Download Chapter 16 - Las Positas College

Chapter 16
The Special Senses
SUGGESTED LECTURE OUTLINE
I. The Chemical Senses: Taste and Smell (pp. 480–483, Figs. 16.1–16.3, Fig. 13.11b, Fig. 21.18, Table
16.1)
A. The receptors for taste (gustation) and smell (olfaction) are classified as chemoreceptors. (p. 480)
B. Anatomically, taste receptors are located in taste buds in the mouth, pharynx, and on the epiglottis; most taste
buds are on the tongue and occur in fungiform and circumvallate papillae. (pp. 480–481, Fig. 16.1)
C. The four basic sensations of taste are sweet, sour, salty, and bitter; a fifth distinctive taste, umami, is also
recognized. (p. 481)
D. The gustatory pathway from taste buds to the brain stem and cerebral cortex is served by cranial nerves VII, IX,
and X. (p. 481, Fig. 16.2)
E. The receptors for smell (olfaction) lie in the olfactory epithelium in the roof of the nasal cavity; smells are
analyzed in the olfactory cortex and limbic system; olfactory nerves and tracts serve the sense of smell. (pp.
481–483, Figs. 16.3 and 13.11b)
F. Disorders of smell are more common than disorders of taste; examples are anosmia and uncinate fits. (p. 483)
G. In the embryo, olfactory epithelium is derived from olfactory placodes; taste buds develop from epithelium
lining the embryonic mouth and pharynx. (p. 483, Fig. 21.18)
II. The Eye and Vision (pp. 483–496, Figs. 16.4–16.15)
A. The eyeball is the organ of vision; vision is the dominant sense in humans. (p. 483)
B. The accessory structures of the eye include the eyebrows, eyelids, conjunctiva, lacrimal apparatus, and extrinsic
eye muscles. (pp. 483–486, Figs. 16.4–16.6)
C. The anatomical features of the eyeball are the following: the fibrous tunic, the vascular tunic, the sensory tunic
(retina), internal chambers and fluids, and the lens. (pp. 486–492, Figs. 16.7–16.12)
1. Special features of the retina are photoreceptors, regional specializations of the retina, and the blood supply
to the retina.
D. As an optical device, light enters the eye and then the cornea and the lens bend it; light is then focused on the
retina. (pp. 492–493, Fig. 16.13)
E. Visual information processing begins in the retina and travels to the brain for complex processing; the visual
pathway to the cerebral cortex is the main visual pathway and is supported by cranial nerve II and optic tracts;
additional pathways go to the midbrain. (pp. 493–496, Fig. 16.14)
F. Examples of disorders of the eye and vision are types of blindness due to retinal damage and corneal damage.
(p. 496)
G. The eyes develop from outpocketings of the embryologic brain. (p. 496, Fig. 16.15)
III. The Ear: Hearing and Equilibrium. (pp. 496–506, Figs. 16.16–16.23, Table 16.1)
A. The outer (external) ear consists of the auricle and the external auditory meatus; the tympanic membrane is the
boundary between the outer ear and the middle ear. (pp. 496–497, Fig. 16.16)
B. The middle ear (tympanic cavity) is an air-filled space housed in the temporal bone; it contains three tiny ear
ossicles and an opening into the pharyngotympanic tube. (pp. 498–500, Figs. 16.16–16.18)
C. The inner (internal) ear consists of two main divisions: the bony labyrinth and the membranous labyrinth;
identify specific anatomical structures and their functions of the inner ear. (pp. 500–505, Figs. 16.16, 16.18–
16.22, Table 16.1)
D. Information on equilibrium and hearing travels to the brain for processing and integration; impulses generated
by the equilibrium receptors travel along the vestibular nerve; impulses generated by the hearing receptors
travel along the cochlear nerve. (p. 505, Fig. 16.23)
E. Disorders of equilibrium and hearing include motion sickness, Ménière’s syndrome, and deafness. (p. 506)
F. Embryonic development of the ear begins in the fourth week. (p. 506, Fig. 16.24)
IV. Special Senses Throughout Life (pp. 506–507)
A. The senses of taste and smell are sharpest at birth; vision develops during early childhood; hearing is reflexive
in infants, and critical hearing develops in toddlers. (pp. 506–507)
B. By age 60, obvious age-related loss of hearing and vision deterioration occur in most people. (p. 507)
Chapter 16: The Special Senses
To the Student
The special senses explored in this chapter are the chemical senses of taste and smell, vision in the eye, and hearing and
equilibrium in the ear. These senses have specific receptor cells that differ from the receptors of the general senses and
are not like the dendritic endings of sensory neurons. The receptors for taste, smell, hearing, and equilibrium are
specialized sensory epithelium that interfaces with the nervous system and the environment. Photoreceptors in the eye
are considered neurons, but they also closely resemble epithelial cells.
This chapter summarizes basic functional anatomy of the special senses and explains the basic concepts of sensory
processing for taste, smell, vision, hearing, and equilibrium.
Step 1: Understand the chemical senses: taste and smell.
- Describe the receptors for taste and outline the gustatory pathway.
- Distinguish between sensation and perception.
- Identify the taste sensations.
- Describe the receptors for smell and outline the pathway that the smell sensory information travels to the brain.
- Distinguish between olfactory tract and olfactory nerve.
Step 2: Understand the eye and vision.
- Describe the structure and function of the accessory structures of the eye: eyebrows, eyelids, conjunctiva, lacrimal
apparatus, and extrinsic eye muscles.
- List the three tunics of the eyeball, describing the parts and functions of each.
- Describe the structure and function of the lens.
- Describe the structure and function of the internal chambers and fluids (humors) of the eyeball.
- Explain the structure of the retina and the photoreceptors.
- Distinguish between the rod cells and the cone cells.
- Explain how light is focused for close vision.
- Trace the pathway of visual information from the retina to the cerebral cortex.
- Label a card with each of the structures in the visual pathway and practice placing the cards in the correct
sequence.
- Define decussation.
- Distinguish between optic nerve, optic tract, and optic chiasma.
- Describe stereoscopic vision.
- Explain the visual fields of the eyes.
Step 3: Understand the ear: hearing and equilibrium.
- List the basic structures of the outer ear, middle ear, and inner ear, and their corresponding functions.
- Name the parts of the bony labyrinth in the inner ear.
- Name the parts of the membranous labyrinth and corresponding functions in the inner ear.
- Describe the receptors for hearing.
- Describe the receptors for equilibrium.
- Describe how the equilibrium pathway transmits information on the position and movements of the head.
- Discuss how the auditory pathway transmits auditory information from the cochlear receptors to the cerebral
cortex.