All about sensory organs

1. Sensory receptor
• A major role of sensory receptors is to help us learn about the
environment around us, or about the state of our internal
environment.
• Different types of stimuli from varying sources are received and
changed into the electrochemical signals of the nervous system.
This process is called sensory transduction.
• This occurs when a stimulus is detected by a receptor which
generates a graded potential in a sensory neuron.
• If strong enough, the graded potential causes the sensory neuron to
produce an action potential that is relayed into the central nervous
system (CNS), where it is integrated with other sensory
information—and sometimes higher cognitive functions—to
become a conscious perception of that stimulus. The central
integration may then lead to a motor response.

2. sensory receptors may be:
– a) neurons (distal tip of peripheral axon of sensory neuron) –
e.g. in skin receptors.
– b) specialized cells (that release neurotransmitter and generate
action potentials in neurons) – e.g. in complex sense organs
(vision, hearing, equilibrium, taste).
• sensory receptor is often associated with nonneural cells
that surround it, forming SENSE ORGAN.
• to stimulate receptor, stimulus must first pass through
intervening tissues (stimulus accession).
• each receptor is adapted to respond to one particular form
of energy at much lower threshold than other receptors
respond to this form of energy.

4. Classification of sense organ
According to stimulus source:
• 1. Exteroceptors - concerned with external environment.
– teleceptors ("distance receivers") - concerned with external events at
distance (e.g. light, sound).
• 2. Interoceptors (s. enteroceptors) - concerned with internal
environment (e.g. chemoreceptors, baroreceptors, proprioceptors
According to stimulus energy:
• 1. Mechanoreceptors (e.g. skin deformation, pressure, sound).
• 2. Photoreceptors
• 3. Thermoreceptors
• 4. Chemoreceptors - receptors that are stimulated by chemical
environment composition (e.g. taste, smell, level of O2, pH,
osmolality).
• 5. Nociceptors - pain receptors.

5. Nervous system
• The function of the nervous system is to CONTROL
and COORDINATE the body
• The nervous system consists of 2 parts:
• CENTRAL NERVOUS SYSTEM
a. Brain
b. Spinal Cord
• PERIPHERAL NERVOUS SYSTEM
Nerves and sensory receptors

6. Stimulus
• A thing or event that causes an organism to
react

7. Neuron
• Nerve cell
• Carries messages through impulses
• They send messages from the brain to the other
parts of the body
• They can carry messages from the body to the brain
• Contain receptor molecules that respond to
external stimuli

8. 3 types of sensory receptor
1. Electromagnetic
2. Mechanical
3. Chemical

9. Electromagnetic receptor
• Sense waves of light, heat, electricity and
magnetic fields
• Picked up by sensors in the retina of the eyes
• Color is picked up by nerve cells called cones
• Brightness is picked up by nerve cells called
rods
• Messages are sent from the optic nerve to the
brain

11. Mechanical receptor
• Allow organisms to sense movement
• Hearing and touch
• Hair cells in our ears sense sound waves
• Motion in the body: position of bones,
muscles and joints
• Receptors pick up the sound or touch and
send message to the brain

13. Chemical receptor
• Sense smelling (olfactory sensation) and tasting
(gustatory sensation)
• Olfactory glands help our nose sense a variety of
smells and send messages to the brain.
• Memories are associated with smells and tastes.