CLOSED MEDULLA (MOTOR DECUSSATION) The medulla is traversed by the central canal. It retains some of the features of the spinal cord.

HORNS The ventral horn becomes much attenuated. The dorsal horn is replaced by The caudal part of the Trigeminal Sensory Nucleus (Nucleus of the Spinal Tract of the Trigeminal Nerve). It is a large nucleus that lies medial to the spinal tract of the trigeminal nerve.

The TRIGEMINAL SENSORY NUCLEUS It is the brain stem continuation of the Substantia Gelatinosa of the dorsal horn of the spinal cord. It extends through the whole length of the brain stem. It receives pain and temperature from the face, forehead and the mucous membrane of the mouth and nose.

SPINAL TRACT OF THE TRIGEMINAL NERVE It lies superficial to its nucleus between the cuneate nucleus and the spino-cerebellar tracts. It is formed of descending fibers that terminate in the trigeminal nucleus caudal to the level of the pons (where the trigeminal nerve is attached).

PYRAMIDAL DECUSSATION (MOTOR DECUSSATION) It is the distinguishing feature of this level. 75-90% of the pyramidal fibers ( cortico spinal) cross to the opposite side and descend in the lateral white column of the spinal cord as the Lateral Corticospinal tract.

LATERAL & ANTERIOR WHITE COLUMNS Spinocerebellar and Spino thalamic tracts can be identified.

GRACILE & CUNEATE NUCLEI A small part of these nuclei lie deeper to their corresponding Gracile and Cuneate tracts.

MID MEDULLA (SENSORY DECUSSATION) It is still traversed by the central canal.

THE GRACILE & CUNEATE NUCLEI They are Large in size and located deeper to their corresponding tracts. Their axons will form the internal arcuate fibers. They cross the median plane forming with the opposite side the Sensory Decussation.

MEDIAL LEMINISCUS It is a distinct tract which is formed from the crossed sensory fibers. It ascends through the rostral medulla, pons and midbrain. It lies adjacent to the middle line and ventral to the central canal. It terminates in the thalamus.

PYRAMIDS Are prominent above their decussation. They are present in the antero medial part of the section.

ARCUATE NUCLEI They lie antero lateral to the pyramids. Their axons form the External Arcuate Fibers. The nuclei can be considered as the inferior extension of the pontine nuclei. Their fibers reach the cerebellum through the inferior cerebellar peduncle.

RETICULAR FORMATION It is in the form of a diffuse mixture of nerve fibers and small groups of nerve cells which are located posterolateral to the pyramids and ventral to the spinal tract and nucleus of the trigeminal nerve.

ACESSORY CUNATE NUCLEUS It is lateral to the cuneate nucleus. It receives unconscious fibers from the cervical region. The cell axons reach the cerebellum through the inferior cerebellar peduncle.

THE OPEN (ROSTRAL) MEDULLA The posterior surface of the medulla here forms the lower part of the floor of the 4th ventricle.

MEDIAL LEMINISCUS It is dorsal to the medial aspect of the pyramids on each side of the midline.

INFERIOR OLIVARY NUCLEUS It is a convoluted mass of gray matter with its hilum directed medially. It lies postero lateral to the pyramid and lateral to the medial leminiscus. It receives fibers from (motor and sensory cortices of the cerebral cortex, red nucleus of the mid brain and the corpus striatum). It is concerned with the control of movement.

INFERIOR CEREBELLAR PEDUNCLE (RESTIFORM BODY) It lies in the dorso lateral part of the medulla. It forms the connection between the medulla and cerebellum. Among the fibers it carries are the olivocerebellar, vestibulocerebellar and dorsal spinocerebellar from the limbs.

COCHLEAR NUCLEI Dorsal and Ventral Nuclei: They lie dorsal and lateral to the inferior cerebellar peduncle. They receive afferents from the cochlear nerve.

NUCLEI BENEATH THE FLOOR OF THE 4TH VENTRICLE Hypoglossal nucleus : It forms a longtudinal column just lateral to the midline and immediately beneath the floor of the fourth ventricle.

