Locomotion and Movement

What to remember

• Muscle contraction follows the sliding filament theory: Ca²⁺ released from the sarcoplasmic reticulum binds troponin, myosin heads form cross bridges with actin and pull the thin filaments towards the centre of the A band. The A band keeps its length; the I band and the H zone shorten.
• The sarcomere (between two Z lines) is the functional unit of contraction. Thin filaments (actin) are attached to the Z line; thick filaments (myosin) lie in the A band and are held by the M line.
• The human skeleton has 206 bones: axial skeleton 80 and appendicular skeleton 126. Skull 22 bones (8 cranial + 14 facial); vertebral column 26 bones (7 cervical, 12 thoracic, 5 lumbar, 1 sacrum, 1 coccyx); 12 pairs of ribs.
• Joints are fibrous (no movement), cartilaginous (limited movement) or synovial (free movement). Disorders to know: myasthenia gravis, tetany, muscular dystrophy, arthritis, osteoporosis and gout.

Types of movement and types of muscle

Movement is a basic feature of living organisms. Locomotion is movement from one place to another. Three types of movement are seen in human cells and tissues.

Type	Mechanism	Examples
Amoeboid	Pseudopodia formed by streaming of protoplasm, with help of cytoskeletal elements such as microfilaments	Amoeba; macrophages and leucocytes in blood
Ciliary	Coordinated beating of cilia	Ciliated epithelium of the trachea (removes dust); movement of ova through the female reproductive tract
Muscular	Contraction and relaxation of muscles	Movement of limbs, jaws, tongue

Muscular movement and locomotion need the coordinated working of the muscular, skeletal and neural systems.

There are three kinds of muscle.

Feature	Skeletal	Visceral (smooth)	Cardiac
Appearance	Striated	Non-striated	Striated
Control	Voluntary	Involuntary	Involuntary
Location	Attached to skeletal bones (tendons)	Walls of hollow visceral organs such as the alimentary canal and blood vessels	Heart
Special feature	Used in locomotion and body posture	Helps in transport of food, gametes etc.	Cells branch and are joined by intercalated discs

Structure of skeletal muscle

Each skeletal muscle is made of many bundles called fascicles. A fascicle is wrapped in collagenous connective tissue and contains many muscle fibres.

Part	Description
Fascicle	Bundle of muscle fibres
Muscle fibre	One muscle cell, a syncytium with many nuclei
Sarcolemma	Plasma membrane of the muscle fibre
Sarcoplasm	Cytoplasm of the muscle fibre
Sarcoplasmic reticulum	Endoplasmic reticulum of the fibre; stores Ca²⁺
Myofibrils	Parallel thread-like units in the sarcoplasm, made of filaments

Myofibrils show alternating dark and light bands, so the muscle looks striated.

Band or line	Meaning
A band (anisotropic)	Dark band; contains thick myosin filaments and also parts of thin filaments
I band (isotropic)	Light band; contains only thin actin filaments
Z line	Elastic fibre in the middle of the I band; thin filaments are attached to it
M line	In the middle of the A band; holds the thick filaments together
H zone	Central part of the A band where thin filaments do not overlap thick filaments
Sarcomere	Portion between two successive Z lines; the functional unit of contraction

In a resting sarcomere, the thin filaments from both sides partly overlap the thick filaments. The central part of the thick filaments is not overlapped and forms the H zone.

Contractile proteins

Actin (thin filament). Each thin filament has two F (filamentous) actin strands twisted around each other like a helix. Each F actin is a polymer of G (globular) actin monomers. Two filaments of the protein tropomyosin run close to the F actin along its length. Troponin is a complex protein found at regular intervals on tropomyosin. In the resting state, a subunit of troponin masks the active binding sites for myosin on actin.

Myosin (thick filament). Myosin is a polymer of many monomers called meromyosins. Each meromyosin has two parts: a globular head with a short arm, called heavy meromyosin (HMM), and a tail, called light meromyosin (LMM). The HMM projects out from the thick filament at regular distances and angles and is called the cross arm. The globular head is an active ATPase enzyme. It has binding sites for ATP and active sites for actin.

Mechanism of muscle contraction

Contraction follows the sliding filament theory. Thin filaments slide over thick filaments and the sarcomere shortens.

