Life Processes in Living Organisms — Science STD 9 — Question

• The brain is the main controlling part of the nervous system and is safely located in the cranial cavity.
• The brain is covered by protective layers called the Meninges.
• Cavities present in various parts of the brain are called ventricles.
• The ventricles are filled with cerebrospinal fluid. This fluid supplies nutrients to the brain and also protects it from shock.
• The brain of an adult human weighs about 1300 -1400 grams and consists of approximately 100 million neurons.
• The left side of our brain controls the right side of our body and right side of our brain controls left side of the body.
• In addition, the left side of the brain controls our speech and conversation, writing, logical thinking etc., whereas the right side controls artistic abilities.

Human brain is made up of following parts:

(a) Cerebrum:

• This is the largest part of the brain and consists of two cerebral hemispheres. These hemispheres are joined with each other with the help of tough fibres and nerve tracts.
• The cerebrum occupies two-thirds of the brain. Hence, it is also called as large brain.
• Its surface has deep, irregular ridges and grooves which are called convolutions, convolution increases the surface area of the cerebrum and therefore a large number of nerve cells can be accommodated.

(b) Cerebellum:

• This is the smaller part of the brain situated below the cerebrum at the back of the cranial cavity.
• Its surface shows shallow grooves instead of deep convolutions.

(c) Medulla Oblongata:

• This is the hind-most part of the brain.
• There are two triangular swollen structures called pyramids on the upper side of medulla oblongata.
• The medulla oblongata continues downwards the spinal cord.