Ans. BRAIN
In animals, all life activities are under the control of brain. The structure of brain is suitable to perform these functions.
i)Cranium
Brain is situated inside a bony cranium i.e., brain box, (part of skull).
.ii) Meninges
Inside cranium, brain is covered by three layers called meninges. Meninges protect brain and also provide nutrients and oxygen to brain tissue through their capillaries.
iii) Ventricles
The brain contains fluid-filled ventricles that are continuous with the central canal of spinal cord.
iv) Cerebrospinal fluid
Fluid within ventricles and central canal is called cerebrospinal fluid (CSF)
The Divisions of Brain •
There are three major regions in the brain of human and other vertebrates. These are forebrain, midbrain and hindbrain. Important parts of each of these regions are described below. Figure 12.3
Forebrain
Forebrain is the largest area of brain: It is most highly developed in humans.
Parts of Forebrain
Following are the important parts of forebrain.
Thalamus
Location ,
It lies just below the cerebrum.
Functions
It serves as a relay centre between various parts of brain and spinal cord. It also receives and modifies sensory impulses (except from nose) before they travel to cerebrum, Thalamus is also involved in pain perception and consciousness (sleep and awakening)
Figure12.3 Structure of human brain (longitudinal section to show internal parts)
ii) Hypothalamus Location
It lies above midbrain and just below thalamus.
Size
In humans, it is roughly the size of an almond.
Functions
One of the most important functions of hypothalamus is to link nervous system and endocrine system. It controls the secretions of pituitary gland. It also controls feelings such as rage, pain, pleasure and sorrow.
iii) Cerebrum
It is the largest part of forebrain.
Functions
It controls skeletal muscles, thinking, intelligence and emotions.
Division
It is divided into two cerebral hemispheres.
The anterior parts of cerebral hemispheres are called olfactory bulbs which receive impulses from olfactory nerves and create the sensation of smell.
The upper layer of cerebral hemispheres i.e. cerebral cortex consists of grey matter. The grey matter of nervous system consists of cell bodies and nonmyelinated axons. Beneath this layer is present the white matter. The white matter of nervous system consists of myelinated axbns. Cerebral cortex has a large surface area and is folded in order to fit in skull. It is divided into four lobes.