Chapter 6 - Hearing, Mechanical and Chemical Senses

What are the main properties of sound and what do they determine?

• Amplitude → loudness,

• Frequency (Hz) → pitch

• Timbre → tone quality.

What is the human hearing range and how does it change?

~20–20,000 Hz (children hear higher); high-frequency hearing declines with age/noise.

How do sound properties convey emotion in speech?

Pitch, loudness, and timbre convey emotional tone, called prosody.

What is sound physically made of?

Vibrations (compressions) in air or other media.

What are the three main parts of the ear?

Outer ear, middle ear, and inner ear.

What is included in the outer ear?

The pinna (the visible part on each side of the head).

What are the functions of the outer ear?

Changes how sound waves enter the ear and helps locate where sounds come from.

What does the middle ear contain that vibrates with sound?

The tympanic membrane (eardrum).

Which three tiny bones are in the middle ear?

Malleus, incus, and stapes.

What is the function of the middle ear bones?

Amplify sound and pass it to the oval window.

What does the oval window do?

Sends vibrations into the fluid of the inner ear.

What snail-shaped structure is in the inner ear?

The cochlea.

What does the cochlea contain?

Three fluid-filled tunnels.

What are hair cells and where are they located?

Auditory receptors lying on the basilar membrane in the cochlea.

How do hair cells transmit sound information?

Vibrations in cochlear fluid displace hair cells, opening ion channels and exciting auditory nerve cells.

What does frequency theory state about pitch perception?

What is the volley principle?

Neuron groups take turns firing to handle sounds up to ~4000 Hz.

What does place theory propose?

According to the updated view, which parts of the cochlea respond to which frequencies?

• Base (stiff) → high frequencies

• Apex (flexible) → low frequencies.

Where is A1 and what input does it get?

Superior temporal cortex; mainly from opposite ear.

What are A1’s functions and organization?

“What” pathway → sound identity

“Where” pathway → sound location; auditory imagery and sound motion detection.

What is a tonotopic map and how does experience affect A1?

Cells respond to specific tones

A1 develops less in people deaf from birth.

Is A1 necessary for hearing and what happens if damaged?

Not needed for hearing itself

damage may impair processing but usually doesn’t cause complete deafness.

Where do auditory signals start?

At the ear’s receptors.

Which structure receives input only from the same-side ear?

The cochlear nucleus.

After the cochlear nucleus, where do auditory signals come from?

Both ears.

How do we locate sounds?

By comparing input from both ears.

What are the three main cues for sound localization?

• Time of arrival (which ear hears it first)

• Sound shadow (difference in loudness)

• Phase difference (difference in wave phase)

Which cue is used for low-frequency sounds?

Phase difference.

Which cue is used for high-frequency sounds?

Loudness difference (sound shadow).

How does the phase of sound waves at both ears affect perceived direction?

• In-phase → sounds seem straight ahead or behind;

• Out-of-phase → sounds seem to come from the side.

What causes conductive/middle ear deafness?

When middle ear bones fail to transmit sound properly to the cochlea.

What are common causes of this deafness?

Disease, infections, or tumorous bone growth.

Can people with conductive deafness hear their own voice clearly?

Yes, because the cochlea and auditory nerve are normal.

How can conductive deafness be treated?

Surgery or hearing aids that amplify sound.

What causes nerve or inner-ear deafness?

Damage to the cochlea, hair cells, or auditory nerve.

How can this deafness vary?

It can vary in degree and can affect only certain parts of the cochlea, so people may hear only certain frequencies.

What are common causes of nerve/inner-ear deafness?

Inherited conditions, disease, or loud noise that damages the auditory system.

What is tinnitus?

Ringing or buzzing in the ears.

Who commonly experiences tinnitus?

People with nerve (inner-ear) deafness.

What causes tinnitus?

Often occurs after cochlear damage; brain hearing areas are taken over by signals from other body parts.

What is tinnitus similar to?

Phantom limb pain, where the brain perceives sensations that aren’t there.

Who is most likely to have absolute pitch?

People who started music early and speakers of tonal languages that focus on pitch.

What do mechanical senses respond to?

Pressure, bending, or other distortions of a receptor.

What senses are included in mechanical senses?

Touch, pain, other body sensations, and vestibular sensation (detects head position and movement).

Why is audition considered a mechanical sense?

Because hair cells are modified touch receptors.

Where is the vestibular organ located?

In the ear, next to the cochlea.

What structures are in the vestibular organ?

Two otolith organs (saccule and utricle) and three semicircular canals.

What are otoliths and what do they do?

Tiny calcium carbonate particles that move and stimulate hair cells when the head tilts.

How do semicircular canals detect movement?

They contain jelly-like fluid and hair cells that activate when the head moves.

What is the somatosensory system?

