The nervous system is composed of a central nervous system (CNS), brain and spinal cord, and the peripheral nervous system (PNS), cranial nerves and spinal nerves. The CNS is located within the dorsal cavity, and the PNS extends through the ventral cavity. The central nervous system provides control and coordination of all eleven body systems and utilizes the endocrine system to form hormone chemical messengers that transport through the blood to influence the activity of individual cells of the body and their associated tissues, organs and systems.
The CNS receives sensory (afferent) input from the PNS and directs the flow of information to association neurons (interneurons) to create chemical synapse responses which in turn cause the formation of motor (efferent nerve) responses to stimulus. Association neurons are located in the grey matter of the spinal cord and the brain.
The CNS is protected by the cranium, vertebral column, meninges, cerebrospinal fluid. The spinal cord is an extension of the brain. The spinal cord and the brain stem are joined at the base of the cranium at the foramen magnum. Most of the functions of the head and neck are directly influenced by the brain and transmitted to the PNS via the cranial nerves and spinal nerves of the cervical portion of the spine.
The PNS has two subdivisions
- somatic nervous system (SNS). The SNS is associated with the voluntary control of body movements through the action of skeletal muscles, and also the reception of external stimuli.
- the autonomic nervous system (ANS). The ANS is divided into subsystems: the sympathetic nervous system (SNS) and the parasympathetic (PNS) nervous systems. The SNS and PNS often have opposing effects in the same organs or physiological systems, and the ANS is a major factor in maintaining homeostasis.
Read more about this topic: Head And Neck
Famous quotes related to nervous system:
“A two-week-old infant cries an average of one and a half hours every day. This increases to approximately three hours per day when the child is about six weeks old. By the time children are twelve weeks old, their daily crying has decreased dramatically and averages less than one hour. This same basic pattern of crying is present among children from a wide range of cultures throughout the world. It appears to be wired into the nervous system of our species.”
—Lawrence Kutner (20th century)