PSY 256: Senses

Sound

Vibrations of air that our ears detect as hearing

Compressed air

Air molecules pushed closely together; higher density

Rarefied air

Negative pressure; lower density

Hertz

How sound is measured; cycles per second

• Intensity/loudness (amplitude)

• Frequency (pitch)

• Complexity/layered sounds (timbre)

Intensity (Amplitude)

High the wave = loud sound // lower wave = soft sound

Frequency (Pitch)

Waves far apart = low pitch // waves close together = high pitch

Complexity (Timbre)

Pure tone vs tones layered on top of one another

• ex) One section of an orchestra playing vs the whole orchestra

Outer Ear

The part of the ear you can actually see

Pinna: Cartilage that acts as a funnel; Grabs sound waves and funnels them down the auditory canal

Auditory canal: Channel that directs sound waves to the eardrum

Middle Ear

Ear drum (tympanic membrane): Vibrates when struck by sound waves, converting air pressure changes into mechanical movement for the ossicles

Ossicles: 3 bones in the middle ear that are hinged together

Inner ear

Cochlea: 3 fluid filled canals

• cochlea —> brain; exam mention

Transduction

Going from one modality to another; takes place in cochlea (inner ear)

• Sound waves —> electrical chemical signals

• Converting mechanical energy from sound vibrations into neural (electrical) signals by hair cells

How sound travels

Pinna → auditory canal → Tympanic membrane (ear drum): flexible, as it is hit with compressed air it will flex and move → ossicles: as the eardrum moves the bone will shift to amplify the signal so it can be detected by the brain → Oval window (on the cochlea): where the ossicles contact the cochlea by banging against it rhythmically → cochlea, filled with fluid, fluid is moved → basilar membrane → cilia → auditory nerve → brain

Ear infection

Bacteria growing inside of the fluid in the middle ear

• Swelling; push on ear drum and irritate ear

• Treatment for chronic infections = putting tube through ear drum to open it up

Middle Ear Fluid

Fluid exchanges everyday; typically clear

• Eustachian tube: Allows middle ear fluid to drain regularly

  • During ear infections, the tube can narrow allowing the fluid to sit rather than drain

Cochlear duct

Middle chamber of the cochlea containing endolymph and the organ of Corti (where hearing transduction occurs)

• Endolymph: The fluid inside of the cochlear duct; mostly potassium (K+)

  • Organ of corti: 2 membranes in your hair cells where transduction happens inside of the cochlear duct; runs the whole length of cochlea curl

Basilar membrane

Membrane in the cochlea that moves in response to fluid waves; movement bends hair cells to trigger electrical signals

Tectorial Membrane: Structure above hair cells; movement of the basilar membrane causes hair cells to press against it, bending the cilia

Perilymph (tympanic and vestibular canals)

Fluid in the tympanic and vestibular canals that carries sound-induced waves through the cochlea

Mechanically gated ion channels

Opens when hair cell cilia bend, allowing ions to enter and generate receptor potentials

Tiplink

Pulls the lid open on these ion channels → diffusion and electrostatic pressure push ions inside (depolarize)

• Depolarization (more positive): Bending towards the tall tiplink = ion channel open

• Hyperpolarization (more negative): Bending towards the short tiplink = ion channel close

Cilia

Hair cells on the basilar membrane

• Inner: Mediate transduction; less common

  • Losing all of these would make a person deaf

• Outer: Amplify the signal of the inner cilia; more common

  • Can have less but still have sound

Place Coding

Different frequencies cause vibration at specific spots along the basilar membrane

• Base: Needs stronger waves (high frequency) to move the base because it's narrow

  • When this is activated ur brain knows it's a high pitch/frequency sound

• Apex: Easier to move, wide, flexible

  • When this is activated, your brain knows it's a low pitch/frequency sound

Temporal Lobe

Brain region that receives and interprets auditory information like pitch and volume

• Auditory cortex: Part of the temporal lobe responsible for processing and identifying sounds

Superior Olivary Nucleus (hind brain/brainstem)

Brainstem structure that compares input from both ears to determine sound location; Can help up respond to sounds before we hear it

• Input from right and left side of ear

• Hindbrain: Cerebellum (movement/balance/posture), Pons (breathing, sleep, facial expressions), Medulla (heart rate, blood pressure, digestion)

• Brainstem: Midbrain, Pons, Medulla

Medial geniculate Nucleus

Subsection of the thalamus (diencephalon) that sends auditory information to the auditory cortex

Conduction Deafness

Sound waves aren't hitting the ear drum OR aren’t being relayed to the cochlea; involves an issue with the middle or outer ear; usually temporary

Sensorineural Deafness

An issue in your cochlea; Hair cilia are dying off or didnt form/ didn’t form properly; most common/born deaf

Central Deafness

Damage to auditory structures in the brain (auditory cortex/temporal lobe); very rare

Fiber Types (skin)

Aa (Alpha): Fastest because of myelination and bigger diameter

Ab (Beta): Mechanorecepters use the Aa beta fibers

Aδ (delta): Used for pain/temp/itching

C: Used for pain/temp/itching

Adaptation (skin)

Rapid: Sensory stimulus adapts quickly; mark the start and stop of a stimulus

Slow: Start firing when the stimulus is presented and maintain/continue it; isnt as instant

Stimulus Strength (skin)

How strong a stimulus is; affects how often a neuron fires, not the size of each AP

• AP frequency: number of action potentials per second (rate law)

• ex) As you get pressure applied to the skin, onion like shaped thing pulls and deforms it (based on strength of vibration/pressure)

Receptive Field

The point where sensory info is picked up

• Smaller receptive fields in smaller areas (like fingers); higher number of sensory neurons in these places

  • Density: High receptor density = smaller receptive fields and greater sensitivity (e.g., fingertips).

