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In vertebrates, the brain can be anatomically divided into the forebrain (also known as, prosencephalon), midbrain (also known as, mesencephalon) and hindbrain (also known as, rhombencephalon). These three primary brain vesicles are formed during the embryonic development of the nervous system.
Division of the Forebrain
The forebrain is divided into diencephalon and telencephalon. Let us look at them in detail.
Diencephalon
The diencephalon, also known as the interbrain, is located between the telencephalon and midbrain. It consists of the thalamus, hypothalamus, epithalamus and subthalamus. During the third week of embryo development, a neural tube develops from the ectoderm (one of the three germ layers) that gives rise to the three parts of the brain: prosencephalon, mesencephalon and rhombencephalon.
Structures of Diencephalon
- Thalamus: The thalamus is a large structure of grey matter that is situated in the posterior portion of the diencephalon. From the thalamus, nerve fibres project out to the cerebral cortex in all directions, which allows the exchange of information. Functions of the thalamus include relaying sensory information and the regulation of alertness, sleep and consciousness.
- Hypothalamus: The hypothalamus forms the ventral portion of the diencephalon that is almost almond sized in a human brain. It is found situated below the thalamus and also forms a part of the limbic system. The primary function of the hypothalamus is to connect the nervous system with the endocrine glands with the help of the pituitary gland. The pituitary gland is present as a projection at the bottom of the hypothalamus.
Other functions of the hypothalamus include the secretion of neurohormones that regulate the secretion of hormones from the pituitary gland, regulation of metabolic processes, and also control activities such as hunger, thirst, sleep, fatigue and circadian rhythms.
- Epithalamus: The epithalamus is located in the dorsal portion of the diencephalon. Components of the epithalamus include habenular commissure, habenular nuclei, stria medullaris and the pineal gland. The primary function of the epithalamus is to connect the limbic system with other parts of the brain. The components of the epithalamus secrete melatonin and hormones from the pineal gland, regulate emotions, and also look after energy conservation in the body.
- Subthalamus: The subthalamus, also known as the prethalamus, is located ventrally to the thalamus and laterally to the hypothalamus. It is formed by the nuclei of grey matter and their associated white matter structures.
Attachments to the Diencephalon
The optic nerve, which is a sensory nerve responsible for vision and light, is attached to the diencephalon. It extends from the eye via the optic canal in the skull and meets at the diencephalon.
Telencephalon
The telencephalon, also known as endbrain, forms the cerebrum in a fully developed brain. It is the largest part of the brain that consists of the cerebral cortex of both the cerebral hemispheres and other subcortical structures such as the hippocampus, olfactory bulb and basal ganglia. The primary function of the cerebrum is to control all voluntary actions in our body with the assistance of the cerebellum.
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Also Read:
- Difference between Cerebellum and Cerebrum
- Difference between Forebrain, Midbrain and Hindbrain
- Brain Diseases
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