Muscle Structure

Question 1

What are skeletal muscles?

Answer 1

Smooth muscle that lines an incompressible skeletons
And pulls to create movement by acting in antagonistic pairs

Question 2

Movement can either be…

Answer 2

Reflex
Controlled by conscious thought

Question 3

Levels of structure of the skeletal muscle

Answer 3

Gross structure (see with eye)
Microscopic structure (cells, requires seeing through microscope)
Ultra structure (proteins that require special techniques to see)

Question 4

Skeletal Muscle divides into…

Answer 4

Bundle of muscle fibres

Question 5

A single muscle fibre is..

Answer 5

A muscle cell

Question 6

Myofibril

Answer 6

Divisions of muscle fibre (muscle cell)

Question 7

Sarcomere

Answer 7

Repeating unit of the myofibril containing proteins

Question 8

Proteins in the myofibril

Answer 8

Actin
Myosin

Question 9

How is a muscle TRIGGERED in the first place to begin contracting?

Answer 9

If the sarcolemma (membrane of muscle fibre) is depolarised due to neurotransmitters generating an action potential and sends impulses along muscle fibres

Question 10

What happens when the sarcolemma is depolarised?

Answer 10

Triggers release of Ca2+ ions from sarcoplasmic reticulum ER) of muscle fibre
Which diffuse into myofibril

Question 11

Released Ca2+ ions can do what?

Answer 11

Trigger the protein called tropomyosin to move away by changing tertiary structure so it unblocks the myosin binding sites on actin

Question 12

Forming a cross bridge

Answer 12

Myosin heads can now bind to unblocked binding sites on actin
As bonded ATP is hydrolysed to release energy to ADP and Pi
= cross bridge with tension

Question 13

Formation of a cross bridge and tension means…

Answer 13

Actin can slide along the myosin as the ADP and Pi that had been hydrolysed in formation of the cross bridge is released

Question 14

How does myosin unbind to actin?

Answer 14

ATP binds to myosin which causes shape in myosin head (change in tertiary structure)
So it will detach from actin

Question 15

Movement of proteins that causes contraction?

Answer 15

The sliding of actin over myosin together and shortening of sarcomere =contraction of muscles

Question 16

Neuromuscular junction

Answer 16

Synapse between a presynaptic neurone and 1 muscle fibre (cell)

Question 17

What is the mechanism of synaptic transmission over a neuromuscular junction?

Answer 17

Same as over a regular cholinergenic synapse but differences in what receives the neurotransmitter
SARCOLEMMA as the post synaptic membrane
MUSCLE FIBRE as the receiving structure

Question 18

What do neurotransmitters bind to in a neuromuscular junction?

Answer 18

omplementary protein receptors on
SARCOLEMMA as the post synaptic membrane

Question 19

What is the structure that receives neurotransmitters in a neuromuscular junction?

Answer 19

MUSCLE FIBRE
AKA MUSCLE CELL

Question 20

Where are action potentials sent along when receiving stimulation from a presynaptic neurone in the neuromuscular junction?

Answer 20

The muscle fibre

Question 21

Is the myofibril a muscle cell>?

Answer 21

NO

Question 22

Normal cholinergenic synapse vs neuromuscular synapse

Answer 22

Normal = neurone to neurone vs neuromuscular = neurone to muscle fibre
Normal = can be excitatory OR inhibitory vs neuromuscular = always excitatory

Question 23

What happens at neuromuscular junction when impulses stop?

Answer 23

Acetyl choline in synapse hydrolysed to acetate and choline by acetylcholinesterase
Triggers Ca 2+ actively transported from the myofibril back into the sarcoplasmic reticulum

Question 24

What happens when Ca2+ leaves myofibril by active transport?

Answer 24

Tropomyosin goes back to its original shape and blocks the myosin binding sites on actin
Myosin heads can no longer bind to actin so no actinomyosin cross-bridges form = no sliding, muscle relaxed

Question 25

What happens when a muscle in an antagonistic pair is relaxed?

Answer 25

Freely lengthened by the pull from contraction of the other muscle in the antagonistic pair Since when one contracts, the other relaxes

Question 26

Full name for actin myosin cross bridge

Answer 26

Actinomyosin cross bridge

Question 27

Power stroke

Answer 27

Pulling of actin along by myosin heads because: Head of myosin angle changing shape when ATP is hydrolysed to ADP and Pi which causes tension in Actinomyosin cross bridge

Question 28

What is required to form actinomyosin cross bridge?

Answer 28

Hydrolysis of ATP to ADP and Pi