Sequence of events:

• 1. A signal from the central nervous system travels along a motor neuron to the neuromuscular junction (motor end plate).
• 2. The neurotransmitter acetylcholine is released. It generates an action potential in the sarcolemma.
• 3. The action potential spreads through the muscle fibre and causes release of Ca²⁺ from the sarcoplasmic reticulum into the sarcoplasm.
• 4. Ca²⁺ binds to a subunit of troponin on the actin filaments. This removes the masking of the active sites for myosin.
• 5. Using energy from ATP hydrolysis, the myosin head binds to the exposed active site on actin and forms a cross bridge.
• 6. The myosin head pulls the actin filament towards the centre of the A band. The Z lines attached to the actin are also pulled inwards, so the sarcomere shortens.
• 7. Myosin releases ADP and Pi and returns to its relaxed state. A new ATP binds and breaks the cross bridge. ATP is hydrolysed again and the cycle repeats.

Relaxation: Ca²⁺ is pumped back into the sarcoplasmic reticulum. Active sites on actin are masked again. The thin filaments return to their original position and the muscle relaxes.

Region	During contraction
A band	Length stays the same
I band	Shortens
H zone	Shortens
Sarcomere (Z to Z)	Shortens

Red and white fibres, fatigue

Feature	Red (aerobic) fibres	White fibres
Myoglobin	High (gives the red colour)	Low
Mitochondria	Plenty	Few
Energy supply	Aerobic; use a lot of oxygen	Anaerobic glycolysis
Contraction	Slow, sustained	Fast, quickly tired

Myoglobin is an oxygen-storing pigment in muscle. When muscle is repeatedly active, glycogen is broken down anaerobically and lactic acid builds up. This causes muscle fatigue.

The skeletal system

The human skeleton has 206 bones and a few cartilages. It is divided into the axial and appendicular skeletons.

Division	Number of bones	Parts
Axial	80	Skull, vertebral column, sternum, ribs
Appendicular	126	Limbs and girdles

Skull (22 bones). Cranial bones are 8 and facial bones are 14. The cranium has frontal (1), parietal (2), temporal (2), occipital (1), sphenoid (1) and ethmoid (1). The hyoid is a single U-shaped bone at the base of the buccal cavity. Each middle ear has three ear ossicles: malleus, incus and stapes. The skull joins the vertebral column through two occipital condyles (dicondylic).

Vertebral column (26 bones).

Region	Number
Cervical	7
Thoracic	12
Lumbar	5
Sacral (fused)	1
Coccygeal (fused)	1

The first cervical vertebra is the atlas. It articulates with the occipital condyles. The neural canal encloses the spinal cord. The number of cervical vertebrae is seven in almost all mammals.

Sternum and ribs. The sternum is a flat bone on the ventral midline of the thorax. There are 12 pairs of ribs. They are of three kinds.

Rib type	Pairs	Attachment
True ribs	1 to 7	Join the thoracic vertebrae dorsally and the sternum ventrally by hyaline cartilage
False (vertebrochondral) ribs	8, 9, 10	Do not join the sternum directly; joined to the seventh rib by cartilage
Floating ribs	11, 12	Not connected ventrally

Thoracic vertebrae, ribs and the sternum together form the rib cage.

Limbs and girdles. Each limb has 30 bones.

Part	Bones
Forelimb	Humerus, radius, ulna, 8 carpals, 5 metacarpals, 14 phalanges
Hind limb	Femur, tibia, fibula, 7 tarsals, 5 metatarsals, 14 phalanges, patella (knee cap)

The pectoral girdle has two halves. Each half has a clavicle and a scapula. The scapula is a flat triangular bone with a raised ridge called the spine, which projects as the acromion. The acromion articulates with the clavicle. The scapula has a depression, the glenoid cavity, into which the head of the humerus fits to form the shoulder joint.

The pelvic girdle has two coxal bones. Each coxal bone is formed by the fusion of the ilium, ischium and pubis. At the point of fusion is the acetabulum, a cavity where the thigh bone (femur) articulates. The two halves meet ventrally at the pubic symphysis, which has fibrous cartilage.

