The Sensory system reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Sensory system

A sensory system is a part of the nervous system that consists of sensory receptors, neural pathways, and those parts of the brain responsible for processing the information. Specific sensory systems are thise for somatic sensation, vision (sense), and hearing (sense).

Functions

Coding

Sensory systems code for four aspects of a stimulus; type (modality), intensity, location, and duration.

Modality

There are many stimulus modalities; temperature, taste, sound, pressure.

The type of sensory receptor activated by a stimulus plays the primary role in coding the stimulus modality.

Human sensory system

Human receptors are:

• thermoreceptors
• photoreceptors
• mechanosensors
• chemosensors

All the 5 types of sensors contain protein channels.

Mechanosensor:

• Has deformed protein when subjected to pressure
• Stretch receptors
• Nerve sense the stretch of muscle cells or tendons
• Stretching of the nerve cell membrane physically opens sodium channels

 which polarizes the membrane (increase in cell voltage).

Thermoreceptor:

• In our skin (dermis), bare nerve endings sense temperature
• Snake has pit organ to response to temperature with accuracy.

Chemosensors: Two main classes

1. Direct: taste, bood sensors
2. Distance: smell, antennae

Photosensor in eyes:

• In insects such as fly has compound eyes that its own retina in each of the lens.
• In camera-type eye in human, light goes through retina. Adjustment is made by changing the length of lens
• Human have high resolution and lower feel of motion while compound eyes are in opposite.

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