Flashcards in Pharmacology Deck (81)
Where are motor neurone cell bodies located?
- Inner spinal cord
- Surface of brain
Are motor neurones myelinated?
Are motor neurone branches supplying individual muscle fibres myelinated?
What does each branch of a motor neurone divide into? What is the function of this?
- Forms a chemical synapse at NMJ
- Releases ACh
Where do synaptic vesicles move to in the terminal bouton to release ACh?
What part of the muscle fibre receives the incoming ACh?
What happens to the sarcolemma in the end-plate?
Thrown into folds:
- Nicotinic ACh receptors at junctional folds
Describe briefly an overview of synaptic transmission
1. Choline + AcetylCoA = ACh
2. ACh storage
3. ACh release upon Calcium influx
4. Receptor activation
5. ACh inactivation by acetylcholinesterase
6. Re-uptake of choline and acetylCoA
How is choline transported into the pre-synaptic nerve?
Via choline transporter:
- Symported with sodium
Where dose the AcetylCoA come from for ACh formation?
Where is ACh synthesised and what enzyme catalyses it?
What happens when an action potential arrives at the pre-synapse?
2. Opening of voltage-gated calcium channels
3. Calcium influx
What happens after calcium influx?
ACh-containing vesicles exocytose into cleft at active zones
What is the structure of the nicotinic ACh receptor?
Pentamer of glycoprotein subunits:
- [(Alpha1)2, Beta1, Delta, Epsilon]
What is the epsilon subunit in embryonic muscle nicotinic ACh receptors?
A Gamma subunit
What does the nicotinic ACh receptor surround?
Central, cation sensitive pore:
- Five M2 helices
What is the conformation of the pore in:
1. Absence of ACh
2. The binding of one ACh
3. The binding of two ACh
4. The binding of three ACh
4. Not possible
Which one of the following values is the rough true value for the permeability ratio of the nicotinic ACh pore to potassium and sodium (PK+/PNa+):
They have roughly the same permeability
What ions move in/out of the pore in the sarcolemma?
At resting potential, which effect is the greatest; the sodium driving force or the potassium driving force and what does this result in?
Sodium driving force since sodium in > potassium out:
- Depolarisation -> End Plate Potention (e.p.p.)
How do we describe the amount of ACh contained in a vesicle?
What do we call the electrical response on the sarcolemma upon exposure to one quantum of ACh?
What dose the term 'Electrotonic repsonse' mean?
Many m.e.p.p. sum to produce the e.p.p
What does the End Plate Potential need to be greater than to trigger an 'all-or-nothing' AP to be generated?
What happens when threshold is reached?
Voltage-activated sodium channels open up along the sarcolemma resulting in contraction along the muscle
Why do we need sodium channels along the length of the muscle fibre?
To allow AP propagation
What feature of the sarcolemma does the AP enter that is in close proximity to the sarcoplasmic reticulum?
Transverse (T) Tubules
What does the AP trigger when it gets close to the SR?
When calcium is released from inside the SR into the cell what happens?
It interacts with troponin on myofibrils -> Contraction