Medulla oblongata

1. MEDULLA OBLONGATA
Dr. Prabhakar Yadav
Associate Professor
Department of Human Anatomy
B.P. Koirala Institute of Health Sciences

2. PARTS OF BRAIN
• Forebrain
1. Cerebrum
2. Thalamus
3. Hypothalamus
• Midbrain
• Hindbrain
1. Pons
2. Medulla oblongata
3. Cerebellum

3. Brain stem= Midbrain
+
pons
+
Medulla oblongata

4. Occupies: posterior cranial fossa
Connects : spinal cord with forebrain.
Function of Brain stem
1. Conduit for ascending and descending tracts
2. Contains reflex centers – associated with respiratory and
cardiovascular system & control of consciousness
3. Contain nuclei of cranial nerve III - XII

5. Medulla oblongata:
Connection:
Superiorly- pons
Inferiorly- spinal cord
(At origin of anterior and posterior roots of 1st
cervical nerves at level of foramen magnum)
Shape: conical

6. Central canal of spinal cord :
continues into lower half of medulla
Upper half – forms cavity of 4th ventricle

7. Anterior surface:
Anterior median fissure – continuous with anterior
median fissure of spina cord
On each side of it – Pyramid
( composed of bundles of corticospinal fibres which
originate in precentral gyrus of cerebral cortex)

8. Pyramids taper inferiorly
Decussation of pyramids-
Majority of descending fibres cross opposite side
posterolateral to pyramid- olive
(oval elevation produced by underlying inferior olivary
nuclei)
Hypoglossal nerve( rootlets): in groove between pyramid
and olive

9. Anterior external arcuate fibers:
– emerge from anterior median fissure above
decussation- pass laterally to enter cerebellum.
 A collection of nerve fibres that connects two
masses of grey matter within the central
nervous system,is called a Tract.
 They are sometimes referred to as fasciculi (=
bundles) ; or lemnisci (= ribbons).

10. Posterior to olive – inferiro crebellar peduncle – connects medulla to cerebellum

11. Roots of
1. Glossopharyngeal nerve
2. Vagus nerve &
3. Cranial root of accessory nerve
emerge in groove between olive and
inferior cerebellar peduncle.

12. Posterior surface
superior half- lower part of 4th ventricle
Inferior half – continuous with posterior aspect of spinal cord
Posterior median sulcus
Gracile tubercle( produced by underlying gracile nucleus) – on each
side of posterior median sulcus
Cunate tubercle (produced by underlying nuneate nucleus)-Lateral
to gracile tubercle.

13. a. At level of decussation of pyramids
b. At level of decussation of lemnisci
c. At level of olives
d. At level just inferior to the Pons

14. Level of Decussation of Pyramids
A transverse section through decussation of pyramids (Great motor
decussation).
In superior part, pyramid is formed by corticospinal fibers
Inferiorly, 3/4th of the fibers cross the median plane & continue down
the spinal cord in the lateral white column as lateral corticospinal tract.

15. • As these fibers decusssate, they break the continuity
between anterior column of the gray matter & gray matter
that surrounds the central canal
• Fasciculus gracilis & Fasciculus cuneatus continue to
ascend superiorly posterior to the central gray matter.
• Nucleus gracilis & Nucleus cuneatus appear as posterior
extensions of the central gray matter.

16. • Apex of posterior horn gets swollen up to form Spinal
nucleus of trigeminal nerve.
• Substantia gelatinosa is continuous with inferior end of
Spinal nucleus trigeminal nerve.
• Spinal tract of the trigeminal nerve are situated between
the nucleus & surface of medulla.

17. Zone containing a network of fibres & scattered nerve cells within it the lateral white column adjacent to spinal nucleus
trigeminal nerve is called reticular formation.

18. Ascending tracts: conduct the impulses from the periphery to the brain through the cord.
Important ascending tracts fall into the following three types:
1. Those concerned with pain & temperature sensations and crude touch- lateral & anterior spi-nothalamic tracts.
2. Those concerned with fine touch & conscious proprioceptive sensations- fasciculus gracilis & fasciculus cuneatus.
3. Those concerned with unconscious proprioception & muscular coordination- anterior & posterior
spinocerebellar tracts.

