(A) Exercise 19: Cutaneous Senses

(A) Exercise 19: Cutaneous Senses 1.​ Stimuli and Receptors ○​ Stimuli: Sensory stimuli detected by receptors can be mechanical (touch, pressure), thermal (temperature), or chemical (pain). ○​ Receptors: ■​ Mechanoreceptors: Detect touch, pressure, vibration, and stretch. ■​ Merkel discs: Respond to light touch and pressure. ■​ Meissner’s corpuscles: Detect light touch and vibrations, especially in hairless skin ■​ Pacinian corpuscles: Respond to deep pressure and vibrations ■​ Ruffini endings: Detect stretch and sustained pressure ■​ Thermoreceptors: Detect changes in temperature (cold or warm) ■​ Nociceptors: Detect painful stimuli due to tissue damage ■​ Proprioceptors: Detect the position and movement of the body, found in muscles, joints, and tendons ■​ Chemoreceptors: Chemical receptors (detects gas levels, CO2, etc) ■​ Baroreceptors: Presse receptors (detects internal pressure ; blood pressure) 2.​ Mapping Fine-Touch Receptors ○​ Fine-touch receptors are distributed unevenly across the skin. Areas like the fingertips, lips, and face have a higher density of mechanoreceptors, leading to more acute touch sensation in these regions 3.​ Two-Point Discrimination Test ○​ This test measures the smallest distance at which two points of stimuli are perceived as distinct. ○​ Areas with more sensory receptors (e.g., fingertips) can differentiate stimuli more precisely. ○​ Example: On the back, the threshold for two-point discrimination is larger than on the fingertips, indicating less sensitivity. 4.​ Mapping Temperature Receptors ○​ Cold receptors: Respond to a decrease in skin temperature and are typically located closer to the surface of the skin. They are more sensitive to temperatures between 10-20°C. ○​ Warm receptors: Respond to increased skin temperature, located deeper in the skin. They are more sensitive to temperatures between 30-45°C. ○​ Thermoreceptors adapt to a constant temperature over time, which is why we stop noticing the temperature of water once we’ve been in it for a while 5.​ Adaptation to Touch ○​ Sensory adaptation: The process by which receptors decrease their response to a constant stimulus. Tonic Receptors Vs. Phasic Receptors Tonic Receptors > adapts to stimuli slowly (example: posture adjustment) Phasic Receptors > adapts to stimuli quickly (example: wearing a watch) 6.​ Proprioception ○​ Proprioception refers to the sense of body position and movement, which allows us to know where our limbs are even without looking at them. ○​ Key proprioceptors include muscle spindles (sense muscle stretch) and Golgi tendon organs (sense tension in tendons). ○​ Vestibular system (inner ear) also plays a role in proprioception by helping to maintain balance and orientation 7.​ Temperature Judgement ○​ Thermoreceptors help the brain determine if something is hot or cold based on the rate at which heat is transferred to or from the skin. ○​ Temperature judgment can be influenced by context, such as ambient temperature or humidity, which may affect the sensitivity of thermoreceptors 8.​ Referred Pain ○​ Referred pain occurs when pain is perceived in an area of the body that is not the actual source of the pain. This happens due to convergence of sensory nerve pathways. ○​ Example: Pain from a heart attack may be felt in the left arm because the sensory input from the heart and left arm share the same neural pathways.