CH15 Skeletal muscles

Question 1

3 types of muscles and their location

Answer 1

Cardiac - heart
Smooth - walls of blood vessels and intestines
Skeletal - attached to incompressible skeletons by tendons

Question 2

What is an antagonistic pair of muscles

Answer 2

Pairs pull in opposite directions - agonist contracts while antagonist is relaxed

Question 3

Describe gross structure of skeletal muscle

Answer 3

Muscle cells fused together to form myofibrils

Question 4

Describe microscopic structure of skeletal muscles

Answer 4

Myofibrils - site of contraction
Sarcoplasm - shared nuclei and cytoplasm with lots of mitochondria and ER
Sarcolemma - folds inwards towards sarcoplasm to form transverse tubules

Question 5

Ultrastructure of a myofibril

Answer 5

Z-line - boundary between sarcomeres
I-band - only actin
A-band - overlap of actin and myosin
H-zone - only myosin

Question 6

How does each band appear under optical microscope

Answer 6

I-band - light

A-band - dark

Question 7

Role of Ca2+ in muscle contraction

Answer 7

1. Action potential moves through T-tubules in sarcoplasm = Ca2+ channels in sarcoplasmic reticulum open
2. Ca2+ binds to tropomyosin triggering a conformational change
3. Exposes binding sites on actin filaments so myosin can bind

Question 8

Sliding filament theory

Answer 8

1. Myosin head with ADP attached binds to actin
2. Myosin head changes shape and loses ADP, pulling actin over myosin
3. ATP attaches to myosin head, causing it to detach from actin
4. ATPase hydrolyses ATP to form ADP so myosin head returns to original position
5. Myosin head attaches to actin further along filament

Question 9

How does sliding filament cause myofibril to shorten

Answer 9

Myosin heads flex in opposite directions - actin pulled towards each other
Distance between Z lines shortens

Question 10

4 pieces of evidence that support sliding filament theory

Answer 10

H-zones narrow
I-band narrows
Z-lines get closer
A-zone stays the same

Question 11

What happens during muscle relaxation

Answer 11

Ca2+ actively transported into endoplasmic reticulum

Tropomyosin blocks actin binding site

Question 12

Role of phosphocreatine

Answer 12

Phosphorylates ADP directly to ATP when oxygen is limited

Question 13

Where are slow twitch muscle fibres found

Answer 13

Sites of sustained contraction

Calf muscle

Question 14

Where are fast twitch muscle fibres found

Answer 14

Sites of short-term, rapid powerful contraction

biceps

Question 15

Role of slow twitch fibres

Answer 15

Long duration contraction

Adapted to aerobic respiration to prevent lactate buildup

Question 16

Role of fast twitch fibres

Answer 16

Powerful short term contraction

Adapted to anaerobic respiration

Question 17

Structure and properties of slow twitch fibres

Answer 17

Glycogen store - many terminal ends can be hydrolysed to release glucose
Contain myoglobin - higher affinity for oxygen than haemoglobin
Many mitochondria - aerobic respiration produces more ATP
Surrounded by blood vessels - high supply of oxygen and glucose

Question 18

Structure and properties of fast twitch fibres

Answer 18

Large store of phosphocreatine
More and thicker myosin filaments
High conc of enzymes in anaerobic respiration