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Reflexes

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  • 1. REFLEXES
  • 2. Actions performed automatically in response to a stimulus without conscious thought or decision are called reflex actions or reflexes.
    • Simple reflex actions are handled by the spinal cord without involvement of the brain.
    • Other reflexes are carried out in various relay centers in the lower brain or brainstem , but no conscious thought is involved.
    • Reflex actions carried out by the spinal cord occur automatically, but at the same time as the reflex occurs, sometimes a signal is sent to the brain by a connecting interneuron. When this happens, a stimulus is processed by the spinal cord as an arc and a response is sent back to the periphery, but a signal is also sent to the brain for interpretation and additional reaction .
  • 3. Examples of each of these are:   a. Knee jerk response (simple/spinal cord only)
  • 4. b. Sneezing – one of the reflex centers in the medulla (involves brainstem activity only)
  • 5. c. Hand on a hot stove – a simple reflex pulls the hand away (spinal cord arc only, no brain involvement) followed by a reaction due to an interneuron connection to the brain from the spinal cord.
  • 6. **optional
    • The systems described above represent the simplest units of the nervous system and are called reflex arcs . There are 5 parts to these:
    •   1. Sensory receptor(s) is/are stimulated.
    • Sensory neuron(s) send(s) message to the spinal cord.
    • ** Interneuron(s) in CNS transmit the message to one or more motor neurons.
    • Motor neurons transmit the message to the effector.
    • Effector (muscle) is stimulated.