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 | Learn NCERT solution | Education portal Class 11 Biology | Study online Unit-21 Neural Control and Coordination

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

(a) The process through which two or more organs interact and complement the functions of one another through the neural system, it is called neural coordination. All the physiological processes in the body are closed linked and dependent upon each other. The neural system and the endocrine system jointly coordinate and integrate all the 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 a quick coordination. The endocrine system provides chemical integration through hormones.
(b) The forebrain consists of cerebrum, thalamus and hypothalamus.
→ Cerebrum forms the major part of the human brain. A deep cleft divides the cerebrum longitudinally into two halves, which are termed as the left and right cerebral hemispheres. The hemispheres are connected by a tract of nerve fibres called corpus callosum. The layer of cells which covers the cerebral hemisphere is called cerebral cortex and is thrown into prominent folds. The cerebral cortex is referred to as the grey matter due to its greyish appearance. The cerebral cortex contains motor areas, sensory areas and large regions that are neither clearly sensory nor motor in function. These regions called as the association areas are responsible for complex functions like intersensory associations, memory and communication.Fibres of the tracts are covered with the myelin sheath, which constitute the inner part of cerebral hemisphere. They give an opaque white appearance to the layer and, hence, is called the white matter.
→ Thalamus: It is a region present at the centre of the forebrain and wrapped by cerebrum. It is coordination center for sensory and motor signalling.

→ 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.