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Biology Y2 > 6.3: Skeletal muscle > Flashcards

6.3: Skeletal muscle Flashcards

(47 cards)

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1
Q

What is the role of skeletal muscle, linked to the role of tendons and joints

A

Muscles act in antagonistic pairs against an incompressible skeleton

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2
Q

Explain how muscles which move bones that form part of a joint, work as antagonistic pairs

A

When a muscle contracts it shortens and pulls on bones moving the limb around a joint, when a muscle relaxes it generates no force and so cannot push the bone. Different muscles are required to flex and extend a limb and when one muscle contracts (e.g. bicep) the antagonistic pair relaxes (e.g. tricep)

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3
Q

Describe the structure of skeletal muscles

A

Muscle tissue is made up from bundles of long thin cells called muscle fibres, these are multinucleate and contain many mitochondria. The cell membrane of the muscle fibre is the sarcolemma, the endoplasmic reticulum is the sarcoplasmic reticulum, and its cytoplasm is the sarcoplasm

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4
Q

What is the sarcoplasmic reticulum

A

the endoplasmic reticulum of a muscle fibre

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5
Q

What is the sarcoplasm

A

The cytoplasm of a muscle fibre

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6
Q

What is the sarcolemma

A

The cell membrane of a muscle fibre

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7
Q

Explain what is meant by a myofibril

A

Inside a muscle fibre are longitudinal cylindrical structures called myofibrils which are made up from different protein filaments

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8
Q

What are the main structures within muscle fibres

A

myofibrils

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9
Q

What are infoldings of the sarcolemma called

A

T-tubules

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10
Q

What are T-tubules

A

infoldings of the sarcolemma

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11
Q

What does the sarcoplasmic reticulum contain

A

Stores of calcium ions

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12
Q

What 2 types of fibrous protein are myofibrils mainly composed of

A

actin and myosin

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13
Q

What other protein is associated with the actin fibres in myofibrils

A

tropomyosin

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14
Q

What appearance do skeletal muscle have when viewed under a microscope

A

striped/banded appearance

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15
Q

What gives skeletal muscle a striped appearance

A

Actin and myosin fibres overlap

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16
Q

Myofibrils are made up of repeating units, what is an individual unit called

A

a sarcomere

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17
Q

What is a sarcomere

A

Myofibrils are made up of repeating units, an individual unit is called a sarcomere

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18
Q

What are the Z lines

A

The limits of the sarcomere and provide attachment for the actin filaments

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19
Q

What is the M-line

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A

provides attachment for the myosin filaments - the line in the middle (of the H zone and A band)

20
Q

What is the I band

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A

Contains actin only (light band due to thin filaments only) - region between the A band and Z line

21
Q

What is the A band

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A

Contains actin and myosin (dark band due to thick and thin filaments) - region between either end of I bands

22
Q

What is the H zone

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A

contains myosin only (intermediate shade due to thick filaments only) - region in A band, with M line in the middle

23
Q

What is a neuromuscular junction

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A

A synapse between a motor neurone and muscle fibre.

24
Q

Which neurotransmitter do motor neurones at a neuromuscular junction always release

