1
Q
Define muscle fibre?
A
A muscle cell (It’s many fused cells and has many nuclei)
2
Q
Define Sarcolemma?
A
the cell membrane of muscle fibre
3
Q
Define sarcoplasm?
A
The cytoplasm of the cell
4
Q
Define transverse tubules?
A
Tubes made from infolding of the membrane that transmits the nerve impulse into the cell
5
Q
Define sarcoplasmic reticulum?
A
Membranous sacs (cisternae which store and release calcium ions to initiate a contraction)
6
Q
What are the two muscles working in an antagonistic pair called?
A
Since muscles can only pull (not push), they work in pairs called antagonistic muscles. The muscle that bends (flexes) the joint is called the flexor muscle, and the muscle that straightens (extends) the joint is called the extensor muscle.
7
Q
What does the skeletal muscles cause to happen?
A
The skeletal muscles cause the skeleton to move at joints
8
Q
How are the muscles attached to the skeleton?
A
Skeletal muscles are attached to the skeleton by tendons, which transmit the muscle force to the bone and can also change the direction of the force
9
Q
what are tendons made of?
A
tendons are made of collagen fibres and are very strong and stiff (i.e. not elastic)
10
Q
What type of muscle brings about movement of the skeleton?
A
Striated (voluntary muscle/ skeletal)
11
Q
What is a muscle fibre?
A
a cell
12
Q
What is the contractile organelle of a muscle fibre?
A
myofibrils
13
Q
what is the contractile unit of a myofibril?
A
sarcomere
14
Q
what are the two types of protein in a myofibril that make up the filaments?
A
- actin
- myosin
15
Q
what makes up the thin filaments?
A
actin
16
Q
What makes up the thick filaments?
A
myosin
17
Q
What is the cell membrane of a muscle cell called?
A
sarcolemma
18
Q
what is the specialised endoplasmic reticulum of a muscle cell called?
A
sarcoplasmic reticulum
19
Q
what is the cytoplasm of a muscle cell called?
A
sarcoplasm
20
Q
what are the infoldings of the cell membrane that form tubes through the cell cytoplasm called?
A
T-tubules
(transverse tubules)
→ they transmit action potentials to middle of nerve
21
Q
what is the end of a motor neurone where an impulse arrives called?
A
neuromuscular junction
22
Q
Describe a myofibril.
(2)
A
- a cylindrical organelle
- made up of myofilaments (thick and thin)
23
Q
Each myofibril is composed of numerous sarcomeres. What is a sarcomere?
A
(the contractile unit of a myofibril)/ distance between two z lines.
24
Q
what is the I band made of?
A
(light band)
Thin filaments only
[actin]
25
What is the A bands made of?
(dark band)
thick and thin filaments
[myosin and actin]
26
What are the z lines?
proteins joining the thin actin filaments
27
what is the H zone?
a lighter zone in the dark band, made of only thick filament.
[myosin]
28
Describe the changes to a sarcomere when it contracts?
- thin filaments pulled along myosin filaments to centre of sarcomere
- A band unchanged
- I band smaller
- H zone smaller (or disappears)
29
Do the filaments change length during the shortening of the sarcomere?
No, they slide together
30
Describe the cross bridge cycle/ sliding filament theory?
- initially, ATP binds to the myosin head and is hydrolysed to give ADP and Pi. This activates ('cocks') the myosin head, so cycle can begin
1- cross-bridge formation: myosin head binds to actin and inorganic phosphate is released, making head tightly bound
2- power stroke: ADP released from myosin head, and head moves, so pulling the actin filaments past the myosin, towards the centre of the sarcomere.
(filaments slide together.)
3- cross-bridge detachment: ATP binds to the myosin head which detaches and returns to the un-cocked position
4- reactivation of the myosin head: ATP binds to the myosin head and is hydrolysed to give ADP and Pi. This activates ('cocks') the myosin head again
31
What is a neuromuscular junction?
A specialised cholinergic synapse between a motor neurone and a muscle cell
32
What happens during depolarisation of a muscle fibre?
- action potential arrives at axon terminal
- voltage-gated calcium ion channels open
- calcium ions diffuse into presynaptic membrane
- vesicles fuse with pre-synaptic membrane
- neurotransmitter released into synaptic cleft which diffuses across cleft and binds to receptor on post-synaptic membrane
- sodium ions enter causing depolarisation
33
What is the name for the structure where a motor neurone joins a muscle fibre?
a neuromuscular junction
34
what is the name for the regulatory protein that wraps around actin filaments?
tropomyosin (which has another protein troponin attached to it)
35
what does the tropomyosin cover when the muscle is relaxed?
myosin binding sites
36
why does the tropomyosin cover the binding site when the muscle is relaxed?
to stop the myosin heads from binding to the actin
37
what ion can bind to troponin which is attached to the tropomyosin?
calcium ion
38
what binds to the troponin (attached to the tropomyosin), which causes the tropomyosin to move and expose the myosin binding sites?
calcium ions
39
what causes calcium ions to be releases to the myofibril, so the cross-bridge cycle starts (the muscle contracts)?
A nerve impulse arrives at the neuromuscular junction
40
what is the neurotransmitter that is released called?
acetylcholine
41
what does the acetylcholine cause?
- an action potential travels deep into the t-tubules
- calcium ion channels in the sarcoplasmic reticulum open
- calcium ions diffuse around the myofibrils
42
why does the cross-bridge cycle start?
the calcium ions bind to the troponin, causing the tropomyosin to pull away from actin, exposing the myosin binding sites
43
where are the calcium ions released from?
the sarcoplasmic reticulum
44
why does the cross-bridge cycle stop?
