36.2 Somatosensation
3 min read•june 14, 2024
Our skin is a marvel of sensory detection, packed with specialized receptors that help us navigate the world. From light touches to deep pressure, these receptors work together to give us a rich tactile experience, allowing us to feel textures, temperatures, and even potential dangers.
Pain perception is a complex interplay of physical and psychological factors. Our bodies have dedicated pain sensors and pathways, but our brains can modulate these signals. This explains why pain can feel different based on our emotions, attention, and past experiences.
Somatosensory Receptors and Pain Perception
Mechanoreceptors in human skin
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- Rapidly adapting receptors respond to light touch and low-frequency vibrations (gentle stroking)
- Located in dermal papillae of (fingertips, palms, soles)
- Enable fine touch discrimination and precise manipulation of objects
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- Slowly adapting receptors detect sustained pressure and texture (Braille dots)
- Found in basal layer of epidermis in both and hairy skin
- Provide information about object shape and edges during static touch
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- Slowly adapting receptors sensitive to skin stretch and joint position
- Situated in dermis of glabrous and hairy skin
- Help maintain hand and finger position during grasping
- Contribute to , the sense of body position and movement
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- Rapidly adapting receptors detect deep pressure and high-frequency vibrations (power tools)
- Embedded in dermis and subcutaneous tissue, particularly in load-bearing areas (heels)
- Allow perception of distant vibrations and pressure changes
Glabrous vs hairy skin receptors
- Glabrous skin (palms, soles)
- High density of Meissner's corpuscles and Merkel's discs
- Fewer Ruffini endings and Pacinian corpuscles compared to hairy skin
- Adapted for fine touch discrimination, precise manipulation, and grip control
- Hairy skin (arms, legs)
- Lower density of Meissner's corpuscles and Merkel's discs than glabrous skin
- More Ruffini endings and Pacinian corpuscles
- Additional hair follicle receptors detect hair movement and skin deformation (wind, insects)
- Specialized for detecting broader tactile sensations, temperature changes, and
Additional Somatosensory Components
- : Specialized receptors in the skin that detect temperature changes
- : Region of the brain responsible for processing and interpreting touch, pressure, and temperature sensations
- : Distinct areas of skin innervated by specific spinal nerves, important for localizing sensations and diagnosing nerve injuries
Factors influencing pain perception
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- Specialized sensory neurons detect noxious stimuli (heat, cold, pressure, chemicals)
- Respond to potentially damaging stimuli to protect the body from harm
- Classified as thermal, mechanical, or polymodal based on their sensitivity
- Pain pathways
- Nociceptors synapse with secondary neurons in spinal cord dorsal horn
- Signals transmitted to thalamus and then to somatosensory cortex for processing
- Descending pathways from brain modulate pain signals at the spinal cord level
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- Proposes non-nociceptive input (touch, pressure) can inhibit pain signals in spinal cord
- Explains how cognitive factors (distraction) and touch (rubbing) influence pain perception
- Suggests balance between pain-facilitating and pain-inhibiting signals determines pain experience
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- Natural pain-relieving compounds produced by the body (endorphins, enkephalins)
- Bind to opioid receptors in brain and spinal cord to modulate pain perception
- Released during exercise, stress, and positive experiences (runner's high)
- Psychological factors
- Emotions (anxiety, depression), attention, and past experiences shape pain perception
- Stress and negative emotions amplify pain, while relaxation and positive emotions reduce it
- Cognitive-behavioral therapies target psychological aspects of pain management
- Chronic pain
- Persists beyond expected healing time or occurs without apparent tissue damage (fibromyalgia)
- Involves changes in nervous system leading to increased pain sensitivity ()
- Influenced by complex interactions of biological, psychological, and social factors ()
- Requires multidisciplinary approach to management (medication, therapy, lifestyle changes)
- Can lead to , where pain is felt in a different location from its source
Key Terms to Review (23)
Biopsychosocial model: The biopsychosocial model is an interdisciplinary framework that considers the interplay between biological, psychological, and social factors in understanding health and illness. This approach emphasizes that health outcomes are not solely determined by biological factors but also significantly influenced by psychological processes and social environments, making it crucial for a comprehensive understanding of somatosensation.
Central sensitization: Central sensitization is a condition where the central nervous system becomes hypersensitive to stimuli, leading to an exaggerated pain response. This process occurs when there is an increase in the excitability of neurons in the spinal cord and brain, which can result from injury, inflammation, or persistent pain signals. It is crucial for understanding how chronic pain conditions develop and persist, as it highlights the role of neural mechanisms in pain perception.
Dermatomes: Dermatomes are specific areas of skin that are mainly supplied by a single spinal nerve root. They play a crucial role in the somatosensory system by helping to map sensory input from the body to the corresponding spinal nerves, allowing for the localization of sensations such as touch, pain, and temperature. Understanding dermatomes is essential for diagnosing nerve injuries and conditions that affect sensation in different regions of the body.
Endogenous opioids: Endogenous opioids are naturally occurring peptides in the body that bind to opioid receptors, helping to modulate pain and stress responses. These molecules play a significant role in the pain management system, affecting how the body perceives and reacts to painful stimuli. They are crucial for promoting feelings of pleasure and well-being, thus influencing emotional states and behavior.
