Transcript The Senses
The Senses Chapter 29 Sensory Input • All senses trigger the same TYPE of action potential – Distinction occurs in activated brain area • The brain detects sensations and interprets them – Action potentials from sensory receptors – Greater stimuli = higher frequency of AP’s • Brain constructs perceptions from integrating sensations with other information – Neuronal communication involving multiple brain areas The Working Brain Sensory Receptor Types • Nociceptors – Respond to excess heat, pressure, or chemicals – Tissue damage – All parts of the body but brain • Thermoreceptors – Temperature of skin and blood – Maintains homeostasis via the hypothalamus • Photoreceptors – Light absorbing pigments – Light detection Sensory Receptor Types Mechanoreceptors • Touch, pressure, & vibrations • Bend or stretch PM of receptor cell = changing permeability – Stretch receptors – position of body parts – Hair cells - sound waves and H2O movements Chemoreceptors • Chemicals in the internal & external environment – O2 in arterioles – Osmoreceptors - changes in [blood solute] – Pheromone detection Sensory Adaptation • Sensory receptors become less responsive – Fewer action potentials • Limits reactions to normal background stimuli – Shower or hot tub temperature – Odors over time The Evolving Eye • Invertebrates – Eye cups: light intensity and direction only – Simple eye: light dark, some distance and color – Compound eye: form mosaic images • Multiple photoreceptors w/own eye • Acute motion detectors and color vision • Vertebrates (Cephalopods too) – Single-lens eye: b&w, color, motion, image formation • Amount of light entering the pupil is regulated by an iris • Passes through a lens which focuses light on the retina – Upside down and inverted – Rods, cones, and fovea • 3D images from 2 eyes Single–Lens Eye • Changes lens shape to focus light onto retina – Squid and fish have rigid eyes so use muscle movement – Mammals use ciliary muscles • Humors maintain shape and carry nutrients – Blockage of ducts = glaucoma • Tears only in humans – Excess solution for eye moisture – Drains to nose • Conjunctivitis Correcting Vision • Vision tests measure visual acuity or ability to distinguish fine detail – 20/20 is normal – chart read at 20 feet – 20/10 is better than normal – at 20 feet, read as if at 10 feet – 20/50 is worse than normal – at 20 feet, read as if at 50 feet • Visual problems are often focusing problems – Nearsightedness: can’t focus at distances, eye longer – Farsightedness: can’t focus close, eye shorter – Astigmatism: blurred vision from misshaped lens • LASIK reshapes cornea to change focusing ability Gross Anatomy of the Ear • 3 main regions • Eardrum separates outer and middle – Sound pressure moves ear drum to move ossicles in inner ear amplify • Eustacian tube equalizes pressure b/w middle ear and atmosphere (‘pop’) • Cochlea houses the hearing organ • Semicircular canals for balance Cochlea • Organ of Corti is the hearing organ – Contains hair cells embedded in a basilar membrane • Tectorial membrane bends hairs as basilar membrane moves • Sensory neurons to auditory nerve Semicircular Canals • Proprioception and movement – 3, 1 in each plane of movement • Head mov’ts change fluid direction – AP frequency change – Sudden stop causes dizziness b/c fluid still moves – Brain interprets and commands skeletal muscles • Motion sickness – Feel, but don’t see movement – Brain think drugs = vomiting Olfaction • Olfactory receptors detect airborne molecules – Upper portion of nasal cavity – Impulses to olfactory bulb – Cilia from tips in mucous to detect substances • Odorants bind to specific receptors that trigger membrane changes • Cause action potentials • Humans can detect 1000’s of odors – Animals can detect more, sensation is more important Taste • Taste buds detect molecules in solution • Four familiar and 1 other taste – – – – – Sweet: organics Sour: acids Salty: inorganics Bitter: caffiene, nicotine, aspirin Umami –meats, cheeses, and protein-rich foods (MSG) • Each receptor responsive to a particular type of substance – Many ‘tastes’ are really smell (head colds) – Spicy foods are pain response