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Chapter 9 Study Guide
The Special Senses
9-1: Sensory receptors connect our internal and external environments with
the nervous system.
a) The general senses are temperature, pain, touch, pressure, vibration, and
proprioception; receptors for these sensations are distributed throughout the body.
Receptors for the special senses (smell, taste, vision, balance, and hearing) are located
in specialized areas or in sense organs.
b) A sensory receptor is a specialized cell that, when stimulated, sends a sensation to the
CNS. The simplest receptors are free nerve endings; the most complex have
specialized accessory structures that isolate the receptors from all but a specific type
of stimulus.
c) Each receptor cell monitors a specific receptive field.
d) Sensory information is relayed in the form of action potentials in a sensory (afferent)
fiber. In general, the larger the stimulus, the greater is the frequency of action
potentials. The CNS interprets the nature of the arriving sensory information on the
basis of the area of the brain stimulated.
e) Adaptation – a reduction in sensitivity in the presence of a constant stimulus – involves
changes in receptor sensitivity or inhibition along sensory pathways.
9-2: General sensory receptors can be classified by the type of stimulus that
excites them
a) Nociceptors respond to a variety of stimuli usually associated with tissue damage. The
two types of these painful sensations are fast pain, or prickling pain, and slow pain, or
burning and aching pain.
b) The perception of pain in parts of the body that are not actually stimulated is called
referred pain.
c) Thermoreceptors respond to changes in temperature.
d) Mechanoreceptors respond to physical distortion of, contact with, or pressure on their
cell membranes; tactile receptors respond to touch, and vibration; baroreceptors
respond to pressure changes in the walls of blood vessels, and digestive and urinary
tracts, and the, lungs; and proprioceptors respond to positions of joints and muscles.
e) Fine touch and pressure receptors provide detailed information about a source of
stimulation; crude touch and pressure receptors are poorly localized.
f) Baroreceptors in the walls of major arteries and veins respond to changes in blood
pressure, and those along the digestive tract help coordinate reflex activities of
digestion.
g) Proprioceptors monitor the position of joints, tension in tendons and ligaments, and the
state of muscular contraction.
Anatomy and Physiology
Chapter 8 Study Guide 2012-13.docx
h) In general, chemoreceptors respond to water-soluble and lipid soluble substances
dissolved in the surrounding fluid. They monitor the chemical composition of body
fluids.
9-5: Internal eye structures contribute to vision, while accessory eye
structures provide protection
a) The accessory structures of the eye include the eyelids and associated exocrine glands,
the superficial epithelium of the eye, structures associated with the production and
removal of tears, and the extrinsic eye muscles.
b) An epithelium called the conjunctiva covers most of the exposed surface of the eye
except the transparent cornea.
c) The secretions of the lacrimal gland bathe the conjunctiva; these secretions contain
lysozyme (an enzyme that attacks bacteria). Tears reach the nasal cavity after passing
through the lacrimal canal, the lacrimal sac, and the nasolacrimal duct.
d) Six extrinsic eye muscles control external eye movements: The inferior and superior
rectus, the lateral and medial rectus, and the superior and inferior obliques
e) The eye has three layers: an outer fibrous tunic, a vascular tunic, and an inner neural
tunic. Most of the ocular surface is covered by the sclera (a dense fibrous connective
tissue), which is continuous with the cornea, both of which are part of the fibrous tunic.
f) The vascular tunic includes the iris, the ciliary body, and the choroid. The iris forms
the boundary between the eye’s anterior and posterior chambers. The iris regulates the
amount of light entering the eye. The ciliary body contains the ciliary muscle and the
ciliary processes, which attach to the suspensory ligaments of the lens.
g) The neural tunic consists of an outer pigmented part and an inner neural part; the latter
contains visual receptors and associated neurons.
h) From the photoreceptors, information is relayed to bipolar cells, then to ganglion cells,
and to the brain by the optic nerve. Horizontal cells and amacrine cells modify the
signals passed between other retinal components.
i)
The ciliary body and lens divide the interior of the eye into large posterior cavity and a
smaller anterior cavity. The anterior cavity is subdivided into the anterior chamber,
which extends from the cornea to the iris, and a posterior chamber between the iris
and the ciliary body and lens. The posterior cavity contains the vitreous body, a
gelatinous mass that helps stabilize the shape of the eye and supports the retina.
j)
Aqueous humor circulates within the eye and reenters the circulation after diffusing
through the walls of the anterior chamber and into veins of the sclera through the canal
of Schlemm.
k) The lens, held in place by the suspensory ligaments, focuses a visual image on the retinal
receptors. Light is refracted (bent) when it passes through the cornea and lens. During
accommodation, the shape of the lens changes to focus an image on the retina.
9-6: Photoreceptors respond to light and change it into electrical signals
essential to visual physiology.
a) Light is radiated in waves with a characteristic wavelength. A photon is a single energy
packet of visible light. The two types of photoreceptors (visual receptors of the retina)
are rods and cones. Rods respond to almost any photon, regardless of its energy
content; cones have characteristic ranges of sensitivity. Many cones are densely packed
within the fovea (the central portion of the macula lutea), the site of sharpest vision.
b) Each photoreceptor contains an outer segment with membranous discs containing visual
pigments. Light absorption occurs in the visual pigments, which are derivatives of
rhodopsin (opsin plus the pigment retinal, which is synthesized from vitamin A). A
photoreceptor responds to light by changing its rate of neurotransmitter release and
thereby altering the activity of a bipolar cell.
c) The message is relayed from photoreceptors to bipolar cells to ganglion cells within the
retina. The axons of ganglion cells converge at the optic discs and leave the eye as the
optic nerve. A partial crossover occurs at the optic chiasm before the information
reaches a nucleus in the thalamus on each side of the brain. From these nuclei, visual
information is relayed to the visual cortex of the occipital lobe, which contains a
sensory map of the field of vision.
9-3: Olfaction, the sense of smell, involves olfactory receptors responding to
chemical stimuli
a) The olfactory organs consist of an olfactory epithelium containing olfactory receptor
cells (neurons sensitive to chemicals dissolved in the overlying mucus), supporting cells,
and basal cells (stem cells). Their surfaces are coated with the secretions of the
olfactory glands.
b) The olfactory receptors are modified neurons.
c) The olfactory system has extensive limbic and hypothalamic connections.
9-4: Gustation, the sense of taste, involves taste receptors responding to
chemical stimuli
a) Taste (gustatory) receptors are clustered in taste buds; each taste bud contains
gustatory cells, which extend taste hairs through a narrow taste pore.
b) Taste buds are associated with papillae, epithelial projections on the superior surface
of the tongue.
c) The primary taste sensations are sweet, salty, sour, and bitter; umami and water
receptors are also present.
d) The taste buds are monitored by cranial nerves that synapse within a nucleus of the
medulla oblongata.