At the end of this section you can:
- Describe the basic functions of the chemical senses.
- Explain the basic functions of the somatosensory, nociceptive and thermoceptive sensory systems.
- Describe the basic functions of the vestibular, proprioceptive, and kinesthetic sensory systems.
Vision and hearing have received an incredible amount of attention from researchers over the years. Although much remains to be learned about how these sensory systems work, we have a much better understanding of them than of our other sensory modalities. In this section we will explore our chemical senses (taste and smell) and our body senses (touch, temperature, pain, balance and posture).
THE CHEMICAL SENSES
Taste (taste) andOdor(Smell) are called chemical senses because they both have sensory receptors that respond to molecules in the food we eat or the air we breathe, as opposed to sight, which converts light, and hearing , which converts sound waves. There's a pronounced interplay between our chemical senses of taste and smell, suggesting they work together to provide additional information to gauge the contents of something based on its taste or smell. For example, when we describe the taste of a particular food, we are actually referring to both the flavor and olfactory properties of the food working in combination. The senses of taste and smell are capable of discerning an incredible number of differences between the chemical compounds that tell us about food availability and the potential danger or pleasure that could be implied by consuming those compounds. Smell and taste can also initiate and signal gustatory and digestive traits, and can also be used as cues for social interactions, as in the case of some animals that recognize pheromones that indicate innate physiological or behavioral responses. The human nose has approximately 400 different types of chemoreceptors, enabling us to detect at least a trillion different types of odors (Bushdid, Magnasco, Vosshall, & Keller, 2014). However, there are differences between species in which some chemosensation traits have been conserved through evolution, and there are adaptations that allow species to use chemosensation more effectively in their specific environment.
You've been taught since elementary school that there are four basic groups of tastes: sweet, salty, sour, and bitter. However, research shows that we have at least sixGustoUmami is our fifth taste. Umami is actually a Japanese word that roughly translates to “delicious” and is associated with a fondness for MSG (Kinnamon & Vandenbeuch, 2009). There is also a growing body of experimental evidence that we like the fat content of a particular food, suggesting that detection of long-chain fatty acids (LCFA) can trigger receptors to cause physiological changes that affect food intake such as digestive functions . Mizushige, Inoue, and Fushiki, 2007; Besnard, Passilly-Degrace & Khan, 2015).
The sense of taste has evolved over the centuries to be extremely useful for human survival. Our ability to distinguish between so many different tastes takes us away from food or drink that could make us sick and toward food and drink that we can use for energy. They have also been drawn to salty foods, which may contain beneficial minerals and umami, suggesting the presence of proteins essential for cell maintenance and growth. Molecules in the food and drink we eat are dissolved in our saliva and interact with taste receptors in the tongue, mouth and throat. Taste buds are composed of clusters of taste receptor cells with hair-like projections that protrude from the central pore of the taste bud (Figure below). Taste buds have a life cycle of ten days to two weeks, so even destroying a few by burning the tongue has no long-term effect; they just grow back. Taste molecules bind to receptors to this extent, causing chemical changes within the sensory cell that cause nerve impulses to travel down different nerves to the brain, depending on where the receptor is located. Taste information is transmitted to the medulla oblongata, thalamus, and limbic system, as well as to the taste cortex, which lies under the overlap between the frontal and temporal lobes (Maffei, Haley, & Fontanini, 2012; Roper, 2013).
(a) Taste buds consist of several individual taste receptor cells that transmit information to the nerves. (b) This micrograph shows a close-up of the tongue surface. (Credit a: modified work by Jonas Töle; Credit b: scale bar data by Matt Russell)
Based on the nutritional benefits of carbohydrates and proteins, both sweet and umami are the taste categories most likely to evoke pleasurable sensations in humans and attraction in animals, while bitter flavors, often found in poisonous plants, evoke an aversive response in animals and humans to avoid an injection . of toxic substances. Although most human taste buds are located on the tongue, some are also found on the palate, pharynx, epiglottis, and upper third of the esophagus. Taste buds also occur in groups called papillae, of which there are three different types of papillae based on morphology and where they are located.mushroom-shaped papillaeLocated in the front two-thirds of the tongue, they are cone-shaped structures on which the taste bud sits. Heleafy papillae, located on the posterior edge of the tongue, and theencloses the nipples, present only on the back of the tongue, are surrounded by grooves lined with taste buds. Each mushroom-shaped papilla consists of one to five taste buds, and each effervescent or laminar papilla contains hundreds of taste buds.
