• Route the afferent and efferent between the CNS and the rest of the body
• Treatment of partial information by spinal reflexes.

Embryonic Development:
It develops from the caudal portion of embryonic neural tube. Distinguish a few weeks, two separate parts in the gray matter: the basal plate and alar plate, separated by a furrow, eventually becoming the central canal. As it grows, the blades extend and produce the gray mass of adult marrow. The white outer marrow is formed from neural axons.
Anatomophysiological:
The bone extends from the foramen magnum to the first or second lumbar vertebra. Hence, a filament fiber, fossil embryogenesis, from the meninges, extends to the coccyx, the terminal filum.
31 pairs of spinal nerves exit the spinal cord and innervate the body. She has two bulges, one from which the cervical nerves of upper limbs, forming the brachial plexus, the other from which the lumbar nerves of the lower limbs forming the lumbosacral plexus.
It has a slightly flattened and has two grooves, the median anterior and posterior midline.
Composition of the spinal cord:
Like the brain, spinal consists essentially of “white” and substance “gray”:
The white matter contains the myelinated neurons extensions: It completely surrounds the gray matter which way, is framed into three parts, called posterior, lateral and anterior. These cables, made up of groups of neurons called a type beams carry impulses to a specific destination (beams spinal ascending and descending)
The gray matter contains the bodies of neurons and the neuroglia: It has roughly the shape of an H, the side deck is appointing gray commissure, dug a thin channel called the central canal, extension of the 4th ventricle. The ‘pipes’ of H divide into pairs of posterior and anterior horns. Note that exists in some regions, particularly the chest, lateral horns.


The posterior horns contain sensory neurons of the spinal nerves, other neurons form the reflex arc with spinal motor neurons of anterior horns.
The anterior horn contains motor neurons whose axons form the spinal nerves.
The lateral horns contain them when to visceral motor neurons (involuntary)
But unlike the organization of the brain, spinal level, is the gray matter that lies at the center and white edge.
The gray matter:
As the cerebral gray matter, it contains multipolar neuronal cell bodies, extending them, and glial cells. Seen in cross section, spinal presents an aspect of H whose center is the central canal. From both sides, there are symmetrical gray masses, linked by a bridge, the gray commissure. The anterior and posterior projections are called respectively the posterior horns and anterior horns.


The anterior horn contains mostly cell bodies of motor neurons, while the posterior horns are very rich in interneurons. The axons of motor neurons extend into the spinal nerves before reaching their target. The horns on its side when serving visceral smooth muscles via the anterior roots.
The sensory receptors when to them, carry nerve impulses via the posterior roots. Their cell body is located in a bulge of the posterior root, the spinal ganglion. The two roots, anterior and posterior then join to form the spinal nerves, which is observed on both sides of the spinal cord.
The white matter:
Made up of nerve fibers, it is the color white to the presence of myelinated fibers, as bundles of predominantly vertical. It divides into the posterior cord, lateral and anterior, thus linking the bodies of a somatotopic manner, by ascending and descending.
Physiology:
The beams descending spinal
These are bundles s engine, leading nervous impulses from the brain down to the anterior horns of the spinal cord where the neurons coordinate the activity of skeletal muscles:
The pyramidal tracts, also called cortico-spinal drive the motor impulses to skeletal muscles. These are the main vehicles of voluntary control. Their origin dates back to the pyramidal cells of the frontal gyrus, then descend in the midbrain, pons and pyramids of the medulla
The beams extrapyramidal from subcortical structures influence motility by interfering with muscle coordination and balance
The ascending spinal bundles:
they drive the influx of sensory receptors associated with the affected areas of the brain or cerebellum. We note several major ascending spinal bundles: bundles Goll, cuneiform, spino-thalamic, spino-cerebellar ….
The columns of Goll for example, lead information on the members’ position and posture, and touch sensations throughout the body.

The reflex arc:
When you accidentally burn yourself on the edge of a hot pan, have you not noticed that you had already withdrawn your hand before you even have felt the pain? This is made possible by the existence of the spinal reflex arc, which can react to stimuli given automatically and much faster than if it did need intervention and analysis of higher centers. In our case, although the stimulus arrives at the brain, but for information since the reflex arc has averted the immediate danger.
The reflex arc is divided into 5 sequences:
A receiver receives information (often nociceptors)
A sensory neuron via the spinal nerve transmits nerve impulses to the spinal cord
One or several synapse between sensory neuron and an efferent motor neuron transmits information leading to the creation of a nerve impulse at the anterior horn gray
The information is transmitted to an effector (often, a skeletal muscle).
The CNS is then optionally informed.
Example:the tendon reflex, reflex front stretch

B-vascularization:
There are two blood circulation in the lungs: the first is provided by the bronchial vessels (arteries and veins, bronchial) and provide the organ of oxygen and substances necessary for its operation. The second, consisting of veins and pulmonary arteries serves the function of gas exchange.

C-The pleura
The pleura consists of two sheets, one attached to the lungs, the visceral and the other adjacent to the chest wall, the parietal. The pleural space is imbued with a thin layer of liquid, which by capillary action, holds the two layers joined together, and provides a sliding sheets against one another without friction excessive. The pleural cavity is a “virtual”, but becomes really in certain pathologies, such as pneumothorax (presence of air between the two layers, causing their uncoupling and retraction lung), hemothorax (even principle), pleurisy.
The pleura can grow the lung during the expansion of the chest, thus causing a depression which results in the incoming air into the lungs is inspiration. This mechanism of variation of pressure in the socket which allows gas exchange.

