anatomy and physiology i chapter 16 sense organs
TRANSCRIPT
Anatomy and Physiology I
Chapter 16Sense 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• Lateral tongue
– 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– Retina– Optic nerve
3 Layers• Outer 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
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– 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