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

Sources of Input

• Sensory Transduction - The ability to detect and translate a stimulus.

• Sensory Receptors - The systems or organs which receive specific stimuli.

Examples of Sensory Receptor Systems

1.Visual Apparatus 2.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.

3.Auditory Apparatus4.Sensory Nerves

Classification of Sensory Receptors

Based on the Source of the Stimulus 1. Interoreceptors – Detect input from within the

body2. Proprioceptors – Detect input regarding the

position of body parts relative to each other.3. Exteroreceptors – Detect input from outside of

the body.a) Teloreceptors – Deal with stimuli not touching the

bodyb) Somatoreceptors – Deal with stimuli that contact the

body’s surface.

Classification of Sensory Receptors Based on the Type of Stimulus

1. Chemoreceptors – Sensitive to chemicals

a) Taste

b) Smell

c) Detection of lower pH in blood caused by increased CO2 levels. (Results in increased breathing rate.)

2. Mechanoreceptors – Stimulated by mechanical forces, usually pressure

a) Sense of touch

b) Baroreceptors which detect degree of lung inflation

Classification of Sensory Receptors Based on the Type of Stimulus

(continued)3. Proprioceptors – Sense changes in the conditions of

muscle and connective tissue

a) Muscle spindles

b) Golgi tendon organs

4. Thermoreceptors – Detect temperature changes

5. Pain Receptors

a) Also called nociceptors

b) Vital to detecting dangerous compromise of tissues

6. Photoreceptors – Detect light

Exteroceptive Feedback

1. 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

2. Withdrawal reflex – A protective reflex causing sudden withdrawal from a source of pain. Also called the flexor reflex.

Exteroceptive Feedback (continued)

3. 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.

Cutaneous (Skin) Receptors

• Detect changes in surface condition of the skin (deformation)

1. Near the skin’s surface (These receptors provide information about light touch and low frequency vibration):

a) Meissner’s corpusclesb) Merkel’s discsc) Ruffini corpuscles

Cutaneous (Skin) Receptors (continued)

2. Deeper receptors in the skin– Pacinian corpuscles– Respond more to deep compression and high

frequency vibration

Receptors in the Skin

Meissner’s Corpuscles

Pacinian Corpuscle

Pacinian Corpuscle

Joint Receptors

1. Modified Ruffini corpuscles and Modified Pacinian corpuscles

a) Found in deeper tissues, joint capsules, and ligaments

b) Detect pressure, high frequency vibration and stretch in joint capsules and ligaments

c) Detect possible compromise of joint structure as well as angular position of joints

Applications of Proprioceptive and Exteroceptive Feedback

1. Relieving muscle cramps• Muscle cramps often occur in a muscle which is in an

extremely shortened statea) Tension in tendons actually decreases in this state

b) Golgi tendon activity is reduced (Golgi tendon organs reduce muscle tension in response to tension in the tendons)

c) EXAMPLE: Swimmers are prone to calf cramps, possibly due to prolonged plantar flexion during exercise.

d) Passive stretching (which would activate the Golgi tendon organs) often relieves muscle cramps

Applications of Proprioceptive and Exteroceptive Feedback

2. Stretching exercises (PNF) – Use feedback to reduce tension in muscles

3. Wind-up (preparative phase) – Uses the sense of stretching and acceleration in muscle tissue to increase force output in agonists and reduce antagonist resistance

Applications of Proprioceptive and Exteroceptive Feedback

4. 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.

a) Useful for movements involving rapid changes of whole body orientation (diving, gymnastics, etc.)

b) Important for fine motor control (playing a musical instrument)

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.

Exercise

• increases oxidative and therefore signal transmitting capacity of neurons

Immobilization

• decreases proprioceptive feedback