Neuromuscular Junction

Question 1

How is skeletal muscle innervated

Answer 1

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

Question 2

How does the motor neurone innervate the muscle

Answer 2

Axon divides into unmyelinated branches near to the muscle

Each branch innervates an individaul skeletal muscle fibre

Question 3

What is a motor unit

Answer 3

The neurone and the number of fibres that it innervates

Question 4

What are some key features of neuromuscular junction

Answer 4

Terminal bouton
Synaptic vesicles
Synaptic cleft
End plate region

Question 5

What are active zones

Answer 5

Synaptic vesicles containing ACh awaiting release cluster at sites

Question 6

How is choline ttansported into the terminal

Answer 6

By choline transporter

Question 7

Where is ACh syn and form what

Answer 7

Syn in cytosol from choline and acetyl coenzyme A by enzyme

Choline acetyl transferase

Question 8

What does the arrival of the AP do to the terminal

Answer 8

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

Question 9

What does ACh activate

Answer 9

Nicotinic ACh receps located at muscle end plate

Question 10

Where are the nicotinic ACh receps

Answer 10

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

Question 11

Coz driving force for sodium > pottasium =

Answer 11

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

Question 12

What causes a miniature end plate potential

Answer 12

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

Question 13

What do multiple mepp sum mate to produce

Answer 13

The end plate potential a graded electrical response

Question 14

What does an End plate potentail do

Answer 14

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

Question 15

Why is the muscle action potential required for contraction

Answer 15

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

Question 16

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

Answer 16

T tubules which close to sarcoplasmic reticulum

Which triggers release of calcium by interacting with troponin associated with myofibrils

Question 17

How can a neuromuscular transmission be rapidly terminated

Answer 17

By hydrolysis ACh by using acetylcholinesterase anytime associated with end plate

Hydrolyses to: choline and acetate

Question 18

What is neuromyotonia

Answer 18

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

Question 19

What is lambert-eaton myasthenia syndrome

Answer 19

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

Question 20

Myasthenia gravis

Answer 20

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

Question 21

What is botulinum toxin

Answer 21

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

Question 22

What are curare-like compounds

Answer 22

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

Question 23

What is skeletal muscle

Answer 23

Voluntary muscle