Neuromuscular Junction Flashcards Preview

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Flashcards in Neuromuscular Junction Deck (23):
1

How is skeletal muscle innervated

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

2

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

3

What is a motor unit

The neurone and the number of fibres that it innervates

4

What are some key features of neuromuscular junction

Terminal bouton
Synaptic vesicles
Synaptic cleft
End plate region

5

What are active zones

Synaptic vesicles containing ACh awaiting release cluster at sites

6

How is choline ttansported into the terminal

By choline transporter

7

Where is ACh syn and form what

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

8

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

9

What does ACh activate

Nicotinic ACh receps located at muscle end plate

10

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

11

Coz driving force for sodium > pottasium =

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

12

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

13

What do multiple mepp sum mate to produce

The end plate potential a graded electrical response

14

What does an End plate potentail do

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

15

Why is the muscle action potential required for contraction

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

16

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

17

How can a neuromuscular transmission be rapidly terminated

By hydrolysis ACh by using acetylcholinesterase anytime associated with end plate

Hydrolyses to: choline and acetate

18

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

19

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

20

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

21

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

22

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

23

What is skeletal muscle

Voluntary muscle