MAVO Year 4 · Senses · Section 11.1

The sensory system

What are sensory organs?

Sensory organs contain receptors detecting particular kinds of stimuli. Taste receptors respond to dissolved chemicals, while visual receptors respond to light. Together with sensory pathways, these structures form the sensory system. Receptors also detect changes inside the body.

How are impulses produced?

A receptor converts a stimulus into an electrical change. If activity reaches a sufficient level, nerve impulses arise in the sensory pathway. The minimum stimulus strength needed for a particular response is its threshold.

Each receptor is particularly sensitive to one kind of stimulus, its adequate stimulus. The threshold for this is relatively low. An unusually strong stimulus of another kind can sometimes activate a pathway, such as pressure on the eye producing a sensation of light.

Adaptation, attention and perception

Perception is influenced by more than the physical stimulus.

• Sensory adaptation: During a continuing stimulus, some receptors or sensory pathways respond less strongly. This helps explain why a constant sensation, such as clothing touching the skin, becomes less noticeable.
• Attention and motivation: Focusing on information can make it easier to notice. This involves processing in the nervous system, rather than simply making every receptor more sensitive.
• Brain processing: Incoming signals are interpreted alongside other information and experience, influencing awareness and response speed.

Sensory adaptation and learned habituation both reduce responses but are not exactly the same process.