Which of the following statements correctly describe(s) T tubules and their role

1) T tubules have receptor proteins that bind neurotransmitters released from the synaptic terminal of the motor neuron.
2)  T tubules carry action potentials into the interior of the muscle cell via voltage-gated Na+ and K+ channels.
3)  T tubules are extensions of the sarcoplasmic reticulum that are in contact with the plasma membrane.
4)  T tubules lack the voltage-gated Na+ and K+ channels that are present in the plasma membrane.
5)  Without T tubules, the muscle cell would not be able to contract.
6)  T tubules are infoldings of the plasma membrane that encircle the myofibrils and are in contact with the sarcoplasmic reticulum.