The document provides a comprehensive overview of the brainstem, particularly the medulla oblongata, including its anatomy, functions, cranial nerves, and clinical syndromes associated with it. It details the internal and external structures of the brainstem and highlights important clinical conditions such as Arnold-Chiari syndrome and lateral medullary syndrome. The document serves as an educational resource for understanding cranial nerve classification and the complexities of the brainstem's development and function.

1. Brainstem (1)
Overview & Medulla Oblangata
By: Ahmed A. E. Eljack

2. Objectives
By the end of this session you should be able to:
● Describe the brainstem, its internal and
external parts, and its anatomical relations.
● List the major functions of the brainstem.
● Describe the development of the brainstem.
2

3. 3
Objectives
● Mention the different components of cranial
nerves.
● Describe the location and external features of
the medulla oblangata.

4. 4
Objectives
● Describe the internal structure of the medulla
oblangata at different levels of section
● Mention the important clinical syndromes
affecting the medulla oblongata and their
clinical features.

5. General Information on the
Brainstem
5

6. Definition and Relations
● 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)
6

7. 7
Definition and Relations
○ 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.

8. Definition and Relations
● It’s composed of three parts mainly:
○ Midbrain.
○ Pons.
○ Medulla oblongata.
● The cerebellum is considered a part of the
brainstem in some references.
8

9. Eljack’s Lecture Notes in Neuroscience. Fig. 4-1
©2015 all rights reserved 9

10. Siegel, A, Sapru, H.N. Essential Neuroscience.
(3rd ed.). Philadelphia: Lippincott Williams &
Wilkins; 2015. Fig. 9-1 10

11. External Features of the Brainstem
● 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
has parallel horizontal fibers.
11

12. ● 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 the Brainstem
12

13. Eljack’s Lecture Notes in Neuroscience. Fig. 4-1
©2015 all rights reserved 13

14. Siegel, A, Sapru, H.N. Essential Neuroscience.
(3rd ed.). Philadelphia: Lippincott Williams &
Wilkins; 2015. Fig. 9-1 14

15. Internal Structures of the Brainstem
● 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.
15

16. 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.
16
Internal Structures of the Brainstem

17. 17
Internal Components of the
Brainstem
● The reticular formation lies in the tegmentum of
the brainstem.
● The basilar areas lie anterior to the tegmentum.
Internal Structures of the Brainstem

18. Haines, Duane. Fundamental
Neuroscience For Basic And
Clinical Applications. 4th ed.
Philadelphia: Elsevier, 2013. Fig.
10-2
18

19. Principles of Cranial Nerves Nuclei
19

20. Importance of This Section
● 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.
20

21. Classification of Cranial Nerves Components
● 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].
21

22. Classification of Cranial Nerves Components
● According to the innervated tissue:
○ Somatic: innervates primarily skeletal
muscles, joints, tendons, skin, and other
somatic parts.
○ Visceral: innervates primarily smooth
muscles, viscera, and glands.
22

23. Classification of Cranial Nerves Components
● 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).
23

24. Classification of Cranial Nerves Components
● Every component has one classification of the
each category.
● Examples of components:
○ General somatic efferent (GSE).
○ Special visceral efferents (SVE).
○ General visceral efferent (GVE).
○ General somatic afferent (GSA).
24

25. 25
Snell, R.S. Clinical Neuroanatomy. (7th ed.). Philadelphia: Lippincott Williams &
Wilkins; 2010. Table 11-1

26. 26
Haines, Duane. Fundamental
Neuroscience For Basic And Clinical
Applications. 4th ed. Philadelphia: Elsevier,
2013. Fig. 10-7

27. Anatomy of the Medulla Oblongata
27

28. 28
External Features
● It develops from the myelencephalon (lower
part of the hindbrain.
● Connected to the pons rostrally and to the
spinal cord caudally.
● It has a conical shape (broader superiorly).

29. 29
● 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.
External Features

30. 30
External Features
● The medulla is divided based on the presence
of the fourth ventricle into:
○ Caudal (closed) medulla
○ Rostral (open) medulla

31. 31
Waxman, S.G. Clinical Neuroanatomy. (27th ed.).:
McGraw-Hill; 2013. Fig. 7-7B

32. 32Waxman, S.G. Clinical Neuroanatomy. (27th ed.).:
McGraw-Hill; 2013. Fig. 7-7C

33. 33
External Features
● 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).

34. 34
External Features
● 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.

35. 35
Snell, R.S. Clinical Neuroanatomy. (7th ed.). Philadelphia:
Lippincott Williams & Wilkins; 2010. Fig. 5-9A

36. 36
External Features
● 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.

37. 37
Snell, R.S. Clinical Neuroanatomy. (7th ed.). Philadelphia: Lippincott
Williams & Wilkins; 2010. Fig. 5-9B

38. 38
Basics on the Internal Features
● Medulla oblongata contains grey and white
matter.
● Sulcus limitans is important to differentiate
between sensory and motor nuclei.

39. 39
Basics on the Internal Features
● 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 pontomedullary junction

40. 40
Level of Pyramidal Decussation
● Around 90% of corticospinal tracts fibers
decussate at this level.
● The cuneate and gracile nuclei (posterior
column nuclei) appear at this level to their
respective fasciculi.

41. 41
Level of Pyramidal Decussation
● 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.

42. 42
Haines, Duane. Fundamental Neuroscience For Basic And Clinical
Applications. 4th ed. Philadelphia: Elsevier, 2013. Fig. 11-6

43. 43
Level of Lemniscus Decussation
● 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.

44. 44
Level of Lemniscus Decussation
● 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.

45. 45
Haines, Duane. Fundamental Neuroscience For Basic And Clinical
Applications. 4th ed. Philadelphia: Elsevier, 2013. Fig. 11-8

46. 46
Level of the Olives
● 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.

47. 47
● 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 the Olives

48. 48
Haines, Duane. Fundamental Neuroscience For Basic And Clinical
Applications. 4th ed. Philadelphia: Elsevier, 2013. Fig. 11-11

49. 49
Lesions of the Medulla Oblongata

50. 50
Arnold-Chiari Syndrome
● 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.

51. 51
Lateral Medullary Syndrome
● 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

52. 52
Lateral Medullary Syndrome
○ Loss of coordination
○ Vertigo
○ Loss of the gag reflex
○ Difficulty with speech and swallowing
○ Horner’s syndrome

53. 53
Snell, R.S. Clinical Neuroanatomy. (7th ed.). Philadelphia:
Lippincott Williams & Wilkins; 2010. Fig. 5-31

54. 54
Medial Medullary Syndrome
● 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.

55. 55
Medial Medullary Syndrome
○ Contralateral impaired prorioception and
tactile sensations
○ Ipsilateral paralysis of the tongue muscles
● In case of anterior spinal artery oclusion, signs
and symptoms may be bilateral

56. 56
Snell, R.S. Clinical Neuroanatomy. (7th ed.). Philadelphia:
Lippincott Williams & Wilkins; 2010. Fig. 5-32

57. Further Readings
● 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.
57

58. Further Readings
● Eljack, A. A. E. Eljack’s Lecture Notes in
Neuroscience. Khartoum; 2015.
● Siegel, A, Sapru, H.N. Essential Neuroscience.
(3rd ed.). Philadelphia: Lippincott Williams &
Wilkins; 2015.
58

59. ● 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
Further Readings
59