3.6 Skeletal muscles are stimulated to contract by nerves

Question 1

What is an antagonistic pair ?

Answer 1

One muscle contacts and the other relaxes

Question 2

What is an antagonist ?

Answer 2

The muscle that is relaxing

Question 3

What is an agonist ?

Answer 3

The muscle that is contracting

Question 4

Name the 5 main structures of a muscle

Answer 4

• Sarcolemma
• Sacrcoplasmic reticulum
• Mitochondria and nuclei
• Myofibrils
• Tubules

Question 5

What is the structure/ function of the sarcolemma ?

Answer 5

It is the membrane of muscle fibres and folds inwards to the sarcoplasm (Membrane). These inward folds are called tubules and are important at initiating muscle contraction

Question 6

What is the sarcoplasmic reticulum a store for and why is this important ?

Answer 6

Ca2+ ions that are important for contraction

Question 7

Why do muscle fibres have lots of mitochondria ?

Answer 7

In order to provide lots of ATP for muscle contraction

Question 8

What are myofibrils and why are they important ?

Answer 8

They are cylindrical organelles that run along the length of muscle fibres and are the site of muscle contraction

Question 9

What is the A band ?

Answer 9

The total width of myosin (thick band)

Question 10

What is the H zone ?

Answer 10

Just the parts where it is myosin only (In the centre). It overlaps the A band

Question 11

What is the I band ?

Answer 11

Labels just where the actin is by itself. There is no overlap with myosin

Question 12

What is the M line ?

Answer 12

The middle point of myosin

Question 13

What do the Z lines indicate ?

Answer 13

The parameters of one sarcomere

Question 14

On a micrograph does actin or myosin show up darker ?

Answer 14

Myosin will show up darker as it is a much thicker protein, Actin will show up a lot paler

Question 15

What happens to the I band when the muscle contracts ?

Answer 15

It decreases in width

Question 16

What happens to the H zone when a muscle contracts ?

Answer 16

It decreases in width

Question 17

What happens to the A band when a muscle contracts ?

Answer 17

It stays constant as the myosin does not move, only actin

Question 18

What is the sliding filament model ?

Answer 18

Explains how muscle contraction is coordinated in myofibrils

Question 19

How is muscle contraction initiated ?

Answer 19

When an action potential reaches the muscle cells which depolarises the sarcolemma

Question 20

What does depolarisation of the sarcolemma cause ?

Answer 20

Causes the myosin and actin filaments to slide over each other. This sliding movement causes the sarcomeres to contract

Question 21

What is the job or globular heads and where are they located ?

Answer 21

Globular heads are found on myosin filaments and they allow actin and myosin filaments to slide over each other in muscle contraction

Question 22

How many binding sites are there on a myosin head and what can they bind to ?

Answer 22

There are 2 binding sites that can bind to :
- ATP
- Actin

Question 23

What is tropomyosin ?

Answer 23

A protein located on actin filaments that blocks the actin-myosin binding site when muscles are at rest

Question 24

What are 3 ways ATP can be produced for muscles ?

Answer 24

• Aerobic respiration
• Anerobic respiration
• Phosphocreatine

Question 25

How does phosphocreatine produce ATP ?

Answer 25

It donates a pi group to ADP to produce ATP, this leaves creatine

Question 26

What is the name for the bond between actin and myosin when the myosin head binds to the actin filament?

Answer 26

Actin-Myosin cross bridge

Question 27

Outline the steps followed by calcium ions in muscle contraction

Answer 27

1- Depolarisation of the sarcolemma
2- Influx of calcium ions by the SR
3- Movement of tropomyosin from the action-myosin binding sites
4- Formation of actin-myosin cross bridges

Question 28

How are calcium ions transported into the SR ?

Answer 28

By active transport

Question 29

Where are slow twitch fibres found ?

Answer 29

Found in muscles used for posture such as the back and neck

Question 30

Where are fast twitch fibres found ?

Answer 30

Found mainly in muscles such as the arms or legs

Question 31

What is the structure and function of slow twitch fibres ?

Answer 31

Function:
- Adapted for endurance and slow movement over long periods of time
Structure:
- Fibres are long and thin
- The muscles fatigue slowly and contract slowly

Question 32

What is the structure and function of fast twitch fibres ?

Answer 32

Function:
- Adapted for fast or strong movement over short periods of time
Structure:
- Fibres are short and wide
- The muscles fatigue quickly and contract quickly