<P> Transverse tubules ( T - tubules ) are extensions of the sarcolemma ( muscle cell membrane ) that penetrate into the centre of skeletal and cardiac muscle cells . T - tubules are highly specialised structures , that form within the first few weeks of life , containing large amounts of specific proteins known as ion channels that allow for electrical impulses ( action potentials ) travelling along the sarcolemma , to enter rapidly into the cell , to initiate muscle contraction . </P>
what allows the nerve impulses that initiate muscle contraction to travel along the sarcolemma
Transverse tubules