The nervous system is a complex system of nerves and specialized cells that allows the body to transmit and receive messages. It serves as the body’s primary control and communications center, responsible for transmitting and receiving messages between every other system in the body.
The sensory function involves transmitting data from sensory receptors, which register internal and external stimuli to the central nervous system (CNS), where it is processed by the brain. The CNS relies on the sonscious and subconscious signals from the body’s sensory receptors to make it aware of any threats. It is also charged with the higher functions of language, imagination, emotion, and personality.
When the CNS receives sensory input, a complex network of neurons in the brain and brain stem evaluates, categorizes, and files this information, making it available for decision-making and future retrieval. After the incoming sensory signals are evaluated, a signal is sent through the nerves of the peripheral nervous system (PNS) to effector cells, which release hormones or otherwise cause the body to respond to the stimulus.
The somatic nervous system (SNS), which is part of the PNS, directs the conscious, voluntary movements of the body. The autonomic nervous system (ANS), on the other hand, controls all the involuntary neurons, those that do not require conscious direction to the function, such as cardiac, visceral, and glandular tissues.
The ANS is further divided into the sympathetic and parasympathetic systems. The sympathetic system is responsible for the body’s fight or flight response which, when activated, increases respiration, heart rate, and adrenaline and stress hormone levels in the blood, whil suppressing digestive functions. The parasympathetic system takes over when the body rests and digests. This system tries to undo what the sympathetic system does when it encounters a threat, e.g. decreasing respiration and heart rate, while increasing digestion and waste elimination.
The enteric nervous system (ENS) is yet another division of the autonomic nervous system and is in charge of regulating the digestive system. As mentioned above, it receives input from both the sympathetic and parasympathetic divisions of the ANS, instructing it what to do. The majority of the ENS’s functions, however, are regulated independently, warranting the nickname “the second brain,” and rightly so, for it alone boasts as many neurons as exist in the spinal cord.