Locomotion and Movement Class 11 Biology: Muscle Contraction, Skeleton and Joints

What Locomotion and Movement is about

Weightage: This chapter is part of Unit V, Human Physiology, which carries 18 of the 70 theory marks in the school annual exam together with Breathing and Exchange of Gases, Body Fluids and Circulation, Excretory Products and their Elimination, Neural Control and Coordination and Chemical Coordination and Integration.Source: CBSE Biology (044) syllabus 2026-27, Class XI course structure, Unit V Human Physiology

Key concepts

Types of movement

NCERT section 17.1 Types of Movement

Cells of the human body show three main types of movement: amoeboid, ciliary and muscular. Flagellar movement, closely related to ciliary movement, is described alongside them.

1. Amoeboid movement:

• Seen in specialised cells such as macrophages and leucocytes in blood.
• Effected by pseudopodia formed by streaming of protoplasm (as in *Amoeba*).
• Cytoskeletal elements like microfilaments are also involved.

2. Ciliary movement:

• Occurs in most internal tubular organs lined by ciliated epithelium.
• Coordinated movement of cilia in the trachea removes dust particles and foreign substances inhaled with air.
• Passage of ova through the female reproductive tract is also helped by ciliary movement.

Flagellar movement (cilia and flagella are outgrowths of the cell membrane):

• Helps the swimming of spermatozoa, maintains water current in the canal system of sponges, and moves protists like *Euglena*.

3. Muscular movement:

• Movement of limbs, jaws, tongue and so on requires muscular movement.
• The contractile property of muscles is used for locomotion and other movements by humans and most multicellular organisms.
• Locomotion requires the perfect coordination of muscular, skeletal and neural systems.

Example of the link between movement and locomotion: *Paramecium* uses cilia to move food through the cytopharynx and to swim; *Hydra* uses tentacles to capture prey and to move; we use limbs to change posture and to walk.

Worked example

Classify each movement as amoeboid, ciliary, flagellar or muscular: (a) a macrophage engulfing bacteria, (b) a sperm swimming towards the egg, (c) dust being cleared from the trachea, (d) the tongue moving food while chewing. Name the cytoskeletal elements involved in (a). (2 marks)

Try it first, then show the solutionSolution

1. (a) Amoeboid (pseudopodia formed by streaming of protoplasm); (b) flagellar. (1)
2. (c) Ciliary; (d) muscular. In (a), microfilaments of the cytoskeleton are involved. (1)

Answer: Amoeboid, flagellar, ciliary, muscular; microfilaments help amoeboid movement.

Muscle types and structure of skeletal muscle

NCERT section 17.2 Muscle (17.2.1 Structure of Contractile Proteins, first part)

Muscle is a specialised tissue of mesodermal origin. About 40-50% of an adult human's body weight is muscle. Muscles show excitability, contractility, extensibility and elasticity.

Three types (by location, appearance and control):

• Skeletal muscles: attached to bones; striped (striated); voluntary (under nervous control); used in locomotion and posture.
• Visceral (smooth) muscles: in the inner walls of hollow organs such as the alimentary canal and reproductive tract; non-striated; involuntary; help move food and gametes.
• Cardiac muscles: heart; striated with branching cells; involuntary.

Structure of a skeletal muscle:

• Made of muscle bundles, the fascicles, held together by a collagenous connective tissue layer, the fascia.
• Each fascicle has many muscle fibres. Each fibre is lined by the plasma membrane, the sarcolemma, enclosing the sarcoplasm.
• A muscle fibre is a syncytium: its sarcoplasm contains many nuclei.
• The endoplasmic reticulum of the muscle fibre, the sarcoplasmic reticulum, is a store of calcium ions.
• The sarcoplasm has many parallel filaments called myofilaments or myofibrils.

Striped appearance:

• Each myofibril has alternate dark and light bands formed by two proteins: actin and myosin.
• Light band (I-band, isotropic): contains actin (thin filaments).
• Dark band (A-band, anisotropic): contains myosin (thick filaments).
• Thin and thick filaments lie parallel and in the length of the myofibril.
• The Z-line (elastic fibre) bisects each I-band; thin filaments are firmly attached to it.
• Thick filaments in the A-band are held together at the middle by the thin M-line.
• The portion of the A-band not overlapped by thin filaments is the H-zone.
• Sarcomere: the portion of a myofibril between two successive Z-lines: the functional unit of contraction.
• At rest, the thin filaments reach only partway over the ends of the thick filaments, so a central H-zone is left uncovered.