The system for sensing the body and its movements.

Is somatosensation a single sense?

No, it includes many senses.

What senses are part of somatosensation?

Touch, deep pressure, joint position and movement, pain, and temperature.

What does the Pacinian corpuscle detect?

Vibrations or sudden displacements on the skin.

How does the Pacinian corpuscle respond to stimuli?

• Their outer layer blocks steady pressure.

• Quick or vibrating touches bend the membrane, letting in sodium to trigger a signal.

What receptors respond to light touch?

Merkel disks.

How does sensitivity differ between men and women for Merkel disks?

Both have similar numbers, but women tend to have smaller fingers, making them more sensitive.

What are somatosensory receptors?

Sensors in the skin that detect touch, pressure, vibration, temperature, and pain.

What is the main function of somatosensory receptors?

To send signals to the brain so you can perceive what’s happening to your body.

What do free nerve endings respond to and where are they located?

Pain and temperature; found in any skin area.

What do hair-follicle receptors detect?

Movement of hairs and light skin strokes; found in hair-covered skin.

What do Meissner’s corpuscles detect and where are they found?

Discriminative touch and vibration; in hairless areas, mainly fingertips.

What do Pacinian corpuscles respond to?

Vibration or sudden touch; found in any skin area.

What do Merkel’s disks detect?

Light touch; found in any skin area.

What are Ruffini endings responsible for?

Detecting skin stretch and roughness; found in any skin area but scarce in humans.

What do Krause end bulbs respond to and where are they found?

Function uncertain; found mostly in hairless areas.

Why must humans regulate body temperature?

Because overheating or overcooling can be deadly.

How do cold-sensitive neurons respond to temperature?

They react quickly to temperature drops but adapt to constant cold.

How do heat-sensitive neurons respond?

They respond to the actual temperature level.

What chemicals can activate temperature receptors?

Capsaicin (heat) and menthol (cold).

Why can’t we tickle ourselves?

Because the brain predicts the touch and reduces the response.

How does touch information from the head reach the brain?

Through cranial nerves.

How does touch information from the body reach the brain?

Through 31 spinal nerves.

How do different types of somatosensory information travel?

Touch, pressure, and pain signals travel in separate spinal cord pathways toward the thalamus.

What is the role of the thalamus in somatosensation?

It sends impulses to specific areas of the primary somatosensory cortex (S1) for processing.

What are the two parts of each spinal nerve?

Sensory and motor parts.

What is a dermatome?

A body area served by one sensory spinal nerve.

How do sensory signals travel in the spinal cord?

In separate, distinct pathways.

Do touch and pain signals follow the same route?

No, they follow different routes in the spinal cord.

How are body sensations organized in the brain?

They remain separate up to the somatosensory cortex.

Where does the somatosensory thalamus send signals?

To specific parts of the somatosensory cortex in the parietal lobe.

How does the somatosensory cortex represent the body?

Different parts of the cortex respond to different body areas.

What happens if the somatosensory cortex is damaged?

It can cause loss of body sensation, known as numbsense.

What is the main purpose of pain?

To signal harm and focus attention on danger.

Where do pain sensations start?

With bare nerve endings, the simplest receptors.

Do males and females respond to pain the same way?

No, they respond differently.

How do midbrain neurons affect pain in males vs. females?

Activating certain midbrain neurons reduces pain in male mice but not in females.

How do opiates and cannabinoids differ in pain relief between sexes?

They relieve pain differently in males and females.

Do pain axons have myelin?

No, they have little or no myelin, so impulses travel slowly.

How does the brain process pain information?

Very quickly, allowing fast motor responses.

What neurotransmitter is released during mild pain?

Glutamate.

What happens during stronger pain?

Glutamate and neuropeptides such as substance P and CGRP are released.

Where do pain signals cross in the spinal cord?

Immediately to the opposite side.

Where do touch signals cross?

Later, at the medulla.

How are touch and pain represented in the brain?

Signals from the right side of the body go to the left side of the brain (and vice versa).

What brain pathway does emotional pain activate, and which brain areas does it reach?

Emotional pain activates a pathway through the medulla’s reticular formation that reaches the thalamus, amygdala, hippocampus, prefrontal cortex, and cingulate cortex.

It triggers similar brain areas as physical pain.

How does the opioid system respond to pain?

The opioid system responds to opiates and similar chemicals that bind to receptors mainly in the spinal cord and periaqueductal gray of the midbrain.

What are endorphins and how do they relieve pain?

Endorphins are natural brain chemicals that activate opioid receptors. Different endorphins respond to different types of pain.

How does morphine affect pain?

Morphine blocks dull, slow pain but does not block sharp pain from large-diameter axons.

How do neurons use endorphins to block pain?

Neurons release endorphins at synapses, which activate opioid receptors to block pain signals.