Q.5:- Write short notes on the following:
(a) Neural coordination (b) Forebrain (c) Midbrain (d) Hindbrain (e) Retina (f) Ear ossicles
(g) Cochlea (h) Organ of Corti (i) Synapse
→ Hypothalamus: It lies at the base of the thalamus which contains a number of centres which control body temperature, urge for eating and drinking. It also contains the nerve centres for temperature regulation, hunger, thirst, heart beat and respiration regulation and emotions such as anger, love, cool, etc. It has connection with pituitary gland hence also controls growth and sexual behaviour.
(c) The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passess through the midbrain. The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora quadrigemina. Midbrain and hindbrain form the brain stem.
(d) The hindbrain comprises pons, cerebellum and medulla.
→ Pons consists of fibre tracts that interconnect different regions of the brain.
→ Cerebellum has very convoluted surface in order to provide the additional space for many more neurons.
→ The medulla of the brain is connected to the spinal cord. The medulla contains centres which control respiration, cardiovascular reflexes and gastric secretions.
(e) Retina is the innermost layer which contains three layers of neural cells – from inside to outside – ganglion cells, bipolar cells and photoreceptor cells. There are two types of photoreceptor cells, namely, rods and cones. The daylight vision and colour vision are functions of cones and twilight vision is the function of the rods. The light enters through cornea, the lens and the images of objects are formed on the retina.
(f) The middle ear contains three ear ossicles called malleus, incus and stapes which are attached to one another in a chain-like fashion. The malleus is attached to the tympanic membrane, incus is connected with stapes. and the stapes is attached to the oval window of the cochlea.The ear ossicles increase the efficiency of transmission of sound waves to the inner ear.
(g) The coiled portion of the labyrinth is called cochlea. The membranes constituting cochlea, the reissner’s and basilar, divide the surounding perilymph filled bony labyrinth into an upper scala vestibuli and a lower scala tympani. The space within cochlea called scala media is filled with endolymph. At the base of the cochlea, the scala vestibuli ends at the oval window, while the scala tympani terminates at the round window which opens to the middle ear.
(h) The organ of corti is a structure located on the basilar membrane which contains hair cells that act as auditory receptors. The hair cells are present in rows on the internal side of the organ of corti.
(i) A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called synaptic cleft. These are of two types electrical synapses and chemical synapses.