The Interplay Between Endocrine and Nervous Systems
4 The Endocrine System
The endocrine or hormonal system is another system of coordination. This system is closely related to the nervous system and is dependent on each other. In some cases, the nervous system stimulates or inhibits the secretion of hormones, and in other cases, hormones stimulate or inhibit the action of the nervous system.
The endocrine system consists of a set of glands located throughout the body, called endocrine glands or glands of internal secretion, which empty their secretory products directly into the blood.
The endocrine glands are formed by specialized cells of secretory type, synthesizing chemicals called hormones.
Hormones, once produced, are discharged into the blood and transported to all parts of the body through blood vessels. However, they only exert their action on certain cells or organs, called target cells or target organs.
Hormones are “chemical messengers” that have the following features:
– Perform remote functions where they have been synthesized.
– The reactions are slower than those produced by the nervous system, but are more durable.
– They act in very small quantities, and when serving, they degrade rapidly. It is therefore important that the release of endocrine glands occurs continuously as needed.
Unlike other organ systems, the endocrine system is not connected together; the various bodies that constitute it are located in different parts of the body.
5 The Functioning of the Nervous System
When we hear a voice calling us or feel a prick from a needle unexpectedly, our nerve centers produce two types of different responses. In the first case, we can consciously move our head toward the source of the sound, and in the latter, we quickly withdraw our hand unconsciously. The two types of responses are developed by the nerve centers of the central nervous system, but are made differently: one voluntary and one reflexive.
Voluntary Acts
Moving the head toward the source of a sound is a voluntary act. All voluntary acts, from the simplest to the more complex, are performed under the control of the brain.
The stimulus recorded by the receiver, in this case the ears, is transmitted through sensory nerves to the brain, which analyzes and prepares a response, such as turning your head. The response is sent in the form of nerve impulses from the brain through the motor nerves to the muscles (effectors), which move the head.
In response, a voluntary act is conscious and deliberate. The development of the response takes place in the brain.
Reflex Actions
When we feel a prick, we make a reflex action. Such acts do not depend on the will, so they produce involuntary responses that are not controlled.
In a reflex action, the brain is not involved, so the path of the nerve impulse is much shorter, and the response is much faster.
The body’s response to a stimulus in a reflex action is involuntary, and the nerve center involved in the elaboration of the response is the spinal cord.
The reflex actions are performed by a structure called the nerve reflex arc, which involves the following elements:
– A receptor, which captures the stimulus (e.g., skin, which receives the prick).
– A sensory neuron, which carries the nerve impulse from the receptor to the spinal cord.
– An association neuron, located in the spinal cord, which connects the sensory neuron to the motor neuron.
– A motor neuron, which leads to the effector response.
– An effector (muscle), which performs the movement in response (the muscle contracts and withdraws the arm).