The Special Senses Chapter 17
Objective Describe the structure of vertebrate sensory organs and relate structure to function in vertebrate sensory systems.
The 5 Special Senses 1. Olfaction 2. Gustation 3. Vision 4. Equilibrium 5. Hearing
Vision - Eye Anatomy Cornea clear protective layer of eye (also refracts light) Iris colored muscle of eye which protects retina by changing pupil size Pupil allows light into eye Aqueous humor watery fluid filled substance that gives the front of eye its shape Lens refracts light onto retina Vitreous humor jelly like fluid that gives eye it s shape
Eye Anatomy Retina back part of eye that contains rods & cones for detecting light Fovea centralis contains cones for color vision Optic nerve impulses sent via this nerve to the occipital lobe of the brain Blind spot part of the retina where the optic nerve attaches (lacks rods & cones) Sclera White part of external eye (Outermost protective layer) Choroid middle layer in eye with blood vessels
LASIK
Eyebrow Eyelid Eyelashes Site where conjunctiva merges with cornea Palpebral fissure Lateral commissure Iris Eyelid Pupil Sclera (covered by conjunctiva) (a) Surface anatomy of the right eye Lacrimal caruncle Medial commissure
Problems of Refraction Myopia (nearsightedness) focal point is in front of the retina, e.g. in a longer than normal eyeball Corrected with a concave lens Hyperopia (farsightedness) focal point is behind the retina, e.g. in a shorter than normal eyeball Corrected with a convex lens Astigmatism caused by unequal curvatures in different parts of the cornea or lens Corrected with cylindrically ground lenses, corneal implants, or laser procedures
Emmetropic eye (normal) Focal plane Focal point is on retina. Figure 15.14 (1 of 3)
Myopic eye (nearsighted) Eyeball too long Uncorrected Focal point is in front of retina. Corrected Concave lens moves focal point further back. Figure 15.14 (2 of 3)
Hyperopic eye (farsighted) Eyeball too short Uncorrected Focal point is behind retina. Corrected Convex lens moves focal point forward. Figure 15.14 (3 of 3)
Diabetic retinopathy Cataracts Glaucoma Macular degeneration
Olfactory Organs Sensory organs of smell Organs have 2 layers: Olfactory epithelium Lamina propria Contains olfactory glands secretions absorb water, form a thick, pigmented mucus
Special Senses of the Ear Special senses of equilibrium and hearing are provided by the inner ear Equilibrium Position of the head in space Hearing Detect and determine sound waves
3 regions: Anatomy of the Ear External ear Detects sound waves towards middle ear Middle ear Collects sound waves Inner ear Contains sensory organs
External Ear Fleshy and cartilagenous auricle (pinna) Provides directional sensitivity Ends at the tympanic membrane Ear drum Thin, semitransparent sheet Delicate Protected by cerumen
Middle Ear Air-filled chamber Auditory tube permits equalization on both sides of the tympanic membrane 3 tiny bones: Malleus Hammer Incus Anvil Stapes Stirrup
Inner Ear Labyrinth of dense bones 3 subdivisions: Vestibule Saccule Utricle Sensations of gravity and linear acceleration Cochlea Snail shell Sense of hearing
Equlibrium Hair cells receive signals Provide info about the direction and strength of stimuli
Hearing Receptors can detect frequency and intensity of sounds Intensity is measured in decibels (db) Normal conversation 60-70dB Telephone dial tone 80dB Sustained exposure resulting in hearing loss: 90dB Rock concert 115dB Loudest recommended with protection: 140dB Gun blast 140dB
Olfactory Discrimination Olfactory system can distinguish thousands of chemical stimuli Olfactory receptors decline with age
Gustatory Receptors Taste receptors Aka taste buds An adult has ~3000 taste buds 3 types of projections: Filiform Fungiform Circumvallate
Filiform Papillae Provide friction Help the tongue move around the mouth Do not contain taste buds
Fungiform Papillae Each contains about 5 taste buds
Circumvallate Papillae Contain ~100 taste buds each Form a V near the posterior region of the tongue
Aging and Taste 10,000 taste buds when born # declines dramatically by age 50 ** olfactory stimuli has a powerful effect on mood & behavior ** if we cannot smell the food, we believe it is more bland