Types of Receptors

Chemoreceptors
 Respond to changes in chemical concentrations

Pain receptors
 Respond to tissue damage

Thermoreceptors
 Respond to temperature changes

Mechanoreceptors
 Respond to changes in pressure or movement

Photoreceptors
 Respond to light
Sensation and Projection
 Brain:
 Sensations come from here
 Impulses are interpreted based on what area of
the brain they end up in
 Brain projects the sensation back to the sensor so
the person feels the sensation at the sensor
 Sensory Adaptation:
 Ability of the PNS or CNS to block sensory
impulses that it deems unimportant or has
become used to
Somatic senses
Sensors are widely
spread throughout
body and are fairly
simple
 Include:

 Touch
 Pressure
 Temperature
 Pain
Touch and Pressure
 Three kinds of receptors
 1) Free nerve endings
○ Sensations of touch and pressure
 2) Meissner’s corpuscles
○ Provide sensations of light touch, usually
located in regoins of skin without hair
 3) Pacinian corpuscles
○ Respond to heavy pressure, located in
deeper tissues
Temperature Receptors

Warm and cold receptors in skin
 Free nerve endings

Receptors adapt very fast

Pain receptors
 Extreme temperatures and injury stimulate
these
Pain Receptors
Sensations arise from free nerve ending
throughout body except brain
 Pain receptors adapt poorly
 Visceral pain

 Refers pain to areas on the skin
Special senses
Sensations arise from specially adapted
sensors
 Includes:

 Smell
 Taste
 Hearing
 Equilibrium
 Sight
Smell
Olfactory receptors are located in small
patches along the roof of the nasal cavity
 They are chemoreceptors

 Incoming gases must dissolve in the mucous
covering the nasal cavity

Dissolved particles interact with the cilia
and may stimulate an action potential
Taste

Taste buds
 Located primarily on tongue, although some
found on roof of mouth and sides of the throat
Each taste bud has many gustatory
receptors and tiny cilia projections
 These are chemoreceptors

 Incoming foods must be dissolved in saliva to be
tasted
Areas of the Tongue

Four main taste areas:
1. Sweet - concentrated on the tip of the tongue
2. Sour - concentrated along the margins of the
tongue
3. Bitter - concentrated along the back of the
tongue
4. Salty - spread throughout
The Outer Ear
Sound waves are directed into the ear by
the external auricle
 They travel down the external acoustic
meatus
 Bounce against tympanic membrane
(eardrum) and make the eardrum move

The Middle Ear






Occurs in the tympanic cavity
Has three small auditory ossicles/bones
Vibrations at the tympanic membrane cause
the three bones to vibrate
The final bone vibrates against the oval window
of the inner ear
The bones amplify the sound
Eustachian tube
 Connects middle ear to throat, equalizes pressure for
eardrum, often where earaches occur
Inner Ear

Includes two labyrinths:
 1) Osseous labyrinth - bony canals
 2) Membranous labyrinth - membrane-bound tube
inside the bony canals
 Perilymph separates the two
 Endolymph is found inside the membranous labyrinth

Two parts to the labyrinth:
 1) Semicircular canals - used in equilibrium
 2) Cochlea – organ for hearing
Inner Ear (cont)
Vibrations at the oval window cause vibrations in
the perilymph of the scala vestibuli
 Vibrations pass through vestibular membrane
into endolymph
 Vibrations than pass through basilar membrane
to perilymph of scala tympani
 Organ of Corti

 Found in basilar membrane, contains hearing sensors
with hairs; vibrations cause hairs to move
 Animation
 Animation
Equilibrium
 Two divisions:
 1) Static Equilibrium - senses posture while at
rest
○ Occurs in vestibule
○ Position of head is determined by hairs on the
macula, hairs respond to shifting of otoliths
 2) Dynamic Equilibrium – maintaining balance
during movement
○ Occurs in the semicircular canals, in particular
the ampulla
○ Movements cause the perilymph to stimulate
hairs in the ampulla
Sight
Visual receptors located in eye
 Accessory organs aiding eye:

 Eyelids
 Lacrimal apparatus
○ Gland that produces tears to cleanse and protect
eye and ducts to carry the tears to the nasal cavity
 Muscle
○ Moves the eye
The Eye

Posterior portion
 Sclera
○ Tough fibrous covering
 Choroid coat
○ Contains melanocytes to help darker the inside of
the eye
 Retina
○ Thin complex inner layer that is continuous with the
optic nerve and contains the receptors
 Vitreous humor
○ Jelly-like fluid filling internal eye
The Eye (cont)

Anterior portion
 Cornea
○ Transparent covering
 Aqueous humor
○ Fluid that is made between the iris and lens but can move to
between the cornea and the iris through the pupil
 Iris
○ Pigmented layer containing smooth muscle to control size of
pupil
 Lens
○ Layer that focuses the image on the retina; can change shape
to change focus
The Retina

Contains two types of receptors:
 1) Rods
○ Black-and-white vision; more indistinct image; pigment is
rhodopsin
 2) Cones
○ Color vision; refined image; pigments are sensitive to red,
green, and blue hues

Fovea centralis
 Part of retina containing high concentration of cones; area
with sharpest focus

Optic disc
 Area of retina with connection to optic nerve; lacks
receptors (blindspot)
Eye Dissection
Cow's Eye Dissection