ANATOMY IV
(Neuroanatomy)
To review the anatomy of the brainstem
(Medulla oblongata)
 To develop the three- dimensional picture of the
interior of Medulla oblongata
 To know the position of f the cranial nerve nuclei
 The pathways of ascending and descending
Nerve tracts.
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7
THE BRAIN STEM
Location:
The medulla
oblongata is the
lower portion of the
brainstem.
 It is above the spinal
cord, below the
Pons, and anterior to
the cerebellum.
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Medulla oblongata is conical in shape.
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The central canalof spinal cord continues
upward in the lower half of medulla.
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In the upper half of the medulla it expand as
the cavity of the fourth ventricle.
Funiculus:
A slender cordlike strand or band, especially a bundle of ner
ve fibers in a nerve trunk
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The medulla has an anterior median fissure
and a posterior median sulcus corresponding
to the structures seen in the spinal cord.
On each side of the median fissure, there is a
swelling called the pyramid.
The Pyramids contain the bundle of nerve
Corticospinal fiber.
Corticospinal:
A tract of nerve cells that carries motor commands from the brain to the spinal
cord.

Posterolateral to the pyramids are the olives,
oval elevation produce by underlying Inferior
olivary nuclei.

In the groove b/w Pyramid and olive the
rootlets of Hypoglossal nerve

Posterior to the olive are the inferior
cerebellar peduncles.
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In the groove b/w the olive and the inferior
cerebellar peduncles emerge the root of
Glossopharyngeal, Vagus & Cranial roots of
the Accessory nerve.
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Superior half = lower part of the fourth ventricle.
Inferior half = Posterior median sulcus

On each side of the median sulcus there is a
Gracile tubercle , produce by underlying Gracile
nucleus.

Lateral to the Gracile tubercle there is Cuneate
tubercle , produce by underlying Cuneate
nucleus.
Cuneate tubercle
Gracile tubercle
Posterior median sulcus
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1.
2.
3.
4.
Internal structure of medulla is considered at
four level.
Level of decussation of Pyramids
Level of decussation of Leminisci
Level of Olives
Level just inferior to Pons
The medullary pyramids are paired white matter structures of
the brainstem's medulla oblongata that contain motor fibers of
the corticospinal and corticobulbar tracts – known together as the pyramidal
tracts. The lower limit of the pyramids is marked when the fibers cross
(decussate).
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The corticobulbar (or corticonuclear) tract is
a two neuron white matter motor pathway
connecting the cerebral cortex to
the brainstem primarily involved in carrying
the motor function of the non-oculomotor
cranial nerves.
The corticobulbar tract is one of
the pyramidal tracts, the other being
the corticospinal tract.
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In superior part the corticospinal fiber occupy
and form pyramids.
The inferior half of medulla passes through
the decussation of pyramids, the great
motor decussation.
Inferiorly three-fourth of fiber cross median
plane and continue down the spinal cord in
the lateral white column as the lateral
corticospinal tract.
CorticospinalTract
A tract of nerve cells that carries motor commands from the
brain to the spinal cord.
 Pyramide
The pyramids are just big fiber bundles that lie on the ventral
surface of the caudal medulla.
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The lateral corticospinal tract
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The spinocerebellar tract is a set of axonal fibers originating
in the spinal cord and terminating in the
ipsilateral cerebellum. This tract conveys information to the
cerebellum about limb and joint position (proprioception).
MedialLongitunalFasciculus:
Pathway in the brainstem that connects the vestibular
system with the cranial nerves that serve the eye muscles (e.
g., CNs III, IV, VI).

(also called
the crossed pyramidal tract or lateral cerebrospinal
fasciculus) is the largest part of the corticospinal tract.
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The fasciculus gracilis and fasciculus cuneatus
continue to ascend superiorly posterior to
the central gray matter.
The nucleus gracilis and nucleus cuneatus
appear as posterior extension of the central
gray matter.
The substantia gelatinosa in posterior gray
column of spinal cord become continuous
with the inferior end of the nucleus of spinal
tract of the trigeminal nerve.
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SUBSTANTIA GELATINOSA. : a mass of
gelatinous gray matter that lies on the dorsal
surface of the dorsal column and extends the
entire length of the spinal cord into the
medulla oblongata and that functions in the
transmission of painful sensory information.
Typically, the perception of pain travels through three
orders of neurons.
1. The first-order neurons carry signals from the periphery
to the spinal cord
2. The second-order neurons relay this information from the
spinal cord to the thalamus
3. The third-order neurons transmit the information from the
thalamus to the primary sensory cortex,
where the information is processed, resulting in the
"feeling" of pain.
Name
Location Function
Fasciculus
gracilis
Posterior
Column
Fasciculus
Cuneatus
Posterior
Column
Lateral
Spinothalamic
Lateral
Column
Anterior
Column
Lateral
Column
Anterior
Spinothalamic
Posterior and
Anterior
Discriminative touch,
proprioception
Weight discrimination
Same as FG
Pain and Thermal
sensations
Itch, Tickle, Pressure,
Crude touch sensations
Proprioceptors
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The decussation of leminisci,the great
sensory decussation.
The leminisci have been formed from the
internal arcuate fiber.
The nucleus of the spinal tract of trigeminal
nerve lies lateral to the internal arcuate fiber.
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The medial lemniscus, also known as Reil's
band or Reil's ribbon, is a large ascending
bundle of heavily myelinated axons that
decussate in the brain stem, specifically in the
medulla. The medial lemniscus is formed by
the crossings of internal arcuate fibers.
Internal arcuate fibers are the axons of
second-order neurons contained within
the gracile and cuneate nuclei of the medulla
oblongata.
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A transverse section through the olives
passes across the inferior part of the fourth
ventricles.
The amount of gray matter has increased at
this level owing the presence of
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Olivary nuclear complex
Nuclei of vestibulocochlear
Nucleus ambiguus
Glossopharyngeal, Vagus, accessory and
hypoglossal nerve and the arcuate nuclei.

The nucleus ambiguus contains the cells
bodies of nerves that innervate the muscles
of the soft palate, pharynx, and larnyx which
are strongly associated with speech and
swallowing.
3. LEVEL OF THE OLIVES
 Olivary nuclear complex
▪ Inferior olivary nucleus (large)
▪ Dorsal accessory olivary nucleus (small)
▪ Medial accessory olivary nucleus (small)
▪ Function
▪ Connect spinal cord to cerebellum & cerebellum to
cerebral cortex
▪ Associated with voluntary muscle movement
Spino-Olivary Tracts
 Nuclei of vestibulocochlear
▪ Medial vestibular nucleus
▪ Inferior vestibular nucleus
▪ Lateral vestibular nucleus
▪ Superior vestibular nucleus
 Nucleus ambiguus
▪ Consist of the large motor neuron & situated deep
within the reticular formation, join fibers of
Glossopharngeyal,vagus,acessory nerve, and are
distributed to voluntary skeletal muscle.
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In the last level no major changes
The lateral vestibular nucleus has replaced
the inferior vestibular nucleus.
And cochlear nuclei now are visible on the
anterior and posterior surfaces of the inferior
cerebellar peduncles.