Two point discrimination

Putting 2 pencils on someones arm; “how many things are touching your skin?”

• If the 2 pencils are in the same receptive field, theyll say one thing but if they are in different receptive field theyll say 2 things

  • Receptive field size varies

Dorsal Column System (Ascension sensory)

Ascending spinal pathway that carries sensory info to the thalamus → primary somatosensory cortex in the parietal lobe

Nocireceptors

Pick up painful stimuli; free nerve endings

• Multiple types of pain receptors

• chemical signal → nocireceptor → Signal sent through dorsal root ganglia → into dorsal column of spinal cord

Types of nocireceptors

Mechanical: Respond to intense pressure, cuts, or tissue damage
Chemical: Respond to irritating chemicals or inflammation
Thermal: Respond to extreme heat or cold

Fiber nocireceptor types

• Aδ: Pain/temp; initial pain response

• C: Pain/temp/itch; secondary pain response throbbing or lingering pain/irritation

Antrolateral (spinothalamic) system

• Ascending pain pathways

  • Fibers are taken in through dorsal root ganglia and cross over immediately and ascend on the right side (contralateral side)

  • Spinal cord → medulla → pons → Midbrain → forebrain

    • Messy signal because it hits multiple levels

Decussation

Crossing of neural fibers from one side of the body to the opposite side of the brain

• Touch: Decussation happens in Hindbrain and medulla

• Pain: That decussation or crossing to contralateral side is happening at the Spinal cord

Psychological control of pain

Study done measuring pain using voltage shocks. They tell participants they have 2 drugs (cheap vs expensive) when in reality they were both placebo. People taking the more expensive sugar pill was more effective compared to the cheaper pill, people said wasn't as effective

Analgesic

A drug that is supposed to reduce pain

• Aspirin, morphine

5 basic tastes

1. Salty

2. Sour

3. Sweet

4. Bitter

5. Umami (msg, smelly cheeses, meatiness)

Flavor

Taste (20%) combined with smell (80%)

Taste buds

Found in trenches/grooves of tongue

• regenerate 10-14 a say

• peripheral nervous system

Gustatory pathway

Sense of taste; ipsilateral (stays on the same side)

• Insular cortex: Where sensory info from taste is processed; ticked inside lateral sulcus

• Hits the thalamus before it goes to it's primary cortical region; true for most

Taste cells (Gustatory cells)

Receptor cells in taste buds that detect one type of taste (sweet, sour, salty, bitter, umami)

• Gustatory (afferent) axons: Carry taste information from taste buds to the brain

Cranial Nerves

Takes taste information to the brain

• Glossopharyngeal (IX-9): Carries taste from the posterior third of the tongue.

• Facial nerve (VII-7): Carries taste from the front two-thirds of the tongue.

• Vagus nerve (X-10): Carries taste and sensory input from the epiglottis and throat.

Oval Window

a membrane-covered opening in the inner ear that connects the middle ear to the cochlea

Round Window

a membrane-covered opening in the inner ear that connects the middle ear to the cochlea and is crucial for hearing

Olfactory epithelium

Tissue high in nasal cavity holding receptor neurons

Olfactory receptor cells

Bipolar neurons with cilia containing odorant receptors

• Odorant receptors: Proteins on cilia binding odor molecules

• Regeneration: Receptor cells regularly replaced from basal cells

Odorant receptors cell transduction

Odorant binding opens ion channels (depolarization)
Na+ Influx: Sodium enters, depolarizing the receptor cell

Ca+ Influx: Calcium enters, amplifying depolarization and triggering Cl- channel opening

Cl- efflux: Chloride flows out of the cell, further depolarizing it

Coding odorant molecules

Each odor activates a unique combination of receptors

Supporting cells

Provide metabolic and physical support

Basal Cells

Stem cells that form new receptor neurons

Cribriform plate

Perforated bone through which axons pass to olfactory bulb

Olfactory Nerve (Cranial Nerve I)

Axons of receptor neurons

Olfactory Bulb

First brain relay; contains glomeruli (bundles where receptor axons synapse on mitral cells)

Mitral Cell

Relay olfactory info to higher brain regions

Glomerulus/Glomeruli

Spherical structures that organize receptor input by odor type

Intranasal drug delivery

Drugs absorbed through nasal mucosa directly reach brain via olfactory pathways

Relaying Ofactory info to the brain

Signals go from bulb to cortex without passing through thalamus

• skips thalamus

Touch as first sensory system developed

Somatosensation forms early in development

Somatosensation: The body’s sense of touch, temp, body position, pain

Skin

Protective organ containing sensory receptors

Epidermis: Outer layer; barrier

Dermis: Inner layer with blood vessels, nerves, and receptors

Glabrous skin

Hairless areas with dense mechanoreceptors for fine touch

• ex) Palms, soles

Hairy skin

Contains hair follicles and associated receptors for movement and light touch

Tonotropic mapping (auditory cortex)

Spatial arrangement of neurons mirrors frequency layout of basilar membrane

Resting (hair cells)

Slight K⁺ and Ca²⁺ influx keeps cell partially depolarized and ready to respond

cochlear implant

Device that electrically stimulates different parts of cochlea to mimic place coding and restore hearing