Joints

Type	Feature	Examples
Fibrous	Bones joined by dense fibrous tissue; no movement	Sutures between flat skull bones
Cartilaginous	Bones joined by cartilage; limited movement	Joints between adjacent vertebrae
Synovial	Fluid-filled synovial cavity between bones; free movement	See below

Types of synovial joints:

Synovial joint	Example
Ball and socket	Shoulder joint (humerus and pectoral girdle); hip joint
Hinge	Knee joint
Pivot	Joint between atlas and axis
Gliding	Joints between the carpals
Saddle	Joint between carpal and metacarpal of the thumb

Disorders of the muscular and skeletal systems

Disorder	Cause or feature
Myasthenia gravis	Autoimmune disorder affecting the neuromuscular junction; causes fatigue, weakening and paralysis of skeletal muscle
Muscular dystrophy	Progressive degeneration of skeletal muscle, mostly due to a genetic disorder
Tetany	Rapid spasms (wild contractions) of muscle due to low Ca²⁺ in body fluid
Arthritis	Inflammation of joints
Osteoporosis	Age-related decrease in bone mass with higher chance of fractures; low oestrogen is a common cause
Gout	Inflammation of joints due to accumulation of uric acid crystals

NEET traps

• 1. Z line lies in the middle of the I band; M line lies in the middle of the A band.
• 2. During contraction, the A band does not change in length; the I band and H zone shorten.
• 3. Troponin binds Ca²⁺; tropomyosin runs along actin. The ATPase and actin-binding sites are on the myosin head, not on actin.
• 4. Ca²⁺ is stored in the sarcoplasmic reticulum, not in the sarcolemma.
• 5. Red fibres have more myoglobin and mitochondria and are aerobic; white fibres are anaerobic.
• 6. True ribs are the first seven pairs; false ribs are pairs 8 to 10; floating ribs are pairs 11 and 12.
• 7. The axial skeleton has 80 bones and the appendicular has 126. Skull has 22 bones, but the vertebral column has 26 bones.
• 8. Cardiac muscle is striated like skeletal muscle but is involuntary; visceral muscle is non-striated and involuntary.
• 9. Myasthenia gravis affects the neuromuscular junction (autoimmune); muscular dystrophy is genetic. Tetany is caused by low Ca²⁺; gout is caused by uric acid crystals.
• 10. Pivot joint is between atlas and axis; hinge is at the knee; saddle is at the thumb base; gliding is between carpals.

One-liners

• 1. Amoeboid movement is seen in Amoeba and in macrophages and leucocytes.
• 2. Ciliary movement removes dust in the trachea.
• 3. A muscle fibre is a syncytium with many nuclei.
• 4. The sarcolemma is the plasma membrane of the muscle fibre.
• 5. A band is dark; I band is light.
• 6. The sarcomere is the portion between two Z lines.
• 7. F actin is a polymer of G actin.
• 8. The myosin head has ATPase activity.
• 9. Acetylcholine is released at the neuromuscular junction.
• 10. Ca²⁺ binding to troponin exposes the myosin binding sites on actin.
• 11. Lactic acid accumulation leads to muscle fatigue.
• 12. The human skeleton has 206 bones.
• 13. Atlas is the first cervical vertebra.
• 14. The acetabulum is the cavity of the coxal bone for the femur.
• 15. The patella is the knee cap bone of the hind limb.

Practice questions

1. Amoeboid movement is seen in

   1. Ova in the oviduct
   2. Skeletal muscle fibres
   3. Macrophages
   4. Cells lining the trachea
   Answer

   C. Macrophages

   Amoeba, macrophages and leucocytes move by pseudopodia formed by streaming of protoplasm.

2. Ciliary movement helps to remove dust particles in the

   1. Trachea
   2. Amoeba
   3. Leucocytes
   4. Biceps muscle
   Answer

   A. Trachea

   The ciliated epithelium of the trachea beats in coordination to remove dust.

3. Which type of muscle is striated and involuntary?

   1. Skeletal
   2. Cardiac
   3. Smooth muscle of the gut
   4. Visceral
   Answer

   B. Cardiac

   Cardiac muscle is striated like skeletal muscle but is not under voluntary control.

4. The plasma membrane of a muscle fibre is called the

   1. Sarcoplasm
   2. Myofibril
   3. Sarcoplasmic reticulum
   4. Sarcolemma
   Answer

   D. Sarcolemma

   The sarcolemma is the plasma membrane; the sarcoplasm is the cytoplasm inside it.

5. Ca²⁺ ions required for muscle contraction are stored in the

   1. M line
   2. Z line
   3. Sarcoplasmic reticulum
   4. Sarcolemma
   Answer

   C. Sarcoplasmic reticulum

   The sarcoplasmic reticulum is the endoplasmic reticulum of muscle and stores Ca²⁺.