At the base of each taste cell are dendritic branches derived from the axons of the facial nerve (cranial nerve 7), glossopharyngeal nerve (cranial nerve 9), and accessory nerve (cranial nerve 10). These nerves carry information from the tongue to thesolitary tract core, a structure in the brainstem medulla that extends vertically upward and acts as a transmission point for taste information. Flavor information is transmitted from the core of the solitaire tract to theventral posterior nucleus of the thalamus. Remember that the thalamus is an important structure that sits right in the center of the brain and acts as a hub between the information that enters the brain and the specific areas of the cortex where that information is further processed. Taste information is sent from the ventral posterior nucleus of the thalamus to thetaste cortex, which is located in the fold of the anterior temporal lobe in an area known as the anterior frontal islet operculum, as well as to the hypothalamus, a structure that coordinates both the autonomic nervous system and the activity of the pituitary gland, which maintains and alters body temperature , thirst, hunger and other homeostatic systems related to sleep and emotions.
Taste buds relay chemical information about the tongue and other areas of the mouth via cranial nerves 7, 9, and 10 to the nucleus of the solitary tract. The information is then relayed to the ventral posterior medial nucleus of the thalamus and hypothalamus, and finally to the gustatory cortex, which is tucked into the temporal lobe. Adapted from Hummel, Landis & Hüttenbrink, 2011).
The taste cortex is believed to generate conscious perception and discrimination between different tastes. Recordings of the electrical activity of the taste cortex suggest that some neurons respond to multiple taste classes, while others respond to only one type of taste, e.g. B. bitter or sweet. Some believe that encoding individual tastes is more related to innate responses of attraction to sweet tastes or avoiding something likely to contain poison, while other groups of neurons encode taste mixtures through sensations. In addition to all the information transmitted by taste buds in different parts of the tongue, much of what we know and understand about the taste of something also comes from smells transmitted through the olfactory system.
Olfactory receptor cells are located on a mucous membrane known as theolfactory epitheliumat the tip of the nose in the nasal cavity. The olfactory sensory neuron is a bipolar neuron that extends from the apical end to the epithelial surface with numerous thin branchesciliapresent in the mucus lining the nasal cavity.ciliaThe tiny hair-like extensions at the ends of these bipolar cells serve as sites for mucus-dissolved odorant molecules to interact with chemical receptors on these extensions (pictured below). Once an odorant molecule has bound to a specific receptor, chemical changes within the cell cause signals to be sent to the receptor.olfactory bulb: an onion-shaped structure at the tip of the frontal lobe, where the olfactory nerves begin. Information is sent from the olfactory bulb to regions of the limbic system and to the primary olfactory cortex, which is in close proximity to the gustatory cortex (Lodovichi & Belluscio, 2012; Spors et al., 2013). multigenic family found in all vertebrate species (Kandel, Schwartz, Jessel, Siegelbaum & Hudspeth, 2013).
Olfactory receptors are the hair-like parts that extend from the olfactory bulb to the lining of the nasal cavity.
Olfactory information, as shown in Figure 3, is transmitted through the olfactory epithelium in the nasal cavity to the olfactory bulb via bipolar sensory neurons. The olfactory bulb then transmits the signals to different areas of the brain, such as the anterior olfactory nucleus and periform cortex, which are located in the temporal lobe, the amygdala and hypothalamus, which are associated with emotions and the body's autonomic regulation, respectively, and the entorhinal cortex and hippocampus related to the maintenance and storage of memories.
