Lecture 12 - Touch, Taste, Smell Flashcards
What is the somatosensory system?
The somatosensory system provides information about touch, pressure, temperature, and pain from both the skin’s surface and inside the body.
What are the three interacting systems within the somatosensory system?
The three interacting systems are the exteroceptive system (skin senses), the interoceptive system (organic senses), and the proprioceptive system (kinesthesia).
What does the exteroceptive system respond to?
The exteroceptive system responds to outside stimuli that touch the skin, such as touch and temperature.
What is the role of the interoceptive system?
The interoceptive system provides information about internal conditions of the body and helps regulate processes like heart rate, breathing, hunger, and bladder control.
What is kinesthesia, and which system does it belong to?
Kinesthesia, part of the proprioceptive system, is the sense of body position, posture, and movement, including muscle tension.
What types of stimuli do the cutaneous senses encode?
The cutaneous senses encode pressure (touch), vibrations, temperature, and pain.
Which skin layer provides oxygen to cells directly from the air?
The epidermis, the outermost layer of skin, provides oxygen directly from the air to its cells.
What is the role of Merkel’s disks?
Merkel’s discs are specialized mechanoreceptors that detect light touch and pressure, located in the skin’s epidermis, particularly in areas like the fingertips and hairless skin. They detect simple touch, like gentle contact with the skin.
Which sensory receptor helps sense skin stretching and finger position?
Ruffini corpuscles sense skin stretching and help with finger position and movement.
Where are Meissner’s corpuscles found, and what do they detect?
Meissner’s corpuscles are found in glabrous (hairless) skin and are involved in detecting dynamic, light touch (e.g., feeling Braille)
How do temperature receptors function in the skin?
Temperature receptors detect warmth or coolness, and some also send pain signals. The axons of these receptors have little or no myelin (the protective coating around nerve fibers), which makes their signals slower and less precise compared to other sensory neurons with more myelin.
(Temperature receptors don’t need to be fast, since they are often detecting less urgent sensations like mild changes in temperature or discomfort, rather than immediate, sharp pain or touch.)
Which chemicals activate temperature receptors, and how?
Capsaicin (in chili peppers) activates heat receptors, while menthol (in mint) activates cold receptors.
What are nociceptors?
Nociceptors are pain receptors that detect harmful stimuli, including strong pressure and extreme temperatures.
What type of pain do high-threshold mechanoreceptors detect?
High-threshold mechanoreceptors respond to strong pressure, such as hitting, stretching, or pinching.
How do signals from the body reach the primary somatosensory cortex?
Sensory signals from the body travel through spinal nerves into the central nervous system (CNS). These signals take one of two pathways: the spinothalamic tract (which transmits pain and temperature) or the dorsal column (which carries touch and proprioception information). These pathways converge in the midbrain, where they are processed further, and then continue to the thalamus. The thalamus acts as a relay station, directing the signals to the primary somatosensory cortex in the parietal lobe, where they are interpreted as sensations like touch, pain, and temperature.
What is the spinothalamic tract, and what type of sensations does it carry?
The spinothalamic tract carries less precise sensations, like general touch, temperature, and pain, crossing to the opposite side of the spinal cord early on.
Which pathway carries fine touch information to the brain, and where does it cross sides?
The dorsal column pathway carries fine touch information and crosses sides in the medulla before continuing to the thalamus.
Imagine you touch a hot stove with your hand. Which receptors and pathways are involved in detecting and processing this sensation?
Temperature and pain are detected by free nerve endings, with signals sent via the spinothalamic tract to the thalamus and then to the primary somatosensory cortex.
If someone feels a light touch on their palm, which receptors are likely involved?
Meissner’s corpuscles, which detect light touch and are located in glabrous (hairless) skin like the palm, are likely involved.
What is the somatosensory homunculus?
The somatosensory homunculus is a map of the body surface, representing how different areas of the primary somatosensory cortex correspond to sensations in specific body parts.
How does the somatosensory homunculus demonstrate the connection between the brain and body sensations?
By stimulating different areas of the primary somatosensory cortex, sensations are felt in specific body parts, which reveals the brain’s organization of sensory input from the body.
Why might stimulating the primary somatosensory cortex create a sensation in a particular body part?
Each region of the somatosensory cortex is mapped to a specific body part, so electrical stimulation of these regions can produce a sensation as if that body part were being touched.
What is tactile agnosia?
Tactile agnosia is a condition where patients have difficulty recognizing objects by touch alone, often mistaking one object for another.
How might tactile agnosia affect a patient’s daily life?
A person with tactile agnosia might struggle to identify objects by feel, which could make tasks like finding items in a bag difficult. However, they might recognize these objects if they can see or draw them.
Imagine a person with tactile agnosia picks up a pine cone. What might they experience?
They might describe the pine cone as feeling like a different object, such as a brush, due to their inability to recognize it by touch alone.
What is phantom limb pain?
Phantom limb pain is a sensation where individuals feel as if their amputated limb is still present and may even experience pain in that missing limb.
Why might a person with an amputated limb still feel pain in the area where their limb used to be?
Phantom limb pain may be caused by the brain receiving mixed signals from nerves that were once connected to the limb, confusing the brain about the limb’s presence.
