Q: Q8. Match the following:\n(a) Smooth muscle\t(i) Myoglobin\n(b) Tropomyosin\t(ii) Sutures\n(c) Red muscle\t(iii) Actin filament\n(d) Skull\t\t(iv) Involuntary\n(e) Pectoral girdle\t(v)

The correct matches are:\n(a) Smooth muscle - (iv) Involuntary\n(b) Tropomyosin - (iii) Actin filament\n(c) Red muscle - (i) Myoglobin\n(d) Skull - (ii) Sutures\n(e) Pectoral girdle - (v) Glenoid cavity

Q: Q10. Name the type of joint between the following:\n(a) Atlas/axis\n(b) Carpal/metacarpal of thumb\n(c) Phalanges\n(d) Femur/acetabulum\n(e) Cranial bones\n(f) Between vertebrae

(a) **Atlas/axis:** Pivot joint (or Atlanto-axial joint)\n(b) **Carpal/metacarpal of thumb:** Saddle joint\n(c) **Phalanges:** Hinge joint (Interphalangeal joints)\n(d) **Femur/acetabulum:** Ball and socket joint (Hip joint)\n(e) **Cranial bones:** Fibrous joint / Sutures\n(f) **Between vertebrae:** Cartilaginous joint (Symphysis) / Gliding joint (between articular processes)

Question 1

Q1. Draw the diagram of a sarcomere of skeletal muscle showing different regions.

Accepted Answer

A sarcomere is the basic contractile unit of a muscle fiber. It is the region between two successive Z-lines. The diagram should clearly illustrate the arrangement of actin (thin) and myosin (thick) filaments and the various bands and lines associated with them.

**Key regions to be shown in the diagram:**
1.  **Z-line (Z-disc):** A dense line that marks the boundaries of a sarcomere. Actin filaments are anchored to the Z-line.
2.  **I-band (Isotropic band):** Contains only thin (actin) filaments. It is bisected by the Z-line. During contraction, the I-band shortens.
3.  **A-band (Anisotropic band):** Contains the entire length of the thick (myosin) filaments and the overlapping portions of the thin (actin) filaments. It remains constant in length during contraction.
4.  **H-zone (Hensen's zone):** A central region within the A-band that contains only thick (myosin) filaments. It shortens and may disappear during muscle contraction.
5.  **M-line (M-disc):** A central line within the H-zone that holds the thick (myosin) filaments together.
6.  **Actin filaments:** Thin filaments, primarily composed of actin, tropomyosin, and troponin.
7.  **Myosin filaments:** Thick filaments, primarily composed of myosin.

The diagram should show the parallel arrangement of these filaments, with actin filaments extending from the Z-lines towards the center of the sarcomere, and myosin filaments occupying the central region (A-band). The overlap between actin and myosin filaments should be visible.

Question 2

Q2. Define sliding filament theory of muscle contraction.

Accepted Answer

The **sliding filament theory** is the most widely accepted model explaining how muscles contract. It states that muscle contraction occurs by the sliding of the thin (actin) filaments over the thick (myosin) filaments, without any change in the length of either filament itself. This sliding action results in the shortening of the sarcomere, and consequently, the entire muscle fiber.

**Key aspects of the theory:**
*   During contraction, the myosin heads form cross-bridges with the actin filaments.
*   These cross-bridges then pull the actin filaments towards the center of the sarcomere (M-line).
*   This pulling action causes the Z-lines to come closer, leading to the shortening of the I-band and H-zone, while the A-band's length remains unchanged.
*   The energy for this process is supplied by the hydrolysis of ATP by the ATPase activity of the myosin head.
*   Calcium ions (Ca2+) play a crucial role in initiating and regulating this process by binding to troponin, which in turn moves tropomyosin away from the actin binding sites, allowing myosin to bind.

Question 3

Q3. What are the important differences between actin and myosin?

Accepted Answer

Actin and myosin are the primary contractile proteins responsible for muscle contraction. While both are essential, they differ significantly in their structure, composition, and specific roles.

**Differences between Actin and Myosin:**

Question 4

Q4. Outline the structure of the following:
(a) actin filament
(b) myosin filament

Accepted Answer

The structure of actin and myosin filaments is highly specialized to facilitate their role in muscle contraction.

