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McKinley/O’Loughlin
Human Anatomy, 2nd Edition
CHAPTER 19
Answers to “What Did You Learn?”
1.
A sensation is our conscious awareness of incoming sensory information. A stimulus
is a change in the environment that is detected by a receptor. Only a stimulus leading
to an impulse that reaches the cerebral cortex results in a sensation.
2.
The three groups of receptors classified by stimulus origin are exteroceptors,
which detect stimuli from the external environment; interoceptors, which detect
stimuli in internal organs; and proprioceptors, which detect body and limb
movements.
3.
Mechanoreceptors respond to touch, pressure, vibration, and stretch.
Thermoreceptors respond to increases or decreases in temperature.
4.
Unencapsulated receptors have no connective tissue wrapping around them and
are relatively simple in structure. Encapsulated receptors are covered either by
connective tissue or glial cells.
5.
Ruffini corpuscles are encapsulated receptors that detect both continuous deep
pressure and distortion in the skin. They are tonic receptors that do not exhibit
adaptation; they are housed within the dermis and subcutaneous tissue. Ruffini
corpuscles are the least lamellated of the encapsulated receptors. Some are
located within joint capsules, where they detect the position and movement of the
joint.
6.
Cranial nerves VII and IX receive taste sensations from the tongue. Cranial
nerves V and X receive general sensory information from the tongue.
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7.
Human Anatomy, 2nd Edition
Within the nasal cavity, paired olfactory organs provide the sense of smell. The
lining of their olfactory epithelium is composed of three distinct cell types:
olfactory nerves (also called olfactory receptor cells) to detect odors; supporting
cells that sandwich the olfactory nerves and sustain and maintain the receptors;
and basal cells that function as stem cells to replace olfactory epithelium
components.
8.
Olfactory hairs are cilia that project into the mucus that covers the olfactory
epithelium and house receptors for inhaled airborne molecules.
9.
A lacrimal gland continuously produces lacrimal fluid (tears). Excretory ducts
conduct the tears into the conjunctival sac of the superior eyelid. There, the
blinking motion of the eyelids "washes" the tears over the eyes. The tears drain
through the lacrimal puncta into the lacrimal canaliculi. A lacrimal sac
temporarily stores the tears. The nasolacrimal duct receives the tears and delivers
it into the nasal cavity.
10.
The fibrous tunic, the external layer of the eye wall, is composed of the anterior
cornea and the posterior sclera. The cornea refracts incoming light rays into the
interior of the eye, while the tough, white sclera provides for eye shape and
protects its delicate internal components. The vascular tunic, the middle layer of
the eye wall is composed of three distinct regions: the choroid, the ciliary body,
and the iris (from posterior to the anterior). The choroid houses a vast network of
capillaries that supply both nutrients and oxygen to the retina. Cells of the
choroid are filled with pigment from the numerous melanocytes in this region.
The ciliary body is composed of four bands of smooth muscle organized into a
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Human Anatomy, 2nd Edition
ring and collectively called the ciliary muscle, which functions in lens shape
change for near and far vision. The most anterior region of the middle layer of
the eye is the iris. It is readily visible anteriorly as the colored diaphragm with a
central black hole, called the pupil. The iris is composed of two layers of
pigment-forming cells (anterior and posterior layers), and two groups of smooth
muscle fibers, whose contractions adjust the diameter of the pupil to regulate light
entry. The internal tunic is called the retina. It is composed an outer pigmented
layer and an inner neural layer. The outer pigmented layer absorbs light rays that
pass through the inner layer. The inner neural layer houses all of the
photoreceptors and their associated neurons. This inner layer of the neural layer
is responsible for receiving light rays and converting them into nerve impulses
that are transmitted to the brain.
11.
The three cell layers in the neural layer of the retina are the photoreceptors,
bipolar cells, and ganglionic cells. Photoreceptors include the visual receptor
cells called rods and cones, which detect incoming light. The rods and cones
converge to synapse on the bipolar cells. Neuronal convergence continues as
bipolar neurons transmit information about stimulated rods and cones to
ganglionic neurons. The axons of the ganglionic neurons form the optic nerve,
which conducts visual information to the brain.
12.
The hyaloid canal is a remnant of the embryonic hyaloid vessel that once supplied
the retina and lens. As the eye develops, the distal parts of the hyaloids vessels
regressed, leaving the proximal parts of the vessels to become the retinal vessels.
The path left by the distal part of the hyaloids vessels became this hyaloids canal.
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13.
Human Anatomy, 2nd Edition
The auditory ossicles conduct the energy of sound waves striking the tympanic
membrane to the inner ear, causing the footplate of the stapes to move in and out
of the oval window. The movement of the stapes initiates pressure waves in the
fluid within the closed compartment of the inner ear.
14.
Membranous labyrinths are membrane-lined, fluid-filled tubes and spaces within
bone. The membranous labyrinth is housed within a cavernous space in dense
bone, called the bony labyrinth, which is located within the petrous part of the
temporal bone.
15.
The macula is a small, raised oval area in the saccule and utricle along the internal
wall of both sacs. Its function is to report on changes in the position of the head.
16.
Vibration of the tympanic membrane causes movement by the auditory ossicles in
the middle ear. This movement results in the generation of pressure waves within
the inner ear that travel through the perilymph in the scala vestibule. Pressure
waves in the scala vestibule cause the vestibular membrane to vibrate, ultimately
resulting in pressure wave formation in the endolymph of the cochlear duct. A
region of the basilar membrane is displaced resulting in the distortion of spiral
organ hair cells against the tectorial membrane.
Answers to “Content Review”
1.
