biological psychology: other sensory systems

© Cengage Learning 2016 © Cengage Learning 2016

Chapter 6

Other Sensory Systems

© Cengage Learning 2016

6.1 Audition

• Hearing alerts us to many types of useful information

• Auditory signals are sensed as periodic compressions of air, water, or other media


Sound and the Ear

• Humans experience hearing by detecting sound waves

• Sound waves are periodic compressions of air, water, or other media

• Sound waves vary in amplitude and frequency


Properties of Sound

• Amplitude refers to the intensity of the sound wave

• Frequency is the number of compressions per second and is measured in hertz (Hz)– Related to the pitch (high to low)

• Timbre is tone quality or tone complexity


Amplitude and Frequency of Sounds


Properties of Sound (cont’d.)

• Children hear higher frequencies than adults; the ability to recognize high frequencies diminishes with age and exposure to loud noises

• People communicate emotion by alterations in pitch, loudness, and timbre


Structures of the Ear – The Outer Ear

• Anatomists distinguish the outer ear, the middle ear, and the inner ear

• The outer ear includes the pinna, the structure of flesh and cartilage attached to each side of the head

• Responsible for:– Altering the reflection of sound waves into the

middle ear from the outer ear

– Helping us to locate the source of a sound


Structures of the Ear – The Middle Ear to the Inner Ear

• The middle ear contains the tympanic membrane, which vibrates at the same rate when struck by sound waves– Also known as the ear drum

– Connects to three tiny bones (malleus, incus, & stapes) that transform waves into stronger waves to the oval window

• Oval window is a membrane in the inner ear: transmits waves through the viscous fluid of the inner ear


Structures of the Ear – The Inner Ear

• The inner ear contains a snail shaped structure called the cochlea– Contains three fluid-filled tunnels (scala

vestibuli, scala media, & the scala tympani)

• Hair cells are auditory receptors that lie between the basilar membrane and the tectorial membrane in the cochlea– When displaced by vibrations in the fluid of the

cochlea, they excite the cells of the auditory nerve


Structures of the Ear


Electron Micrographs of the Hair Cells of Humans


Theories of Pitch Perception

• Place theory: each area along the basilar membrane has hair cells sensitive to only one specific frequency of sound wave

• Frequency theory: the basilar membrane vibrates in synchrony with the sound and causes auditory nerve axons to produce action potentials at the same frequency


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


The Volley Principle

• The auditory nerve produces volleys of impulses (for sounds up to about 4,000 per second)– No individual axon solely approaches that

frequency

– Requires auditory cells to precisely time their responses

• Hearing of higher frequencies not well understood


Pitch Perception Illustration


Variations in Sensitivity to Pitch

• “Amusia”: the impaired detection of frequency changes (tone deafness)

• Associated with thicker than average auditory cortex in the right hemisphere, but fewer connections from auditory cortex to frontal cortex


Variations in Sensitivity to Pitch Cont.

• Absolute pitch (“perfect pitch”) is the ability to hear a note and identify it– Genetic predisposition may contribute to it

– The main determinant is early and extensive musical training

• More common among people who speak tonal languages, such as Vietnamese and Mandarin Chinese


The Auditory Cortex

• The primary auditory cortex (area A1) is the destination for most information from the auditory system– Located in the superior temporal cortex

• Each hemisphere receives most of its information from the opposite ear


Organization of the Auditory Cortex

• Parallels that of the visual cortex– Superior temporal cortex allows detection of

the motion of sound

– Area A1 is important for auditory imagery

– Requires experience to develop properly• Axons leading from the auditory cortex develop less

in people deaf since birth


Path of Auditory Impulses


Functions of the Auditory Cortex

• Not necessary for hearing, but for processing the information

• 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

• Damage to A1 does not necessarily cause deafness unless damage extends to the subcortical areas


The Human Primary Auditory Cortex


Additional Auditory Areas

• Areas around the primary auditory cortex exist in which cells respond more to changes in sound than to prolonged sounds

• Surrounding the primary auditory cortex are additional auditory areas that respond best to what we might call auditory “objects”—sounds such as animal cries, machinery noises, and music


Hearing Loss

• Two categories of hearing impairment– Conductive or middle ear deafness

– Nerve deafness or inner ear deafness


Conductive/Middle Ear Deafness

• Occurs if bones of the middle ear fail to transmit sound waves properly to the cochlea

