Abdominal reflex

Definition
noun, plural: abdominal reflexes
Abdominal wall muscle contraction of the umbilicus toward the abdominal quadrant upon stimulation of the skin at the abdomen (superficial abdominal reflex) or by tapping neighboring bony structures (as in deep abdominal reflexes)
Supplement
An abdominal reflex is a reflex resulting in the contraction of abdominal muscles in the quadrant of the abdomen. This involuntary contraction of the abdominal muscles can be activated by scraping the skin tangential to or towards the umbilicus.¹ It can also be stimulated by tapping neighboring bony structures, such as in deep abdominal reflexes.
The abdominal reflex is a superficial neurological reflex, and is polysynaptic, i.e. with several neurons interposed.¹ Thoracic 7th – 12th segments are the roots involved in abdominal reflex.
The superficial reflex may be weak or absent, for example after a stroke, a sign of upper (suprasegmental) motor neuron lesions. Thus, it can be used to determine the level of lesions in a neurology case. Other factors that may lead to the absence of abdominal reflex include multiple sclerosis, neurogenic bladder, Brown-Séquard syndrome, Chiari malformations, obesity, multiparous lax abdominal wall, inguinal region and abdominal surgeries, etc.
This reflex is said to be an evolutionary advantage as a way to protect the internal viscera from damage.²
See also:

• upper abdominal periosteal reflex
• deep abdominal reflexes

Reference(s):

¹ Disorders Of The Nervous System – Reeves & Swenson. 2008. Retrieved from http://www.dartmouth.edu/~dons/part-1/chapter-8.html.

² Abdominal Reflexes. (2011). Retrieved from http://teachneuro.blogspot.com/2011/10/abdominal-reflexes.html.