MEDULLA OBLONGATA

Dorsal nucleus of Vagus(motor nucleus )-Is a long vertical column .Upper end lies deep to the vagal triangle in the floor

of the fourth ventricle.Traced downwards in the closed part, it occupies a

position in the lateral part of central grey matter dorsal to the hypoglossal nucleus.

Main source of parasympathetic fibres of vagus nerve.

The upper part of the nucleus lies in the reticular formation,-ventrolateral to the dorsal nucleus of vagus.Traced downwards lies dorsomedial.The rostral portion of the nucleus-Gustatory –VII,IX, AND X cranial nerves nuclei terminate in it.The caudal portion-receives-IX AND X cranial nerve nuclei.

Nucleus of tractus solitarius:

Nucleus ambiguus:Elongated column of typical motor neuron.Is so named because it is not clearly defined

in sections of the medulla.Occupies a position dorsal to the inferior

olivary nucleus,ventromedial to the nucleus of spinal tract of Vth nerve.

Hypoglossal nucleus:Elongated motor cells,Extends in the paramedian plane ,The medial longitudenal bundle lies ventral to it.The upper part lies deep to hypoglossal triangle,In the closed part,lies in the grey matter ventral to the

central canalThe fibres course ventrally,emerge on ventral aspect a

series of 12 rootlets in the sulcus between pyramid and olive

Inferior Olivary nucleus :1.receive input from the wide areas of

cerebral cortex, red nucleus and from the periaqueductal

region.Medial accessory Dorsal accessory olivary nucleus receive

input from the spinal cord ,red nucleus,

TRANSVERSE SECTION AT THE LEVEL OF PYRIMIDAL DECUSSATION

TRANSVERSE SECTION AT SENSORY DECUSSATION

TRANSEVERSE SECTION AT THE ,LEVEL OF SENSORY DECUSSATION

The section passes through the

middle of medulla:

The central grey matter

contains-

1.Hypoglossal nucleus

2.Dorsal nucleus of vagus

3.Nucleus of tractus solitarius.

TRANSVERSE SECTION AT THE LEVEL OF SENSORY DECUSSATION

The nucleus gracilis and nucleus cuneatus become more pronounced and are separated from the central grey matter.

The fibres of fasciculus gracilis and fasciculus cuneatus occupy the broad posterior white column and terminate in the nucleus

Sensory Decussation of the internal arcuate fibres ;

In this decussation the gracile fibres are medial to that of cuneate fibres

The internal arcuate fibres cut off the spinal nucleus and tract of trigeminal nerve from the central grey matter.

Immediately dorsolateral to the cuneate nucleus lies the accessory cuneate nucleus-receive the more lateral fibres (derived from the cervical segments) of the fasciculus cuneatus –posterior external arcuate fibres conveying proprioceptive impulses to the cerebellum of the same side through inferior cerebellar peduncle.

The separated spinal nucleus and tract of trigeminal nerve lies ventrolateral to the cuneate nucleus.

The lower part of the olivary nucleus is seen.The pyramids lie on either side of the anterior median fissure.Medial longitudinal bundle lies posterior to the medial

leminiscus.Spinocerebellar and lateral spinothalamic tracts lie in the

anterolateral area of lateral white column.Lateral and anterior spinothalamic tracts-spinal leminiscus.

TRANSVERSE SECTION AT THE LEVEL OF OLIVE

1. AT THE LEVEL OF OLIVE

The central grey matter spread over the floor of the fourth ventricle from medial to lateral-1.hypoglossal2.nucleus intercalatus 3.dorsal nucleus of vagus 4.vestibular nuclei.(inferior and medial).

The nucleus of tractus solitarius lies ventral to vestibular nuclei.

The nucleus ambiguus lies deep within the reticular formation and give origion to the motor fibres of IX,X, AND XIth cranial nerves.

On either side of the midline from dorsal to ventral lie-1.medial longitudinal fasciculus2.tecto spinal tract,3.medial leminiscus4.pyrimidal tract.The arcuate nuclei-inferiorly displaced pontine nuclei are

situated on the anteromedial aspect of the pyramids.Laterally from dorsal to ventral-inferior cerebellar peduncle

and inferior olivary nucleus. Close to it lies medial and dorsal accessory olivary nucleus.

BLOOD SUPPLYThe medulla is

supplied by-Two vertebral

arteries.Anterior and

Posterior spinal arteries.

Anterior and Posterior inferior cerebellar arteries.

Basilar artery.

VASCULAR DISORDERSAre Lateral Medullary syndrome(syndrome of

wallenberg).

Medial medullary syndrome(Dejerine’s anterior bulbar syndrome)

Lateral medullary syndrome-

Due to the Thrombosis of Posterior inferior cerebellar artery,

Which supplies the dorsolateral part of the medulla and inferior surface of the cerebellum.

Medial medullary syndrome:

The paramedian region of medulla is supplied by the branches of vertebral artery.

VASCULAR DISORDERSLateral medullary

syndrome:1.controlateral loss

of pain and temperature sensation-spinothalamic tract.

2.Ipsilateral loss of pain and temperature over the face-spinal nucleus and spinal tract of trigeminal nerve.

3.Ipsilateral paralysis of muscles of palate pharynx and larynx-nucleus ambiguus.

4.Ipsilateral ataxia-inferior cerebellar peduncle and cerebellum

Giddiness-vestibular nuclei.

Horner’s syndrome-descending sympathetic pathway of reticular formation of medulla.

HORNER’S SYNDROME

Occurs due the interruption of sympathetic pathway of head and neck.

Common sites of lesion are-brain stem,cervical part of spinalcord or stellate ganglion

HORNER’S SYNDROME contd…

CHARACTERISTIC FEATURES:Miosis-Due to the paralysis of dilator pupillae,

and unopposed action of sphincter pupillae.Partial ptosis-Due to the paralysis of smooth

muscle fibres (muller’s) of levator palpebrae superioris.

Anhidrosis-(loss of sweating)-Due to involvement of sudomotor fibres.

Enophthalmos-(sunken eyeball)-Due to paralysis of ORBITALIS muscle.

Flushing of the face-Due to the involvement of vasoconstrictors fibres of face.

Medial medullary syndrome

Controlateral hemiplegia due to damage of pyramid.

Ipsilateral paralysis and atrophy of half of the tongue- hypoglossal nerve.

Controlateral loss of position and vibration sense-medial lemniscus.

Transverse section at the level of pyrimidal decussation(picture and label the parts with brief explanation).

Transverse section at the level of sensory decussation.

Lateral medullary syndrome.