Sensory Receptors; specialized cells that
monitor internal and external conditions.
Receptors
CNS for interpretation
Adaptation is a decreased sensitivity to the
presence of a constant stimulus.
I.e. not feeling your watch; jumping into cold lake
(Work of RAS)
Your Senses can be divided into two
categories
 General Senses – receptors for temperature,
pain, touch, pressure, vibration and body
position
Scattered throughout the body
Special Senses – smell, taste, vision,
balance and hearing
Concentrated with specific structures, called
sense organs
General Senses
• Part of PNS
• Pain Receptors (Nociceptors)
– Common in the superficial portions of the skin,
joint capsules, along periosteum of bones,
– Fast pain: carried by myelinated fibers
– Slow pain: carried by unmyelinated fibers
– Referred Pain: perception coming from other
parts of body; parts of body are connected to by
same spinal nerves. I.e. cardiac pain –
originates in chest and left arm.
Temperature
(thermoreceptors)
• Nerve endings scattered beneath skin
surface
• Located in skeletal muscles, liver and
hypothalamus as well. Why?
• Receptors RAS system (Working right
now in this room!!!)
Touch, Pressure and Position
(Mechanoreceptors)
• Respond to stretching, compression,
twisting or other distortions of the cell
membrane.
3 classes of Mechanoreceptors
• Tactile (touch)
• Baroreceptors (pressure)
• Proprioceptors (position)
6 Types of Touch
Receptors
1. Free Nerve
endings
2. Hair Plexus
3. Merkel’s
4. Meissner’s
5. Pacinian
6. Ruffini’s
Baroreceptors: monitor changes
in pressure
• Surround the walls of hollow organs. I.e.
blood vessels, lungs, stomach, bladder
• Monitors BP – plays a role in regulating
cardiac function and blood flow to tissues
Examples of pressure receptors
Proprioceptors
• Monitors the position of joints,
• tension in tendons and ligaments
• State of muscle contraction
• Lab Activity
Smell and Taste
Chemoreceptors respond to chemical in a water
solution.
Olfactory organs – provide a sense of smell
•Consists of olfactory epithelium, receptors, supporting
cells and basal (stem) cells
•Olfactory glands produce a mucus that covers
epithelium
•Keeps area moist and free of dust/debris
•Solvent that captures and dissolves air borne
molecules
•Constantly replaced; flushes away old odors
Olfactory Receptors: modified neurons
• An odor causes olfactory receptors to open
Na+ channels and change membrane
permeability.
• Research in the 1990’s suggests we have
1000 smell genes
– Genes only active in nose
– Each gene codes for an odor binding protein;
these receptor proteins only allow certain odors
to bind to it.
10-20 million receptor cells are packed into a 5 cm2 area.
Olfactory Bulb: Cranial Nerve I
• Axons leaving bulb travel to the olfactory
cortex of cerebrum, hypothalamus and part
of limbic system.
• Elicits emotional responses to odors
– Smells associated with danger (smoke, skunk)
– Pleasant smells cause increased secretion of
saliva and gastric juice
– Unpleasant smells trigger protective reflexes
(sneezing/coughing)
Lab Activity
• Tongue contains 3 types of cells: receptor,
support and basal cells
• Taste buds are the gustatory receptors
distributed all over tongue.
– Basal cells replace receptors q 7-10 days
• Taste hairs extend from receptor cells and
are bathed in saliva
• Dissolved chemicals touch hair (microvilli),
causing Na+ channels to open → A.P.
Four Primary Tastes
Sweet – tip of tongue
Salt – lateral tip
Sour – sides of tongue
Bitter – back of tongue
• Taste Receptors
respond more to
unpleasant stimuli
• Taste buds are
monitored by cranial
nerve 7 (facial), 9
(glossopharyngeal),
10 (vagus).
• Taste is 80 % smell.
• Think of how food
tastes when you have
a cold.
• Try This!
• Eyes are hollow organs divided into two
cavities.
• Aqueous humor – liquid inside eyeball
gives the eye shape
• Wall of the eye contains 3 layers
– Fibrous tunic – outer layer
– Vascular tunic – middle layer
– Neural tunic – inner layer
• Contains
– Sclera – white of
eye
• 6 eye muscles
attach
• Posterior surface
contains blood
vessels and nerves
– Cornea –
transparent light
passes thru.
