Phase II Nervous System Module

Brainstem

Medulla Oblongata and its Lesions

Prof. Narayana Kilarkaje FRSB

Department of Anatomy
 Objectives

• Describe external and internal features of the medulla oblongata at

different levels
• Correlate the structure of the medulla oblongata with the clinical
manifestation arising from medial and lateral medullary syndromes
• Describe the intracranial course and distribution of the 9th, 10th, 11th and
12th cranial nerves
 Brainstem
Anterior view Posterolateral view • Brainstem - between the forebrain and spinal

F
cord
• Parts- midbrain (mesencephalon), pons, and
medulla oblongata
Midbrain

Pons
•
•
I
Fourth ventricle – cavity of hindbrain
The midbrain, pons and medulla are connected

i
to the cerebellum by paired superior, middle
and inferior cerebellar peduncles
Medulla • Nine pairs (cranial accessory not included) of
oblongata cranial nerves are attached to the brainstem
• Sensory and motor pathways (tracts) that
jÉ commute between the cerebrum and spinal
cord pass through the brainstem
Sagittal section
• Brainstem contains reflex centers for
I
respiratory and cardiovascular (medulla)
regulation, pons contains pneumotaxic and
apneustic centers
 External Features of Medulla Oblongata ephrinmagnum
Anterior view
anterior • Anterior median fissure - two symmetrical halves
• Pyramids - corticospinal tract fibers
Pons
• At the lower end of the fissure, pyramidal tract
fibers cross to the opposite side in such a way that
Abducens nerve (VI) Vestibulocochlear nerve (VIII) upper limb fibers cross superiorly, and lower limb
Facial nerve (VII)
fibers cross inferiorly
Crossed diplegia (Fig B)-
--------Produced when meningiomas compress the

Imi
Hypoglossal nerve (XII) Choroid plexus of 4th Ventricle
Glossopharyngeal nerve (IX)
pyramidal crossing fibers – after upper limb fibers
Pyramid
cross and before lower limb fibers cross
Olive Vagus nerve (X)
Anterior median fissure --------Ipsilateral paralysis of upper limb and
Inferior cerebellar peduncle contralateral paralysis of lower limb
Antero-lateral sulcus

I
Spinal accessory nerve (XI)
Pyramidal decussation
J
Posterolateral sulcus Upper limb fibers • Olives - inferior olivary nuclear complex
• Posterolateral sulcus separates the olive from the
Fig A inferior cerebellar peduncle

Meningioma compression site

• At the ponto-medullary junction, abducens, facial
producing crossed diplegia and vestibulocochlear nerves emerge

Fig B • From the anterolateral sulcus, hypoglossal nerve,

and from the posterolateral sulcus, the
Lower limb fibers glossopharyngeal and vagus nerves emerge
Right Left
 External Features of Medulla Oblongata
• Posterior aspect of the medulla shows the superior open
posterior
Median sulcus
Sulcus limitans Posterior view and the inferior closed parts
Stria medullares Closed part:

Open part
Vestibular area • Posterior median sulcus – divides the posterior aspect

I
Inferior fovea
Hypoglossal trigone
• Gracile and cuneate tubercles - nuclei gracilis and cuneatus
Trigeminal tubercle • The fasciculi gracilis and cuneatus (posterior column tracts)
(tuberculum cinerium) Vagal trigone
Cuneate tubercle • Trigeminal tubercle - spinal nucleus of the trigeminal nerve
Area postrema (CN V)
exactlyther
Gracile tubercle Open part:

Closed part
Ijf
Posterior
• Median sulcus - two symmetrical halves
Fasciculus cuneatus median
sulcus • Sulcus limitans divides each half into medial and lateral
Fasciculus gracilis parts
• Medial part- hypoglossal and vagal trigones - hypoglossal
and dorsal vagal nuclei
• Lateral part- vestibular area - vestibular nuclei
• Pontomedullary junction is demarcated by the stria

s
medullares
• Area postrema is a chemoreceptor trigger zone, which
lacks blood-brain barrier, and a part of the vomiting center
along with solitary tract nucleus. It senses emetics and
hidden Iffy anatomically
causes vomiting reflex
 n MRI grayiswhite
Internal Structure of Medulla Oblongata
andwhiteisblack • The internal structure of medulla oblongata is studied at
three different levels

