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The Senses Reception of a Stimulus

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The Senses Reception of a Stimulus The Senses eg. individual sensitivities, eg colorblindness we spend our lives in an ocean of sensory stimuli: ! unusual pathways, eg synesthesia light gravity electrical currents vibrations time our survival depends on our ability to perceive, interpret and respond to these signals Reception vs Perception Reception is the mechanism and structures involved in detecting and transmitting sensory information our body has millions of sensory receptors All sensory receptors are “connected to” our CNS by way of sensory neurons these neurons travel through the Cranial or Spinal nerves to the brain or spinal cord Perception is the conscious awareness of sensory stimuli is a higher level process of integration and interpretation depends on how the brain processes the signals it is receiving Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 1 Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 2 photoreceptor - light Reception of a Stimulus chemoreceptor - chemicals mechanoreceptor - bending, pressure, touch Reception of a sensation is determined by: thermoreceptor - temperature osmoreceptor – salt/water conc 1. Source of Sensory Stimuli baroreceptor - fluid pressure each sensory receptor is designed to transduce we can classify receptors by their location or only one kind of stimulus regardless of the source of the stimulus they respond to: how it is stimulated a. exteroceptors eg hard hit on head ! “see stars” near surface of body eg. spicy food monitor external environment eg. menthol cough drop most special senses 3. Density of Receptors & Size of Receptive b. visceroceptors (interoceptors) Field deep monitor internal environment 99% of receptors in body not evenly distributed over surface of body c. proprioceptors most tip of tongue (specialized kind of visceroceptor) lips monitors relationship of external to internal fingertips environment nose position and movement back of hand orientation wrt gravity least back of neck 2. Kind of Transducer (Modality) braille exploits high tactile acuity of fingertips 4. Intensity of stimulus sensory receptors are transducers ! receptors convert one form of energy into another increase in stimulus intensity that the brain can interpret ! increased frequency of firing sensory receptors are designed to respond best to a single kind of stimulus: if over stimulated – become pain receptors Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 3 Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 4 5. Duration of Stimulus eg. pain receptors, some touch, heat, cold, pressure, smell tonic receptors = the sensory neuron fires as long as it is being stimulated B. Encapsulated Receptors (=corpuscular receptors) eg. taste, pain, body position, chemicals in blood a simple receptor encapsulated in layers of connective tissue phasic receptors = continuous stimulation of receptors eventually results in loss of eg. Meissners Corpuscles egg shaped response just beneath skin in dermal papillae especially lips and finger tips !sensory adaptation exteroceptors mechanoreceptors – light pressure important in detecting changes in eg. Pacinian Corpuscles stimuli, not duration of the deep subcutaneous tissues and viscera same stimulus deep pressure and vibrations largest simple receptor cells (2mm, naked eye) mechanoreceptors eg. smell, touch, temperature 6. Structure of Sensory Receptor receptors for special senses are more complex C. Receptor Cells that synapses with Sensations can be produced by very simple sensory neuron kinds of receptors or complex sense organs eg. taste receptors receptors for General Senses are relatively simple D. Complex Sense Organs Receptor Cells are part of more complex sense A. Free Nerve Endings organ Direct stimulation of sensory neurons components of rather elaborate sense organs eg. eye, ear, etc the sensory neuron is also the receptor ! dendrites of sensory neurons Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 5 Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 6 Cutaneous Sensations 5. Temperature free nerve endings (=”Touch”) heat and cold are separate receptors the skin possesses ~200,000 thermoreceptors “touch” is a combination of perceptions from a variety 6. Pain of simple receptors nocioceptors in almost every tissue of body located in skin, connective tissue and all receptor types, if overstimulated, become pain receptors mucous membranes may be free nerve endings or enclosed in capsule of epithelial tissue or connective tissue !