221 Human Body Parts Encyclopedia

Hypermetropia is another visual disorder. It is also known as long-sightedness or far- sightedness. In this condition, the eye focuses better on distant objects than nearby objects, hence nearby objects appear blurred (this is just opposite to myopia). Physiologically, a person presenting this disorder has smaller eyeballs than the normal size or cornea with smaller […]

Myopia is a common visual deformity. It is also known as nearsightedness or short sightedness. In myopia, the eye focuses better on the objects that are nearer than the objects which are at a farther distance. In this visual disorder, a person has enlarged eyeballs or excessively curved cornea. This physiological defect alters the image

Image formation by an eye is based on the passage of light in the eye. It is an instant process. 1.    Firstly, the light enters the eye and passes through the transparent cornea to the pupil in the centre of the iris. 2.    Then, the adjustable lens and the fixed cornea focus the light rays

Pupil Both the eyes and the camera have a black dot in the centre. This black dot helps capture an image. In case of the eye, it is called the pupil which is an opening on the iris. It lets the light fall on the retina and acts as a regulator, i.e. it regulates the

Choroid is the middle layer located just after the sclera. Choroid is supplied with blood vessels and it forms the iris. There is a central opening in the choroid layer, the pupil. The main function of the choroid is to supply nutrients and oxygen to the sclera and the retina. The iris is a thin,

Sclera (white portion of the eye) is the outer sheath of the eyeball. Sclera protects the eye from damage as it is the toughest pigmented fibrous coat of the eye. Sclera consists of an inner circular muscle and an outer radial muscle. Sclera controls the amount of light entering the eye. The cornea is the

The eye is a delicate organ; it is the sense organ for vision. Eyes are connected with the optic nerves. The eye sockets of the skull in which the eyes are present are lined by soft tissues. Eyelids, eyelashes, eyebrows and tears protect the eye from dust and dirt. The special cells known as photo

Sense organs connect a human body to the external environment by the means of five senses: vision, smell, taste, hearing and touch. These sense organs work in coordination with the nervous system. Hence, the central nervous system is responsible for sensing the external environments and responding accordingly. Each sense organ has specific receptors in the

What is reflex action? We can understand it simply with this question. What happens when we accidently place our hand on a pin? Answer: We move away our hand instantly. This action, that our body performs automatically when there is an emergency is known as reflex action. It occurs quickly and unconsciously. In a reflex

Autonomic System This part of the peripheral nervous system controls the involuntary movements in the body, such as–controlling and coordinating smooth and cardiac muscle functions, and the endocrine glands. This system is further divided into the sympathetic and the parasympathetic nervous system. These two sub-divisions of autonomic system work in opposition to each other to

Spinal Nerves The spinal nerves are part of the peripheral nervous system. These nerves arise directly from the spinal cord. There are 31 pairs of spinal nerves in the peripheral nervous system. The major function of these nerves is to exchange sensory, motor and autonomic signals between the spinal cord and the body. Cranial Nerves

The part of the peripheral nervous system that sends motor impulses to skeletal muscles is the somatic nervous system. The sensory neurons (afferent neuron) and the motor neurons (efferent neuron) are the part of this nervous system. The main function of somatic nervous system is to exchange impulses between the central nervous system and organs,

The peripheral nervous system (PNS) is the part of the nervous system which includes the nerves and ganglia that are outside of the brain and spinal cord. It consists of 3 types of nerves: spinal nerves, cranial nerves and visceral nerves which are the connecting wires between CNS and sensory organs. The system is further

Central Nervous System The central nervous system is also called the cerebrospinal nervous system, where ‘cerebro’ refers to the brain and ‘spinal’ refers to the spinal cord. The brain and the spinal cord together weave a wide network of nerves that work day and night and keep the body functioning. The brain is said to

Brain-stem Brain-stem is a stem-like part of the brain that connects the cerebrum and the spinal cord. It usually includes the medulla oblongata, pons, and mid-brain. A pair of ten cranial nerves comes from the brain-stem. The parts of the brain-stem work together to control the movements in the body. Mid-brain The mid-brain is also