question_answer 1)

Briefly describe the structure of the following (a) Brain (b) Eye (c) Ear  

Answer:

(a)      Structure of Brain The human brain is well protected by the skull. The brain can be divided into three major parts forebrain, midbrain and hindbrain.   (i) Forebrain The various parts of forebrain are cerebrum, thalamus and hypothalamus. Cerebrum is responsible for complex functions  like  intersensory  associations,  memory  and communication. (ii) Midbrain The   midbrain   is   located   between   the thalamus/hypothalamus of the forebrain and pons of the hindbrain. (iii) Hindbrain The hindbrain comprises pons, cerebellum and medulla (also called the medulla oblongata). The medulla contains centres, which control- respiration cardiovascular reflexes and gastric secretions. (b) Structure of Eye The wall of the human eye ball is composed of three layers. The external layer is called the sclera. The anterior portion of this layer is called the cornea. The middle layer, choroid, contains many blood vessels and looks bluish in colour. The ciliary body itself continues forward to form a pigmented and opaque structure called the iris. The eye ball contains a transparent crystalline lens. In front of the lens, the aperture surrounded by the iris is called the pupil.   There are two types of photoreceptor cells namely rods and cones. The optic nerves leave the eye and the retinal blood vessels enter it at a point medial to and slightly above the posterior pole of the eye ball. Photoreceptor cells are not present in that region and hence, it is called the blind spot. (c)       Structure of Ear Anatomically, the ear can be divided into three major sections called the outer ear, the middle ear and the inner ear. (i)        Outer ear The outer ear consists of the pinna and external auditory meatus (canal). (ii)       Middle ear The middle ear contains three ossicles called malleus, incus and stapes which are attached to one another like a chain. The malleus is attached to the tympanic membrane and the stapes is attached to the oval window of the cochlea. An eustachian tube connects the middle ear cavity with the pharynx. (iii)      Inner ear The fluid-filled inner ear called labyrinth consists of two parts, the bony and the membranous labyrinths. The organ of Corti is a structure located on the basilar membrane which contains hair cells that act as auditory receptors. The inner ear also contains a complex system called vestibular apparatus, located above the cochlea. The vestibular apparatus is composed of three semi-circular canals and the otolith organ.