C Inferior olivary nucleus

A) Internal structure of medulla oblongata at pyramidal
B decussation level
Sensory decussation
A • Grey mater forms nuclei- nuclei gracilis and cuneatus, spinal
Pyramidal decussation nucleus of V cranial nerve, and ventral grey horn
• White mater - ascending and descending tracts
• Pyramidal fibers (corticospinal) cross to the opposite side to
A. Section of medulla oblongata at pyramidal decussation form the lateral corticospinal tract
moderfacianticus • The crossing fibers separate the ventral horn
• Uncrossed pyramidal fibers form the anterior corticospinal
tract
• Ascending tracts - fasciculi gracilis and cuneatus, anterior
(ventral) and posterior (dorsal) spinocerebellar tracts,
anterolateral spinothalamic tract system, spino-olivary and
spinotectal tracts
• Ascending tract arising from the medulla- spinal tract of
trigeminal nerve
• Descending tracts- lateral and anterior corticospinal,
rubrospinal, tectospinal, vestibulospinal, and medial
longitudinal fasciculus
• Reticular formation occupies the remaining part
 Internal Structure of Medulla Oblongata
Osensory (lemniscal) decussation level
B. Section of medulla oblongata at B) Internal structure of medulla oblongata at
sensory decussation
B • The structures seen at the pyramidal decussation

Fasciculus and
E• The differences seen at this level are- separation of
level (in previous slide) are also seen at this level
Nucleus gracilis
central grey mater from the nuclei gracilis and
Fasciculus and
cuneatus, and spinal nucleus of V cranial nerve
Solitary tract and nucleus Nucleus cuneatus • In the central grey mater- hypoglossal, dorsal vagal,
and solitary tract nuclei are present bilaterally

Miss
Dorsal nucleus
Hypoglossal nucleus S • The other nuclei- nucleus ambiguus, part of inferior
Nucleus ambiguus ICP with posterior olivary nucleus , medial accessory nucleus,
spinocerebellar tract accessory cuneate nucleus and arcuate nucleus are
Spinal tract and nucleus seen
of CN V
Anterior spinocerebellar
tract Spinal lemniscus
• Most important feature is the crossing internal
arcuate fibers arising from the nuclei gracilis and
Medial longitudinal fasciculus
Crossing internal arcuate fibers cuneatus to the opposite side and continuing as
(sensory decussation) Tectospinal tract the medial lemniscus
Medial lemniscus
• Fibers arising from the nucleus gracilis lie anteriorly
Inferior olivary nucleus
and from the nucleus cuneatus lie posteriorly,
CN XII therefore, the legs are represented ventrally, and
the upper limb is represented posteriorly
 Internal Structure of Medulla Oblongata
C. Section of medulla oblongata through
C the middle of inferior olivary nuclei C) Internal structure of medulla oblongata at mid-

of
olivary (open part; through the inferior olivary
nuclei) level
• Section passes through the 4th ventricle and shows
the grey mater and white mater
• The hypoglossal, dorsal vagal and solitary tract
nuclei are shifted to just deep to the floor of the 4th
ventricle
• Grey mater shows the following additional features
compared to the previous section- Inferior olivary

y
nucleus, medial and dorsal accessory olivary nuclei,

I postenorsisinfed inferior and medial vestibular nuclei, and anterior

and posterior cochlear nuclei
• White mater shows - medial longitudinal fasciculus,
tectospinal tract and medial lemniscus

