You can add vertical lines using xline:
% create sample data
x = 1:2544;
y = rand(1,length(x));
% store indices that will be plotted
inds = 1:30:length(x);
% store indices of every 7th point (starting at 8th)
inds_7 = inds(8:7:end);
plot(x(inds),y(inds))
for inds_7
% plot a vertical line between the 7th point and the next point, the 14th and 15th, etc.
xline( (x(inds_7-1)+x(inds_7))/2 )
end
