Sensory system > Vision > Hearing Exteroreceptors > Transduction of external information (light, acoustic waves, temperature, chemicals, ...) to the neural system in the language of action potentials > Mechanoreception (hearing, touch), chemoreception (olfactory system, taste) photoreception Cyclic nucleotide-gated catwn channel Odorant Receptor G protein Adenylate cyclase Photoreceptor! > mechanism of light detection that leads to vision > main human sense, provides almost 85% of incoming information, > angle seen by fixed eye is about 100°, about 230° when extraocular muscles involved > Blind spot - the optic nerve passes through the optic disc, lack of light-detecting photoreceptors > Macula with fovea - small pit that contains the largest concentration of cone cells in the eye and is responsible for central, high-resolution vision Superior rectus m. Fovea centralis Vitreous Body Central retinal a \ Ora serrata Ciliary body Posterior chamber Anterior Chamber Cornea Pupil Optic disc Optic Nerve Central retinal v Interior rectus m Retina > Inverted eye - light passes through the layers of nervous tissues to the photoreceptors 1 he vertec reE.^a 'I'Jie inverted retine Rods& Cones Horizontal Bipolar Amacrine Retinal Ganglion Receptor cells > Rods - black-and-white vision, 120 mil. > Cones - color vision, 6 mil. Membrane shelves lined with rhodopsi ,pr color pigment n Outer segment Mitochondria ► Inner segment Outer limiting membrane Nucleus —- Synaptic body Invaginations of cell membranes that form a stacks of /. membranous disks V where photopigments '*. exist as transmembrane proteins Cone cell Center of Fovea Phototransduction Transducin >Conversion of a photon into an electrical signal > Process occurs via G-protein coupled receptors called opsins which contain the ichromophore 11-cis retinal. 11-cis retinal is covalently linked to the opsin. When struck by a photon, 11-cis retinal undergoes photoisomerization to all-trans retinal which changes the conformation of the opsin GPCR leading to signal transduction cascades which causes closure of cyclic GMP-gated cation channel, and hyperpolarization of the photoreceptor cell. Defects of the eye > Glaucoma - characteristic intraocular pressure-associated optic neuropathy , visual field loss > Cataract - clouding of the lens, treated by surgery Hyperopia Color vision > In human retina 3 types of cones > Pigments detects light of wavelenghts corresponding to red, blue and green color > Unequal stimulation of different types of cones —»• different colors > Mosct common deficiency -daltonism (red/green) > Color blindness - Ishihara test Normal I 700 650 Protanopia 600 550 500 1 450 1 400 1 700 650 Deuteranopia 600 i 550 i 500 450 400 700 650 600 I 550 I 500 450 400 Tritanopia 700 650 i 600 i 550 i 500 450 400 450 500 550 Wavelength [nrn] 600 «50 Experiment n.1 - VISION > Visual field detecting (perimetry test) 8 measurements in 4 axis (0°, 45°, 90°, 135°, 180°, ...) for 1 eye and 1 color > Blind spot detection ► about 15°, bellow horizontal axis > Color vision deficiency Ishihara color test, on-line test 290 --250 2S0 2'0 260 HEARING > Sound = periodical waves of pressure > Transforming sound pressure |J waves from the outside into -s a signal of nerve impulses sent to the brain > Amplitude + frequency volume Frequency Cochlea external acoustic meatus oval window scala vestibuli sound wave scala tympani tympanic cavity auditory tube ..... basilar membrane > hair cells - mechanoreceptors, auditory receptors in inner ear (organ of Corti) mna outer hair cells BNOOOWB VIDEO! Normal Acoustic 6t audiometry Senses are most sensitive to changes of weak stimuli, receptors do not register linear change in intensity, but logarithm of this change > Sound pressure level (Pa, dBell) logarithmic scale to represent the sound pressure of a sound relative to a reference pressure. The sound pressure level at the threshold of human hearing is actually 0 dB, which has the same pressure as the reference pressure, 2 x 10~5 Pa. Threshold of pain 20 Pa 2 Pa 0.2 Pa 0.02 Pa 0.002 Pa 0.0002 Pa 0.00002 Pa 130 dB-Pneumatic drill 120 dB - Loud car horn one metre away 120 db-Airport 100 d B -1 n side li nd erg rou nd tra in or a loni mainline railway 90 dB - Bus interior 60 dB - Busy residential \ 70 d B - Co nversatfo nal 60 dB - Living room with musk or television playing qui 50 dB - Quiet office 40 dB- Bedroom 30 dB - Recording studio 20 dB - Broadcasting studio 10 dB - Threshold of hearing OdB level 82240882 Experiment n. 2 Audiogram Audiogram = graph that shows the audible threshold for standardized frequencies as measured by an audiometer Human hearing frequency range: 16-20.000 Hz, best in 2-5kHz Absolute treshold of hearing 20 Hz 50 100 200 500 U 2k 5 k 10 k 20 kHz on-line test > Set the frequency of the sound, mark the first point the sound is present, go to an another frequency etc. iJB KK! 45Hi (OKI 1» 1ISH. ID Hi mhi 375Hi SMK. JHHi lift 1.5 klb lift 3 Mi Wi, tUi IMi 11 Ui lSklb 24 30--36--a.7--43 -54--60--66 -72--78-■ 34--90- -yfl - izn izn izn izn izn izn izn izn izn izn izn izn izn izn izn izn izn izn izn dB -21 -48 -54 -57 -57 -54 -57 -57 -54 -48 -57 -69 -75 -69 -75 -69 -84 -75 -45 THF UN1VFKSITY OF S'FW $0 U TH WM FS Audiograms Mr— 70 -50 -30 -10 - -10 - -30 D.Q1 ptiraktL't yoldrhh J_.......I_..... dolphin ........I_........I_..... Figure 1. 83 70 CL «5 CO c 40 S 30 -I o "5 20 \ 0 •10 -20 1 10 frequency; kHz 1 DO 1EJDEJ 016 03? 064 125 250 500 1 2 4 8 16 32 64 90 Frequency (in kHz) (Heffner & Heffner) Experiment n. 3 - Sound localization > Where does the sound come from? Detection based on: ► Intensity ► Time delay (ms) Humans can detect ±4° spatial angle > Mechanical tapping on the special board, person under the test reports sides where the sound came from Sound shadow Extra length of sound path to far ear Sound source torn siiuti.-t > I ■ I-* I « I % I I-\ » • Sound localization - results Was the side guess right or wrong? Distance from centre of the table 20 18 16 14 12 10 8 6 4 2 J2 4 6 8 10 12 14 16 18 20 + + + + + + + - - J- + + + + + + + + + + + + + + - - - l + + + + + + + + + + + + + + + - - l + + + + + + + + + + + + + + + - - !- + + + + + + + + + + + - - |- + + + + +