While neurons are the building blocks of the body’s communication system, it is the networks of neurons that allow signals to move between the brain and body. These organized networks, composed of up to one trillion neurons, make up what is known as the nervous system. The human nervous system is composed of two parts: the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which is composed of nerves and nerve networks throughout the body.
The endocrine system is also essential to communication. This system utilizes glands located throughout the body, which secrete hormones that regulate a variety of things such as metabolism, digestion, blood pressure and growth. While the endocrine system is not directly linked to the nervous system, the two interact in a number of ways.
The Central Nervous System:
The central nervous system (CNS) is made up of the brain and spinal cord. The primary form of communication in the CNS is the neuron. The brain and spinal cord are absolutely vital to life and functioning, so there are a number of protective barriers surrounding them starting with the bone (skull and spine) and membrane tissues known as meninges. In addition, both structures are suspended in a protective liquid known as cerebrospinal fluid.
Why are the brain and spinal cord so important? Think of these structures as the literal "center" of the body’s communication system. The CNS is responsible for processing every sensation and thought you experience. The sensory information that is gathered by receptors throughout the body then passes this information on to the central nervous system. The CNS also sends messages out to the rest of the body in order to control movement, actions and responses to the environment.
The Peripheral Nervous System:
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.
- Sympathetic Nervous System: The sympathetic system controls the body’s response to emergencies. When this system is aroused, a number of things begin to occur: your heart and breathing rates increase, digestion slows or stops, the pupils dilate and you begin to sweat. Known as the fight-or-flight response, this system responds by preparing your body to either fight the danger or flee.
- Parasympathetic Nervous System: The parasympathetic nervous system functions to counter the sympathetic system. After a crisis or danger has passed, this system helps to calm the body. Heart and breathing rates slow, digestion resumes, pupil contract and sweating ceases.
The Endocrine System:
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.