6. The dark band of a sarcomere that contains the thick myosin filaments is the

   1. A band
   2. I band
   3. Z line
   4. H zone
   Answer

   A. A band

   The A band (anisotropic band) is dark and holds the myosin filaments.

7. The Z line is present in the middle of the

   1. M line
   2. A band
   3. H zone
   4. I band
   Answer

   D. I band

   The Z line is an elastic fibre that bisects the I band.

8. The functional unit of contraction in a myofibril is the

   1. Muscle fibre
   2. Sarcomere
   3. Myofilament
   4. Fascicle
   Answer

   B. Sarcomere

   The portion between two successive Z lines is the sarcomere.

9. Which protein subunit binds Ca²⁺ to expose the active sites on actin?

   1. Troponin
   2. Tropomyosin
   3. F actin
   4. Myosin
   Answer

   A. Troponin

   Ca²⁺ binds a subunit of troponin, which unmasks the myosin binding sites on actin.

10. The globular head of a myosin molecule has

    1. Binding sites for Ca²⁺ only
    2. ATPase activity and binding sites for ATP and actin
    3. A binding site for acetylcholine
    4. No enzyme activity
    Answer

    B. ATPase activity and binding sites for ATP and actin

    The head is an active ATPase with ATP binding sites and active sites for actin.

11. How many bones does the human skeleton have?

    1. 80
    2. 22
    3. 206
    4. 126
    Answer

    C. 206

    The human skeleton has 206 bones: 80 axial and 126 appendicular.

12. The number of cranial bones in the human skull is

    1. 6
    2. 14
    3. 22
    4. 8
    Answer

    D. 8

    The skull has 22 bones: 8 cranial and 14 facial.

13. The number of cervical vertebrae in humans is

    1. 12
    2. 5
    3. 7
    4. 9
    Answer

    C. 7

    The human vertebral column has 7 cervical, 12 thoracic, 5 lumbar, 1 sacral and 1 coccygeal bone.

14. Floating ribs are

    1. The 1st to 7th pairs
    2. The 11th and 12th pairs
    3. The 7th pair
    4. The 8th, 9th and 10th pairs
    Answer

    B. The 11th and 12th pairs

    The 11th and 12th pairs are not connected ventrally.

15. The joint between the atlas and the axis is a

    1. Pivot joint
    2. Hinge joint
    3. Gliding joint
    4. Saddle joint
    Answer

    A. Pivot joint

    The atlas and axis form a pivot joint.

16. The joint between the carpal and metacarpal of the thumb is a

    1. Ball and socket joint
    2. Hinge joint
    3. Pivot joint
    4. Saddle joint
    Answer

    D. Saddle joint

    This joint at the base of the thumb is a saddle joint.

17. Given below are two statements: Statement I: During muscle contraction the A band remains the same in length. Statement II: The I band becomes shorter during contraction.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Thin filaments slide inward, so the I band and H zone shorten while the A band keeps its length.

18. Given below are two statements: Statement I: In a resting muscle a subunit of troponin masks the active sites for myosin on actin. Statement II: Tropomyosin is the protein that binds Ca²⁺.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Troponin masks the sites and binds Ca²⁺. Tropomyosin only runs along the F actin.

19. Given below are two statements: Statement I: Red muscle fibres have less myoglobin than white fibres. Statement II: White fibres depend mainly on anaerobic glycolysis.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Red fibres have a lot of myoglobin. White fibres have few mitochondria and use anaerobic glycolysis.

20. Given below are two statements: Statement I: Visceral muscle is striated and voluntary. Statement II: Cardiac muscle has intercalated discs.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Visceral muscle is non-striated and involuntary. Cardiac muscle cells are joined by intercalated discs.

21. Which of the following statements are correct? 1. The axial skeleton has 80 bones. 2. The skull has 22 bones. 3. The vertebral column has 33 bones in humans.

    1. 1 and 3 only
    2. 2 and 3 only
    3. 1 and 2 only
    4. 1, 2 and 3
    Answer

    C. 1 and 2 only

    The human vertebral column has 26 bones, as sacrum and coccyx count as one bone each.

22. Given below are two statements: Statement I: Myasthenia gravis is an autoimmune disorder that affects the neuromuscular junction. Statement II: Muscular dystrophy is caused by accumulation of uric acid crystals.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Muscular dystrophy is progressive degeneration of muscle, mostly genetic. Uric acid crystals cause gout.