• Can be caused by disease, infections, or tumorous bone growth

• Normal cochlea and auditory nerve allow people to hear their own voice clearly

• Can be corrected by surgery or hearing aids that amplify the stimulus


Nerve or Inner-Ear Deafness

• Results from damage to the cochlea, the hair cells, or the auditory nerve

• Can vary in degree

• 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


Tinnitus

• 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

innervate parts of the brain previously responsive to sound

– Similar to the mechanisms of phantom limb


Hearing, Attention, and Old Age

• Brain areas responsible for language comprehension become less active

• Many older people have a decrease in the inhibitory neurotransmitters in the auditory portions of the brain – Thus, they have trouble suppressing the

irrelevant sounds and attending to the important one

• Attention improves if the listener watches the speaker’s face


Sound Localization

• Depends upon comparing the responses of the two ears

• Three cues:– Sound shadow

– Time of arrival

– Phase difference

• Humans localize low frequency sound by phase difference and high frequency sound by loudness differences


Three Mechanisms of Sound Localization

• High-frequency sounds (2000 to 3000Hz) create a “sound shadow”

• Difference in time of arrival at the two ears most useful for localizing sounds with sudden onset

• Phase difference between the ears provides cues to sound localization with frequencies up to 1500 Hz


Loudness and Arrival Times as Cues for Sound Localization


Sound Waves in Phase or Out of Phase


Phase Differences as a Cue for Sound Localization


6.2 The Mechanical Senses

• The mechanical senses respond to pressure, bending, or other distortions of a receptor– These include touch, pain, and other body

sensations, as well as vestibular sensation, which detects the position and movement of the head

• Audition is a complex mechanical sense


Vestibular Sensation

• The vestibular sense: system that detects the position and 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 Vestibular Organ

• Comprises two otolith organs (the saccule and utricle) and three semicircular canals– Otoliths are calcium carbonate particles that

push against different hair cells and excite them when the head tilts

• Semicircular canals are filled with a jellylike substance and hair cells that are activated when the head moves– Action potentials travel to the brain stem and

cerebellum


Structures for Vestibular Sensation


Somatosensation

• 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


Somatosensory Receptors

• Touch receptors may be:– Simple bare neuron ending

– A modified dendrite (Merkel disks)

– An elaborated neuron ending

– A bare ending surrounded by non-neural cells that modify its function

• Stimulation opens sodium channels to trigger an action potential


Sensory Receptors in the Skin


Somatosensory Receptors and Probable Functions

Receptor Location Responds to

Free nerve ending (unmyelinated or thinly myelinated axons)

Near base of hairs and elsewhere in skin Pain, warmth, cold

Hair-follicle receptors Hair-covered skin Movement of hairsMeissner's corpuscles Hairless areas Sudden displacement of skin; low-frequency vibration

(flutter)

Pacinian corpuscles Both hairy and hairless skin Sudden displacement of skin; high-frequency vibration

Merkel's disks Both hairy and hairless skin Light touch

Ruffini endings Both hairy and hairless skin Stretch of skinKrause end bulbs Mostly or entirely in hairless areas, perhaps including

genitalsUncertain


The Pacinian Corpuscle

• A type of touch receptor that detects sudden displacement or high-frequency vibrations on the skin– Onion-like outer structure resists gradual or

constant pressure

– Sudden or vibrating stimulus bends the membrane and increases the flow of sodium ions to triggers an action potential

• Chemicals can stimulate receptors for heat and cold: e.g., capsaicin & menthol


A Pacinian Corpuscle


Merkel Disks

• Receptors that respond to light touch (i.e., gentle stroking of the skin)

• Men and women generally have the same number of Merkel disks, but women tend to have smaller fingers – Results in Merkel disks compacted into a

smaller area and being more sensitive to feeling the distances between grooves


Tickle

• The sensation of tickle is poorly understood

• The reason we cannot tickle ourselves is that our brain compares the resulting stimulation to the “expected” stimulation and generates a weaker somatosensory response


Somatosensation in the CentralNervous System (CNS)

• Information from touch receptors in the head enters the CNS through the cranial nerves

• Information from receptors below the head enters the spinal cord and travel through the 31 spinal nerves to the brain


The Human Central Nervous System


Somatosensation in the Spinal Cord

• Each spinal nerve has a sensory component and a motor component and connects to a limited area of the body

• A dermatome: a body area innervated by 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


Dermatomes Innervated by 31 Sensory Spinal Nerves


The Somatosensory Cortex

• Various aspects of body sensations remain separate all the way to the cortex– Various areas of the somatosensory 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


Pain

• The experience evoked by a harmful stimulus and directs one’s attention toward a danger– Pain sensation begins with the least

specialized of all receptors (bare nerve endings)

– Some pain receptors also respond to acids, heat, or cold

• The prefrontal cortex responds to pain as long as the pain lasts


Pain (cont’d.)

