Lecture 29- Myofibrils And Neuromuscular Junctions

Question 1

Myofibrils

Answer 1

Contain contractile element of muscle cell

Account for 80% of cellular volume

Question 2

A bands

Answer 2

Dark striation of myosin

Question 3

I bands

Answer 3

Light striations of actin

Question 4

Sarcoplasmic reticulum

Answer 4

smooth endoplasmic reticulum that regulates availability of calcium ions, surrounds each myofibril, and forms terminal cisterns at the A band–I band junction.

Question 5

Dark A band (part of sacromere)

Answer 5

Middle of sacromere
Both a thick(myosin) and thin (actin) myofilaments

Question 6

Light i band (part of sacromere)

Answer 6

on either side of the A band, has only thin (actin) myofilaments.

Question 7

H zone (parts or sacromere)

Answer 7

slightly lighter region in the centre of the A band, has only thick (myosin) myofilaments

Question 8

M line (parts of sacromere)

Answer 8

middle of the H zone, is where fine protein strands hold adjacent thick (myosin) myofilaments together.

Question 9

Thick filaments

Answer 9

Composed of bundles of myosin

Question 10

Thin filaments

Answer 10

Composed of strands of actin

Question 11

Titian

Answer 11

Anchors myosin filaments

Question 12

Regulatory proteins (tropomyosin)

Answer 12

wraps around actin filaments, stabilizing them and blocking the myosin binding sites.

Question 13

Regulatory protein (troponin)

Answer 13

binds to both actin and tropomyosin,
and binds calcium ions if they are present.

Question 14

What do actin filaments consist of?

Answer 14

polymerized globular actin (G actin) subunits that have active sites that bind myosin heads during contraction.

Question 15

What does it take for a muscle to contract?

Answer 15

fibre must be stimulated by a nerve ending so there is a change in membrane potential

muscle fibre will generate an action potential, in its sarcolemma.

The action potential propagates along the sarcolemma

Intracellular calcium levels rise briefly, providing the final trigger for contraction.

Question 16

Neuromuscular junction

Answer 16

connection between an axon terminal of a somatic motor neuron and a muscle fibre

is the route of electrical stimulation of the muscle cell.

Question 17

Gap that separates axon terminal and muscle fibre

Answer 17

Synaptic cleft

Question 18

Synaptic vesicles

Answer 18

Within axon terminal
Contain acetylcholine

Question 19

Motor neuron

Answer 19

stimulates a skeletal muscle fibre when a nerve impulse causes the release of ACh to the synaptic cleft, which diffuses across the cleft and binds to Ach receptors on the sarcolemma, creating a graded end plate generator potential that leads to an action potential.

After acetylcholine binds to ACh receptors, an enzyme in the synaptic cleft, acetylcholine, breaks down acetylcholine to acetic acid and choline, to prevent continued contraction in the absence of stimulation.

Question 20

Motor neuron stimulate muscle order

Answer 20

Action potential arrives at axon terminal at the neuromuscular junction

Acetylcholine is released and binds to chemically-gated channels on the sarcolemma, producing a graded response.

The graded potential exceeds the action potential threshold and opens membrane voltage-gated channels.

Acetylcholinesterase breaks down acetylcholine in the synapse.