1. Feedback
A response resulting from some form of input as in a reflex reaction that results from a stimulus
The source of our interaction with the physical world
Involves input which is interpreted at some neural level

2. Sources of Input
Sensory Transduction - The ability to detect and translate a stimulus.
Sensory Receptors - The systems or organs which receive specific stimuli.

3. Examples of Sensory Receptor Systems
Visual Apparatus
Vestibular apparatus – Detects the orientation of the head with respect to the direction of gravitational pull or acceleration. Found in the structure of the inner ear.
Auditory Apparatus
Sensory Nerves

4. Classification of Sensory Receptors Based on the Source of the Stimulus
Interoreceptors – Detect input from within the body
Proprioceptors – Detect input regarding the position of body parts relative to each other.
Exteroreceptors – Detect input from outside of the body.
Teloreceptors – Deal with stimuli not touching the body
Somatoreceptors – Deal with stimuli that contact the body’s surface.

5. Classification of Sensory Receptors Based on the Type of Stimulus
Chemoreceptors – Sensitive to chemicals
Taste
Smell
Detection of lower pH in blood caused by increased CO2 levels. (Results in increased breathing rate.)
Mechanoreceptors – Stimulated by mechanical forces, usually pressure
Sense of touch
Baroreceptors which detect degree of lung inflation

6. Classification of Sensory Receptors Based on the Type of Stimulus (continued)
Proprioceptors – Sense changes in the conditions of muscle and connective tissue
Muscle spindles
Golgi tendon organs
Thermoreceptors – Detect temperature changes
Pain Receptors
Also called nociceptors
Vital to detecting dangerous compromise of tissues
Photoreceptors – Detect light

7. Exteroceptive Feedback
Extensor-thrust reflex – Pressure on mechanoreceptors in the feet promotes contraction of extensors of the legs.
Provides the foundation for standing balance without conscious control
Withdrawal reflex – A protective reflex causing sudden withdrawal from a source of pain. Also called the flexor reflex.

8. Exteroceptive Feedback (continued)
Crossed-extensor reflex - .2 to .5 seconds after the flexor reflex is activated in one limb, the crossed extensor reflex produces extension in the opposite limb.
The extending limb extends to push away from the painful stimulus which caused the activation of the flexor or withdrawal reflex.

9. Cutaneous (Skin) Receptors
Detect changes in surface condition of the skin (deformation)
Near the skin’s surface (These receptors provide information about light touch and low frequency vibration):
Meissner’s corpuscles
Merkel’s discs
Ruffini corpuscles

10. Cutaneous (Skin) Receptors (continued)
Deeper receptors in the skin
Pacinian corpuscles
Respond more to deep compression and high frequency vibration

11. Receptors in the Skin

12. Meissner’s Corpuscles

13. Pacinian Corpuscle

14. Pacinian Corpuscle

15. Joint Receptors
Modified Ruffini corpuscles and Modified Pacinian corpuscles
Found in deeper tissues, joint capsules, and ligaments
Detect pressure, high frequency vibration and stretch in joint capsules and ligaments
Detect possible compromise of joint structure as well as angular position of joints

16. Applications of Proprioceptive and Exteroceptive Feedback
Relieving muscle cramps
Muscle cramps often occur in a muscle which is in an extremely shortened state
Tension in tendons actually decreases in this state
Golgi tendon activity is reduced (Golgi tendon organs reduce muscle tension in response to tension in the tendons)
EXAMPLE: Swimmers are prone to calf cramps, possibly due to prolonged plantar flexion during exercise.
Passive stretching (which would activate the Golgi tendon organs) often relieves muscle cramps

17. Applications of Proprioceptive and Exteroceptive Feedback
Stretching exercises (PNF) – Use feedback to reduce tension in muscles
Wind-up (preparative phase) – Uses the sense of stretching and acceleration in muscle tissue to increase force output in agonists and reduce antagonist resistance

18. Applications of Proprioceptive and Exteroceptive Feedback
Kinesthesis – Senses of body and limb position and velocity, joint angle, and degree of pressure and tension being applied are critical for the successful performance of many skills.
Useful for movements involving rapid changes of whole body orientation (diving, gymnastics, etc.)
Important for fine motor control (playing a musical instrument)

19. Conflicts in Input Sources
Input from vision will override information from other sensory systems.
Test subjects were placed on a surface that remained stationary while visual reference points were subtly moved.
Although the body’s sensory apparatus should have indicated that the subjects were still balanced, the subjects responded as though balance was being lost, strictly due to visual input.

20. Exercise
increases oxidative and therefore signal transmitting capacity of neurons

21. Immobilization
decreases proprioceptive feedback