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

Lens focuses light by altering its shape 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 The Retina 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 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. http://www.rhsmpsychology.com/images/olfaction.jpg

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 brain https://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