Muscle

Question 1

What are the three major types of muscle?

Answer 1

1. Skeletal
2. cardiac
3. smooth.

Question 2

What are features of skeletal muscle?

Answer 2

1. Voluntary control
2. Attached to bone
3. Long muscle fibre cells,
4. uni nuclear
5. Very organised stripy pattern - called striations
6. For posture and movement

Question 3

What are the features of cardiac muscle?

Answer 3

1. Involuntary
2. Not attached to bone
3. Specialised form of skeletal muscle
4. Small nucleated cells
5. Branched cells
6. Have striations
7. Made up on intercalated discs.

Question 4

What are the features of smooth muscle?

Answer 4

1. Involuntary
2. Not attached to bone
3. e.g. blood vessels
4. made of myocyte cells which have a ‘fusiform’ shape
5. Small nucleated cells
6. Tapered at the end
7. Not striated

Question 5

What is the sarcomere?

Answer 5

1. the functional unit of skeletal and cardiac muscle (striated muscle)
2. it is the distance between one Z line (or disc) to the next Z line

Question 6

What is the A band?

Answer 6

1. Thick filaments of myosin that are found at the centre of the sarcomere.

Question 7

What is the I band?

Answer 7

1. Contains thin filaments (actin) that do not overlap with the thick filaments(myosin)
2. Found either side of the A band with the Z disc in the centre

Question 8

What is the M line?

Answer 8

1. Proteins that link the central regions of the thick filaments.

Question 9

What is the H zone?

Answer 9

1. light area found between the ends of the thin filaments in the region of thick filaments where there are no thin filaments.
2. Found in the centre of the sarcomere.

Question 10

What is the Z line?

Answer 10

1. The network of proteins that anchor the thin filaments.

Question 11

What lies on top of actin?

Answer 11

1. A band called tropomyosin.

Question 12

What does troponin do?

Answer 12

1. Connects the tropomyosin to the actin and blocks the receptors so that myosin cannot bin.
2. This is the case when the muscle is not contracting.

Question 13

What does the thick filaments contain

Answer 13

1. Myosin
2. Have a head group which projects out
3. Has an actin binding site and an ATP binding site on the head

Question 14

What role does calcium have in muscle contraction?

Answer 14

1. It causes a conformational change to move the tropomyosin so a cross bridge can form and contraction can occur.

Question 15

What are thin filaments made up of?

Answer 15

1. Made from globular actin proteins (G-actin)
2. G-actin forms protein chains called filament-actin (F-actin)
3. Has accessory proteins around it: troponin and tropomyosin
4. Has a myosin binding site
5. Tropomyosin filaments cover the myosin binding sites preventing myosin binding

Question 16

What is the first step (resting muscle) in the sliding filament mechanism?

Answer 16

1. Myosin molecule is bound to ADP and Pi
2. The myosin head is projected out at 90 degrees and ready to bind to the actin filament
3. This is called an energized cross bridge
4. Tropomyosin covers and masks the myosin binding sites on the actin filament (prevents interaction between the two filaments)

Question 17

What is the second step in the sliding filament mechanism?

Answer 17

1. Muscle stimulated and cytosolic calcium levels increase
2. The calcium binds to the troponin complex causing a conformational change
3. Calcium-bound troponin moves away from the binding site and pulls tropomyosin with it, which exposes the binding site

Question 18

What is the third step in the sliding filament mechanism?

Answer 18

1. The binding site is exposed and is in an energised position
2. Energized myosin molecule (+ADP) binds to actin

Question 19

What happens when the myosin head is bound in the sliding filament mechanism? (fourth step).

Answer 19

1. Cross bridge formation causes the release of ADP and Pi

2. Also causes movement of the myosin to 45 degrees whilst bound to actin so the crossbridge moves

Question 20

What happens after the myosin head changes shape? (fifth step)

Answer 20

1. Affinity for ATP is increased in this 45 degree position
2. ATP binds myosin and breaks the actin-myosin cross bridge
3. ATP is hydrolysed to ADP
4. If there is no ATP, no ATP can bind to the myosin head group so it cannot be released and the muscle stays in a state called rigor mortis

Question 21

What is the final step in the sliding filament mechanism?

Answer 21

1. The myosin head returns to its original position of 90 degrees from the 45 degrees.

Question 22

How is the synaptic cleft adapted for efficient binding of neurotransmitter?

Answer 22

1. Lots of folds to increase the surface area.

Question 23

What happens to choline after ACh has been broken down?

Answer 23

1. It is recycled and goes back into the terminal.

Question 24

How is ACh formed

Answer 24

1. acetyl-CoA and choline make Ach (acetyl group is transferred to choline)
2. The enzyme used to do this is choline acetyltransferase
3. Ach is made and CoA is released

Question 25

What does tubocurarine do?

