This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
In spinal anaesthesia the drug is deposited between 
Select and explain. 
A. Dura and arachnoid, B. Pia and arachnoid, C. Dura and veebra, D. Into the cord substance
B: Pia and arachnoid
Answer: B: Pia and arachnoid 
Explanation: Ans. is 'b' i.e., Pia and arachnoid matter Spinal anaesthesia In spinal anaesthesia LA is injected into subarachnoid space (space between pia matter and arachnoid matter). Structure pierced during SA (from outside in) - Skin - Subcutaneous tissue --> Supraspinous & intraspinous ligament --> Ligamentum falvum --> Duramater -->Arachnoidmater. Site of spinal anaesthesia L2_3 or L3_4 interveebral space in adult (In adult spinal cord ends at lower border of Ll veebrae). L4_5 interveebral space in children (spinal cord ends at lower border of L3 veebrae in children). Spinal anaesthesia leads to creation of a zone of differential blockade, ie motor fibres are blocked two levels lower and autonomic fibres are blocked two levels higher than the sensory blockade due to different sensitivity of different fibres.