Touch. Lecture Notes 10/3 -Brenna

Transcription

1 Lecture Notes 10/3 -Brenna Touch Cutaneous Sense Somatosenses o Cutaneous sense (touch) o Kinesthesia, proprioception: joint and muscle stretch information, giving body position (proprioception) and dynamics (kinesthesia) o Organic senses: receptors on organs such as stomach, gallbladder Physical stimulus: Vibration: tested with tuning fork o Function: e.g. texture perception (surface) Temperature: tested with water bath o Function: body temperature regulation Pain: tested chemically, mechanically o Function: protection from damage Pressure: tested mechanically o Function: sensation, protection Sensory apparatus: the skin and its receptors Skin: o Epidermis Upper layer, peals off, 27 day cycle Damaged by skin cancer o Dermis Affected by deep burns. Contains hair follicles Hairy skin (being touched) Glabrous skin (touching) o Subcutaneous tissue Fat Functions of the skin o Protection: mechanical, chemical o Prevent fluid loss o Temperature regulation o Communication: blushing (emotional state), state of health, camouflage o Excretion (urea, water) o Respiration (oxygen absorption)

2 Cutaneous Mechanoreceptors Ruffini corpuscle: free nerve ending, deep in Dermis, responds to skin stretch, static force. E.g. poke Pacinian corpuscle: encapsulated nerve ending, large-onionlike structure, deep in Dermis, respond to high frequency vibrations. E.g. tickle Meissner s corpuscles: low frequency/ tap vibrations, detection of texture. Glabrous skin only. E.g. finger tips Merkel s disc: light mechanical pressure. Finger tips, lips, genitalia. Mostly on glabrous skin. Sensory Perception sual_library/apvl/index.html Touch o Sensation= mechanoreceptors: pressure and vibration o Sensation: emotional o Sensation: in some animals (humans?), used to sense heat (snakes) o Sense of touch can be modified by learning/experience Musicians

3 Blind people (Braille) The sensitivity of a body area is reflected in the amount of neurons responsive to touch (Homunculus) Pathway: spinal cord.. Somatosensory cortex Dermatomes Somatosensations go through the spinal cord Different levels ( (C,T,L,S) of the spinal cord receive information from different parts of the skin (dermatomes) o Cervical= shoulders + arms o Thoracic= torso o Lumbar= hips and legs o Sacral= genital and heels Neural deficit-> damage to somatosensory area- Tactile agnosia (tactile apraxia) ared/visual_library/apvl/index.html

4 Temperature Two temperature receptors (free nerve endings): cold (superficial dermis) and warmth (deep dermis) receptors Transduction mechanisms involve a family of dedicated receptors (TRP) Neural pathways are similar to those of pain Hypothalamus is in charge of temperature regulation: sweating (to decrease temperature, like a swamp cooler ), vasoconstriction (conserve heat, erection of hair/fur) o Physiology Adaption to constant (or slow) temperature changes. The same temp. may feel cold or warm, depending on the initial conditions. 8 degree C=47 deg F <-> 122 degree F are the threshold for pain Temp. is naturally variable. E.g. female reproductive cycle: temperature increases just after ovulation Pain Pain sensation o Pain receptors (nociceptors): free nerve endings Mechanoreceptors: intense pressure Intense heat + acids Irritant receptors: chemicals that may produce inflammation (e.g. tear gas) o Different components of pain sensations: Sensory: receptors -> spinal cord -> thalamus (VPN) -> primary sensory cortex pain intensity Emotional: primary sensory cortex -> anterior cingulate cortex (hypnosis) Pain color (how much is it disruptive? Unpleasantness) Long term psychology (chronic pain): prefrontal cortex (lobotomy) Pain memory Pain perceptions o Perception of pain can be controlled: Hypnosis Primary sensory cortex: sensation of pain Cingulate cortex: perception of pain o Pain can be imagined : empathy o Pain can be managed with learning and experience

5 Ex: brain plasticity result in reorganization (phantom limb and the mirror box) **Perception: Two sensory pathways Spino-thalamic tract: Pain, temperature Dorsal column: precise touch, movements Taste

6 Taste o Chemical sense o Taste- gustation, flavor= olfaction o 6 independent dimensions/ stimuli: bitterness o sweetness o sourness o saltiness (NaCl) o Umami (M.S.G) o Fat Taster apparatus= tongue + palate + pharynx + larynx Taste receptors= taste buds 10,000 receptors. Renewed every ~10 days sense of taste has genetic basis: o supertasters: bitter sensitivity, more prevalent in women and Europeans (reason why culinary art so important in Europe?) o non-tasters Tongue Taste transduction: o Dissolve in saliva -> bind to receptors -> ion flow -> receptor potentials Sourness: acidity, bind H+, potassium channels Saltiness: NaCl, direct through sodium channels Bitterness: many receptors (protective function: detection of bad foods ) Sweetness: specific receptors (genetically absent in felines) Umami: Glutamic acid, MSG, metabotropic channels Gustatory pathway Lateral Hypothalamus (LH): perceptions of hunger, metabolism Amygdala: perception of like/dislike, aversion Primary gustatory cortex: perception of taste Gustatory cortex Maps for taste may very from subject to subject o Established genetically and through experience o Size of the map may explain individual differences (e.g. sweet tooth?)

7 Olfaction es/ch17/print/pap15_17_03e_li.jpg Olfaction 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 (analysis). Strong associations with memories Olfaction: sensation Molecules -- Perception o Odorants dissolve in mucus

8 o Bind to olfactory cells (cilia). Molecule specific binding o Each cell send one axon to olfactory bulbs Mitral cells. ~35 per bundle o Synapses on mitral cells form glomeruli (10,000). Glomeruli are molecule specific (olfactory chemical map ) o Axons of mitral cells go to associated areas in the brain. Olfactory nerve Olfactory pathway Cognitive/emotion route o Olfactory bulb -> -> Thalamus -> Orbitofrontal cortex (cognitive) -> Amygdala -> Limbic system (emotional) Olfaction facts Humans can perceive 10,000 odors, but have only ~300 receptor types. How can recognition be achieved? -> Pattern matching Major problem in studying olfaction: basic odors are unknown Olfaction is still an art: o Cooking, perfume industry, wine tasting nt/pap15_17_01ab_li.jpg