The t wo arms of the nervous system
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”