SENSES: CHAPTER

10

Types of Receptors

Chemoreceptors Respond to changes in chemical concentrations

Pain receptorsRespond to tissue damage

Thermoreceptors Respond to temperature changes

MechanoreceptorsRespond to changes in pressure or movement

Photoreceptors Respond to light

Sensation and Projection

Brain:Sensations come from hereImpulses are interpreted based on what area of

the brain they end up inBrain 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:TouchPressureTemperaturePain

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 hair3) 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 receptorsExtreme 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 TasteHearingEquilibriumSight

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 chemoreceptorsIncoming 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 tongue2. Sour - concentrated along the margins of the

tongue3. Bitter - concentrated along the back of the

tongue4. 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 canals2) Membranous labyrinth - membrane-bound tube

inside the bony canalsPerilymph separates the twoEndolymph 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

AnimationAnimation

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 otoliths2) 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:

EyelidsLacrimal apparatus○ Gland that produces tears to cleanse and protect

eye and ducts to carry the tears to the nasal cavityMuscle○ 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 receptorsVitreous 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 pupilIris○ Pigmented layer containing smooth muscle to control size

of pupilLens○ 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

rhodopsin2) 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 discArea of retina with connection to optic nerve; lacks

receptors (blindspot)

Eye DissectionCow's Eye Dissection