Write short notes on the following: (Any four)
$(a)$ Neural coordination $(b)$ Forebrain $(c)$ Midbrain $(d)$ Hindbrain $(e)$ Retina

(A-D) The process through which two or more organs interact and complement the functions of one another through the neural system is called neural coordination. All physiological processes in the body are closely linked and dependent upon each other. The neural system and the endocrine system jointly coordinate and integrate all activities of the organs so that they function in a synchronised fashion. The neural system provides an organised network of point-to-point connections for quick coordination. The endocrine system provides chemical integration through hormones.
$(b)$ The forebrain consists of the cerebrum,thalamus,and hypothalamus. The cerebrum forms the major part of the human brain. $A$ deep cleft divides the cerebrum longitudinally into two halves,termed as the left and right cerebral hemispheres. These hemispheres are connected by a tract of nerve fibres called the corpus callosum. The layer of cells covering the cerebral hemisphere is called the cerebral cortex,which is thrown into prominent folds. The cerebral cortex is referred to as the grey matter due to its greyish appearance. It contains motor areas,sensory areas,and large association areas responsible for complex functions like intersensory associations,memory,and communication. Fibres of the tracts covered with the myelin sheath constitute the inner part of the cerebral hemisphere,giving an opaque white appearance,hence called white matter. Thalamus is a region at the centre of the forebrain,acting as a coordination centre for sensory and motor signalling. The hypothalamus lies at the base of the thalamus and contains centres that control body temperature,hunger,thirst,and emotions.
$(c)$ The midbrain is located between the thalamus/hypothalamus of the forebrain and the pons of the hindbrain. $A$ canal called the cerebral aqueduct passes through the midbrain. The dorsal portion of the midbrain consists mainly of four round swellings called corpora quadrigemina. The midbrain and hindbrain form the brain stem.
$(d)$ The hindbrain comprises the pons,cerebellum,and medulla. The pons consists of fibre tracts that interconnect different regions of the brain. The cerebellum has a very convoluted surface to provide additional space for many more neurons. The medulla is connected to the spinal cord and contains centres that control respiration,cardiovascular reflexes,and gastric secretions.
$(e)$ The retina is the innermost layer of the eye,containing three layers of neural cells - from inside to outside - ganglion cells,bipolar cells,and photoreceptor cells. There are two types of photoreceptor cells: rods and cones. Daylight vision and colour vision are functions of cones,while twilight vision is the function of rods. Light enters through the cornea and lens,and images are formed on the retina.