### (a) Structure of Actin Filament (Thin Filament)

An actin filament is a thin filament, approximately 5-8 nm in diameter, and is composed of three different proteins:

1.  **F-actin (Filamentous Actin):**
    *   Each actin filament is made up of two 'F' (filamentous) actins helically wound around each other.
    *   Each F-actin is a polymer of monomeric 'G' (globular) actins.
    *   Each G-actin monomer has a binding site for the myosin head.

2.  **Tropomyosin:**
    *   Two strands of tropomyosin proteins run almost the entire length of the F-actin filament.
    *   In a resting state, tropomyosin covers the myosin-binding sites on the G-actin monomers, preventing the binding of myosin heads.

3.  **Troponin:**
    *   Troponin is a complex of three globular proteins (Troponin T, Troponin I, and Troponin C) that is distributed at regular intervals on the tropomyosin molecules.
    *   **Troponin C (TnC):** Binds to calcium ions (Ca2+), which initiates the conformational change that uncovers the myosin-binding sites on actin.
    *   **Troponin I (TnI):** Inhibits the binding of myosin to actin.
    *   **Troponin T (TnT):** Binds to tropomyosin, anchoring the troponin complex to the thin filament.

### (b) Structure of Myosin Filament (Thick Filament)

A myosin filament is a thick filament, approximately 10-16 nm in diameter, and is a polymer of many monomeric proteins called **meromyosins**. Each meromyosin has two main parts:

1.  **Heavy Meromyosin (HMM):**
    *   This part consists of a globular head and a short arm.
    *   The **globular head** is the most crucial part, projecting outwards from the thick filament at a regular distance and angle. It possesses:
        *   **ATPase activity:** It can hydrolyze ATP to release energy for muscle contraction.
        *   **Actin-binding sites:** Specific sites that bind to actin filaments to form cross-bridges.
        *   **ATP-binding sites:** Sites where ATP molecules bind.
    *   The short arm acts as a hinge, allowing the head to move and pull the actin filament.

2.  **Light Meromyosin (LMM):**
    *   This part consists of a long, fibrous tail.
    *   The LMM forms the core of the thick filament, with the HMM portions projecting outwards. The tails of many meromyosins are bundled together to form the thick filament.

The globular heads and short arms (HMM) project outwards from the myosin filament, forming cross-bridges that interact with the actin filaments during muscle contraction.

Question 5

Q5. Write a brief account of:
(a) Gout
(b) Osteoporosis
(c) Myasthenia gravis
(d) Muscular dystrophy
(e) Arthritis

Accepted Answer

Here is a brief account of the mentioned disorders related to the muscular and skeletal systems:

### (a) Gout
*   **Definition:** Gout is a form of inflammatory arthritis characterized by sudden, severe attacks of pain, swelling, redness, and tenderness in the joints, often the joint at the base of the big toe.
*   **Cause:** It is caused by an accumulation of uric acid crystals (monosodium urate) in the joints. This occurs due to either an overproduction of uric acid or an under-excretion of uric acid by the kidneys, leading to hyperuricemia.
*   **Symptoms:** Intense joint pain (typically in the big toe, but can affect ankles, knees, elbows, wrists, and fingers), swelling, redness, and warmth in the affected joint.
*   **Affected System:** Skeletal system (joints).

### (b) Osteoporosis
*   **Definition:** Osteoporosis is a skeletal disorder characterized by reduced bone mass and deterioration of bone tissue, leading to increased bone fragility and a higher risk of fractures.
*   **Cause:** The primary cause is an imbalance between bone formation and bone resorption, where bone resorption outpaces bone formation. Common contributing factors include:
    *   **Age:** Bone density naturally decreases with age.
    *   **Hormonal changes:** Decreased estrogen levels in post-menopausal women (most common cause) and decreased testosterone in men.
    *   **Nutritional deficiencies:** Insufficient intake of calcium and Vitamin D.
    *   **Lifestyle factors:** Sedentary lifestyle, smoking, excessive alcohol consumption.
*   **Symptoms:** Often asymptomatic until a fracture occurs. Common fracture sites include the hip, spine, and wrist. Other symptoms may include loss of height and a stooped posture (kyphosis).
*   **Affected System:** Skeletal system (bones).

