Nervous System III, part 2 Chapter 12

Special senses Sensory receptors within complex sensory organs Found in the head Smell in olfactory organs Taste in taste buds Hearing and equilibrium in ears Sight in eyes

Smell Chemoreception Olfactory bulb

Olfactory epithelium 3 cm 2

An individual neuron contains a single type of odorant receptor Combine signals for diversity Cilia Nerve fibers within the olfactory bulb Olfactory receptor cells Columnar epithelial cells

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Olfactory stimulation Receptors undergo sensory adaptation rapidly Sense of smell drops by 50% within one second after stimulation

Taste (gustation) Chemoreceptors on taste buds Sweet, sour, salty, bitter, umami Each sensation triggered by the presence of different ions (e.g., H + sour, Na + salty)

Taste receptors One taste bud = taste cells

Tasting Substance must be dissolved in saliva Molecules interact with receptor on epithelial taste cell Each cell is only responsive to one type taste sensation

Hearing Perception of energy carried by sound waves (pressure)

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Hearing loss Conductive- external, middle ear; reconstruction of bones in middle ear Central- rare, damage to neural pathway Sensorineural- inner ear, death of hair cells

Cochlear implants

Equilibrium Dynamic- movement through space Static- head position Inner ear Vestibular apparatus- endolymph

Equilibrium Semicircular canal system – Rotational acceleration – Movement of endolymph, hair cells transduce (a) Head in still position (b) Head rotating

Equilibrium Semicircular canal system – Linear acceleration – Movement of otoliths, hair cells transduce – Some otoliths horizontal, some vertical

Vision Light translated to a mental image Light enters eye, lens focuses light on retina Retina photoreceptors transduce light into electrical signal Electrical signals through neural pathways to brain

Optics of the eye Focal point must hit the back of the eye (retina)

Lens- bends light to focus on retina Pupil- changes amount of light that enters

24 Focusing On Retina As light enters eye, it is refracted by: Convex surface of cornea Convex surface of lens Image focused on retina is upside down and reversed from left to right Light waves Object Cornea Image Retina Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Light energy changes to electrical energy Occurs at retina Hits visual receptors behind retina

26 Visual Receptors Rods Long, thin projections Contain light sensitive pigment called rhodopsin Hundreds of times more sensitive to light than cones Provide vision in dim light Produce colorless vision Produce outlines of objects Cones Short, blunt projections Contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe Provide vision in bright light Produce sharp images Produce color vision Fovea centralis contains just cones

Photoreceptors under layer of transparent neurons

Fovea- nothing to impede light

Stereoscopic Vision Provides perception of distance and depth Results from formation of two slightly different retinal images Light waves Right eyeLeft eye

In the brain Nerves cross in brain Binocular zone, constructs 3D representation