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PA10315 COPY > Muscle > Flashcards

Muscle Flashcards

1
Q

What are the three major types of muscle?

A
  1. Skeletal
  2. cardiac
  3. smooth.
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2
Q

What are features of skeletal muscle?

A
  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
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3
Q

What are the features of cardiac muscle?

A
  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.
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4
Q

What are the features of smooth muscle?

A
  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
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5
Q

What is the sarcomere?

A
  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
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6
Q

What is the A band?

A
  1. Thick filaments of myosin that are found at the centre of the sarcomere.
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7
Q

What is the I band?

A
  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
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8
Q

What is the M line?

A
  1. Proteins that link the central regions of the thick filaments.
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9
Q

What is the H zone?

A
  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.
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10
Q

What is the Z line?

A
  1. The network of proteins that anchor the thin filaments.
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11
Q

What lies on top of actin?

A
  1. A band called tropomyosin.
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12
Q

What does troponin do?

A
  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.
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13
Q

What does the thick filaments contain

A
  1. Myosin
  2. Have a head group which projects out
  3. Has an actin binding site and an ATP binding site on the head
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14
Q

What role does calcium have in muscle contraction?

A
  1. It causes a conformational change to move the tropomyosin so a cross bridge can form and contraction can occur.
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15
Q

What are thin filaments made up of?

A
  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
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16
Q

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

A
  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)
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17
Q

What is the second step in the sliding filament mechanism?

A
  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
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18
Q

What is the third step in the sliding filament mechanism?

A
  1. The binding site is exposed and is in an energised position
  2. Energized myosin molecule (+ADP) binds to actin
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19
Q

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

A
  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

20
Q

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

A
  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
21
Q

What is the final step in the sliding filament mechanism?

A
  1. The myosin head returns to its original position of 90 degrees from the 45 degrees.
22
Q

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

A
  1. Lots of folds to increase the surface area.
23
Q

What happens to choline after ACh has been broken down?

A
  1. It is recycled and goes back into the terminal.
24
Q

How is ACh formed

A
  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
25
Q

What does tubocurarine do?

A

It blocks ACh from binding to the receptor.

26
Q

Name 3 inhibitors and what they do

A
  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
27
Q

What is the sarcoplasmic reticulum a store of?

A
  1. similar to endoplasmic reticulum in other cells

2. It is the Ca2+ store for skeletal muscles (contains high conc. of Ca2+)

28
Q

What are the purpose of T tubules?

A
  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
29
Q

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

A
  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.
30
Q

How is calcium recycled?

A
  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.
31
Q

What is Myasthenia Gravis?

A
  1. autoimmune disease
  2. Antibody destruction of Ach receptors so less Ach receptors
  3. development of muscle weakness
32
Q

How can individuals suffering from Myasthenia Gravis be treated?

A
  1. AChesterase inhibitors which increases the time ACh is in the synapse so there is a greater chance of contraction occuring.
33
Q

What type of neurones innervate skeletal muscle

A
  1. motor
34
Q

What neurotransmitter do motor neurones release

A

Ach

35
Q

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

A
  1. motor end plate

2. neuromuscular junction

36
Q

relative striation of different types of muscle

A
  1. skeletal is striated
  2. cardiac has striations
  3. smooth has no striations
37
Q

what is a myofibril

A
  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
38
Q

Where is Ach stored and how is it released

A
  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
39
Q

How is Ach broken down

A
  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
40
Q

What is the neuromuscular junction and what happens there

A
  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
41
Q

What is the presynaptic neurone

A
  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
42
Q

What does the postsynaptic neurone contain

A
  1. Postsynaptic neuron has lots of nicotinic Ach receptors
43
Q

Describe what happens when an action potential reaches a nueromuscular junction

A
  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
44
Q

Muscle in skeletal muscle

A
  1. skeletal muscle made from bundles of multinucleated muscle cells
45
Q

Tendons in skeletal muscle

A
  1. Bundles of collagen fibres that attach muscle to bone

PA10315 COPY (48 decks)

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