Skeletal muscles are stimulated to contract by nerves and act as effectors

Question 1

What are muscles?

Answer 1

Effector organs that respond to nervous stimulation and bring about muscle contraction

Question 2

What are muscles made up of?

Answer 2

Bundles of myofibrils

Question 3

What do you call muscles that work in pairs?

Answer 3

Antagonistic muscles

Question 4

Why do muscles work in pairs to create movement?

Answer 4

Muscles can only contract and pull, they cannot push therefore they work in pairs to create movement

Question 5

What are muscles attached to?

Answer 5

Bones via tendons

Question 6

What happens when the bicep contracts?

Answer 6

• Tricep relaxes
• Bicep pulls the bone so the arm flexes at the elbow
• Bicep: agonist
• Tricep: antagonist

Question 7

What happens when the tricep contracts?

Answer 7

• Bicep relaxes
• Tricep pulls the bone so the arm straightens at the elbow
• Bicep: antagonist
• Tricep: agonist

Question 8

What are muscle cells made up of?

Answer 8

Millions of myofibrils which are made up of fused cells that share nuclei and ctyoplasm referred as sacroplasm.

Question 9

What are the 3 types of muscle cells and where are they found? Are they conscious or unconscious control?

Answer 9

Cardiac muscle - Heart - Unconscious

Skeletal muscle - Wall of blood vessel - Unconscious

Smooth muscle cell - Attached to bones - Conscious

Question 10

What is the ultra-structure of a myofibril?

Answer 10

• Made up of 2 protein filaments called actin and myosin
• Actin filament is thinner and consists of 2 strands wrapped around into a helix
• Myosin filament is thicker, long rod shaped tail with a bulbous head.
• Under microscope myosin appears dark and actin appears light.

Question 11

How is contraction of a myofibril and muscle possible?

Answer 11

Actin and myosin slide over each other to make sarcomere contract. The simultaneous contraction of sarcomere allows myofibrils and muscles to contract.

Question 12

What happens to each band during contraction?

Answer 12

I-band - gets shorter
A-band - stays same
H-zone - gets shorter
Z-lines - move closer together
Sarcomeres - gets shorter

Question 13

Describe and explain how muscle contraction occurs

Answer 13

In resting muscle
- Tropomyosin blocks the myosin head from binding to the actin-myosin binding site which means myofilaments cannot slide past each other

Contracting muscle
- An action potential reaches the neuromuscular junction which causes acetylcholine to be released which binds to the receptors on the muscle cell membrane.

• This depolarises the membrane causing Ca2+ to be released from the sarcoplasmic reticulum.
• Calcium ions bind to troponin on the actin filaments causing it to change shape which pulls tropomyosin out of the actin-myosin binding site.
• The myosin head binds to the actin-myosin binding site forming a cross-bridge
• Ca2+ activate ATP hydrolase which hydrolyses the ATP that is bound to the myosin head. The energy released from this causes the myosin head to bend which pull the actin filament along.
• Another ATP attaches to the myosin head and is hydrolysed to provide energy to break the cross bridges
• The myosin head binds to a different actin-myosin binding site further along, the process is repeated