The auditory and samatosensory systems Flashcards
in what range can human’s perceive sound?
30- 20,000 Hertz
Amplitude (loudness)
is determined by the degree to which air molecules are pushed together and pulled apart; more vigorous vibrations of an object cause larger amplitude sound waves, which in turn leads to more intense sounds
Frequency (pitch)
pitch is determined by the frequency of the sound waves produced by a vibrating object; the more sound waves per second the higher pitched the sound
Complexity (timbre)
timbre (sound quality) is determined by the complexity of the sound waves; the more little peaks and troughs in the waveform the more complex the sound. A completely smooth sinusoidal waveform is a pure tone
Outer ear
consist of the outer fleshy pinna, the auditory canal and the tympanic membrane (ear drum). The tympanic membrane vibrates with the soundwaves that enter the auditory canal, and this signal is transmitted on to the middle ear
Middle ear
consists of 3 tiny bones called the ossicles. The malleus (hammer) is connected to the tympanic membrane. It transmits vibrations via the incus (anvil) to the stapes (stirrup), which is connected to a structure called the cochlea
Inner ear (cochlea)
The cochlea contains the receptors for analysing sound. the cochlea is a bony structure, but it has two small membranes that form windows on its fluid filled interior
oval window
the stapes is connected to the oval window. Soundwaves that cause the stapes to move in and out move the fluid over the receptors in the cochlea
round window
allows the fluid to move within the cochlea
Basilar membrane
a sheet of tissue that contains the auditory receptors. The basilar membrane sits in the middle of the cochlea, and runs all the way from its base to its apex
Organ of corti
composed of the basilar membrane as its base, receptors in the middle called hair cells, and a rigid shelf over the top called the tectorial membrane
Hair cells and stereocilia
on top of the hair cells are tiny filaments called stereocilia. bending of the stereocilia of hair cells is what produces receptor potentials that convert sound into neural signals
Auditory nerve
the axons of thousands of spiral ganglion cells. The axons of auditory nerve neurons form synapses with neurons in the medulla
95% of all axons of the auditory nerve form synapses with the inner hair cells, and just 5% do so with outer hair cells. therefore it is the inner hair cells that are crucial for hearing. It is believed that outer hair cells modulate the effects of sound waves on the inner hair cells
place coding of frequency (basilar membrane)
sounds of different frequencies cause different regions of the basilar membrane to flex back and forth. Higher frequencies produce greater displacements as the basal end and lower frequencies produce more displacement at its apex
Binaural processing
The signals from the auditory nerve of each ear are transmitted to both cerebral hemispheres. Binaural processing is essential for localising sounds in space