Answer 25

It blocks ACh from binding to the receptor.

Question 26

Name 3 inhibitors and what they do

Answer 26

1. Anticholinesterases decrease breakdown of Ach e.g. neostigmine 2. Hemicholinium, prevents reuptake of choline via the choline transporter 3. Tubocurarine, blocks nicotinic Ach receptor

Question 27

What is the sarcoplasmic reticulum a store of?

Answer 27

1. similar to endoplasmic reticulum in other cells | 2. It is the Ca2+ store for skeletal muscles (contains high conc. of Ca2+)

Question 28

What are the purpose of T tubules?

Answer 28

1. They project down into the reticulum and means that action potentials can travel deep down into the muscle fibre/cell. 2. Tubes go from surface of muscle fibre into centre of muscle fibre 3. They propagate action potentials into the interior of the myofibril from the surface

Question 29

What happens after action potentials are spread across the muscle cell into the T tubules?

Answer 29

1. Depolarisation spreads down the tubules 2. DHP receptor detects action potential (they are switched on when there is depolarisation) 3. DHP receptor changes shape and interacts with the Ryanodine receptor. 4. The change in shape is transmitted from DHP to the ryanodine receptor which changes shape and causes Ca2+ is released from the lateral sac 5. The sarcoplasmic reticulum releases the calcium into the cytosol which activates the cross-bridge cycling.

Question 30

How is calcium recycled?

Answer 30

1. Calcium ATPase aids the transfer across the sarcoplasmic reticulum membrane back into the lumen of the reticulum 2. along with ATP as a source of energy.

Question 31

What is Myasthenia Gravis?

Answer 31

1. autoimmune disease 2. Antibody destruction of Ach receptors so less Ach receptors 3. development of muscle weakness

Question 32

How can individuals suffering from Myasthenia Gravis be treated?

Answer 32

1. AChesterase inhibitors which increases the time ACh is in the synapse so there is a greater chance of contraction occuring.

Question 33

What type of neurones innervate skeletal muscle

Answer 33

1. motor

Question 34

What neurotransmitter do motor neurones release

Answer 34

Ach

Question 35

The region directly under the axon terminal of a motor neurone is called ................ and the junction between them is ........

Answer 35

1. motor end plate | 2. neuromuscular junction

Question 36

relative striation of different types of muscle

Answer 36

1. skeletal is striated 2. cardiac has striations 3. smooth has no striations

Question 37

what is a myofibril

Answer 37

1. each muscle cell is formed from bundles of actin and myosin filaments organised into myofibrils 2. A single myosin filament is surrounded by six actin filaments

Question 38

Where is Ach stored and how is it released

Answer 38

1. Ach is stored in vesicles 2. When stimulated, vesicles fuse with cell membrane releasing Ach into synaptic cleft 3. Ach binds to nicotinic Ach receptors on the postsynaptic neurone

Question 39

How is Ach broken down

Answer 39

1. Enzyme acetylcholinesterase is found in synaptic cleft 2. This breaks down Ach to choline and acetate 3. Choline carrier transports choline back into the presynaptic neurone 4. Ach is then resynthesised

Question 40

What is the neuromuscular junction and what happens there

Answer 40

1. Neuromuscular junction is when nerves terminate at skeletal muscle 2. Calcium is released from calcium stores in skeletal muscle when there is a stimulus from the neuromuscular junction

Question 41

What is the presynaptic neurone

Answer 41

1. Presynaptic neurone is a myelinated motor nerve fibre 2. Junctional folds increase SA of the presynaptic terminal 3. Axon presynaptic terminal has lots of acetylcholine vesicles

Question 42

What does the postsynaptic neurone contain

Answer 42

1. Postsynaptic neuron has lots of nicotinic Ach receptors

Question 43

Describe what happens when an action potential reaches a nueromuscular junction

Answer 43

1. Action potential arrives at neuromuscular junction 2. Opens the Ca channels 3. Fusion of Ach vesicles with membrane 4. Ach released into synaptic cleft 5. Ach binds to Ach receptor 6. Ach receptor is a ligand gated ion channel 7. Ion channel opens 8. Influx of Na 9. Causes local depolarisation 10. This activates Na voltage gated ion channels 11. Action potential generated 12. Propagation of action potential across surface of muscle fibre

Question 44

Muscle in skeletal muscle

Answer 44

1. skeletal muscle made from bundles of multinucleated muscle cells

Question 45

Tendons in skeletal muscle

Answer 45

1. Bundles of collagen fibres that attach muscle to bone