O
Spinothalamic tract
• Posterior spinocerebellar tract joins the inferior
cerebellar peduncle, spinal nucleus and tract of CN

o
V lie medial to the inferior cerebellar peduncle

Framefunction
 Cranial Nerves (and their Nuclei) Originating from Medulla Oblongata
• Cranial accessory nerve is now considered as a part of the vagus
nerve and, therefore, does not exist as a separate nerve
• The spinal accessory is now considered as the CNXI

accessory twopart

Inferior salivatory nucleus Solitary tract nucleus

Hypoglossal nucleus

Glossopharyngeal nerve
Dorsal vagal nucleus
Hypoglossal nerve
Vagus
nerve
Nucleus ambiguus
Glossopharyngeal
Tentorial (IX) nerve

D
Pass through
notch Vagus (X) nerve
the jugular
Spinal accessory (XI) Accessory nucleus Spinal nucleus and tract of
foramen
nerve CN V

Tentorium cerebelli Hypoglossal (XII) nerve passes

through the hypoglossal canal
Cranial nerve nuclei and emergence of cranial
Cranial cavity (superior view)
nerves IX-XII from medulla oblongata
 Nuclei and Distribution of Cranial Nerves Emerging from Medulla Oblongata
Glossopharyngeal nerve • Nucleus ambiguus-motor - stylopharyngeus muscle
• Inferior salivatory nucleus- motor-parasympathetic
Glossopharyngeal nerve nucleus - fibers supply the parotid gland to
Otic ganglion Solitary tract nucleus stimulate its secretion
Inferior salivatory nucleus • Spinal nucleus of CN V- sensory nucleus of V cranial
Nucleus ambiguus nerve, but shared by IX and X cranial nerves, it
Parotid gland Spinal tract and nucleus É stimuli (through CN IX,
receives general sensory
of V nerve
Superior and inferior ganglia proprioceptive sensations from stylopharyngeus
Tympanic plexus of IX nerve and skin of auricle)
Jugular foramen • Solitary tract nucleus- is a sensory and motor
Stylopharyngeus nucleus- in this case, it receives general sensations
muscle and a
branch from IX from mucus membrane of pharynx, tonsil, soft
palate and posterior 1/3 of tongue (taste too)
Tonsillar branch Pharyngeal branches to
pharyngeal plexus • Glossopharyngeal nerve lesions are rare, but if
Lingual branch happens, presents sensory loss over soft palate,
of IX nerve pharynx and posterior 1/3 of tongue (weakness or
Carotid nerve loss of gag reflex), paralysis of stylopharyngeus, loss
of parotid gland secretion, and hypertension due to
carotid nerve involvement. Jugular foramen
syndrome, paraganglioma, etc can cause injury to
Carotid sinus
the nerve
Carotid body

gagreflex isn'trefteadrea postrema

 Nuclei and Distribution of Cranial Nerves Emerging from Medulla Oblongata
Vagus nerve and accessory nerve • Vagus is a mixed nerve and the longest one- connected to 4 nuclei in
Dorsal vagal nucleus
the medulla
Vagus nerve Solitary tract nucleus
• Nucleus ambiguus- motor - muscles of palate, pharynx, and larynx
Nucleus ambiguus
Spinal nucleus and • Dorsal vagal nucleus- motor and sensory- in this case, it gives
tract of V nerve parasympathetic fibers- supply heart, bronchial tree, and most of GIT
Pharyngeal branch of vagus • Solitary tract nucleus- sensory – receives taste sensations from
Spinal accessory nerve posterior most part of tongue and epiglottis and general sensations
Superior laryngeal nerve from thoracic and abdominal organs
• Spinal nucleus of CN V- receives sensations from the external ear

I
Pharyngeal plexus
• Vagus nerve injury- may be due to jugular foramen syndrome,
compression by tumors or trauma
Superior and inferior cervical
Left recurrent laryngeal nerve cardiac, and thoracic cardiac • The presentation is – loss of palatal arch, nasal regurgitation of
branches of vagus nerve swallowed liquids, nasal twang and hoarseness of voice, cadaveric
Cardiac plexus position of vocal cord, and dysphagia
Pulmonary plexus

