Nervous system

Nervous system

The nervous system provides the fastest means of communication within the body so that suitable response to stimuli can be made at once.Central nervous system consists of brain and spinal cord.The function of some of these parts are as follows :
1.Thalamus deals with pain,presure and temperature.
2.Hypothalamus deals with water balance is body,behavioural patterns of sex,sleep,stress,emotions,etc.It also regulates pituitary hormones and metabolism of fat,carbohydrate and water.
3.Spinal cord deals with impulses to and from the brain and is the centre for reflax actions like blinking of the eye when an object comes near to our eyes suddenly ,Rapid withdrawal of hand while burned,knee jerk reflax ,etc.

Sense Organ

Eye : Eyes are the sensitive detectors of light .The human eye can distinguish about 10 million colours.It consists three parts :
Sclerotic Layer : It is the outermost ,bony layer ,which includes-cornea and conjunctiva.
Choroid Layer : It is the middle layer and consists of
(1)Pupil is the black hole in the centre of the iris.it changes size as the amount of light changes.
(2)Iris is the coloured part of the eye.It controls the amount of light that enters the eye by changing the size of the pupil.
(3)Lens is a biconvex transparent circular solid located just behind the iris .It focuses light onto the retina.
Retina : Light sensitive tissue that lines the back of the eye.It contains millions of Photoreceptors(rod and cones)That convert light rays into electrical impulses that are relayed to the brain via the optic nerve.The image formed on retina is real and inverted.Rods are highly sensitive to dim light.Cones are sensitive to bright light ,hence differentiated the colours.

Eye Defects

Nearsightedness(Myopia) : A condition in which nearby objects are seen more clearly than distant objects because light is focused in front of the retina,not on it.It can be corrected by using concave glasses.
Farsightedness(Hypermetropia) : a condition in which distant objects are seen more clearly than nearby objects because light is focused behind the retina ,not on it.It can be corrected by using convex glasses.
Astigmatism : A condition in which the lens is wraped causing images not to focuse properly on the retina.A cylindrical glasses can correct the defect.

Ear

Ears are meant for both balancing and hearing.Hearing is controlled by auditory area of temporal lobe of cerebral cortex.Human ear can hear the sound of 60-80 decibel.Human ear is sensitive to sound s frequency 50-20,0000 cycles/sec