The Chemical Context of Life

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Stimuli from different sensory receptors travel as action potentials along different neural pathways.

The brain distinguishes stimuli from different receptors by the area in the brain where the action potentials arrive.

Slide 10

Amplification and Adaptation

Amplification is the strengthening of stimulus energy by cells in sensory pathways.

Sensory adaptation is a decrease in responsiveness to continued stimulation.

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Types of Sensory Receptors

Based on energy transduced, sensory receptors fall into five categories:

Mechanoreceptors

Chemoreceptors

Electromagnetic receptors

Thermoreceptors

Pain receptors

Slide 12

Mechanoreceptors

Mechanoreceptors sense physical deformation caused by stimuli such as pressure, stretch, motion, and sound.

The sense of touch in mammals relies on mechanoreceptors that are dendrites of sensory neurons.

Slide 13

Sensory receptors in human skin

Connective tissue

Heat

Strong pressure

Hair movement

Nerve

Dermis

Epidermis

Hypodermis

Gentle touch

Pain

Cold

Hair

Slide 14

Chemoreceptors

General chemoreceptors transmit information about the total solute concentration of a solution.

Specific chemoreceptors respond to individual kinds of molecules.

When a stimulus molecule binds to a chemoreceptor, the chemoreceptor becomes more or less permeable to ions.

The antennae of the male silkworm moth have very sensitive specific chemoreceptors.

Slide 15

Chemoreceptors in an insect

0.1 mm

Slide 16

Electromagnetic Receptors

Electromagnetic receptors detect electromagnetic energy such as light, electricity, and magnetism. Photoreceptors are electromagnetic receptors that detect light.

Some snakes have very sensitive infrared receptors that detect body heat of prey against a colder background.

Many mammals, such as whales, appear to use Earth’s magnetic field lines to orient themselves as they migrate.

Slide 17

Specialized electromagnetic receptors

(a) Rattlesnake – infrared receptors detect body heat of prey

(b) Beluga whales sense Earth’s magnetic field – as they navigate migrations.

Eye

Infrared receptor

Slide 18