2Audition: The Sense of Hearing Physical stimulus: sound wavesSound waves are periodic compressions of air, water or other media.Sound waves are “transduced” into action potentials sent to the brain.
3AuditionAmplitude refers to the height and subsequent intensity of the sound wave.Loudness refers to the perception of the sound wave.Amplitude is one factor.
4AuditionFrequency refers to the number of compressions per second and is measured in hertz.Related to the pitch (high to low) of a sound.
5Anatomy of the Ear The ear is divided into 3 parts: Outer ear Middle earInner ear
6Neuroanatomy Handout #5: The Auditory System The outer ear includes:pinna (pl: pinnae) (A):focus sound waves into middle earhelp locate the source of a soundexternal auditory canal (B):pathway to middle ear
7Neuroanatomy Handout #5: The Auditory System The middle ear includes:Tympanic membrane (C) (eardrum)vibrates when struck by sound waves3 middle ear bones transmit information to the inner ear:malleus (D)incus (E)stapes (F)
8Neuroanatomy Handout #5: The Auditory System The Inner Ear The inner ear includes:Oval window (G): a second membrane, like the eardrumSemicircular canals (H): part of the vestibular system, involved in balance and equilibrium
9Neuroanatomy Handout #5: The Auditory System Cochlea (I): a snail shaped structure containingthree fluid-filled tunnelsauditory receptors (hair cells)
10Hair cells: auditory receptors (A,B) frogs(C) cat(D) lizardFigure 7.3: Hair cells from the auditory systems of three species.(a, b) Hair cells from a frog sacculus, an organ that detects ground-borne vibrations. (c) Hair cells from the cochlea of a cat. (d) Hair cells from the cochlea of a fence lizard. Kc = kinocilium, one of the components of a hair bundle.Fig. 7-3, p. 192
11Neuroanatomy Handout #5: The Auditory System Organ of Corti (K)Hair cells and two surrounding membranes in the cochlea
12The Organ of Corti Hair cells (K1): auditory receptor cells Supporting cells (K2): attached to flexible basilar membrane (L)Tectorial membrane (J) is more rigid and runs along other end of hair cells
13Audition Auditory nerve (M) exits the inner ear and carries information about sound to the auditory cortex
14Theories of Pitch Perception 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.
15Theories of Pitch Perception 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.
16Theories of Pitch Perception 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
17AuditionWhich part of the brain helps process information about hearing?Primary auditory cortex located in the superior temporal cortexEach hemisphere receives most of its information from the opposite ear.
18Audition The primary auditory cortex provides a tonotopic map cells are responsive to preferred tonesDamage can lead to deficits processing auditory info:loss of ability to identify a song or voiceIt does not result in a loss of hearing
19Hearing LossAbout 99% of hearing impaired people have at least some response to loud noises.Two categories of hearing impairment include:Conductive or middle ear deafnessNerve deafness
20Hearing Loss Conductive or middle ear deafness: Bones of middle ear fail to transmit sound waves properly to cochleaCaused by disease, infections, or tumerous bone growth near the middle ear.Can be corrected by surgery or hearing aids that amplify the stimulus.
21Hearing Loss Nerve or inner-ear deafness: Results from damage to cochlea, hair cells or auditory nerveCan be confined to one part of the cochleapeople can lose certain frequenciesCan be inherited or caused by prenatal problems or early childhood disorders
22Audition Tinnitus: frequent or constant ringing in the ears Experienced by many people with nerve deafnessSometimes occurs after damage to cochlea
23Sounds that cause hearing loss Heavy city traffic = 90 decibelsCar horn = 110 decibelsHeadphones = 120 decibels (common volume)Jackhammer = 130 decibelsRock band at close range = 140 decibelsRocket launching = 180 decibels
24The Mechanical SensesMechanical senses respond to pressure, bending, or other distortions of a receptor.Mechanical senses include:Vestibular sensation (balance)TouchPainOther body sensations
25The Mechanical SensesThe 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.
26The Mechanical SensesVestibular organ: in inner ear, adjacent to cochlea, consists of:two otolith organscalcium carbonate particles (otoliths) activate hair cells when head tiltsthree semicircular canalsoriented in three different planesfilled with jellylike substance that activates hair cells when the head moves
27The Mechanical SensesWhich part of the brain helps process information about our vestibular sense?Angular gyrusintegrates balance and movement info with other sensationsLocated at border between parietal and temporal cortex
28The Mechanical SensesSomatosensory system refers to sensation of the body and its movements and includes:discriminative touchdeep pressurecoldwarmthpainitchtickleposition and movement of joints
29The Mechanical Senses Touch receptors can be: simple bare neurons elaborated neuron endingbare ending surrounded by non-neural cells that modify its functionFig. 7-11, p. 201
30The Mechanical SensesPacinian corpuscle: type of touch receptor that detects sudden displacement or high-frequency vibrations on skinMechanical pressure bends membraneincreases flow of sodium ions and triggers an action potential
31The Mechanical SensesWhich part of the brain helps process information about touch?Somatosensory cortex of parietal lobeInfo from touch receptors in head enters CNS through cranial nervesInfo from receptors below head enters spinal cord and travels through spinal nerves to brain
32The Mechanical Senses 31 spinal nerves each has a sensory component and a motor componentconnects to a limited area of the bodyDermatome: the skin area connected to a single sensory spinal nerve
33The Mechanical SensesPain depends on many axon types, neurotransmitters, and brain areas.Mild pain triggers the release of glutamate.Strong 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.
34The Chemical Senses: Taste Taste refers to the stimulation of taste buds by chemicals.Our perception of flavor is the combination of both taste and smell.Taste and smell axons converge in the endopiriform cortex.
35The Chemical Senses: Taste Taste receptorsmodified skin cellsexcitable membranes release neurotransmitters and excite neighboring neuronsreplaced every 10 to 14 days
36The Chemical Senses: Taste Papilla(e): structure(s) on surface of tongue that contain up to 10 taste budsEach taste bud contains approx. 50 receptorsMost taste buds are located along the outside of the tongue in humans.
37The Chemical Senses: Taste Western societies have traditionally described sweet, sour, salty and bitter tastes as the “primary” tastes and four types of receptors.Evidence suggests a fifth type of glutamate receptor.
38The Chemical Senses: Taste Various areas of the brain are responsible for processing different taste information.Somatosensory cortex responds to the touch aspect of tasteThe insula is the primary taste cortex.
39The Chemical Senses: Smell Olfaction: detection and recognition of chemicals that contact membranes inside the noseOlfactory cells: receptor cells for smellOlfactory epithelium:membrane in rear of nasal passageContains olfactory cells
40The Chemical Senses: Smell Which part of the brain helps process information about smell?Axons from olfactory receptors carry information to the olfactory bulb in the brain.The olfactory bulb sends axons to many areas of the cerebral cortex.Coding in the brain is determined by which part of the olfactory bulb is excited.
42The Chemical Senses: The VNO Vomeronasal organ (VNO): set ofreceptors located near the olfactoryreceptors that are sensitive to pheromonesPheromones: chemicals released by an animal to affect the behavior of others of the same speciesThe VNO and pheromones are important for most mammals, but less so for humansIt is tiny in human adults and has no receptors.Humans unconsciously respond to some pheromones through receptors in the olfactory mucosa.Example: synchronization of menstrual cycles
43Integration of the Senses Synesthesia is the experience of one sense in response to stimulation of a different sense.Suggests some axons from one area have branches to other cortical regions.