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Sound. Why sound is a useful and versatile form of communication. Sound is a form of energy that travels in waves. Sound waves can be compared by determining their frequency. Sound requires a medium such as solid, liquid or gas through which to travel. It cannot travel through a vacuum.
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Why sound is a useful and versatile form of communication • Sound is a form of energy that travels in waves. Sound waves can be compared by determining their frequency. Sound requires a medium such as solid, liquid or gas through which to travel. It cannot travel through a vacuum. • Sound is a useful for communication to many because of the enormous variety of sounds that can be produced. Sound is useful both day and night. It travels over long distances and can go around corners. Sound is also versatile because variation can occur in the actual sound or the loudness of the sound, and the pitch and duration of a message can be readily changed • Advantages of sound communication: • A variety of sounds can be made by an individual • Sound travels well in both air and water • The sender does not have to be visible to the receiver • It is useful at night and in dark environments • Sound can go around objects • It provides directional information • It works over long distances
How is sound produced? • Sound is a form of energy that requires a medium. It cannot travels in a vacuum. It is a longitudinal wave where the particles move backwards and forwards in the direction of the wave. Sound is a form of energy produced by an object that vibrates. • The vibrating object causes nearby air molecules to vibrate back and forth, and these molecules causes other to vibrate at the same frequency. This results in a compression wave, which travels through a medium. The frequency of the vibration of air molecules is the same as the frequency of the vibrating object.
The structure of the human larynx • The larynx or voice box lies directly below the tongue and soft palate. Inside the larynx are the vocal cords, which consist of muscles, which can adjust pitch by altering their position and tension. • Together, the larynx, tongue and hard and soft palate make speech possible. When air passes over the vocal cords in the larynx, they produce sounds that can be altered by the tongue, together with the hard and soft palate, the teeth and the lips
Outline and compare the detection of vibrations by insects, fish and mammals Insects • Insects have hearing organs in many different parts of their bodies. Three main types of sound detection organs in insects are: • Tympanic organs - consists of a membrane stretched across an air sac. In grasshoppers, tympanic organs are located on the legs. When sound waves reach the tympanic organ the membrane vibrates and this stimulates the hair cells and a message is sent via nerve to the brain. • Auditory hairs - Many insects are covered with auditory hairs that are sensitive to sound waves. These hairs have different lengths and stiffness and respond to vibrations at different frequencies. The hairs are particularly abundant on the antennae and legs. • Vibration receptors - Insects that fly at night have adaptations that can detect ultrasonic sound produced by bats. Hawk moths can hear ultrasonic sound through two sets of modified mouthparts.
Fish Fish have several organs to detect sound waves. These include: • Internal ears - Fish have an ear but unlike mammals, there is no external opening or an eardrum. Otoliths and the labyrinth make up the inner ear of fish. The movement of otolith across sensory hair cells is interpreted as sound by fish. • Lateral line organ - visible line along the body of fish. It consists of fluid-filled canals that are collections of sensory hairs called neuromasts. These respond to low frequency sound. The neuromast consists of hair cells that detect vibration in the surrounding water • Swim bladder - primarily responsible for equalizing pressure between the surrounding water and the fish. It acts as an amplifier to any sound, passing the vibrations directly onto the inner ear.
Mammals • Mammals have ears to detect sound. Sound enters the ear, and travels along the auditory canal. • It then causes the tympanic membrane to vibrate at the same frequency as the sound waves. In the middle ear the ossicles transfer and amplify the sound vibrations to the oval window. It then transfers the sound vibrations to the fluid-filled cochlea. • Inside the cochlea is the organ of Corti, which has rows of hair cells that respond to different frequencies, convert vibrations into an electrochemical impulse and transfer the message to brain via the auditory nerve.6
Anatomy and function of the human ear • Pinna • Tympanic membrane • Ear ossicles • Oval window • Round window • Cochlea • Organ of Corti • Auditory nerve
Role of the Eustachian tube • The Eustachian tube connects the middle ear with the back of the throat. It is filled with air and responds to changes in pressure. The role of the Eustachian tubes is to keep the pressure in the middle ear and the throat and therefore the outside atmosphere equal and to drain the middle ear. It also replaces the air in the middle ear after it has been absorbed.
Path of sound wave through the external, middle and inner ear • When sound waves enter the pinna they travel along the auditory canal and cause the tympanic membrane (eardrum) to vibrate. These vibrations are carried and amplified by the ossicles in the middle ear. The ossicles are three tiny bones also known as the malleus (hammer), the incus (the anvil) and the stapes (the stirrup). The ossicles join the inner ear at the oval window. • The cochlea is a snail-shaped, fluid-filled structure in the inner ear. Inside the cochlea is another structure called the organ of Corti. Inside the organ of Corti there are hair cells located on the basilar membrane. These are in contact with the tectorial membrane. When vibrations reach the hair cell the message is converted into an electrochemical response, which travels via the auditory nerve to the brain.
Relationship between the distribution of hair cells in the organ of Corti and the detection of sounds of different frequencies • Frequencies of sounds are detected in the organ of Corti. This has three main components: the basilar membrane, hair cells and the tectorial membrane. • The basilar membrane is composed of transverse fibres of varying lengths. Vibrations received at the oval window are transmitted through the fluids of the cochlea causing the transverse fibres of the membrane to vibrate at certain places according to the frequency.
Relationship between the distribution of hair cells in the organ of Corti and the detection of sounds of different frequencies • High frequency sounds cause the short fibres of the front part of the membrane to vibrate and low frequency sounds stimulate the longer fibres towards the far end. • As the basilar membrane vibrates, the hairs of the hair cells are pushed against the tectorial membrane. This causes the hair cells to send an electrochemical impulse along the auditory nerve to the brain
Role of the sound shadow cast • Humans and other animals use two methods to locate the source of sound: the difference in time between the sound arriving at each ear, and the difference in the intensity of the sound arriving at each ear. These differences occur because the head casts a sound shadow that causes one ear to receive less intense sound than the other. • Humans usually trace the location of a sound by turning their heads until the intensity of the sound is equal in both ears; at this point people should be looking in the direction of the source of the sound. Other animals have more mobile ears, rather than their heads, to pick up a sound
Comparison of frequency range • Humans can hear in the range 20 to 20000 Hz. Younger children can hear frequencies up to 25000 Hz but this ability decreases with age. Human hear best from about 2000-4000 HZ because this is the range in which human speech falls. • Bats produce sound in 2000 to 110000Hz range through their mouths or through elaborate nose organs. The insect-catching bats use echolocation to locate their prey in mid air. To do this they send out high frequency sound (ultrasonic) and then interpret the echo that bounces back. This gives them information on the distance and the direction of movement.
Comparison of frequency range • Dolphins belong to the toothed whales group, which have a very high frequency hearing range between 75 to 150000 Hz. They have specialized inner ears. They have more nerve endings than terrestrial animals. Dolphins have adaptations for very high frequency sound detection such as a thick basilar membrane and bony supports for the cochlea. • Sound becomes important in environments where visual information is limited. It plays an important role in finding mates, prey and avoiding predators. Bats use sound to navigate in dark environments to avoid objects and to locate prey. They use high frequency sound, which is only useful over short distances. Dolphins have high frequency hearing. High frequency sound is used over short distances to locate prey.
