Catholic University
Name: Alanies Castillo Level IV “B” Professor MA John Moscoso
The Nervous System
The nervous system is the part of an animal's body that coordinates the actions of the animal and transmits signals
between different parts of its body. In most types of animals it consists of two main parts, the central nervous system
(CNS) and the peripheral nervous system (PNS). The CNS contains the brain and spinal cord. The PNS consists
mainly of nerves, which are long fibers that connect the CNS to every other part of the body. The PNS includes motor
neurons, mediating voluntary movement, the autonomic nervous system, comprising the sympathetic nervous
system and the parasympathetic nervous system and regulating involuntary functions, and the enteric nervous
system, a semi-independent part of the nervous system whose function is to control the gastrointestinal system.
At the cellular level, the nervous system is defined by the presence of a special type of cell, called the neuron, also
known as a "nerve cell". Neurons have special structures that allow them to send signals rapidly and precisely to
other cells. They send these signals in the form of electrochemical waves traveling along thin fibers called axons,
which cause chemicals called neurotransmitters to be released at junctions called synapses. A cell that receives a
synaptic signal from a neuron may be excited, inhibited, or otherwise modulated. The connections between neurons
form neural circuits that generate an organism's perception of the world and determine its behavior. Along with
neurons, the nervous system contains other specialized cells called glial cells (or simply glia), which provide
structural and metabolic support.
Nervous systems are found in most multicellular animals, but vary greatly in complexity.[1] The only multicellular
animals that have no nervous system at all are sponges, placozoans and mesozoans, which have very simple body
plans. The nervous systems of ctenophores (comb jellies) and cnidarians (e.g., anemones, hydras, corals and
jellyfishes) consist of a diffuse nerve net. All other types of animals, with the exception of a few types of worms, have
a nervous system containing a brain, a central cord (or two cords running in parallel), and nerves radiating from the
brain and central cord. The size of the nervous system ranges from a few hundred cells in the simplest worms, to on
the order of 100 billion cells in humans.
At the most basic level, the function of the nervous system is to send signals from one cell to others, or from one
part of the body to others. The nervous system is susceptible to malfunction in a wide variety of ways, as a result of
genetic defects, physical damage due to trauma or poison, infection, or simply aging. The medical specialty of
neurology studies the causes of nervous system malfunction, and looks for interventions that can prevent it or treat
it. In the peripheral nervous system, the most commonly occurring type of problem is failure of nerve conduction,
which can have a variety of causes including diabetic neuropathy and demyelinating disorders such as multiple
sclerosis and amyotrophic lateral sclerosis.
Neuroscience is the field of science that focuses on the study of the nervous system.
Structure
The nervous system derives its name from nerves, which are cylindrical bundles of fibers that emanate from the brain
and central cord, and branch repeatedly to innervate every part of the body.[2] Nerves are large enough to have been
recognized by the ancient Egyptians, Greeks, and Romans,[3] but their internal structure was not understood
