1. The Senses Classification of Sense Organs
Converting a Stimulus into a Sensation
General Sense Organs

2. Sensory receptors vary
Not just sense organs…
Millions throughout the body in skin, internal organs, muscles
Sensory receptors respond to:
Touch
Pressure
Temperature
Pain
Located at the tips of sensory neuron dendrites

3. Importance of senses
“Sense” changes in external and internal environments
Required to maintain homeostasis, survival
Initiate protective reflexes important for homeostasis

4. Classifying Sense Organs
Special sense
Large, complex organs
Localized groupings of specialized receptors in areas (nasal mucosa, tongue)
General sense
Microscopic
Widely distributed throughout the body

5. Classifying Receptors
Classified according to:
Types of stimuli that activate them
Light (photoreceptors)
Taste, smell – chemical (chemoreceptors)
Physical damage/injury (pain receptors)
Temperature (thermoreceptors)
Mechanical (mechanoreceptors)
Encapsulated or unencapsulated
Whether they are covered by some sort of capsule or not

6. Converting a Stimulus into a Sensation
All receptors must be able to sense or detect a stimulus in environment
Stimulus must be changed into an electrical signal (nerve impulse)
Generates a “receptor potential”

7. Receptor Potentials
Must reach threshold to generate an action potential in the axonal portion of the neuron
RP is a graded, decremental response (gradually diminishes)
Strength of RP depends upon which ion the membrane becomes more permeable to (Na, K)

8. Signal transmitted over nervous system “pathway” to the brain

9. 2 Types of Receptors Primary (1) Secondary (2)
Receptor membrane is part of the afferent neuron (e.g. pain receptors, Pacinian corpuscles)
Secondary (2)
Receptor membrane is a specialized sensory cell
Synapses with afferent neuron

10. General Sense Organs Found in almost every part of the body
Concentrated in the skin
Two-point discrimination
Ability to distinguish one touch stimulus from two
Clinically significant (lesions to parietal lobe impair it)
Close in the fingertips (2-8 mm)
Relatively close in palms (8-12 mm)
Far over the back (40-60 mm)

11. Stimulation type varies
Some leads to sensation of vibration
Others lead to sensation of pressure, pain, temperature
Proprioceptors
Provide information about position/movement of different parts of body
Length, extent of contraction of muscles (eye and depth perception)

12. “My leg fell asleep!”
Temporary impairment of general sense receptors happens when blood flow is slowed
Pressure of a crossed leg leads to…
“Can’t feel legs!”
“Can’t walk!”
May not be able to tell where your legs are without looking at them
Reactivation of sense organs leads to “tingling”
Can also result from diabetes, cardiovascular disease, stroke, spinal cord/brain injury

13. Make a Flip Chart
Read 10-1: General sense organs; make flip chart  with:
1. name
2. main location
3. general sense
4. picture of structure
Chapter Review: 1, 2, 3