Reflex

Reflex

• Maintain homeostasis 
• Automatic action 
• Maintain balance and posture 
• Brain reflex center in brain stem 

Class:

• Development: innate & acquire
• Response: somatic & visceral
• Complexity of circuit: mono & polysynaptic 
• Processing site: spinal & cranial 

Polysynaptic:

Golgi tendon 

• Monitor tension during contraction 
• Prevent tear or break of tendon 
• Stimulate receptor when stretch to dangerous degree 
• Greater tension greater inhibitory effect on motor neurons 

Withdrawal 

Move affected part away from stimulus 

• Flexor contract 
• Extensor relax 

Crossed extensor 

• Contralateral + flexor 
• Flexor contract 
• Extensor relax 
• Crossed extensor occurs simultaneously同时发生, excitatory interneurons stimulate extensor, inhibitory interneurons relax flexor, leg straighten support shift in weight 

Reflex assessment 

Babinski 

• Dorsiflexion, plantar flexion, spreading of toes
• Occurs due to lack of inhibition by descending motor fibers 
• Absence is damage to corticospinal tract 

Abdominal 

• Move navel towards stimulus 
• Absence is damage to descending tracts