Central Nervous System

  • Central Nervous  System(CNS)  consists of Brain and Spinal cord.
  • CNS controls and coordinates various functions of the body.


  • In an adult, the average weight of the brain is 1.4kg(1400gm).
  • Protective membrane which envelops the brain and spinal cord – Meninges.
  • Part of the skull that encloses the brain – Cranium.


    i. Cerebrum

  • The  largest part of the human brain.
  • Cerebral  hemisphere is divided into frontal, parietal, temporal and occipital lobes.
  • Cerebrum controls voluntary actions.
  • It is the centre for intelligence, thoughts, emotion, willpower, memory, consciousness, imagination, experience, recognition, reasoning, weeping, laughing, voluntary controls etc.
  • The part of cerebrum which is  known as sensory speech area(motor speech area) – Broca’s area.


  • Also known as Little Brain.
  • Centre for co-ordination of muscular movement.
  • Primary centre for balancing, equilibrium  and  orientation of body.
  • It is the part of the body on which Alcohol affects.

    NB: The part of brain on which painkillers work - Thalamus

   iii.Medulla  Oblongata

  • Controls involuntary actions like working of heart, contraction of blood vessels, respiratory and digestive movements.
  • Central control of respiratory activity.
  • Centre for vomiting, coughing and sneezing.
  • An injury to medulla oblongata may cause sudden death.

  iv. Hypothalamus

  •  Centre for hunger, thirst, sweating, sleep, temperature, love and hate.
  • The thermo regulatory centre of the human body.
  • Hormones produced by Hypothalamus – Oxytocin & Vasopressin.


  • Controls reflex actions in humans.
  • Spinal cord is the part of brain passing through the vertebrae or spine.
  • Spinal cord has a length  of 45cm.
  • There are 12 pairs of cranial nerves and 31 pairs of spinal nerves.


  • Neurons carry message intheform of electric signals.
  • The basic functionalunit of the nervous system is the neurons .
  • Neurons are connectedtoeach other to form networks.
  • Parts of neuron are – Axon, Dendron and Synaptic nobe.
  • Sensory neurons respond to stimuli like touch, sound, light etc. and send signals to spinal cord and brain.
  • Motor neurons receive signals from brain and spinal cord.
  • Part of the neuron which carries in impulses is called  the Axon.
  • Axon passes an impulse into another neuron through a junction called synapse.
  • Part of neuron which receives nerve impulse – Dendrites.
  • Normally  signals are sent from the axon of one neuron to a dendrite of another.
  • Chemical which helps in transmission of nerve – Acetyl Colin.
  • Protective sheath of Axons – Myelin Sheath.
  • Colour of Myelin Sheath – White.

  • The disease occurs due to the loss of neuron in the brain – Alzheimer’s disease.
  • The loss of motor neuron in the body causes – Parkinson’s disease.
  • Meningitis is affected to Meninges. It is caused by Bacteria, Virus, Fungus and Parasites. Bacterial Meningitis is more severe than viral meningitis.
  • Encephalitis is an infectious brain disease caused by virus.
  • A disability of brain to recognize letters and words properly – Dyslexia.
  • Clotting of blood in the blood vessels of brain – Cerebral Thrombosis.
  • Bleeding caused by the breakage of blood vessels of brain – Cerebral haemorrhage.
  • When the flow of blood to the brain is obstructed for more than 5 sec. , it results inunconsciousness.