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A

Acetylcholine

25
Describe the release of Ach at a neuromuscular junction and how this triggers the release of calcium ions
When Ach attaches to receptors on the sarcolemma, it will depolarise and if the threshold is reached, an action potential will spread along the entire muscle fibre. This depolarisation spreads down the T-tubules stimulating Calcium ion channel proteins in the sarcoplasmic reticulum to open and Calcium ions diffuse into the myofibrils
26
Explain how the release of calcium ions from the sarcoplasmic reticulum leads to a change in shape of tropomyosin
The calcium ions bind to the troponin on the actin filaments, this causes the tropomyosin to change shape exposing the myosin-head binding sites on the actin filaments
27
Explain the sliding-filament theory of myofibril contraction
1- Hydrolysis of ATP releases energy which causes the myosin head to extend 2- and become attached to the actin filament forming a temporary actinomyosin cross-bridge 3- ADP + Pi are released from the myosin head causing the myosin head to change position, pulling the actin filament past the stationary myosin filament 4- A new molecule of ATP attaches to the myosin head 5- causing the myosin head to become detached from the actin filament, breaking the actinomyosin cross-bridge. This cycle repeats itself with the myosin head binding to the next site on the actin filament
28
How do the number of actinomyosin cross-bridges affect the strength of muscle contraction
Reduced cross-bridges = weaker muscle contraction More cross-bridges = stronger muscle contraction
29
Explain how actin and myosin are arranged within a myofibril to produce contraction of a sarcomere and what visible changes occur at the sarcomere
Within a sarcomere, the myosin does not move. When muscle contraction occurs, the actin filaments slide over the myosin towards the middle of the sarcomere. Z-lines move closer together I-band shorts H-band shortens/disappears A-band remains the same length
30
Explain what happens during muscle relaxation
At the end of muscle contraction: 1- Calcium ions are actively transported back into the sarcoplasmic reticulum 2- The myosin binding sites once again become blocked causing the muscles to relax and ATP is resynthesised
31
What happens if ATP runs out whilst actinomyosin cross bridges are formed during muscle contraction
The muscle cannot relax and so remains in the rigor complex (contracted)
32
What molecule in the sarcomere attaches to the Z line at the end of the sarcomere
Actin
33
What molecule in the sarcomere breaks down ATP
myosin
34
What molecule in the sarcomere covers binding site on actin in relaxed myofibril
tropomyosin
35
What are the 2 main types of muscle fibre
slow twitch (type 1) fibres fast twitch (type 2) fibres
36
Explain differences in the properties of slow and fast skeletal muscle fibres
Slow twitch contract slower and for longer, carry out aerobic respiration and fatigue slowly whereas fast twitch contract faster and for short periods, carry out anaerobic respiration and fatigue quickly
37
Where is a high proportion of slow twitch skeletal muscle fibres found
in muscles that maintain posture, such as extensore muscles
38
Where is a high proportion of fast twitch skeletal muscle fibres found
in muscles involved in locomotion, such as flexor muscles
39
Describe the difference in colour of fast and slow twitch skeletal muscle fibres and what causes this
Slow twitch fibres are mainly a red colour due to myoglobin saturation -> myoglobin has a very high affinity for oxygen -> aerobic respiration which is relatively slow whereas fast twitch are mainly a white colour due to lack of myoglobin -> anaerobic respiration which is relatively fast
40
What type of movements/sport would an athlete with a high proportion of slow twitch skeletal muscle fibre be doing
endurance type movements/sports
41
What type of movements/sport would an athlete with a high proportion of fast twitch skeletal muscle fibre be doing
explosive type movements/sports
42
Why do fast twitch skeletal muscle fibres fatigue quickly relative to slow twitch
as they mainly produce ATP from anaerobic respiration, this produces lactic acid which causes faster fatigue
43
Describe differences in the structure of slow and fast skeletal muscle fibres
slow twitch have more capillaries, more mitochondria, smaller store of calcium ions and a low amount of glycogen. Fast twitch have high amount of glycogen and phosphocreatine
44
How do creatine supplements benefit sprinters, weightlifters and other athletes
At rest creatine is phosphorylated by ATP to phosphocreatine which is stored in fast-twitch muscle fibres. During exercise PC reacts with ADP to quickly regenerate ATP
45
How does carbohydrate loading benefit endurance athletes
Eating more carbs for a few days before competitions maximises glycogen stores in muscle, so that during the event, glycogen is hydrolysed to glucose to be used in aerobic respiration in slow-twitch muscle fibre
46
Where is myoglobin found
myoglobin is found in slow twitch skeletal muscle.
47
What is the function of myoglobin
Has a very high affinity for oxygen, acts as a store of oxygen and only dissociates at a very low pO2. Delays the onset of anaerobic respiration

Biology Y2 (18 decks)

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