You can extract them as (MxN) matrices, but you have to do operations on them inside the loop (unless you want to do the extremely unwise and strongly discouraged operation of creating individually-named (MxN) matrices).
For example, this works:
S = randi(25, 7, 6, 5);
v = randi(10, 6, 1);
for k1 = 1:size(S,3)
R(:,:) = squeeze(S(:,:,k1));
Q(:,k1) = R*v;
end
The Q matrix here contains the results of the vector multiplications inside the loop.
