General principles of development and histogenesis
The formation of the brain is a regular process during which the initial cylindrical structure undergoes significant changes. The neural tissue itself develops intensively from the walls of the primary dilations.
With rapid cellular growth and an increase in tissue mass, the internal lumens of the rudiments relatively decrease in size. In the mature organ, these residual spaces persist and function as the brain ventricles and the connecting channels (aqueduct).
Transition from three vesicles to five
The morphological division of the cranial end of the neural tube occurs in two main stages:
- Three-vesicle brain stage. Primary separation occurs due to the formation of transverse constrictions. At this stage, three major segments are distinguished: the forebrain (Prosencephalon), midbrain (Mesencephalon), and hindbrain (Rhombencephalon).
- Five-vesicle brain stage. It arises at later stages due to the appearance of additional longitudinal bends. During this period, the terminal rudiments (anterior and posterior) divide in two. The middle vesicle does not undergo division and remains intact. As a result, five clearly separated parts are formed, giving rise to all structures of the mature brain.
Anatomical derivatives of the brain vesicles
The formed brain consists of five consecutive parts. Traditionally, they are examined in the caudal-to-cranial direction — i.e., from bottom to top, starting from the border with the spinal cord.
Hindbrain (in the broad sense)
Develops from the primary posterior vesicle (Rhombencephalon), whose common cavity transforms into the fourth ventricle.
- Medulla oblongata (Myelencephalon): is the direct anatomical continuation of the spinal cord, transitioning into the brainstem.
- Pons proper (Metencephalon): includes the pons (located ventrally) and the cerebellum (located dorsally).
Midbrain
Develops from the intact middle vesicle.
- Midbrain (Mesencephalon): consists of the cerebral peduncles and the tectal plate (corpora quadrigemina) located above them. The primary cavity of this region narrows significantly, turning into a narrow channel — the cerebral aqueduct.
Forebrain (in the broad sense)
Formed from the structures of the primary anterior vesicle (Prosencephalon).
- Diencephalon (Diencephalon): includes the hypothalamic region and the thalamus. The thalamus is a large paired cluster of gray matter. Its most important function is the relay of practically all sensory (afferent) pathways heading to higher cortical centers.
- Telencephalon (Telencephalon): gives rise to the cerebral hemispheres.
| Primary vesicle | 5-part stage | Main structures | Cavity |
|---|---|---|---|
| Hindbrain | Myelencephalon, Metencephalon | Medulla oblongata, pons, cerebellum | Fourth ventricle |
| Neuter | Mesencephalon | Cerebral peduncles, tectal plate | Cerebral aqueduct |
| Forebrain | Diencephalon, Telencephalon | Thalamus, hypothalamus, cerebral hemispheres | Ventricles of the brain |
Briefly: answers to topical questions
What structures develop from the diencephalon?
The following structures develop from the diencephalon (Diencephalon):
- Thalamus (thalamus);
- Epithalamus (epithalamus) — includes the pineal gland and habenular nuclei;
- Metathalamus;
- Subthalamus — includes the subthalamic nucleus;
- Hypothalamus (hypothalamus) — hypothalamic region.
What do the cavities of the prosencephalon turn into?
The cavities of the prosencephalon turn into the ventricles of the brain. In particular, they form:
- Lateral ventricles (I and II) — in both halves of the telencephalon (Telencephalon);
- Third ventricle (ventricle III) — in the diencephalon (Diencephalon).
What derivatives does the telencephalon give rise to?
The telencephalon (Telencephalon) is represented by the right and left cerebral hemispheres (hemispheria cerebri). It includes:
- Cerebral cortex (cortex cerebri, pallium) — the mantle;
- Rhinencephalon (rhinencephalon);
- Basal nuclei (nuclei basales) — subcortical nuclei;
- White matter — conduction pathways;
- Lateral ventricles (ventriculi laterales) — cavities of the telencephalon.
From which germ layer does the primary neural tube develop?
The primary neural tube develops from the ectoderm (neuroectoderm). During neurulation, under the inductive influence of the notochord, a neural plate forms in the ectoderm, which bends to form a neural groove, and then its edges close into a closed neural tube that separates from the surface ectoderm.
It is easy to remember the direction of differentiation of the forebrain vesicle: it gives rise to the "higher authorities" — the Diencephalon and Telencephalon.
Class and exam questions
What is the embryological origin of the neural tissue of the brain?
Neural tissue develops directly from the thickening walls of the brain vesicles, which form at the cranial end of the neural tube.
What do the cavities of the primary brain vesicles turn into?
They transform into the internal cerebrospinal fluid system: the brain ventricles and the connecting cerebral aqueduct. At the same time, the sizes of the cavities relatively decrease against the background of active neural tissue growth.
What structures develop from the mesencephalic vesicle?
The middle vesicle does not divide during the five-vesicle stage. The midbrain (Mesencephalon), which includes the cerebral peduncles and the tectal plate, is formed entirely from it.
What is the role of the thalamus, which develops from the diencephalon?
The thalamus is a large paired mass of gray matter that serves as the main relay station. It is the site where almost all afferent (sensory) pathways heading to higher brain centers are relayed.
What else to study on this topic
- Histogenesis of the cerebral cortex layers (Telencephalon)
- Development and differentiation of hypothalamic nuclei
- Formation of cerebellar structures from the dorsal part of the Metencephalon
- Mechanisms of formation of longitudinal flexures of the neural tube
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