Chapter 8 Special Senses Essentials of Human Anatomy & Physiology Seventh Edition Elaine N. Marieb Chapter 8 Special Senses Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Senses General senses of touch Special senses Temperature- thermoreceptors Pressure/Pain- mechanoreceptors Special senses Smell/taste- chemoreceptors Sight- photoreceptors Hearing/equilibrium- mechanoreceptors

The Eye and Vision 70 percent of all sensory receptors are in the eyes Protection for the eye skull bones (orbit) fat eyelids/eyebrows lacrimal apparatus (gland, duct, tears) conjunctiva

Extrinsic Eye Muscles Muscles attach to the outer surface of the eye Produce eye movements

When Extrinsic Eye Muscles Contract Superior oblique- eyes counterclockwise Superior rectus- eyes looks up Lateral rectus- eyes look outward Medial rectus- eyes look inward Inferior rectus- eyes looks down Inferior oblique- eyes clockwise

Structure of the Eye The wall is composed of three tunics Fibrous tunic (sclera) – outside layer Choroid – middle layer Sensory tunic (retina) – inside layer

The Fibrous Tunic Sclera white of the eye/tough connective tissue Cornea https://www.youtube.com/watch?v=517SoY62Bw4 Transparent Allows for light to pass through - refracts light Repairs itself easily The only human tissue that can be transplanted without fear of rejection

http://www.phys.ufl.edu/~avery/course/3400/vision/eye_photo.jpg

Choroid Layer Blood-rich nutritive tunic Pigment (melanin) prevents light from scattering Cilliary body – smooth muscle; changes shape of lens distant object - muscle relaxes, lens flattens near object - muscle contracts, lens rounded Iris- pigmented layer that gives eye color; regulates size of pupil

Lens Biconvex structure Refracts light greatly

Lens Accommodation Light must be focused to a point on the retina for optimal vision The lens must change shape to focus for closer objects

Internal Eye Chamber Fluids Refracts light slightly Aqueous humor Watery fluid found in chamber between the lens and cornea Helps maintain intraocular pressure Provides nutrients for the lens and cornea

Internal Eye Chamber Fluids Vitreous humor Gel-like substance behind the lens Keeps the eye from collapsing Lasts a lifetime and is not replaced Refracts light slightly Holds lens and retina in place http://faculty.washington.edu/kepeter/119/images/eye3.jpg

Sensory Tunic (Retina) Contains receptor cells (photoreceptors) Rods Cones Signals leave the retina toward the brain through the optic nerve

Neurons of the Retina and Vision Rods Most are found towards the edges of the retina Allow dim light vision and peripheral vision (more sensitive to light, do not respond in bright light) Perception is all in gray tones

Neurons of the Retina and Vision Cones Allow for detailed color vision (red, green, blue) Densest in the center of the retina Fovea centralis and Optic Disk

COLORBLINDNESS TEST PLATES http://www.geocities.com/Heartland/8833/coloreye.html

COLORBLINDNESS Comes from a lack of one or more types of color receptors. Most are green or red or both and that is due to a lack of red receptors. Another possibility is to have the color receptors missing entirely, which would result in black and white vision. An inherited trait that is transferred on the sex chromosomes (23rd pair)- sex-linked trait Occurs more often in males Can not be cured or corrected

The Ear Houses two senses Receptors are mechanoreceptors Hearing Equilibrium (balance) Receptors are mechanoreceptors

Anatomy of the Ear The ear is divided into three areas Outer (external) ear Middle ear Inner ear

The External Ear Involved in hearing only Structures: Pinna (auricle)- collects sound External auditory canal- channels sound inward

The External Auditory Canal Narrow chamber in the temporal bone- through the external auditory meatus Lined with skin Ceruminous (wax) glands are present Ends at the tympanic membrane (eardrum)

The Middle Ear or Tympanic Cavity The opening from the auditory canal is covered by the tympanic membrane (eardrum) The auditory tube connecting the middle ear with the throat (also know as the eustacian tube)

Bones of the Tympanic Cavity Three bones span the cavity Malleus (hammer) Incus (anvil) Stapes (stirrip)

http://medicine.wustl.edu/~oto/bbears/images/ossic.jpg http://www.ghorayeb.com/files/STAPES_on_a_Penny_375_SQ.jpg

Inner Ear or Bony Labyrinth Includes sense organs for hearing and balance Filled with perilymph

Inner Ear or Bony Labryinth A maze of bony chambers within the temporal bone Cochlea Vestibule Semicircular canals

Organ of Corti Located within the cochlea Receptors = hair cells on the basilar membrane Endolymph flows through and bends hair cells Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Organs of Equilibrium Receptor cells are in two structures Vestibule Semicircular canals

Organs of Equilibrium Equilibrium has two functional parts Static equilibrium- in the vestibule Dynamic equilibrium- in the semicircular canals