16.1: Organization of the Nervous System
The nervous system is one of the most complex systems in our body. It is organized into two main divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS, comprising the brain and spinal cord, houses billions of neurons. The brain is housed in the skull, while the spinal cord is linked to the brain through the foramen magnum of the occipital bone and is surrounded by the protective structure of the vertebral column. It is responsible for processing various types of sensory information, as well as being the source of thoughts, emotions, and memories. It also initiates signals that trigger muscle contractions and gland secretions.
On the other hand, the PNS includes all nervous tissue outside the CNS. It comprises nerves and sensory receptors—structures that monitor changes in both external and internal environments.
The PNS is further divided into sensory and motor divisions. The sensory division brings input to the CNS from sensory receptors throughout the body, providing sensory information about both somatic and special senses. The motor division, which transmits output from the CNS to effectors like muscles and glands, is divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS). The SNS controls the activity of skeletal muscles, while the ANS controls the activities of smooth muscles, cardiac muscles, and glands.