- calcium ions are actively transported back into the sarcoplasmic reticulum
- troponin returns to its original shape when calcium ions unbind from it and the tropomyosin recovers the myosin binding sites on the actin
45
when does muscle relaxation occur?
- occurs when no more nerve impulses arrive at the neuromuscular junction
- calcium ions pumped back into sarcoplasmic reticulum (active transport; requires ATP)
- calcium ions unbind from troponin so tropomyosin moves to reblock myosin-binding sites on the thin filaments so no cross links can form
- ADP + Pi remain bound to 're-cocked' myosin heads
- thin filaments pulled back to relaxed position by action of antagonistic muscle
46
what is rigor mortis?
- occurs when no ATP available cross links not broken (need ATP for them to break).
- so filaments unable to move so muscles remain contracted.
47
Describe the roles of calcium ion and ATP in muscle contraction. (6)
1- calcium ions diffuse into myofibrils from sarcoplasmic reticulum;
2 - calcium ions bind to troponin so tropomyosin is pulled away from the myosin;
3 - this causes exposure of the binding sites on actin;
4 - myosin heads attach to binding sites on actin (cross-bridge formation);
5 - hydrolysis of ATP on myosin heads causes myosin heads to bend;
6 - bending pulls actin molecules;
7 - attachment of a new ATP molecule to each myosin head causes myosin heads to detach from actin sites.
48
what three things is energy needed for in muscle contraction?
- to move the actin filament when attached to myosin
- to break the actin myosin cross bride
- to return calcium ions back into the sarcoplasmic reticulum via active transport once muscle contraction has stopped
49
what two ways is ATP synthesised for muscle contraction?
- aerobic respiration
. most ATP is made via oxidative phosphorylation in the cells mitochondria
. only works when there is plenty of oxygen
i.e. low intensity exercise
- anaerobic respiration
. ATP is rapidly made in glycolysis
. the end product of glycolysis is pyruvate which is converted into lactate
. lactate builds up in muscles and causes muscle fatigue
50
What is the ATP - phosphocreatine (PCr) system?
- ATP is made by phosphorylating ADP;
ADP + Pi → ATP
- The phosphate comes from phosphocreatine (PCr);
- The ATP-PCr system generates ATP very quickly (PCr runs out in seconds);
- The ATP-PCr is anaerobic (but doesn't form lactate);
ATP + PCr → ATP + Cr (creatine)
51
who has higher creatine levels than other people?
- creatine levels are higher in people who exercise regularly and those with high muscle mass
- some of the creatin gets broken down into creatinine which is removed by the kidneys
- high creatine levels can also indicate kidney damage
52
Skeletal muscles are made up of two different fibres. What are they?
- slow twitch
- fast twitch
53
What are the features of slow-twitch fibres?
- specialised for slow, sustained contractions over a long period;
- lot's of myoglobin (gives the muscle its red colour);
- cells contain many mitochondria (mainly aerobic);
- many capillaries;
54
What are the features of fast-twitch fibres?
- produce rapid, intense contraction;
- very little myoglobin;
- few mitochondria (mainly anaerobic);
- store lots of glycogen;
- few capillaries.
55
What is the role of phosphocreatine (PC) in providing energy during muscle contraction?
- (Phosphocreatine) provides phosphate;
(Reject phosphorus)
- to make ATP;
56
Explain the role of calcium ions in muscle contraction.
1. Action potential moves through T-tubules in the sarcoplasm = calcium ion channels in sarcoplasmic reticulum open
2. Calcium ions bind to troponin, triggering conformational change in tropomyosin
3. Exposed binding sites in actin filaments is actinomyosin bridges can form
57
How is muscle contraction stimulated?
Q.
1. Neurotransmitter junction: action potential causes voltage-gated calcium ion channels to open
2. Vesicles move towards and fuse with presynaptic membrane
3. Exocytosis of acetylcholine, which diffuses across synaptic cleft
4. Acetylcholine binds to receptors on sodium ion channels proteins on skeletal muscle cell
5. Influx of sodium ions leading to depolarisation
58
What is the role of ATP in muscle contraction?
The roles of ATP are to provide energy for:
1. To break actinomyosin bridges (detach or attach myosin and actin)
2. To move/ bend the myosin head (the power stroke or recocking movement) so the actin filaments are moved inwards
3. For active transport of calcium ions back into the sarcoplasmic reticulum when nerve stimulation stops
59
What is the role of calcium ions in the contraction of a myofibril?
. When an action potential reaches the muscle fibre, calcium ions are released from the sarcoplasmic reticulum and diffuse into the myofibrils
. These calcium ions bind to tropomyosin, causing it to move towards expose the binding sites on the actin filaments
. With these sites now accessible, the myosin heads attach to actin, forming actinomyosin cross-bridges
60
What happens during muscle relaxation?
1. Calcium ions are actively transported back into the sarcoplasmic reticulum
2. Tropomyosin once again blocks actin binding sites
Biology
flashcards
Decks in class (21)
# Cards
-
Biological molecules Yr 195
-
Cells Yr 1130
-
organisms exchange substances with their environment Yr 1102
-
Genetic information Yr 192
-
Photosynthesis Yr 2133
-
Respiration Yr 280
-
Energy and ecosystems Yr 260
-
Nutrient cycles Yr 221
-
Organisms respond to changes in their internal and external environments Yr 2109
-
nervous coordination Yr 2127
-
Homeostasis Yr 2181
-
Genetics, population, evolution and ecosystems Yr 2223
-
Unit 8: Control of gene expression Yr 2280
-
skills6
-
Stats12
-
Control of heart rate34
-
Muscles60
-
y1 key sequences3
-
y2 key sequences3
-
scholarship exams39
-
Little test61
