(a) Neural Coordination

The neural system provides rapid coordination among the organs of the body. This coordination is in the form of electric impulses and is quick and short lived. For example, during exercise, our body requires more oxygen and food. Hence, the breathing rate increases automatically and the heart beats faster. This leads to a faster supply of oxygenated blood to the muscles. Moreover, the cellular functions require regulation continuously. These functions are carried out by the hormones. Hence, the neural system along with the endocrine system control and coordinate the physiological processes.

(b) Forebrain

It is the main thinking part of the brain. It consists of cerebrum, thalamus, and hypothalamus.

i. Cerebrum: Cerebrum is the largest part of the brain and constitutes about four-fifth of its weight. Cerebrum is divided into two cerebral hemispheres by a deep longitudinal cerebral fissure. These hemispheres are joined by a tract of nerve fibre known as corpus callosum. The cerebral hemispheres are covered by a layer of cells known as cerebral cortex or grey matter. The innermost part of cerebrum gives an opaque white appearance to the layer and is known as the white matter.

ii. Thalamus: Thalamus is the main centre for sensory and motor signalling. It is wrapped by cerebrum.

iii. Hypothalamus: It lies at the base of thalamus and contains a number of centres that regulate body temperature and the urge for eating and drinking. Some regions of cerebrum, along with hypothalamus, are involved in the regulation of sexual behaviour and expression of emotional reactions such as excitement, pleasure, fear, etc.

Midbrain

It is located between the thalamus region of the forebrain and pons region of hindbrain. The dorsal surface of midbrain consists of superior and inferior corpora bigemina and four round lobes called corpora quadrigemina. A canal known as cerebral aqueduct passes through the midbrain. Midbrain is concerned with the sense of sight and hearing.

Hindbrain

It consists of three regions-pons, cerebellum, and medulla oblongata.

i. Pons is a band of nerve fibre that lies between medulla oblongata and midbrain. It connects the lateral parts of cerebellar hemisphere together.

ii. Cerebellum is a large and well developed part of hindbrain. Which is located below the posterior sides of cerebral hemispheres and above medulla oblongata. It is responsible for maintaining posture and equilibrium of the body.

iii. Medulla oblongata is the posterior and simplest part of the brain. Which is located beneath the cerebellum. It lowers and extends in the form of spinal cord and leaves the skull through foramen magnum.

(e) Retina

Retina is the innermost layer. It contains 3 layers of cells - inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. The receptor cells present in the retina are of two types - rod cells and cone cells.

i. Rod cells-The rods contain rhodopsin pigment (visual purple), which is highly sensitive to dim light. It is responsible for twilight vision.

ii. Cone cells-The cones contain iodopsin pigment (visual violet) and are highly sensitive to high intensity light. They are responsible for daylight and colour visions.

The innermost ganglionic cells give rise to optic nerve fibre that forms optic nerve in each eye and is connected with the brain. In this region, the photoreceptor cells are absent. Hence, it is known as the blind spot. At the posterior part, lateral to blind spot, there is a pigmented spot called macula lutea. This spot has a shallow depression at its middle known as fovea. They are devoid of rod cells. Hence, it is the place of most distinct vision.

(f) Ear Ossicles

The middle ear contains a flexible chain of 3 middle bones called ear ossicles. The three ear ossicles are as follows.

i. Malleus

ii. Incus

iii. Stapes

The malleus is attached to tympanic membrane on one side and to incus on the other side. The incus connected with stapes. Stapes, in turn, are attached with an oval membrane, fenestra ovalis, of internal ear. The ear ossicles act as a lever that transmits sound waves from external ear to internal ear.

(g) Cochlea

Cochlea is a long, coiled outgrowth of sacculus. It is the main hearing organ. The cochlea forms three chambers.

i. Upper - scala vestibule

ii. Middle - scala media

iii. Lower - scala tympani

The floor of the scala media is a basilar membrane while its roof is Reissner's membrane.
Reissner's membrane gives out a projection called tectorial membrane. The organ of corti, a hearing organ, is located on the basilar membrane. Organ of corti contains receptors hair cells.

(h) Organ of Corti

Organ of corti is the hearing organ. It is located on the basilar membrane that contains hair cells. Hair cells act as auditory receptors. They are present on the internal side of organ of corti.

(i) Synapse

Synapse is a junction between the axon terminal of one neuron and the dendrite of next neuron. It is separated by a small gap known synaptic cleft. There are two types of synapses.

i. Electrical synapse

ii. Chemical synapse

In electrical synapses, the pre and post synaptic neurons lie in close proximity to each other. So, the impulse can move directly from one neuron to another across the synapse. It represents a faster method of impulse transmission.

In chemical synapses, the pre and post synaptic neurons are not in close proximity. They are separated by a synaptic cleft. The transmission of nerve impulses is carried out by chemicals such as neurotransmitters.