The t wo arms of the ner­vous sys­tem

Your Horse (UK) - - Your Horse's Care -

The ner­vous sys­tem is di­vided into two: the cen­tral ner­vous sys­tem (CNS) and the pe­riph­eral ner­vous sys­tem (PNS).

Cen­tral ner­vous sys­tem

“The CNS is made up of the brain and the spinal cord, a tube that runs along the neck and back and is pro­tected by the spine,” ex­plains Leti­cia. “The brain is con­nected to the spinal cord by the brain stem, and the brain is where all the sen­sory in­for­ma­tion ends up. It quickly pro­cesses it and then trig­gers a vol­un­tary or in­vol­un­tary re­sponse.” The cere­bel­lum at the back of the brain con­trols all of this traf­fic, a bit like an air traf­fic con­troller. This most com­plex of or­gans is home to mem­o­ries, thoughts and emo­tions and also de­ter­mines your horse’s be­hav­iour. “The spinal cord trans­mits in­for­ma­tion be­tween the brain and the rest of the body, but can also gen­er­ate re­sponses on its own, known as re­flexes,” says Leti­cia.

Pe­riph­eral ner­vous sys­tem

The PNS con­tains sen­sory cells, nerves and gan­glions. In each sen­sory or­gan and along the skin are sen­sory cells re­spon­si­ble for col­lect­ing in­for­ma­tion from their en­vi­ron­ment, such as vi­sion, taste and touch, and send­ing it through the nerves. “Spinal nerves orig­i­nate at the spinal cord, exit the spine and go to the rest of the body,” ex­plains Leti­cia. “Cra­nial nerves start at the brain stem, as they supply the face and struc­tures in the head and neck, and play a vi­tal role in help­ing to check the health of the ner­vous sys­tem.” There are 12 pairs of cra­nial nerves (one left nerve and one right nerve in each pair) and they supply very spe­cific struc­tures of the sen­sory or­gans in the face. “Your vet can try to iden­tify whether there are prob­lems in spe­cific nerves with a few sim­ple tests,” ex­plains Leti­cia. “For ex­am­ple, if it’s sus­pected the op­tic nerve is dam­aged, your vet will make the horse pass through dif­fer­ent ob­sta­cles in vary­ing light con­di­tions to see how he re­sponds. “It gets com­pli­cated, be­cause some nerves share func­tions. A few sim­ple checks of the sen­sory or­gans on the horse’s face will help if we sus­pect dam­age in the brain or brain stem — or it could be af­fect­ing the cra­nial nerves them­selves.” Gan­glions are pe­riph­eric struc­tures next to im­por­tant or­gans. They are formed by neu­rons that con­trol in­vol­un­tary pro­cesses and con­sti­tute part of the au­to­nomic sys­tem.

“All sen­sory in­for­ma­tion ends up in the brain, which quickly pro­cesses it”

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