Worked example

Define a sarcomere and name the bands and lines it contains. Which protein lies in the I-band? (3 marks)

Try it first, then show the solutionSolution

1. Sarcomere: the part of a myofibril between two successive Z-lines; the functional unit of contraction. (1)
2. It contains one A-band (with the H-zone and M-line in its middle) and half an I-band on each side, bounded by Z-lines. (1)
3. The I-band contains actin (thin filaments). (1)

Answer: Z to Z unit with A-band, H-zone, M-line and half I-bands; actin in the I-band.

Contractile proteins: actin and myosin

NCERT section 17.2.1 Structure of Contractile Proteins

Thin (actin) filament:

• Made of two 'F' (filamentous) actins helically wound around each other.
• Each F-actin is a chain of many small globular G-actin units.
• Two strands of tropomyosin lie along the F-actins for their whole length.
• Troponin, a complex protein, sits on the tropomyosin at regular gaps.
• At rest, part of the troponin covers the sites on actin where myosin would bind, so no cross bridges can form.

Thick (myosin) filament:

• A polymerised protein: many monomers called meromyosins form one thick filament.
• Each meromyosin has two parts:
• Heavy meromyosin (HMM): a globular head with a short arm.
• Light meromyosin (LMM): the tail.
• The HMM (head and short arm) projects outwards at regular distances and angles from the surface of the polymerised myosin filament: the cross arm.
• The globular head works as an ATPase (splits ATP) and carries a site for ATP and a site that attaches to actin.

Actin vs myosin:

• Actin: thin filament; in the I-band (and overlapping part of A-band); has tropomyosin and troponin; attached to Z-line.
• Myosin: thick filament; in the A-band; made of meromyosins; heads act as ATPase and form cross bridges.

Worked example

Describe the structure of a myosin monomer and state two properties of its head. (2 marks)

Try it first, then show the solutionSolution

1. Each meromyosin has a globular head with a short arm (heavy meromyosin) and a tail (light meromyosin); the head and arm project as the cross arm. (1)
2. The head acts as an ATPase and can bind both ATP and actin. (1)

Answer: HMM head + arm, LMM tail; head is an ATPase and binds ATP and actin.

Mechanism of muscle contraction (sliding filament theory)

NCERT section 17.2.2 Mechanism of Muscle Contraction

Sliding filament theory: contraction of a muscle fibre happens by the sliding of thin filaments over thick filaments.

Steps:
1. A signal from the CNS reaches the muscle through a motor neuron. A motor neuron and the muscle fibres connected to it form a motor unit. The junction between a motor neuron and the sarcolemma is the neuromuscular junction (motor end plate).
2. The neural signal releases the neurotransmitter acetylcholine, which generates an action potential in the sarcolemma.
3. This spreads through the muscle fibre and causes release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.
4. Ca²⁺ binds to a subunit of troponin on actin, which removes the masking of active sites for myosin.
5. Using energy from ATP hydrolysis, the myosin head binds to the exposed active sites on actin, forming a cross bridge.
6. The cross bridge pulls the attached actin filaments towards the centre of the A-band. The Z-lines attached to these actins are also pulled inwards, so the sarcomere shortens: contraction.
7. The head lets go of ADP and Pi and returns to its resting angle; when a fresh ATP attaches, the head detaches from actin.
8. The head splits this ATP, re-cocks, binds actin further along and pulls again; repeated attach-pull-detach cycles slide the filaments further.
9. The process continues until Ca²⁺ is pumped back into the sarcoplasmic reticulum, which masks the actin sites again. The Z-lines return to their original position: relaxation.

Band changes during contraction:

• I-bands shorten.
• A-band keeps its length.
• H-zone shortens/disappears as thin filaments overlap more.
• Sarcomere shortens.

Fatigue: repeated activation of muscles can cause accumulation of lactic acid from anaerobic breakdown of glycogen, causing fatigue.

Red and white muscle fibres:

• Red fibres: contain a red, oxygen-storing pigment, myoglobin, in high amounts; many mitochondria; use stored O₂ for ATP: aerobic muscles.
• White fibres: little myoglobin, pale or whitish; fewer mitochondria, but a large amount of sarcoplasmic reticulum; depend on anaerobic processes for energy.

