Class 11: Touch, Smell and Taste PSY 302 Lecture Notes October 3, 2017

Transcription

1 Katie Cutaneous (skin) Senses: Somatosenses: Class 11: Touch, Smell and Taste PSY 302 Lecture Notes October 3, 2017 Cutaneous senses (touch) Kinesthesia, proprioception: joint and muscle stretch information, giving body position (proprioception) and dynamics (kinesthesia) Organic senses: receptors on organs such as stomach, gallbladder. Physical Stimulus (4): Vibration: tested with tuning fork. Function: texture perception (surface) Temperature: tested with water bath. Function: body temperature regulation, very important. Pain: Tested chemically, mechanically. Function: protection from damage. Pressure: tested mechanically. Function: sensation, protection. Sensory Apparatus: the skin and its receptors. Skin: Epidermis: upper layer, peels off, regenerated every 27 days. Damaged by skin cancer. Dermis: affected by deep burns, contains hair follicle o Have two kinds of dermis and epidermis: Hairy Skin: being touched Glabrous skin: never with hair, touching. Example: your palm. Subcutaneous Tissue: fat and blood vessels. Functions of the skin: Protection Prevent fluid loss Temperature regulation Communication (blushing-emotional state, state of health, camouflage) Excretion (loss urea and water through sweat) Respiration (oxygen absorption). Cutaneous Mechanoreceptors: different skins receptors are specialized for different aspects of touch. Ruffini Corpuscles: free nerve ending, deep in dermis, respond to skin stretch, static force (poke) Pacinian corpuscles: encapsulated nerve ending, large onion like structure, deep in dermis, respond to high frequency vibrations (tickle)

2 Meissner s corpuscles: low frequency/tap vibrations, detection of texture. Glabrous skin only (finger tips) Merkel s disks: light mechanical pressure. Finger tips, lips, genitalia. Mostly glabrous skin. Sensory Receptors Source: e14.html Sensory Perception: Touch: o Sensation=mechanoreceptors: pressure and vibration o Sensation: emotional o Sensation: in some animals, used to sense heat (snakes and humans but we aren t very good at it) o Sense of touch can be modified y learning/experience. (musicians, bind people) o The sensitivity of a body area is reflected in the amount of neurons responsive to touch (recall the homunculus)

3 o Pathway: Receptors > Spinal Cord > > Somatosensory cortex Sensory Perception: Dermatomes Somatosensations go through the spinal cord Different levels (Cervical, Thoracic, Lumbar and Sacral) of the spinal cord receive information from different parts of the skin o Cervical: shoulders and arms o Thoracic: torso o Lumbar: hips and legs o Sacral: genitalia and heels Source: Sensory Perception: Homunculus (same map as before). Damage in somatosensory cortex: Tactile agnosia (tactile apraxia), loss of sensation due to neural deficit. Temperature:

4 2 temperature receptors (free nerve endings): Cold (superficial dermis) and Warm (deep dermis) Transduction mechanisms involve family of dedicated receptors (TRP). Neural pathways are similar to those of pain Hypothalamus is in charge of temperature regulation: Sweating (to decrease temperature through evaporation), vasoconstriction (conserve heat, erection of hair/fur) Physiology: o Adaption to constant or slow temperature changes.. The same temperature may feel cold of warm, depending on the initial conditions. o 8 C=47 F <->52 C =122 F are the thresholds for pain o Temperature is naturally variable, female reproductive cycle: temperature increases just after ovulation. o Normal ranges of temperature: Oral: F, Rectal: F Pain Sensation Pain receptors (nociceptors): free nerve endings o Mechanoreceptors: intense pressure o Intense heat and acids o Irritant receptors: chemicals that may produce inflammation (tear gas) Different components of pain sensations: o Sensory: receptors > Spinal Cord > Thalamus > Primary Sensory Cortex Pain intensity o Emotional: Primary sensory cortex > anterior cingulate cortex Pain color (how much is it disruptive? Unpleasantness) o Long term psychological (Chronic pain): prefrontal cortex Pain memory Pain Perception: Perception of pain can be controlled: Hypnosis o Primary Sensory cortex: sensation of pain o Cingulate Cortex: perception of pain Pain can be imagined: empathy Pain can be managed with learning and experience. o Example: brain plasticity result in reorganization (phantom limb and mirror boxnatural for us to see our two hands together, because that is what we are used to) Perception: 2 sensory pathways Spino-thalamic tract: pain and temperature Dorsal Column: precise touch and movement Taste Chemical Sense. Taste=gustation, flavor=olfaction

5 6 independent taste dimensions/stimuli: o Bitterness o Sweetness o Sourness o Saltiness o Fat o Umami (MSG) Taste apparatus= tongue + palate + pharynx + larynx Taste receptors: taste buds 10,000 receptors, renewed ever 10 days Sense of taste has genetic basis: o Supertasters: bitter sensitivity, more prevalent in woman and Europeans (reason why culinary art is so important in Europe??) o Non-tasters Taste: Tongue Taste Transduction: Dissolve in Saliva > bind to receptors > ion flow > receptor potentials Taste bud nerves are Facial, Vagus and Glossopharyngeal Sourness: Acidity, H+, potassium channels Saltiness: NaCl, directly through sodium channels Bitterness: Many receptors (protective function: direction of bad foods) Sweetness: specific receptors (genetically absent in felines) Umami: Glutamic acid, MSG, metabotropic channels Gustatory Pathway: Olfaction: Lateral Hypothalamus: perception of hunger, metabolism Amygdala: perception of like/dislike, aversion Primary gustatory cortex: perception of taste Ipsilateral pathway, the information does not switch. Taste on right side goes to right side of the brain. Maps for taste vary from subject to subject: Established genetically and through experience. Size of the map may explain individual differences (sweet tooth?) Chemical sense. Stimulus: volatile molecules. Receptors: olfactory mucosa/epithelium, 6 million receptors Transduction: slow sodium channels Strong genetic bases (from insects to humans) In human: good sensation, poor perception (analyses). Strong associations with memory.

6 Olfaction Sensation: Molecules o Odorants dissolve in the mucus o Bind to olfactory cells (cilia). Molecule specific binding o Each cell sends one axon to olfactory bulbs-mitral Cells ~35 per bundles o Synapses on mitral cells from glomeruli (10,000). Glomeruli are molecule specific (olfactory chemical map) Source: o Axons of mitral cells go to associations areas in brain. o Olfactory nerve Perception Olfactory Pathway: Olfactory bulb> o Thalamus > Orbitofrontal cortex (Cognitive) o Amygdala > Limbic system (Emotional) Olfaction Humans can perceive 10,000 odors, but have only ~300 receptors types. How can recognition be received? o Pattern Matching!! 8 odors but only 4 receptors o Major problem in studying olfaction: basic odors are unknown