### (c) Myasthenia Gravis
*   **Definition:** Myasthenia gravis is a chronic autoimmune neuromuscular disease characterized by varying degrees of weakness of the skeletal (voluntary) muscles.
*   **Cause:** It is an autoimmune disorder where the body's immune system mistakenly attacks and destroys or blocks the acetylcholine receptors at the neuromuscular junction. This prevents acetylcholine (a neurotransmitter) from effectively stimulating muscle contraction.
*   **Symptoms:** Muscle weakness that worsens with activity and improves with rest. Commonly affected muscles include those controlling eye movements (ptosis, double vision), facial expression, chewing, swallowing, and speech. In severe cases, respiratory muscles can be affected, leading to a myasthenic crisis.
*   **Affected System:** Muscular system (neuromuscular junction).

### (d) Muscular Dystrophy
*   **Definition:** Muscular dystrophy (MD) is a group of inherited genetic disorders that cause progressive weakness and loss of muscle mass.
*   **Cause:** It is caused by mutations in genes responsible for making proteins vital to muscle fiber structure and function. The most common form, Duchenne Muscular Dystrophy (DMD), is caused by a mutation in the gene for dystrophin, a protein essential for maintaining the integrity of muscle fibers.
*   **Symptoms:** Progressive muscle weakness, loss of muscle bulk, difficulty with motor skills (walking, running), frequent falls, and in later stages, may affect cardiac and respiratory muscles. Symptoms vary depending on the type of MD.
*   **Affected System:** Muscular system.

### (e) Arthritis
*   **Definition:** Arthritis is an inflammatory condition that affects the joints, causing pain, swelling, stiffness, and reduced range of motion.
*   **Cause:** There are over 100 different types of arthritis, each with its own specific cause. Common types include:
    *   **Osteoarthritis:** Caused by the wear and tear of cartilage that cushions the ends of bones.
    *   **Rheumatoid Arthritis:** An autoimmune disorder where the immune system attacks the joint lining (synovium).
    *   **Gouty Arthritis (Gout):** Caused by uric acid crystal deposition (as described above).
    *   **Psoriatic Arthritis:** Affects some people who have psoriasis.
*   **Symptoms:** Joint pain, stiffness (often worse in the morning), swelling, redness, warmth, and decreased range of motion in the affected joints.
*   **Affected System:** Skeletal system (joints).

Question 6

Q6. Write notes on:
(a) Humerus
(b) Pelvic girdle
(c) Synovial joints

Accepted Answer

### (a) Humerus
The humerus is the single long bone of the upper arm, extending from the shoulder to the elbow. It is the largest and longest bone of the upper limb.

**Structure:**
1.  **Proximal End:** It articulates with the scapula (shoulder blade) to form the shoulder joint. It consists of:
    *   **Head:** A large, smooth, rounded structure that fits into the glenoid cavity of the scapula.
    *   **Anatomical Neck:** A slight constriction inferior to the head.
    *   **Greater Tubercle:** A prominent lateral projection, site of attachment for supraspinatus, infraspinatus, and teres minor muscles.
    *   **Lesser Tubercle:** A smaller anterior projection, site of attachment for the subscapularis muscle.
    *   **Intertubercular (Bicipital) Groove:** A groove between the two tubercles, through which the long head of the biceps brachii tendon passes.
    *   **Surgical Neck:** A common site for fractures, inferior to the tubercles.
2.  **Shaft:** The long, cylindrical body of the humerus. It has a deltoid tuberosity laterally, where the deltoid muscle attaches, and a radial groove posteriorly, through which the radial nerve and profunda brachii artery pass.
3.  **Distal End:** It articulates with the radius and ulna (forearm bones) to form the elbow joint. It consists of:
    *   **Capitulum:** A rounded lateral condyle that articulates with the head of the radius.
    *   **Trochlea:** A spool-shaped medial condyle that articulates with the trochlear notch of the ulna.
    *   **Medial Epicondyle:** A prominent projection on the medial side, providing attachment for forearm flexor muscles and the ulnar nerve passes posteriorly to it.
    *   **Lateral Epicondyle:** A smaller projection on the lateral side, providing attachment for forearm extensor muscles.
    *   **Coronoid Fossa:** An anterior depression above the trochlea, accommodating the coronoid process of the ulna during elbow flexion.
    *   **Radial Fossa:** An anterior depression above the capitulum, accommodating the head of the radius during elbow flexion.
    *   **Olecranon Fossa:** A large posterior depression above the trochlea, accommodating the olecranon process of the ulna during elbow extension.

