21.4 CENTRAL NEURAL SYSTEM NEET (brain)

21.4 CENTRAL NEURAL SYSTEM

The brain is the central information processing organ of our body, and acts as the ‘command and control system’. 

  • It controls the voluntary movements, balance of the body, functioning of vital involuntary organs (e.g., lungs, heart, kidneys, etc.), thermoregulation, hunger and thirst, circadian (24-hour) rhythms of our body, activities of several endocrine glands and human behaviour. 
  • It is also the site for processing of vision, hearing, speech, memory, intelligence, emotions and thoughts. 
  • The human brain is well protected by the skull. 
  • Inside the skull, the brain is covered by cranial meninges consisting of-
  1. an outer layer called dura mater, 
  2. a very thin middle layer called arachnoid and 
  3. an inner layer (which is in contact with the brain tissue) called pia mater. 
  • The brain can be divided into three major parts: (i) forebrain, (ii) midbrain, and (iii) hindbrain (Figure 21.4).
21.4.1 Forebrain (Proencephalon)


  • The forebrain consists of cerebrum, thalamus and hypothalamus (Figure 21.4). 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 layer of cells which covers the cerebral hemisphere is called cerebral cortex and is thrown into prominent folds. 
  • 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. 
  • The cerebral cortex contains motor areas, sensory areas and large regions that are neither clearly sensory nor motor in function. 
  • These regions called as the association areas are responsible for complex functions like intersensory associations, memory and communication. 
  • 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. 
Thalamus: 
  • The cerebrum wraps around a structure called thalamus, which is a major coordinating centre for sensory and motor signaling. 
Hypothalamus: 
  • Another very important part of the brain called hypothalamus lies at the base of the thalamus. 
  • The hypothalamus contains a number of centres which control body temperature, urge for eating and drinking. 
  • It also contains several groups of neurosecretory cells, which secrete hormones called hypothalamic hormones. 
Limbic system: 
  • The inner parts of cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus, etc., form a complex structure called the limbic lobe or limbic system. 
  • Along with the hypothalamus, it is involved in the regulation of sexual behaviour (libido), expression of emotional reactions (e.g., excitement, pleasure, rage and fear), and motivation. 
                             Think Tank Centre: The Limbic System

21.4.2 Midbrain 


  • The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. 
  • A canal called the cerebral aqueduct passess through the midbrain. 
  • The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora quadrigemina. 
  • Midbrain and hindbrain form the brain stem.
21.4.3 Hindbrain 
  • The hindbrain comprises pons, cerebellum and medulla (also called the medulla oblongata). 
  • Pons consists of fibre tracts that interconnect different regions of the brain. 
  • Cerebellum has very convoluted surface in order to provide the additional space for many more neurons. 
  • The arbor vitae:  literally meaning the “tree of life” and is the name given to the cerebellar white matter that has a tree-like branching pattern.
  • It brings sensory and motor information to and from the cerebellum.
  • The medulla of the brain is connected to the spinal cord. 
  • The medulla contains centres which control respiration, cardiovascular reflexes and gastric secretions.

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