Reflex

1. Reflex The word reflex comes from the Latin word reflexus which means “to reflect” Term introduced by 19th century neurologist Marshall Hall who thought muscles reflected a stimulus as a wall reflects a ball thrown against it.

2. Reflexes • Physical actions resulting from specific stimuli • Don’t involve conscious activity • Produce stereotyped, immediate responses • If a stimulated response requires any thought or analysis it is not a reflex. It is a conditioned response (EXAMPLE: Pavlovian response). (Reflex functions take place in the spinal cord and lower brain but not at the higher brain or cerebral cortex.)

3. Reflexes (continued) • Innate forms of behavior that are genetically inherited • Form the basis of much of what is considered instinctive behavior

4. Reflex Behavior Can Be Altered • When a stimulus is repeated regularly, two changes occur in the response • Sensitization – An increase in reflex response • Habituation – A decrease in reflex response

5. Sensitization • Generally occurs in the first 10 – 20 responses • Implies an increased sensitivity to the stimulus that causes the response

6. Habituation • Sometimes called desensitization • Occurs after a large number (greater than 20) regular occurrences of the stimulus • Results in a reduced level of response to the stimulus • When the repetition of the stimulus is irregular, habituation doesn’t occur

7. Reflex Suppression • Reflex responses can often be controlled or suppressed by signals from higher levels of the central nervous system Examples: The cough reflex can be suppressed fairly easily The gag reflex can be suppressed with training

8. Reflex Arc The anatomical path of reflex action Concept introduced in the 1800s Defined by John Dewey (1896) Outlines the coordinated connection and pathway between sensory input and motor response A biological basis of the study of social behaviorism in psychology Provided the foundation of the modern usage of the term “attitude” in behavioral sciences

9. Reflex Arc (continued) • Components • Receptors – Afferent or sensory organs that receive stimuli. (Receptors RECeive a stimulus) • Afferent Neurons – The neural pathways from the receptors to the central nervous system. • Interneurons or Internuncial Neurons – Neural connections between the Afferent and Efferent Neurons. Found in the spinal chord or brainstem. (inter = between nuncia = messenger) • Efferent Neurons – Nerves (motor, secretory, or secreto-motor nerves) that transmit the reflex response. • Effector Organs – Stimulate or produce reflex action. (Effectors produce an EFFECT or response)

10. Reflex Arc (continued)

11. Reflex Arc (continued) EXAMPLE: Withdrawal Reflex (A protective response to pain) Touching a hot surface with the hand causes an involuntary withdrawal of the affected limb.

12. Reflex Arc (continued) Cause – The hand touches a hot surface. Sensation – Pain signals are generated by receptors in the hand. Stimulus Transmission – Pain information is transmitted to the spinal cord where the signal is interpreted.

13. Reflex Arc (continued) Action Transmission – Response information is transmitted to the appropriate efferent motor neurons. Response – The hand is rapidly withdrawn in response to signals by the effectors in the arm.

14. Feedback • Reflexes comprise a feedback mechanism. • Important for a variety of protective and survival functions.