Medulla oblongata

• internal anatomy of medulla oblongata is often studied at 3 distinct levels, each corresponding to specific anatomical landmarks and structures.

  • level of pyramidal decussation: most caudal lower levels. This decussation explains the contralateral control of motor functions by the brain.
  • level of decussation of leminisci (sensory decussation), slightly above pyramidal decussation. characterised by the crossing over of the internal arcuate fibers, which form the medial lemniscus.
  • level of olives: most upper level, where inferior olivary nuclei are located.
• • Medulla oblongata is divided by anterior and posterior median fissures into right and left half
  • Right and left half respectively are subdivided by anterolateral and posterolateral sulcu into
  • Anterior, lateral and posterior regions

  
• • Medulla oblongata is the lowest part of brainstem
  • Extends from lower border of pons to foramen magnum
  • lies in anterior part of posterior cranial fossa
  • Relations: anterior (clivus and meninges) posterior (valleculla of cerebellum)
  • medulla is divided into lower closed part with central canal and upper open part where central canal opens into 4 ventricle

  
• • Anterior region of medulla (anterior suf)
  • Has 2 longitudinal elevations: pyramids
  • pyramids are made up of corticospinal fibers
  • on lower medulla fibers of pyramids cross and decussates to opposite side forming pyramidal decussation. This decussation is the reason why each side of the brain controls the opposite side of the body.

  
• Lateral region of medulla

  • Upper part shows 2 elevations one on each side: olives
  • they are produced by the underlying grey matter nuclei: inferior olivary nuclei
  • rootlets of hypoglossal nerved emerge from anterolateral sulcus present btw pyramids and olives
  • rootlets of glossopharyngeal, vagus and cranial part of acessory n emerge through posterolateral fissure behind olives

  
• Posterior region of medulla oblongata

  • Lies btw posterolateral sulcus and posterior median sulcus
  • upoer part shows V-shape depression which corresponds to lower part of floor of fourth ventricle
  • bellow the floor, 3 longitudinal elevations are present:

  1. fasciculus grascilis
  2. Fasciculus cuneatus
  3. Inferior cerebellar peduncle

  • upper end of fasciculus gracilis and cuneatus expand to form fasciculus gracilis and cuneatus tubercles, which corresponds to underlying their underlying nuclei

  
• Pyramid - contains descending motor tracts that originate in the primary motor area of the frontal lobe and descend down the spinal cord. The pyramid is crossed, meaning that the left pyramid carries information about movement on the right side of the body, while the right pyramid carries information about movement on the left side of the body.
• Transverse section of medulla at level of pyramidal decussation

  • Resembles spinal cord grey matter distributions, on having anterior, lateral and posterior gray matter regions.

  
• Gracile nuclei

  • Medially located
  • Receives sensory information from lower body via gracile fasciculus
• Cuneate nuclei

  • Laterally to gracile nucleus
  • Receives sensory information from upper body via cuneate fasciculus
• Spinal trigeminal nuclei

  Extends into medulla from pons and continues down into cervical spinal cord<|>Processes pain and temperature sensations from face
• Spinal trigeminal tract


  Runs adjacent to spinal trigeminal nuclei<|>Carries afferent fibers to nucleus
• Spinal accessory n nuclei

  Nucleus gives rise to fibers of spinal accessory nerve<|>Innervates sternocleidomastoid and trapezius muscles
• Transverse section of medulla at pyramidal decussation

  Gray matter

  • Nucleus gracilis
  • Nucleus cuneatus
  • spinal trigeminal nuclei and tract
  • nucleus of spinal acessory nerve
  • reticular formation

  White matter:

  1. pyramids
  2. medial lemniscus
  3. spinothalamic tract
  4. anterior and posterior spinocerebellar tracts
  5. spinal trigeminal tracts
  6. fasciculus gracilis and cuneatus

  
• Medulla at level pf pyramidal decussation

  
• Medulla at sensory decussation

  • Sensory decussation (decussation of lemnisci): at level of closed medulla in posterior white column, nucleis gracilis and cuneatus are found
  • the 2 nuclei receives impulses from fasciculus gracilis and cuneatus. After the two tracts terminate upon these nuclei, heavily myelinated fibers arise and ascend anteromediallt around periaqueduct gray as internal arcuate fibers. These fibers decussate to contralateral side the so called sensory decussation, and ascend as medial leminiscus.

  
• White matter of medulla at sensory decussation

  • Fasciculus gracilis and cuneatus
  • inferior cerebellar peduncles
  • descending cerebellar tract
  • spinal trigeminal tract
  • Spinocerebellar tract: ventral + dorsal
  • olivo-spinal tract
  • spino-olivary tract
  • corticospinal tract
  • medial leminuscus
  • tectospinal tract
  • MLF
  • spinotectal tract
  • spinothalamic tract: lateral + ventral
  • vestibulospinal tract

  
• Medulla at level of inferior olivary nuclei

  Grey matter has the following nuclei

  • Nuclei of following cranial nerves: hypoglossal n, dorsal nucleus of vagus, nucleus of tractus solitarius, inferior and medial vestibular nuclei
  • Nucleus ambigous: lies deep in reticular formation. gives origin to motor fibers of glossopharyngeal, vagus, spinal accessory nerve.
  • dorsal n ventral cochlear nuclei
  • inferior olivary nuclei
  • medial and dorsal accessory olivary nuclei
  • arcuate nucleus.
  • viceral centers: respiratory center, cardiac center for regulation of HR.
  • vasomotor center for BP regulation.

  
• White matter of medulla at level of inferior olivary nuclei

  • Inferior cerebellar peduncles
  • olivocerebellar fibers
  • stria medularis
  • emerging fiber of glossopharyngeal, vagus, spinal acessory nerve
  • various ascending tracts.