Chemoreceptors detect specific molecules in our environment (taste buds on the
tongue detect specific molecules in our food and drink. Thermoreceptors respond to
changes in temperature (in our skin free nerve endings alert us as we touch things that
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Human Anatomy, 2nd Edition
are hot). Mechanoreceptors respond to touch, pressure, vibration and stretch (hair
cells in the ear detect changes in our equilibrium). Baroreceptors detect changes in
pressure within body structures (these receptors alert us to an expanding bladder
and the need to evacuate it). Nociceptors are receptors that respond to pain as a
result of tissue damage (in the skin they report that damage has occurred).
2.
There are differences between nociceptors associated with the body periphery and
external environment Somatic nociceptors detect molecules in our external
environment, whereas visceral nociceptors detect molecules in our internal
environment. Referred pain occurs when impulses from some viscera are not
perceived as originating with the organ, but instead, the sensations are mistaken as
originating in dermatome(s) of the skin. This misinterpretation of the pain source
is related to both the site of visceral pain origin and the superficial area to which
the pain is referred. Often these sensations occur because neurons from the same
spinal segment innervate both the visceral region where the damage occurs and
the superficial region to which the pain is referred.
3.
Sensory stimuli detected by gustatory cells within taste buds results in nerve
impulses conducting this information through CN VII (facial) from the
anterior two-thirds of the tongue and CN IX (glossopharyngeal) from the
posterior one-third of the tongue. All gustatory information projects first to
the nucleus solitarius in the medulla oblongata then to the thalamus for
processing. From the thalamus, axons of thalamic neurons project gustatory
information to the primary gustatory cortex in the insula for analysis of taste
sensations.
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4.
Human Anatomy, 2nd Edition
Receptor molecules in olfactory hairs bind to odor molecules dissolved in the
mucus line the olfactory epithelium. The olfactory neurons (receptor cells)
project axons through the cribriform plate into the paired olfactory bulbs lying
inferior to the frontal lobes of the brain. They synapse on neurons in the olfactory
bulbs, which then project axons bundles through the olfactory tracts directly to the
primary olfactory cortex in the temporal lobe.
5.
Pupil size or diameter is controlled by the two smooth muscle layers in the iris.
One group of smooth muscle fibers [the sphincter pupillae muscle, or pupillary
constrictors] is arranged in a pattern that resembles concentric circles around the
pupil. This smooth muscle layer is controlled by the parasympathetic division of
the ANS. When these muscle fibers contract, they constrict the pupil. The other
group of muscle fibers [the dilator pupillae muscle, or pupillary dilators] is
organized in a radial pattern extending peripherally through the iris from the outer
edge of the pupil. This smooth muscle layer is controlled by the sympathetic
division of the ANS. When these muscle fibers contract, they dilate the pupil.
Only one set of these smooth muscle can contract at any one time.
6.
The ciliary muscles in the ciliary body contract to produce the tension in the
suspensory ligaments. When the ciliary muscles relax, the ciliary body moves
posteriorly, away from the lens, and so the tension on the suspensory ligaments
increases. Constant tension applied to the suspensory ligaments causes the lens to
flatten so that distant objects may be observed. The process of making the lens
more spherical in order to view close-up objects is called accommodation. It is
controlled by the parasympathetic division of the ANS. Stimulation of the ciliary
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Human Anatomy, 2nd Edition
muscle by parasympathetic axons causes the muscle to contract. When the ciliary
muscle contracts, the entire ciliary body moves anteriorly and thus moves closer
to the lens itself. This process allows for a reduction in the suspensory ligaments
tension and a release in some of their "pull" on the lens, so the lens can become
more spherical.
7.
The anterior cavity contains a fluid called aqueous humor, which is a filtrate of
plasma that resembles CSF and is produced by the epithelium covering the ciliary
body. The aqueous humor is secreted into the posterior chamber, an open area
between the lens and the iris. From the posterior chamber, it flows through the
pupil into the anterior chamber, which is the space between the iris and the
internal surface of the cornea. The aqueous humor is continually reabsorbed
across the covering epithelium into a vascular space, called the scleral venous
sinus [previously called the canal of Schlemm] that is located in the limbus
between the cornea and sclera. The scleral venous sinus conducts the reabsorbed
aqueous humor to the veins that drain the eye.
8.
They are two tiny skeletal muscles located within the middle ear. These muscles
function to restrict ossicle movement if exposure to loud noises occurs, thus
protecting sensitive receptors in the inner ear.
9.
The inner ear is located within the petrous portion of the temporal bone. Here,
there are spaces or cavities called the bony labyrinth. Within the bony labyrinth
are membrane-lined, fluid-filled tubes and spaces, called the membranous
labyrinth. Receptors for equilibrium and hearing are housed along with
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Human Anatomy, 2nd Edition
supporting cells within a sensory epithelium lining part of the membranous
labyrinth.
10.
1. Sound waves are collected by the auricle and funneled through the external
auditory canal to make the tympanic membrane vibrate. 2. The vibration of the
tympanic membrane causes movement in the auditory ossicles. 3. The foot of the
stapes vibrates moves like a piston in the oval window, causing pressure waves in
the perilymph fluid of the inner ear. 4. Pressure waves travel through the
perilymph in the scala vestibuli. 5. Pressure waves cause the vestibular
membrane to vibrate, resulting in pressure wave formation in the endolymph of
the cochlear duct. 6. Pressure waves in the cochlear duct displace a specific
region of the basilar membrane causing distortion of stereocilia on hair cells of
the spiral organ. This distortion causes a stimulus in the cochlear nerve.
Remaining pressure waves are transferred to the perilymph of the scala tympani.
7. Excess pressure waves leave the inner ear through the round window.