23. Which of the following statements are correct? 1. Sutures of the skull are fibrous joints. 2. Joints between adjacent vertebrae are cartilaginous. 3. The knee joint is a pivot joint.

    1. 1 and 2 only
    2. 1 and 3 only
    3. 2 and 3 only
    4. 1, 2 and 3
    Answer

    A. 1 and 2 only

    The knee is a hinge joint, not a pivot joint.

24. Given below are two statements: Statement I: Tetany is caused by a high level of Ca²⁺ in body fluid. Statement II: Osteoporosis is a decrease in bone mass with a higher chance of fractures.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Tetany is due to low Ca²⁺. Osteoporosis reduces bone mass.

25. Given below are two statements: Statement I: Gout is caused by accumulation of uric acid crystals in joints. Statement II: Arthritis is inflammation of joints.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Both statements are correct.

26. Given below are two statements: Statement I: The pelvic girdle consists of a clavicle and a scapula on each side. Statement II: The glenoid cavity of the scapula receives the head of the femur.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    The pectoral girdle has the clavicle and scapula. The glenoid cavity receives the humerus; the femur fits the acetabulum.

27. Assertion (A): The sarcomere shortens during muscle contraction. Reason (R): Myosin heads pull the thin filaments towards the centre of the A band.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Cross bridge movement pulls actin and the attached Z lines inward, shortening the sarcomere.

28. Assertion (A): Sutures of the skull allow no movement. Reason (R): The bones at sutures are joined by cartilage.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    C. A is true but R is false

    Sutures are fibrous joints with dense fibrous connective tissue, not cartilage.

29. Assertion (A): Floating ribs articulate with the sternum. Reason (R): Floating ribs are the 11th and 12th pairs.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    D. A is false but R is true

    Floating ribs are not connected ventrally, so A is false. R is true.

30. Assertion (A): Osteoporosis increases the chance of bone fractures. Reason (R): Gout is caused by accumulation of uric acid crystals.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    B. Both A and R are true but R is not the correct explanation of A

    Both are true but unrelated; R does not explain A.

31. Assertion (A): Myasthenia gravis causes weakening of skeletal muscles. Reason (R): It is an autoimmune disorder that affects the neuromuscular junction.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Attack on the neuromuscular junction by the immune system causes fatigue, weakness and paralysis of muscle.

32. Assertion (A): Troponin is a part of the thick filament. Reason (R): Troponin binds Ca²⁺ during muscle contraction.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    D. A is false but R is true

    Troponin is on the thin filament (with actin and tropomyosin); thick filaments are made of myosin.

33. Match List I with List II. List I: a. F actin b. Tropomyosin c. Troponin d. Myosin head List II: i. Binds Ca²⁺ ii. Polymer of G actin iii. ATPase activity iv. Runs along the F actin

    1. a-iii, b-iv, c-i, d-ii
    2. a-ii, b-iv, c-i, d-iii
    3. a-ii, b-i, c-iv, d-iii
    4. a-iv, b-ii, c-i, d-iii
    Answer

    B. a-ii, b-iv, c-i, d-iii

    F actin is a polymer of G actin, tropomyosin runs along F actin, troponin binds Ca²⁺ and the myosin head has ATPase activity.

34. Match List I with List II. List I: a. A band b. I band c. Z line d. H zone List II: i. Contains myosin filaments ii. Thin filaments only iii. Elastic fibre bisecting the I band iv. Central part of the A band with no overlap

    1. a-ii, b-i, c-iv, d-iii
    2. a-ii, b-i, c-iii, d-iv
    3. a-iii, b-i, c-ii, d-iv
    4. a-i, b-ii, c-iii, d-iv
    Answer

    D. a-i, b-ii, c-iii, d-iv

    A band has myosin; I band has only actin; Z line bisects the I band; the H zone is the non-overlapped centre of the A band.

35. Match List I with List II. List I: a. Ball and socket b. Hinge c. Pivot d. Gliding List II: i. Atlas and axis ii. Knee iii. Humerus and pectoral girdle iv. Carpals

    1. a-iii, b-i, c-ii, d-iv
    2. a-ii, b-iii, c-i, d-iv
    3. a-iii, b-ii, c-i, d-iv
    4. a-iii, b-ii, c-iv, d-i
    Answer

    C. a-iii, b-ii, c-i, d-iv

    Shoulder is ball and socket, knee is hinge, atlas-axis is pivot and carpals form gliding joints.

