Chapter Seven The Nonvisual Sensory Systems Audition Sound and the Ear Physical and Psychological Dimensions of Sound Amplitude=intensity of wave=loudness frequency=number of waves/second=pitch Figure 7.1 Four sound waves The time between the peaks determines the frequency of the sound, which we experience as pitch. Here the top line represents five sound waves in 0.1 second, or 50 Hz—a very low-frequency sound that we experience as a very low pitch. The other three lines represent 100 Hz. The vertical extent of each line represents its amplitude or intensity, which we experience as loudness. Anatomy of the Ear Structures of the Ear Pinna-cartilage attached to the side of the head Tympanic Membrane-eardrum middle ear bones-hammer/anvil/stirrup oval window-membrane leading to inner ear cochlea-three fluid-filled tunnels scala vestibuli scala media scala tympani basilar membrane-flexible membrane tectorial membrane-rigid membrane hair cells-auditory receptors Figure 7.2 Structures of the ear When sound waves strike the tympanic membrane in (a), they cause it to vibrate three tiny bones—the hammer, anvil, and stirrup—that convert the sound waves into stronger vibrations in the fluid-filled cochlea (b). Those vibrations displace the hair cells along the basilar membrane in the cochlea. (c) A cross section through the cochlea. The array of hair cells in the cochlea is known as the organ of Corti. (d) A closeup of the hair cells. Pitch Perception Theories of Pitch Perception Frequency theory-the basilar membrane vibrates in synchrony with a sound, causing auditory nerve axons to produce action potentials at the same frequency Place theory-the basilar membrane resembles the strings of a piano in that each area along the membrane is tuned to a specific frequency and vibrates whenever that frequency is present Volley principle-the auditory nerve as a whole can have volleys of impulses up to about 5,000 per second, even though no individual axon can approach that frequency by itself Figure 7.4 The basilar membrane of the human cochlea High-frequency sounds produce their maximum displacement near the base. Low-frequency sounds produce their maximum displacement near the apex. Figure 7.5 Traveling waves in the basilar membrane set up by different frequencies of sound Note that the peak displacement is closer to the base of the cochlea for high frequencies and is toward the apex for lower frequencies. In reality the peak of each wave is much narrower than shown here. Pitch Perception in the Cerebral Cortex Primary auditory cortex Each cell responds best to one tone Cells preferring a given tone cluster together Secondary auditory cortex Each cell responds to a complex combination of sounds Figure 7.6 Route of auditory impulses from the receptors in the ear to the auditory cortex The cochlear nucleus receives input from the ipsilateral ear only (the one on the same side of the head). All later stages have input originating from both ears. Hearing Loss Conductive Deafness bones of the middle ear fail caused by tumors, infection, disease usually corrected by surgery or hearing aids Nerve Deafness damage to cochlea, hair cells or auditory nerve usually treated with hearing aids caused by genetics, disease, ototoxic drugs, etc. Localization of Sound Sound Shadow-loudest in nearest ear Time of arrival-arrives at one ear soonest Phase difference-sounds arrive out of phase dependent on frequency Figure 7.10 Phase differences between the ears as a cue for sound localization Note that a low-frequency tone (a) arrives at the ears slightly out of phase. The ear for which the receptors fire first (here the person’s left ear) is interpreted as being closer to the sound. If the difference in phase between the ears is small, then the sound source is close to the center of the body. However, with a high-frequency sound (b) the phase differences become ambiguous. The person cannot tell which sound wave in the left ear corresponds to which sound wave in the right ear. The Mechanical Senses Vestibular Sensation Utricle and saccule Contain calcium carbonate crystals that bend hair cells when the head is moved Semicircular canals oriented in three different planes canals are filled with jellylike substance that moves with movement of the head causing bending of hair cells Figure 7.11 Structures for vestibular sensation (a) Location of the vestibular organs. (b) Structures of the vestibular organs. (c) Cross section through an otolith organ. Calcium carbonate particles, called otoliths, press against different hair cells depending on the direction of tilt and rate of acceleration of the head. The Mechanical Senses Somatosensation-the sensation of the body and its movements Somatosensory Receptors Vary in complexity and stimuli that they respond to Ex: Pacinian Corpuscle-detects sudden displacements or high-frequency vibrations on the skin Mechanical Senses Somatosensation cont’d Input to the Spinal Cord and the Brain Sensory information is brought in via spinal nerves innervating dermatomes specific pathways dedicated to different kinds of information transfer information to the brain Pain Transmission moderate-glutamate intense-glutamate and substance P Gate Theory the spinal cord receives messages from pain and other receptors of the skin and descending pathways of the brain if pathways other than pain are sufficiently active, they close the “gates” for pain messages Modification of pain messages Opiates-decrease substance P activity The Chemical Senses General Issues About Chemical Coding each taste and smell stimulus excites several kinds of receptors the meaning of a particular response depends on the context of responses by other receptors Figure 7.12 Some sensory receptors found in the skin, the human body’s largest organ Different receptor types respond to different stimuli, as described in Table 7.1. Somatosensation Table 7.1 The Chemical Senses Taste Taste Receptors-taste buds located in papillae How Many Kinds of Taste Receptors-at least four Sweet, Salty, Bitter, Sour…Umami? Mechanisms of Taste Receptors Salt-allows sodium ions to pass through membrane Sour-closes potassium channels Sweet, Bitter and Umami-activate metabotropic mechanisms Figure 7.19 The organs of taste The tip, back, and sides of the tongue are covered with taste buds. Taste buds are located in papillae. Chemical Senses The Coding of Taste Information-taste depends on a pattern of responses across fibers Taste Coding in the Brain carried along 7th, 9th, and 10th cranial nerves nerves project to nucleus of the tractus solitarius (medulla) projecting to the pons, the lateral hypothalamus, the amygdala, the ventral-posterior thalamus, and cortex Figure 7.20 Major routes of impulses related to the sense of taste in the human brain The thalamus and cerebral cortex receive impulses from both the left and the right sides of the tongue. Video Olfaction Olfactory Receptors Cilia extend to mucous of the sinus receptors located in cilia transferred to olfactory bulb (coded in terms of what area of the bulb is excited) projects to forebrain and prefrontal cortex Figure 7.21 Olfactory receptors (a) Location of receptors in nasal cavity. (b) Closeup of olfactory cells. The Chemical Senses Vomeronasal Sensation and Pheromones Pheromones are chemicals released by an animal that affect the behavior of other members of the same species Human body secretions have subtle pheromone effects Figure 7.23 The human vomeronasal organ This organ detects certain chemicals, especially those found on the human skin, but produces no conscious experience. Perhaps for that reason, researchers were slow to discover this organ.