There are enormous differences in the sensitivity of the olfactory systems of different species. We often think that dogs have an olfactory system vastly superior to ours, and in fact, dogs can do some remarkable things with their noses. There is evidence that dogs can sniff out dangerous hypoglycemia and cancerous tumors (Wells, 2010). The exceptional olfactory abilities of dogs may be due to the larger number of functional genes for olfactory receptors (between 800 and 1,200) compared to fewer than 400 observed in humans and other primates (Niimura & Nei, 2007).
Many species respond to chemical messages, known as pheromones, sent by another individual (Wysocki & Preti, 2004). Communicating with pheromones often involves providing information about a potential mate's reproductive status. For example, when a female rat is ready to mate, she secretes pheromone signals that attract the attention of nearby male rats. Indeed, pheromone activation is an important component in triggering sexual behavior in male rats (Furlow, 1996, 2012; Purvis & Haynes, 1972; Sachs, 1997). Much research (and controversy) has also been done about pheromones in humans (Comfort, 1971; Russell, 1976; Wolfgang-Kimball, 1992; Weller, 1998).
TOUCH, THERMOCEPTION AND NOCEPTION
A number of receptors are distributed throughout the skin to respond to various tactile stimuli (Figure below). These receptors include Meissner bodies, Pacini bodies, Merkel discs, and Ruffini bodies. Meissner corpuscles respond to pressure and low-frequency vibration, and Pacini corpuscles detect transient pressure and high-frequency vibration. Merkel's intervertebral discs respond to slight pressure, while Ruffini's bodies feel stretched (Abraira & Ginty, 2013).
There are many types of sensory receptors in the skin, each tuned to specific touch-related stimuli.
In addition to the receptors located in the skin, there are also a number of free nerve endings that perform sensory functions. These nerve endings respond to a variety of different types of touch-related stimuli and serve as sensory receptors for both thermoception (temperature perception) and nociception (a signal that indicates potential damage and possible pain) (Garland, 2012; Petho & Reeh, 2012 ; Aerosol, 1986). Sensory information collected by receptors and free nerve endings travels down the spinal cord and is transmitted to regions of the medulla oblongata, thalamus, and finally to the somatosensory cortex, located in the postcentral gyrus of the parietal lobe.
Pain is an unpleasant experience that includes both physical and psychological components. Feeling pain is quite adaptive because it alerts us to an injury and motivates us to move away from the cause of that injury. In addition, pain makes us less susceptible to further injury because we treat the injured parts of our body more gently. Pain perception is a subjective process, meaning that only the person experiencing pain can accurately understand it, and pain perception can differ between different people experiencing the same injury. For example, many wounded soldiers report not feeling any pain until they are removed from the battlefield. Injured athletes have reported not realizing the injury-related pain they were experiencing until after the game or match. These examples demonstrate that pain is not a response to a specific sensory event, but rather arises from the contributions of many different sensory processes and neural signals.
Many peripheral organs (organs outside of the spinal cord, brainstem, and central nervous system brain), such as skin, joints, and muscles, contain free nerve endings known asof Nociceptthey give rise to sensory neurons that can relay information to other processing sites. There are three main types of nociceptors that process thermal, mechanical, and polymodal information (responsive to various forms of sensory stimulation), as well as a fourth class known as silent nociceptors, which respond to mechanical stimulation during inflammation and after tissue injury.thermal nociceptorsNerve endings usually have a very thin outer layer of myelin fat cells and are activated by extreme temperature differences, typically above 45 °C (115 °F) and below 5 °C (41 °F).mechanical nociceptorsThey are activated by intense pressure on the skin and are also finely myelinated.polymodale NozizeptorenThey can be triggered by intense mechanical, chemical, or thermal (hot and cold) stimuli and are located at the tips of very small diameter, unmyelinated axons that transmit information more slowly than thermal nociceptors and mechanical nociceptors, specifically. Thermal, mechanical, and polymodal nociceptors are widely distributed across the skin and are often activated in larger clusters.silent nociceptorsThey are found in internal organs in the main cavities of the body, such as the abdomen and intestines, and are activated by inflammation and exposure to various chemical agents.
