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