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Chapter 7 The Other Sensory Systems. Audition. Our senses have evolved to allow us to detect and interpret biologically useful information from our environment . However, we do not detect all sensory information in the world. Some sensory information lies beyond our ability to detect it.
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Audition • Our senses have evolved to allow us to detect and interpret biologically useful information from our environment . • However, we do not detect all sensory information in the world. • Some sensory information lies beyond our ability to detect it. • We also tend to focus on information that is important or relevant.
Audition • Audition refers to our sense of hearing. • Audition depends upon our ability to detect sound waves. • Sound waves are periodic compressions of air, water or other media. • Sound waves are “transduced” into action potentials sent to the brain.
Audition • The amplitude refers to the height and subsequent intensity of the sound wave. • Loudness refers to the perception of the sound wave. • Amplitude is one factor. • Frequency refers to the number of compressions per second and is measured in hertz. • Related to the pitch (high to low) of a sound.
Audition • Anatomist distinguish between: • The outer ear • The middle ear • The inner ear
Audition • The outer ear includes the pinna and is responsible for: • Altering the reflection of sound waves into the middle ear from the outer ear. • Helping to locate the source of a sound.
Audition • The middle ear contains the tympanic membrane which vibrates at the same rate when struck by sound waves. • Three tiny bones (malleus, incus, & stapes) transmit information to the oval window or a membrane in the middle ear.
Audition • The inner ear contains a snail shaped structure called the cochlea which contains three fluid-filled tunnels (scala vestibuli, scala media, and the scala tympani). • Hair cells are auditory receptors that excite the cells of the auditory nerve when displaced by vibrations in the fluid of the cochlea. • Lie between the basilar membrane and the tectorial membrane in the cochlea.
Audition • Pitch perception can be explained by the following theories: • Frequency theory - the basilar membrane vibrates in synchrony with the sound and causes auditory nerve axons to produce action potentials at the same frequency. • Place theory - each area along the basilar membrane is tuned to a specific frequency of sound wave.
Audition • The current pitch theory combines modified versions of both the place theory and frequency theory: • Low frequency sounds best explained by the frequency theory. • High frequency sounds best explained by place theory.
Audition • Volley principle states that the auditory nerve can have volleys of impulses (up to 4000 per second) even though no individual axon approaches that frequency by itself. • provides justification for the place theory and
Audition • The primary auditory cortex is the ultimate destination of information from the auditory system. • Located in the superior temporal cortex. • Each hemisphere receives most of its information from the opposite ear.
Audition • The superior temporal cortex contains area MT which allows for the detection of the location of sound. • Area A1 of the brain is important for auditory imagery. • The auditory cortex requires experience to develop properly. • Auditory axons develop less in those who are deaf from birth.
Audition • The cortex is necessary for the advanced processing of hearing. • Damage to A1 does not necessarily cause deafness unless damage extends to the subcortical areas. • The auditory cortex provides a tonotopic map in which cells in the primary auditory cortex are more responsive to preferred tones. • Some cells respond better to complex sounds than pure tones.
Audition • Areas around the primary auditory cortex exist in which cells respond more to changes in sound. • Cells outside A1 respond to auditory “objects” (animal cries, machinery noise, music, etc.). • Because initial response is slow, most likely responsible for interpreting the meaning of sounds.
Audition • About 99% of hearing impaired people have at least some response to loud noises. • Two categories of hearing impairment include: • Conductive or middle ear deafness. • Nerve deafness.
Audition • Conductive or middle ear deafness occurs if bones of the middle ear fail to transmit sound waves properly to the cochlea. • Caused by disease, infections, or tumerous bone growth near the middle ear. • Can be corrected by surgery or hearing aids that amplify the stimulus. • Normal cochlea and normal auditory nerve allows people to hear their own voice clearly.
Audition • Nerve or inner-ear deafness results from damage to the cochlea, the hair cells or the auditory nerve. • Can be confined to one part of the cochlea. • people can hear only certain frequencies. • Can be inherited or caused by prenatal problems or early childhood disorders (rubella, syphilis, inadequate oxygen to the brain during birth, repeated exposure to loud noises, etc).
