Brainstem - bowenstaff.bowen.edu.ng

BrainstemOverview & Medulla Oblongata ANATOMY PROGRAMME

Definition andRelations

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● The brainstem is the part of the brain that lies

between the cerebrum and the spinal cord.

● It has the following important functions:

○ Regulatory functions (respiratory and

cardiovascular centers along with autonomic

functions)


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○ Cranial nerves nuclei (from III to XII)

○ Regulation of the level of consciousness

○ Serves as a conduit for ascending and

descending tracts

● It lies in the posterior cranial fossa.


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● It’s composed of three parts mainly:

○ Midbrain.

○ Pons.

○ Medulla oblongata.

● The cerebellum is considered a part of the

brainstem in some references.

Eljack’s Lecture Notes in Neuroscience. Fig. 4-1

©2015 all rights reserved9

Siegel, A, Sapru, H.N. Essential Neuroscience.

(3rd ed.). Philadelphia: Lippincott Williams &

Wilkins; 2015. Fig. 9-1 10

External Features of theBrainstem

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● There are four hillocks in the posterior aspect

of the midbrain: two superior and two inferior

colliculi.

● Pons is the largest part of the brainstem and it

hasparallel horizontal fibers.

● The superior, middle, and inferior cerebellar

peduncles connect the midbrain, pons, and

medulla with the cerebellum, respectively.

● It may be difficult to distinguish the lower part

of the medulla from the spinal cord.

External Features of theBrainstem

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Eljack’s Lecture Notes in Neuroscience. Fig. 4-1

©2015 all rights reserved13

Siegel, A, Sapru, H.N. Essential Neuroscience.


Wilkins; 2015. Fig. 9-1 14

Internal Structures of theBrainstem

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● The brainstem constitute a passage for all

tracts that originate from the brainstem or

terminate in the spinal cord.

● All ascending tracts that reach cerebral cortex

pass through the brainstem.

Internal Components of the Brainstem

● All cranial nerves nuclei are located in the

brainstem except the olfactory and optic

nerves.

● The tectum constitute the roof of the midbrain.

● The tegmentum is a part of the brainstem

resembling the core of the midbrain and pons.


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Internal Components of the Brainstem

● The reticular formation lies in the tegmentum of

the brainstem.

● The basilar areas lie anterior to the tegmentum.


13

Haines, Duane. Fundamental

Clinical Applications. 4th

Neuroscience For Basic And

ed.

Philadelphia: Elsevier, 2013. Fig.

10-218

Principles of Cranial NervesNuclei

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Importance of ThisSection

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● Understanding these principle enable the

student to understand the complexity of the

cranial nerves development, origin, structure,

and functions.

● This part is poorly understood by medical

students which results in difficulty in learning

about cranial nerves.

Classification of Cranial NervesComponents

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● There are some overlaps and exceptions!

● According to the direction of the component:

○ Afferent: means going from peripheral

tissues to the brain (inward signal).

○ Efferent: means going from the brain to

peripheral tissues (outward signal). [consider

Efferent=Exit to memorize].


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● According to the innervated tissue:

○ Somatic: innervates primarily

muscles, joints, tendons, skin,

somatic parts.

○ Visceral: innervates primarily

skeletal

and other

smoothmuscles, viscera, and glands.


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● According to the receptors and muscle:

○ General: standard afferents and efferents

going to different body parts.

○ Special: to the muscle from mesenchyme of

the branchial arches (muscles of

mastication) and from highly specialized

receptors (e.g.chemoreceptors).


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● Every component has one classification of the

each category.

● Examples of components:

○ General somaticefferent (GSE).

○ Specialvisceral efferents (SVE).

○ General visceralefferent (GVE).

○ General somaticafferent (GSA).

25Snell, R.S. Clinical Neuroanatomy. (7th ed.). Philadelphia: Lippincott Williams &

Wilkins; 2010. Table 11-1

26

Duane. FundamentalHaines,

Neuroscience For Basic And Clinical

Applications. 4th ed. Philadelphia: Elsevier,

2013. Fig. 10-7

Anatomy of the MedullaOblongata

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ExternalFeatures

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● It develops from the myelencephalon (lower

part of thehindbrain.

● Connected to the pons rostrally and to the

spinal cord caudally.

● It has a conical shape (broader superiorly).

● The junction between the spinal cord and the

medulla is at the origin of the first cervical

spinal nerve (level of foramen magnum).

● The central canal of the spinal cord continues

to the lower part of the medulla.

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ExternalFeatures

ExternalFeatures

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● The medulla is divided based on the presence

of the fourth ventricle into:

○ Caudal (closed) medulla

○ Rostral (open) medulla

Waxman, S.G. Clinical Neuroanatomy. (27th ed.).:

McGraw-Hill; 2013. Fig. 7-7B

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32Waxman, S.G. Clinical Neuroanatomy. (27th ed.).:

McGraw-Hill; 2013. Fig. 7-7C

ExternalFeatures

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● There is the anterior median fissure in the

anterior surface of the medulla.

● Lateral to the anterior median fissure lie the

medullary pyramids (containing the

corticospinal and corticobulbar tracts).

ExternalFeatures

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● The medullary olives lie posterolaterally to the

pyramids. They are produced by the inferior

olivary nuclei.

