Neuroanatomy

1. Anatomy of the medulla oblongata
Dr. Mohammed Mahmoud Mosaed

2. Gross Appearance of the Medulla Oblongata
• The medulla oblongata connects the pons superiorly with
the spinal cord inferiorly.
• The junction of the medulla and spinal cord is at the
origin of the roots of the first cervical spinal nerve (at the
level of the foramen magnum).
• The medulla is conical in shape.
• It has broad upper extremity.
• The central canal of the spinal cord continues upward into
the lower half of the medulla (closed part); in the upper
half of the medulla, it expands as the cavity of the fourth
ventricle (open part)
• Blood supply of the medulla
• The anterior spinal artery and medullary branches of the
vertebral artery
• The posterior inferior cerebellar artery

4. The anterior surface of the medulla
• On the anterior surface of the medulla is:
The anterior median fissure, which is continuous inferiorly
with the anterior median fissure of the spinal cord.
The pyramid which is a swelling on each side of the median
fissure. The pyramids are composed of bundles of nerve
fibers, called corticospinal fibers. In the lower part of the
medulla the majority of the fibers descending to the
opposite side, forming the decussation of the pyramids.
The anterior external arcuate fibers are a few nerve fibers
that emerge from the anterior median fissure above the
decussation and pass laterally over the surface of the
medulla oblongata to enter the cerebellum.

5. The olives which lies posterolateral to the pyramids,
the olives are oval elevations produced by the
underlying inferior olivary nuclei.
The groove between the pyramid and the olive is the
anterolateral fissure from which emerge the rootlets of
the hypoglossal nerve.
Posterior to the olives are the inferior cerebellar
peduncles, which connect the medulla to the
cerebellum. In the groove between the olive and the
inferior cerebellar peduncle (posterolateral fissure)
emerge the roots of the glossopharyngeal and vagus
nerves and the cranial roots of the accessory nerve

7. Posterior Surface
• The posterior surface of the superior
half of the medulla oblongata (open
medulla) forms the lower part of the
floor of the fourth ventricle.
• The posterior surface of the inferior
half of the medulla (closed medulla)
is continuous with the posterior
aspect of the spinal cord

8. Lower part of posterior surface of the medulla
• It possesses a posterior median sulcus.
On each side of the median sulcus, there
is an elongated swelling, the gracile
tubercle, produced by the underlying
gracile nucleus. Lateral to the gracile
tubercle is a similar swelling, the cuneate
tubercle, produced by the underlying
cuneate nucleus.

9. Upper part of posterior surface of the medulla
• Forms the lower part of floor of 4th ventricle.
• It separates from the pontine part by the stria
medullares
• On either side of the median slcus, an elevated
inverted V-shaped area; Hypoglossal triangle or
trigone which overlies hypoglossal nucleus
• Lateral to the hypoglossal trigon is the vagal triangle
depressed upright triangle overlies dorsal vagal
nucleus
• The slcus limitants lies lateral to the vagal triangle and
separate it from the vestibular area which overlies
vestibular nuclei

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12. Internal structures of the medulla
• As in the spinal cord, the medulla oblongata
consists of white matter and gray matter
• The internal structure of the medulla oblongata is
considered at four levels:
• (1) Level of decussation of pyramids
• (2) Level of decussation of lemnisci
• (3) Level of the olives
• (4) Level just inferior to the pons.

13. Level of decussation of pyramids
• A transverse section through the inferior half of the
medulla oblongata passes through the decussation of the
pyramids in which the following structures are seen
• Nuclei
• Cranial nerve nuclei: Spinal nucleus of trigeminal nerve,
Accessory nucleus
• Nucleus gracilis,
• Nucleus cuneatus ,
• Motor tracts
• Decussation of corticospinal tracts, pyramids
• Sensory tracts
• Spinal tract of trigeminal nerve, posterior spinocerebellar tract,
lateral spinothalamic tract, anterior spinocerebellar tract

16. Decussation of the pyramids
• The decussation of the pyramids is the great motor
decussation.
• In the superior part of the medulla, the corticospinal
fibers occupy and form the pyramid, but inferiorly,
about three-fourths of the fibers cross the median
plane and continue down the spinal cord in the
lateral white column as the lateral corticospinal tract.
• As these fibers cross the midline, they serve the
continuity between the anterior column of the gray
matter of the spinal cord and the gray matter that
surrounds the central canal.

