5.7.4 Sensory Receptors and Their Working

Sensory receptors are specialized structures that detect changes in the internal and external environment. They convert various forms of energy (light, sound, chemicals, pressure, temperature) into electrical signals that the nervous system can process. This topic covers olfactory receptors (smell), taste receptors (taste), and touch/pain receptors.

Definition

Sensory Receptors: Sensory receptors are specialized structures that detect changes in the internal and external environment and convert them into electrical signals (nerve impulses).

Olfactory Receptors: Olfactory receptors are chemoreceptors stimulated by chemicals dissolved in liquids. They are located in the upper part of the nasal cavity.

Taste Receptors: Taste receptors are chemoreceptors located in taste buds on the surface of the tongue.

Main Idea

• The body must detect what is occurring inside and outside the body.
• This is performed by sensory receptors.
• Sensory receptors detect stimuli and convert them into nerve impulses.
• This topic covers:

Core Concept

• Sensory receptors = detect changes; convert energy into electrical signals
• Olfactory receptors = chemoreceptors; smell
• Taste receptors = chemoreceptors; taste
• Touch receptors = mechanoreceptors; touch
• Pain receptors = nociceptors; pain
• Chemoreceptors = stimulated by chemicals
• Mechanoreceptors = stimulated by mechanical pressure
• Thermoreceptors = stimulated by temperature
• Nociceptors = stimulated by pain

Detailed Explanation

Olfactory Receptors

• The smell or olfactory receptors are chemoreceptors, stimulated by chemicals dissolved in liquids.
• The olfactory organs, which contain the olfactory receptors, are present in the upper part of the nasal cavity.
• The olfactory receptor cells are neurons.
• These cells are surrounded by columnar epithelial cells having cilia at the distal ends.
• Chemicals that stimulate the olfactory receptors enter the nasal cavity as gases.
• They must dissolve at least partially in the water fluids that surround the cilia before they can be detected.

Taste Receptors

• Taste buds occur primarily on the surface of the tongue and are associated with tiny elevations called papillae.
• Each taste bud includes a group of modified epithelial cells, the taste cells, which function as receptors.
• The taste bud has an opening, the taste pore on its surface.
• Tiny projections, called taste hairs, protrude from outer ends of taste cells and just protrude through the taste pore.
• There are four primary taste sensations:
• These are situated at various regions on the tongue.
• All the four regions overlap at certain places.

Touch and Pain Receptors

The skin contains several types of sensory receptors that detect touch, pressure, temperature, and pain.

Summary Table of Sensory Receptors

Summary of Taste Sensations

Note: All four regions overlap at certain places.

Intermediate Level

Olfactory Receptors

Taste Receptors

Taste Sensations

Touch and Pain Receptors

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Sensory receptors detect changes in the environment.
• 2. They convert energy into electrical signals.
• 3. Olfactory receptors are chemoreceptors.
• 4. Olfactory receptors are in the upper part of the nasal cavity.
• 5. Olfactory receptor cells are neurons.
• 6. Olfactory receptor cells are surrounded by columnar epithelial cells with cilia.
• 7. Chemicals must dissolve in water fluids to be detected.
• 8. Taste receptors are chemoreceptors.
• 9. Taste receptors are in taste buds on the tongue.
• 10. Taste buds are associated with papillae.
• 11. Taste cells are modified epithelial cells.
• 12. Taste bud has a taste pore.
• 13. Taste hairs protrude through the taste pore.
• 14. Four primary taste sensations: sweet, sour, salty, bitter.
• 15. Taste regions overlap at certain places.
• 16. Touch receptors are mechanoreceptors.
• 17. Thermoreceptors detect temperature.
• 18. Nociceptors detect pain.
• 19. Proprioceptors detect body position.
• 20. All receptors send signals to the brain.

Remember

• - Sensory receptors = detect changes; convert energy into electrical signals
• - Olfactory receptors = chemoreceptors; smell; upper nasal cavity
• - Taste receptors = chemoreceptors; taste; taste buds on tongue
• - Touch receptors = mechanoreceptors; touch
• - Pain receptors = nociceptors; pain
• - **Thermoreceptors** = temperature
• - Proprioceptors = body position
• - Four primary tastes = sweet, sour, salty, bitter
• - Taste regions overlap = at certain places

Common Mistakes

• 1. Confusing olfactory and taste receptors — Olfactory = smell; taste = taste.
• 2. Thinking taste buds are only on the tongue — Taste buds are primarily on the tongue but also in other areas.
• 3. Forgetting that chemicals must dissolve — Chemicals must dissolve in liquids to be detected.
• 4. Mixing up the taste sensations — Sweet, sour, salty, bitter.
• 5. Thinking taste regions are separate — They overlap.
• 6. Confusing mechanoreceptors and thermoreceptors — Mechanoreceptors = touch/pressure; thermoreceptors = temperature.
• 7. Forgetting the role of nociceptors — They detect pain.
• 8. Mixing up the locations — Olfactory = nasal cavity; taste = tongue.
• 9. Thinking all receptors are chemoreceptors — Some are mechanoreceptors, thermoreceptors, nociceptors.
• 10. Believing receptors do not convert energy — They convert energy into electrical signals.

Quick Revision

The body must detect what is occurring inside and outside the body and is performed by sensory receptors. The smell or olfactory receptors are chemoreceptors, stimulated by chemicals dissolved in liquids. The olfactory organs, which contain the olfactory receptors, are present in the upper part of the nasal cavity. The olfactory receptor cells are neurons. These cells are surrounded by columnar epithelial cells having cilia at the distal ends. Chemicals that stimulate the olfactory receptors enter the nasal cavity as gases. They must dissolve at least partially in the water fluids that surround the cilia before they can be detected. Taste buds occur primarily on the surface of the tongue and are associated with tiny elevations called papillae. Each taste bud includes a group of modified epithelial cells, the taste cells, which function as receptors. The taste bud has an opening, the taste pore on its surface. Tiny projections, called taste hairs, protrude from outer ends of taste cells and just protrude through the taste pore. There are four primary taste sensations i.e., sweet, sour, salty and bitter, which are situated at various regions on the tongue. All the four regions overlap at certain places.

60-Second Revision

• Sensory receptors = detect changes; convert energy into electrical signals
• Olfactory receptors = chemoreceptors; smell; upper nasal cavity
• Taste receptors = chemoreceptors; taste; taste buds on tongue
• Touch receptors = mechanoreceptors; touch
• Pain receptors = nociceptors; pain
• Thermoreceptors = temperature
• Proprioceptors = body position
• Four primary tastes = sweet, sour, salty, bitter
• Taste regions overlap = at certain places
• Warning: Chemicals must dissolve in liquids to be detected by olfactory and taste receptors

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