Worked example

During contraction, which of these change in length: A-band, I-band, H-zone, sarcomere? Explain using the sliding filament idea. (3 marks)

Try it first, then show the solutionSolution

1. A-band stays the same, because it equals the length of the thick (myosin) filaments, which do not shorten. (1)
2. I-band and H-zone shorten, because thin filaments slide inwards and overlap more of the thick filaments. (1)
3. The sarcomere shortens because the Z-lines attached to actin are pulled towards the centre. (1)

Answer: A-band unchanged; I-band, H-zone and sarcomere shorten.

Skeletal system: axial and appendicular skeleton

NCERT section 17.3 Skeletal System

The skeletal system is a framework of bones and a few cartilages. It plays a major role in movement. Bone has a very hard matrix due to calcium salts; cartilage has a slightly pliable matrix due to chondroitin salts. In humans there are 206 bones.

Axial skeleton: 80 bones along the main axis.

• Skull (22 bones): cranial bones (8) form the hard protective outer cover for the brain (cranium); facial bones (14) form the front of the skull.
• A single U-shaped hyoid bone at the base of the buccal cavity.
• Ear ossicles: three tiny bones in each middle ear: malleus, incus and stapes (6 in all).
• The skull articulates with the top of the vertebral column through two occipital condyles: a dicondylic skull.
• Vertebral column: 26 serially arranged vertebrae, dorsally placed, from the base of the skull. Each vertebra has a central hollow, the neural canal, through which the spinal cord passes. The first vertebra is the atlas, which articulates with the occipital condyles.
• Regions: cervical (7), thoracic (12), lumbar (5), sacral (1, fused) and coccygeal (1, fused).
• The number of cervical vertebrae is seven in almost all mammals, including humans.
• Functions: protects the spinal cord, supports the head, attachment point for ribs and back muscles.
• Sternum: a flat bone on the ventral midline of the thorax.
• Ribs: 12 pairs. Each rib is a thin, flat bone running from the vertebral column at the back to the sternum in front; its back end has two joint surfaces, so it is called bicephalic.
• True ribs: first seven pairs, attached directly to the sternum by hyaline cartilage.
• Vertebrochondral (false) ribs: 8th, 9th, 10th pairs; join the 7th rib's cartilage, not the sternum directly.
• Floating ribs: last 2 pairs (11th, 12th); not connected ventrally.
• Thoracic vertebrae, ribs and sternum together form the rib cage.

Appendicular skeleton: 126 bones (limbs and girdles).

• Each limb has 30 bones.
• Forelimb: humerus, radius and ulna, carpals (8), metacarpals (5), phalanges (14).
• Hind limb: femur (longest bone), tibia and fibula, tarsals (7), metatarsals (5), phalanges (14), and the patella (knee cap).
• Pectoral girdle (one on each side): clavicle (collar bone, long slender bone with two curvatures) and scapula (large triangular flat bone on the dorsal thorax between the 2nd and 7th ribs). The scapula has a slightly elevated ridge, the spine, which ends as an expanded process, the acromion; the clavicle articulates with it. Below the acromion lies a shallow socket, the glenoid cavity; the rounded top of the humerus fits here, making the shoulder joint.
• Pelvic girdle: two coxal bones, each formed by fusion of ilium, ischium and pubis. At their fusion point is a cavity, the acetabulum, into which the thigh bone fits. The two halves meet ventrally at the pubic symphysis, which contains fibrous cartilage.

Worked example

Show that the axial skeleton has 80 bones by adding its parts. (2 marks)

Try it first, then show the solutionSolution

1. Skull 22 (8 cranial + 14 facial) + hyoid 1 + ear ossicles 6 = 29. (1)
2. Vertebrae 26 + sternum 1 + ribs 24 = 51; 29 + 51 = 80. (1)

Answer: 22 + 1 + 6 + 26 + 1 + 24 = 80.

Joints

NCERT section 17.4 Joints

Joints are points of contact between bones, or between bones and cartilages. They are essential for all movements involving the bony parts of the body. The force generated by muscles is used to move the bones across a joint, with the joint acting as a fulcrum. The movability of joints varies with type.

1. Fibrous joints: do not allow any movement. The bones are fused end to end with dense fibrous connective tissue, as sutures. Example: the flat skull bones fused to form the cranium.

2. Cartilaginous joints: bones are joined together with the help of cartilage, allowing limited movement. Example: joints between adjacent vertebrae of the vertebral column.

