Chapter 36.4, Problem 11SAQ

Summary Introduction

To explain:

“The difference in action between a hormone, a paracrine signal, a neurotransmitter and a pheromone”.

Introduction:

A neurotransmitter is a chemical released by the nerve cells in response to external stimuli. A hormone is a chemical substance which is secreted by the body cells. They are regulatory chemical substance that plays an important role in the growth and development of the body. There are three types of signals: endocrine signal, paracrine signal and autocrine signal. The pheromones are a chemical substance released by an organism in environment to transmit the signal to another organism. This pheromone affects the physiology and behaviour of other organisms.

Explanation of Solution

The difference between the action of a neurotransmitter, a hormone, a paracrine signal and a pheromone are described below:

Mode of action of neurotransmitter.	Mode of action of hormone.	Mode of action of paracrine.	Mode of action of pheromones.
When there is a detection of external stimuli, the central nervous system sends signals to the nerve cells. This nerve impulse is then passed to the axon. The axons conduct the signal very quickly and release the neurotransmitter at the synapse. At the short distance of synapses, the neurotransmitters diffuse and pass the information to target organ.	A hormone is released by the organ system when it receives an internal stimulus. The released hormone then reaches the target site by travelling through the cardiovascular system. Then the target organ will respond to this signal.	Paracrine signalling is a form of signal through which two cells interact with each other. In paracrine signal, the hormone cannot enter into the bloodstream, rather its transmitted signal through receptor and influence the activity of nearby cells.	Pheromones are hormones secreted by organism into the environment. This hormone secreted by one organism that influence the behavioural and physiological activity of another organism which is present within the population.
A neurotransmitter releases their signal to the axon of the same individual.	A hormone directly release into the bloodstream of an individual.	A paracrine send signals through the receptor to nearby cell of the same individual.	A pheromones  are secreted to outside the body of an organism into the environment.

Conclusion

The central nervous system sends impulses to axons to release the neurotransmitter and pass the information to target cells. A hormone pass information to target cells by travelling through the cardiovascular system. A paracrine signal influences the activity of nearby cells of the same individual. A pheromone signals influence the activity of other organisms that present within the populations and the endocrine hormone influence the activity of distant cells within the individual.