D-The respiratory muscles
To achieve the inspiration, the respiratory muscles must oppose the elastic resistance of lungs, tending naturally to retract on itself and the friction of two layers of the pleura. For this, several muscles are involved: the diaphragm, scalene and intercostal and, to a lesser extent, sternocleidomastoid mastoid:

• Like all fluids, air flows from areas of high pressure to low pressure areas. The respiratory muscles act together on the coast. They have a special, double obliquity (hat down and forward reverse).
• The diaphragm, large muscle dome separates the abdominal cavity of the chest cavity, innervated by the phrenic nerves (C 3 C 4 C 5). The contraction causes a decrease in its curvature, up to 10cm.
• The external intercostal muscles, they are innervated by the intercostal nerves, from D1 to D12.
• The scalene, sternocleidomastoid mastoid, trapezius and paravertebral them, can be contracted at a rate significant ventilatory.

The expiration, it is naturally passive part of the natural elasticity of the lungs. Forced expiration will involve the abdominal muscles (by raising the diaphragm), the external intercostal.

II-Physiology:

A – Volumes usual
There are several types of respiratory volumes, highly dependent on age, size and sex of the subject:
The tidal volume, VC, firstly, is the volume inhaled normally and naturally in a quiet breathing at rest.
The inspiratory reserve volume, IRV is the volume available during a forced inspiration, as well as the expiratory reserve volume, ERV, obviously is the volume expired during a forced expiration. It thus determines the vital capacity (VC) of an individual as the sum of its current volume, added an inspiration and forced expiration: one obtains the formula
CV = VRI + VC + ERV
At the end of forced expiration, there remains an air volume expellable by the individual, this is called the residual volume RV determining the functional residual capacity RV + ERV.

B – Control of breathing
To adapt to changing circumstances, whether they be internal during physical exertion, for example, or external, when changes in the composition or pressure of the atmosphere, ventilation suits by situations, witnessed a complex neural activity can interpret all necessary information.

a – the nerve centers:
The nerve centers located in the hemispheres (the central nervous system) are responsible for modifications volunteers in activities developed, but are absolutely not sensitive to changes in blood composition and different metabolic requirements. It has also been demonstrated by sections of the central nervous system, the basic ventilation system was not affected as the pons and the medulla remained intact.

In 1890, L. FREDERICQ was the first to demonstrate that the nervous breathing are directly sensitive to the composition of the blood passing through them: He has therefore made the experience of traffic cephalic cross two dogs.
In this experiment, represented by the diagram above, Fredericq irrigated head of the first dog with the blood of the second body, and vice versa. He then strangled the first dog breath closed, and found that it is the second dog hyperventilates increasing, while the former will leave quietly suffocate the body.
This experience has highlighted the sensitivity of nerve centers respiratory blood composition, while the rest of the body did not respond and left stifle.
We now know that this is the content of O 2 / CO 2 and pH of blood stimulant activity of respiratory centers, through chemo and baroreceptors (usually located on the junction of the butt aorta).
Similarly, a significant decrease in the partial pressure of O 2 (Pa O2), determine an increase in breathing rate. Here, the pH and Pa CO2 did not change, the decrease in Pa O2 is the only stimulus.

Reflexes modifying the respiratory rate:
In addition to the cerebral hemispheres, which voluntarily alter this rate, there are different reactions that can alter significantly the respiratory rate.
The cough reflex: There are many nerve endings located on the epithelial cells of mucous larynx, the bronchi, which are stimulated by inhalants, dust, gases, irritants, foreign bodies … Their stimulation triggers the cough reflex by laryngeal and bronchial constriction.
Similarly, stimulation of myelinated fibers in the epithelium of the bronchi and bronchioles results in hyperventilation, bronchoconstriction, and a contraction of the larynx.
The propriorecepteurs placed at the limb muscles causes an increase of respiration during stimulation, to increase the intake of oxygen before the changes of partial pressures of O2 CO2 does it charge.
Baroreceptor blood pressure causes hypo ventilation in cases of hypertension and conversely.
Other stimuli:

• Stimulus hormones: adrenaline in large quantities shows hyperventilation. It would act by stimulating chemoreceptors arterial
• Stimulus temperature: a temperature increase from 37 to 39 degrees Triple naturally ventilation, hypocapnia resulting mask by reducing it by half. This stimulus is seen, but its mechanism is still unknown.

C – Physiology of pulmonary respiration
In adult humans, there are about 23 divisions between the trachea and air sacs. The first 16 have a role in conduction and there goes on no gas exchange. The 3 following these few cells, but especially beyond the 20th Division that will form the respiratory bronchioles. The exchange surface of cells is particularly extensive, there were 3 500 000 000 cells for an area of 80-90 m 2.
The cell wall has a striated by the blood capillaries in contact. This wall is very thin, about 0.3 mu.m and contains pores allowing gas flow between them. There are also elastic fibers, giving the lung’s skeleton, phagocytic cells and epithelial cells secrete surfactant. There are two blood systems, the pulmonary and bronchial system, one for oxygenation and the other in the vasculature.
The gas exchange there are so passive, pressure gradient, according to the law of Henry. At inspiration, the pressure O 2 atmosphere is higher than that of blood, it causes its dissolution, while at the end is the partial pressure of blood CO 2 which is lower than atmospheric.
The airways provide a variety of roles, in addition to the conduction of gas: The adjusting temperature and humidity of inspired air that reaches those of the body at cellular as well as purification and filtration the latter, thanks to hair cells, mucus and cough.