Cenral Neural System (CNS) | BIOLOGY | NEET

CENTRAL NEURAL SYSTEM ( CNS )

Central neural system is the processing centre of the nervous system . It receives and sends information to peripheral neural system

The brain and spinal cord are continuous structures , which together form the CNS . They are both protected by hard bony coverings - brain by the cranium and spinal cord by the vertebral column and by a continuous , tough three layered membrane of connective tissue called the meninges surface .

Both the brain and spinal cord are bathed in cerebrospinal fluid ( CSF ) , which is continuously circulated through the cerebral ventricles , the cavity of the spinal cord and the sub - arachnoid space . It serves as a pad to cushion the CNS from shocks and mechanical injuries . The CSF also carries oxygen and nutrients from the blood to the neurons and neuroglia of the CNS .

Brain

Brain is the central information processing organ of our body . Human brain weighs around 1.2-1.4 kg . It lies in the cranium of skull . Brain and spinal cord are surrounded by connective tissue membranes called meninges . There are three meninges in humans , an outer layer called duramater a middle layer called arachnoid membrane and an inner thin layer called piamater .

Human brain is divided into three parts : forebrain ( prosencephalon ) , midbrain (mesencephalon ) and hindbrain (rhombencephalon)

Forebrain

Forebrain consists of olfactory lobes , cerebrum and diencephalon

Olfactory lobes are paired club shaped structures , forming anterior part of brain , concerned with sense of smell .

Cerebrum forms the major part of the human brain . A deep cleft divides the cerebrum longitudinally into two halves , which are termed as the left and right cerebral hemispheres . The hemispheres are connected by a tract of nerve fibres called corpus callosum . The outer portion of cerebrum is called the cerebral cortex that makes up the grey matter of the cerebrum . Beneath the grey matter there are present millions of medullated nerve fibres which give an opaque white appearance , hence are collectively called white matter . Each cerebral hemisphere is divided into four lobes : frontal ( monitors complex thoughts , actions and ideas and controls intellectual ability ) , parietal ( registers sensory perception and takes in information from environment , organises it and communicates it to rest of the brain ) , temporal ( decodes and interprets sound , smell , memory and emotion ) and occipital lobes ( decodes and interprets visual information , shape and colour ) .

Diencephalon is completely covered by cerebral hemispheres . Its main parts are - epithalamus , thalamus and hypothalamus .

Epithalamus is thin and its anterior part is folded to form anterior choroid plexus and just behind it , there is pineal stalk which has pineal body . Thalamus , is major coordinating centre for sensory and motor signalling and is composed primarily of grey matter . Hypothalamus lies at the base of the thalamus and contains a number of centres which control body temperature urge for eating and drinking , growth and sexual behaviour , etc. Hypothalamus is an important link between neural and endocrine system (neuroendocrine role ).

Midbrain

Midbrain is located between the thalamus / hypoth of the forebrain and pons of the hindbrain . The upper or superior surface of the midbrain consists mainly of four round swellings ( lobes ) called corpora quadrigemina . Corpora quadrigemina control visual reflexes and auditory reflexes , and are equivalent to optic lobes of lower animals . The lower or inferior surface have two bundles of fibres called cerebral peduncles . They relay impulses back and forth between cerebrum , cerebellum , pons and medulla

Hindbrain

Hindbrain comprises of cerebellum , pons varolii and medulla oblongata .

Cerebellum is the second largest part of the human brain . It consists of two lateral cerebellar hemispheres and central vermi. The middle layer contains characteristic purkinje cells. A cross section of cerebellar hemispheres shows branching tree like arrangement of grey and white matter called arbor vitae. The cerebellum controls rapid muscular activities , such as running , typing and even talking .

Pons varolii is situated in front of the cerebellum below the midbrain and above the medulla oblongata . It consists of fibre tracts that interconnect different regions of brain .

Medulla oblongata contains centres which control respiration , cardiovascular reflexes and gastric secretions .

The study of the brain is called encephalogy

Brain stem forms the connections between the brain and spinal cord . It comprises of : midbrain , pons and medulla oblongata .

Manish Mevada

M.Sc, M.Phil, B.Ed