Reflexes Interactive (pgs.439-446)

1. ReflexesInteractive (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 ExamplePatellar 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 ReflexesPlantar 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.