Differences Between Hormonal and Nervous Communication

Hormones are organic compounds produced in one part of the body, form which they are transported to other parts where they produce a response. A minute quantity may exert a profound effect on the organism’s development, structure or behavior. Here we shall only be concerned with the general principles involved in their activities especially in what we shall henceforth refer to as hormonal and nervous communication.

Hormones are secreted by endocrine organs directly into the blood stream. The word endocrine means internal secretion and the endocrine organs are therefore glands of internal secretion. Since they shed their secretion into the bloodstream, they have no ducts and are hence known as ductless glands. Once in the bloodstream, the hormones are carried round the body, bringing about responses in various places. Structures that respond to them are called target organs.

Though they may be widely separated from one another spatially, endocrine organs do not exist in functional isolation. They influence one another and through their integrations, are integrated into a highly coordinated system, the endocrine system.

Hormonal Compared With Nervous Communication

A basic similarity between hormonal and nervous communication, i.e the endocrine and nervous systems, is that both provide means of communication within the body of an organism. Both involve transmission of a message which is triggered by a stimulus and produces a response. The target organs of a hormone are equivalent to a nerve’s effectors. The main difference between the two systems concerns the nature of the message. In the endocrine system the message takes the form of a chemical substance conveyed through the blood system. In the nervous system the message is a discrete, all – or – nothing action potential transmitted along a nerve fibre. All other differences spring from this fundamental one. They can be listed as follows:

  1. Because of the comparatively high speed at which impulses are transmitted along nerves, nervous responses are generally evoked more rapidly than hormonal ones.
  2. Since it is shed into the bloodstream, there is nothing to stop a hormone being carried to every part of the body. Nervous impulse, however, are transmitted by particular neurons to specific destinations.
  3. As a result of (2), hormonal responses are often widespread, sometimes involving the participation of numerous target organs far removed from one another. In contrast, nervous responses may be very localized, involving perhaps, the contraction of only one muscle
  4. Hormonal responses frequently continue over a long period of time: obvious examples of such long – term responses are growth and metabolism. Nervous responses, on the other hand, are usually rapid ad short – lived, such as the contraction of a muscle.

Despite these obvious differences between hormonal and nervous communication, there is one fundamental similarity between the two systems: both involve chemical transmission. We saw earlier that in the nervous system remission of the message across the neuro-muscular junctions is achieved by a chemical substance. The latter is equivalent to a hormone in the endocrine system. The principal difference between them is that the neuromuscular transmitter has to travel a mere fraction of a micrometer, whereas a hormone may have to travel the full length of the body to achieve its full effect.

This may seem a rather academic point of comparison, but in fact it provides a basis for linking the two systems. This is best illustrated by the adrenal glands. The middle part of these glands, the adrenal medulla, secretes the hormone adrenaline which is chemically almost identical to the transmitter substance noradrenaline produced at the ends of the sympathetic nerves. It is interesting that adrenaline evokes the ames responses as impulses in the sympathetic nerves: acceleration of the heart, constriction of arterioles, dilatation of the pupils, etc. in addition adrenaline induces a marked increase in the metabolic rate, so that the combined effect of the endocrine and nervous systems is to prepare the body for emergency.

We see, then, that there is a close connection between the endocrine and nervous system(hormonal and nervous communication system). In the case of the adrenal medulla and sympathetic nerves, the connection is so close that one suspects that the two share a common evolutionary origin. Innervated by the sympathetic nervous system, the adrenal medulla can be looked upon as an enormous conglomeration of modified nerve cells which being far removed from any effectors shed their transmitter substance into the bloodstream.

In-dept Look at Both Hormonal and Nervous Communication 

There are two primary systems in the body that coordinate and control internal activities. One is the nervous system, the other is the endocrine system.

The nervous system uses electrical impulses to collect and respond to information from the environment. The endocrine system, on the other hand, uses chemical messages (hormones) that travel through the bloodstream.

1. Hormones are Chemical Messages

Unlike the nervous system which relies on electrical impulses, the endocrine system uses chemical signals to communicate with specific cells in the body. A hormone is a chemical that is secreted by endocrine glands and travels via the bloodstream to cells that have receptor molecules on their surfaces. When a hormone binds to its target cell, it sends a signal that changes the activity of that cell. For example, if the adrenaline hormone binds to cells that line the heart, it will increase their heart rate.

In comparison, neurons use chemicals called neurotransmitters to send their messages. These are released at the end of the axon terminals of one neuron and pass to dendrites on other neurons in a region known as a synapse. They then carry the message to other nerve cells or to muscle cells, sensory organs, glands and other structures. Hormones are similar to neurotransmitters, but they work over a much larger range of distances and for much longer periods of time.

The endocrine system is made up of a network of specialised glands that produce and release hormones into the body’s bloodstream. These chemical messengers act to keep the body at a stable internal temperature, regulate metabolism – how the body gets energy from the food we eat – and control other functions such as sexual function, growth, and sleep.

When a hormone arrives at its target cell, it is recognised by the special lock (receptor) molecules on its surface. This is called the “lock and key” system. The hormone will only affect the target cell if it fits the receptors on its surface. If the hormone binds to the target cell, it will activate a series of biochemical reactions that change the cell’s activity and can lead to a number of different effects such as changing the rate at which the cell takes up glucose from the bloodstream or turning off genes involved in production of inflammatory proteins.

