page_title: Brainstem
section_title: Appearance
hierarchical_section_title: Brainstem / Structure / Appearance
caption_attribution_description: English: Anatomical dissections
context_page_description: The brainstem is the posterior part of the brain, continuous with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.
  The brainstem is a very small component of the brain, making up only around 2.6 percent of its total weight. It has the critical role of regulating cardiac and respiratory function, helping to control heart rate and breathing rate. It also provides the main motor and sensory nerve supply to the face and neck via the cranial nerves. Ten pairs of cranial nerves come from the brainstem. Other roles include the regulation of the central nervous system and the body's sleep cycle. It is also of prime importance in the conveyance of motor and sensory pathways from the rest of the brain to the body, and from the body back to the brain. These pathways include the corticospinal tract, the dorsal column-medial lemniscus pathway, and the spinothalamic tract.
context_section_description: From the front
  In the medial part of the medulla is the anterior median fissure.  Moving laterally on each side are the medullary pyramids.  The pyramids contain the fibers of the corticospinal tract (also called the pyramidal tract), or the upper motor neuronal axons as they head inferiorly to synapse on lower motor neuronal cell bodies within the anterior grey column of the spinal cord.
  The anterolateral sulcus is lateral to the pyramids.  Emerging from the anterolateral sulci are the CN XII (hypoglossal nerve) rootlets.  Lateral to these rootlets and the anterolateral sulci are the olives.  The olives are swellings in the medulla containing underlying inferior nucleary nuclei (containing various nuclei and afferent fibers).  Lateral (and dorsal) to the olives are the rootlets for CN IX (glossopharyngeal), CN X (vagus) and CN XI (accessory nerve).  The pyramids end at the pontine medulla junction, noted most obviously by the large basal pons.  From this junction, CN VI (abducens nerve), CN VII (facial nerve) and CN VIII (vestibulocochlear nerve) emerge.  At the level of the midpons, CN V (the trigeminal nerve) emerges.  Cranial nerve III (the oculomotor nerve) emerges ventrally from the midbrain, while the CN IV (the trochlear nerve) emerges out from the dorsal aspect of the midbrain.
  Between the two pyramids can be seen a decussation of fibers which marks the transition from the medulla to the spinal cord. The medulla is above the decussation and the spinal cord below.
  From behind
  The most medial part of the medulla is the posterior median sulcus.  Moving laterally on each side is the fasciculus gracilis, and lateral to that is the fasciculus cuneatus.  Superior to each of these, and directly inferior to the obex, are the gracile and cuneate tubercles, respectively.  Underlying these are their respective nuclei.  The obex marks the end of the fourth ventricle and the beginning of the central canal.  The posterior intermediate sulcus separates the fasciculus gracilis from the fasciculus cuneatus.  Lateral to the fasciculus cuneatus is the lateral funiculus.
  Superior to the obex is the floor of the fourth ventricle.  In the floor of the fourth ventricle, various nuclei can be visualized by the small bumps that they make in the overlying tissue.  In the midline and directly superior to the obex is the vagal trigone and superior to that it the hypoglossal trigone.  Underlying each of these are motor nuclei for the respective cranial nerves.  Superior to these trigones are fibers running laterally in both directions.  These fibers are known collectively as the striae medullares.  Continuing in a rostral direction, the large bumps are called the facial colliculi.  Each facial colliculus, contrary to their names, do not contain the facial nerve nuclei.  Instead, they have facial nerve axons traversing superficial to underlying abducens (CN VI) nuclei.  Lateral to all these bumps previously discussed is an indented line, or sulcus that runs rostrally, and is known as the sulcus limitans.  This separates the medial motor neurons from the lateral sensory neurons.  Lateral to the sulcus limitans is the area of the vestibular system, which is involved in special sensation.  Moving rostrally, the inferior, middle, and superior cerebellar peduncles are found connecting the midbrain to the cerebellum.  Directly rostral to the superior cerebellar peduncle, there is the superior medullary velum and then the two trochlear nerves.  This marks the end of the pons as the inferior colliculus is directly rostral and marks the caudal midbrain. Middle cerebellar peduncle is located inferior and lateral to the superior cerebellar peduncle, connecting pons to the cerebellum. Likewise, inferior cerebellar peduncle is found connecting the medulla oblongata to the cerebellum.
caption: The appearance of a cadaveric brainstem from behind, with major parts labelled.
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