Audition • Tinnitus is a frequent or constant ringing in the ears. • experienced by many people with nerve deafness. • Sometimes occurs after damage to the cochlea. • axons representing other part of the body invade parts of the brain previously responsive to sound. • Similar to the mechanisms of phantom limb.
Audition • Sound localization depends upon comparing the responses of the two ears. • Humans localize low frequency sound by phase difference and high frequency sound by loudness difference.
Audition • Three mechanisms: • High-frequency sounds (2000 to 3000Hz) create a “sound shadow”, making the sound louder for the closer ear. • The difference in the time of arrival at the two ears is most useful for localizing sounds with sudden onset. • Phase difference between the ears provides cues to sound location for localizing sounds with frequencies up to 1500 Hz.
The Mechanical Senses • The mechanical senses include: • The vestibular sensation • Touch • Pain • Other body sensations • The mechanical senses respond to pressure, bending, or other distortions of a receptor.
The Mechanical Senses • The vestibular sense refers to the system that detects the position and the movement of the head. • Directs compensatory movements of the eye and helps to maintain balance. • The vestibular organ is in the ear and is adjacent to the cochlea.
The Mechanical Senses • The vestibular organ consists of two otolith organs (the saccule and untricle) and three semicircular canals. • The otolith organs have calcium carbonate particles (otoliths) that activate hair cells when the head tilts. • The 3 semicircular canals are oriented in three different planes and filled with a jellylike substance that activates hair cells when the head moves.
The Mechanical Senses • The vestibular sense is integrated with other sensations by the angular gyrus. • Angular gyrus is an area at the border between the parietal and temporal cortex.
The Mechanical Senses • The somatosensory system refers to the sensation of the body and its movements. • Includes discriminative touch, deep pressure, cold warmth, pain, itch, tickle and the position and movement of the joints. • Touch receptors may be simple bare neurons, an elaborated neuron ending, or a bare ending surrounded by non-neural cells that modify its function.
The Mechanical Senses • The pacinian corpuscle is a type of touch receptor that detects sudden displacement or high-frequency vibrations on the skin. • Mechanical pressure bend the membrane. • increases the flow of sodium ions and triggers an action potential.
The Mechanical Senses • Information from touch receptors in the head enters the CNS through the cranial nerves. • Information from receptors below the head enter the spinal cord and travel through the 31 spinal nerves to the brain.
The Mechanical Senses • Each spinal nerve has a sensory component and a motor component and connects to a limited area of the body. • A dermatome refers to the skin area connected to a single sensory spinal nerve. • Sensory information entering the spinal cord travel in well-defined and distinct pathways. • Example: touch pathway is distinct from pain pathway.
The Mechanical Senses • Various aspects of body sensations remain partly separate all the way to the cortex. • Various areas of the thalamus send impulses to different areas of the somatosensory cortex located in the parietal lobe. • Different sub areas of the somatosensory cortex respond to different areas of the body. • Damage to the somatosensory cortex can result in the impairment of body perceptions.
The Mechanical Senses • Pain depends on several types of axons, several neurotransmitters, and several brain areas. • Mild pain triggers the release of glutamate while stronger pain triggers the release of glutamate and substance P. • Substance P results in the increased intensity of pain. • Morphine and opiates block pain by blocking these neurotransmitters.
The Mechanical Senses • Opioid mechanisms are systems that are sensitive to opioid drugs and similar chemicals. • Activating opiate receptors blocks the release of substance P in the spinal chord and in the periaqueductal grey of the midbrain. • Enkephalins refer to opiate-type chemical in the brain. • Endorphins- group of chemicals that attach to the same brain receptors as morphine.
The Mechanical Senses • Discrepancy in pain perception can partially be explained by genetic differences in receptors. • Gate theory suggests that the spinal cord areas that receive messages from pain receptors also receive input from other skin receptors and from axons descending from the brain. • These other areas that provide input can close the “gates” and decrease pain perception.
The Mechanical Senses • Special heat receptors account for the pain associated with a burn. • Heat receptors can also be activated by acids. • Capsaicin is a chemical found in hot peppers that directly stimulates these receptors and also triggers an increase in the release of substance P.
