THE NERVOUS SYSTEM

The nervous system collects stimuli - both information from the outside world and information originating within the animal. It creates nerve impulses that cause voluntary or involuntary muscles to contract (including skeletal muscles that control movement, as well as visceral muscles and the muscles involved in glandular secretion).

The nervous system is composed of nerve cells, known as neurons and their supporting structures, which form the neuroglia.

Neurons can act as receptors, when they receive a stimulus; as transmitters, when they send nerve impulses; and as associative neurons, when they serve as a connection between two different neurons.

Nerve fibers have different levels of excitability and conductivity. The speed of nerve conduction from peripheral areas of the body to the brain (or vice versa) is about 30 m/second.

A reflex is the conversion of external sensory information received by the general nervous system directly into motor, secretory or inhibitory information and the transmission of this information from the nervous system to the organ involved, all within a relatively short time.

The central nervous system includes the cerebrum, cerebellum, medulla oblongata (in the cranial cavity) and the spinal cord (in the spinal column).

In addition to the bones that surround it, the central nervous system is covered by three membranes: the dura mater, which is in contact with the bone; the arachnoid membrane; and the pia mater, which is in direct contact with the nerve tissue.

These membranes protect against both physical shocks and internal attack (there is a barrier between the blood and the meninges, known as the blood-brain barrier, which is resistant to various substances). It is needed because neurons are cells that do not regenerate, so any damage is irreparable.

·         The cerebrum contains motor, sensory, visual, auditory, olfactory (smell) and gustatory (taste) centers. It is also the seat of memory and association.

·         The cerebellum controls balance and coordination.

·         The spinal column is an important reflex center, as is the medulla oblongata, which controls vomiting, salivation, etc., as well as automatic functions such as respiration, heartbeat and constriction/dilation of blood vessels.

Ø  The Peripheral Nervous System

The peripheral nervous system is constituted of nerve fibers grouped into nerves that branch symmetrically throughout the body. Sensory nerves carry sensory information from the peripheral areas of the body to the central nervous system's collecting centers. Motor nerves carry nerve impulses generated by the central nervous system to the targeted organ. Many nerves carry out both functions and contain both sensory and motor fibers.

Ø  The Autonomic Nervous System

The autonomic nervous system is centered in ganglia on either side of the spinal column. It controls an organism's involuntary functions (those that are not controlled by the central or peripheral nervous systems). It is subdivided into the sympathetic and parasympathetic systems, which have opposing effects in activating or inhibiting the functions of an organ. For example, the parasympathetic system stimulates intestinal activity, while the sympathetic system decreases it.

The nervous system is involved in many diseases and interactions between medications. Various illnesses can arise, requiring a thorough knowledge of the subject.