3. LECTURE NO 12 THE BRAINSTEM MEDULLA OBLONGATA
ANATOMY IV (Neuroanatomy)

4. CHAPTER OBJECTIVE
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.

8. THE BRAIN STEM
MEDULLA OBLONGATA

9. MEDULLA OBLONGATA 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.

10. Continue… Medulla oblongata is conical in shape.
The central canalof spinal cord continues upward in the lower half of medulla.
In the upper half of the medulla it expand as the cavity of the fourth ventricle.

13. Funiculus: A slender cordlike strand or band, especially a bundle of nerve fibers in a nerve trunk

14. GROSS APPEARANCE ANTERIOR SURFACE
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.

16. GROSS APPEARANCE ANTERIOR SURFACE
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.

20. GROSS APPEARANCE ANTERIOR SURFACE
In the groove b/w the olive and the inferior cerebellar peduncles emerge the root of Glossopharyngeal, Vagus & Cranial roots of the Accessory nerve.

23. GROSS APPEARANCE POSTERIOR SURFACE
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.

24. Cuneate tubercle
Gracile tubercle
Posterior median sulcus

26. INTERNAL STRUCTURE OF MEDULLA
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).

27. 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.

30. LEVEL OF DECUSSATION OF PYRAMIDS
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.

31. 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. 

32. The lateral corticospinal tract (also called the crossed pyramidal tract or lateral cerebrospinal fasciculus) is the largest part of the corticospinal tract. 
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).

34. continue
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.

35. SUBSTANTIA GELATINOSA
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.

36. ASCENDING TRACTS

37. Typically, the perception of pain travels through three orders of neurons.
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.

38. Major Sensory or Ascending Tracts
Name
Location
Function
Fasciculus gracilis
Posterior Column
Discriminative touch, proprioception
Weight discrimination
Fasciculus Cuneatus
Posterior
Column
Same as FG
Lateral Spinothalamic
Lateral
Pain and Thermal sensations
Anterior Spinothalamic
Anterior
Itch, Tickle, Pressure, Crude touch sensations
Posterior and Anterior Spinocerebellar
Proprioceptors

40. 2. LEVEL OF DECUSSATION OF LEMINISCUS
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.

41. 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.

43. 3. LEVEL OF THE OLIVES
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
Olivary nuclear complex
Nuclei of vestibulocochlear
Nucleus ambiguus
Glossopharyngeal, Vagus, accessory and hypoglossal nerve and the arcuate nuclei.

44. 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.

45. 3. LEVEL OF THE OLIVES

46. 3. LEVEL OF THE OLIVES Function 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

48. Spino-Olivary Tracts

49. 3. LEVEL OF THE OLIVES Nuclei of vestibulocochlear
Medial vestibular nucleus
Inferior vestibular nucleus
Lateral vestibular nucleus
Superior vestibular nucleus

51. 3. LEVEL OF THE OLIVES 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.

53. 4. LEVEL JUST INFERIOR TO THE PONS
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.

55. END OF NEUROANATOMY LECTURE 12