The human ear has three main sections, which consist of the outer ear, the middle ear, and the inner ear. Sound waves enter your outer ear and travel through your ear canal to the middle ear. The ear canal channels the waves to your eardrum, a thin, sensitive membrane stretched tightly over the entrance to your middle ear. The waves cause your eardrum to vibrate. It passes these vibrations on to the hammer, one of three tiny bones in your ear. The hammer vibrating causes the anvil, the small bone touching the hammer, to vibrate. The anvil passes these vibrations to the stirrup, another small bone which touches the anvil. From the stirrup, the vibrations pass into the inner ear. The stirrup touches a liquid filled sack and the vibrations travel into the cochlea, which is shaped like a shell. Inside the cochlea, there are hundreds of special cells attached to nerve fibers, which can transmit information to the brain. The brain processes the information from the ear and lets us distinguish between different types of sounds.

The human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world than we do with any of the other four senses. We use our eyes in almost every activity we perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways. Most people probably would agree that sight is the sense they value more than all the rest.
The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit. The eye is able to detect bright light or dim light, but it cannot sense objects when light is absent.
process of vision
Light waves from an object (such as a tree) enter the eye first through the cornea, the clear dome at the front of the eye. The light then progresses through the pupil, the circular opening in the center of the colored iris.
Fluctuations in incoming light change the size of the eye’s pupil. When the light entering the eye is bright enough, the pupil will constrict (get smaller), due to the pupillary light response.
Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens (located immediately behind the iris and the pupil), to a nodal point (N) located immediately behind the back surface of the lens. At that point, the image becomes reversed (turned backwards) and inverted (turned upside-down).
The light continues through the vitreous humor, the clear gel that makes up about 80% of the eye’s volume, and then, ideally, back to a clear focus on the retina, behind the vitreous. The small central area of the retina is the macula, which provides the best vision of any location in the retina. If the eye is considered to be a type of camera, the retina is equivalent to the film inside of the camera, registering the tiny photons of light interacting with it.
Within the layers of the retina, light impulses are changed into electrical signals. Then they are sent through the optic nerve, along the visual pathway, to the occipital cortex at the posterior (back) of the brain. Here, the electrical signals are interpreted or “seen” by the brain as a visual image.
Actually, then, we do not “see” with our eyes but, rather, with our brains. Our eyes merely are the beginnings of the visual process.

The circulatory system is made up of the vessels and the muscles that help and control the flow of the blood around the body. This process is called circulation. The main parts of the system are the heart, arteries, capillaries and veins.
As blood begins to circulate, it leaves the heart from the left ventricle and goes into the aorta. The aorta is the largest artery in the body. The blood leaving the aorta is full of oxygen. This is important for the cells in the brain and the body to do their work. The oxygen rich blood travels throughout the body in its system of arteries into the smallest arterioles.
On its way back to the heart, the blood travels through a system of veins. As it reaches the lungs, the carbon dioxide (a waste product) is removed from the blood and replace with fresh oxygen that we have inhaled through the lungs.

Respiratory system (video)

Respiratory system's function is to allow gas exchange. The space between the alveoli and the capillaries, the anatomy or structure of the exchange system, and the precise physiological uses of the exchanged gases vary depending on the organism. In humans and other mammals, for example, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscle. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs.
Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange. Plants also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of leaves known as stomata.

The nervous system, together with the endocrine system it(he,she) integrates(repays) and controls the numerous functions that allow that the animal should regulate his(her,your) internal environment and reacts to his(her,your) external environment or faces it. The functional unit of the nervous system is the "neuron", which consists of a cellular body that contains the core(nucleus), the metabolic machinery, in dendritas to receive stimuli, and in an axón that broadcasts stimuli to other cells.

The nervous system divides in two parts(reports): the nervous central system and the nervous peripheral system.

It is constituted by the spinal marrow and the encephalon.


The spinal marrow:
It is a white brilliant cord that parts with the base of the encephalon and crosses the vertebral column, in the low prolongation of the rachidial bulb, measures approximately 45 to 50 cms of length and weight between(among) 26 and 30 gr., it(she) is lodged inside the vertebral conduit that the vertebrae and certain ligaments form(train).


The encephalon:
It is the extensive portion that is situated over the spinal marrow, is contained in the cranial cavity and joins the spinal marrow level of the first cervical vertebra, weighs approximately 1400 grams, and has the consistency of a semisoft(semismooth) cheese. The encephalon receives nervous impulses proceeding from the spinal marrow and from the cranial nerves that go directly towards him(it) from the eyes, the internal ear(hearing), or other sites(places) of the body.


Though the knowledge of the structure and function of the encephalon increase rapidly, many people think that it(he,she) was never managing to understand everything. Nevertheless, his(her,your) functions are essential, not only for the integration and control of a multitude of physiological activities that happen in the whole body. Also for the processes that we identify as mind, conscience, perception and interpretation of the information from the external environment, thought, memory(report) and the variety of evasions(escapes) that characterize the human experience. The association of a stimulus with other one with the memory(report) and the coordinated action(share) of the body necessary for a suitable irritability, they depend on the circuits that follow(continue) the nervous impulses in the brain.


In the functional thing, the nervous system differs from the endocrine one in his(her,your) aptitude to answer rapidly, so(then) the nervous impulse can cross the whole organism(organisation) concerning milliseconds. The hormones, on the other hand, move to a minor speed (by means of the blood torrent) and it(he) is typical that provoke slower but lasting answers.

The nervous system

Test Bite

You scored 5 out of 5

1. What is the eye an example of?

You said: A sense organ

Correct.

2. Which type of neurone transmits a signal from a sense organ to the central nervous system?

You said: Sensory

Correct.

3. Which type of neurone transmits a signal from the central nervous system to an effector such as a muscle?

You said: Motor

Correct.

4. What is a synapse?

You said: A junction between two neurones

Correct.

5. Which part of the nervous system is not involved in producing reflex actions?

You said: Brain

Correct.

1. Your answer: c - retina (0 points) Hard luck. Remember the lens focuses light on the retina. 2. Your answer: a - iris (1 point) Well done! The iris narrows in bright light to protect the retina and widens to let in enough light in dim conditions. 3. Your answer: c - retina (1 point) Well done. You remembered that the retina has cells that converts light energy into electrical energy. 4. Your answer: true (1 point) Well done! You remembered that both eyes give binocular vision that allows us to judge distance. 5. Your answer: false (1 point) Spot on! You must have remembered two facts. The semi-circular canals are used to sense our head position for balance and the listening parts of two ears are needed to detect the direction of a sound. 6. Your answer: true (1 point) Great stuff! Yes a reflex action is so fast that evasive action is already in progress before impulses have even reached the brain. 7. Your answer: c - cochlea (1 point) Well done! The cochlea converts vibrations into electrical impulses. 8. Your answer: d - auditory nerve (1 point) Well done! yes the auditory nerve carries electrical signals produced by the cochlea to the brain. 9. Your answer: c - cerebellum (1 point) Well done! The cerebellum uses signals from the semi-circular canals to control balance and muscle co-ordination. 10. Your answer: b - medulla (1 point) Well done! Yes the medulla controls the heart and breathing rate.

You scored 9 out of 10 (90%).

Well done! You are revising incredibly well.