E-C coupling Flashcards
State the primary function of muscle
Generate force or movement in response to a physiological stimulus
What do muscles do in order to generate a mechanical response?
Transduce a chemical or electrical signal
What is the trigger for contraction of all 3 types of muscle?
An increase in Ca2+
What causes skeletal muscle to contract?
Contracts in response to neuromuscular synaptic transmission
A skeletal muscle fibre has a single NMJ where Ach receptors are located. What happens when ACh is released from the pre-synaptic nerve terminal?
It binds to nicotinic ACh receptors at the NMJ
Are nicotinic ACh receptors selective or non-selective?
What happens when ACh binds to them?
Non-selective cation channels
Open in response to ACh binding, resulting in depolarisation of Em known as end plate potential (epp)
What happens if the epp exceeds threshold for activating V-gated Na+ channels?
An action potential is generated
How is ACh rapidly inactivated?
Ach-esterase
How are skeletal muscles arranged?
Striated
Highly organised internal arrangement
What components make up a single skeletal muscle cell?
- Multiple nuclei
- Abundance of mitochondria
- 10-100 um in diameter and up to ~75cm in length
Define myofibrils
Specialised contractile elements that extend the entire length of the muscle fibre
What does thick and thin myofibril mean?
Thick- special assemblies of the protein myosin
Thin- made up primarily of the protein actin
Describe what an A band is made up of
What is the H zone?
Stacked set of thick filaments along with the portions of the thin filaments that overlap on both ends of the thick filaments
H-zone: The lighter area within the middle of the A band, where the thin filaments do not reach
What is the M-line and where is it located?
A system of supporting proteins that hold the thick filaments together vertically within each stack
Extends vertically down the middle of the A bnad within the centre of the H zone
What does the I band consist of and what is it visible in the middle of each I band?
The remaining portions of the thin filaments that dont project into the A band
Dense verticle line called the Z line
What is the area between two Z-lines called and what is it?
Sarcomere
Functional unit of the skeletal muscle
What are the characterisitics of the Z-line?
Flat, cytoskeletal disc that connects the thin filaments of the two adjoining sarcomeres
What is the width of a sarcomere?
2.5 um
List the levels of organisation in a skeletal muscle?
- Whole skeletal muscle (organ)
- Muscle fibre (single cell)
- Myofibril (specialised intracellular structure)
- Thick and thin filaments (cytoskeletal elements)
- Myosin and actin (protein molecules)
What do the thin filaments consist of?
Actin, tropomyosin and troponin
Explain the backbone of the thin filaments
A double stranded alpha helical polymer of filamentous-actin (F-actin molecules
What is F-actin associated with?
2 regulatory, actin proteins- tropomyosin and troponin
What does tropomyosin consist of?
2 identical a-helices that coil around eachother
head-to-tail contact between neighbouring tropomyosin molecules forms a ribbon that lies alongside the groove of the actin helix and physically covers the binding sites on actin molecules for attachment to what?
Myosin cross bridges
Prevents thin filaments attaching to cross bridges