Chain
Esophageal plexus • Spinal accessory nerve is motor, arises from the spinal cord (C1-C6)
foramenmayhem
enter • The spinal accessory supplies sternocleidomastoid and trapezius

Vagus nerve branches exit juglarforamen• Accessory

trapezius.
nerve injury causes paralysis of sternocleidomastoid and

supply abdominal organs

• Supranuclear lesion predominantly affects contralateral trapezius
• Trapezius paralysis causes brachial plexus neuralgia due to drooping of
d the upper limb which stretches the plexus
 Nuclei and Distribution of Cranial Nerves Emerging from Medulla Oblongata
Hypoglossal nerve
• Hypoglossal nerve is purely motor

I
• It leaves the cranial cavity through the hypoglossal
canal
Hypoglossal canal
Hypoglossal nucleus • The nerve supplies all muscles of tongue- both extrinsic
Hypoglossal nerve
and intrinsic- except palatoglossus
• LMN paralysis of hypoglossal nerve (the nerve or its

E
C1 fibers joining the
hypoglossal nerve nucleus) causes ipsilateral paralysis of tongue (all

I
muscles on that side except palatoglossus), tongue
atrophies, and protrudes to the side of the lesion
• The hypoglossal nucleus is controlled bilaterally by the
corticonuclear fibers except that part of the nucleus
which is supplying the genioglossus, which is controlled
Hypoglossal nerve
supplying the tongue only by the contralateral corticonuclear fibers
• UMN paralysis of hypoglossal nerve– would result in no

E
atrophy or fibrillation of tongue, upon protrusion, the

E
tongue will deviate to the opposite side of UMN lesion
(if left UMN injured, the tongue deviates to the right
side), but to the same side of affected genioglossus
 Lesions of Medulla Oblongata
Downward herniation (F in left lower figure)
• Medulla oblongata gives origin to cranial nerves IX-X and XII, it contains vital centers
for heart rate and respiration, and transmits several ascending and descending tracts,
thus, demyelinating diseases, vascular lesions and neoplasms affecting the medulla
are very serious
• Increased intracranial pressure in the posterior cranial fossa - herniation of medulla
oblongata and tonsils of cerebellum through the foramen magnum into the vertebral
canal
• Withdrawal of CSF from such patients is even more dangerous as that would further
exaggerate the herniation
• Vital functions of medulla along with the cranial nerves attached to it would be
affected and they are fatal
Congenital abnormality

F
• Arnold-Chiari phenomenon/malformation- is a congenital anomaly in which the
medulla and cerebellar tonsils are herniated through the foramen magnum into the
congenital vertebral canal resulting in blockade of drainage of CSF from the 4th ventricle
resulting in hydrocephalus, and dysfunction of the cranial nerves attached to the
medulla oblongata

O
 Blood Supply of Medulla Oblongata
AICA

PICA

Posterior spinal
Anterior spinal

O
Lower medulla
Vertebral
(closed part)

Posterior

Posterior spinal Posterior

Itebellar
PICA AICA

Vertebral

I
PICA

D
Upper medulla
Anterior spinal (open part)
Anterior Vertebral

Anterior spinal

AICA: Anterior inferior cerebellar artery

PICA: Posterior inferior cerebellar artery Anterior
 Vascular Lesions of Medulla Oblongata infraction
Medial medullary syndrome
Medial medullary syndrome (alternate names: Dejerine syndrome, inferior alternating syndrome, hypoglossal
alternating hemiplegia, lower alternating hemiplegia)
Lesion: Anterior spinal artery and/or bulbar branches of vertebral artery
Lateral medullary syndrome (PICA syndrome; Wallenberg syndrome)
Lesion: Posterior inferior cerebellar artery

Lateral medullary syndrome

I
 References

Snell RS, Snell’s Clinical Neuroanatomy, 8th Edition, Chapter 5 Brainstem, Pages 185-226

The figures used in this presentation have been reproduced from Netter’s atlas, internet sources, Grant’s atlas, and
BD Chaurasia’s neuroanatomy