18. Gracile nucleus
• This nucleus lies close to the posterior median sulcus. This
nucleus receive the termination of the gracile tract, the axons of
the nucleus arch around the central canal forming the internal
arcuate fibers. the gracil tract carries proprioceptive and fine
touch impulses from the lower half of the body and the lower
limb on the same side.
Cuneate nucleus
• It lies lateral to the gracile nucleus it receive the termination of
the cuneate tract, the axons of the cells arch around the central
canal forming with the axons of gracile the internal arcuate
fibers
• The cuneate tract carries proprioceptive and fine touch
impulses from the upper half of the body and the upper limb

20. Accessory cuneate nucleus
• It lies dorsolateral to the cuneate nucleus this
nucleus receive fibers from the cervical region of
the spinal cord which ascend through the cuneate
tract.
• axons of the cells of this nucleus form the dorsal
external arcuate fibers which reach the cerebellum
through the inferior cerebellar peduncle
• These fibers carry proprioceptive impulses from the
neck and the upper limb to the cerebellum on the
same side
• The dorsal spinocerebellar tract carry the
proprioceptive impulses from the trunk and lower
half of the body to the cerebellum.

21. Level of Sensory Decussation
A transverse section through the inferior half of the medulla oblongata, a
short distance above the level of the decussation of the pyramids, passes
through the decussation of lemnisci in which The following structures are
seen
• Nuclei
• Cranial nerve nuclei: spinal nucleus of trigeminal nerve,
accessory nucleus, hypoglossal nucleus
• Nucleus gracilis, nucleus cuneatus,
• Motor tract: Pyramids
• Sensory tracts
Decussation of medial lemnisci, fasciculus gracilis, fasciculus
cuneatus, spinal tract of trigeminal nerve, posterior
spinocerebellar tract, lateral spinothalamic tract, anterior
spinocerebellar tract

22. Sensory decussation
• It is formed by the axons of the cells of gracile and
cuneate nuclei which forms the internal arcuate
fibers and then decussate in the midline with the
fibers of the opposite side forming the sensory
decussation
• After crossing to the opposite side the fibers
collecte into a band close to the midline called
medial lemniscus the fibers ascend through the
brain stem to terminate in the posterolateral vental
nucleus of the thalamus

24. Level of the Olives
• A transverse section through the olives passes across the
inferior part of the fourth ventricle and the following
structure are seen
• 1. Nuclei
• Cranial nerve nuclei: spinal nucleus of trigeminal nerve,
vestibular nucleus, glossopharyngeal nucleus, vagal nucleus,
hypoglossal nucleus, nucleus ambiguus, nucleus of tractus
solitarius
• Inferior olivary nucleus,
• Motor tracts: Pyramids
• Sensory tracts: Medial longitudinal fasciculus, tectospinal
tract, medial lemniscus, spinal tract of cranial nerve V,
lateral spinothalamic tract, anterior spinocerebellar tract

26. The Inferior Olivary Nucleus
• This is a prominent structure that is responsible
for the surface swelling of the olive.
• It is a corrugated bag of the gray matter with a
hilus (mouth) directed medially. Smaller dorsal
and medial accessory olivary nuclei also are
present. The cells of the inferior olivary nucleus
send fibers medially across the midline to enter
the cerebellum through the inferior cerebellar
peduncle.
• Afferent fibers reach the inferior olivary nuclei
from the spinal cord (the spino-olivary tracts) and
from the cerebellum and cerebral cortex.
• The function of the olivary nuclei is associated
with voluntary muscle movement.

