Chief inspiratory muscle is:

Ans: a (Diaphragm) Ref: BDC, 4th ed, Vol. II, p. 311Diaphragm is the chief muscle of inspiration. On contraction, it descends, increasing the vertical diameter of the thorax. (Max. excursion: 6-10 cm)DiaphragmNerve supply: Motor: Phrenic nerve (C-3, 4, 5)Sensory: Lower six thoracic nervesActions: 1) Principal muscle of inspiration2) Acts in all expulsive acts to give additional power3) Right crus has a sphincteric action on the lower end of the oesophagus.Structures passing through the DiaphragmT12- Aortic openingT10- Oesophageal openingT8- Vena caval opningAortaAzygos veinThoracis ductOesophagusVagus nerveEsophageal branch of leftGastric arteryIVCRt. phrenic nerveSmall openings* Each crus is pierced by the greater and lesser splanchnic nerves* Lt. crus is pierced by the (a) hemiazygos vein (b) Lt. phrenic nerve* Sympathetic chain- behind the medial arcuate ligament* Subcostal nerves and vessels- behind the lateral arcuate ligament* Larry sSpace (Space of Morgagni)- Superior epigastric vessels; this space lies between the xiphoid process and costal cartilage* Musculophrenic vessels- pierce at the level of the 8th and 9th costal cartilage