Central Nervous System

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

BRAIN

• 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.

   ii.Cerebellum

• 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.

SPINAL CORD

• 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

• 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.