The parietal pleura is supplied by the intercostal nerves and the phrenic nerve. The costal pleura is innervated by the intercostal nerves. Other tributaries include the bronchial veins, pericardial veins, and posterior right intercostal veins. It is in the same layer as the subcostal muscles and the innermost intercostal muscles. Without the rib cages, costal cartilages, and intercostal muscles, the lungs would collapse. The posterior intercostal arteries are arteries that supply blood to the intercostal spaces. During exhalation the diaphragm and intercostal muscles relax. The latter gives out the remaining anterior intercostal branches. Exhalation may be aided by the abdominal, internal intercostal and lower pelvis/pelvic muscles. The intercostobrachial nerves are cutaneous branches of the intercostal nerves. The electrical impulse follows the spinothalamic tract, which begins by innervation of fourth intercostal nerves. It protects the intercostal space containing the intercostal veins, intercostal arteries, and intercostal nerves. These rami are called the intercostal nerves. The diaphragm is less affected than the intercostal muscles. Relief can be provided by anesthetizing the relevant intercostal nerve with local anesthetic.