THE BRAIN
In proportion to the size of the body, the human brain is
the largest among all animals. The brain is a very delicate organ well protected
inside the brain box (cranium) of the skull.
Bulk- The adult brain weighs about 1.35 kg and constitutes about 2% of the total body weight.
It is 80% water and consumes more than 25% (one-fourth) of
the total oxygen taken into the body.
Coverings (Meninges)- The brain is protected by 3 membranous coverings called meninges which continue backwards on the spinal cord.
Dura mater - the
outermost tough fibrous membrane.
Arachnoid - the
thin delicate middle layer giving a web-like cushion.
Pia mater- the
innermost highly vascular membrane, richly supplied with blood.
The space between the covering membranes is filled with a watery fluid-cerebrospinal fluid which acts like a cushion to protect the brain from shocks. The same fluid also fills the central spaces (ventricles) of the brain and the central canal of the spinal cord.
PARTS OF THE BRAIN
The brain has three main parts visible externally,
(1) cerebrum, (2) cerebellum and (3) medulla oblongata.
CEREBRUM (“Brain”)
The cerebrum is the largest portion of the brain.
➤It is divided into two (right and left) halves called
cerebral hemispheres. Their outer surface is highly convoluted with ridges and
grooves.
➤Each cerebral hemisphere is hollow internally and the
walls have two regions- an outer (cortex) and an inner portion (medulla).
➤The outer portion (cortex) of the cerebrum contains cell
bodies of the neurons and, being grayish in colour, is called the gray matter.
➤It is the layer of gray matter which is folded to form
the convolutions. The folds are called gyri and the grooves are called sulci
(creases). Such a system increases surface area to accommodate more nerve
cells.
➤It is believed that the higher number of convolutions in
the human brain is due to the larger number of brain (nerve) cells and hence greater
intelligence.
➤The inner portion of the cerebrum consists of “white
matter” which mainly contains the axons (nerve fibres) of the neurons.
➤Corpus callosum (“hard body”) is a sheet of fibres
connecting the two cerebral hemispheres. Its function is to transfer information
from one hemisphere to the other.
The highly developed cortex (gray matter) enables us to think, reason out, invent, plan and memorise. Overall, the cerebrum is the seat of intelligence, consciousness and will-power. It controls all voluntary actions.
What is generally called the subconscious or unconscious mind is also located in the cerebrum. Many past experiences are covered up by more recent impressions which dominate conscious activity.
In dreams or when hypnotised and skilfully questioned, past experiences may be recalled.
CEREBELLUM (“Little Brain”)
The cerebellum is a much smaller area of the brain located just at the base and under the large cerebrum. It has no convolutions, but has numcrous furrows. This also has an outer cortex made of gray matter. Centrally, it has white matter which, in a median section, appears like a branching tree.
The main function of the cerebellum is to maintain ‘balance’ of the body and coordinate muscular activity. The impulse for performing a muscular act, originates in the cerebrum and not in the cerebellum. for example- if you stand up and walk, the impulse for this activity arises in the cerebrum (conscious part). The act of walking involves coordinated working of many muscles. Proper coordination and timing of their contraction and relaxation is the responsibility of the cerebellum.
MEDULLA OBLONGATA
The medulla oblongata is the lowest portion of the brain
located at the base of the skull. It is roughly triangular and is continued
behind as the spinal cord. Its function is to control the activities of the internal
organs, for example- peristaltic movement of the alimentary canal,
movement of breathing, beating of the heart and many other involuntary actions.
Injury to the medulla generally results in death.
THREE PRIMARY REGIONS OF THE BRAIN
All parts taken together, the brain may be said to consist
of three primary regions-forebrain, midbrain and hindbrain. The various parts
under each region and their principal functions are as follows:
FOREBRAIN
➤Cerebrum (cerebral hemispheres) (seat of intelligence,
memory, consciousness, will power, voluntary actions).
➤Diencephalon
➤Thalamus (relays pain and pressure impulses to
cerebrum).
➤Hypothalamus (controls the body temperature and
pituitary).
2. MIDBRAIN
A small tubular part (Reflexes involving eyes and ears).
3. HINDBRAIN
➤ Cerebellum (coordinates muscular activity, balance of
the body),
➤Pons. It is located in the centre of the brain below
the cerebellum. It carries impulses from one hemisphere of the cerebellum to
the other hemisphere and coordinates muscular movements on both the sides of
the body.
