Nervous system

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The nervous system receives information from the outside world and from other parts of the body. It also sends out nerve impulses, which cause voluntary or involuntary contractions of the skeletal muscles that control movement, visceral muscles and the muscles involved in glandular secretion.
The nervous system is composed of specialised nerve cells known as neurons and their supporting structures, which form the neuroglia.
Neurons are receptors when they receive a stimulus, transmitters when they send nerve impulses and relays when they connect two different neurons.
Nerve fibres have different levels of excitability and conductivity. The speed of nerve conduction from the periphery to the brain and vice versa is about 30 milliseconds.
A reflex is the immediate conversion, via the general nervous system, of sensory information from the outside into motor, secretory or inhibitory information, which is then transmitted to the organ concerned by the reflex in question. This all occurs in a short space of time.

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Central nervous system

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The central nervous system comprises the cerebrum, cerebellum, medulla oblongata (in the cranial cavity) and spinal cord (in the medullary cavity, all along the spinal column). Besides the protective bones that surround it, the central nervous system is covered by three membranes, the meninges: 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. This protection from both physical shocks and internal attack is vital
because neurons do not regenerate, so any damage will be irreparable. There is a barrier too between the blood and the meninges, known as the blood-brain barrier, which blocks various substances to help provide protection.

• The cerebrum is the centre of motor and sensory nerves, sight, hearing, smell and taste, as well as memory and association.

• The cerebellum is the centre of balance and coordination.

• The spinal column is an important centre of reflex, as is the medulla oblongata which is also the centre of autonomic functions, such as respiration, vomiting, salivation, cardiac function and vessel dilation/constriction.

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Peripheral nervous system

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The peripheral nervous system is composed of nerve fibres grouped into nerves which form symmetrical branches throughout the body. Sensory nerves convey sensory information from the periphery to the collecting centres of the central nervous system. Motor nerves convey nerve impulses generated by the central nervous system to the target organ. Many nerves contain both sensory and motor fibres.

Autonomic nervous system

Duhayer_Royal Canin

The autonomic nervous system is centred in ganglia on either side of the spinal column. It controls the autonomic or visceral functions, which are those not controlled by the central or peripheral nervous systems. It is divided into the sympathetic and parasympathetic systems, which have opposing effects, activating or inhibiting an organ’s functions. The parasympathetic system stimulates intestinal activity, for example, whereas the sympathetic system decreases it.

The nervous system is involved in many diseases and interactions between medications. Disorders can be highly varied and exceptional knowledge of the subject is required.

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