AP Biology - Plants and Human Body Systems
OpenStax Biology for AP — Chapter 29: The Musculoskeletal System — AP BIOLOGY Revision Notes & Topical Questions
5 min read 7 parts Lesson 10 of 15 Unit quiz
Lesson summary
OpenStax Biology for AP — Chapter 29: The Musculoskeletal System — AP BIOLOGY notes: Describe skeleton types, bone, joints, muscle types and the sliding filament model of contraction.Skeletal muscle is striated and voluntary, for example the biceps.Cardiac muscle is found only in…
- Hydrostatic skeleton
- Exoskeleton
- Endoskeleton
- Tropomyosin
- Antagonistic pair
- Osteoclast
Section 1 of 7Muscle types
Muscle types
Skeletal muscle is striated and voluntary, for example the biceps.
Cardiac muscle is found only in the heart and contracts without conscious control.
Smooth muscle forms the walls of the gut, blood vessels, uterus and bladder and is involuntary.
Section 2 of 7Sliding filament contraction
- Structure
- a muscle fibre contains myofibrils made of sarcomeres, with thin actin and thick myosin filaments.
1
A motor neuron releases acetylcholine at the neuromuscular junction, and an action potential spreads through the fibre.
2
Ca2+ is released from the sarcoplasmic reticulum.
3
Ca2+ binds troponin, which moves tropomyosin and exposes myosin-binding sites on actin.
4
Myosin heads bind, pivot (the power stroke) and release, using ATP.
5
The filaments slide past each other and the sarcomere shortens.
6
The muscle relaxes when Ca2+ is pumped back.
- Evidence
- during contraction the I band and H zone shorten while the A band stays the same length, so filaments slide rather than shorten.
Section 3 of 7Skeleton types and bone
Skeleton types and bone
Hydrostatic skeleton
- Hydrostatic skeleton fluid under pressure in a compartment, with muscles acting on the fluid.
Exoskeleton
- Exoskeleton a hard external skeleton with muscles attached on the inside.
Endoskeleton
- Endoskeleton internal mineralised skeleton to which muscles attach;
- the human skeleton has axial and appendicular parts.
Bone is living connective tissue of cells, mineral salts and collagen.
- Compact bone (osteons) forms the outer layer and spongy bone (trabeculae) the inner part.
- Osteoblasts deposit bone and osteoclasts resorb it, so bone is remodelled continuously.
Section 4 of 7Joints and muscle action
1
Muscles work in antagonistic pairs, such as biceps and triceps, because muscles can only pull.
2
Tendons attach muscle to bone and ligaments attach bone to bone.
3
Synovial joints include hinge, ball-and-socket and pivot types, which allow different movements.
4
The skeleton supports the body, protects organs, stores calcium and makes blood cells in the marrow.
Section 5 of 7Energy for muscle
1
ATP comes from creatine phosphate, aerobic respiration or anaerobic glycolysis with lactate formation in intense exercise.
2
Slow-twitch fibres are rich in mitochondria and suited to endurance.
3
Fast-twitch fibres contract quickly but tire sooner.
4
Without ATP, myosin heads cannot detach from actin, causing rigor mortis.
5
Without Ca2+ release, tropomyosin continues to block the binding sites and no contraction occurs.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Sarcomere | Functional contractile unit of skeletal muscle. |
| Actin | Thin filament protein in muscle. |
| Myosin | Thick filament protein whose heads form cross-bridges. |
| Tropomyosin | Protein that blocks myosin-binding sites until Ca2+ binds troponin. |
| Antagonistic pair | Two muscles that produce opposite movements. |
| Osteoclast | Cell that resorbs bone. |
Section 7 of 7Exam technique
1
Thinking the filaments themselves shorten during contraction — they slide past each other
2
Forgetting that ATP is needed both for the power stroke and for release
3
Saying that cardiac muscle is voluntary — it is involuntary
4
Confusing tendons with ligaments — tendons join muscle to bone, ligaments join bone to bone
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