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