• Functions
– Mechanical support
and some
protection
– Attachment site for
6 extrinsic eye
muscles
– Assists in focusing
• Iris – contains blood vessels, pigment cells, smooth muscle
– Controls the size of pupil (center of iris) in response to light
• Ciliary body – Thickened ring of tissue surrounding lens; forms
aqueous humor and muscles maintain lens shape
– Glaucoma – increased pressure in eye due to imbalance of A.
humor
• Choroid – blood vessel-rich membrane; delivers oxygen and nutrients
to retina
Functions
• Provide route for blood and lymph tissue
• Transmits and Regulates amount of light entering eye
• Circulate aqueous humor within eye
• Control shape of lens
Contains
• Photoreceptors –
respond to light
– Rods – light sensitive
– Cones – color vision
• 3 types of cones
Red/Green/Blue
• provides perception of
color
• Give more clarity than
rods
• Fovea – largest
concentration of cones;
sharpest vision
• Volunteers??? Anyone,
Anyone!!
What number
do you see?
Red/Green
Colorblind?
Optic disc – where the axons from neurons
converge, forms optic nerve
No photoreceptors are found here.
Lens
Primary function is to focus image on the retinal receptors in the
back of eye.
Focusing requires two steps
•Light is bent when it passes between mediums of varying
densities
•Greatest refraction occurs when light passes thru cornea.
•Focal point – when light bends to form a point
•Focal Distance – distance between center of lens and focal point.
Depth Perception
Two eyes are better than one, especially when it comes to
depth perception. Depth perception is the ability to judge
objects that are near or farther than others.
To demonstrate the difference of using one vs. two eyes to
judge depth, hold the ends of two pencils, one in each hand.
Hold them either vertically or horizontally facing each other
at arms-length from your body. With one eye closed, try to
touch the end of the pencils together. Now try with two eyes,
it should be much easier. (Can use fingers if you don’t have
2 pencils.)
Close Images – longer focal distance; lens is rounded
because ciliary muscles contract.
The closer the source, the
longer the focal distance
Distant Objects –Shorter focal distance and flattened
lens.
• The lens constantly changes shape to keep
the focal distance constant. – Image stays
focused on retina.
• I.e. looking at the board and then your
paper.
• 20/20 vision means a person can see details
at a distance of 20 feet as clearly as the
“normal population” would.
Normal Vision; what is happening in the eye.
• Near sighted (myopia) 20/30 vision
• Images forms in front of retina
• Vision at close range will be normal, because lens
can adjust and round up to focus.
Corrected by wearing a diverging lens!
Far Sighted (Hyperopia)
Eyeball is too shallow
Person can see distant objects; not near objects
Corrected by wearing converging lens!
Astigmatism occurs when the cornea is more oval than
spherical. The result is an unequal bending of the light
which results in multiple focal points.
Test for Astigmatism
To test your vision, stand about 20 feet from the chart. Test
one eye at a time. If you see lines grey and other black you
have an astigmatism.
3 Sections of EAR
• Organs
– Pinna (auricle)
– External Auditory Canal
– Functions to collect, direct sound waves to ear drum.
Tympanum – ear drum; Auditory Tube (Eustachian tube)
Auditory Ossicles –
1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup)
• Vestibule – provides sensations of gravity
and acceleration
• Semicircular Canals – detect movement of
head
• Cochlea – provide sense of hearing
• Hair Cells – receptors of inner ear for sound
How do we hear?
• Sound waves cause the tympanic membrane
to vibrate which moves the ossicles. Sound
energy are converted to mechanical energy.
• Ossicles transmit the in/out vibrations from
tympanic membrane to ear’s inner fluidfilled chamber.
How Do you Hear?
• Sounds set up vibrations in air that beat against the
tympanic membrane.
• Vibrations push the ossicles that press fluid in the
inner ear against membranes.
• Fluid causes forces that pull on tiny hair cells and
stimulate neurons.
• Neurons send impulses to the brain, which
interprets them.
Tiny Hair cells are in the
cochlea in an area called
the Organ of Corti.
Larger view of Organ of Corti.
Maintaining Equilibrium: How does it work?
When the head is upright, otoliths pushes the sensory hairs downward rather than
side to side.
By tilting the head, the otoliths move causing the sensory hairs to be distorted.
This is sent to the CNS for interpretation.
• Ear responds to various
head movements.
• Static Equilibrium is
controlled by the vestibule.
Respond to straight-line
changes in speed and
direction, but not rotation.
•Dynamic Equilibrium is
controlled by the semicircular
canals.
•Respond to changes in head
position; rotating the head to
say no.