PS1509L4-ChemoThermo(1)

7/27/2019 PS1509L4-ChemoThermo(1)

1/24

Sensation & Perception Lecture 4

Sensing Chemicals and Temperature


2/24

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


3/24

Chemoreceptors

Function like a lock and key: specific classes of

receptors are sensitive to specific molecule

types.

Found in:

a) tongue (gustation)

b) nasal epithelium (olfaction)

c) other locations in the body (lungs, stomach)


4/24


5/24

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).

PS1009 Perception: Sensory Transduction


6/24

Based on pattern coding, not

the firing of one or another

receptor type in particular

What is the relationship between taste receptors and tastants?

Receptor Signals

Salty NaCL (Electrolytes)

Sour Acid (Spoiled/unripe foods?)

Bitter Toxins, inedible substances

Sweet Sucrose (Calorie-dense foods)

Umami Glutamate (protein-rich food)

Most taste is based on smell


7/24Figure from Chandrashekar, Hoon, Ryba & Zuker, Nature, 2006

Consensus in recent taste literature is that taste receptors are specific, not

graded. Pattern coding (b and c below) is unnecessary and unlikely.

This simple model is also the most accurate


8/24

Taste preferences

Innate preferences (salty, sweet over bitter, sour)

Exposure to amniotic fluid and breast milk (flavor

determined by maternal diet)

Exposure to flavours over lifespan

Genetic variability in taste bud numbers (supertasters,

nontasters)


9/24

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


10/24

Nasal epithelium

(smell/olfaction)

Inhaling brings odorants to the nasal epithelium

Odorants bind to proteins in the cilia of the receptor cells and activate the cell

Each cell has only a single receptor type



11/24

There are ~1000 different odorant receptors, each one coded by a

different gene Genetic codes for olfaction receptors alone comprise 3% of our genes!

Axel & Buck, 2004 Nobel prize


12/24

Can we localize smells?

Orthonasal vs. Retronasal clear differences in

perception/recognition Left vs. Right nostril arrival times

Might be mediated by pain pathways

Scent tracking better with two nostrils than one


13/24

Human pheremones? McClintock effect (controversial)

Lots of smell recognition/preference

studies (but are these really

pheremones?) Pheremone receptor organ in humans is

present but probably nonfunctional

Pheremones: Odorants to

communicate and control

conspecific behaviour


14/24

Anosmia

Loss of sense of smell

Temporary loss due to

inflammation / blockage isroutine

Permanent loss due to range

of causes (congenital, head

trauma, disease, aging)

common (1-2% in young,

>12% in elderly)


15/24

Chemoreceptors in the body

The aortic and carotid arteries contain CO2 and O2

sensitive chemoreceptors that sample blood leaving the

heart and communicate with brain areas that control

breathing rate

Chemoreceptors in the gastric system cause stomach pain,

nausea, vomiting


16/24




1. Photoreceptors sense light

2. Mechanoreceptors sense mechanical pressure3. Chemoreceptors sense molecules

4. Thermoreceptors sense temperature


17/24

Thermoreceptors

At least two types: cold and hot

Found in

the skin

in the cornea (to trigger blinking)

In the brainstem (to regulate core temperature).


18/24

Sensing skin temperature

UnmyelinatedC-fibers in the skin

Myelin speeds up neural transmission, so

unmyelinated nerves are slow takes several

seconds to get to the brain

Adaptation of thermoreceptors


19/24




1. Photoreceptors (light)

2. Chemoreceptors (molecules)3. Mechanoreceptors (mechanical pressure)

4. Thermoreceptors (temperature)



20/24

There are more than 5 senses! Photoreceptors vision

Mechanoreceptors hearing, balance, skin pressure,

limb position, internal organ sense Chemoreceptors taste, smell, blood oxygen level

Thermoreceptors skin, eye, and internal bodytemperature


21/24

Perception comes from the brain

Receptors are distributed and

send input to the brain

If they did not transmit to the

brain, there would be noperception.

Does your foot feel warmth? No

it comes from the brain!


22/24

Getting sensory input to the brain Vision, audition, and touch all have a similar general architecture

Input goes through the thalamus first, and then to specialized

areas in the cerebral cortex.

PS1009 Perception: The Sensory Brain

Thalamus


23/24

Primary

Visual Cortex

Primary

Auditory Cortex

Primary

Somatosensory

Cortex


24/24

Where are we?

Step Process Lecture

1. Sample information Sensory Transduction

- light (the eye) 2

- pressure (the ear, skin, etc.) 3

- chemicals (tongue, nose, etc.) 4

- temperature (skin, etc.) 4

2. Encode / register it Sensory Pathways and Networks

- vision 4? +5- audition & somatosensation 6

3. Organize, interpret,

and use it

Perception 7-12 (Dr Pilz)

Documents

PS1509L4-ChemoThermo(1)