Free nerve ending: Free nerve endings are unspecialized, afferent nerve fibers that respond to a variety of stimuli such as pain and temperature. They are the most common type of nerve endings in the skin and other tissues.
Gate control theory: Gate control theory is a scientific model that explains how the perception of pain is controlled in the body, suggesting that there is a neural 'gate' in the spinal cord that can either allow or block pain signals from reaching the brain. This theory highlights the interplay between sensory nerve fibers and the nervous system in regulating pain perception, emphasizing that psychological factors and the context of a stimulus can influence how pain is experienced.
Glabrous: Glabrous skin is skin that is hairless and typically found on the palms of the hands, soles of the feet, and lips. It contains a high density of sensory receptors for detecting fine touch and pressure stimuli.
Glabrous skin: Glabrous skin refers to hairless regions of the body that are characterized by a smooth, hair-free surface. This type of skin is found in areas such as the palms of the hands and soles of the feet, where it serves critical functions in touch sensitivity and protection against environmental factors. The unique structure of glabrous skin allows for a higher density of sensory receptors, which play an important role in somatosensation.
Mechanoreceptors: Mechanoreceptors are specialized sensory receptors that respond to mechanical stimuli such as pressure, vibration, and touch. They play a crucial role in the peripheral nervous system by converting physical forces into neural signals that can be interpreted by the brain. This process is vital for somatosensation, allowing organisms to perceive their environment and respond appropriately to various physical changes.
Meissner’s corpuscles: Meissner's corpuscles are specialized nerve endings located in the dermal papillae of glabrous skin. They are responsible for detecting light touch and low-frequency vibrations.
Meissner's corpuscles: Meissner's corpuscles are specialized mechanoreceptors found in the skin, primarily responsible for detecting light touch and texture. These structures are located in the dermal papillae, making them sensitive to changes in surface texture and vibrations at low frequencies. They play a crucial role in our ability to perceive fine details and textures, enhancing our tactile sense.
Merkel's discs: Merkel's discs, also known as Merkel cells or tactile discs, are specialized mechanoreceptors found in the skin that are responsible for sensing light touch and texture. They are located in the basal layer of the epidermis and are closely associated with sensory nerve endings, playing a crucial role in the somatosensory system by providing the brain with information about gentle contact and shape discrimination.
Merkel’s disks: Merkel’s disks are specialized nerve endings found in the skin, responsible for detecting light touch and pressure. They play a crucial role in the sense of fine tactile discrimination.
Muscle spindles: Muscle spindles are sensory receptors located within muscles that detect changes in muscle length and the rate of that change. They play a crucial role in regulating muscle contraction and maintaining posture.
Nociception: Nociception is the sensory process that provides signals that trigger pain. It involves the detection of harmful stimuli by nociceptors, which are specialized nerve endings.
Nociceptors: Nociceptors are specialized sensory neurons responsible for detecting pain and transmitting signals related to potential or actual tissue damage. They play a crucial role in the peripheral nervous system by alerting the brain to harmful stimuli, allowing the body to respond appropriately to protect itself from injury. Nociceptors can be activated by various stimuli, including mechanical, thermal, and chemical signals, which contribute to our perception of pain.
Pacinian corpuscles: Pacinian corpuscles are specialized mechanoreceptors located deep within the dermis and subcutaneous tissue, primarily responsible for detecting pressure and vibration. These sensory receptors play a crucial role in somatosensation by transforming mechanical stimuli into electrical signals that the nervous system can interpret, thus allowing us to perceive touch and pressure changes in our environment.
Proprioception: Proprioception is the body's ability to sense its position and movement in space. It involves receptors in muscles, tendons, and joints sending information to the brain for coordination and balance.
Proprioception: Proprioception is the body's ability to sense its position and movement in space, allowing for coordinated physical actions and balance. This sensory feedback comes from proprioceptors located in muscles, tendons, and joints, which provide the brain with information about body posture and movement. Proprioception is vital for activities ranging from simple tasks like walking to complex athletic movements, and it plays a significant role in maintaining balance and preventing injuries.
Referred pain: Referred pain is a phenomenon where pain is perceived in a different location from its actual source. This occurs because the body’s nervous system pathways can overlap, leading to confusion in the brain about where the pain signals are coming from. Understanding referred pain is crucial for diagnosing various medical conditions since it can indicate underlying issues in different organs or tissues.
Ruffini endings: Ruffini endings are specialized sensory receptors located in the skin and connective tissues that respond to sustained pressure and skin stretch. They play a key role in proprioception, helping the body perceive its position and movement in space. These mechanoreceptors contribute to the sensation of deep pressure and are essential for tasks requiring fine motor skills and the detection of changes in joint angles.
Somatosensory cortex: The somatosensory cortex is a region of the brain located in the parietal lobe that processes sensory information from the body, including touch, temperature, pain, and proprioception. It plays a critical role in interpreting tactile stimuli and integrating sensory input to help create an awareness of body position and movement.
Thermoreceptors: Thermoreceptors are specialized sensory receptors that detect changes in temperature, allowing organisms to perceive thermal stimuli. These receptors play a crucial role in the peripheral nervous system by providing vital information about environmental temperature, which is essential for maintaining homeostasis and enabling appropriate physiological responses. Thermoreceptors can be categorized into two main types: cold receptors, which respond to decreases in temperature, and warm receptors, which respond to increases in temperature.