Muscle structure and contraction Flashcards
(42 cards)
1
Q
What happens in a reflex action?
A
- Stimulus (heat)
- Pain receptor-stimulated
- Signal sent along sensory neuron
- Signal passed along relay neuron (message sent to brain)
- Signal sent along motor neuron
2
Q
Muscles
A
- Effectors
- Carry out a response to a stimulus
- Bring about movement
3
Q
Three types of muscle
A
- Cardiac
- Smooth
- Skeletal
4
Q
Cardiac muscle
A
- Found in heart
- Involuntary
- No conscious
- Striated
5
Q
Smooth muscle
A
- Found in walls of blood vessels and digestive systems
- Involuntary
- No conscious control
6
Q
Skeletal muscle
A
- Found attached to the bone
- Voluntary
- Conscious control
- Striated
Contract - pulling on incompressible bone to move them
- Can’t push - must work in antagonistic pairs = opposing actions
7
Q
Antagonistic examples
A
- Biceps and triceps
- Hamstring and quadriceps
8
Q
What are skeletal muscles made of?
A
- Tiny muscle fibres - Myofibrils
- Made up of 2 types of myofilaments (even smaller)
- The fibres line up parallel to each other to maximise strength and increase power
9
Q
Muscle is an example of tissue
A
- Made up of many similar cells = work together to carry out specific function
- Movement
- Separate muscle cells fuse together into muscle fibres - share nuclei and cytoplasm = SARCOPLASM
10
Q
Sarcoplasm
A
- Mainly found around muscle fibres
- Contains many mitochondria = ATP in respiration and ER
11
Q
Two myofilaments
A
- Actin and Myosin
- Both fibrous proteins
- Arranged in repeated units - Sacromeres
12
Q
Actin
A
- Protein filament
- Thinner
- Made up of 2 strands twisted around each other
13
Q
Myosin
A
- Protein filament
- Thicker
- Long rod shaped tails with bulbous heads
- Project the side
14
Q
Sarcomere structure
A
- Myofibrils - striated - alternating light and dark coloured bands
- Light = I bands - only actin - no overlap with myosin
- Dark = A bands - overlapping actin and myosin
- End of each A band - lighter coloured area - H-Zone - myosin filaments - no overlap with actin
- Centre of I band - Z line - distance between z lines in sacromere
15
Q
What do skeletal muscles contain?
A
- Mixture of slow and fast twitch fibres
- Proportion may change depending on location and function of muscle
16
Q
Two types of muscle fibre
A
- Fast twitch
2. Slow twitch
17
Q
Fast twitch
A
- Quick and powerful contraction
- Tire quickly - act for short period
- Dominant in athletes for power events
- Appear dark stained
18
Q
Fast twitch muscle adaptions
A
- Aneraboic respiration
- Thicker + more numerous myosin filaments
- High concentration of glycogen
- Rely on glycolysis - ATP production = rapid contraction
- Lots of ATPase to synthesis ATP from ADP and Pi
- Lots of phosophocreatine - molecule rapidly generate ATP
= Lactic acid can build up
19
Q
Slow twitch
A
- Slow, less powerful contraction
- Don’t tire quickly - act over a longer period
- More common in endurance exercise (tennis)
- White
20
Q
Slow twitch muscle adaptions
A
- Aerobic respiration
- Lots of mitochondria to supply ATP
- High conc of myoglobin - stores o2
- Numerous blood vessels deliver o2 and glucose
- Contraction is delayed due to complex aerobic reactions
21
Q
Silent filament mechanism
A
- Theory of muscle contraction
- Actin and myosin don’t get shorter = slide past each other = overall size of sacromere + muscle decrease
22
Q
Sacromere is contracted
A
- Shorter I band
- Z lines move closer together
- Little/no H zone (myosin)
- A band remains the same width as the myosin filaments have not become shorter
23
Q
Muscle proteins
A
- Actin
- Myosin
- Tropomyosin
- Troponin
24
Q
Actin
A
Binding sites
25
Tropomyosin
- Forms long threads that are wound around actin filaments - prevent myosin-binding
- Muscle relaxed
26
Myosin
- Tails
- 2 bulbous heads at one end
- Heads fit into the binding sites on actin
27
Cross bridges
- Relaxed muscles - tropomyosin molecules block binding sites of the actin
- Myosin heads = resting position
- ADP + Pi bound to myosin head
- CA2+ stimulates - troponin = tropomyosin to change shape which exposes the binding site on actin
- Myosin head attach = cross-bridge + head tilts
- Moves the actin filament along = sarcomere is shorter
- ADP molecule detaches
28
Power stroke
- Movement of myosin
- Dragging actin = power stroke
- Myosin cross bridge binds to actin molecule
- Cross bridge bends - pulling thin myofilament inward
- Cross bridge at end of power stroke + returns to original conformation
- Cross bridge binds to more distal actin molecule = repeat
29
Detachment
- ATP attaches to each myosin head
= detach from actin-binding site
- ATP hydrolysed by ATPase = energy for myosin head to return to original position
REPEAT
- Myosin head + ADP molecule reattaches itself further along the actin filament
30
Sarcolemma
- Cell membrane of a striated muscle fibre cell
31
Sarcoplasmic Reticulum
- System of flattened membranes
| - Stores and pumps out Ca2+ ions
32
Sarcomeres
- Repeated units of myosin and actin in the muscle
33
Troponin
- Globular protein
| - Moves tropomyosin so myosin can bind
34
Muscle relaxation
- Nerve stimulation stops
- Ca2+ are actively transported back to SR - energy from hydrolysis of ATP
- Reabsorption of Ca2+ allows tropomyosin to block the actin filament again
- Myosin heads no longer bind to actin filament = muscle no longer contracts
- Sarcomere will lengthen
35
ATP
- Hydrolysed to ADP + Pi = energy
- For myosin heads to return to their original position
- Reabsorption of Ca2+ into SR by active transport
36
ATP synthesis
- Synthesised in small amounts in anaerobic respiration
- Larger amounts in aerobic respiration - series of reactions - can be slow (not immediate)
- Generated more rapidly anaerobically using phosphocreatine
- Stored in muscle + acts as a reserve supply of phosphate which can combine with ADP to make ATP
- Phosphocreatine store - replenished using phosphate from ATP when the muscle is relaxed.
37
ATP synthesis formula
Phosphocreatine + ADP = creatine + ATP - energy
| ATP + creatine = ADP + phosphocreatine
38
Neuromuscular junction
- The point where a motor neurone meets a muscle fibre
- Lots of them along a muscle - enable muscle fibres to contract simultaneously
= Muscle action fast and powerful
- Action to transmit the message across the synapse - same as in a cholinergic synapse (acetylcholine)
39
What happens when acetylcholine diffuses to the postsynaptic membrane
- Causes SR to release its store of Ca2+ into the myofibrils
- Calcium binds to troponin on thin filament = changes shape, moving tropomyosin into the groove in the process
- Myosin cross bridges can now attach + cross bridge cycle can take place
40
Motor unit
- Motor fibres supplied by a single motor neurone
41
Small force
- Only a few units are stimulated
42
Large force
- A lot of units are stimulated
