to:1292 Ant/Phys II - Fall 2012
Sept. 03, 2012
Special Senses - Handout Chapter 16.wpd
Handout Chapter 16
canal of Schlemm
levator palpebrae superioris
extrinsic eye muscles
organ of Corti
Aud-, to hear
olfact-, to smell
Sense of Smell
!. Olfactory organs
a. The olfactory organs consist of receptors and supporting cells in the nasal cavity.
b. Olfactory receptors are neurons with cilia that are sensitive to lipid-soluble chemicals.
c. Nerve impulses travel from the olfactory receptors through the olfactory nerves, olfactory bulbs, and olfactory tracts to interpreting centers in the cerebrum.
2. Olfactory stimulation
a. Olfactory impulses may result when various gaseous molecules combine with specific sites on the cilia of the receptor cells.
b. Primary odors include camphoraceous, musky, floral, pepperminty, ethereal, pungent, and putrid.
c. Olfactory receptors adapt rapidly.
d. Olfactory receptors are often damaged by environmental factors, but are not replaced.
Sense of Taste
1. Taste receptors
a. Taste buds consist of receptor cells and supporting cells.
b. Taste cells have taste hairs that are sensitive to particular chemicals dissolved in water.
c. Taste hair surfaces seem to have receptor sites to which chemicals combine and trigger impulses to the brain.
d. There are four primary kinds of taste cells, each particularly sensitive to a certain group of chemicals.
2. Taste sensations
a. The four primary taste sensations are sweet, sour, salty, and bitter.
b. Various taste sensations result from the stimulation of one or more sets of taste receptors.
c. Sweet receptors are most plentiful near the tip of the tongue, sour receptors along the margin, salt receptors in the tip and upper front, and bitter receptors toward the back.
Sense of Hearing
1. The external ear collects sound waves created by vibrating objects.
2. Middle ear
a. Auditory ossicles of the middle ear conduct sound waves from the tympanic membrane to the oval window of the inner ear. They also increase the force of these waves.
b. Skeletal muscles attached to the auditory ossicles act in the tympanic reflex to protect the inner ear from the effects of loud sounds.
3. Eustachian tubes connect the middle ears to the throat and function to help maintain equal air pressure on both sides of the eardrums.
4. Inner ear
a. The inner ear consists of a complex system of interconnected tubes and chambers--the osseous and membranous labyrinths. It includes the cochlea, which in turn houses the organ of Corti.
b. The organ of Corti contains the hearing receptors that are stimulated by vibrations in the fluids of the inner ear.
c. Different frequencies of vibrations are thought to stimulate different receptor cells; the human ear can detect sound frequencies from about 20 to 20, 000 vibrations per second.
a. Conductive deafness is caused by disorders in the external or middle ear. The most common type is due to growth of bone around the base of the stapes.
b. Sensorineural deafness is caused by damage to the cochlea, auditory nerve, auditory pathway, or temporal lobe of the brain. It can result from exposure to loud sounds, diseases, injuries, or various drugs.
Sense of Equilibrium
1. Static equilibrium is concerned with maintaining ht stability of the head and body when these parts are motionless. The organs of static equilibrium are located in the vestibule.
2. Dynamic equilibrium is concerned with balancing the head and body when they are moved or rotated suddenly. The organs of this sense are located in the ampullae of the semicircular canals.
3. Other parts that help with the maintenance of equilibrium include the eyes and the proprioceptors associated with certain joints.
Sense of Sight
1. Visual accessory organs include the eyelids and lacrimal apparatus that function to protect the eye, and the extrinsic muscles that move the eye.
2. Structure of the eye
a. The wall of the eye has an out, a middle, and an inner layer than tunction as follows:
1) The outer layer (sclera) is protective, and its transparent anterior portion (cornea) refracts light entering the eye.
2) The middle layer (choroid) is vascular and contains pigments that help to keep the inside of the eye dark.
3) The inner layer (retina) contains the visual receptor cells.
b. The lens is a transparent, elastic structure whose shape is controlled by the action of ciliary muscles.
c. The iris is a muscular diaphragm that controls the amount of light entering the eye: the pupil is an opening in the iris.
d. Spaces within the eye are filled with fluids (aqueous and vitreous humors) that help to maintain its shape.
3. Refraction of light
a. Light waves are refracted primarily by the cornea and lens to focus an image on the retina.
b. The lens must be thickened to focus on close objects.
4. Refraction problems
a. Farsightedness of age (presbyopia) is caused by a diminishing of the elasticity of the lens.
b. Another type of farsightedness is caused by an eyeball that is too short: nearsightedness is caused by an eyeball that is to long; and astigmatism is caused by disorders in the curvatures of the cornea or lens.
5. Visual receptors
a. The visual receptors are called rods and cones.
b. Rods are responsible for colorless vision in relatively dim light, and cones are responsible for color vision.
6. Visual pigments
a. A light-sensitive pigment in rods (rhodopsin) decomposes in the presence of light and triggers nerve impulses.
b. Color vision seems to be related to the presence of three sets of cones containing different light-sensitive pigments, and each is sensitive to a different wavelength of light; the color perceived depends on which set or sets of cones are stimulated.
7. Stereoscopic vision
a. Stereoscopic vision involves the perception of distance and depth.
b. Stereoscopic vision occurs because of the formation of two slightly different retinal images that the brain superimposes and interprets as one image in three dimensions.
c. A one-eyed person uses relative sizes and positions of familiar objects to judge distance and depth.
8. Visual nerve pathways
a. Nerve fibers from the retina form the optic nerves.
b. Some fibers cross over in the optic chiasm.
c. Most of the fibers enter the thalamus and synapse with others that continue to the visual cortex.
--adapted from Hole, 1981.
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