Medulla oblongata

1. Medulla

2. Location
• Part of brainstem
• Lower part of brainstem
• Between pons and spinal cord
• Part of Rhombencephalon
• Hindbrain
• Pons, medulla & cerebellum
• Lies
• Above spinal cord
• Below Pons
• Anterior to cerebellum

3. Extent
• Superiorly
• Pontomedullary sulcus
• Inferiorly
• Lower extent of pyramidal
decussation
• Through foramen magnum
to the level of the atlas

4. External features
• Ventral surface
• Ventral median fissure
• Pyramid
• Olive
• Nerves emerging
• Hypoglossal (12th)
• Sulcus between pyramid & olive
• Glossopharyngeal (9th), Vagus
(10th) & cranial part of accessory
(11th)
• Sulcus dorsolateral to olive

5. External features
• Dorsal surface
• Differ in
• Caudal part (closed medulla)
• Cranial part (open medulla)

6. Medulla - Closed
• Cavity
• Central canal
• Dorsal median sulcus
• Divides medulla into 2 halves
• Fasciculus gracilis
• On either side of dorsal median sulcus
• Gracile tubercle
• An elevation produced at upper part of fasciculus
gracilis,
• Site of gracile nucleus
• Fasciculus cuneatus
• On either side of fasciculus gracilis
• Cuneate tubercle
• An elevation produced at the upper part of
fasciculus cuneatus
• Site of cuneate nucleus
Lateral to cuneate tubercle
Tuber cinereum
Spinal nucleus of V nerve is present

7. Medulla - open
• Cavity
• 4th ventricle
• Caudal 1/3rd of floor of 4th ventricle
• On either side of median sulcus
• An inverted V-shaped sulcus divides
the area into 3 parts
• From medial to lateral
• Hypoglossal triangle
• Overlies hypoglossal nucleus
• Vagal triangle
• Overlies dorsal vagal nucleus
• Vestibular area
• Overlies vestibular nuclei

8. Internal structure
• 2 important events happen by white
matter
• Pyramid decussation
• Sensory decussation
• By this action
• Grey matter is subdivided

9. Pyramidal system
• Primary system of voluntary movements
• Upper motoneurons are located in cerebral
cortex
• Lower motoneurons can be found in
• Motor nuclei of cranial nerves or in spinal ventral
horn
• Descending axons of upper motoneurons that
terminate in
• Motor nuclei of cranial nerves constitute
• Corticonuclear Tract
• Motor nuclei of Spinal cord constitute
• Corticospinal tracts
• Corticonuclear tract reaches the lower
motoneurons of both sides (bilateral
innervation)
• While corticospinal fibres target the lower
motoneurons of the opposite side only
(crossed pathway)

10. Rubrospinal Tract
• Origin
• From red nucleus
• Located in midbrain
• Termination
• Lateral column of spinal cord
• Seen at
• Lower midbrain
• Pons
• Medulla

11. Tectospinal Tract
• Origin
• Superior colliculus of midbrain
• Termination
• Anterior Column
• Function
• Motor function of the Skeletal muscles
of the head and eyes in response to
visual stimuli

12. Dorsal system
• Medial lemniscus
• Carry dorsal column modalities
• From contralateral side
• Can be seen
• Upper medulla
• Pons
• Midbrain

13. Anterolateral system
• Spinal lemniscus
• Carry contralateral
• Anteior spinothalamic
• Crude touch
• Lateral spinothalamic
• Pain & temperature
• Can be seen
• Medulla
• Pons
• Midbrain

14. Spinocerebellar tracts
• Carry impulses of a subconscious
level
• Fibres of spinocerebellar tracts form
dorsal and ventral tracts
• Carry information derived from muscle
spindles, Golgi tendon organs and
tactile receptors to the cerebellum

15. Dorsal (Direct) Spinocerebellar tract
• Fibers originate from the cells of
Clarke's column
• At base of posterior horn
• Axons ascend ipsilaterally to
enter the cerebellum through
inferior cerebellar peduncle

16. Ventral (Indirect) Spinocerebellar Tract
• Fibers of ventral spinocerebellar
tract decussate
• Ascend on contralateral side of cord
• Enter the cerebellum via
• Superior cerebellar peduncle
• Some axons then recross within the
cerebellar white matter

17. Grey matter - At pyramidal (motor) decussation level
• Central canal present
• Anterior horn of grey matter
• Cut off from remaining grey matter by
• Fibres of pyramidal decussation
• Becomes accessory nerve nucleus
• Posterior grey horn shows
• 2 projections
• Nucleus gracilis – medially
• Nucleus cuneatus – laterally

