NEUROMUSCULAR NEUROMUSCULAR TRANSMISSIONTRANSMISSION

Secretion of acetylcholine, Effect Secretion of acetylcholine, Effect of acetylcholine on muscle fiberof acetylcholine on muscle fiber

Secretion of acetylcholine on nerve Secretion of acetylcholine on nerve terminalsterminals

• Nerve impulse reaches at neuromuscular junction• No. of released synaptic vesicles are 125

• NEURAL MEMBRANE• On inside of neural membrane linear dense bars• To each side of dense bars, protein particles are

present• Voltage gated calcium channels• Action potential

PRESYNAPTIC NERVE TERMINALPRESYNAPTIC NERVE TERMINALOR NEURAL MEMBRANEOR NEURAL MEMBRANE

• Channels opening• Permission of calcium ions for diffusion• From synaptic space of interior of terminal• Calcium ions exert infuence on acetylcholine

vesicles• Carrying and pushing them towards neural

membrane• Fuse with neural membrane• Exocytosis

EFFCTIVE STIMULUSEFFCTIVE STIMULUS

• Effective stimulus for causing acetylcholine release is calcium ions

• Ach is emptied

Effect of acetylcholine on Effect of acetylcholine on postsynaptic muscle fiberpostsynaptic muscle fiber

Sub-neural cleft• Acetylcholine receptors• Acetylcholine gated ion channels• Location is at the mouth of sub-neural cleft• Lying immediately below the dense bars• Lying side by side in a circle• Tubular channels

ACECTYLCHOLINE RECEPTORACECTYLCHOLINE RECEPTOR

• A Protein complex• Five sub-unit proteins • Two alpha, one beta, one

delta, one gamma• Channel remain

constricted• Two acetylcholine

molecules attach with two alpha subunit

OPENINGOF CHANNELOPENINGOF CHANNEL

• Conformational change• Opening of channels• Opened acetylcholine channel has

diameter 0.65nanometer• Permission to ions• Na, K and Ca• Negative ions cannot move such as Cl

OPENIN OF CHANNELOPENIN OF CHANNEL

• Strong negative charges in the mouth of channel

• Repel the negative ions

Why Na ion rush insideWhy Na ion rush inside

• Why large amount of Na ions rush inside• Two positive ions in large concentration• Sodium and potassium ion• Sodium ion in extracellular fluid• Potassium ion in intracellular fluid

ACTION POTNTIALACTION POTNTIAL

Negative potential inside the membrane• -80-------------90mv• Pull sodium ions to inside of fiber• Prevention of efflux of potassium ions

END PLATE POTENTIALEND PLATE POTENTIAL

• Large no of Na ions move inside of muscle fiber

• Carrying with them large no of positive ions• Local positive potential change• End plate potential• Creates an action potential• Initiation of action potential

ONSET OF ACTION ONSET OF ACTION POTENTIALPOTENTIAL

• Action potential spreads along the muscle fiber

• Cause muscle contraction

DESTRUCTION OF DESTRUCTION OF ACETYLCHOLINEACETYLCHOLINE

• Ach is released in synaptic space• Continues to activate the Ach receptor• Destruction by two means• Ach is destroyed by the action of

acetylcholinesterase• Attached to spongy layer of fine connective

tissue• Fill the synaptic pace between presynaptic and

postsynaptic terminal

DESTRUCTION OF DESTRUCTION OF ACETYLCHOLINEACETYLCHOLINE

• Small amount of acetylcholine diffuses out• Of the synaptic space• No longer available• To act on muscle fiber membrane• Short time for ach stay is fewmillisec• Sufficient to excite the membrane

END PLATE POTENTIALEND PLATE POTENTIAL

• Sudden insurgence of sodium ions• Increase local potential• Positive potential• 50------------75mv• Creating a local potential• Sudden increase in nerve membrane

potential• More than 20---------30mv

EXCITATION OF SKELETAL EXCITATION OF SKELETAL MUSCLE FIBERMUSCLE FIBER

• Sufficient to initiate more sodium channels opening

• Initiation of action potential