7 - Muscle

Question 1

What are the 2 parts of an antagonistic muscle pair?

Answer 1

flexor - bicep

extensor - tricep

Question 2

What is a concentric and eccentric muscle contraction?

Answer 2

concentric - shortening

eccentric - lengthening

Question 3

What is another name for muscle cells?

Answer 3

myofibres

Skeletal muscles are bundle of myofibres

Question 4

What are the properties of myofibres?

Answer 4

• large and cylindrical
• multinucleate
  packed with myofibrils

Question 5

What are the bands and lines that can be seen in myofibrils?

Answer 5

light and dark bands give a ‘striated’ appearance

• A band: dark bands containing the thick myosin filament
• H zone: in the A band - where there is no actin superimposed
• I band: lighter bands containing just actin filaments and no myosin
• Z line: made up of α-actinin and CapZ

Question 6

What is actin made up of?

Answer 6

2 twisted α helices

Question 7

Describe the sliding filament theory

Answer 7

1- the presence of Ca2+ causes the movement of troponin from the tropomyosin chain
2- this exposes the myosin binding site on actin
3- the ‘charged’ myosin head binds to the exposed site on the actin filament
4- the binding and discharge of ATP causes the myosin head to pivot i.e. the ‘power stroke’ —> pulling the acid filament towards the centre of the sarcomere
5- ATP binding causes the release of the myosin head from the actin chain
6- ATP hydrolysis provides the energy to ‘recharge’ the myosin head

Question 8

Give some characteristics of cardiac muscle

Answer 8

• striated muscle
• have intercalated discs:
• —-> have desmosomes hold the membrane structures together) and gap junctions (communication between cells)
• mechanism of contraction is the same as in skeletal muscle

Question 9

Where is the action potential in the heart generated from?

Answer 9

pacemaker cells in the sinoatrial node

Question 10

How is contraction in cardiomyocytes different to that in skeletal muscle cells?

Answer 10

• voltage gated calcium channels instead of DHPR on the sarcolemma
• the VGCC open to allow Ca2+ influx
• THERE IS NO CONTACT BETWEEN VGCC AND RYR RECEPTORS
  Ca2+ binds to RyR and causes calcium induced calcium release

Question 11

Where do you fund smooth muscle in the body?

Answer 11

present within the walls of all hollow organs

Question 12

Give some characteristics of smooth muscle

Answer 12

• does not have a regular arrangement of actin and myosin - no striated pattern
• contraction is different to that in skeletal and cardiac muscle