Unlike the quick responses to neural signals, hormonal changes take place over a longer period of time and may last for the rest of an organism’s life. They are also more likely to be associated with long-term changes in the body such as those that occur during puberty.

2. Hormones Travel Longer Distances

The nervous system relays information by sending electrical action potentials down neurons and, at the end of a neuron, releasing chemical neurotransmitters into the gap (synapse) between it and the next cell. These neurotransmitters carry the message across the synapse and interact with receptors on the receiving cell to initiate a response. The response may be continuing electrical signaling or the cellular response itself, such as an increase in a protein’s activity. Hormones, on the other hand, travel in blood plasma and affect cells throughout the body at a distance from their place of origin.

Hormones are chemical messengers secreted by endocrine glands and travel through the bloodstream to bind with receptors on target cells. Unlike neurotransmitters that are released in the synapse, hormones operate over a much longer distance and over a greater time length and mediate long-term changes. Similarly, a single hormone can only bind with a receptor with which it has specific affinity – similar to how a key fits into a lock.

A hormone’s cellular responses may also be modified at the protein or genetic level. This means that hormones can have a wide range of effects on the body, from promoting growth to inhibiting reproduction. Because of their longer-term effects, hormonal changes often have a significant impact on behavior as well.

An example of a behavioral response to a hormone is the fight-or-flight reaction that occurs when the brain detects danger in the environment. The nervous system signals the adrenal glands to release a hormone, adrenaline, that increases heart rate and blood pressure and provides energy for a quick reaction to the threat.

Behavioral endocrinologists study the interactions between hormones and behavior. They want to know how a hormone influences the behavior of an animal and how that behavior might influence the concentration of that hormone in the bloodstream. They are interested in how the nervous and endocrine systems coordinate to respond quickly to the environment, maintain homeostasis, control development, and mediate reproduction.

3. Hormones are Graded Events

The human body communicates through two different mechanisms: hormonal and nervous control. Hormonal control involves the endocrine system secreting hormones into the bloodstream from glands throughout the body to produce an effect on target organs throughout the body. Neural control occurs when nerve cells in the nervous system generate electrochemical impulses that travel along nerve fibres.

In general, nerve signals are much faster than hormones. This is because nerve signals can be transmitted across a synapse at speeds of up to 100 m/s, whereas it takes a matter of seconds for a hormone to travel the same distance from its source in the endocrine system into the bloodstream and then to the target tissue.

However, when comparing the speed of nerve and hormonal communication it is important to remember that nervous responses are a result of the occurrence of a change in the environment or external stimuli called a ‘stimulus’. A hormone on the other hand is a response to an internal stimulus, which may be the production of a particular steroid by the ovaries in order to prepare for childbirth or the secretion of oxytocin by the pituitary gland to trigger a mother’s bond with her unborn baby.

It should be noted that the interaction between hormones and behavior is bidirectional, which means that hormone concentrations can influence behavior, and behavior can also influence hormonal concentrations. For example, a decrease in the osmotic pressure of water in the blood stimulates the production and transport of antidiuretic hormones (ADH or vasopressin) by the kidneys, which increases the permeability of the walls of the collecting ducts to water so that the body can retain more fluids.

Another difference between neural and hormonal communication is that while neural messages are digital, all-or-none events that have rapid onset and offset, hormonal messages are analog, graded events that can take seconds, minutes or even hours to occur. The result of this is that the nervous system mediates changes in behavior that are short-term, whereas the endocrine system is more capable of regulating long-term processes like growth, development and reproduction.

4. Hormones are not a part of the Nervous System

The human body uses two primary systems to control and coordinate functions. The nervous system is responsible for quick responses to stimuli, and the endocrine system controls slower, longer-lasting changes in the body. Both systems use chemical signals to convey information, but they differ in how they do so.

The endocrine system secretes hormones into the bloodstream from glands that regulate various aspects of bodily function, including growth, metabolism, reproduction and movement. Hormones are molecules that can bind to specific docking sites on cells throughout the body, known as receptors, and trigger different responses. Some hormones affect a single cell type, while others can have many target organs.

Nervous system communication primarily occurs because of the propagation of an electrical signal through the axon terminals of neurons to their dendrites across a synapse with a neighboring neuron. Neurons can respond quickly to stimuli, and the axons of nerve cells will release chemicals called neurotransmitters that carry the action potential to the dendrites of the next cell.

In the endocrine system, the chemical messengers are hormones that travel from the endocrine cell to a cell with a specific receptor. A hormone will bind to its receptor, which will then send a message to the cell that says “this is what needs to be done.”

The differences between hormonal and neural communication are important for maintaining homeostasis in the human body. Hormonal communication is much slower than neural, but it can affect multiple target cells in the body. Neuronal communication is much faster, but it can only send messages to one or a few cells at a time.

The endocrine system is responsible for long-term regulation of the body, such as growth, reproduction and metabolism. If the endocrine system isn’t working properly, then it can cause a wide variety of diseases and disorders that include weight gain or loss, menstrual abnormalities, fatigue, headaches, and high blood pressure. There are also a number of neurological illnesses that affect the brain and spinal cord, such as epilepsy and seizures, stroke, and Alzheimer’s and Parkinson’s disease. While some of these conditions are a result of certain lifestyle habits, most are a result of a malfunctioning nervous or endocrine system.

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