The Senses

Stimulation of Senses All sense organs must be able to detect a stimulus in the environment Depending on the stimulus, a different receptor will be activated Signal is transmitted to the brain

Types of Receptors Photoreceptors – light Chemoreceptors – chemicals Pain receptors – physical damage Thermoreceptors – change in temperature Mechanoreceptors – change in position

Chemical Senses: Taste and Smell Receptors are chemoreceptors Associated with food intake, influence flow of digestive juices, and affect appetite

Anatomy of the Tongue Papillae contain taste buds Types: Filiform and Fungiform papillae Small, all over the top and sides of the tongue Circumvallate Papillae Large, on the back of the tongue

Taste - Gustation Chemoreceptors are found in taste buds found on the sides of the papillae Taste bud consists of three types of cells: Gustatory Cells: contain chemical receptors Supporting Cells Basal Cells: immature cells that grow into either gustatory cells or supporting cells

Taste Bud Anatomy Gustatory hairs project through the taste pore to bring in chemicals from the mouth Information then moves through the gustatory cells to sensory neurons

Smell Chemoreceptorsthat allow for smell are found in the olfactory epithelium Located in the nasal cavity

Olfactory Epithelium Anatomy Three Types of Cells in Olfactory Epithelium: Olfactory Cells Supporting Cells Basal Cells Olfactory cells have olfactory hairs that extend out into the nasal cavity and bind chemicals

How Smell Works Pathway: Olfactory Hairs  Olfactory Cell  Olfactory Nerve Fibers  Olfactory Bulb in the Brain Neurons connect directly into the brain from the nasal epithelium through the cribriform plate

The Ear Two functions: Hearing and Equilibrium Physical forces from sound and movements stimulate the mechanoreceptors in the inner ear

External Ear Made up of: Auricle (aka Pinna) – appendage on side of head External auditory canal – tube carries sound Tympanic membrane - eardrum Sound waves travel thru canal, strike the tympanic membrane and cause it to vibrate

Middle Ear (Tympanic Cavity) Tiny cavity hollowed out of temporal bone Also connects to the throat by Pharyngotympanic tube Sore throat could spread to ear, causes middle ear infection Contains three small bones called ossicles Malleus (hammer), Incus (anvil), Stapes (stirrup)

Middle Ear Tympanic membrane  Malleus  Incus  Stapes  Oval Window Oval window - small opening in inner ear covered by a membrane Sounds cause tympanic membrane to vibrate, which is amplified by the ossicles Causes movement of fluid in inner ear

Inner Ear Vestibule – Senses gravity Cochlea - Hearing Circle in the middle that contains the oval window Cochlea - Hearing Snail shaped structure on one side of the vestibule Semicircular Canal – Balance Three circular structures on other side of the vestibule

Inner Ear Outer structure made of bony labyrinth Contains perilymph There is an inner membrane within the perilymph called the membranous labyrinth Contains endolymph and the Organ of Corti Organ of Corti contains the mechanoreptors, so when the endolymph around it moves they are stimulated

Ear Disorders CONDUCTIVE DEAFNESS Conditions in outer or middle ear blocks vibrations NERVE DEAFNESS Nerve impulse doesn’t make it to brain Correction Cochlear Implant

Outer Layers of the Eye SCLERA (aka “whites of the eyes”) Front has a transparent portion – Cornea Conjuntiva – mucous membrane keeps eye moist Lacrimal Gland – produces tears

Middle Layer of the Eye CHOROID Contains dark pigment to prevent scattering of incoming rays of light Made up of 2 involuntary muscles: Iris: constricts and dilates pupil, the hole at the center of it Ciliary Muscles: helps focus on objects

Inner Layer of the Eye RETINA Contains microscopic photorecepotors: Rods – nightime vision, black and white Cones – daytime vision, color 3 types detect color – red, green, blue Surrounds fovea centralis – a depression that contains the most cones Visual sharpness is obtained by focusing the image on the fovea centralis

Inside the Layers of the Eye Fluid maintains intraocular pressure of eyeball Aqueous Humor – fluid in front of lens Vitreous Humor – Jellylike material in the posterior cavity Lens – directly behind pupil Elastic to allow change of shape

How You See

Disorders of the Eye

Focusing Problems Myopia - Image focuses in front of retina, distant objects blurry Hyperopia - Image focuses behind retina, close objects blurry Astigmatism – Abnormal curvature of cornea or lens, fails to refract light properly

Focusing Problems

Eye Disorders CATARACTS Lens becomes cloudy so less light enters the eye GLAUCOMA Aqueous humor not drained properly, intraocular pressure builds up, can cause blindness

Color Blindness Unable to distinguish certain colors Occurs when cones are nonfunctional Most common – red cones missing Can’t distinguish red from green