Stimulus: Definition, Types, and Examples
What is Stimulus?
Our sensitivity to temperature allows us to recognise hot or cold situations. Sweating (perspiration) begins in our bodies when the temperature is too high. Similarly, in a cold environment, our bodies’ small hairs stand up. Piloerection is the term for this occurrence. As a result, we attempt to stay cool in the summer and layer up in the winter to be warm.
So, how can humans and other animals sense and respond to changes in the environment’s temperature? You’ve probably noticed that many plants drop their leaves in the winter. What is the source of this transition? How do plants detect this transition? Snakes, hares, squirrels, and other animals, too, run when they detect human presence. What is it that makes them flee? Understanding the term “stimulus” or its plural “stimuli” is the key to answering all of these issues.
Stimulus Definition
In biology, a stimulus is defined as a “detectable change (physical or chemical) in an organism’s environment that results in some functional activity.” Sunlight, for example, works as a stimulant for plants, causing them to grow or migrate towards it. High temperatures, for example, activate (stimulate) the sweat system in our bodies, causing our bodies to cool down as a result.
Stimulus Examples
The act of nature or the environment on an organism that activates (stimulates) it or a component of it to react in some way is also referred to as a stimulus. It is a frequent observation that frogs come out leaping after rain. As a result, rain serves as a motivator for them.
Human behaviour researchers frequently use the term stimulus (or its plural, stimuli). Stimuli are activities, behaviours, or processes that elicit a response from the human mind in psychology. Visual, auditory, tactile, or a combination of these stimuli may be used. The use of stimuli in the therapy of achluophobia is one example (fear of the dark).
The patient (human) is exposed to darkness after therapy. The trigger for achluophobia is darkness. The patient’s bodily responses are monitored in order to determine the patient’s reaction and stage of healing.
Using their sensory organs, the creatures can sense the changes. The sensory organs can sense changes in the environment (temperature, light, sound, etc.) as well as changes within the body (loss of energy results in hunger).
The sensory system sends signals to the mind that cause it to react. Physical action (moving, running, changing shape, etc.) or an internal response can be used as a response (perspiration). Furthermore, an organism can only perceive a signal if it exceeds an absolute threshold.
A stimulus is an item, event, or circumstance that can cause a physiological reaction. Any of the five senses can be elicited by a stimuli. There are two sorts of stimuli based on the stimuli applied to the sensory organs: (1) homologous stimulus and (2) heterologous stimulus. The origin is Latin stimuli (“goad, prick”).
Science of Stimulus
The method of stimulus recognition in animals is as follows:
• An observable change in the environment is referred to as a stimulus.
• Receptors: Environmental inputs are converted into electrical nerve impulses by the receptor.
• Neurons: Neurons are the carriers of nerve signals to the central nervous system.
• Effectors: As a result of the stimuli, effectors create a reaction. Muscles and glands are examples.
In the stimulus-response circuit, three kinds of neurons are involved.
• Sensory Neurons: These cells carry messages from receptors to the brain and spinal cord.
• Relay Neurons: As part of the decision-making process, they transfer signals within the central nervous system.
• Motor neurons: send signals from the central nervous system to effectors (muscles or glands) to initiate a reaction.
What method does the central nervous system employ to assess stimulus strength?
The stimulus’s intensity determines whether or not a nerve fibre fires. If a particular threshold is achieved, the stimulus will have an effect. The neurons will not communicate any data to the brain if they fall below that threshold.
Types of Stimulus
The exterior stimulus and the interior stimulus are the two primary forms of stimuli. Any sort of response to a stimuli is either learnt or instinctive in nature. A deer, for example, will escape if it sees a predator, but a human response may be anything from hiding to driving away in a car to shooting a gunshot. All of these answers were learnt, whereas the deer’s behaviour was intuitive.
I. External Stimulus
Touch and pain are examples of external stimuli, as are vision, smell, taste, sound, and balance (equilibrium). External alterations activate these sensory stimuli.
i. Touch and Pain
Pain is a stimuli that can elicit a strong reaction from the body. Pain has the ability to alter an organism’s behaviour. If the mind thinks that a response is required in response to pain, a signal will be delivered to the muscles, which will respond appropriately.
The pain receptors known as nociceptors detect the pain signal. Another input that might affect an organism’s behaviour change is touch. Touch stimuli, for example, cause the sensitive plant (also known as touch-me-not) to close its leaves.
ii. Vision
Photoreceptor cells are a specific sort of neuron that detects vision inputs. The creatures use eyesight to assess the state of the environment or space around them. Visual cues might entice an animal to pursue its prey. Visual stimulation, on the other hand, will cause prey to escape in order to survive. Visual stimuli aid us in nearly everything we do as humans, from crossing the street to flying an aeroplane.
iii. Taste
Taste is an external stimulus since it is elicited by the tongue’s contact with an external object (food). Gustatory cells are the cells that line the taste buds. They are in charge of developing a sense of taste. The tongue is stimulated to create several digestive enzymes as a result of this perception of taste. As a result, taste triggers the creation of saliva and digesting enzymes.
iv. Smell
Smell is a stimulant for many creatures that either attracts them to the food or repels them if it is rotten or toxic. Before eating, goats, sheep, and other animals of similar breeds usually smell their food. Because of the fragrance, they will avoid the plants even before tasting them.
