Comprehensive Sensory Systems: Sound, Smell, Taste, Touch, and Pain

Physical definition of sound

Pressure changes in air.

Perceptual definition of sound

Experience of hearing.

How does sound travel?

Vibrations create compressions/rarefactions that move through the air to your ear.

How do loudspeakers work?

A diaphragm vibrates back and forth, pushing air to create sound waves.

Three properties of pure tones

Frequency (pitch), amplitude (loudness), waveform (timbre).

Human hearing range

20-20,000 Hz.

Frequencies humans are most sensitive to

2,000-4,000 Hz.

What is the audibility curve?

Graph showing the threshold for hearing at different frequencies.

What is the auditory response area?

Range of frequencies and intensities we can detect.

What is echolocation?

Using echoes of sound to determine distance/shape.

What frequency do bats emit?

20,000-100,000 Hz (ultrasonic).

Parts of the outer ear

Pinna, auditory canal, tympanic membrane.

Functions of outer ear parts

Pinna funnels sound; canal amplifies; tympanic membrane vibrates.

Parts of the middle ear

Malleus, incus, stapes.

Functions of ossicles

Amplify vibrations and transmit them to the inner ear.

Function of the middle ear overall

Overcomes impedance mismatch and boosts vibration.

Main structures of the inner ear

Cochlea, basilar membrane, organ of Corti.

Function of cochlea

Transduction of sound into neural signals.

Where are high frequencies processed?

Base of cochlea.

Where are low frequencies processed?

Apex of cochlea.

Is the auditory system unilateral or contralateral?

Mostly contralateral (crosses over).

What part of the brain relays sound to auditory cortex?

Medial Geniculate Nucleus (MGN).

Where does sound localization occur?

Superior Olivary Complex.

How does sound localization work?

Using interaural time differences (ITD) and interaural level differences (ILD).

Function of Inferior Colliculus

Sound integration and reflexive orientation.

Function of Medial Geniculate Nucleus

Thalamus relay to auditory cortex.

Three parts of auditory cortex

Core, belt, parabelt.

Function of the core area

Processes simple tones.

Function of belt area

Processes complex sounds.

Function of parabelt area

Processes meaning/speech-level information.

What are cochlear implants?

Devices that stimulate the auditory nerve electrically, bypassing damaged hair cells.

How do cochlear implants work?

Electrodes in the cochlea convert sound into electrical impulses.

What are phonemes?

Smallest units of speech sound.

What is motherese?

Exaggerated infant-directed speech that helps babies learn phonemes.

What is the segmentation problem?

Speech has no clear breaks between words.

Is speech processed top-down or bottom-up?

Mostly top-down.

What is the McGurk effect?

Visual speech info changes what you hear (ba + ga = da).

Broca's area function

Speech production.

What happens with Broca's damage?

Non-fluent, broken speech.

Wernicke's area function

Speech comprehension.

What happens with Wernicke's damage?

Fluent but meaningless speech.

Why do some animals have better smell than humans?

They are macrosmatic with more olfactory receptors.

How much of a shark's brain is for olfaction?

About two-thirds.

What is microsmatic?

Weak sense of smell (humans).

What is macrosmatic?

Strong smell sense (dogs).

What are glomeruli?

Structures in the olfactory bulb that receive input from similar olfactory receptors.

Where are glomeruli located?

Olfactory bulb.

Receptors

Important structures of the olfactory system..

Olfactory bulb

Important structuress of the olfactory system.

Glomeruli

Important structures of the olfactory systemm.

Piriform cortex

Importantt structures of the olfactory system.

Orbitofrontal cortex

Important structures of the olfactoryy system.

Difference threshold for odors

Smallest detectable difference between two smells.

Odor threshold measurement

Forced-choice tests.

Human odor discrimination

About 1 trillion.

Anosmia

Inability to detect odors.

Causes of anosmia

Head injury, infection, genetics.

Pheromones

Chemicals used for social/sexual communication.

Vomeronasal organ (VNO)

What detects pheromones in many animals.

McClintock's pheromone studies

Proposed menstrual synchrony from pheromones; findings inconsistent.

Henning's Odor Prism

Early smell classification model; not useful.

Flavor

Combination of taste + smell (retronasal) + texture + temperature.

Infants' taste preferences

Yes, prefer sweet and reject bitter.

Four papillae on tongue

Filiform, fungiform, foliate, circumvallate.

Function of filiform papillae

Texture only.

Supertasters

People with dense papillae who taste more intensely.

Five basic tastes

Sweet, sour, salty, bitter, umami.

Human taste buds

About 10,000.

Taste transduction

When chemicals bind to receptors on taste cells.

Three primary receptor types in taste buds

Receptor cells, support cells, basal cells.

Three nerves carrying taste info

Facial (VII), glossopharyngeal (IX), vagus (X).

Taste signal pathway

→ Thalamus → gustatory cortex.

Neurogenesis

Creation of new cells.

Neurogenesis in taste

Occurs in taste receptor cells.

Frequency of neurogenesis

Every 1-2 weeks.

Purpose of touch

Protection, object recognition, emotional bonding.

Harlow's tactile study

Monkeys preferred soft cloth mother → tactile comfort > food.

Functions of skin

Protection, temperature control, sensation.

Layers of skin

Epidermis, dermis, subcutaneous layer.

Four mechanoreceptors

Merkel, Meissner, Ruffini, Pacinian.

Function of Merkel receptors

Fine detail, pressure.

Function of Meissner receptors

Light touch, flutter.

Function of Ruffini receptors

Stretch.

Function of Pacinian corpuscles

Vibration, deep pressure.

Two nerve fibers

Aβ fibers (touch), C tactile fibers (emotional touch).

Density of Merkel receptors

Most dense in fingertips.

Two tests for tactile acuity

Two-point threshold, grating orientation.

Cortical magnification

More cortex devoted to a body part = higher acuity.

Two cues for texture perception

Spatial cues and temporal cues.

Two forms of touch humans use

Passive and active touch.

Two main pathways from skin to cortex

Medial Lemniscal (touch), Spinothalamic (pain/temp).

Plasticity and sensory strip

Cortical areas can reorganize with experience.

Focal dystonia

Muscle cramping from blurred cortical maps (musicians).

Three types of pain

Nociceptive, inflammatory, neuropathic.

Pain signal pathway

Nociceptors → spinal cord → thalamus → cortex.

Cognitive component to pain

Yes, expectation/emotion affect pain.

How do opioids work?

Block pain signals in the spinal cord and brain.

Endorphins

Natural opioid chemicals that reduce pain.