18. White matter - At pyramidal (motor) decussation level
• Dorsal side
• Fasciculus gracilis, fasciculus cuneatus
& spinal tract of trigeminal
• Lateral side
• Lateral corticospinal tract
• Anterior side
• Pyramid & its decussation

19. At the level of sensory decussation
• Fibres arising from nucleus gracilis
and nucleus cuneatus
• They cross the midline
• Known as internal arcuate fibres
• And turn upwards as medial lemniscus
of the opposite side
• Nucleus gracilis, cuneatus & nucleus
of trigeminal nerve get detached
from central grey matter

20. Grey matter - At sensory decussation level
• Nuclei present in central grey matter
• Hypoglossal
• To tongue muscles
• Dorsal nucleus of vagus
• Gives parasympathetic fibres to
• Heart, Lungs & abdominal organs
• Nucleus tractus solitaries
• Receives gustatory fibres from tongue
• Through VII, IX & X

21. Grey matter - At sensory decussation level
• Nuclei in dorsal side
• Nucleus gracilis & Nucleus cuneatus
• More prominent
• Accessory cuneatus
• Dorsolateral to cuneatus
• Receives
• Lateral fibres of fasciculus cuneatus
• Sends fibres to
• Posterior external arcuate fibers
• Spinal nucleus of trigeminal
• Nucleus ambiguus
• Lies between
• Nucleus of trigeminal & central grey matter
• Supplies
• Muscles of palate pharynx & larynx
• Through IX, X & cranial accessory

22. Grey matter - At sensory decussation level
• At ventral side
• Inferior olivary nucleus

23. White matter - At sensory decussation level
• Fasciculus gracilis & cuneatus
terminates
• Internal arcuate fibres
• Medial longitudinal fasciculus
• Connect the cranial nerve nuclei of
• 3rd, 4th, 6th , 8th &spinal nucleus of XI
• Spinocerebellar & lateral
spinothalamic tracts
• Pyramids

24. Grey matter – Inferior olivary level
• In dorsal part
• Central grey matter spread over floor of
IV ventricle
• Hypoglossal nucleus
• Dorsal nucleus of vagus
• Nucleus tractus solitaries
• Vestibular nucleus (inferior & medial)
• Spinal nucleus of trigeminal

25. Grey matter – Inferior olivary level
• In middle part
• Nucleus ambiguus
• Lies in deep part of reticular formation
• Gives fibres to
• CN 9,10 & 11
• Olivary complex
• Inferior olivary
• Dorsal accessory olivary
• Medial accessory olivary
• In anterior part
• Arcuate nucleus
• Displaced pontine nucleui
• Lies anteromedial part of pyramid

26. White matter – Inferior olivary level
• On either side of midline
• From dorsal to ventral
• Medial longitudinal fasciculus
• Tecto spinal tract
• Medial leminiscus
• Pyramidal tract
• Lateral part
• Lateral spinothalamic
• Spino cerebellar
• Posterolateral
• Inferior cerebellar peduncle

27. Autonomic centres in medulla
• Cardioinhibitory and
cardiostimulatory centers
• Affect the rate and force of cardiac
contraction
• Vasomotor centers
• Affect smooth muscle fibers tone
• Respiratory center

28. Other centres
• Emesis
• Deglutition
• Coughing
• Hiccupping
• Sneezing

29. Blood supply
• Ventrally by
• Branches of vertebral and basilar arteries
• Supply region next to midline
• i.e. the part containing pyramid, medial
lemniscus and hypoglossal nucleus
• Laterally and dorsally by
• Posterio-inferior cerebellar artery
• Lateral and dorsal sides

30. Medial medullary syndrome
• Due to loss of blood supply to
ventral side
• Structures affected
• Pyramid
• Medial lemniscus
• Hypoglossal nucleus
• Resulted in
• Paralysis of tongue on same side
• Hemiplegia (crossed pyramid
damage)
• Loss of touch and kinaesthetic sense
on the opposite side ( medial
lemniscus damage)

31. Lateral medullary syndrome
• Loss of blood supply to lateral area

32. Lateral medullary syndrome
• Loss of nucleus ambiguus
• Paralyses of laryngeal, palatal and
pharyngeal muscles on that side,
causing dysphonia and dysphagia
• Loss of uncrossed spinal tract of
the trigeminal and of crossed
spinal lemniscus
• Loss of pain and temperature
sensation on the same side of face
and opposite side of the body

33. Lateral medullary syndrome
• Involvement of vestibular nuclei
• Causes vertigo and nystagmus with
nausea and vomiting