19. Level of Decussation of Lemnisci (sensory decussation):
Transverse section passes through decussation of lemnisci (Great sensory decussation)
Internal arcuate fibers- (second order sensory neurons conducting sensations of discriminative touch, position & vibration)
emerge from anterior aspects of nucleus gracilis & nucleus cuneatus that runs anteriorly & laterally around central gray matter &
then curve medially toward the midline, where they decussate with the corresponding fibers of the opposite side.
In this decussation the gracile fibres are medial to that of cuneate fibres.
As the fibres from nucleus gracilis and nucleus cuneatus pass forwards and medially they intercross so that the most medial
fibres (from the feet and leg) come to lie anteriorly in the medial lemniscus.

20.  Lemnisci are formed from Internal arcuate fibers.
• Decussation of lemnisci takes place anterior to central gray matter & posterior to the pyramids
 Fibres of lemniscus relay into corresponding thalamus
• Spinal nucleus of the trigeminal nerve lies lateral to internal arcuate fibers.
Spinal tract of the trigeminal nerve lies lateral to the nucleus of the trigeminal nerve.
 Anterior, Lateral spinothalamic tracts & spinotectal tracts are close to one another & collectively known as spinal lemniscus
lies lateral to decussation of lemnisci.
• Spinocerebellar & lateral spinothalamic tracts lie in the anterolateral area of lateral white column.

21. • Dorsolateral to cuneate nucleus lies Accessory cuneate nucleus -receives lateral fibres of the fasciculus cuneatus & gives rise to
posterior external arcuate fibres conveying proprioceptive impulses to the cerebellum of the same side through inferior
cerebellar peduncle
• Central grey matter contains: (a) hypoglossal nucleus, (b) dorsal nucleus of vagus,& (c) nucleus of tractus solitarius.
1.Hypoglossal nucleus: occupies ventro-medial position close to the midline.
2. Dorsal nucleus of vagus lies dorsolateral to hypoglossal nucleus.
3. Nucleus of tractus soli-tarius lies dorsolateral to dorsal nucleus of vagus.
• Medial longitudinal bundle lies posterior to medial lemniscus. It is tract of nerve fibres which interconnect the IIIrd, IVth, VIth,
VIIIth & spinal nucleus of XIth cranial nerve nuclei.

22. Level of the Olives:
Transverse section through the olives passes across the inferior part of the fourth ventricle.
Amount of gray matter has increased at this level due to the presence of
1. Olivary nuclear complex;
2. Nuclei of the vestibulocochlear, glossopharyngeal, vagus, accessory & hypoglossal nerves and
3. Arcuate nuclei.

23. Olivary Nuclear Complex
• Largest nucleus of this complex is Inferior olivary nucleus - shaped like a crumpled bag with its mouth directed medially.
• It is responsible for elevation on the surface of the medulla- olive.
• Afferent fibers reach the inferior olivary nuclei from the spinal cord via spino-olivary tracts
• Cells of Inferior olivary nucleus send fibers medially across the midline to enter cerebellum through Inferior cerebellar
peduncle.
• Smaller dorsal and medial accessory olivary nuclei also are present
• Function of the olivary nuclei is associated with voluntary muscle movement.

24. Vestibulocochlear Nuclei:
Vestibular nuclear complex is made up of:
(1) medial vestibular nucleus, (2) inferior vestibular nucleus, (3) lateral vestibular nucleus, and (4) superior vestibular nucleus.
• Medial & inferior vestibular nuclei can be seen on section at this level.
Anterior cochlear nucleus is situated on anterolateral aspect of inferior cerebellar peduncle.
Posterior cochlear nucleus is situated on posterior aspect of the peduncle & lateral to the floor of the fourth ventricle.

25. Nucleus Ambiguus:
consists of large motor neurons, situated deep within the reticular formation.
Gives origin to the motor fibres of IXth, Xth and XIth cranial nerves.

