Biology Mammalians hearing organ is within the ear – The inner ear also contain organs of equilibrium A lateral line system and inner ear detect pressure waves in most fishes and aquatic amphibians Many invertebrates have gravity sensors and are sound-sensitive Ultrasound
Ear Special sensory organ Mechanoreceptors – Pressure from sound waves are detected by hairs inside the inner ear
Outer Ear Ear canal – Collects sound waves and channels them to tympanic membrane – Pressure variations in the sound waves exert forces on the eardrum and cause it to vibrate
Middle ear Contains three bones (smallest bones in your body) – These bones transmit force exerted on the eardrum to the inner ear through oval window – Three small bones: Malleus, incus, stapes Uses lever system with mechanical advantage of 2 – Force delivered to oval window is multiplied by 2 The area of the oval window is 1/20 of the size as tympanic membrane – The pressure created in the fluid-filled inner ear is about 20 times more Overall amplification is(initial pressure*2*20) 40 times the initial pressure is transmitted – Enables our ear to detect very low intensity sound
Inner ear - hearing The inner ear consists of a labyrinth of channels housed within the temporal bone. – The cochlea is the part of the inner ear concerned with hearing. Structurally it consists of the upper vestibular canal and the lower tympanic canal, which are separated by the cochlear duct. The vestibular and tympanic canals are filled with perilymph.
From inner ear structure to a sensory impulse: follow the vibrations. – The round window functions to dissipate the vibrations. Vibrations in the cochlear fluid basilar membrane vibrates hair cells brush against the tectorial membrane generation of an action potential in a sensory neuron.
A lateral line system and inner ear detect pressure waves in most fishes and aquatic amphibians Most fish and amphibians have a lateral line system along both sides of their body. – Contains mechanoreceptors that function similarly to mammalian inner ear. – Provides a fish with information concerning its movement through water or the direction and velocity of water flowing over its body. Fig. 49.20
Statocysts are mechanoreceptors that function in an invertebrates sense of equilibrium. – Statocysts function is similar to that of the mammalian utricle and saccule. Many invertebrates have gravity sensors and are sound-sensitive Fig. 49.21
Sound sensitivity in insects depends on body hairs that vibrate in response to sound waves. – Different hairs respond to different frequencies. Many insects have a tympanic membrane stretched over a hollow chamber. Fig. 49.22
Sound perception Awareness of sound Remarkable sensitivity and range – Frequency between 20 -20,000 Hz Pitch – perception of frequency easily detect difference between 1000 and 1003 Hz Loudness is the perception of intensity – Ear does not respond linearly to intensity – Ear is more sensitive (2000 – 5000 Hz) at certain frequencies than others – Very large intensities are needed to hear near the extremities – The threshold of normal hearing is often defined as 0 dB at 1000Hz
Units Sound intensity is defined as the sound power per unit area. The basic units are watts/m 2 or watts/cm 2 Decibels measure the ratio of a given intensity I to the threshold of hearing intensity, so that this threshold takes the value 0 decibels (0 dB). – sound level Frequency: 20 Hz - 20,000 Hz(corresponds with pitch) Intensity: 10 -12 - 10 watts/m 2 Sound level: (0 to 130 decibels)
Ultrasound The term "ultrasonic" applied to sound refers to anything above the frequencies of audible sound, and nominally includes anything over 20,000 Hz. Sounds in the range 20-100kHz are commonly used for communication and navigation by bats, dolphins, and some other species. Much higher frequencies, in the range 1-20 MHz, are used for medical ultrasound. – echo time and the Doppler shift of the reflected sounds to measure the distance to internal organs and structures and the speed of movement of those structures. – Intensity is kept low 1-10 W/m 2 – for ultrasound 1000 W/m 2 to destroy cancerous tissue
Bats Bats use ultrasound for navigation. Their ability to catch flying insects while flying full speed in pitch darkness is astounding. Their sophisticated echolocation permits them to distinguish between a moth (supper) and a falling leaf. http://www.npr.org/templates/story/story.ph p?storyId=106733884
Infrasound A number of animals produce and use sounds in the infrasonic range. The rumbling vocalizations of elephants were measured to have frequencies as low as 14 Hz which were detectable at a range of 10 km. – Observations of elephant behavior suggests that they responded to the waves through the ground before they heard them in the air - plausible since the waves would travel faster in the solid material. Whales and rhinos produce some very low frequency sounds. The flightless cassowary birds of Papua New Guinea and Australia emit low frequency calls around 23 Hz.
Whales Individual pods of whales have their own distinctive dialect of calls, similar to songbirds. Some such calls are known to be stable over a period of 10 years. Humpback whales produce a variety of moans, snores, and groans that are repeated to form what we might call songs. The frequency of these songs range from about 40 Hz to 5 kHz. Whales are also known to produce some very intense low frequency sounds which they may use to stun or disorient small fish for prey.