~64 million receptors in skin they deliver more kinds of information than any single receptor of the special senses Elements of Sense of Touch 1. Touch Meisner’s corpuscles esp fingertips, palms, soles, tongue, lips, nipples, penis 2. Pressure Pacinian corpuscles 3. Vibration Pacinian corpuscles 4. Itch and Tickle free nerve endings Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 7 Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 8 The Nose & since they are neurons, they are replaced only very The Physiology of Smell slowly and not as quickly as they are lost both our senses of taste and smell are based mainly on ! some replacement chemoreceptors ! but overall, we loose ~1%/yr ! loose sense of smell as we get older smell ! detects airborne chemicals that enter nasal olfactory receptors are extremely sensitive cavity we are able to detect >10,000 different chemicals a chemical can be smelled only if it is volatile (most: 2000 – 4000) (=ie. able to become airborne) mostly small molecules we have ~350 distinct kinds of receptor proteins long range ! seem to be grouped into 15 – 30 “families” of odors receptors are located in roof and walls of nasal some can detect a single molecule of certain chemicals passages eg. can smell mercaptans (skunks) 1pt in 30 Billion 10-20 Million olfactory neurons in olfactory mucosa in an area about the size of a postage stamp women are more sensitive to smells than are men receptors are free nerve endings though very sensitive, they adapt quickly !dendrites of bipolar neurons olfactory signals can reach the cerebral cortex neurons pass through cribiform plate and connect to (temporal lobe) before they pass through the olfactory bulb on anterior ventral surface of brain thalamus olfactory neurons are the only neurons in the body some applications of olfactory physiology: directly exposed to external environment eg. Morning Sickness ! life span of only ~60 days Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 9 Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 10 during pregnancy sense of smell becomes much more acute due to action of estrogen which increases during pregnancy Taste Buds & ! may lead to morning sickness The Physiology of Taste almost all stimuli for nausea are odors also due to chemoreceptors: esp smell of cooking foods, esp meats and bacon ! detects certain chemicals in foods and drink sometimes also coffee, perfumes, cigarette smoke, petroleum products, etc must be water soluble eg. Military use of smell for crowd control eg. starch powder in insoluble ! has no taste short range; requires direct contact with “food” taste receptors are much less sensitive than smell receptors taste receptors located in tastebuds !4000 - 10,000 taste buds !most on tongue ! on papillae each papilla contains up to 200 taste buds some on soft palate and in throat, cheeks each taste bud is a cluster of 50-150 spindle shaped taste cells taste cells synapse with sensory neurons taste cells are replaced every 7-10 days Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 11 Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 12 !continually replaced throughout life also, many flavors depend on smell each taste bud acts as a chemoreceptor ! taste is up to 80% smell ! presence of specific chemical initiates nerve hold nose to take medicine impulse older people complain of lost taste but actually are losing smell ! most taste buds respond to 2-4 taste modalities interaction of all these kinds of receptors produces Flavors detected by taste receptors: all the flavors of food and drink sweet - respond to sugars, some amino acids sour - respond to acids bitter - respond to alkaloids (eg. quinine, nicotine, caffeine) salty - respond to inorganic salts and metal ions umami - (=’delicious, savory’) respond to meaty flavor, glutamate, aspartate, MSG all primary taste sensations are detected in all areas of the tongue in spite of “taste maps” of the tongue: tonic receptors ! don’t adapt quickly the sense of taste also involves additional receptor types: thermoreceptors (spicy hot, menthol) mechanoreceptors (texture) nocioceptors (spicy) Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 13 Human Anatomy & Physiology: The Senses; Ziser, Lecture Notes 2010.3 14 The Eye & The Physiology of Vision contains numerous blood vessels highly pigmented eye might be considered our most important sense organ anteriorly is modified into 2 sphincter muscles: of all the nerve fibers making up the 12 pairs of cranial iris – smooth muscle in doughnut shape nerves: pupil – opening in center of iris 38% of them are contained in the optic nerve ciliary body – ring of muscle behind iris we usually use data from our other senses only to supplement visual information lens – held in place by ciliary body Structure flattened, tightly compressed cells=lens fibers the eyeball is spherical 3. retina consists of 3 layers: innermost coat of eyeball
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