36. Match List I with List II. List I: a. Myasthenia gravis b. Tetany c. Gout d. Osteoporosis List II: i. Autoimmune; neuromuscular junction ii. Low Ca²⁺ in body fluid iii. Uric acid crystals iv. Decreased bone mass

    1. a-ii, b-i, c-iii, d-iv
    2. a-i, b-ii, c-iii, d-iv
    3. a-i, b-iii, c-ii, d-iv
    4. a-i, b-ii, c-iv, d-iii
    Answer

    B. a-i, b-ii, c-iii, d-iv

    Each disorder is matched to its cause or feature as described.

37. Match List I with List II. List I: a. Cranial bones b. Facial bones c. Vertebral column d. Appendicular skeleton List II: i. 14 ii. 26 iii. 126 iv. 8

    1. a-iv, b-ii, c-i, d-iii
    2. a-iv, b-i, c-iii, d-ii
    3. a-i, b-iv, c-ii, d-iii
    4. a-iv, b-i, c-ii, d-iii
    Answer

    D. a-iv, b-i, c-ii, d-iii

    Cranial 8, facial 14, vertebral column 26, appendicular skeleton 126.

38. Match List I with List II. List I: a. Scapula b. Coxal bone c. Hyoid d. Patella List II: i. Glenoid cavity ii. Acetabulum iii. U-shaped bone at the base of the buccal cavity iv. Knee cap

    1. a-ii, b-i, c-iii, d-iv
    2. a-i, b-ii, c-iii, d-iv
    3. a-i, b-ii, c-iv, d-iii
    4. a-iii, b-ii, c-i, d-iv
    Answer

    B. a-i, b-ii, c-iii, d-iv

    Glenoid cavity is on the scapula, acetabulum on the coxal bone, hyoid is U-shaped and patella is the knee cap.

39. In a muscle fibre, ATP is not available. What is expected for the myosin heads?

    1. They release acetylcholine
    2. They bind troponin
    3. They stay attached to actin because a new ATP is needed to break the cross bridge
    4. They detach from actin and the muscle relaxes
    Answer

    C. They stay attached to actin because a new ATP is needed to break the cross bridge

    Binding of a new ATP breaks the cross bridge. Without ATP the cross bridges stay attached.

40. Which statement is most likely true about the muscles of a long-distance runner compared with those of a sprinter?

    1. Sprinter muscles have more red fibres for slow sustained work
    2. Both depend only on anaerobic glycolysis
    3. Runner muscles have more red fibres rich in myoglobin and mitochondria
    4. White fibres have more mitochondria than red fibres
    Answer

    C. Runner muscles have more red fibres rich in myoglobin and mitochondria

    Red fibres are aerobic, rich in myoglobin and mitochondria, and suited to sustained work.

41. A patient has repeated muscle spasms because the Ca²⁺ level in body fluid is low. This disorder is

    1. Tetany
    2. Myasthenia gravis
    3. Gout
    4. Osteoporosis
    Answer

    A. Tetany

    Low Ca²⁺ in body fluid causes rapid spasms of muscle called tetany.

42. Which observation fits a skeletal muscle sarcomere that is contracting?

    1. The thin filaments become shorter
    2. The thick filaments become shorter
    3. The A band becomes shorter
    4. Z lines come closer, the I band shortens and the A band stays the same
    Answer

    D. Z lines come closer, the I band shortens and the A band stays the same

    Filaments slide but do not change length. Only the I band, H zone and sarcomere shorten.

43. A person has weakness that increases with activity because of an autoimmune attack at the junction between nerve and muscle. The likely disorder is

    1. Gout
    2. Myasthenia gravis
    3. Tetany
    4. Muscular dystrophy
    Answer

    B. Myasthenia gravis

    Myasthenia gravis is an autoimmune disorder of the neuromuscular junction.

44. How many pairs of ribs are not attached directly to the sternum?

    1. 2
    2. 3
    3. 7
    4. 5
    Answer

    D. 5

    Pairs 8 to 10 join the seventh rib by cartilage and pairs 11 and 12 are floating, so 5 pairs in all.

45. How many bones are present in one hind limb, including the knee cap?

    1. 30
    2. 24
    3. 33
    4. 26
    Answer

    A. 30

    Femur 1, tibia 1, fibula 1, tarsals 7, metatarsals 5, phalanges 14 and patella 1 give 30.