Page 9 - LN-NEURAL CONTROL & COORDINATION

(iii) The innermost membrane, the piamater is thin, very

delicate, which is in contact with the brain tissue.
Note:
The human brain weights from 1200-1400 g. The human neural system has
about 100 billion neurons, majority of them occur in the brain.
The human brain is divisible into three parts
(i) Forebrain (ii) Midbrain (iii) Hindbrain
i. The forebrain
It consists of Olfactory lobes The anterior part of the brain is formed by a pair

of short club-shaped structures, the olfactory lobes. These are concerned with
the sense of smell.
Cerebrum It is the largest and most complex of all the parts of the human
brain. A deep cleft divides the cerebrum longitudinally into two halves, which
are termed as the left and right cerebral hemispheres connected by a large
bundle of myelinated fibres the corpus callosum.
* The outer cover of cerebral hemisphere is called cerebral cortex. The

cerebral cortex is referred to as the grey matter due to its greyish appearance
(as neuron cell bodies are concentrated here).
The cerebral cortex is greatly folded. The upward folds, gyri, alternate with the
downward grooves or sulci. Beneath the grey matter there are millions of
medullated nerve fibers, which constitute the inner part of the cerebral
hemisphere. The large concentration of medullated nerve fibres gives this
tissue an opaque white appearance. Hence, it is called the white matter.
* Lobes A very deep and a longitudinal fissure, separates the two cerebral

hemispheres. Each cerebral hemisphere of the cerebrum is divided into four
lobes, i.e., frontal, parietal, temporal and occipital lobes.
In each cerebral hemisphere, there are three types of junctional areas
* Sensory areas receive impulses from the receptors and motor areas transmit
impulses to the effectors.
* Association areas are large regions that are neither clearly sensory nor motor

in junction. They interpret the input, store the input and initiate a response in
light of similar past experience. Thus, these areas are responsible for complex
functions like memory, learning, reasoning and other intersensory
associations.
Distction the posterioventral part of forebrain.
Its main parts are as follows
* Epithalamus is a thin membrane of non-nervous tissue. It is the posterior
segment of the diencephalon.
* The cerebrum, wraps around a structure called thalamus, which is a major

coordinating center for sensory and motor signalling.