Need help with these activities Tactile Localization Sensation 347 Activity 4: Demonstrating Adaptation of Touch Receptors The subjects should be able to determine how long the sensation persists for each location of the stimulus. Repeat the test placing the coin at a different location. How long does the sensation persist at the second location? Testing Tactile Localization After awareness of the first location has been achieved, the subject touches the palm of the subject’s hand with a coin. The coin should have a different color or a marked point to indicate the exact point of touch. Measure the distance between the two marks in millimeters. Repeat the test in the same spot twice more, recording the error of localization for each test. Average the results of the three determinations and record it in the Activity 3 chart. Are the receptors being stimulated when the four coins are used rather than the one coin? Body area tested Average error (mm) Palm of hand Explain how perception of the stimulus intensity has changed. Fingerpad Anterior forearm Back of hand Back of neck Repeat the procedure on the body areas listed and record the results. Activity 5: Demonstrating Adaptation of Temperature Receptors Which area has the smoothest error of localization? Obtain a finger bone and fit it with a 45°C water bath. Place the finger bone in the warm and cold water baths alternately. Keep one hand in the warm water bath and the other hand in the cold water bath. Adaptation of Sensory Receptors What is the sensation of the finger when it is placed in the warm and cold water baths? The number of impulses transmitted by sensory receptors often changes both with the intensity of the stimulus and with the length of time the stimulus is applied. In many cases, when a stimulus is applied for a prolonged period without movement, the rate of receptor discharge slows and conscious awareness of the stimulus declines or is lost until some type of stimulus change occurs. This phenomenon is referred to as adaptation. The touch receptors adapt particularly rapidly, which is highly desirable. Who, for instance, would want to be continually aware of the pressure of clothing on their skin?
The Correct Answer and Explanation is:
Tactile Localization Sensation – Activity Explanation
1. Demonstrating Adaptation of Touch Receptors
The process of tactile localization involves determining the ability of a subject to identify the exact location on their body where a stimulus, like a touch or a coin, is applied. The skin has specialized sensory receptors that detect various forms of stimuli, including pressure, temperature, and texture. When you touch the skin with an object like a coin, the receptors in the skin send signals to the brain, which processes these signals and allows the individual to perceive the location of the touch. The sensation persistence at a given location refers to how long the subject is aware of the stimulus once it is applied.
In Activity 4, you are asked to apply a coin to the palm of the subject’s hand and ask them to indicate how long they can perceive the sensation. This activity examines how sensory receptors adapt over time, meaning that they stop firing as intensely after being exposed to the same stimulus for a prolonged period. This adaptation is useful because it prevents our sensory systems from being overwhelmed with constant stimuli (like the pressure of clothes).
When repeating the test by placing the coin at different locations, it is expected that the sensation of touch might persist differently depending on the area tested. For example, some areas of the body, like the fingertips, may maintain sensitivity for longer periods, while areas like the back of the hand may exhibit faster adaptation and diminished sensitivity after initial touch.
2. Testing Tactile Localization
Tactile localization is tested by having a subject touch the palm of their hand with a coin that has a marked point or different color to indicate the exact spot of the touch. The error of localization is determined by measuring the distance between the mark placed on the skin and the subject’s perceived location of the touch. This error is recorded in millimeters.
- Receptors’ Role: The receptors responsible for tactile sensation are called mechanoreceptors. They can be divided into different types depending on their adaptation speed and the kind of stimuli they respond to. For instance, Meissner’s corpuscles are sensitive to light touch and adapt quickly, while Merkel’s disks respond to sustained pressure but also adapt over time.
When performing the experiment, the subject may initially have difficulty accurately perceiving the location of the stimulus because the touch receptors are still adapting. As more trials are conducted, the subject may become more accurate at identifying the location due to the brain’s neural plasticity and ability to adjust to the tactile input.
3. Sensory Adaptation and Error in Localization
The error of localization can vary across different body areas, and this variability is largely determined by the distribution of tactile receptors. Areas such as the fingerpads and lips have a high density of sensory receptors, allowing for very precise localization, while other areas like the back of the neck or back of the hand may exhibit larger errors in localization due to a lower receptor density.
Explanation of Perception of Stimulus Intensity:
Perception of intensity refers to how strong or weak a sensation feels. The intensity of a stimulus is related to both the physical magnitude of the stimulus and the number of sensory receptors activated. When a stimulus like touch is applied to a highly sensitive area (such as the fingertips), the subject is more likely to perceive a strong sensation even with a light touch. In contrast, less sensitive areas like the back or forearm require a greater stimulus intensity to elicit the same sensation.
Over time, sensory receptors adapt, meaning they stop firing at the same rate after constant stimulation, and as a result, the sensation fades or becomes less intense. This adaptation process prevents the brain from being overwhelmed by constant input. The rate of receptor discharge slows down, and the perception of intensity decreases.
4. Activity 5: Demonstrating Adaptation of Temperature Receptors
In Activity 5, the adaptation of temperature receptors is tested by alternately placing a subject’s hand into warm and cold water baths. The temperature receptors in the skin, called thermoreceptors, detect changes in temperature and send this information to the brain. When the same temperature is maintained for a period, the body undergoes sensory adaptation, and the sensation of temperature changes.
- Warm Water Bath: When placed in warm water (about 45°C), the skin’s temperature receptors send signals to the brain, and the subject perceives warmth. Over time, the perception of heat diminishes because the thermoreceptors have adapted to the continuous stimulus.
- Cold Water Bath: When placed in cold water, the receptors that detect cold sensations (mainly free nerve endings) respond to the stimulus. However, just like with the warm bath, the sensation of coldness fades after prolonged exposure, as the thermoreceptors adapt.
The sensation change of the finger when placed in both warm and cold water baths shows how the body becomes less sensitive to constant temperatures over time. The intensity of the temperature sensation reduces after a period of exposure due to adaptation.
5. The Mechanism of Sensory Adaptation
Sensory receptors do not continue to send signals at a high rate if the stimulus is constant. Instead, the receptors slowly reduce the frequency of their firing. This phenomenon, called sensory adaptation, helps prevent the nervous system from being overloaded with information. For example, when you wear a watch, you are aware of its presence initially, but over time, you stop noticing it because the receptors adapt to the pressure and vibration it causes on your skin.
- Mechanoreceptors for touch and thermoreceptors for temperature adaptation both follow this pattern. These receptors are initially highly responsive to changes in stimulus intensity but become less responsive if the stimulus persists without change.
- Significance: The phenomenon of adaptation is crucial for survival. It allows the nervous system to focus attention on new or changing stimuli rather than being overwhelmed by continuous, unchanging signals. This allows for the detection of new sensations or changes in the environment, such as a sudden change in temperature or an unexpected pressure, which could indicate a threat or an important event.
Conclusion: Sensory Adaptation and Its Importance
The adaptation of sensory receptors is vital for efficient functioning of the sensory system. By reducing the sensitivity to constant stimuli, the body avoids unnecessary distraction and can focus on new or more pressing stimuli. This adaptation can be observed through tactile tests, such as measuring localization errors on the skin, and temperature adaptation when exposed to different water baths. Understanding these processes is crucial for a deeper appreciation of how the nervous system processes and prioritizes sensory information.
In your experiment, you can conclude that the finger pads will exhibit the smoothest error of localization due to their dense population of tactile receptors, and sensory adaptation will make the sensations from the warm and cold baths fade over time.
