5.1.3 - Animal Responses ( Part 2 )

Question 1

What are the different types of muscle ?

Answer 1

• Skeletal muscle
• Cardiac muscle
• Involuntary muscle

Question 2

What is the role of skeletal muscle ?

Answer 2

They are cells responsible for movement ( eg. Biceps and triceps )

Question 3

What is the role of cardiac muscle ?

Answer 3

• These cells are myogenic
• They contract without needing a nervous stimulus and cause the heart to best in a regular rhythm

Question 4

What is the role of the involuntary muscle ?

Answer 4

They are responsible for moving food along the gut via peristalsis

Question 5

Where are involuntary muscles found ?

Answer 5

• In the walls of hollow organs ( eg. Bladder )
• In the walls of blood vessels and digestive track

Question 6

What are features of skeletal muscles ?

Answer 6

Question 7

What are the features of cardiac muscles ?

Answer 7

Cardiac muscle fibres are connected to each other via specialised connections called intercalated discs

Question 8

What are the features of involuntary muscles ?

Answer 8

Question 9

Identify what type of muscle is shown in the following images ?

Answer 9

Question 10

Label the structures of a muscle fibre ?

Answer 10

Question 11

What is a muscle made up of ?

Answer 11

Muscle is made up of numerous muscle fibres

Question 12

Explain the structure of a muscle fibre ?

Answer 12

• Each muscle fibre contains many nuclei
• Each muscle fibre is surrounded by a cell surface membrane, called sarcolemma
• Muscles fibres contain sarcoplasm
• Muscle fibres contain sarcoplasmic reticulum

Question 13

Explain features of the sarcolemma ?

Answer 13

Sarcolemma contains many deep tube-like projections that fold in from its outer surface, called T-tubules

Question 14

What is the role of T-tubules ?

Answer 14

• This helps the spread of electrical impulses throughout the sarcoplasm
• This ensures that the whole fibre receives the impulse to contract at the same time

Question 15

Explain features of the sarcoplasm ?

Answer 15

• Contains a lot of mitochondria which provides ATP for muscle contraction during aerobic respiration
• Contains myofibrils

Question 16

What is the role of the sarcoplasmic reticulum ?

Answer 16

Contains calcium ions required for muscle contraction

Question 17

What are myofibrils ?

Answer 17

They are bundles of actin and myosin filaments which slide past each other during muscle contraction

Question 18

What proteins are myofibrils composed of ?

Answer 18

• Thinner filaments made of actin
• Thicker filaments made of myosin

Question 19

What are the key features of myofibrils ?

Answer 19

• H band/ H zone
• I band/ Light band
• A band/ Dark band
• Z line
• M line
• Sarcomere

Question 20

What are H bands/ H zones ?

Answer 20

Areas were only thick myosin filaments are present

Question 21

What are I bands/ light bands ?

Answer 21

Areas were only thin actin filaments are present

Question 22

What are A bands/ dark bands ?

Answer 22

• Areas where only myosin filaments are present
• As well as areas where myosin and actin filaments overlap ( edges of dark band )

Question 23

What is an M line ?

Answer 23

Attachment for myosin filaments

Question 24

What is a Z line ?

Answer 24

Attachment for actin filaments

Question 25

What is a sarcomere ?

Answer 25

the section of myofibrilles between two Z lines

Question 26

Do you understand the structure of a myofibril ?

Answer 26

Yes

Question 27

Are you able to identify the histology of a skeletal muscle ?

Answer 27

Yes You should be able to identify the following structures : - Individual muscle fibres - long and thin multinucleated fibres that are crossed with a regular pattern of fine red and white lines. - The highly structured arrangement of sarcomeres which appear as dark (A-bands) and light (I-bands) bands. - Streaks of connective and adipose tissue. - Capillaries running in between the fibres.

Question 28

What is a neuromuscular junction ?

Answer 28

The point between a ( motor neurone ) and a muscle cell

Question 29

Explain the transmission across a neuromuscular junction ( part 1 ) ?

Answer 29

- Action potential/ electrical impulse arrives at the presynaptic membrane of motor neurone - This causes voltage-gated calcium ion channels to open and allows calcium ions to diffuse into the neurone - This stimulates ACh-containing vesicles to fuse with the presynaptic membrane and release ACh via exocytosis - ACh diffuses across the neuromuscular junction and binds to receptor proteins on the sarcolemma - This stimulates sodium ion channels in the sarcolemma to open, allowing sodium ions to diffuse into the sarcolemma - This depolarises the sarcolemma, generating an action potential that passes down the T-tubules towards the centre of the muscle fibre

Question 30

Explain the transmission across a neuromuscular junction ( part 2 ) ?

Answer 30

- This causes voltage-gated calcium ion channel in the membranes of the sarcoplasmic reticulum to open - Calcium ions diffuse out of the sarcoplasmic reticulum and into the sarcoplasm surrounding the myofibrils - Calcium ions bind to troponin molecules, stimulating them to change shape - This causes the troponin and tropomyosin proteins to change position on the thin actin filaments - This exposes myosin binding dites on actin filaments

Question 31

What are the differences between a cholinergic synapse and neuromuscular junction ?

Answer 31

Question 32

Describe the structure of myosin ?

Answer 32

- Fibrous proteins with a globular head - Fibrous part of myosin molecule anchors the molecule in thick filament - Globular heads all point away from M line

Question 33

Describe the structure of actin ?

Answer 33

- Globular proteins - Many actin molecules join together to form chains - Two actin chains twist to form an actin filament - Fibrous protein tropomyosin is twisted around the two actin chains - protein troponin is attached to the actin chains at regular intervals

Question 34

Explain what happens during muscle contraction ( part 1 ) ?

Answer 34

- This causes troponin and tropomyosin proteins to change position on the actin filaments - This exposes the myosin binding site on actin filaments - The globular heads of the myosin molecules bind with these sites, forming cross-bridges between the two types of filament - The myosin heads bend and pull the actin filaments towards the centre of the sarcomere, causing the muscle to contract a very small distance; power-stroke

Question 35

What happens when the myosin heads bend ?

Answer 35

A molecule of ADP is released

Question 36

Explain what happens during muscle contraction ( part 2 ) ?

Answer 36

- ATP binds to the myosin head breaking cross-bridges between myosin and actin filaments - Hydrolysis of ATP into ADP and Pi releases energy used to reset myosin head to original position - The myosin head can now bind to a new binding site on the actin filaments - The myosin heads move again, pulling the actin filaments even closer to the centre of the sarcomere and causing the sarcomere to shorten further - This process repeats until the muscle is fully contracted

Question 37

What is the role of ATP during muscle contraction ?

Answer 37

- ATP needed for breaking cross-bridges between myosin and actin filaments - ATP hydrolyses to ADP and Pi resetting myosin head to original position - Active transport of calcium ions back into the sarcoplasmic reticulum

Question 38

What is creatine phosphate ?

Answer 38

A molecule stored by muscles that can be used for the rapid production of ATP

Question 39

How does Creatine phosphate work ?

Answer 39

- A phosphate ion from Creatine phosphate is transferred to ADP - ADP + Creatine phosphate → ATP + creatine

Question 40

What is the aim of creatine phosphate ?

Answer 40

- It allows for muscles to continue contracting for a short period of time until the mitochondria are able to supply ATP

Question 41

What happens once the supply of creatine phosphate has ran out ?

Answer 41

For prolonged activity, once the supply of phosphocreatine has been used up then the rate of muscle contraction must equal the rate of ATP production from both aerobic and anaerobic respiration