Anatomy and Physiology I Chapter 16 Sense Organs

Sensory Receptors Structure specialized to detect stimulus Sense organ- structure composed of nervous tissue along w/ other tissue types Enhance response to stimulus Fundamental purpose of sensory receptor is transduction- conversion of one form of energy to another Light, sound Sensation- subjective awareness of stimulus Signal must reach brain Most filtered out in brain stem- keeps from being distracted

Sensory Receptors Transmits 4 kinds of information Modality- type of stimulus or sensation it produces Vision, hearing, taste (all have same action potential) Assumes that if signal comes from retina  vision, taste bud  taste, etc Location- depends on nerve fibers stimulated Receptive field- skin touch Intensity- brain distinguish intensities based on fibers sending signals, how many, how fast fibers firing Loud/ soft sound, bright/ dim light, soft/ hard touch Duration- length stimulus lasts Sensory adaptation- prolonged stimulus, neuron fires more slowly, become less aware of stimulus (hot bath water)

Receptor Classification Stimulus modality Thermoreceptors- heat and cold Photoreceptors- light (eyes) Nociceptors- pain receptors Chemoreceptors- chemical (taste, odors) Mechanoreceptors- physical deformation (touch, pressure) Stimulus origin Exteroceptors- sense stimuli from external body Interorecptors- detect stimuli in internal organs Proprioceptors- sense the position and movements of body parts Receptor distribution General senses- widely distributed throughout body (skin, muscles, tendons, viscera) Touch, pressure, temperature, pain Special senses- limited to head Vision, hearing, equilibrium, taste, and smell

Taste Anatomy Gustation- sensation that results from the action of chemicals on the taste buds Taste buds- lemon shaped (4000) Taste cells- epithelial cells Taste hairs- receptor surface for taste molecules Taste pore- on surface of tongue

Taste Physiology Molecules dissolve in saliva and flood taste pore 5 primary taste sensations 1. Salty- vital electrolytes (sodium) Lateral tongue 2. Sweet- associated w/ carbohydrates Tip of tongue (triggers licking, salivation) 3. Sour- associated w/ acidic foods 4. Bitter- associated w/ spoiled foods and alkaloids Trigger rejection response (gagging) Rear of tongue 5. Umami- “meaty” taste produced by amino acids

Taste Physiology Flavors we perceive are not only due to combination of 5 taste regions, but they are also influenced by Food texture Aroma Temperature Appearance State of mind Many flavors depend on smell

Smell Anatomy- Olfaction Smell receptors form a patch of epithelium on roof of nasal cavity Olfactory mucosa Olfactory mucosa consists of 10-20 million olfactory cells- neurons Cilia on olfactory cells- olfactory hairs Binding sites for odor molecules Directly exposed to external environment Life span of 60 days Replaceable

Smell Anatomy Olfactory fibers pass through roof of nose and enter a pair of olfactory bulbs Beneath frontal lobe Turn into olfactory tracts End at inferior surface of temporal lobe

Smell Physiology Poorer sense of smell than most mammals Declined as visual sensation grew Smell more sensitive than taste Women more sensitive to odors than men Distinguish b/t 2000-4000 odors, some up to 10,000 350 kinds of olfactory receptors Olfactory cell has only one receptor type, therefore binds one odorant

Smell Physiology Odorant molecule binds with receptor on one olfactory hair Triggers action potential of the olfactory cell and the signal is transmitted to the brain

Hearing and equilibrium Hearing- response to vibrating air molecules Equilibrium- sense of motion, body orientation, balance Reside in inner ear Sound- any audible vibration of molecules Transmitted through water, air, solids

Ear Anatomy 3 sections Outer Middle Inner Outer and middle ear transmit sound to inner ear Inner ear converts vibrations into nerve signals

Outer Ear Funnel for conducting vibrations to the tympanic membrane Pinna- elastic cartilage Auditory canal- passage leading to tympanic membrane External acoustic meatis- external opening

Middle Ear Located in tympanic cavity of temporal bone Tympanic membrane (ear drum)- vibrates in response to sound Auditory tube- filled with air, equalizes air pressure 3 bones of middle ear- Auditory ossicles (smallest bones of the body) Connect tympanic membrane to inner ear Malleus- handle and head Incus- triangular body Stapes – stirrup shaped

Inner Ear Filled with fluid Vestibule- organ of equilibrium Semicircular ducts- organ of equilibrium Cochlea- organ of hearing Round window Vestibulocochlear nerve- Cranial nerve VIII

Ear Physiology- Hearing Sound waves directed toward tympanic membrane by outer ear Tympanic membrane vibrates in response to sound waves Vibrations sent through middle ear Each ossicle vibrates the next Stapes vibrates cochlear hair cells Signal sent to brain via cochlear nerve Brain interprets signal as sound

Ear Physiology- Equilibrium Coordination, balance, orientation in 3-D space Receptors for equilibrium constitute the vestibular apparatus 3 Semicircular ducts Rotary movements Hair cells Saccule- anterior chamber Hair cells vertically Responds to vertical acceleration and deceleration Utricle- posterior chamber Hair cells horizontally Responds linear movements Detects tilt of head

Vision Perception of objects in the environment by means of the light they emit or reflect

Accessory Structures Eyebrows- enhance facial expressions, protect eyes from glare and sweat Eyelids- block foreign objects from eye, blink to moisten eye Medial and lateral commissures Eyelashes- guard hairs that keep debris from eye Lacrimal apparatus- Lacrimal gland- tear gland Ducts and canals- empty into eye or nose

Extrinsic Eye Muscles Superior Rectus- moves eye up Medial Rectus- moves eye medially Lateral Rectus- moves eye laterally Inferior Rectus- move eye down Superior oblique- rotates eye medially Inferior oblique- rotates eye laterally

Components of the Eye 1. 3 layers that form the wall of the eyeball Sclera Choroid Retina 2. Optical components that admit and focus light 3. Neural components Optic nerve

3 Layers Outer Layer Middle Layer Inner Layer Sclera- white of eyes Covers most of the eye surface Cornea- anterior, transparent region that admits light into the eye Middle Layer Choroid- highly vascular, deeply pigmented Iris- extension of choroid, controls diameter of pupil Ciliary muscles- found on posterior region of iris Controls lens, pupil Pupil- central opening of iris Inner Layer Retina Beginning of optic nerve 3 Layers

Optical Components Transparent elements that admit light rays, refract them, and focus images on retina Cornea Aqueous humor- fluid secreted by ciliary body and fills anterior chamber (between cornea and iris) Lens- suspended behind pupil, composed of transparent cells Vitreous humor- transparent jelly, fills posterior chamber, supports retina and lens

Neural Components Retina- thin, transparent membrane Optic nerve Attached to eye at optic disc- where optic nerve leaves the eye Depends on choroid for O2, nutrition, waste removal Detached retinas cause blurry vision If detached for too long, leads to blindness Optic nerve Optic disc- contains no receptor cells (blind spot) Visual filling

Image Formation Begins w/ light entering eye through pupil Image formation depends on refraction Bending of light rays Focused on retina Produces tiny, inverted image Image sent up optic nerve to brain

Retina 3 layers 1. Photoreceptors- absorb light, generate chemical and electrical signal Rods and cones- produce visual images Rods- responsible for night vision, produce images in shades of gray Cones- responsible for day vision, function in bright light, produce images in color 2. Bipolar cells- synapse for cones and rods w/ ganglion cells 3. Ganglion cells- receive input from bipolar cells (close to vitreous) Absorb light, and detect light intensity