Lecture Outline - Chapter 13

13.1 Receptors and Sensations (p. 266)
	1.	Receptors According to Stimuli (p. 266)
		a.	Chemoreceptors (used for smell and taste) are sensitive to chemical substances. They also monitor blood pH.
		b.	Mechanoreceptors are stimulated by mechanical forces. Baroreceptors in the aortic wall sense changes in blood pressure.
		c.	Proprioceptors sense the degree of muscle contraction, the stretch of tendons, and the movement of ligaments in special structures called muscle spindles.
		d.	Thermoreceptors sense temperature changes and these are located in the skin and the hypothalamus.
		e.	Pain receptors (nociceptors) are naked dendrites that respond to chemicals released by damaged tissues.
		f.	Photoreceptors are sensitive to light.
	2.	Senses According to Receptors (p. 266)
		a.	Somatic Senses (p. 266)
			Somatic senses are associated with the skin, muscles, joints, and internal organs. They employ mechanoreceptors, thermoreceptors, pain receptors, and proprioceptors.
		b.	Special Senses (p. 266, Table 13.1)
			i.	Taste and smell employ chemoreceptors.
			ii.	Vision uses photoreceptors.
			iii.	Equilibrium and hearing employ mechanoreceptors.
13.2 Skin (p. 267, Fig. 13.2)
	1.	The dermis of the skin houses receptors for touch, pressure, pain, and temperature. The number of receptors varies with different regions of the skin. The fingertips have abundant touch receptors.
	2.	The sense of touch uses several types of mechanoreceptors.
		a.	Deep in the dermis are Pacinian corpuscles that sense pressure.
		b.	Near the surface are the touch receptors called Meissner corpuscles and Merkel disks.
		c.	Adaptation occurs in touch receptors.
13.3 Chemoreceptors (p. 268)
	1.	Chemoreceptors in the aortic arch detect changes in pH in the blood.
	2.	Taste Buds in the Mouth (p. 268, Fig. 13.3)
		a.	Taste buds are located on the tongue and open at a taste pore. Supporting cells nearby have microvilli that bear receptor proteins for certain chemicals.
		b.	Taste receptors do not generate nerve impulses but are in contact with the ends of sensory fibers that transmit the messages.
		c.	Four types of taste are concentrated on different regions of the tongue: sweet at the tip, sour along the margins, salt at the tip and upper front, and bitter at the back of the tongue.
	3.	Olfactory Cells in the Nose (p. 269, Figs. 13.4, 13.5)
		a.	Olfactory cells are modified neurons located high in the nasal cavity. Each cell has a tuft of cilia with receptor proteins.
		b.	Odorous molecules combine with a receptor and generate a nerve impulse that travels to the olfactory bulb. Olfactory input is processed in the temporal lobes.
		c.	Olfactory receptors adapt to outside stimuli and stop sending impulses.
		d.	The senses of taste and smell work together.
13.4 Eyes (p. 270)
	1.	How the Eye Looks (p. 270, Fig. 13.6, Table 13.2)
		a.	The eyeball has three coats: the outer, tough, white sclera, which continues in the front of the eye as the cornea; the middle pigmented layer called the choroid that absorbs light and is highly vascular; and the innermost layer, the retina, which houses the sight receptors.
		b.	Also within the choroid are the lens, the ciliary body that controls the shape of the lens, and the iris, which regulates the amount of light entering the eye.
		c.	The anterior cavity is filled with aqueous humor; the posterior cavity is filled with vitreous humor.
		d.	Glaucoma can result when the drainage ducts leading from the aqueous humor become blocked.
		e.	How the Retina Is Structured (p. 271, Fig. 13.7)
			i.	The retina has three layers of cells. The photoreceptors are in the deepest layer, near the choroid.
			ii.	Photoreceptors consist of rods and cones, which synapse with bipolar cells that pass impulses to ganglionic cells in front of the retina. Ganglionic cells form the optic nerve, which sends impulses to the occipital lobe for processing.
			iii.	Where the optic nerve passes through the retina, no rods or cones are present, resulting in a blind spot.
			iv.	The fovea centralis on the retina contains only cones and is where vision is most acute.
	2.	How the Eyelids and Eyelashes Work (p. 272)
		a.	The inner lining of the eyelid is the conjunctiva, a transparent mucous membrane that folds back to attach to the sclera. The conjunctiva prevents tears from flowing back around the eyeball.
		b.	Eyelashes trigger blinking when particles fly at the eye.
		c.	Lacrimal glands produce tears that drain into the nose.
