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f00u2le2 - ACOUSTICAL OCEANOGRAPHY Unit 2 Lesson 2 Sound...

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©P ROJECT O CEANOGRPAHY S PRING 2000 66 A COUSTICAL O CEANOGRAPHY Unit 2. Lesson 2. Sound Production and Reception Lesson Objectives: After completing this lesson and the activities, students will be able to grasp the basic ideas of how sound is generated and how it is interpreted in the human and marine mammal ear. Vocabulary Words: vocal cords, phonating, rostrum, pharynx, and nasal system Note: Remember the words cetaceans, sirenians, dolphins, whales and manatees will be used continuously through the unit, referring to marine mammals Sound Production Before beginning the study of how a marine mammal makes sound, let’s briefly discuss how humans talk. Humans have elastic ligaments called vocal cords attached to the bones in the throat. When air is passed over these cords, they vibrate and make sound. The sound can be modified in intensity, and by using the tongue, teeth and lips in vocalization . Marine mammals also make many sounds by vibrating elastic ligaments (vocal cords) in the larynx . Passing air across these ligaments makes vibrations (much like in the human body). Actions of the tongue, teeth and mouth shape can alter the sound produced. The nasal system , the sinuses, and air sacs found in the pharynx (pharyngeal air sacs) also have an effect on the sound produced. These structures are set up to provide a marine mammal with optimum ability to communicate. Seals, sea otters, and polar bears create sounds like barking, crying, growling and roaring. Manatees make squeaky and ragged sounds using vocal cords. Phonating (of, or pertaining to making sound) dolphins do not move the larynx during high frequency vocalization. They actually use a combination of structures in the nasal system. These structures include the nasal plug and the elaborate nasal air sac system. The processes marine mammals use to make and
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©P ROJECT O CEANOGRAPHY S PRING 2000 67 A COUSTICAL O CEANOGRAPHY Cranium Maxillary bone an air sac receive sound signals is complex. Cetaceans in particular have a very complicated system of sound production and propagation. After the sound is generated, it must be sent through the environment, so that other animals can receive it or so it can return to the dolphin or whale to collect information. Nasal air sacs, sloping maxillary bones , and the cranium (it is cup-shaped and acts like a satellite receiver) reflect sound within the animal’s head, and help focus the sound beam forward through a structure call the melon. (Humans do not have this special structure.) The melon is composed of fat, and transmits sounds produced in the head to the environment. Sounds pass easily from animal to head because the densities in the melon and saltwater are about equal. Sound Reception Many marine mammals rely on the reception of sound to communicate, navigate, and explore their environment for things like food and predators.
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