1. Reflexes Interactive (pgs.439-446)

2. Development of Reflexes
A reflex is a rapid, predictable motor response to a stimulus.
Innate reflexes are unlearned and involuntary
Acquired reflexes are complex, learned motor patterns

3. Nature of Reflex Responses
Somatic: involve skeletal muscles and somatic motor neurons.
Autonomic (visceral) Reflexes controlled by autonomic neurons
Heart rate, respiration, digestion, urination, etc
Spinal reflexes are integrated within the spinal cord gray matter while cranial reflexes are integrated in the brain.
Reflexes may be monosynaptic or polysynaptic

5. Components of a Reflex Arc
1. Activation of a Receptor: site of stimulus
2. Activation of a Sensory Neuron: transmits the afferent impulse to spinal cord (CNS)
3. Information processing at the Integration center: synapses (monosynaptic reflexes) or interneurons (polysynaptic) between the sensory and motor neurons.
In CNS
Spinal reflexes or cranial reflexes

6. Components of a Reflex Arc
4. Activation of a Motor Neuron: transmits the efferent impulse to effector organ
5. Response of a peripheral Effector: Muscle or gland that responds

7. Interneuron

8. Spinal Reflexes 4 important somatic spinal reflexes Stretch Tendon
Flexor(withdrawal)
Crossed extensor reflexes

9. Stretch Reflexes
1. Stretching of the muscle activates a muscle spindle (receptor)
2. An impulse is transmitted by afferent fibers to the spinal cord
3. Motor neurons in the spinal cord cause the stretched muscle to contract
4. The integration area in the spinal cord
Polysynaptic reflex arc to antagonist muscle causing it to to relax (reciprocal innervation)

10. Notice hammer
Stretch Reflex

11. Stretch Reflex Example Patellar Reflex
Tap the patellar tendon
muscle spindle signals stretch muscle
motor neuron activated & muscle contracts
Quadriceps muscle contracts
Hamstring muscle is inhibited (relaxes)
Reciprocal innervation (polysynaptic- interneuron)
antagonistic muscles relax as part of reflex
Lower leg kicks forward
Demonstrates sensory and motor connections between muscle and spinal cord are intact.

12. Tendon Reflexes
Monitors external tension produced during muscular contraction to prevent tendon damage
Controls muscle tension by causing muscle relaxation
Golgi tendon organs in tendon (sensory receptor)
activated by stretching of tendon
inhibitory neuron is stimulated
motor neuron is hyperpolarized and muscle relaxes
Both tendon & muscle are protected
Reciprocal innervation (polysynaptic)
causes contraction
Martini pg 443 states the receptor is unidentified; this is incorrect.

13. Notice no hammer
Tendon Reflex

14. Flexor Reflex Withdrawal reflex
When pain receptors are activated it causes automatic withdrawal of the threatened body part.

15. Flexor (Withdrawal) Reflex
Is this a monosynaptic or a polysynaptic reflex?

16. Crossed Extensor Reflex
Complex reflex that consists of an ipsilateral(same side) withdrawal reflex and a contralateral(opposite side) extensor reflex
This keeps you from falling over, for example if you step on something painful. When you pull your foot back, the other leg responds to hold you up.

17. Crossed Extensor Reflex

18. Superficial Reflexes Elicited by gentle cutaneous stimulation
Important because they involve upper motor pathways (brain) in addition to spinal cord neurons

19. Superficial Reflexes Plantar Reflex
Tests spinal cord from L4 to S2
Indirectly determines if the corticospinal tracts of the brain are working
Draw a blunt object downward along the lateral aspect of the plantar surface (sole of foot)
Normal: Downward flexion (curling) of toes

20. Plantar Reflex
Normal
Abnormal
(Babinski’s)

21. Abnormal Plantar Reflex: Babinski’s Sign
Great toe dorsiflexes (points up) and the smaller toes fan laterally
Happens if the primary motor cortex or corticospinal tract is damaged
Normal in infants up to one year old because their nervous system is not completely myelinated.