NEUROMUSCULAR JUNCTION II

1.   Thick myosin filament:
     -     made up of myosin molecule.
     -     has a long tail + double head (projects from filament’s surface).
     -      head - contains ATP binding site.

2.   Thin actin filament made up of:
     -     two strands of globular actin protein (twisted together)
     -     regulatory proteins (troponin + tropomyosin).
3.   When Ca²⁺ is not available:
     -     troponin + tropomyosin - block myosin binding sites (on actin filaments).

4.   Muscular junction:
     -     specialised form of synapse
     -     found between motor neuron + sleletal muscle.
     -     spans across one unit of sarcomere.
5.   Sarcolemma = postsynaptic membrane
6.   Acetylcholine = transmitter substance (in synaptic vesicles).
7.    Acetylecholine binding sites = located in the folds of the sacrcolemma
8.   Calcium ions:
     -     found in abundance
     -     in sarcoplasmic reticulum.
9.   T tubules = very closely associated with sarcoplasmic reticulum.

10. Nervous impulse:
     è arriving at the neuromuscular junction
     è generates action potential
     è which spreads along sarcolemma.

11. Action potential:
     è depolarises T tubule
     è causing sarcoplasmic reticulum
     è to release Ca²⁺ ions
     è into sarcoplasm.
     è allow actin + myosin filaments to interact.

12. ATP:
     -     provides energy needed
     -     to power the sliding + pulling motion
     -     between actin + myosin.

13.  If Ca²⁺ ions + ATP conc. is sufficiently high à sequence will be repeated.