NUCLEI BENEATH THE FLOOR OF THE 4TH VENTRICLE Dorsal motor nucleus of the vagus: It is lateral to the hypoglossal nucleus . It contains the preganglionic parasympathetic fibers that pass through the vagus nerve as far as the distal one third of the transverse colon.

NUCLEI BENEATH THE FLOOR OF THE 4TH VENTRICLE Vestibular nuclei (Complex): They lie in the lateral part of the floor of the 4th ventricle and receive afferents from the vestibular nerve. They consist of medial, lateral, inferior and superior nuclei. The inferior vestibular nucleus is lateral to the inferior fovea.

NUCLEUS AMBIGUUS It lies dorsal to the inferior olivary nucleus. It sends motor fibers to the constrictor muscles of the pharynx and intrinsic muscles of the larynx through the glossopharyngeal, vagus and cranial part of acessory nerve.

MEDIAL LONGTUDINAL BUNDLE It lies ventromedial to the hypoglossal nucleus, dorsal to the medial lemniscus and close to the midline. It can be identified in the pons, midbrain and upper levels of the spinal cord. It receives afferents from the vestibular nerve.

MEDIAL LONGTUDINAL BUNDLE It consists of short ascending and descending fibers that connect the vestibular and cochlear nuclei with the cranial nuclei (111, 1v and v1) which supplies the extra ocular muscles. It serves the coordination of head and eye movements in response to vestibulo- cochlear stimuli.

SPINAL LEMINISCUS It includes the Spinothalamic (lateral &anterior) and the Trigeminothalamic tracts which are very close to one another. It is deeply placed lateral to the medial leminiscus and dorsal to the inferior olivary nucleus.

AREA POSTREMA It is the most caudal point of the floor of the 4th ventricle. It is the site of action of the centrally acting emetics. Because at this site, the blood brain barrier is lost for certain chemicals.

NUCLEUS SOLITARIS It is formed of medial part (well formed in the medulla) and lateral part (well formed in the pons) . The solitary tract lies in between. The lateral nucleus receives taste fibers from the back of the tongue. The medial nucleus receives (GVA) fibers.

RETICULAR FORMATION It consists of a diffuse mixture of nerve fibers and small groups of nerve cells.it is deeply placed posterior to the olivary nucleus. At this level of the medulla, it represents a small part of this system.

DESCENDINGTRACTS The Pyramids at the anterior part. Tectospinal tract dorsal to the medial lemniscus.

ASCENDING TRACTS Medial leminiscus. Spinal leminiscus. Trigemino thalamic tract. Ventral spinocerebellar tract.

MEDULLARY SYNDROMES

Medial Medullary Syndrome It is due to thrombosis of branches of the anterior spinal artery. It is manifested by : (1) Contralateral hemiplegia of the flaccid type (due to involvement of the pyramidal fibers only).

Medial Medullary Syndrome (2) Contralateral loss of proprioceptive sensation and fine touch (affection of medial lemniscus). (3) Ipsilateral lower motor lesion of the hypoglossal nerve (affection of hypoglossal nucleus).

Lateral Medullary (Wallenberg) Syndrome It is due to thrombosis of the inferior cerebellar artery. It is Manifested by (1) Ipsilateral cerebellar ataxia ( affection of cerebellum and spinocerebellar tracts).

Lateral Medullary (Wallenberg) Syndrome 2) loss of pain and temperature of the ipsilateral half of the face ( spinal tract and nucleus of V nerve). (3) loss of pain and temperature from the contralateral half of the body (spinal lemniscus).

Lateral Medullary (Wallenberg) Syndrome (4) Ipsilateral paralysis of the muscles of the palate, pharynx and larynx (nucleus ambiguus ). (5) Ipsilateral loss of taste from the posterior third of the tongue (nucleus solitaris).

Lateral Medullary (Wallenberg) Syndrome (6) Ipsilateral Horner’s syndrome (ptosis, myosis, anhydrosis and enophthalmos ) due to affection of descending autonomic fibers.