● The inferior cerebellar peduncles lie posterior

to the olives.

35Snell, R.S. Clinical Neuroanatomy. (7th ed.). Philadelphia:

Lippincott Williams & Wilkins; 2010. Fig. 5-9A

36

ExternalFeatures

● The posterior median sulcus lies in the posterior

part of the caudal medulla.

● Lateral to the posterior median sulcus in the

caudal medulla there are the gracile and

cuneate tubercles produced by the gracile and

cuneate nuclei, respectively.

37Snell, R.S. Clinical Neuroanatomy. (7th ed.). Philadelphia: Lippincott

Williams & Wilkins; 2010. Fig. 5-9B

Basics on the InternalFeatures

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● Medulla oblongata contains grey and white

matter.

● Sulcus limitans is important to differentiate

between sensory and motor nuclei.

Basics on the InternalFeatures

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● We divided the medulla anatomically into four

levels:

○ Level of pyramidal (motor) decussation

○ Level of lemniscus (sensory) decussation

○ Level of the olives (midmedullary level)

○ Level of pontomedullaryjunction

Level of PyramidalDecussation

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● Around 90% of corticospinal tracts fibers

decussate atthis level.

● The cuneate and gracile nuclei (posterior

column nuclei) appear at this level to their

respective fasciculi.

Level of PyramidalDecussation

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● The substantia gelatinosa of the spinal cord

becomes continuous with the spinal nucleus of

the trigeminal nerve.

● Fibers of the anterolateral system and fibers of

the spinal trigeminal tract lie adjecent to each

other in the lateral medulla.

Haines, Duane. Fundamental Neuroscience For Basic And Clinical

Applications. 4th ed. Philadelphia: Elsevier, 2013. Fig. 11-6

38

Level of LemniscusDecussation

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● The internal arcuate fibers (forming the medial

lemniscus) decussate at this level anterior to

central grey and posterior to the pyramids.

● The spinal nucleus of the trigeminal nerve lies

lateral to the internal arcuate fibers.

Level of LemniscusDecussation

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● The nucleus ambiguus lies medial to the spinal

trigeminal nucleus (SE components to the

glossopharyngeal and vagus nerves).

● The spinothalamic and spinotectal tracts lie

lateral to the lemniscus decussation.

45Haines, Duane. Fundamental Neuroscience For Basic And Clinical


Level of theOlives

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● Section at this level passes across the inferior

part of the fourth ventricle.

● Many cranial nerve nuclei appear at this level.

● The most prominent nuclei are the olivary

nuclear complex especially the inferior olivary

nucleus.

● The restiform body forms a prominent

elevation on the posterolateral aspect of the

medulla. It contains many cerebellar afferents.

● The spinal trigeminal tract and nucleus are

interior to the restiform body.

Level of theOlives

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48Haines, Duane. Fundamental Neuroscience For Basic And Clinical


Lesions of the MedullaOblongata

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Arnold-ChiariSyndrome

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● Congenital herniation of cerebellar tonsils and

medulla through the foramen magnum.

● Results in hydrocephalus and involvement of

the last four cranial nerves along with

cerebellar signs.

Lateral MedullarySyndrome

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● Also known as “Wallenberg’s syndrome”.

● Results from a vascular lesion of the vertebral

and posterior inferior cerebellar arteries.

● Signs and symptoms include:

○ Loss of pain and temperature on the

opposite side of the body and the ipsilateral

face

Lateral MedullarySyndrome

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○ Loss of coordination

○ Vertigo

○ Loss of the gag reflex

○ Difficulty with speech and swallowing

○ Horner’s syndrome


Lippincott Williams & Wilkins; 2010. Fig. 5-31

Medial MedullarySyndrome

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● Also known as the “Déjérine’s syndrome”.

● Results from damage to the medial branches of

the vertebral artery or the anterior spinal artery.

● Signs and symptoms include:

○ Contralateral hemiparesis.

Medial MedullarySyndrome

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○ Contralateral impaired prorioceptionand

tactile sensations

○ Ipsilateral paralysis of the tongue muscles

● In case of anterior spinal artery oclusion, signs

and symptoms may be bilateral


Lippincott Williams & Wilkins; 2010. Fig. 5-32

FurtherReadings

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● Sinnatamby, C.S. Last's Anatomy Regional and

Applied. (12th ed.). : Churchill Livingstone; 2011.

● Snell, R.S. Clinical Neuroanatomy. (7th ed.).

Philadelphia: Lippincott Williams & Wilkins; 2010.

FurtherReadings

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● Eljack, A. A. E. Eljack’s Lecture Notes in

Neuroscience. Khartoum; 2015.

● Siegel, A, Sapru, H.N. Essential Neuroscience.


Wilkins; 2015.

● Waxman, S.G. Clinical Neuroanatomy. (27th

ed.). :McGraw-Hill; 2013.

● Medical Neuroscience MOOC by Duke

University |Coursera.

● Haines, Duane. Fundamental Neuroscience For

Basic And Clinical Applications. 4th ed.

Philadelphia: Elsevier, 2013

FurtherReadings

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Brainstem - bowenstaff.bowen.edu.ng