3. For neuromuscular transmission there are 3
essential components :
 MOTOR UNITS
 SYNAPTIC CLEFT
 MUSCLE (END PLATE)

4. The nerve fibre plus the
muscle fibre/ fibres
it innervate form the
motor unit.

5.  The more delicate the movements, the
fewer muscle fibres per motor neuron.
 More intense contraction = more motor unit
& long muscle fibres
 All types of muscle fibre shows all-or-none
law
 Schwann cell encircles the motor unit

6.  The neuromuscular junction is separated
from the extra cellular fluid by extension of
the terminal Schwann cells and insulates the
entire structure.
 Contents of the presynatic end:
- Calcium channel (P type- fast)
- Acetylcholine vesicles
- Active zones
- Proteins: Synaptotagmin,Synaptobrevin,
Synaptosome associated protein(SNAP)
- Presynaptic nAchRs

7.  3 lacs in an end plate
 45 nm : bound by lipid bilayer memb.
 Active zones
 10,000 mol of Ach in 1 vesicle, loaded by
Mg++ dependent proton pumping ATPase
 1% – Releasable store
80% - Reserve pool
Rest - Stationary pool

8.  Synthesized in the cell body and by axonal
transport it reaches the NMJ end of the
motor neuron.
 ATP + Acetate + CoE- A= Acetyl CoE- A
 Choline + Acetyl CoE- A
↓choline acetyltransferase
Acetylcholine + CoE- A
 Ach: 20%= In free state within axoplasm(VP1)
80%= Vesicles (VP2)

9.  Primary Syn.Cleft
Gap of 20-50µm
 Secondary Syn.
Cleft
Contents:
- Collagen tissue
(BM)
Acetylcholinesterase

10.  nAchRs
 Na Channels
- Voltage dependent gate (VDG)
- Timed dependent gate (TDG)
VDG opens till depol persists but TDG closes
and cuts off the flow of sodium. TDG does not
open again until VDG closes and reopens with a
fresh depol.

14. Depol of N. terminal
Opening of Ca channel
Entry of Ca
Mobilizes membrane bound
Vesicle
Binding to docking protein
Fusion of vesicles
Release of ACh into S. Cleft

16.  The SNARE (soluble N-ethylmaleimide–
sensitive attachment protein receptors)
proteins are involved in fusion, docking, and
release of acetylcholine at the active zone
 Synaptophysin is a glycoprotein component
of the vesicle membrane.
 Phosphorylation of another membrane
protein, synapsin, facilitates vesicular
trafficking to the release site.

17.  Synaptotagmin is the protein on the vesicular
membrane acts as a calcium sensor and localizes
the synaptic vesicles to synaptic zones rich in
calcium channels, stabilizing the vesicles in the
docked state.
 Synaptobrevin is a vesicle associated membrane
protein (VAMP). During depol & entry of Ca
it unfolds & forms a ternary complex with
syntaxin/ SNAP-25

20.  Spontaneous depolarizing potentials at
neuromuscular junctions can be seen. These
potentials have only one hundredth the
amplitude of the evoked end-plate potential
produced when the motor nerve is stimulated.
These small-amplitude potentials are called
miniature end-plate potentials (MEPPs)

21.  Because MEPPs are too big to be produced by a
single molecule of acetylcholine, it was deduced
that they are produced by uniformly sized
packages, or quanta, of transmitter released from
the nerve (in the absence of stimulation). The
stimulus-evoked end-plate potential is the additive
depolarization produced by the synchronous
discharge of quanta from several hundred vesicles

22.  The amount of Ach released by each nerve
impulse is large, atleast 200 quanta of about
50,000 molecules each & the number of AchRs
activated by transmitter released is about
500,000

30. DEPOLARIZING
AGENTS

31. NON-
DEPOLARIZING/
COMPETITIVE
AGENTS