What Is the Rhombencephalon?

In the embryonic development of vertebrates, at the beginning of neural tube formation, the anterior part was the brain-forming region, and soon it was divided into three brain vesicles arranged in tandem. Among them, the last one is Lingnao.

In the embryonic development of vertebrates, at the beginning of neural tube formation, the anterior part was the brain-forming region, and soon it was divided into three brain vesicles arranged in tandem. Among them, the last one is Lingnao.

Its lumen is the fourth ventricle. The rhombohedral brains are separated before and after, the front brain is the hind brain (narrow sense) and the rear brain is the medullary brain.

Chinese name

Lingao

Foreign name

rhombencephalon

Anatomy of rhomboid brain :

1. Ling cerebral vesicles:

The last cerebral vesicles are located at the 3 stages of the embryo. Connected directly to the spinal cord. As the lumen expands into the fourth ventricle, the roof expands and becomes thinner, participating in the formation of the choroid plexus. The wing plate develops into several sensory relay nuclei and olive nuclei in the medulla oblongata and pontine; the substrate develops into several motor nuclei. The limbic layer has cones of longitudinal fiber bundles descending the brain. The anterolateral region at the top of the rhombohedral brain is thickened, called the rhombic lip, which develops into the cerebellum; on the ventral side of the rhombohedral brain, there are transverse fibers (pontine cerebellar fibers) that connect to the brain to form a pontine.

2. Fourth ventricle:

The fourth ventricle is a rhombus-shaped cavity formed by the central tube of the rhombic brain, which is located behind the pons and the cerebellar vermiform. The fourth ventricle is divided into an upper angle, a lower angle, a parietal angle, and a lateral angle.

Upper corner: the third ventricle communicates with the middle cerebral water pipe.

Bottom corner: the central tube that leads to the lower segment of the medulla.

Roof: resembling a tent, with its spire facing the cerebellum. The ventral wall of the mouth is composed of the anterior medullar sail stretched between the left and right joint arms; the caudal wall is composed of the posterior medulla sail and the fourth ventricle choroidal tissue.

Lateral angle: The lateral angles extend to the sides first, and then cross the cord body and then turn to the ventral side to form a fourth ventricle lateral recess. Here, there is a fourth ventricle lateral hole that opens to the ventral side and leads to the arachnoid membrane through this hole. Lower cavity. Near the lower corner of the diamond-shaped fossa, there is a fourth ventricle median hole.

The fourth ventricle choroid plexus is divided into vertical and horizontal parts: the two horizontal parts extend to both sides in a horizontal position, and the outer ends protrude into the subarachnoid space through the lateral foramen. The two longitudinal parts are parallel to the caudal side, and the lower ends meet into the cerebellar medullary cistern through the median foramen.

Morphology of the rhombohedral brain :

The brain originates from the enlarged area at the head of the neural tube. At the end of the 4th week of the embryo, the head end of the neural tube swells to form three primitive brain vesicles, which are called forebrain, midbrain, and rhizome. The forebrain is the largest, and the left and right walls protrude outward into cysts, called eye blebs. By the 5th week, due to the imbalance between the growth of the head and the growth speed of the upper and lower brain walls, a midbrain flexion appeared in the midbrain region and flexed to the abdomen. At the same time, the forebrain is also differentiated into two parts, the telencephalon and the midbrain, and the telencephalon will mainly evolve into the cerebral hemisphere. The midbrain is the thalamus primordium. At the 6th week, the rhomboid brain also began to differentiate into the hindbrain and medulla. In morphology, it is clearly divided into five parts: telencephalon, mesobrain, midbrain, hindbrain, and medulla oblongata (terminal brain), which become the five-brain stage. At this time, cervical curvature appeared at the junction of the medulla oblongata and spinal cord, and pontine curvature was generated due to the uneven growth of the rhomboid brain area between the cervical curvature and the midbrain curvature. At 7-8 weeks, the hindbrain begins to differentiate into the pontine and cerebellum. The cavity in each of the above brain vesicles changes with the thickening and development of the brain wall, and later forms the ventricle.

When the brain begins to develop, its basic structure is similar to that of the early spinal cord. In addition to the top and bottom of the brain wall, there are bounding grooves on the inner side of the side wall to divide it into the dorsal flank and the abdomen's basement. The base plate terminates at its leading edge, so the mesencephalon and telencephalon are almost entirely composed of wing plates. Neuroblasts in the wing plate differentiate into sensory nucleuses in the brain; differentiation in the substrate into motor nucleuses. These nuclei, like gray matter columns in the spinal cord, mostly extend into cell columns. According to the nature of the nucleus, the motor nucleus of the brain can be divided into three types: the somatic effervescent nucleus that dominates the somatic muscles, and the general visceral effervescent nucleus that governs smooth muscle, myocardial, and glandular activity, namely the parasympathetic nucleus And special visceral effervescent nuclei that dominate the muscles of the gill arch (chewing muscle, facial muscle, and laryngeal muscle, etc.). Sensory nuclei are divided into four categories: general somatic afferent nuclei that accept somatic sensory impulses; special somatic afferent nuclei that accept impulses from a hearing device; general visceral afferent nuclei that accept visceral impulse and accept Special viscera is passed into the nucleus. If the boundary ditch is used as the center line, the order of the above-mentioned nucleus groups is: visceral nucleus is located inside, close to the boundary ditch; somatic nucleus is located outside, away from the boundary ditch.