Both the endocrine system and the nervous system are vital to the survival of organisms. However, to appreciate their similarities and differences fully, we must review their function within humans. The nervous system coordinates the activities of muscles, monitors the organs, constructs and processes input from the senses, and initiates actions or responses. The endocrine system controls ductless endocrine glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to affect distant organs (referred to as target organs).
Both systems are similar in that they affect a target organ or organs. However, their affect on these organs is quite different. If we were to examine a simple reflex arc or all nervous coordination in general, we would find that the effect of a nerve impulse, whether it is in a simple reflex arc or a muscle contraction, is short-lived. For example, when touching a hot plate, an immediate response will be produced. In contrast, looking at the mechanisms involved in controlling blood glucose levels, for example, we find that the effect of hormones is long-lasting on target organs.
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Additionally, it is also important to note that hormones have a widespread effect, meaning they affect more than one organ at a time. In contrast, nerve impulses typically only affect one organ at a time. These differences may be related to the speed at which hormones and nerve impulses are transmitted. Nervous impulses travel as waves of depolarization along long nerve fibres by a method known as saltatory conduction, where the impulses jump from one Node of Ranvier to the next, speeding up the transmission. Hormones, however, travel through the blood, in which case they travel slowly.
An exception to this fact can be said to be given by the adrenaline hormone. Adrenaline plays a central role in the short-term stress reaction, i.e. the physiological response to threatening or exciting conditions (fight or flight response). Although it is relatively slower than the transmission of nerve impulses, it is comparatively faster than other hormones, and its effects are usually short-lived, e.g. increasing the heart rate.
A further similarity that can be drawn between the two systems is that they both have receptors. The nervous system uses receptors to coordinate a response to an action. Receptors, a part of the nervous system, can also be referred to as sense organs such as the eyes or skin. Within the endocrine system, some hormones act as secondary messengers having to bind to cell surface receptors to stimulate the production of messenger molecules, leading to a response, e.g. the conversion of glycogen to glucose.
Within the human body, almost all systems work in conjunction with one another. This can also be applied to the endocrine and nervous systems. For example, gonadotropin-releasing hormone (GnRH) is a peptide hormone responsible for releasing FSH and LH from the anterior pituitary. GnRH is considered a neurohormone, a hormone produced in a specific neural cell and released at its neural terminal. A key area for the production of GnRH in the hypothalamus is the preoptic area, which contains most of the GnRH secreting neurons.
This can be said to be an example of how both systems work together. To conclude, the endocrine system is in charge of body processes that happen slowly, such as cell growth. The nervous system monitors faster processes such as breathing and body movement. However, even though the nervous and endocrine systems are separate, they often work together to help the body function properly.