	3.	Focusing Uses the Lens (p. 272, Fig. 13.8)
		a.	Light rays focus on the retina and bend as they pass through the lens and are brought into focus.
		b.	The lens allows us to look at close objects through accommodation. We can see distant objects because the cornea bends the light rays sufficiently on its own.
		c.	The shape of the lens is controlled by the ciliary muscle, which curves the lens when we look at close objects.
		d.	Cataracts develop after years of exposure to UV rays. 
		e.	The Image Is Upside Down (p. 273)
			The image formed on the retina is inverted, and the brain learns to see it right side up.
		f.	The Image Is 3-D (p. 273, Fig. 13.9)
			Two eyes working together produce stereoscopic vision. Some of the nerve fibers cross over at the optic chiasma, causing each half of the brain to receive input from both eyes. The halves of the brain communicate for a three-dimensional image.
	4.	Inability to See Color (p. 274, Fig. 13.10)
		Some people, usually 5-8% of males, lack red or green cones.
	5.	Inability to See Clearly (p. 274, Fig. 13.11)
		a.	When people can see a size 20 letter from 20 feet, they are said to have 20/20 vision. Anyone not seeing the letter is nearsighted, and farsighted people see objects at a distance more clearly.
		b.	Corrective lenses can help people focus properly, and radial keratotomy flattens the cornea to help nearsighted people focus light waves on the retina.
		c.	Astigmatism is caused by an uneven cornea or lens, and can be corrected with unevenly ground lenses.
		d.	As We Age (p. 274)
			The lens loses some ability to focus as we age. Nearsighted people usually have to wear bifocals to compensate for changes in near vision as they age.
	6.	Seeing Uses Chemistry (p. 276, Fig. 13.12)
		a.	Rods help us see in dim light and are more numerous than cones. Rods see only in black and white; cones are responsible for color vision.
		b.	Rods contain a visual pigment (rhodopsin) made up of the protein opsin and the pigment retinal, a relative of vitamin A. When light hits rhodopsin, it sets up a series of biochemical changes that result in the generation of a nerve impulse in bipolar and then ganglionic cells.
		c.	Cones allow us to see in color with sharp detail. Three different pigments in cones are responsible for color vision. The difference in the opsin portion of each pigment accounts for the ability to detect different colors.
13.5 Ears (p. 277)
	1.	Ears are responsible for hearing and equilibrium, and employ special mechanoreceptors, called hair cells.
	2.	How the Ear Appears (p. 277; Figs. 13.13, 13.14; Table 13.3)
		a.	The outer ear consists of the pinna and the auditory canal. The auditory canal contains hairs and modified sweat glands that secrete earwax.
		b.	The middle ear starts at the tympanic membrane (eardrum) attached to the auditory ossicles (malleus, incus, and stapes). The stapes leads to the oval window of the inner ear. An auditory tube leading to the nasopharynx equalizes air pressure.
 		c.	The inner ear contains the semicircular canals and vestibule for the sense of equilibrium, and the cochlea that houses hearing receptors.
			i.	The semicircular canals have expanded portions, called ampullae, in which hair cells with stereocilia are embedded within a gelatinous material called a cupula.
			ii.	The vestibule houses the utricle and saccule, whose sacs contain hair cells in a gelatinous matrix, over which lie otoliths made of calcium carbonate.
			iii.	The cochlea contains three canals (vestibular, cochlear, and tympanic) and a basilar membrane (part of the cochlear canal) upon which sit hair cells embedded in a tectorial membrane. The organ of Corti is made up of these hair cells and cochlear membrane, and it synapses with the cochlear nerve leading to the brain.
				HEALTH FOCUS: Protecting Vision and Hearing (p. 278, Table 13A, Fig. 13A)
				i.	Vision loss can be prevented if the eyes are protected from flying objects, UV radiation, and disease or the effects of systemic diseases.
				ii.	Hearing loss can be prevented by protecting the ears from excessive and repetitive noise and from ototoxic medications and disease.
	3.	Hair Cells Keep Us Balanced (p. 281, Fig. 13.15)
		a.	Equilibrium is two senses: dynamic equilibrium, which involves rotational movement of the head, and static equilibrium, which involves movement of the head in one plane.
		b.	Dynamic equilibrium is possible because of the arrangement of the three semicircular canals at slightly different angles. When a cupula shifts, hair cells generate impulses to the vestibular nerve.
		c.	Static equilibrium is possible because as the otoliths shift position, hair cells in the saccule respond to vertical motion and those in the utricle respond to horizontal changes.
	4.	Hair Cells Let Us Hear (p. 282, Fig. 13.16)
		a.	Sound waves travel in the auditory canal and vibrate the tympanic membrane, which, in turn, vibrates the auditory ossicles. They cause pressure changes in the fluid of the cochlea as the stapes strikes the oval window. As the fluid in the inner ear vibrates, the tectorial membrane shears across the hair cells.
		b.	As pitch varies, so does the region of the basilar membrane that vibrates.
		c.	Greater volume causes greater shifting of fluids inside the cochlea.