26. Central Gray Matter
Lies beneath the floor of the fourth ventricle.
Passing from medial to lateral, structures recognized are:
(1) Hypoglossal nucleus (2) Dorsal nucleus of vagus (3) Nucleus of tractus solitaries & (4)Medial & inferior vestibular nuclei .
Nucleus ambiguus, lie deep within the reticular formation.
(2) Arcuate nuclei are inferiorly displaced pontine nuclei, situated on the anterior surface of the pyramids.
It receive nerve fibers from cerebral cortex & send efferent fibers to cerebellum of the opposite side through anterior external
arcuate fibers.

27. Pyramids containing corticospinal & some corticonuclear fibers are situated in anterior part of medulla
Corticospinal fibers descend to spinal cord & corticonuclear fibers to the motor nuclei of cranial nerves situated within medulla.
Medial lemniscus forms a flattened tract on each side of the midline posterior to the pyramid.
These fibers emerge from the decussation of the lemnisci & convey sensory information to the thalamus.
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 is the main pathway that connects vestibular & cochlear nuclei with the nuclei controlling the extraocular muscles (oculomotor,
trochlear & abducent nuclei).

28. • Inferior cerebellar peduncle is situated in the posterolateral corner of the section on the lateral side of the fourth ventricle
• Spinal tract of the trigeminal nerve and its nucleus are situated on the anteromedial aspect of inferior cerebellar peduncle
• Anterior spinocerebellar tract is situated near the surface in the interval between inferior olivary nucleus & nucleus of spinal
tract of the trigeminal nerve.
• Spinal lemniscus: consisting of anterior spinothalamic, lateral spinothalamic & spinotectal tracts, is deeply placed.

29. • Reticular formation, consisting of a diffuse mixture of nerve fibers & small groups of nerve cells, is deeply placed posterior to
olivary nucleus
• Glossopharyngeal, vagus & cranial part of accessory nerves run forward & laterally through reticular formation. The nerve
fibers emerge between the olives & inferior cerebellar peduncles.
• Hypoglossal nerves run anteriorly & laterally through reticular formation and emerge between pyramids & olives.

30. Level Just Inferior to the Pons (ponto-medullary junction):
• Inferior vestibular nucleus is replaced by Lateral vestibular nucleus
• Cochlear nuclei are visible on the anterior and posterior surfaces of inferior cerebellar peduncle.

31. Blood Supply of the Medulla
The medulla is supplied by the following arteries:
• Two vertebral arteries.
• Anterior and posterior spinal arteries.
• Anterior and posterior inferior cerebellar arteries.
• Basilar artery.

32. Lateral medullary (posterior inferior cerebellar artery) syndrome of Wallenberg
Posterior inferior cerebellar artery supplies: Dorsolateral part of medulla; inferior surface of the cerebellum.
Thrombosis of the artery, affects a wedge shaped area on the dorsolateral aspect of medulla & inferior surface of the cerebellum
producing following signs and symptoms.
1. Dysphagia & dysarthria due to paralysis of the ipsilateral palatal and laryngeal muscles (innervated by nucleus ambiguus)
2. Analgesia & thermoanesthesia on the ipsilateral side of the face (nucleus and spinal tract of the trigeminal nerve)
3. Vertigo, nausea, vomiting, and nystagmus (vestibular nuclei)
4. Ipsilateral Horner syndrome (due to involvement of descending sympathetic pathway in the reticular formation of medulla
5. Ipsilateral cerebellar signs— gait and limb ataxia (cerebellum or inferior cerebellar peduncle)
6. Contralateral loss of sensations of pain and temperature (spinal lemniscus—spinothalamic tract).

33. Medial Medullary Syndrome:
Medial part of the medulla oblongata is supplied by the vertebral artery. Thrombosis of the medullary branch produces the
following signs and symptoms:
1. Contralateral hemiparesis (pyramidal tract)
2. Contralateral impaired sensations of position and movement and tactile discrimination (medial lemniscus)
3. Ipsilateral paralysis of tongue muscles with deviation to the paralyzed side when the tongue is protruded (hypoglossal nerve).

34. THANK YOU