L'œil et la vision

The nerve message is the whole of the information which passes from nerve cell to nerve cell. It is the particular structure of these cells called neurons that allows the propagation of the message. This message, electric along the neurons, is made of elementary units, the action potentials, brief inversions of the membrane potential…

The nerve message is the whole of the information which passes from nerve cell to nerve cell. It is the particular structure of these cells called neurons that allows the propagation of the message. The message is transmitted electrically along the neurons and chemically from one neuron to another at the synapses, by means of…

The 600 striated skeletal muscles in the human body are responsible for all our movements. The shortening of each muscle fiber leads to the shortening of the muscles and therefore, to the expression of a force on the tendons which themselves pull on the bones. The whole constitutes a complex mechanism, at work in all our daily acts,…

What happens when we make a physical effort? We have all noticed that our heartbeat increases and our breathing becomes more intense. But what is the reason for these physiological changes? It is due to the increase in our muscular activity and the needs it generates.

Our muscles are permanently subjected to coordinated but involuntary nerve impulses that govern the position of our body in space, even at rest. This is called the myotatic reflex. It is produced by an incessant circulation of electrical messages in the nerve fibers. Here is a detailed review of this complex mechanism, without which…

Voluntary body movements are controlled by the brain. Specific types of commands correspond to its different areas. The motor cortex, frontal lobe, temporal lobe, parietal lobe, thalamus and cerebellum each play a specific role in the formation and transmission of nerve messages to the end of the neuronal fibers that activate the…

There are three main types of blood vessels: arteries, veins and capillaries. These carry nutrients, oxygen and waste products throughout the body. This set of vessels forms a closed system... nearly 100,000 km long! The blood flowing through the vessels is set in motion by the heart, a hollow, compartmentalized muscle that works like…

Although the heart is an automatic organ, it is covered with nerve fibers that connect it to the bulbar nerve center located at the base of the brain. A constant exchange of information between this cerebral region and the cardiac region allows the heart to regulate its beat frequency in an involuntary manner and to maintain it within…

The functioning of the organs requires the supply of nutrients and oxygen. Nutrients come from the digestion of food and are absorbed into the bloodstream in the small intestine. Oxygen comes from the air, it passes into the blood at the level of the pulmonary alveoli. The blood, set in motion by the heart, brings these elements to…

Food follows a long pathway that begins in the mouth, with its absorption, and continues in the stomach, then in the intestines. It is on the wall of the small intestine, lined with microscopic villi richly vascularized, that the passage of nutrients, rich in glucose, into the blood occurs.

During digestion, the carbohydrates in food are converted into glucose, which is released into the bloodstream through the villi lining the small intestine. The average concentration of glucose in the blood, called blood sugar, varies throughout the day. An average value is maintained, thanks to the intervention of two antagonistic…

The intestinal microbiota is the set of micro-organisms hosted in our digestive tract. It is formed by contamination from the environment from birth. Each individual hosts a biodiversity of its own, consisting of a wide variety of species. The microbiota plays many roles in our health, in particular by intervening during digestion. It…

It is in the pulmonary alveoli, small sacs located in the lungs, that the gas exchanges essential to the functioning of the body take place. The oxygen in the air is absorbed by the blood and transported to the cells, while the carbon dioxide released by the cells passes through the alveoli before being expelled from the body. Breathe…

For cystic fibrosis patients, life expectancy is currently no more than 46 years. Eighty-five percent of patients die of respiratory failure and suffer from numerous chronic infections or inflammations. But how does this incurable genetic disease work? Let's go back to the essential role of mucus in respiratory exchanges.

The male and female sexual organs differentiate from the eighth week of embryonic development under the action of male or female hormones. Before that, they are undifferentiated. At birth, the young child is endowed with a genital apparatus that is not yet active for reproduction: it will be necessary to wait for adolescence and new…