Definition
Definition
The nervous system is the set of nerve centers and nerves that allow the coordination and control of the different devices (set of organs that fulfill a function, in the broad sense of the term) of the organism, but also the reception of messages linked to sensation, cognition (intellectual means by which we acquire knowledge) and the psyche.
Classification
There are two types of nervous systems: the somatic nervous system and the vegetative (autonomic) nervous system.
- Le somatic nervous system corresponds to the motor and sensory nervous system. It is responsible for maintaining attitudes, movements voluntary and involuntary, but also tactile sensations painful et Thermal, after receiving messages through receptors located in the skin.
- Le autonomic nervous system, also called autonomic nervous system, allows to regulate various automatic functions of the organism (digestion, respiration, arterial and venous circulation, blood pressure, secretion and excretion). The regulatory centers of the autonomic nervous system are located in the spinal cord, the brain and the brainstem (area located between the brain and the spinal cord).
This autonomic nervous system includes:
- Le parasympathetic nervous system (general slowing of the organs, stimulation of the digestive system). It is associated with a neurotransmitter: theacetylcholine.
- Le sympathetic nervous system, or sympathetic orthosis, corresponding to the organization being put on alert, and to preparation for thephysical activity et intellectual. It is associated with the activity of 2 neurotransmitters: the noradrenaline and the adrénaline (dilation of the bronchi, acceleration of cardiac and respiratory activity, dilation of the pupils, increased secretion of sweat, increased blood pressure, decreased digestive activity).
Anatomy
The nervous system as such is made up, in its anatomical definition, of the peripheral nervous system and the central nervous system.
The central nervous system (neuraxis) comprises several billion neurons (nerve cells) embedded in a supporting tissue: the neuroglia. Neurons communicate with each other via synapses allowing the passage of nerve impulses (orders, sensations). Transmission is carried out using neurotransmitters (adrenaline, acetylcholine, noradrenaline, etc.) which are hormones of neurobiological origin with excitatory or inhibiting capacities. The central nervous system is made up of the encephalon (cerebrum, cerebellum and brainstem) whose protection inside the skull is provided by the meninges:
- The dura mater (outer membrane).
- The arachnoid (central membrane).
- The pia mater (inner membrane, against the nerve substance.
The brain rests on the spinal cord (consisting of a long white cord), which is also protected by the meninges, then by the spinal column formed by the stack of vertebrae. The spinal cord is approximately 45 centimeters long and extends from the base of the brain to the pelvis. Its diameter is 1 cm on average. It is connected to the brain via the medulla oblongata and ends at the bottom with the cauda equina, also called the filum terminale. On each side of the cord appear 31 pairs of roots (anterior and posterior) regularly spaced and emerging between each vertebra. They join to form a spinal nerve.
The spinal cord (like the brain) is made up of two types of nerve tissue:
- La white matter on the outskirts.
- La gray matter in the center (the opposite in the brain).
In cross-section, it appears as a butterfly with two horns, two pointing forward (anterior) and two backward (posterior). At its center lies the ependyma , the canal that allows the circulation of cerebrospinal fluid between the ventricles of the brain and the spinal cord . Two types of information— sensory and motor— transmit through the gray and white matter . The dorsal (posterior) roots contain sensory nerves, while the ventral (anterior) roots contain motor nerves.
The peripheral nervous system consists of all the nerves connected to the central nervous system. There are two types of peripheral nerves:
- The cranial nerves.
- The spinal nerves (31 pairs).