Sensory Mechanisms

Introduction

•Sensations are action potentials that reach the brain through neurons.

•The sensations mean nothing to us without the perception of the brain.▫Perceptions include smells tastes sounds

and colors.•These perceptions are vital to our

existence, even pain.

Sensory receptors

•Sensory receptors are specialized neurons or epithelial cells in sensory organs like eyes and ears.

•There are two types of sensory receptors▫Exteroreceptors- receive stimuli on the

outside of the body like heat, light, and pressure.

▫Interoreceptors- receive stimuli from inside the body like blood pressure and body position.

5 Categories of Sensory Receptors• Mechanoreceptors- stimulated by physical

deformation like pressure, touch, motion, sound, etc.• Thermoreceptors- stimulated by either heat or cold• Chemoreceptors- transmit information about the

concentration of a solute in a solutoin▫ Example: Osmoreceptors sense a low concentration of

water in blood and stimulate thirst• Pain receptors- respond to excess levels of the three

receptors above• Electromagnetic receptors- detect forms of

electromagnetic energy like magnetism, visible light, and electricity.▫ Example: Photoreceptors in eyes

Touch• The skin has many

mechanoreceptors throughout, which are modified sensory neurons used for touch.

• Ones on the surface detect light pressure while those deeper in the dermis detect stronger pressures.

• Some sensory neurons attach to hairs to detect movement that is very close but not touching the skin.

• Others specialize in detecting cold and heat. http://trjohn.blogspot.com/2008_04_01_archive.html

The Eye Anatomy• Pupil- small opening for light.• Iris- colored, contractible covering

surrounding the pupil.• Sclera- Tough, white portion

surrounding the eye• Cornea- outermost membrane of

eye that serves for protection• Choroid- Pigmented area just

inside the sclera• Lens- bends and deflects light so it

can focus on the retina• Retina- receives light signals and

converts them into electrical impulses▫ Macula- Small sensitive area of

the retina that gives central vision▫ Fovea- center of macula that gives

the sharpest vision• Optic nerve- carries visual

messages from retina to brain• Vitreous humor/gel- gel-like

substance filling the inside of the eye

• Aqueous humor- anterior liquid portion in front of the iris

Basic Physiology•Light passes through cornea and into

pupil•Pupil can contract and retract to allow

different amounts of light in•After passing through pupil light hits lens•Lens deflects light so that it focuses on

the retina

http://en.wikibooks.org/wiki/Anatomy_and_Physiology_of_Animals/The_Senses

The Retina

• Lens focuses light by altering its shape. The flatter the lens, the less focused the object is

• Specialized cells located in the retina known as rod and cone cells are the light receptors▫Rod cells- light

sensitive, no color▫Cone cells- color

detection but need more light

• Fovea consists only of rods

depts.washington.edu

Ear Anatomy• Outer Ear- collects sound waves and

channel them to eardrum• Tympanic membrane- separates the

outer ear from middle ear, vibrated from sound waves

• Middle Ear- contains three small bones where vibrations are conducted▫ Malleus (Hammer)▫ Incus (Anvil)▫ Stapes (stirrup)

• Oval window- Membrane below stapes where vibrations pass through to the inner ear

• Eustachian tube- opening in the middle ear which connects with the pharynx and equalizes pressure in your middle ear with the

• Inner ear- Contains many pathways within the temporal bone that are lined by a membrane and respond to sound or movement of the head.

• Cochlea (latin for “snail”)- part of inner ear which is very complex with two chambers.▫ Tympanic canal- bottom▫ Vestibular canal- top▫ Coclear duct- separates two canals

• Endolymph- fluid housed in the cochlea

http://www.theeargroup.com/id16.html

How we hear

How we hear• Sound waves are collected by the outer ear and are

funneled to the tympanic membrane.• This membrane then vibrates and transfuses these

vibrations into the malleus, incus, and stapes.• These bones transfer the mechanical movements to

the oval window.• The oval window produces pressure waves in the

endolymph which runs through the vestibular canal first, through the cochlear duct, and back down through the tymphanic canal finally hitting the round window.

• The hair cells trigger the release of neurotransmitters which causes the sensation in the brain.

Chemoreception

•Basically a chemical conversation between your senses and the substance giving off the chemical.

•Smell and taste are examples of chemoreception and are very interrelated.

•Chemicals dissolve in either saliva or mucus, and chemoreceptor cells respond to the chemical stimuli and send these signals to the brain.

Smell• Scientifically known

as Olfactory sense.• Takes place in

human’s nasal cavity.

• Chemicals dissolve in mucus

http://www.rhsmpsychology.com/images/olfaction.jpg

• Dissolved chemicals run past the upper portion of nasal cavity where olfactory receptor cells are located.

• The tinny cilia on the end of each receptor cell gets excited when it’s specific molecule passes by.

• The molecule then binds to the cilia and the receptor cell triggers a signal to the olfactory bulb in the brain.

Taste• Very similar to that of

smell.• Receptor cells are

modified epithelial cells.• Clustered into taste

buds which are scattered throughout the surface of papillae.

• Chemicals dissolve in saliva and pass by receptor cells

• Receptor cells get stimulated by chemical and send impulse to brainhttps://sites.google.com/a/luther.edu/genetics/students/kirsten-de-jarlais/ptc-tasting-

polymorphism

4 Tastes

•Sweet, sour, salty and bitter•Each taste has its own separate section

on the tongue

http://svc005.wic040p.server-web.com/bb_site_intro/stage1_modules/Senses/taste.htm