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Senses: Chapter 10. Types of Receptors. Chemoreceptors Respond to changes in chemical concentrations Pain receptors Respond to tissue damage Thermoreceptors Respond to temperature changes Mechanoreceptors Respond to changes in pressure or movement Photoreceptors Respond to light.
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Types of Receptors • Chemoreceptors • Respond to changes in chemical concentrations • Pain receptors • Respond to tissue damage • Thermoreceptors • Respond to temperature changes • Mechanoreceptors • Respond to changes in pressure or movement • Photoreceptors • Respond to light
Sensation and Projection • Brain: • Sensations come from here • Impulses are interpreted based on what area of the brain they end up in • Brain projects the sensation back to the sensor so the person feels the sensation at the sensor • Sensory Adaptation: • Ability of the PNS or CNS to block sensory impulses that it deems unimportant or has become used to
Somatic senses • Sensors are widely spread throughout body and are fairly simple • Include: • Touch • Pressure • Temperature • Pain
Touch and Pressure • Three kinds of receptors • 1) Free nerve endings • Sensations of touch and pressure • 2) Meissner’s corpuscles • Provide sensations of light touch, usually located in regoins of skin without hair • 3) Pacinian corpuscles • Respond to heavy pressure, located in deeper tissues
Temperature Receptors • Warm and cold receptors in skin • Free nerve endings • Receptors adapt very fast • Pain receptors • Extreme temperatures and injury stimulate these
Pain Receptors • Sensations arise from free nerve ending throughout body except brain • Pain receptors adapt poorly • Visceral pain • Refers pain to areas on the skin
Special senses • Sensations arise from specially adapted sensors • Includes: • Smell • Taste • Hearing • Equilibrium • Sight
Smell • Olfactory receptors are located in small patches along the roof of the nasal cavity • They are chemoreceptors • Incoming gases must dissolve in the mucous covering the nasal cavity • Dissolved particles interact with the cilia and may stimulate an action potential
Taste • Taste buds • Located primarily on tongue, although some found on roof of mouth and sides of the throat • Each taste bud has many gustatory receptors and tiny cilia projections • These are chemoreceptors • Incoming foods must be dissolved in saliva to be tasted
Areas of the Tongue • Four main taste areas: • Sweet - concentrated on the tip of the tongue • Sour - concentrated along the margins of the tongue • Bitter - concentrated along the back of the tongue • Salty - spread throughout
The Outer Ear • Sound waves are directed into the ear by the external auricle • They travel down the external acoustic meatus • Bounce against tympanic membrane (eardrum) and make the eardrum move
The Middle Ear • Occurs in the tympanic cavity • Has three small auditory ossicles/bones • Vibrations at the tympanic membrane cause the three bones to vibrate • The final bone vibrates against the oval window of the inner ear • The bones amplify the sound • Eustachian tube • Connects middle ear to throat, equalizes pressure for eardrum, often where earaches occur
Inner Ear • Includes two labyrinths: • 1) Osseous labyrinth - bony canals • 2) Membranous labyrinth - membrane-bound tube inside the bony canals • Perilymph separates the two • Endolymph is found inside the membranous labyrinth • Two parts to the labyrinth: • 1) Semicircular canals - used in equilibrium • 2) Cochlea – organ for hearing
Inner Ear (cont) • Vibrations at the oval window cause vibrations in the perilymph of the scalavestibuli • Vibrations pass through vestibular membrane into endolymph • Vibrations than pass through basilar membrane to perilymph of scala tympani • Organ of Corti • Found in basilar membrane, contains hearing sensors with hairs; vibrations cause hairs to move • Animation • Animation
Equilibrium • Two divisions: • 1) Static Equilibrium - senses posture while at rest • Occurs in vestibule • Position of head is determined by hairs on the macula, hairs respond to shifting of otoliths • 2) Dynamic Equilibrium – maintaining balance during movement • Occurs in the semicircular canals, in particular the ampulla • Movements cause the perilymph to stimulate hairs in the ampulla
Sight • Visual receptors located in eye • Accessory organs aiding eye: • Eyelids • Lacrimal apparatus • Gland that produces tears to cleanse and protect eye and ducts to carry the tears to the nasal cavity • Muscle • Moves the eye
The Eye • Posterior portion • Sclera • Tough fibrous covering • Choroid coat • Contains melanocytes to help darker the inside of the eye • Retina • Thin complex inner layer that is continuous with the optic nerve and contains the receptors • Vitreous humor • Jelly-like fluid filling internal eye
The Eye (cont) • Anterior portion • Cornea • Transparent covering • Aqueous humor • Fluid that is made between the iris and lens but can move to between the cornea and the iris through the pupil • Iris • Pigmented layer containing smooth muscle to control size of pupil • Lens • Layer that focuses the image on the retina; can change shape to change focus
The Retina • Contains two types of receptors: • 1) Rods • Black-and-white vision; more indistinct image; pigment is rhodopsin • 2) Cones • Color vision; refined image; pigments are sensitive to red, green, and blue hues • Fovea centralis • Part of retina containing high concentration of cones; area with sharpest focus • Optic disc • Area of retina with connection to optic nerve; lacks receptors (blindspot)
