The document discusses the classification of sensory organs and how sensory systems function. It details the types of receptors that detect various stimuli, including chemoreceptors for taste and smell, thermoreceptors for temperature, and mechanoreceptors for pressure and touch. Additionally, it describes the structure of receptors and their specific responses to different forms of energy.

1. SENSORY ORGANS:
CLASSIFICATION OF
RECEPTORS-1
S.K. SAIKIA
Department of Zoology
Visva-Bharati

3. HOW SENSORY SYSTEM WORK
From www.jagranjosh.com

5. Sensations takes place when..
 Stimuli initiate afferent impulses
 That eventually reach a conscious level in the
cerebral cortex
 All sensations involve receptor organs
 Simplest receptor organs are bare nerve
endings

6. What are the Sensations we
feel?
 Pain
 Temperature
 Pressure
 Touch
Special Senses
Sight
Hearing
Taste
Smell
Orientation in space

7. Sensory Receptor
 Peripheral component of an afferent
axon and the centrally located nerve cell
body of that axon.
 Convert different types of energy into
nerve signals (sound, light, thermal,
chemical, and mechanical).
 Generally receptors are specific and only
respond to one form of energy.

8.  Sensory receptors are specialized epidermal
cells that respond to environmental stimuli
and consist of structural and support cells
that produce the outward form of
the receptor, and the internal neural
dendrites that respond to specific stimuli.

9. Different types of receptors
include:
 Chemoreceptors
 Pain receptors
 Thermoreceptors
 Mechanoreceptors
 Photoreceptors

10. Types of sensory receptors
(based on structure)
 Free nerve endings or dendrites
 Encapsulated nerve endings
 Specialised receptor cells

11. Free Nerve Endings
From: Wikimedia Commons
From: Slide player

12. Functions of Free Nerve endings
• Free nerve endings can detect temperature,
mechanical stimuli (touch, pressure, stretch)
or danger (nociception). Its overall function is
to respond to superficial pain and touch.

13. Encapsulated Nerve Endings
From Slideplayer.com

14. From Quora.com

15. From Slideplayer.com

16. Specialised receptor cells
• Specialized receptor cells have distinct
structural components that interpret a specific
type of stimulus
• The cells in the retina that respond to light
stimuli are an example of a specialized
receptor cell, a photoreceptor.

17. From mammothmemory.net

18. From mammothmemory.net

20.  CHARACTERISTICS OF RECEPTORS:
 first-order neuron of olfactory pathway
 tips are protected by olfactory hairs
 stimulated by odorants; inhaled chemicals
 cells live about a month and then replaced
OLFACTION: SENSE OF
SMELL (Chemoreceptors)

21. OLFACTION: SENSE OF SMELL

22. GUSTATION:
SENSE OF TASTE

23. • CHARACTERISTICS OF
RECEPTORS:
– chemicals known as
tastants stimulate them
– electrical signal stimulate
release of neurotransmitter
molecules that bind to
gustatory receptors on
dendrites of taste buds’
first-order neurons
– respond to any one of five
primary tastes: sweet, sour,
bitter, salty, or umami
(savory, glutamate
detection)
1. bitter, 2. salty,
3. sour, 4. sweet
GUSTATION: SENSE OF
TASTE (Chemoreceptors)

24. Muscles of the Eye