ANATOMY AND PHYSIOLOGY OF NEUROMUSCULAR JUNCTION
PRESENTOR : Dr Goutham
MODERATOR : Dr Vijesh
NEUROMUSCULAR JUNCTION
Synapse b/w motor nerve and muscleEach motor neuron runs from ventral
horn of spinal cordGap b/w nerve and muscle is the
synaptic cleft which is 20 nm wide
MUSCLE END
Corrugated with invaginations to form primary and secondary cleft along muscle
Shoulders contain Ach receptors which are densely packed
PERIJUNCTIONAL ZONE
Area beyond the junctional areaCritical to NMJ transmission Has high density of sodium channelsResponds to depolarisation produced by
Ach receptors and initiates contraction
Vesicles containing transmitters are seen clustering alongside the nerve terminal – ACTIVE ZONES / RELEASE SITE
Voltage gated calcium channels present in b/w vesicles through which calcium enters and cause release of transmitter
FORMATION OF ACETYLCHOLINE
How ? Axoplasm
CHOLINE + ACETYL CoA
( CAT ) ECF mitochondria
diet hydrolyzed acetylcholine liver
TRANSMISSION
MEPP : produced by quanta/packagesAt rest potential difference is -90 mVDuring AP > Na+ influx >depolarization >
opens Ca channels > release of Ach from vesicles
CALCIUM CHANNELS -TYPES
P type L type 1.voltage dependant non dependant
2.not affected by Ca channel blockers affected
3.release of transmitter
SYNAPTIC VESICLE
SYNAPTIC VESICLE
VESICLE PROTIENSSynaptophysin SynaptotagminSynaptobrevin
CLINICAL ASPECT : Botulinum toxin/tetanus toxin
EXOCYTOSIS
REMOVAL OF Ach
RECEPTORS
Ach RECEPTOR
1. Post junctional,junctional and extra junctional
2. Pre junctional .
CONTD…..
Has 5 subunits. Alpha(2),beta,delta,e
psilon. Both alpha units
occupied by agonist.
MECHANISM OF ION FLOW
Receptor undergo conformational change
Opens channel
Allows cation movement
AP created
MUSCLE CONTRACTION
Myofibrils consists of sacromeres.
Each sacromere –actin and myosin.
Tropomyosin and troponin attached to actin
AP transverse tubules,sarcoplasmic reticulum releases ca++.
EXTRA JUNCTIONAL RECPTORS
Denervation of the muscle. Seen in
1. Fetus
2. Pts with stroke
3. Spinal cord injuries
4. Burns
5. bedridden