3. Synovial joints: have a fluid-filled synovial cavity between the articulating surfaces of two bones, allowing considerable movement. They help locomotion and many other movements. Types:

• Ball and socket joint: between humerus and pectoral girdle (shoulder).
• Hinge joint: knee joint (and elbow).
• Pivot joint: between atlas and axis (head turns side to side).
• Gliding joint: between the carpals.
• Saddle joint: between the carpal and metacarpal of the thumb.

Worked example

Explain why the bones of the cranium cannot move against each other while adjacent vertebrae can move a little, and name the feature that lets synovial joints move freely. What role does a joint play when a muscle moves a bone? (2 marks)

Try it first, then show the solutionSolution

1. Cranial bones meet at fibrous joints (sutures), fused end to end by dense fibrous connective tissue, so no movement is possible; vertebrae are joined by cartilage (cartilaginous joints), allowing limited movement. (1)
2. Synovial joints have a fluid-filled synovial cavity between the articulating surfaces, allowing considerable movement; the joint acts as a fulcrum across which the force generated by muscles moves the bone. (1)

Answer: Sutures (fibrous) allow no movement, cartilage limited movement; the synovial cavity allows free movement; a joint is the fulcrum.

Disorders of muscular and skeletal systems

NCERT section 17.5 Disorders of Muscular and Skeletal System

Myasthenia gravis: the body's own immune system attacks the neuromuscular junction (an autoimmune disorder); skeletal muscles tire, weaken and may become paralysed.

Muscular dystrophy: skeletal muscle wastes away step by step; the cause is usually genetic.

Tetany: muscles go into quick, uncontrolled spasms because body fluids have too little Ca²⁺.

Arthritis: joints become inflamed.

Osteoporosis: with age, bone mass falls and bones fracture more easily; a drop in oestrogen is a frequent cause (hence common in older women).

Gout: joints become inflamed when uric acid crystals build up in them.

Grouping:

• Muscle/nerve-muscle: myasthenia gravis, muscular dystrophy, tetany.
• Bone and joint: arthritis, osteoporosis, gout.

Worked example

Name the disorder: (a) low calcium causes muscle spasms; (b) uric acid crystals in joints; (c) immune system attacks the neuromuscular junction; (d) bones become thin after menopause. (2 marks)

Try it first, then show the solutionSolution

1. (a) Tetany; (b) gout. (1)
2. (c) Myasthenia gravis; (d) osteoporosis (decreased oestrogen). (1)

Answer: Tetany, gout, myasthenia gravis, osteoporosis.

Locomotion and Movement in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Human Skeleton, Joints and Disorders
• Muscle Structure and Sliding Filament Theory

Locomotion and Movement: key facts

Sarcomere

$\text{sarcomere}=\text{Z-line to Z-line}=\frac{1}{2}\text{I}+\text{A (with H-zone and M-line)}+\frac{1}{2}\text{I}$

Functional unit of contraction.

Contraction sequence

$\text{ACh}\to \text{action potential}\to {\text{Ca}}^{2+}\text{from SR}\to {\text{Ca}}^{2+}+\text{troponin}\to \text{cross bridge (ATP)}\to \text{sliding}$

Relaxation when Ca²⁺ is pumped back.

Bone count

$206=80(\text{axial})+126(\text{appendicular})$

Each limb 30 bones; skull 22.

Axial skeleton

$80=22(\text{skull})+1(\text{hyoid})+6(\text{ear ossicles})+26(\text{vertebrae})+1(\text{sternum})+24(\text{ribs})$

Ribs: 12 pairs.

Vertebral formula

$C_7{T}_{12}{L}_5{S}_{1}C{o}_1=26$

Sacral and coccygeal are fused.

Band changes on contraction

$\text{A unchanged};\text{I}\downarrow ;\text{H}\downarrow ;\text{sarcomere}\downarrow$

Filaments slide; they do not shorten.

Locomotion and Movement: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Locomotion and Movement

The question patterns to expect, and the method that works for each.

Tricks to remember Locomotion and Movement

Short memory aids. Say each one aloud once, then use it on a question the same day.

• dArk = A-band, lIght = I-band

  A-band is dArk and Anisotropic with myosin; I-band is lIght and Isotropic with actin.

  Use it when: Band identity.

• H for Hollow middle

  H-zone is the part of the A-band with no thin filaments; it shrinks in contraction.

  Use it when: H-zone changes.

• Breakfast at 7, Lunch at 12, Dinner at 5

  Cervical 7, Thoracic 12, Lumbar 5 vertebrae (then 1 sacral, 1 coccygeal).

