Lecture 9 Flashcards
Whats the anatomy of skeletal muscle?
muscle -> fascicles -> fiber -> myofibril
What myofilaments are there?
Thick (myosin) and thin (actin)
Do muscle cells have single or multiple nuclei?
Multiple
What is the individual contractile unit of a myofibril?
Sarcomere
What structures define the region of the sarcomere?
Z-lines
What does the I band contain?
Actin
What do the A bands contain?
Actin and Myosin
What does the H zone contain?
myosin
Where is the H zone located?
The centre of the A band
What is the M line?
The centre of the H zone (myosin). it contains proteins which organise and align the myosin.
What is the muscle’s length if it is resting?
Long
What is the muscle’s length if it is contracting?
Short
What happens when a muscle is partially contracted?
The actin and myosin filament slide over each other. The Z disc get closer together. the A band stays the same, and the H zone gets smaller.
TRUE or FALSE - skeletal muscle can have intrinsic spontaneous activity
FALSE - it has no intrinsic spontaneous activity
TRUE or FALSE - a single motor neuron can only stimulate itself
FALSE - a single motor neuron can drive the coordinated simultaneous contraction of up to thousands of neutrons
What is the neuromuscular junction (NMJ)?
the synapse between motor neurone axon terminals and a muscle fibre
What is the active zone of the NMJ?
it is the release site of neurotransmitters. the active site has specialised proteins which bind to the vesicles and allow their diffusion. overall, it controls the secretion and release of vesicle.
What is the sarcolemma of the NMJ?
a structure composed of in folds which increase surface area and allow for more receptors.
it also contains an important protein which breaks down Ach (AchE).
What are the functions of vesicles?
They provide metabolic support and regulate neurotransmission.
Where is there the highest density of vesicles in the NMJ?
Near the release site. When Ca2+ reaches the nerve terminal, the vesicles are released.
What is the size of the NMJ’s synaptic cleft?
it is small, so to minimise travel distance and increase transmission speed.
What neurotransmitter is used in the NMJ?
Acetylcholine (Ach)
Transmission at the NMJ:
- action potential propagates down the the motor neuron
- Ach is released
- Muscle fiber is depolarised
- depolarisation triggers an action potential
- muscle fiber AP trigger contraction
How is Ach synthesised?
Acetyl CoA + Choline via choline acetyltransferase
How is Ach broken down?
via acetylcholinesterase, producing acetic acid + choline
