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
• 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 nerveCranial 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
• 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
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
– 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
• 3 layers
Retina
– 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