  Use it when: Vertebral formula.

• 7-3-2 ribs

  7 true, 3 false (vertebrochondral), 2 floating pairs = 12 pairs.

  Use it when: Rib types.

• Three in the hip: I-I-P

  Ilium, Ischium, Pubis fuse into each coxal bone around the acetabulum.

  Use it when: Pelvic girdle.

• Ca²⁺ unlocks, ATP powers

  Calcium removes troponin's mask; ATP powers the myosin head and breaks the cross bridge.

  Use it when: Contraction steps.

Locomotion and Movement: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Locomotion and Movement

The slips examiners see most often, and what to write instead.

• ✗Mistake: Saying the A-band shortens during contraction

  Assuming everything shortens.

  ✓Do this: A-band length (thick filament length) stays the same; I-band and H-zone shorten.

  Usually costs: 1 mark.

• ✗Mistake: Stating that actin and myosin filaments shorten

  Confusing filament sliding with filament shortening.

  ✓Do this: Filaments slide past each other; their lengths do not change.

  Usually costs: 1 mark.

• ✗Mistake: Writing that Ca²⁺ binds tropomyosin or myosin

  Regulatory proteins mixed up.

  ✓Do this: Ca²⁺ binds troponin, which unmasks actin's active sites.

  Usually costs: 1 mark.

• ✗Mistake: Giving 11 pairs of ribs or 33 vertebrae

  Counting individual fused vertebrae or forgetting floating ribs.

  ✓Do this: 12 pairs of ribs; 26 vertebrae (sacrum and coccyx counted as one each).

  Usually costs: ½-1 mark.

• ✗Mistake: Calling the knee a ball and socket joint

  It feels very mobile.

  ✓Do this: Knee is a hinge joint; ball and socket is at the shoulder (and hip).

  Usually costs: ½ mark.

• ✗Mistake: Confusing gout with arthritis in general

  Both involve joint inflammation.

  ✓Do this: Gout is a specific inflammation caused by uric acid crystals in joints.

  Usually costs: ½ mark.

NCERT exercise guide: Locomotion and Movement

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Practice questions on Locomotion and Movement

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   The functional unit of contraction of a muscle fibre is:
   (a) myofibril (b) sarcomere (c) fascicle (d) sarcolemma

   Hint

   Between two Z-lines.

   Answer

   (b) sarcomere

2. Q2 · 1 mark · MCQExam level

   Which of these is a cartilaginous joint?
   (a) Between skull bones (b) Between adjacent vertebrae (c) Knee (d) Shoulder

   Hint

   Limited movement.

   Answer

   (b) Between adjacent vertebrae

3. Q3 · 2 marks · Very short answerExam level

   Name the bones of the human forelimb with their numbers. (2 marks)

   Hint

   30 in all.

   Answer

   Humerus 1, radius 1, ulna 1 (1); carpals 8, metacarpals 5, phalanges 14; total 30 (1).

4. Q4 · 2 marks · Very short answerHarder exam level

   Why is the human skull called dicondylic, and which bone does it articulate with? (2 marks)

   Hint

   Two condyles.

   Answer

   It has two occipital condyles (1), which articulate with the atlas, the first vertebra (1).

5. Q5 · 2 marks · Very short answerHarder exam level

   Describe the structure of an actin filament. (2 marks)

   Hint

   F-actin, G-actin, tropomyosin, troponin.

   Answer

   Two F-actins helically wound, each a polymer of G-actin monomers (1); two tropomyosin filaments run along them and troponin occurs at intervals, masking myosin-binding sites at rest (1).

6. Q6 · 2 marks · Very short answerHarder exam level

   Give the functions of cartilage and bone in the skeleton and the cause of their different hardness. (2 marks)

   Hint

   Calcium vs chondroitin salts.

   Answer

   Bone has a very hard matrix due to calcium salts, giving rigid support and protection (1). Cartilage has a slightly pliable matrix due to chondroitin salts, giving flexibility, e.g. connecting true ribs to the sternum (1).

7. Q7 · 3 marks · Short answerHarder exam level

   Distinguish between true, false and floating ribs. (3 marks)

   Hint

   7-3-2.

   Answer

   True ribs: first 7 pairs, attached directly to the sternum by hyaline cartilage (1). False (vertebrochondral) ribs: 8th-10th pairs, joined to the 7th rib's cartilage, not directly to the sternum (1). Floating ribs: 11th and 12th pairs, not connected ventrally (1).