28. Nucleus Ambiguus
• The nucleus ambiguus is embedded in
the medullary reticular formation.
• It is just dorsal to the inferior olivary
nucleus.
• The emerging nerve fibers (SVE) join the
glossopharyngeal, vagus, and cranial part
of the accessory nerve and are
distributed to voluntary skeletal muscle.

29. Central Gray Matter
• The central gray matter lies beneath the
floor of the fourth ventricle at this level.
Passing from medial to lateral, the
following important structures may be
recognized: (1) the hypoglossal nucleus,
(2) the dorsal nucleus of the vagus, (3)
the nucleus of the tractus solitarius, and
(4) the medial and inferior vestibular
nuclei

30. Hypoglossal nucleus
• This nucleus is situated in the midline just beneath the
floor of the 4th ventricle.
• Here it forms the hypoglossal trigone, a triangular
elevation.
• The hypoglossal nerve originate in the ipsilateral
hypoglossal nucleus and supplies the muscles of the
tongue
Dorsal Motor Nucleus of the Vagus
• This nucleusisthe principle parasympathetic nucleus of
the brain stem.
• It is located in the floor of the 4th ventricle just lateral
to the hypoglossal nucleus.
• It underlies the vagal trigone.
• Its fibers travel to the thoracic and abdominal viscera.

31. Solitary Nucleus
• It lies at a deeper plane in the open medulla,
close to the medial side of the inferior
cerebellar peduncle, it extends downwards
to the closed medulla lateral to the dorsal
nucleus of vagus
• The solitary nucleus is the principle visceral
afferent nuclei.
• It receives both GVA fibre and SVA fibres
from the facial, glossopharyngeal and vagus
nerves.

33. • The medial longitudinal fasciculus forms a small tract of nerve fibers
situated on each side of the midline posterior to the medial lemniscus
and anterior to the hypoglossal nucleus. It consists of ascending and
descending fibers.
• The inferior cerebellar peduncle is situated in the posterolateral
corner of the section on the lateral side of the fourth ventricle.
• The spinal tract of the trigeminal nerve and its nucleus are
situated on the anteromedial aspect of the inferior cerebellar peduncle.
• The anterior spinocerebellar tract is situated near the surface in the
interval between the inferior olivary nucleus and the nucleus of the
spinal tract of the trigeminal nerve.
• The spinal lemniscus, consisting of the anterior spinothalamic, the
lateral spinothalamic, and spinotectal tracts, is deeply placed.
• The reticular formation, consisting of a diffuse mixture of nerve
fibers and small groups of nerve cells, is deeply placed posterior to the
olivary nucleus. The reticular formation represents, at this level, only a
small part of this system, which is also present in the pons and
midbrain.

34. Applied anatomy
• Medial medullary lesion
• Causes mainly vascular due to occlusion of the anterior spinal
artery or medullary branches of the vertebral artery
• Manifestations
• Hemiplagia of the opposite side due to injury of the pyramid
• Loss of prioprioceptive sensation and touch sensation due to
injury of medial lemniscus
• Lower motor neurone paralysis of the muscle of the tongue on
the same side due to injury of hypoglossal nucleus and nerve;
• Inferior alternating hemiplagia, i.e. paralysis of the tongue
on the same side and hemiplagia on the opposite side.

35. Lateral medullary syndrom
• Causes
• Vascular due to occlusion of the posterior inferior cerebellar artery so
it called the posterior inferior cerebellar artery syndrom;
wallenberg’s syndrom
• Manifestations
• Cerebellar ataxia on the same side due to injury of the inferior
cerebellar peduncle
• Bulbar paralysis on the same side due to injury of the nuclei of
glossopharyngeal, vagus, accessory nerves this is manifested by
difficulty in swallowing and phonation
• Loss of pain, temperature and crude touch sensations in the
opposite side due to the injury of spinal lemniscus
• Horner’s syndrom on the same side of the face due to injury of
reticular formation
this is manifested by ptosis, myosis, enophtholmus and anhydrosis