• Axons carrying pain info have little or no myelin: impulses travel slowly– However, brain processes pain information

rapidly and motor responses are fast

• Mild pain triggers the release of glutamate in the spinal cord

• Stronger pain triggers the release of glutamate and releases several neuropeptides including substance P and CGRP (calcitonin gene-related peptide)


Spinal Pathways for Touch and Pain


Emotional Pain

• Emotional associations of pain– Activate a path that goes through the

reticular formation of the medulla

– And then to several of the central nuclei of the thalamus, the amygdala, hippocampus, prefrontal cortex, and cingulate cortex

• Experimenters monitored people’s brain activity and found hurt feelings activate the same pathway


Pain Messages in the Human Brain


Relieving Pain

• Opioid mechanisms are systems that are sensitive to opioid drugs and similar chemicals

• Opiates bind to receptors found mostly in the spinal cord and the periaqueductal gray area of the midbrain

• Endorphins: group of chemicals that attach to the same brain receptors as morphine– Different types of endorphins for different types

of pain


Gate Theory

• Proposes that the spinal cord areas that receive messages from pain receptors also receive input from touch receptors and from axons descending from the brain– These other areas that provide input can close

the “gates” by releasing endorphins and decrease pain perception

– Non-pain stimuli around it can modify the intensity of the pain


Synapses for Pain and Its Inhibition


Ways of Relieving Pain – The Periaqueductal Gray Area


More Ways of Relieving Pain

• Placebo: a drug or other procedure with no pharmacological effect– Decreases the brain’s emotional response to

pain perception, not the sensation itself

• Cannabinoids: chemicals related to marijuana that block certain kinds of pain– Act mainly in the periphery of the body

• Capsaicin: produces a temporary burning sensation followed by a longer period of decreased pain


Sensitization of Pain

• Mechanisms of the body to increase sensitivity to pain– Damaged or inflamed tissue releases

histamine, nerve growth factor, and other chemicals that increase the responses of nearby pain receptors

• Certain receptors become potentiated after an intense barrage of painful stimuli– Leads to increased sensitivity or chronic pain

later


Itch

• The release of histamines by the skin produce itching sensations– Activates a distinct pathway in the spinal cord

to the brain

– Impulses travel slowly along this pathway (half a meter per second)

• Pain and itch have an inhibitory relationship– Opiates increase itch while antihistamines

decrease itch


6.3 The Chemical Senses

• The first sensory system of the earliest animals was a chemical sensitivity

• A chemical sense enables a small animal to find food, avoid certain kinds of danger, and even locate mates


Chemical Coding

• Communication via chemical coding in the sensory system could theoretically follow– The labeled-line principle: each receptor

responds to a limited range of stimuli and sends a direct line to the brain

– Across-fiber pattern: each receptor responds to a wider range of stimuli and contributes to the perception of each of them


Taste

• Taste has one simple function – to tell us whether to swallow something or spit it out– We like sweet tastes even in infancy

– We dislike bitter and sour, but will accept in small amounts

– We vary in our like of salty flavors


Taste and Smell

• Taste refers to the stimulation of the taste buds, which are receptors on the tongue

• Our perception of flavor is the combination of both taste and smell– Taste and smell axons converge in the

endopiriform cortex


Taste Receptors

• Receptors for taste are modified skin cells

• Taste receptors have excitable membranes that release neurotransmitters to excite neighboring neurons

• Taste receptors are replaced every 10 to 14 days


Papillae and Taste Buds

• Papillae are structures on the surface of the tongue that contain the taste buds

• Each papillae may contain up to ten or more taste buds

• Each taste bud contains approximately 50 receptors

• Most taste buds are located along the outside edge of the tongue in humans


The Organs of Taste


Taste Perception – Taste Receptors

• Western societies have traditionally described sweet, sour, salty and bitter tastes as the “primary” tastes and the four types of receptors– Procedures that alter one receptor but not

others can be used to identify taste receptors

• Some substances that can modify tastes– Miracle berries – miraculin

– Gymnema sylvestre tea


Adaptation and Cross-Adaptation

• Adaptation refers to reduced perception of a stimuli due to the fatigue of receptors

• Cross-adaptation refers to reduced response to one stimuli after exposure to another


Taste Perception – Umami

• Although we describe tastes as sweet, sour, salty and bitter as the “primary”, evidence suggests a fifth type of glutamate receptor (umami)

• Tastes like unsalted chicken broth


Responses to Four Tastes


Mechanisms of Taste Receptors

• The saltiness receptor permits sodium ions to cross the membrane– Results in an action potential

