anatomy and physiology of neuromuscular junction

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