Neuromuscular Junction Flashcards Preview

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Flashcards in Neuromuscular Junction Deck (23):

How is skeletal muscle innervated

By motor neurones with myelinated axons and cell bodies in spinal cord


How does the motor neurone innervate the muscle

Axon divides into unmyelinated branches near to the muscle
Each branch innervates an individaul skeletal muscle fibre


What is a motor unit

The neurone and the number of fibres that it innervates


What are some key features of neuromuscular junction

Terminal bouton
Synaptic vesicles
Synaptic cleft
End plate region


What are active zones

Synaptic vesicles containing ACh awaiting release cluster at sites


How is choline ttansported into the terminal

By choline transporter


Where is ACh syn and form what

Syn in cytosol from choline and acetyl coenzyme A by enzyme
Choline acetyl transferase


What does the arrival of the AP do to the terminal

Causes depo and opening of voltage activated calcium channels

Allowing calcium entry to terminal

Calcium causes vesicles at active sites to fuse with presyn mem release ACh to cleft

Activate post syn nicotinic ACh receps in end plate region


What does ACh activate

Nicotinic ACh receps located at muscle end plate


Where are the nicotinic ACh receps

Assembled as pentamers of glycoprotein subunits that surround central cation selective pore which has a gate which is closed without ACh


Coz driving force for sodium > pottasium =

Influx of sodium greater than efflux pottasium which is depo known as end late potentail


What causes a miniature end plate potential

Electrical repsonse of one quantum of transmitter due to activation of nicotinic ACh receptors at the end plate


What do multiple mepp sum mate to produce

The end plate potential a graded electrical response


What does an End plate potentail do

If it exceeds the threshold it exhibits an all or none response initiate contraction


Why is the muscle action potential required for contraction

The voltage activated channel propagates the end plate over the length of the muscle fibre


Whilst the AP propagates over the surface mem of skeletal ,sucked what does it affect

T tubules which close to sarcoplasmic reticulum
Which triggers release of calcium by interacting with troponin associated with myofibrils


How can a neuromuscular transmission be rapidly terminated

By hydrolysis ACh by using acetylcholinesterase anytime associated with end plate

Hydrolyses to: choline and acetate


What is neuromyotonia

Isaacs syndrome
Symptoms - multiple disorders of skeletal muscle including cramps, stiffness, slow relaxation
Autoimmune origin - antibodies against voltage activated pottasium channels in motor neurone disrupt function resulting in hyper excitability


What is lambert-eaton myasthenia syndrome

Characterised by muscle weakness in the limbs, very rare and associated with small cell carcinoma

Autoimmune origin

Drugs used to help increase the conc of ACh in synaptic cleft


Myasthenia gravis

Increasing muscle weakness during activty

Autoimmune origin - antibodies against ACh receps in end plate result in reduction in the num of functional channels and hence amplitude o the epp

Drug treat - anticholinesterasss ehci increase ACh in syn cleft


What is botulinum toxin

Potent exotoxin toxin that acts at motor neurone terminals to reversible inhibit ACh release

Enter presyn nerve terminals to enzymatic modify protiens involved in vesicles contains ACh

BOTOX anti wrinkle and treat over active muscles


What are curare-like compounds

Interfere with postsyn action fo ACh by acting as competitive antagonists of nicotinic ACh receps

Reduce amplitude of endplate potentail to below threshold for muscle fibre AP gen

Clinically used to induce reversible muscle paralysis


What is skeletal muscle

Voluntary muscle