When a person touches a hot plate or catches a ball, the organs of the nervous system are responsible for the body’s coordinated response. This system is made up of the brain, spinal cord, and a network of neurons and glial cells that travel the length and breadth of the body. The organs are found in vertebrate and some invertebrate animals, and all network together to provide response to stimuli.
The nervous system is often called the central processing unit (CPU) for an animal. It translates information from every part of the body and then directs the appropriate response. The nervous system is broken down further into the central nervous system and the peripheral nervous system. The central nervous system is made up of the brain, the spinal cord and even the retina, and it is directly responsible for the translation of the messages sent by the peripheral nervous system, which is the network of nerves that run throughout the body.
Neural pathways are the routes that neurons take to send messages to the brain and spinal cord, which then translate the messages and send responses back. Neurons produce neurotransmitters, special chemicals, at the point of the junction of neurons, called synapses. Every part of the human body is filled with neurons, and they allow the senses to function and the limbs to respond. Humans have as many as one billion cells dedicated to the nervous system.
If the central nervous system is the CPU for an animal, then the brain stem is the CPU for the nervous system itself. The brain stem is comprised of the midbrain, the pons and the medulla oblongata. These are the parts of the brain that connect directly to the spinal cord, and injury to this area can result in permanent paralysis or loss of any type of motor response.
The study of the brain and its functions is called neuroscience. Neuroscience attempts to unlock the mysteries of the brain, as there are still many things that medical experts do not know or understand about this organ and how it functions. The field also studies injuries to the spinal cord that result in partial or full paralysis, as well as strokes and their resulting effects on the different parts of the body.
Sponges, mesozoans and placozoans are examples of multi-cellular organisms that do not have nervous system organs, but most other animals do. This includes the group of animals to which humans belong, called bilateria, as well as most of the vertebrates and invertebrates.