The aroma of delicious food stimulates the salivary glands in humans. The scent of a toxic gas like ammonia, on the other hand, causes the body to flee the region. The smell is detected by the olfactory organs in the nose. The olfactory organs are stimulated when volatile molecules come into contact with them.
v. Sound
Sound is a stimulant for a wide range of species. Sound aids in the detection of other animals or things. Bats, for example, send out sound waves at regular intervals to detect potential obstacles in their path.
Predators like lions and tigers are stimulated by the sounds of buffalo, cows, goats, deer, and other animals. When an eagle is soaring about, the hen makes a sound that serves as a warning to her brood. The chicks will run up to the hen and hide behind her feathers. In this scenario, the voice of a hen serves as a stimulant for chicks. Sound has an impact on humans as well.
vi. Balance
Animals require balance to walk and travel from one location to another. If the animal is not balanced, gravity will continually drag it down, which might result in a fall. Balance is simpler for four-legged creatures than it is for two-legged ones. An animal’s orientation is an external element that serves as a stimulus.
The cochlea sends information about direction to the brain through its signals. The brain then processes this information, and impulses are sent to muscles to maintain balance.
II. External Stimulus
Internal stimulation comes from within the organism, as the term indicates. Hunger, for example, is an internal stimulus that indicates a lack of energy in the body. It encourages us to consume food in order to recover lost energy.
i. Blood Pressure
Blood pressure is a mammalian internal sensation that is detected by artery receptors. The arteries stretch when blood pressure is too high, and receptors transmit a signal to the brain. The heart rate will be lowered by the brain. The absence of a signal from the receptor indicates that the blood pressure is low. To maintain normal blood pressure, the brain will raise the heart rate. All of this occurs in the absence of any discernible symptoms.
ii. Homeostasis
Homeostasis is the internal physical and chemical equilibrium of separate circumstances that a mammal’s body maintains in order to stay alive. Blood levels, nutrition levels, temperature, and other factors are examples of homeostasis. A change in internal circumstances that is detected by a multitude of receptors is the stimulus for homeostasis.
Stimulus Examples
The three types of stimulation, i.e., stimulation in plants, animals, and humans, are discussed here.
Stimulus in Plants
Water and sunshine are two of a plant’s most important necessities. Light, gravity, weather, and touch are only some of the environmental cues that the plant responds to. A plant’s reaction is either positive (growth toward the stimulus) or negative (growth away from the stimulus) (growth away from the stimulus).
Phototropism, for example, is a plant’s reaction to a stimulus, such as sunshine. By stimulating growth in a specific region of a stem, the plant hormone “auxin” preserves the plant’s orientation towards the light.
Plants’ gravitropism also responds to the stimulus, which is gravity. To get the nutrients it needs, the plant should be kept upright. When a plant falls, auxin levels in the lower section of the stem rise, encouraging cell elongation and bending the stem upwards.
Stimulus in Animals
The sight of another animal (particularly predators), which causes them to flee or fight, is an example of stimulation in animals. Animals’ instinctive reactions to stimuli account for the majority of their responses. When motivated by danger, an ostrich can sprint at speeds of up to 70 kilometres per hour. Dogs may be taught to respond to commands like sit, stand, eat, and so on. The dog perceives the human voice as a stimulus and behaves appropriately.
Stimulus in Humans
Humans are superior in terms of intellectual capabilities, and as a result, they respond to a variety of stimuli in addition to the fundamental ones, like taste, smell, temperature, sound, and so on. Humans can be stimulated by the sight of a beautiful landscape or the scent of food. The trigger for another person is human action. Kindness and softness have a beneficial influence on people.
Stimulus Citations
- Behavioral studies of stimulus learning in zebrafish larvae. Behav Processes . 2019 Jul;164:150-156.
- Detraining: loss of training-induced physiological and performance adaptations. Part I: short term insufficient training stimulus. Sports Med . 2000 Aug;30(2):79-87.Â
- Stimulus-Responsive Nanomedicines for Disease Diagnosis and Treatment. Int J Mol Sci . 2020 Sep 2;21(17):6380.
- Stimulus-responsive luminescent hydrogels: Design and applications. Adv Colloid Interface Sci . 2020 Dec;286:102301.
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