The fill3 command can be used to create the surface between your line and the y-axis. The fliplr command is used to make sure the surface vertices are in the correct order. Here's a small example for an arbitrary line.
% Original Line
x1 = linspace(0,pi/2,10);
y1 = linspace(0,pi/2,10);
z1 = sin(linspace(0,pi/2,10));
%
% Y-Axis
x2 = zeros(size(x1));
y2 = y1;
z2 = zeros(size(x1));
%
% Surface between lines
xs = [x1 fliplr(x2)];
ys = [y1 fliplr(y2)];
zs = [z1 fliplr(z2)];
%
figure(1)
plot3(x1,y1,z1,x2,y2,z2)
hold on
fill3(xs,ys,zs,'r','FaceAlpha',0.5);
grid on
xlabel('X axis')
ylabel('Y axis')
zlabel('Z axis')
hold off
