The nervous system of the pig consists of four basic parts.

The brain - The nervous tissue enclosed by the skull. Part of the central nervous system (CNS). It is covered completely by clear membranes called the meninges.

Spinal cord - The other part of the CNS. It extends from the brain as a narrowed bore tube, through the spinal canal to the tail. Between each of the vertebra, which make up the spine itself, it sends branches out to different parts of he body. The spinal cord is responsible for transmitting the electrical impulses from the brain to these branches.

Peripheral nervous system - Nerves leave the brain and the spinal cord and transmit the electrical impulses throughout the body. This system is the voluntary one that is under the pig's control.

Autonomic nervous system - This is the involuntary nervous system of the pig with separate nerves controlling a wide range of involuntary functions. This system partly controls the heart beat, movement of the muscular walls of the digestive system, the hormonal systems and the excretory systems.

There are a number of important bacterial and viral diseases that cause clinical nervous signs in the pig. Such signs arise by infection of the brain, the brain covering, the spinal cord or any of the peripheral nerves. Some common diseases associated with nervous signs include:

• African swine fever (ASF).
• Aujeszky's disease (AD) Pseudorabies (PR).
• Classical swine fever (CSF) - Hog cholerae (HC).
• Congenital tremor - caused by an as yet unidentified virus (possibly a circovirus), swine fever or congenital defects.
• Haemagglutinating encephalomyelitis virus (HEV) infection.
• Iron toxicity.
• Middle ear infection.
• Oedema disease (bowel oedema).
• Poisons - Arsenic, Mercury, Monensin, Organophosphorus compounds.
• Salt - water deprivation
• Porcine stress syndrome (PSS).
• Splay leg - a disease of piglets at birth.
• Streptococcal meningitis (SM).
• Teschen or Talfan diseases.
• Tetanus.

Terminology

Cerebrospinal fluid - Fluid that circulates around within the brain and spinal cord. Samples of this fluid can be obtained by needle and syringe for laboratory tests to diagnose nervous disease.

Congenital tremor - A condition in newborn piglets characterised by muscle tremors and shaking. (See chapter 8).

Encephalitis - Inflammation of the brain.

Encephalomyelitis - Inflammation of the brain and spinal cord. Viruses multiplying in the central nervous system primarily cause encephalitis and encephalomyelitis although they may cause meningitis as well. Such viruses include aujeszky's (pseudorabies), rabies, teschen / talfan, haemagglutinating encephalitis (vomiting and wasting disease), classical swine fever, African swine fever, blue eye disease in Mexico, encephalomyocarditis in the US, Caribbean and some other countries, and Japanese B. encephalitis in S.E. Asia.

Meninges - Clear membranes covering the surface of the brain.

Meningitis - Inflammation of the meninges which is extremely painful and often results in dramatic clinical signs. Bacterial infections causing meningitis include Streptococcus suis (mainly type 2), salmonella, Haemophilus parasuis, E. coli and any bacteria gaining access to the meninges from a septicaemia. Viruses may also cause meningitis. Middle ear infection may be mistaken for meningitis.