Chapter Summary

Internal Affairs (110.0K)

Overview of Sensory Perception

1. Sensory organs are specialized extensions of the nervous system that respond to specific stimuli and conduct nerve impulses.
2. A stimulus to a receptor that conducts an impulse to the brain is necessary for perception.
3. Sensory organs act as energy filters that permit perception of only a narrow range of energy.

Classification of the Senses

1. The senses are classified according to structure or location of the receptors, or on the basis of the stimuli to which the receptors respond.
2. The receptor cells for the general senses are widespread throughout the body and are simple in structure. The receptor cells for the special sensory organs are localized in complex receptor organs and have extensive neural pathways.
3. The somatic senses arise in cutaneous receptors and proprioceptors; visceral senses arise in receptors located within the visceral organs.
4. Phasic receptors respond quickly to a stimulus but then adapt and decrease their firing rate. Tonic receptors produce a constant rate of firing.

Somatic Senses

1. Corpuscles of touch, free nerve endings, and root hair plexuses are tactile receptors, responding to light touch.
2. Lamellated corpuscles are pressure receptors located in the deep dermis or hypodermis. They are also associated with synovial joints.
3. The organs of Ruffini and bulbs of Krause are both mechanoreceptors; they respond to deep and light pressure, respectively.
4. Free nerve endings respond to light touch and are the principal pain receptors. They also serve as thermoreceptors, responding to changes in temperature.
5. Joint kinesthetic receptors, neuromuscular spindles, and neurotendinous receptors are proprioceptors that are sensitive to changes in stretch and tension.

Olfactory Sense

1. Olfactory receptors of the olfactory nerve respond to chemical stimuli and transmit the sensation of olfaction (smell) to the cerebral cortex.
2. Olfaction functions closely with gustation (taste) in that the receptors of both are chemoreceptors, requiring dissolved substances for stimuli.

Gustatory Sense

1. Taste receptors in taste buds are chemoreceptors and transmit the sensation of gustation to the cerebral cortex.
2. Taste buds are found in the vallate and fungiform papillae of the tongue. Filiform papillae are not involved in taste perception; they give the tongue an abrasive feel.
3. The kinds of taste sensation are sweet, salty, sour, and bitter.

Visual Sense

1. Protective structures of the eye include the eyebrow, eyelids, eyelashes, conjunctiva, and lacrimal gland.
2. Six extrinsic ocular muscles control the movement of the eyeball.
3. The eyeball consists of the fibrous tunic, which is divided into the sclera and cornea; the vascular tunic, which consists of the choroid, the ciliary body, and the iris; and the internal tunic, or retina. The retina has an outer pigmented layer and an inner nervous layer. The transparent lens is not part of any tunic.
4. Rod and cone cells, which are the photoreceptors in the nervous layer of the retina, respond to dim and colored light, respectively. Cone cells are concentrated in the fovea centralis, the area of keenest vision.
5. Rod and cone cells contain specific pigments that provide sensitivity to different light rays.
6. The visual process includes the transmission and refraction of light rays, accommodation of the lens, constriction of the pupil, and convergence of the eyes.
1. Refraction is achieved as incoming light rays pass through the cornea, aqueous humor, lens, and vitreous humor.
2. A sharp focus is accomplished as the curvature of the lens is changed by autonomic contraction of smooth muscles within the ciliary body.

7. Neural pathways from the retina to the superior colliculus help to regulate eye and body movements. Most fibers from the retina project to the lateral geniculate body, and from there to the striate cortex.
8. The sensory components of the eye have been formed by 20 weeks; the accessory structures have been formed by 32 weeks.

Senses of Hearing and Balance

1. The outer ear consists of the auricle and the external acoustic canal.
2. The middle ear (tympanic cavity), bounded by the tympanic membrane and the vestibular and cochlear windows, contains the auditory ossicles (malleus, incus, and stapes) and the auditory muscles (tensor tympani and stapedius).
3. The middle-ear cavity connects to the pharynx through the auditory tube.
4. The inner ear contains the spiral organ for hearing. It also contains the semicircular canals, saccule, and utricle (located in the vestibule) for maintaining balance and equilibrium.
5. The development of the ear begins during the fourth week and is complete by the thirty-second week.