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Sensation & Perception Lecture 3

Mechanical pressure: ear, skin and body

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Sensory Transduction

Transforming physical information into neural signals.

Four types of receptors in humans:

1. Photoreceptors sense light

2. Mechanoreceptors sense mechanical pressure3. Chemoreceptors sense molecules

4. Thermoreceptors sense temperature

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Mechanical pressure

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Mechanoreceptors

Physically deforming a mechanoreceptor causes ionchannels to open, which causes the cell to fire.

Mechanical forces can provide a wide range ofinformation1. Movement of hair cells in the inner ear

hearing

inertia

gravity

2. Pressure and stretch receptors in the skin, muscles, and organs Light touch

Texture

Stretch

Pain

Body position

Body movement

Interoception

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1. Hair cells in the inner ear

Three functions

- Sound perception (cochlea)

- Head motion perception

(semicircular canals)- Gravity perception (vestibular

labyrinth)

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PS1009 Perception: Sensory Transduction

Sound is a (sine) wave of moving air.

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The range of human hearing: variable, but ~12Hz to 20KHz

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The function of the

ear is to channel

and amplify sound

waves.


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http://www.youtube.com/watch?v=0jyxhozq89g

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Auditory Hair Cells

Ion channels on adjacent hairs areconnected by a tip link. Movement of

the hair cells pulls the ion channels

open, depolarizing (activating) the cell.


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Hearing damage prolonged exposure to

>85dB, or sudden exposure to 120-145dB


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Mechanoreceptors in the cochlea provide:

Loudness amplitude of sound wave increases firing rate

Pitch which part of the cochlea is activated

Timbre composite frequencies simultaneous activationof multiple locations on the cochlea

NOT Location this comes from time and volumedifferences between the two ears (more on this later!)

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Hair cells in the semicircular canals:

head motion

Semicircular canals contain endolymph

Acceleration and deceleration of rotational head movement endolymph

movement lags behind the hair cells, causes them to bend

Changes in viscosity of endolymph can interfere with perception: alcohol,

Mnire's disease

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Hair cells in the vestibular labyrinth:

gravity

Inner ears also contain the otolith organs

Gravity shifts the otoliths (small crystals) against hair cells

Provides sense of head position relative to upright, and

inertia

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2. Mechanoreceptors in the skin

Multiple systems: light touch, firm pressure, vibration,pain, and skin stretch

All types respond to physical deformation

Receptors shapes are specialized for different types of pressure

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High acuity for textureHigh sensitivity to light touch

Skin is also specialized

Less slippery when wet

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Haptic touch: exploring objects

with your cutaneous

mechanoreceptors

Vibrations = roughness/texture

Pressure = firmness

Position of fingers around object = shape

Skin stretch = weight

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Pain (nociception) Free nerve endings respond to tissue damage

But pain experience is not well correlated with

activity in free nerve endings

Highly influenced by context and emotion

Pain signals are gated from entering the

brain -- can be blocked by endorphins

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Distribution of touch receptors

The two-point discrimination

threshold

Touch the skin with one or two points.

Gradually move the points closer together.

At some point two will feel like one.

This distance is the two-point-

discrimination threshold.

If two points stimulate two different

receptors, you will feel two points. If two

points stimulate only one receptor, you will

feel only one.

Density of receptors in the skin is higheston the hands and face, lowest on the

upper arm, calf, etc.

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Proprioception (body position), kinesthesis (body

movements) and interoception (body state)

Also, stretch receptors in

smooth muscle (e.g. lungs,

bladder, stomach, bowels):

low level (spinal/brain

stem) control + perceptual

input

Stretch receptors in

muscles and tendons: low-

level (spinal/brain stem)

control + perceptual input

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Mechanoreceptors - summary

Physically deforming mechanoreceptors changes their firing Mechanical forces provide a wide range of sensory

information: sound, gravity, pressure, texture, and body state

Hair cells in the cochlea move in response to sound waves

amplified by the ear, the basis for audition Other hair cells in the ear provide the vestibular sense

Mechanoreceptors in skin and body provide somatosensation

Different shapes, sizes, depths, and sensitivity of receptors in

the skin provide tactile information, including nociception

Other stretch receptors in the body provide kinesthesis,

proprioception, and interoception


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Sensory Transduction

Transforming physical information into neural signals.

Four types of receptors in humans:

1. Photoreceptors sense light

2. Mechanoreceptors sense mechanical pressure3. Chemoreceptors sense molecules

4. Thermoreceptors sense temperature

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Chemoreceptors

Function like a lock and key: specific classes of

receptors are sensitive to specific molecule

types.

Found in three locations (among others):

a) tongue (gustation)

b) nasal epithelium (olfaction)

c) the respiratory system (breathing)


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The tongue (gustation)

Each of the papillae on the tongue contains multiple taste buds

Each taste bud contains multiple chemoreceptors

Five (known) receptor types: salty, sweet, bitter, sour, and

savory (AKA umami).


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Aguesia: inability to taste

PS1009 Perception: The Sensory Brain

Temporary loss of taste is

common.Permanent aguesia is rare.

Usually caused by nerve

damage or deformity

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