STRUCTURE AND FUNCTION OF HUMAN BRAIN

                             HUMAN BRAIN

Brain is the most vital organ which is made up of nervous tissue. It lies in cranial cavity and weigh about 1400 gm. It is covered externally by meanings which is made up of 3 layers piamater ( inner), archnoid layer (middle) and a duramater ( outer).

     

    The brain is divided into 3 parts.

1. Prosencephalon ( fore brain )
2. Mesencephalon ( mid brain )
3. Rhombencephalon ( hind brain )

1. Prosencephalon consists of anterior telencephalon and posterior diencephalon. The telencephalon includes cerebral hemisphere or cerebrum and olfactory lobes.

        Cerebrum:- 

                  The cerebrum is folded forming sulci and gyri to accommodate more neurons. It is made up of  inner white matter & outer grey matter. A median fissure divides the brain into two cerebral hemisphere which are joined by a curved thick band of nerve fibres called corpus callosum. Each half divided into 5 lob

• Frontal lobe - It has motor area, speech area and pre motor area.
• Parietal lobe - It includes pain and temperature area, speech area and taste area.
• Tempral lobe - It includes auditory area and visual area.
• Occipital lobe - It concerned with vision and sensory function.
• Insula or Island of Reil - It integrates the activity of other part of cerebrum.            

The floor of the cerebrum is called corpora striatum. The lateral ventricles ( 1st and 2nd cavities in cerebral hemisphere ) open into 3rd ventricle or diocoel ( cavity of diencephalon) by a foramen of Monro. In humans, diencephalon is externally covered by cerebrum.

       

        Cerebral hemisphere are centres of memory, speech, hearing, vision, voluntary action, involuntary muscle movement etc.

        The main parts of diencephalon are 

• Dorsal epithalamus contain pineal body which secretes melatonin
• Lateral thalamus perceives sensation of heat, cold and pain 
• Hypothalamus or floor of the diencephalon contains hypophysis or pituitary glands and mammillary body lies behind the hypophysis. Two optic nerves cross to form optic chiasma in the front of pituitary gland. Hypothalamus is thermoregulatory centre of the brain. It also control hunger, thirst, fear, anger, emotion, sleep and also produced neurohormones which control the secretion of pituitary gland. It also regulate water balance and the carbohydrates and fat mrtabolism.

2. Mesencephalon consists of  4 optic lobes or corpora quadrigemina and crura cerebri.

       It is vision reflex centres. The posteriors pair is called inferior colliculi. It is auditory reflex centre.

3. Rhombencephalon consists of cerebellum, pons varolli and medulla oblongata. Cerebellum is provided with tree like Arbor vitae. Pons varoli is a transverse band of nerve fibres which connect two cerebellar hemisphere. Pons varolli is the controlling centre of respiration. Cerebellum maintains body posture. Medulla oblongata is the cardiac centre, vasomotor, respiratory centre, gastric centre and reflex centre.