Introduction to the Nervous System

The nervous system controls bodily function by gathering sensory input, integrating that information internally, and communicating proper motor output.

Learning Objective

Describe the hierarchical structure of the nervous system

Key Points

The nervous system is the body's main communication system; it gathers, synthesizes, and uses data from the environment.
The most basic unit of the nervous system is the neuron, which serves as both a sensor and communicator of internal and external stimuli.
The nervous system can be broken down into two major parts—the central nervous system and the peripheral nervous system.
The central nervous system, the main data center of the body, includes the brain and spinal cord.
The peripheral nervous system includes all of the neurons that sense and communicate data to the central nervous system.
The peripheral nervous system can be further divided into the autonomic system, which regulates involuntary actions, and the somatic system, which controls voluntary actions.

Terms

central nervous system
In vertebrates, the part of the nervous system comprising the brain, brainstem, and spinal cord.
peripheral nervous system
The part of the nervous system comprising a large system of nerves that are linked to the brain and spinal cord; this system is divided into the autonomic and somatic nervous systems.
neuron
A cell of the nervous system, which conducts nerve impulses; consisting of an axon and several dendrites. Neurons are connected by synapses.
innervate
To supply nerves to a tissue.

Full Text

The nervous system allows organisms to sense, organize, and react to information in the environment. The basic unit of the nervous system is the neuron. Synapses form between the neurons, allowing them to communicate to other neurons or other systems in the body. The general flow of information is that the peripheral nervous system (PNS) takes in information through sensory neurons, then sends it to the central nervous system (CNS) to be processed. After processing, the CNS "tells" the PNS what to do—what muscles to flex, whether the lungs need more oxygen, which limbs need more blood, any number of biological processes—and the PNS makes it happen through muscle control. The neurons responsible for taking information to the CNS are known as afferent neurons, while the neurons that carry the responses from the CNS to the PNS are known as efferent neurons.

The human nervous system

The nervous system of the human body, including the brain and spinal cord (central nervous system) and all the nerves of the body (peripheral nervous system).

The nervous system can be divided into two major parts—the central nervous system (CNS) and the peripheral nervous system (PNS).

Central Nervous System

The central nervous system includes the spinal cord and the brain. The brain is the body's main control center. The main function of the CNS is the integration and processing of sensory information. It synthesizes sensory input to compute an appropriate motor response, or output.

Peripheral Nervous System

The peripheral nervous system includes a large system of nerves that are linked to the brain and spinal cord. It is comprised of sensory receptors, which process changes in internal and external stimuli and communicate that information to the CNS. The PNS can be further subdivided into the autonomic nervous system and the somatic nervous system.

Autonomic Nervous System

The autonomic nervous system regulates involuntary actions such as internal-organ function and blood-vessel movement. It supplies nerves to ("innervates") cardiac and smooth muscle tissue. The autonomic nervous system is made of two components, which work in opposition to one another: the sympathetic nervous system, responsible for the body's "fight-or-flight" response to danger, and the parasympathetic nervous system, which calms the body back down.

Somatic Nervous System

The somatic nervous system controls voluntary movements such as those in the skin, bones, joints, and skeletal muscles.

Both of these systems within the PNS work together with the CNS to regulate bodily function and provide reactions to external stimuli.

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