NervousBrain region

Medulla oblongata

Medulla oblongata (myelencephalon)

Also known as: medulla, bulb, myelencephalon

The lowest part of the brainstem (≈3 cm), continuous with the spinal cord at the foramen magnum; it contains the pyramidal and sensory decussations, the nuclei of CN IX–XII and the vital centres for breathing, heart rate and blood pressure.

Show on body map Brain — Lateral View Brain — Midsagittal Section

Overview

Length≈3 cm

Corticospinal fibres crossing at the decussation≈85–90%

Cranial nerve nucleiIX, X, XI (cranial), XII; parts of V and VIII

The medulla extends from the pontomedullary junction to just above the first cervical rootlets at the foramen magnum. Its lower closed part contains the central canal; its upper open part forms the lower half of the floor of the fourth ventricle. Its surface landmarks are:
• Ventral surface: the pyramids (corticospinal fibres), which cross in the pyramidal decussation (≈85–90% of fibres) at the cervicomedullary junction. Lateral to each pyramid is the olive, overlying the inferior olivary nucleus, which sends climbing fibres to the cerebellum.
• Rootlet sulci: CN XII emerges between the pyramid and olive (preolivary sulcus); CN IX, X and the cranial root of XI emerge behind the olive (retro-olivary sulcus).
• Dorsal surface: the gracile and cuneate tubercles over the dorsal column nuclei. Their axons cross as the internal arcuate fibres (sensory decussation) to form the medial lemniscus.
• Inferior cerebellar peduncles: carry spinal and olivary input to the cerebellum.

The medulla is often called the "vital" part of the brain. The nucleus of the solitary tract (NTS) receives baroreceptor, chemoreceptor, pulmonary stretch and taste afferents. The rostral ventrolateral medulla drives sympathetic vasomotor tone, while the dorsal motor nucleus of the vagus and the nucleus ambiguus provide cardioinhibitory vagal output. The dorsal and ventral respiratory groups, including the pre-Bötzinger complex that generates the inspiratory rhythm, set breathing, and central chemoreceptors near its ventral surface respond to CSF H⁺ (from CO₂). The medulla also coordinates swallowing, coughing, sneezing, gagging and vomiting. The area postrema in the floor of the fourth ventricle lacks a blood–brain barrier and acts as the chemoreceptor trigger zone for emesis.

Location: Lowest brainstem, from the pons to the foramen magnum; anterior to the cerebellum and fourth ventricle; ventral surface on the basilar part of the occipital bone.

Parts & subdivisions

Pyramids and pyramidal decussation
Corticospinal tracts; ≈85–90% cross to form the lateral corticospinal tract; the rest descend uncrossed as the anterior corticospinal tract.
Olive (inferior olivary nucleus)
Source of climbing fibres to the contralateral cerebellum (motor learning, timing).
Gracile and cuneate nuclei
Second-order neurons of the dorsal column pathway; axons decussate as internal arcuate fibres → medial lemniscus.
Nucleus of the solitary tract
Visceral sensory hub: taste (VII, IX, X), baroreceptors and chemoreceptors (IX, X), gut and lung afferents.
Nucleus ambiguus
Branchial motor to the pharynx, larynx and soft palate (IX, X) plus cardioinhibitory vagal neurons.
Dorsal motor nucleus of the vagus
Parasympathetic preganglionic neurons to the thoracic and abdominal viscera.
Hypoglossal nucleus
Under the hypoglossal trigone; motor to the tongue.
Respiratory centres
Dorsal respiratory group (NTS; inspiration), ventral respiratory group with the pre-Bötzinger complex (rhythm generation) and expiratory neurons.
Area postrema
Circumventricular organ at the caudal end of the fourth ventricle; chemoreceptor trigger zone for vomiting (D2, 5-HT3, NK1 receptors).

Anatomy

Arterial supply: Vertebral arteries, anterior spinal artery (medial medulla), posterior inferior cerebellar artery (lateral medulla), posterior spinal arteries.

Function

Cardiovascular control: heart rate, contractility and vasomotor tone (baroreceptor reflex)
Generation of the respiratory rhythm and central chemoreception
Swallowing, coughing, sneezing, gagging and vomiting reflexes
Relay of fine touch and proprioception (dorsal column nuclei)
Origin of cranial nerves IX, X, XI (cranial part) and XII
Conduit for all ascending and descending tracts

Clinical significance

Lateral medullary (Wallenberg) syndrome

Occlusion of the vertebral artery or PICA causes:
• ipsilateral loss of facial pain and temperature (spinal trigeminal nucleus and tract);
• contralateral loss of body pain and temperature (spinothalamic tract);
• ipsilateral Horner syndrome (descending sympathetic fibres);
• ipsilateral ataxia (inferior cerebellar peduncle);
• vertigo, nausea and nystagmus (vestibular nuclei);
• dysphagia, hoarseness and a reduced gag reflex (nucleus ambiguus);
• hiccups.
Motor function is spared.

Tonsillar herniation (coning)

Raised posterior-fossa pressure, or an LP performed in the presence of a mass, forces the cerebellar tonsils into the foramen magnum and compresses the medulla. The result is neck stiffness, then apnoea and cardiovascular collapse.

Bulbar vs pseudobulbar palsy

• Bulbar palsy (LMN lesion of IX, X, XII, e.g. motor neuron disease or Guillain–Barré): wasted, fasciculating tongue, nasal speech and absent gag reflex.
• Pseudobulbar palsy (bilateral UMN corticobulbar lesions, e.g. bilateral strokes or MS): spastic tongue, brisk jaw jerk, spastic dysarthria and emotional lability.

Test yourself

After a stroke, a patient has drooping of the left lower face but can wrinkle the forehead normally on both sides. What does this pattern indicate?

Left facial nerve lesion at the stylomastoid foramen
Bell palsy
Right upper motor neuron (corticobulbar) lesion
Left facial nucleus lesion in the pons

Answer: Right upper motor neuron (corticobulbar) lesion

The part of the facial nucleus that supplies the forehead receives corticobulbar input from both hemispheres, so a unilateral UMN lesion spares the upper face. The weakness is contralateral to the lesion. Any LMN facial lesion paralyses the entire half of the face, forehead included.

Fibres of the dorsal column–medial lemniscus pathway decussate in the:

Anterior white commissure of the spinal cord
Medulla (internal arcuate fibres)
Pons
Midbrain

Answer: Medulla (internal arcuate fibres)

First-order fibres ascend ipsilaterally to the gracile and cuneate nuclei of the medulla. Second-order axons cross as internal arcuate fibres to form the medial lemniscus. Spinothalamic fibres, by contrast, cross in the anterior white commissure of the cord.