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The intercostal nerves are part of the somatic nervous system, and arise from the anterior rami of the thoracic spinal nerves from T1 to T11. [1] [2] The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum, and differ from the anterior rami of the other spinal nerves in that each pursues an independent course without plexus formation.
In the abdomen, general visceral afferent fibers usually accompany sympathetic efferent fibers. This means that a signal traveling in an afferent fiber will begin at sensory receptors in the afferent fiber's target organ, travel up to the ganglion where the sympathetic efferent fiber synapses, continue back along a splanchnic nerve from the ganglion into the sympathetic trunk, move into a ...
These pierce the intercostales externi and the obliquus externus abdominis, in the same line as the lateral cutaneous branches of the upper thoracic nerves, and divide into anterior and posterior branches, which are distributed to the skin of the abdomen and back; the anterior branches supply the digitations of the obliquus externus abdominis ...
With each segment, there is a pair of sensory and motor nerves. 31 segments of nerves are in the spinal cord and 12 are in the brain stem. [4] Interneurons also known as association neurons are present throughout the central nervous system forming links between the sensory and motor fibres. [5] Thus the somatic nervous system consists of two parts:
An abdominal reflex is a superficial neurological reflex stimulated by stroking of the abdomen around the umbilicus. It can be helpful in determining the level of a central nervous system (CNS) lesion. Being a superficial reflex, it is polysynaptic (involving multiple connections between nerves). [1]
Anterior cutaneous nerve entrapment syndrome (ACNES) is a nerve entrapment condition that causes chronic pain of the abdominal wall. [1] It occurs when nerve endings of the lower thoracic intercostal nerves (7–12) are 'entrapped' in abdominal muscles, causing a severe localized nerve (neuropathic) pain that is usually experienced at the front of the abdomen.
The ventral rami of L1–L5 spinal nerves with a contribution of T12 form lumbar plexus. This plexus lies within the psoas major muscle. Nervi of the plexus serve the skin and the muscles of the lower abdominal wall, the thigh and external genitals. The largest nerve of the plexus is the femoral nerve.
Therefore, visceral afferent information traveling to the spinal cord can present in the distribution of the somatic afferent nerve; this is why appendicitis initially presents with T10 periumbilical pain when it first begins and becomes T12 pain as the abdominal wall peritoneum (which is rich with somatic afferent nerves) is involved. [17]