begin{tikzpicture}
 node (a) at (0pt,0pt)[]{$a$};
 node (b) at (0pt,101pt)[]{$b$};

 draw[->] (a)--(b);
 draw[->] (b) arc [start angle=0, end angle=74, x radius=25pt, y    radius=25pt,line width=4pt] node (c) {$c$};
end{tikzpicture}