯体运动核

  • Nucleus of oculomotor n.动眼神经核
  • Nucleus of trochlear n. 滑车神经核
  • Nucleus of abducent n. 展神经核
  • Nucleus of hypoglossal n.舌下神经核

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Nucleus

Site

Cranial n.

Function

Nucleus of

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Oculomotor n.

Midbrain

Ⅲ

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

Nucleus of

trochlear 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

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Special visceral motor nuclei 特殊内脏运动核

  • Motor nucleus of trigeminal n. 三叉神经运动核
  • Nucleus of facial n. 面神经核
  • Nucleus ambiguus 疑核
  • Accessory nucleus 副神经核

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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

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General visceral motor nuclei 一般内脏运动核

  • Accessory oculomotor nucleus 动眼神经副核
  • Superior salivatory nucleus 上泌涎核
  • Inferior salivertory nucleus 下泌涎核
  • Dorsal nucleus of vagus n. 迷走神经背核

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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

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Visceral sensory nuclei ( general and special )

  • Nucleus of solitary tract 孤束核

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Visceral sensory nuclei ( general and special )

Nucleus

Site

Cranial n.

Function

Nucleus of solitary tract

Medulla

Ⅶ,Ⅸ,Ⅹ

Taste and visceral sensation

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General somatic sensory nuclei

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  • Mesencephalic nucleus of trigeminal n. 三叉神经中脑核
  • Pontine nucleus of trigeminal n. 三叉神经脑桥核
  • Spinal nucleus of trigeminal n. 三叉神经脊束核

​

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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

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Special somatic sensory nuclei

  • Cochlear nuclei 蜗神经核

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  • Vestibular nuclei 前庭神经核

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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

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Relay nuclei

  • Gracile nucleus
  • Cuneate nucleus
  • Inferior olivary nucleus
  • Superior olivery nucleus
  • Pontine nucleus
  • Nucleus of inferior colliculus
  • Gray matter layers of superior colliculus
  • Red nucleus
  • Substantia nigra
  • Pretectal area

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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

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Lateral lemniscus

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Reticular formation of brain stem

  • Ascending reticular activating system (ARAS) 上行网状激动系统
  • Motor central and vital centres
    • Reticulospinal tract
    • Cardiovascular center and respiratory center
  • Serotonergic rapheal nuclei

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The characters of internal structure of brain stem

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Medulla oblongata�

Lower part (closed part)

  • Two decussations–
    • Decussations of medial lemniscus
    • Decussations of pyramid

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Midbrain

  • Rectum of midbrain中脑顶盖: includes superior and inferior colliculi
  • Cerebral peduncle 大脑脚
    • Tegmentum 被盖:

contain ascending tracts, central gray matter, recticular formation and so on

    • Substentia nigra 黑质
    • Crus cerebri 大脑脚底:
      • Pyramidal tract锥体束－ middle three-fifths of the crus:
      • Frontopontine tract额桥束 medial one-fifth:
      • pariatotempopontine tract 顶颞桥束lateral one-fifth

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