In general, pain can be considered neuropathic or inflammatory in nature. Pain that indicates tissue damage is called inflammatory pain. In some situations, pain results from damage to neurons in the central or peripheral nervous system. As a result, the pain signals sent to the brain become exaggerated. This type of pain is called neuropathic pain. The diverse treatment options for pain relief range from relaxation therapy to the use of painkillers and deep brain stimulation. The most effective treatment option for any particular individual depends on a number of considerations, including the severity and duration of the pain and any medical/psychological conditions. Therapy. His studies are beginning to show that this form of pain management isn't always the most productive:https://news.wsu.edu/2018/07/02/chronic-dolor-remains-gets-mejor-detener-el-tratamiento-opioide/
Persistent pain can be classified into two different categories known asnociceptive pain, jNeuropathic Pain. Nociceptive pain is produced by the activation of nociceptors in the skin or soft tissues in response to injuries such as cuts, burns, or tissue injury and inflammation. Neuropathic pain, on the other hand, results from direct damage to nerves in the peripheral or central nervous system and is often accompanied by a burning or electric sensation (Kandel, Schwartz, Jessel, Siegelbaum, & Hudspeth, 2013).
There are five distinct sensory pathways that carry pain information from transduction to high-level processing in the brain known as painSpinothalamic tract, Isspinoreticular tract,Spinomesencephalic tract, Iscervicothalamic tract, and theSpinohypothalamic tract. Signals from the various types of nociceptors in the peripheral nervous system are transmitted from nerve endings to cell bodies located in the peripheral nervous system.dorsal root gangliaLocated in the dorsal portion of the spinal cord and organized as vertical layers of perception throughout the body. The spinothalamic tract is the most prominent ascending nociceptive pathway whose axons cross the midline of the spinal cord in their segment of origin. The signals are then sent to areas of the thalamus and to the postcentral gyrus of the cerebral cortex where thesomatosensory cortexit is found.
Sensory information is transmitted through the open nerve endings of the nociceptors and sent from the cell body in the dorsal horn of the spinal cord to the other side of the spinal cord where the signal is sent to the thalamus via the spinothalamus. tract. Image adapted from Min and colleagues (2013).
Some people are born without the ability to feel pain. This very rare genetic disorder is known as congenital insensitivity to pain (or congenital analgesia). While those with congenital analgesia can detect differences in temperature and pressure, they do not feel pain. As a result, they often suffer serious injuries. Young children have serious injuries to their mouths and tongues from being repeatedly bitten. Not surprisingly, people with this condition have a much shorter life expectancy due to their injuries and secondary infections at the injured sites (US National Library of Medicine, 2013).
THE VESTIBULAR SENSE, PROPIOCEPTION AND KINESTHESIS
The sense of balance contributes to our ability to maintain balance and posture. As shown in the figure below, the main sensory organs (utricle, saccule and the three semicircular canals) of this system are located next to the cochlea in the inner ear. The vestibular organs are fluid-filled and have hair cells, similar to those in the auditory system, that respond to head movement and gravitational forces. When these hair cells are stimulated, they send signals to the brain through the vestibular nerve. Although we may not be aware of the sensory input of our vestibular system under normal circumstances, its importance becomes apparent when we experience vertigo and/or vertigo associated with inner ear infections (Khan & Chang, 2013).
The most important sensory organs of the vestibular system are located next to the cochlea in the inner ear. These include the utricle, saccule, and the three semicircular canals (posterior, superior, and horizontal).
In addition to maintaining balance, the vestibular system collects important information to direct movements and reflexes that move different parts of our body to compensate for changes in body position. Therefore, both proprioception (perception of body position) and kinesthesia (perception of body movement through space) interact with information provided by the vestibular system.
