The peripheral system (PNS) is composed of a number of nerves that extend outside of the central nervous system. The nerves and nerve networks that make up the PNS are actually bundles of axons from neuron cells. Nerves can range from relatively small to large bundles that can be easily seen by the human eye.
The PNS can be further divided into two different systems: the somatic nervous system and the autonomic nervous system.
Somatic Nervous System: The somatic system transmits sensory communications and is responsible for voluntary movement and action. This system is composed of both sensory (afferent) neurons, which carry information from the nerves to the brain and spinal cord, and motor (efferent) neurons, which transmit information from the central nervous system to the muscle fibers.
Autonomic Nervous System: The autonomic nervous system is responsible for controlling involuntary functions such as certain aspects of heartbeat, respiration, digestion and blood pressure. This system is also related to emotional responses such as sweating and crying. The autonomic system can then be further subdivided into two subsystems known as the sympathetic and parasympathetic systems.
As noted earlier, the endocrine system is not a part of the nervous system, but it is still essential to communication throughout the body. This system is composed of glands, which secrete chemical messengers known as hormones.
Hormones are carried in the bloodstream to specific areas of the body, including organs and body tissues. Some of the most important endocrine glands include the pineal gland, the hypothalamus, the pituitary gland, the thyroid, the ovaries, and the testes. Each of these glands works in a number of unique ways in specific areas of the body.
So how are the endocrine and nervous system linked? The brain structure known as the hypothalamus connects these two important communication systems. The hypothalamus is a tiny collection of nuclei that is responsible for controlling an astonishing amount of behavior. Located at the base of the forebrain, the hypothalamus regulates basic needs such as sleep, hunger, thirst, and sex in addition to emotional and stress responses. The hypothalamus also controls the pituitary glands, which then controls the release of hormones from other glands in the endocrine system.
