(a) Cerebrum is the most developed.
(b) Hypothalamus acts as a master clock.

Cone cells help detect colors. Most people have three kinds of cone cells. People without all three see fewer colors, sometimes called color blindness. Some cones respond more strongly to blue light.

The size of the pupil is controlled by Iris. Iris contains a group of two smooth muscles attached at the corner of the pupil. They stretch when there is less light and shrink when it is too bright. These muscles are known as sphincter pupillae.

The Eustachian canal extends from the middle ear to the pharynx. It helps to maintain the pressure balance with the outer atmosphere.

Along with the hypothalamus, it is involved in the regulation of sexual behaviour, expression of emotional reactions, e.g., pleasure, excitement, rage and fear and motivation.

The brain might be compared to a computer as its memory banks. The spinal cord to the conducting cable for the computer's input and output and the nerves to a circuit supplying input information to the cable and transmitting the output to muscles and organs. The most important of these components is the Central Processing Unit (CPU) or microprocessor, which acts as the 'brain' of your computer.

External auditory canal, eardrum, malleus,incus, stapes, cochlea and cochlear nerve.

It transmits impulse (sensory) from tissues/organs to the CNS and forms the sensory or afferent pathway.

Nervous tissue is composed of neurons, also called nerve cells, and neuroglial cells. Four types of neuroglia found in the CNS are astrocytes, microglial cells, ependymal cells, and oligodendrocytes.

Choroid: It is a pigmented layer (bluish) present beneath the sclera. It contains numerous blood vessels and nourishes the sclera. The choroid layer is thin over the posterior two-thirds of the eyeball, but it becomes, thick in the anterior part to form the ciliary muscles.

Inner ear

Resting potential The electrical potential difference across the plasma membarance is called the Compare the following resting potential
Action potential It is another name of nerve impluse. The action potential is an electrical signal that travels along an axon.

The ionic gradients across the resting membarance are maintained by the active transport of ions by the sodium-potassium pump.

Bioelectric/electrochemical disturbance (change)

The gap between two neurons is called as synapse.

Differences between cranial nerve and spinal nerve in human are given below.

(i) The daylight (photopic) vision and colour vision are functions of cones. In the human eye, there are three types of cones which possess their own characteristic photopigments that respond to red, green and blue lights. The sensations of different colours are produced by various combinations of these cones and their photopigments. When these cones are stimulated equally, a sensation of white light a is produced.
(ii) The crista and macula are the specific receptors of the vestibular apparatus of inner ear which are responsible for the maintenance of balance of the body and posture.
(iii) The diameter of the pupil is regulated by the muscle fibre of iris. Photoreceptors, rods and cones regulate the amount of light that falls on the retina.

Difference between dendrites and axons are as follows:

(a) Neural Coordination. The functions of the organs/organ systems in our body must be coordinated to maintain homeostasis. Coordination is the process through which two or more organs interact and complement the functions of one another. For example, when we do physical exercises, the energy demand is increased for maintaining an increased muscular activity. The supply of oxygen is also increased. The increased supply of oxygen necessitates an increase in the rate of respiration, heartbeat and increased blood flow via blood vessels. When physical exercise is stopped, the activities of nerves, lungs, heart and kidney gradually return to their normal conditions. Thus, the functions of muscles, lungs, heart, blood vessels, kidney and other organs are coordinated while performing physical exercises. In our body, 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.
(b) Forebrain. 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 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. The cerebrum wraps around a structure called thalamus, which is a major coordinating centre for sensory and motor signaling. Another very important part of the brain called hypothalamus lies at the base of the thalamus. The hypothalamus contains a number of centres which control body temperature, urge for eating and drinking. It also contains several groups of neurosecretory cells, which secrete hormones called hypothalamic hormones. The inner parts of cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus, etc., form a complex structure called the limbic lobe or limbic system. Along with the hypothalamus, it is involved in the regulation of sexual behaviour, expression of emotional reactions (e.g., excitement, pleasure, rage and fear), and motivation.
(c) Midbrain. The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. Acanal called the cerebral aqueduct passes 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) Hindbrain. The hindbrain comprises pons, cerebellum and medulla (also called the medulla oblongata). 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) Synapse. A nerve impulse is transmitted from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a presynaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called synaptic cleft. There are two types of synapses, namely, electrical synapses and chemical synapses. Electrical Synapse. At electrical synapses, the membranes of pre- and postsynaptic neurons are in very close proximity. Electrical current can flow directly from one neuron into the other across these synapses. Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Electrical synapses are rare in our system.

(a) Neuron

(b) Brain

a) Polarisation of the membrane of a nerve fibre. The fluid inside the membrane contains high concentration of K+and negatively charged proteins and low concentration of Na⁺.
In contrast, the fluid outside the axon contains a low concentration of K⁺, a high concentration of Na⁺ and thus forms a concentration gradient. These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3 Na⁺ outwards for 2 K⁺ into the cell. As a result, the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged and therefore is polarised.
b) Depolarisation of the membrane of a nerve fibre. When a stimulus is applied at a site on the polarised membrane, the membrane at the site A becomes freely permeable to Na⁺, This leads to a rapid influx of Na⁺ followed by the reversal of the polarity at that site, i.e., the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged. The polarity of the membrane at the site is thus reversed and hence depolarised.
c) Transmission of a nerve impulse across chemical synapse. At a chemical synapse, the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. The axon terminals contain vesicles filled with these neurotransmitters. When an impulse (action potential) arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft. The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate a new potential in the postsynaptic neuron. The new potential developed may be either excitatory or inhibitory.