Reflex action and reflexes. How various reflexes have different responses

1. Reflex action and reflexes

2. • Reflexes are rapid automatic responses to stimuli
• Neural reflex involves sensory fibers to CNS and
motor fibers to effectors
An introduction to reflexes

3. Reflex arc
• Wiring of a neural reflex
• Five steps
– Arrival of stimulus and activation of receptor
– Activation of sensory neuron
– Information processing
– Activation of motor neuron
– Response by effector

4. Components of a Reflex Arc

5. Properties of reflexes
• Reflexes are automatic, unconscious to changes,
either inside or outside the body.
a. Reflexes maintain homeostasis (autonomic
reflexes) – heart rate, breathing rate, BP,
digestion.
b. Reflexes also carry out the automatic actions of
swallowing, sneezing, coughing, vomiting.
c. Reflexes maintain balance and posture; e.g.,
spinal reflexes control trunk and limb muscles.
d. Brain reflexes involve reflex center in brainstem;
e.g., reflexes for eye movement.

6. Methods of Classifying Reflexes

7. Flexor reflex and withdrawal
• Any type of cutaneous sensory stimulus from
a limb is likely to cause the flexor muscles of
the limb to contract
• Withdrawing the limb from the stimulating
object called flexor reflex
• Also called nociceptive or pain reflex

8. Neuronal mechanism of flexor reflex

9. • The pathway for eliciting the flexor reflex do
not pass directly to the anterior motor
neurons
• 1st interneuron pool of neurons
• Then to the motor neurons
Basic steps in the circuits:
a. diverging circuit to spread the reflex to the
necessary muscles for withdrawal
b. inhibit antagonist muscles
c. cause afterdischarge
 Pattern of withdrawal

12. Crossed extensor reflex
• About 0.2 to 0.5 sec after a stimulus elicits a
flexor reflex in one limb, the opposite limb
begins to extend
• Push the entire body away

14. The Flexor and Crossed Extensor
Reflexes

15. Reciprocal inhibition and innervations
• When a stretch reflex excites one muscle, it
often simultaneously inhibits the antagonist
muscles called reciprocal inhibition
• The neuronal circuit that causes this relation is
called reciprocal innervation