8. Q8 · 3 marks · Short answerHarder exam level

   Describe ciliary and flagellar movement with examples from the human body and other organisms. (3 marks)

   Hint

   Trachea, oviduct, sperm, sponge.

   Answer

   Ciliary: in tubular organs lined by ciliated epithelium; cilia of the trachea remove dust; cilia help move ova in the female tract (1½). Flagellar: sperm swimming; water current in the canal system of sponges; Euglena locomotion (1½).

9. Q9 · 5 marks · Long answerHarder exam level

   (a) Describe the structure of a skeletal muscle from muscle to myofibril. (b) Explain the striated appearance. (5 marks)

   Hint

   Fascicles → fibres → myofibrils → bands.

   Answer

   (a) Muscle made of fascicles held by fascia; each fascicle has many muscle fibres lined by sarcolemma enclosing sarcoplasm; fibre is a syncytium with many nuclei; sarcoplasmic reticulum stores Ca²⁺; sarcoplasm has many parallel myofibrils (2½). (b) Myofibrils show alternate light I-bands (actin) and dark A-bands (myosin); Z-line bisects the I-band; M-line holds thick filaments in the middle of the A-band; H-zone is the A-band region not overlapped by actin; the repeating pattern from Z to Z (sarcomere) gives striations (2½).

10. Q10 · 3 marks · Short answerHOTS / competency

    Suppose a drug prevents Ca²⁺ from being pumped back into the sarcoplasmic reticulum. Predict the effect on the muscle and explain. (3 marks)

    Hint

    Relaxation needs Ca²⁺ removal.

    Answer

    Relaxation requires Ca²⁺ to be pumped back so that troponin again masks actin's sites (1). If Ca²⁺ stays in the sarcoplasm, the sites remain exposed and cross bridges keep forming as long as ATP lasts (1). The muscle would stay contracted (sustained contraction/cramp) and could not relax (1).

11. Q11 · 3 marks · Short answerHOTS / competency

    A person has painful swollen big-toe joints after eating protein-rich meals, and blood tests show high uric acid. Name the disorder and connect it with excretion. (3 marks)

    Hint

    Nitrogenous waste.

    Answer

    Gout (1). Uric acid is a nitrogenous waste from breakdown of nucleic acids/proteins; if produced in excess or poorly excreted by the kidneys, it accumulates (1). Uric acid crystals deposit in joints, causing inflammation and pain (1).

12. Q12 · 1 mark · Assertion-reasonHOTS / competency

    Assertion (A): During muscle contraction the H-zone shortens or disappears.
    Reason (R): Thin filaments slide towards the centre of the A-band and overlap more of the thick filaments.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

    Hint

    Sliding filaments.

    Answer

    (a)

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What percentage of body weight is muscle?Show answer

   About 40-50%.

2. 2.Which organelle stores Ca²⁺ in muscle fibres?Show answer

   Sarcoplasmic reticulum.

3. 3.What is a motor unit?Show answer

   A motor neuron and the muscle fibres connected to it.

4. 4.Which neurotransmitter acts at the neuromuscular junction?Show answer

   Acetylcholine.

5. 5.What masks myosin-binding sites on actin at rest?Show answer

   A subunit of troponin.

6. 6.What are the two parts of a meromyosin?Show answer

   Heavy meromyosin (head and short arm) and light meromyosin (tail).

7. 7.Which pigment is abundant in red muscle fibres?Show answer

   Myoglobin.

8. 8.How many bones make up the skull?Show answer

   22 (8 cranial + 14 facial).

9. 9.Name the ear ossicles.Show answer

   Malleus, incus and stapes.

10. 10.What is the acetabulum?Show answer

    The cavity in the coxal bone where the thigh bone fits.

11. 11.Which joint is between the carpal and metacarpal of the thumb?Show answer

    Saddle joint.

12. 12.What causes tetany?Show answer

    Low Ca²⁺ in body fluid.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you give examples of amoeboid, ciliary and flagellar movement?
• ☐Can you compare skeletal, smooth and cardiac muscle?
• ☐Can you draw and label a sarcomere?
• ☐Can you describe the actin and myosin filaments?
• ☐Can you list the steps of muscle contraction from nerve signal to relaxation?
• ☐Can you say which bands change length during contraction?
• ☐Can you count the axial and appendicular bones and name the girdle bones?
• ☐Can you name five synovial joints with examples and six disorders with causes?

Locomotion and Movement: frequently asked questions