Embryology · Nervous system and senses
Brain vesicles: from three to five and what each becomes !
- Embryonic structure
The head end of the neural tube swells into three vesicles that then split into five; the whole brain grows from them.
Updated 2026-11-01
See it in 3D: Midbrain · Pons · Medulla oblongata · Cerebellum · Thalamus · Hypothalamus · Pineal gland · Frontal lobe · Lateral ventricles · Third ventricle · Cerebral aqueduct · Fourth ventricle
What it is
The brain vesicles are the swellings of the cranial end of the neural tube. Three primary vesicles are present in week 4 and five secondary vesicles by week 5, each with an adult fate and a cavity that becomes a ventricle. This sequence explains brain anatomy, the ventricular system and malformations such as holoprosencephaly.
Key facts
- Week 4: after the anterior neuropore closes, the prosencephalon, mesencephalon and rhombencephalon form.
- Week 5: the prosencephalon splits into telencephalon and diencephalon, the rhombencephalon into metencephalon and myelencephalon; the mesencephalon does not split.
- The lumen of the neural tube persists as the ventricular system and, in the cord, as the central canal.
- Three flexures appear: cephalic (at the midbrain), cervical (between hindbrain and cord) and pontine.
- The optic vesicles bud from the diencephalon: the retina and optic nerve are, by origin, part of the brain.
- The brainstem (midbrain, pons, medulla) keeps alar and basal plates like the cord; the hemispheres and cerebellum expand mainly the alar plates.
Structure
- A wall with three layers: ventricular (proliferating neuroepithelium), mantle (future gray matter) and marginal (future white matter).
- In the brainstem the sulcus limitans separates the alar plate (sensory, dorsal) from the basal plate (motor, ventral).
- The rhombencephalic isthmus marks the midbrain–hindbrain boundary, a key organizing center.
What it becomes
- Telencephalon: cerebral hemispheres, basal nuclei, olfactory bulbs.
- Diencephalon: thalamus, hypothalamus, epithalamus with the pineal gland, neurohypophysis, retina and optic nerve.
- Mesencephalon: adult midbrain (superior and inferior colliculi, cerebral peduncles).
- Metencephalon: pons and cerebellum.
- Myelencephalon: medulla oblongata.
From primary vesicle to adult structure
| Primary | Secondary | Adult structures | Cavity |
|---|---|---|---|
| Prosencephalon | Telencephalon | Hemispheres, basal nuclei | Lateral ventricles |
| Prosencephalon | Diencephalon | Thalamus, hypothalamus, neurohypophysis, retina | Third ventricle |
| Mesencephalon | Mesencephalon | Midbrain (colliculi, peduncles) | Cerebral aqueduct |
| Rhombencephalon | Metencephalon | Pons, cerebellum | Fourth ventricle (upper part) |
| Rhombencephalon | Myelencephalon | Medulla oblongata | Fourth ventricle (lower part) |
| Caudal neural tube | (no vesicle) | Spinal cord | Central canal |
Markers
- SHH
- FGF8
- OTX2
- GBX2
- EN2
- HOX
Clinical notes
- If the prosencephalon fails to split into two hemispheres, holoprosencephaly results.
- A narrow aqueduct (midbrain) is the most common cause of congenital hydrocephalus.
- Defects of the hindbrain and cerebellum underlie Chiari and Dandy–Walker malformations.
Test yourself
Think of the answer, then tap the question to see it.
Which secondary vesicle gives rise to the pons and cerebellum?
The metencephalon, the cranial part of the rhombencephalon.
Which primary vesicle does not subdivide, and what cavity does it leave?
The mesencephalon; its lumen narrows into the cerebral aqueduct.
Which vesicle do the retina and neurohypophysis come from?
The diencephalon: the optic vesicle and the infundibulum are outgrowths of its wall.
In which weeks do three vesicles become five?
The three primary vesicles are seen in week 4 and the five secondary vesicles in week 5.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
- Midbrain
- Pons
- Medulla oblongata
- Cerebellum
- Thalamus
- Hypothalamus
- Pineal gland
- Frontal lobe
- Lateral ventricles
- Third ventricle
- Cerebral aqueduct
- Fourth ventricle
Related
- Neurulation and closure of the neural tube
- Spinal cord: alar and basal plates and the ascent of the cord
- Ventricles and cerebrospinal fluid
- Holoprosencephaly
- Neural tube defects: anencephaly, spina bifida and encephalocele
- Eye: optic vesicle, optic cup and lens
- Pituitary gland: Rathke pouch and the neurohypophysis
Related conditions
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: 13.1 The Embryologic Perspective - Anatomy and Physiology 2e (OpenStax, 2022); Fetal development: MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine, 2024); Langman's Medical Embryology, 13th ed., ch. 18: Central Nervous System (Wolters Kluwer, 2015).
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Representative model, for educational purposes only.