These sensory systems also gather information from receptors that respond to stretch and tension in muscles, joints, skin, and tendons (Lackner & DiZio, 2005; Proske, 2006; Proske & Gandevia, 2012). Proprioceptive and kinesthetic information travels through the spine to the brain. Various cortical regions adjacent to the cerebellum receive and send information to the sensory organs of the proprioceptive and kinesthetic systems.
Taste (taste) and smell (smell) are chemical senses that use receptors on the tongue and nose that connect directly to taste and smell molecules to transmit information to the brain for processing. Our ability to sense touch, temperature, and pain are mediated through a series of receptors and free nerve endings that are distributed throughout the skin and various tissues in the body. The vestibular sense helps us maintain a sense of balance through the response of hair cells in the utricle, saccule, and semicircular canals that respond to changes in head position and gravity. Our proprioceptive and kinesthetic systems provide information about body position and movement through receptors that detect stretch and tension in the muscles, joints, tendons, and skin of the body.
Text from Openstax Psychology by Kathryn Dumper, William Jenkins, Arlene Lacombe, Marilyn Lovett and Marion Perlmutter under license CC BY v4.0. https://openstax.org/details/books/psychology
1.The chemical messages often sent between two members of a species to communicate something about reproductive status are called ________.
C. Merkel's intervertebral discs
D. Meissner corpuscles
2. What flavor is associated with monosodium glutamate?
3.________ serve as sensory receptors for temperature and pain stimuli.
To. free nerve endings
B. Pacini bodies
C. Ruffin's body
D. Meissner corpuscles
4.Which of the following factors is involved in maintaining balance and posture?
To. auditory nerve
D. vestibular system
Critical thinking question:
1.Many people experience nausea when traveling by car, plane, or boat. How could you explain this as a function of sensory interaction?
2.If you heard someone say that they would do anything to not feel the pain that comes with a serious injury, how would you react to what you just read?
3.Do you think women experience pain differently than men? Why do you think that is?
Personal application question:
1.As mentioned above, the taste of a food is an interplay of gustatory and olfactory information. Think about the last time you were severely constipated from a cold or the flu. What changes have you noticed in the taste of the foods you have eaten during this time?
congenital insensitivity to pain (congenital analgesia)
answers to exercises
Critical thinking question:
1. When traveling by car, we often have visual information that suggests we are moving, while our sense of balance indicates that we are not moving (assuming we are traveling at a relatively constant speed). Usually, these two sensory modalities provide congruent information, but the discrepancy can lead to confusion and nausea. The opposite would be the case when traveling by plane or ship.
2. Pain performs important functions that are critical to our survival. As damaging as painful stimuli can be, the experiences of people with innate pain insensitivity make the consequences of painlessness all too clear.
3. Studies have shown that women and men differ in their pain experience and pain tolerance: women tend to cope better with pain than men. Perhaps this is due to women's experience of labor and childbirth. Men tend to be stoic about their grief and don't seek help. Research also shows that gender differences in pain tolerance can vary from culture to culture.
congenital insensitivity to pain (congenital analgesia):genetic disorder that leads to the inability to feel pain
inflammatory pain:Signs that tissue damage has occurred
Cons:Perception of body movement through space
Meissner corpuscles:tactile receptor that responds to pressure and low-frequency vibrations
Merkel disc:tactile receptor that responds to a light touch
Neuropathic Pain:Pain caused by damage to neurons in the peripheral or central nervous system
Nozizeption:sensory signal that indicates potential damage and possible pain
olfactory bulb:Bulbous structure at the tip of the frontal lobe where the olfactory nerves begin
olfactory receptor:Sensory cell for the sense of smell
Pacini bodies:tactile receptor that detects transient pressures and higher frequency vibrations
Pheromones:chemical message sent by another person
Ruffin's Corps:Touch receptor that detects stretch
Main offer:Clusters of taste receptor cells with hair-like projections that protrude from the central pore of the taste bud
umami:I like monosodium glutamate.
vestibular sense:contributes to our ability to maintain balance and posture