why axolemma shows +ve charge outside n -ve charge inside ?
The axolemma is positively charged outside and negatively charged inside due to sodium-potassium ion pump. More sodium ions are present outside as compared to inside and similarly more potassium ions and chloride ions are present inside compared to outside which contributes to the negative membrane inside. During rest, potassium ions are more permeable as compared to sodium ions making outside more positively charged. But during rest sodium ions are not permeable to inside this makes inside negatively charged, as charges are only contributed by potassium ions inside the axolemma.
The axolemma has channels that are freely permeable to K+ ions but are almost impermiable to Na+ ions and negatively charged proteins. Therefore Na+ ions are not allowed to enter the axolemma and negatively charged protein molecules are not allowed to escape. This results in accumulation of positive charge outside the axolemma (due to Na+ ions) and a negative charge inside (due to the negatively charged proteins).