Medulla Oblongata

What part of the brain does medulla oblongata come from?

Mylencephalon and the fourth ventricle

Features of the medulla oblongata

Medulla provides attachment to last four cranial nerves

The junction between the medulla and spinal cord is marked by an imaginary line which passes just above the attachments of first pair of cervical spinal nerves

Ponto-medullary junction is marked by the attachment of 6th, 7th and 8th cranial nerves from medial to lateral side

The lower half is closed and contains the central canal below and above opens into the fourth ventricle

Relations of medulla oblongata

Ventrally rests on the basilar part of occipital bone, but separated from the bone by the meninges and basilar venous plexus

Dorsally separated from the cerebellum by the cavity of the fourth ventricle

External features

Anterior median fissure

• foramen caecum

• decussation of pyramidal fibres

• anterior external arcuate fibres

Posterior median sulcus

Anterolateral sulcus

• gives attachment to the hypoglossal rootlets

Posterolateral sulcus

• gives attachment to vagus, glossopharyngeal and accessory nerve

Anterior area

Pyramid- produces by corticospinal, corticopontine and corticobulbar (end in motor nuclei of cranial nerves) tracts

Arcuate nuclei- cover ventral surface of pyramid

Lateral area

Olive- produced by underlying inferior olivary nucleus

Occupied by ventral and dorsal spinocerebellar, lateral spinothalamic, spino-olivary and olivo-spinal

Posterior area

• fasciculus gracilis and gracile tubercle

• fasciculus cuneatus and cuneate tubercle

• tuberculum cinereum (produced by underlying spinal nucleus and tract of trigeminal

Internal structure of the medulla oblongata

1. At the level of the pyramidal decussation (motor)

2. At the level of the sensory decussation

3. At the level of inferior olivary nucleus

Changes that take place

• Appearance cranial nerve nuclei

• Appearance of ventricles of the brain

• Grey matter loses shape

• Appearance of reticular formation

Transverse -section at the level of the pyramidal decussation

• Nucleus gracilis and cuneatus appear as narrow strips within the fascicules from the posterior aspect of central grey matter

• Anterior horn forms the spinal nucleus of accessory lateral (continuous with hypoglossal nuclei) and supraspinal nucleus medially (in line with nucleus ambiguus

• Spinal tract of trigeminal nerve conveys pain and temperature from face and forehead (in line with chief sensory nucleus)

Transverse section of medulla oblongata at level of sensory decussation

• Nucleus cuneatus and gracilis become more pronounced and fasciculus fibres terminate here

• Internal arcuate fibres from these nuclei courses and contralateral and become medial lemniscus

• Accessory cuneate nucleus receives more lateral fibres (convey proprioceptive fibres from upper limb to cerebellum through inferior cerebellar peduncle)

• Inferior olivary nucleus begins to appear

• Pyramids on either side of the median fissure

• Nucleus of tractus solitarius (receives taste fibres from VII, IX and X), hypoglossal nucleus (supplies muscles of tongue)and dorsal nucleus of vagus (supply heart, smooth muscles)

• Medial longitudinal bundle

• Lateral and anterior spinothalamic tract form spinal lemniscus

Transverse section at the level of the olive

Inferior olivary nuclear complex present

Consists of:

• principal inferior olivary nucleus

• Medial accessory olivary nucleus

• Dorsal accessory olivary nucleus

• Afferents from cerebral cortex, red nucleus, basal nuclei

• Efferents from olivo-cerebellar and paraolivocerbellar (climbing fibres)

Consists of hypoglossal nucleus, nucleus intercalatus, dorsal nucleus of vagus, nucleus solitarius, vestibular nuclei and nucleus ambiguus

Medial longitudinal fasciculus

Tecto-spinal tract

Medial lemniscus

Pyramidal tract

Arcuate nuclei (displaced pontine nuclei)

Blood supply

• Anterior and posterior spinal arteries from vertebral artery

• Posterior inferior cerebellar arteries from vertebral artery

• Basilar artery and its branch anterior inferior cerebellar artery

Lateral medullary syndrome

Vertigo – sensation of whirling and loss of balance

Nystagmus – rapid involuntary movements of the eye

Ataxia – loss of full control of bodily movements

Dysmetria – lack of coordination movement due lack of ability to perceive distance

Dysdiadokokinesis – inability to perform rapid alternate movements

Palatal myoclonus – rapid spasm of palatal muscles

Dysphagia – difficulty in swallowing

• Gag reflex or pharyngeal reflex

Miosis – excessive constriction of pupil

Anhydrosis – failure of sweat glands to secrete

Medial medullary syndrome