How Do Systems Know When to Act?
- Systems only work when they receive accurate information about what is happening inside or outside your body.
- Receptors help them detect those changes, things like temperature shifts, pressure, chemicals, or light, and alert the nervous or endocrine system.
- Once that signal arrives, the system knows exactly when to speed up, slow down, or take action.
Definition
Receptor
A specialized cell or structure that notices a change (stimulus) and sends a signal telling the body what to do next.
Tip
- Receptors are like messengers.
- They do not make decisions, they simply inform the systems so the systems can respond ("decide themselves").
What Exactly Do Receptors Detect?
- Receptors are built to detect very specific kinds of changes.
- Some look outward (light, sound, touch), others monitor your internal state (oxygen levels, temperature, pressure).
- Each type gives the body a different stream of information so systems can react in the right way.
- To help you see the pattern, here’s a quick overview:
| Receptor Type | What It Detects | Example Location |
|---|---|---|
| Photoreceptor | Light | Retina |
| Chemoreceptor | Chemicals, CO₂ | Nose, tongue, blood vessels |
| Mechanoreceptor | Pressure, vibration | Skin, inner ear |
| Thermoreceptor | Temperature | Skin, hypothalamus |
| Nociceptor | Pain | Throughout the body |
Note
- Understand how "form follows function" and the idea of specialization applies here too:
- Photoreceptors respond to light because they contain light-sensitive pigments.
- Mechanoreceptors respond to pressure because they have stretch-sensitive membranes.
- Trying to detect everything would make receptors slow and unreliable, so the body uses specialists instead.
How Do Receptors Convert Stimuli Into Signals?
Definition
Transduction
The process in which receptors turn a stimulus into an electrical or chemical signal the body can interpret.
- The basic idea of transduction is that once a stimulus hits the receptor, the receptor changes its electrical activity, which causes a signal to be sent onward.
- That signal travels through nerves or hormone pathways until it reaches the brain or spinal cord.
- At that point, the body decides what to do, such as adjusting breathing rate or releasing hormones.
- This is how a tiny external or internal change becomes a full-body response.
How Do Receptors Guide Growth, Development, and Life Cycles?
- Receptors do more than just sense the environment, they also control long-term processes inside the body.
- Hormone receptors guide growth, puberty, and repair.
- In plants, receptors detect light and gravity to guide seedling growth and flowering.
- These responses shape the entire life cycle of an organism.
| Process | Receptor Involved | Outcome |
|---|---|---|
| Blood glucose control | Insulin receptors | Cells absorb glucose |
| Plant growth direction | Light receptors | Shoots grow toward light |
| Puberty | Hormone receptors | Development of adult traits |
| Temperature regulation | Thermoreceptors | Sweating or shivering |
Self review
- How do receptors help systems decide when to act?
- What is a stimulus, and how do receptors detect one?
- What is the purpose of transduction?
- Why does the body use different receptors for different stimuli?
- Give one example each of an internal receptor and an external receptor.
- How do receptors influence growth and development?
- Why would an organism struggle to survive without functioning receptors?