• Sour receptors detect the presence of acids

• Sweetness, bitterness, and umami receptors activate a G protein that releases a second messenger in the cell when a molecule binds to a receptor


Bitter Receptors

• Bitter taste is associated with a wide range of dissimilar substances that are toxic– About 25 types bitter receptors are sensitive to

a wide range of chemicals with varying degrees of toxicity

– Most taste cells contain only a small number of these receptors

– We are sensitive to a wide range of harmful substances, but not highly sensitive to any single one


Taste Coding in the Brain

• Different nerves carry taste information to the brain from the anterior two-thirds of the tongue rather than from the posterior tongue and throat

• Taste nerves project to a structure in the medulla known as the nucleus of the tractus solitarius (NTS) – Projects information to various parts of the

brain


Taste Coding in the Brain (cont’d.)

• Various areas of the brain are responsible for processing different taste information– The somatosensory cortex responds to the

touch aspect of taste

– The insula is the primary taste cortex

• Each hemisphere of the cortex is also responsive to the ipsilateral side of the tongue


Major Routes of Impulses Related to Taste


Variations in Taste Sensitivity

• Animal species vary in taste sensitivities– Carnivores like cats, hyenas, seals, and sea

lions have no sweetness receptors

– Dolphins have few taste receptors of any type because they eat only fish which they swallow whole


Variations in Taste Sensitivity Cont.

• In humans, genetic factors and hormones can account for some differences in taste sensitivity– Variations in taste sensitivity are related to the

number of fungiform papillae near the tip of the tongue

– Supertasters have higher sensitivity to all tastes and mouth sensations in general

– Women have higher sensitivity to taste while pregnant


Variations in Taste Sensitivity Image


Fungiform Papillae in Taste Sensitivity


Are You a Supertaster, Taster, or Nontaster?


Olfaction

• The sense of smell

• The detection and recognition of chemicals that contact the membranes inside the nose

• Critical in most mammals for finding food and mates, and avoiding danger– Rats and mice show an immediate, unlearned

avoidance of the smells of cats, foxes, and other predators


Loss of an Olfaction Receptor


Scent Selection

• Even humans can follow a scent trail to some extent, and we get better with practice

• Important for our food selection – Most of what we perceive as taste is actually

olfaction


Following a Scent Trail


Olfaction in Social Behavior

• Humans tend to prefer the smell of potential romantic partners who smell different from themselves and their family members – Decreases the risk of inbreeding

– Increases the probability that children will have a wide range of immunities


Olfactory Receptors

• Olfactory cells line the olfactory epithelium in the rear of the nasal passage and are the neurons responsible for smell

• Olfactory receptors are located on cilia, which extend from the cell body into the mucous surface of the nasal passage

• Vertebrates have hundreds of olfactory receptors, which are highly responsive to some related chemicals and unresponsive to others


Olfactory Receptors Image


Olfactory Receptors and Proteins

• Proteins in olfactory receptors respond to chemicals outside the cells and trigger changes in G protein inside the cell

• G protein then triggers chemical activities that lead to action potentials


An Olfactory Receptor Protein


Olfaction in the Brain

• Axons from olfactory receptors carry information to the olfactory bulb– Chemicals that smell similar excite neighboring

areas; chemicals that smell different excite more separated areas

– Coding in the brain is determined by which part of the olfactory bulb is excited

• The olfactory bulb sends axons to the cerebral cortex, where messages are coded by location


Olfactory Damage

• Olfactory receptors are replaced approximately every month because they are vulnerable to damage from contact with the air– These are subject to permanent impairment

from massive damage


Differences in Olfaction

• Individual differences in olfaction exist– Women detect odor more readily than men

– The ability to detect a faint odor and become more sensitive to it is characteristic of young adult women; seems to be influenced by hormones

– Mice with a gene that controls a channel through which most potassium travels to reach the olfactory bulb developed a sense of super smell


Pheromones

• Chemicals released by an animal to affect the behavior of others of the same species

• The vomeronasal organ (VNO) is a set of receptors found in most mammals located near the olfactory receptors that are sensitive to pheromones


The VNO and Pheromones

• The VNO and pheromones are important for most mammals, but less so for humans– The VNO is tiny in human adults and has no

receptors and is considered vestigial

• Humans unconsciously respond to some pheromones through receptors in the olfactory mucosa– Example: synchronization of menstrual cycles

in women


Synesthesia

• The experience of one sense in response to stimulation of a different sense– An example would be seeing a number or a

letter as a specific color

• Tends to cluster in families that also have perfect pitch– Genetic predisposition

biological psychology: other sensory systems

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