1. Brain stem

2. Brain stem
Medulla oblongata
Pons
Midbrain

3. Brainstem Stalk like in shape
Connects spinal cord to higher centers of forebrain

4. Functions
Conduit for ascending and descending tracts connecting spinal cord and cortex
Contains reflex centers (cardiac and respiratory centers) levels of consciousness
Contains important nuclei of cranial nerves (3rd to 12th cranial nerves)

5. Origin of the 12 cranial nerves CEREBRUM 1 & 2 BRAINSTEM MIDBRAIN
3 & 4
PONS
5, 6, 7, & 8
MEDULLA
9, 10, 11 & 12
Accessory nerve (11th) has dual origin – Cranial & spinal root Only one nerve arise from dorsal aspect – Trochlear nerve (4th)

6. Medulla oblongata Most caudal level of the brain stem
Continuous with the spinal cord
Connects pons to spinal cord
Conical in shape
Cranial nerves VIII–XII attach to the medulla
Central canal of spinal cord continues into the lower medulla (close medulla)
Upper medulla contains cavity of 4th ventricle(open medulla)

10. Medulla Oblongata
Along with the pons, forms the ventral wall of the fourth ventricle
Contains a choroid plexus on the roof of the fourth ventricle
Pyramids – two longitudinal ridges formed by corticospinal tracts
Decussation of the pyramids – crossover points of the corticospinal tracts

11. Gross appearance (ant. surface)
Anterior median fissure
Pyramid – pyramidal decussation
Olives
Groove bt pyramid and olive (12th emerges)
Inferior cerebellar peduncle
Groove bt olive and ICP (10th 9th & cranial 11th emerge)

15. Gross appearance(post. Surface)
Floor of 4th ventricle (upper 1/2)
Posterior median sulcus
Gracile tubercle
Cuneate tubercle

16. Medulla ( post. View)

17. 10: Gracile tubercle
9: Cuneate tubercle
12: Posterior median sulcus

19. Internal structure
Level of decussation of pyramids(motor / close medulla)
Level of decussation of leminisci (sensory/ close medulla)
Level of olives (open medulla)

20. Level of decussation of pyramids

21. Level of decussation of pyramids
85% of Corticospinal
fibers decussate and
continue downward
as lat. Corticospinal
tract

22. Level of decussation of leminsci
Sensory decussation
Leminisci are formed by internal arcuate fibers
internal arcuate fibers emerge from anterior aspect of nucleus gracilis and nucleus cuneatus
Decussation takes place posterior to pyramids

23. Level of sensory decussation
1----ant. Median fissure
2-----post. Median sulcus
6-----nucleus gracile
7-----nucleus cuneatus
8-----int. arcute fibers
9---- decussation of medial leminiscus
10----pyramids

24. Medial leminiscus

25. Level of sensory decussation

27. Level of olives (open medulla)
Passes across the inferior part of 4th ventricle
Nuclei of 12th 11th 10th & 9th
Inf Olivary nucleus
Pyramids
ICP
Medial leminiscus RF
Spinal nucleus of trigeminal and its tract

28. Medulla Oblongata
Figure 12.16c

29. Olivary nuclear complex
Mainly Inf. Olivary nucleus
Gray matter is shaped like a crumpled bag with its mouth directed medially
Responsible of the elevation olive
Has communications with spinal cord, cerebellum & cortex
Function is associated with voluntary muscle movement

30. Medulla oblongata at the level of olives

31. Nucleus ambiguus Large motor neurons Situated deep in RF
Emerging fibers join 9th 10th cranial accessory
an elongated nucleus in the medulla oblongata that gives rise to the motor fibers of the glossopharyngeal, vagus, and accessory nerves supplying striated muscle of the larynx and pharynx

32. Central gray matter Lies beneath the floor of 4th ventricle
Passing from M to L:
Hypoglossal nucleus
Dorsal nucleus of vagus
Solitary nucleus
Vestibular nuclei

33. Others Pyramids (corticospinal&corticonuclear fibers)
Medial leminiscus
Medial longitudinal fasciculus
Inferior cerebellar peduncle
Reticular formation
9th 10th cranial 11th & 12th emerge at this section

34. Medial leminiscus
is a pathway in the brainstem that carries sensory information from the gracile and cuneate nuclei to the thalamus.

35. Medial longitudinal fasciculus
Small tract of nerve fibers
situated on each side of the midline
Posterior to med. Leminiscus
Anterior to 12th nucleus
It is composed largely of ascending fibers from the vestibular nuclei and cochlear nuclei ascending to the motor nuclei (third, fourth and sixth)

36. MLF

37. Spinal nucleus of trigeminal and its tract
Its found anteriomedial to ICP
Seen in all 3 levels of medulla

38. Level of olives 2--Floor of fourth ventricle 3---Hypoglossal nucleus
1--Inferior cerebellar peduncle
2--Floor of fourth ventricle
3---Hypoglossal nucleus
4---Medial longitudinal fasciculus
5---Reticular formation
6---Medial lemniscus
8---Inferior olivary nucleus
9----Pyramids

39. The Brain Stem – The Medulla Oblongata
The core of the medulla contains:
Much of the reticular formation
Nuclei influence autonomic functions
Visceral centers of the reticular formation include:
Cardiac center and Vasomotor center (adjusts force and rate of heart contraction)
The medullary respiratory center (control rate and depth of breathing)
Centers for hiccupping, sneezing, swallowing, and coughing

40. Reticular Formation Widespread connections
Arousal of the brain as a whole
Reticular activating system (RAS)
Maintains consciousness and alertness
Reticular formation The brainstem also contains networks of neurons,
known collectively as the reticular formation, that project up into the cerebral
cortex and basal ganglia and affect general arousal. The reticular formation is also
involved in inducing and terminating the different stages of sleep. The autonomy
of the brain stem can be dramatically illustrated by severing an animal’s brain
stem from the entire brain above it, including its entire cerebral cortex. Cats that
receive this treatment can still walk around and direct attacks at noises; if they
then find themselves holding on to food, they will eat it. Some cases have been reported
of humans born without cerebral cortices, and their behaviors are extremely
basic and reflexive. Such infants tend not to develop normally and also do
not tend to survive

41. Open medulla

42. Exam 1

44. Ventricles of Brain
Hollow chambers filled with CSF
Four ventricles:
(2) Lateral
(1) third ventricle
(1) fourth ventricle
Each lateral ventricle communicates with the third ventricle via a channel called an interventricular foramen (foramen of Monro)
Third ventricle is continuous with the fourth ventricle via the cerebral aqueduct

46. The central canal is the cerebrospinal fluid filled space that runs longitudinally through the length of the entire spinal cord
The central canal is continuous with the ventricles of the brain