Chapter 7 The Other Sensory

Systems

Audition: The Sense of Hearing

• Physical stimulus: 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

• 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.

Audition

• Frequency refers to the number of compressions per second and is measured in hertz.– Related to the pitch

(high to low) of a sound.

Anatomy of the Ear

• The ear is divided into 3 parts:– Outer ear– Middle ear– Inner ear

Neuroanatomy Handout #5: The Auditory System

• The outer ear includes:– pinna (pl: pinnae) (A):

• focus sound waves into middle ear

• help locate the source of a sound

– external auditory canal (B):• pathway to middle

ear

Neuroanatomy Handout #5: The Auditory System

• The middle ear includes:

– Tympanic membrane (C) (eardrum)

• vibrates when struck by sound waves

– 3 middle ear bones transmit information to the inner ear:

• malleus (D)

• incus (E)

• stapes (F)

Neuroanatomy Handout #5: The Auditory System The Inner Ear

• The inner ear includes:– Oval window (G): a

second membrane, like the eardrum

– Semicircular canals (H): part of the vestibular system, involved in balance and equilibrium

Neuroanatomy Handout #5: The Auditory System

• Cochlea (I): a snail shaped structure containing– three fluid-filled

tunnels– auditory receptors

(hair cells)

Hair cells:auditoryreceptors

• (A,B) frogs• (C) cat• (D) lizard

Fig. 7-3, p. 192

Neuroanatomy Handout #5: The Auditory System

• Organ of Corti (K)– Hair cells and two

surrounding membranes in the cochlea

The 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

Audition

• Auditory nerve (M)– exits the inner ear

and carries information about sound to the auditory cortex

Theories 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.

Theories 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.

Theories 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

Audition

• Which part of the brain helps process information about hearing?

• Primary auditory cortex located in the superior temporal cortex

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

Audition

• The primary auditory cortex provides a tonotopic map– cells are responsive

to preferred tones• Damage can lead to

deficits processing auditory info:– loss of ability to

identify a song or voice

• It does not result in a loss of hearing

Hearing Loss

• About 99% of hearing impaired people have at least some response to loud noises.

• Two categories of hearing impairment include:

1. Conductive or middle ear deafness

2. Nerve deafness

Hearing Loss• Conductive or middle ear

deafness:– Bones of middle ear fail to

transmit sound waves properly to 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.

Hearing Loss

• Nerve or inner-ear deafness:– Results from damage to

cochlea, hair cells or auditory nerve

– Can be confined to one part of the cochlea• people can lose certain

frequencies– Can be inherited or

caused by prenatal problems or early childhood disorders

Audition

• Tinnitus: frequent or constant ringing in the ears– Experienced by many people with nerve

deafness– Sometimes occurs after damage to cochlea

Sounds that cause hearing loss

• Heavy city traffic = 90 decibels• Car horn = 110 decibels• Headphones = 120 decibels (common

volume)• Jackhammer = 130 decibels• Rock band at close range = 140 decibels• Rocket launching = 180 decibels

The Mechanical Senses

• Mechanical senses respond to pressure, bending, or other distortions of a receptor.

• Mechanical senses include:– Vestibular sensation (balance)– Touch– Pain– Other body sensations

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 Mechanical Senses• Vestibular organ: in inner ear,

adjacent to cochlea, consists of:– two otolith organs

• calcium carbonate particles (otoliths) activate hair cells when head tilts

– three semicircular canals • oriented in three different

planes• filled with jellylike substance

that activates hair cells when the head moves

The Mechanical Senses

• Which part of the brain helps process information about our vestibular sense?– Angular gyrus

• integrates balance and movement info with other sensations

• Located at border between parietal and temporal cortex

The Mechanical Senses

• Somatosensory system refers to sensation of the body and its movements and includes:– discriminative touch– deep pressure– cold– warmth– pain– itch– tickle– position and movement of joints

The Mechanical Senses

• Touch receptors can be:– simple bare

neurons– elaborated neuron

ending– bare ending

surrounded by non-neural cells that modify its function

Fig. 7-11, p. 201

The Mechanical Senses

• Pacinian corpuscle: type of touch receptor that detects sudden displacement or high-frequency vibrations on skin

• Mechanical pressure bends membrane– increases flow of

sodium ions and triggers an action potential

The Mechanical Senses

• Which part of the brain helps process information about touch?– Somatosensory cortex of

parietal lobe– Info from touch receptors in

head enters CNS through cranial nerves

– Info from receptors below head enters spinal cord and travels through spinal nerves to brain

The Mechanical Senses

• 31 spinal nerves– each has a sensory

component and a motor component

– connects to a limited area of the body

• Dermatome: the skin area connected to a single sensory spinal nerve

The Mechanical Senses

• Pain 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.

The 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.

The Chemical Senses: Taste

• Taste receptors– modified skin cells– excitable membranes release

neurotransmitters and excite neighboring neurons

– replaced every 10 to 14 days

The Chemical Senses: Taste• Papilla(e): structure(s)

on surface of tongue that contain up to 10 taste buds

• Each taste bud contains approx. 50 receptors

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

The 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.

The Chemical Senses: Taste

• Various areas of the brain are responsible for processing different taste information.– Somatosensory

cortex responds to the touch aspect of taste

– The insula is the primary taste cortex.

The Chemical Senses: Smell

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

• Olfactory cells: receptor cells for smell

• Olfactory epithelium:– membrane in rear

of nasal passage– Contains olfactory

cells

The 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.

The Chemical Senses: Smell

The Chemical Senses: The VNO

• Vomeronasal organ (VNO): set of

receptors located near the olfactory

receptors that are sensitive to pheromones• Pheromones: chemicals released by an animal to

affect the behavior of others of the same species– The VNO and pheromones are important for most

mammals, but less so for humans

– It 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

Integration 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.