The Brain
Brain is a highly specialised delicate organ
located in skull or cranium. It is about 1.4 kg.
Brain is covered by three layers known as
meninges.
- Outer layer is duramater -It is just located
below the skull. It is highly vascular tough
white fibrous tissue. It supports the brain and
spinal cord. - Middle layer is arachnoid -It is the middle,
delicate and thin fibrous covering below the
subdural cavity. - Inner layer piamater -It is thin delicate
and highly vascular innermost layer. It is
separated from arachnoid membrane by a
subarachnoid space. The space is filled with
spongy connective tissue and cerebrospinal
fluid (CSF).
A deep cleft called longitudinal fissure divides
the brain into two halves or the cerebrum into
right and left hemispheres.
Human brain is covered by a tough tissue
covering called meninges and is mainly
divided into forebrain, midbrain and hindbrain. - Forebrain: also known as prosencephalon,
having the following parts.
I. Cerebrum – right and left hemispheres
separated by longitudinal fissure.
II. Cerebral cortex
III. Basal ganglia
IV. The limbic system
V. The diencephalon having Thalamus,
Hypothalamus and Epithalamus - Mid Brain: called mesencephalon reflexes
centre of visual and auditory sensation. - Hind-Brain: also called rhombencephalon
I. Cerebellum II. Pons
III. Medulla oblongata
Forebrain:
I. Cerebrum: - It contains two cerebral hemispheres, right
and left separated by a longitudinal fissure,
internally connected by corpus callosum. - Four lobes are present named after the bones
guarding them. Frontal, parietal, temporal and
occipital lobe.
3. Three pairs of bundles of myelinated nerve
fibres called Cerebellar Peduncles form
the communication pathways between the
Cerebellum and other parts of the CNS.
m Superior Cerebellar peduncles – connect the
cerebellum to the midbrain.
m Middle Cerebellar peduncles – have connection
with Pons of Hind brain.
m Inferior Cerebellar peduncles – communicate
with medulla oblongata and spinal cord.
4. There are different areas on the cerebrum.
These are-Motor area for movement, sensory
area for heat, cold, light, pressure, touch,
auditory area for hearing, visual area for
seeing, olfactory area for smell and taste
area for taste. Each hemisphere receives
information from opposite side of the body.
Cavity of each cerebral hemisphere is called
lateral ventricles.
5. Wernicke’s area is known to be important
for the interpretation of language and the
formulation of thought into speech.
6. Functions-
(a) It controls all mental and conscious
activities (such as intelligence, memory,
reason, will, feelings and emotions).
(b) It is the site of originator of voluntary acts
and interpreter of sensations.
(c) It is a control centre of reflex actions.
II. Cerebral Cortex:- This accounts to about 80% of the total brain
weight. These are made of continuous folds
or convolutions, with their raised parts called
gyri and depressions are called sulci. - The cerebral cortex is referred to as the grey
matter due to its greyish appearance. The
neuron cell bodies are concentrated here
giving the colour. - Fibres of the tracts are covered with the
myelin sheath, which constitute the inner part
of cerebral hemisphere. They give an opaque
white appearance to the layer and, hence, is
called the white matter. - The cerebral cortex contains motor areas,
sensory areas and large regions that are
neither clearly sensory nor motor in function.
- This accounts to about 80% of the total brain