Medulla oblongata

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Brain: Medulla oblongata
1311 Brain Stem.jpg
Medulla oblongata purple, part of the brain stem colored
Gray694.png
Section of the medulla oblongata at about the middle of the olivary body.
Latin Medulla oblongata
Gray's p.767
Part of Brain stem
NeuroNames hier-695
MeSH Medulla+Oblongata
NeuroLex ID birnlex_957
TA A14.1.03.003
FMA FMA:62004

The medulla oblongata is the lower half of the brainstem, which is continuous with the spinal cord, the upper half being the pons. It is often referred to simply as the medulla. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and therefore deals with the autonomic (involuntary) functions of breathing, heart rate and blood pressure.

The bulb is an archaic term for the medulla oblongata and in modern clinical usage the word bulbar (e.g. bulbar palsy) is retained for terms that relate to the medulla oblongata, particularly in reference to medical conditions. The word bulbar can refer to the nerves and tracts connected to the medulla, and also by association to the muscles thus innervated, such as those of the tongue, pharynx and larynx.

Anatomy[edit]

Medulla oblongata (animation)
Medulla and parts (10-16) - (10) pyramid; (11) the anterior median fissure; (15) is the choroid plexus in the fourth ventricle; (13) olive and (7) the pons
Medulla-animated as it protrudes from the foramen magnum of the skull-base, after which it gives rise to the spinal cord.

The medulla can be thought of as being in two parts:

  • an open part or superior part where the dorsal surface of the medulla is formed by the fourth ventricle.
  • a closed part or inferior part where the fourth ventricle has narrowed at the obex in the caudal medulla, and surrounds part of the central canal.

External surfaces[edit]

The anterior median fissure (or ventral fissure) contains a fold of pia mater, and extends along the length of the medulla oblongata. It ends at the lower border of the pons in a small triangular area, termed the foramen cecum. On either side of this fissure is a raised area termed the pyramid of medulla oblongata. The pyramids house the pyramidal tracts - the corticospinal and the corticobulbar tracts of the nervous system. At the caudal part of the medulla these tracts cross over in the decussation of the pyramids obscuring the fissure at this point. Some other fibers that originate from the anterior median fissure above the decussation of the pyramids and run laterally across the surface of the pons are known as the external arcuate fibers.

The region between the anterolateral and posterolateral sulcus in the upper part of the medulla is marked by a pair of swellings known as olivary bodies. They are caused by the largest nuclei of the olivary bodies, the inferior olivary nuclei.

The posterior part of the medulla between the posterior median sulcus and the posterolateral sulcus contains tracts that enter it from the posterior funiculus of the spinal cord. These are the fasciculus gracilis, lying medially next to the midline, and the fasciculus cuneatus, lying laterally. These fasciculi end in rounded elevations known as the gracile and the cuneate tubercles. They are caused by masses of gray matter known as the nucleus gracilis and the nucleus cuneatus.

Just above the tubercles, the posterior aspect of the medulla is occupied by a triangular fossa, which forms the lower part of the floor of the fourth ventricle. The fossa is bounded on either side by the inferior cerebellar peduncle, which connects the medulla to the cerebellum.

The lower part of the medulla, immediately lateral to the fasciculus cuneatus, is marked by another longitudinal elevation known as the tuberculum cinereum. It is caused by an underlying collection of gray matter known as the spinal nucleus of the trigeminal nerve. The gray matter of this nucleus is covered by a layer of nerve fibers that form the spinal tract of the trigeminal nerve.

The base of the medulla is defined by the commissural fibers, crossing over from the ipsilateral side in the spinal cord to the contralateral side in the brain stem; below this is the spinal cord.

Blood supply[edit]

Blood to the medulla is supplied by a number of arteries.

Development[edit]

The medulla oblongata forms from the lower (caudal) half of the embryonic rhombencephalon. Neuroblasts from the alar plate of the neural tube at this level will produce the sensory nuclei of the medulla. The basal plate neuroblasts will give rise to the motor nuclei.

Function[edit]

The medulla oblongata connects the higher levels of the brain to the spinal cord, and is responsible for several functions of the autonomous nervous system, which include:

Clinical significance[edit]

A blockage (such as in a stroke) will injure the pyramidal tract, medial lemniscus, and the hypoglossal nucleus. This causes a syndrome called medial medullary syndrome.

Lateral medullary syndrome can be caused by occlusion of either the posterior inferior cerebellar artery or of the vertebral arteries.

In other animals[edit]

Both lampreys and hagfish possess a fully developed medulla oblongata.[2][3] Since these are both very similar to early agnathans, it has been suggested that the medulla evolved in these early fish, approximately 505 million years ago.[4] The status of the medulla as part of the primordial reptilian brain is confirmed by its disproportionate size in modern reptiles such as the crocodile, alligator, and monitor lizard.

Additional images[edit]

References[edit]

  1. ^ Hughes, T. (2003). "Neurology of swallowing and oral feeding disorders: Assessment and management". Journal of Neurology, Neurosurgery & Psychiatry 74 (90003): 48iii. doi:10.1136/jnnp.74.suppl_3.iii48.  [1]
  2. ^ Nishizawa H, Kishida R, Kadota T, Goris RC; Kishida, Reiji; Kadota, Tetsuo; Goris, Richard C. (1988). "Somatotopic organization of the primary sensory trigeminal neurons in the hagfish, Eptatretus burgeri". J Comp Neurol. 267 (2): 281–95. doi:10.1002/cne.902670210. PMID 3343402. 
  3. ^ Rovainen CM (1985). "Respiratory bursts at the midline of the rostral medulla of the lamprey". J Comp Physiol A. 157 (3): 303–9. doi:10.1007/BF00618120. PMID 3837091. 
  4. ^ Haycock, Being and Perceiving

External links[edit]