(See also sense)

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 those for somatic sensation, vision, olfaction, taste and hearing.

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
• mechanoreceptors
• chemosensors

All four types of sensors contain protein channels.

Mechanosensors:

• Hair cells in the cochlea are a type of mechanosensor that responds to vibrations caused by sound waves.
• Muscle spindles sense the stretch of muscle cells or tendons
• In the somatosensory system, pressure is transduced by stretching of the neuron membrane physically, opening sodium channels which polarizes the membrane (increase in cell voltage).

Thermoreceptor:

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

Chemosensors: Two main classes

1. Direct: eg blood sensors, taste bud
2. Distance: eg antennae, olfactory receptor neuron

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 the 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.