**Function:** The humerus provides attachment points for numerous muscles involved in shoulder and elbow movements and facilitates a wide range of motion in the upper limb.

### (b) Pelvic Girdle
The pelvic girdle, also known as the hip girdle, is part of the appendicular skeleton and connects the lower limbs to the axial skeleton. It is a strong, basin-shaped structure that supports the weight of the upper body, protects the pelvic organs, and provides attachment for muscles of the lower limbs and trunk.

**Structure:**
It is formed by two large, symmetrical hip bones (coxal bones or innominate bones) that articulate anteriorly at the pubic symphysis and posteriorly with the sacrum (part of the axial skeleton) to form the sacroiliac joints. Each hip bone is formed by the fusion of three bones during adolescence:
1.  **Ilium:** The largest and most superior part of the hip bone. It forms the superior portion of the acetabulum. Its prominent features include the iliac crest (the superior border), anterior superior iliac spine (ASIS), posterior superior iliac spine (PSIS), and the greater sciatic notch.
2.  **Ischium:** The posteroinferior part of the hip bone. It forms the posterior and inferior part of the acetabulum. Key features include the ischial tuberosity (the rough inferior projection on which we sit) and the ischial spine.
3.  **Pubis:** The anteroinferior part of the hip bone. It forms the anterior part of the acetabulum. The two pubic bones meet at the pubic symphysis, a cartilaginous joint. It has a superior and inferior pubic ramus.

**Acetabulum:** The three bones (ilium, ischium, and pubis) converge to form a deep, cup-shaped socket called the acetabulum, which articulates with the head of the femur to form the hip joint.

**Obturator Foramen:** A large opening in the hip bone, enclosed by the ischium and pubis, which is mostly covered by a membrane and allows passage of nerves and blood vessels.

**Function:** The pelvic girdle provides a stable base for the trunk, transmits weight from the upper body to the lower limbs, protects the urinary bladder, reproductive organs, and parts of the large intestine, and serves as an attachment point for muscles of the lower limbs, abdomen, and back.

### (c) Synovial Joints
Synovial joints are the most common type of joint in the body and are characterized by the presence of a fluid-filled synovial cavity between the articulating bones. This feature allows for a wide range of movement, making them the most movable type of joint.

**Key Characteristics:**
1.  **Articular Cartilage:** The ends of the articulating bones are covered by a layer of hyaline cartilage (articular cartilage), which provides a smooth, slippery surface, reducing friction and absorbing shock during movement.
2.  **Articular Capsule:** The joint is enclosed by a two-layered articular capsule:
    *   **Fibrous Capsule (Outer Layer):** Composed of dense irregular connective tissue, continuous with the periosteum of the bones, providing strength and preventing dislocation.
    *   **Synovial Membrane (Inner Layer):** Lines the fibrous capsule internally (except over the articular cartilage) and secretes synovial fluid.
3.  **Synovial Cavity:** A space between the articulating bones, filled with synovial fluid.
4.  **Synovial Fluid:** A viscous, clear, or pale-yellow fluid secreted by the synovial membrane. Its functions include:
    *   **Lubrication:** Reduces friction between articular cartilages.
    *   **Nutrient Distribution:** Supplies nutrients to and removes waste from the chondrocytes of the articular cartilage.
    *   **Shock Absorption:** Distributes pressure evenly across the articular surfaces.
5.  **Ligaments:** Strong bands of fibrous connective tissue that reinforce the articular capsule, holding the bones together and preventing excessive or undesirable movements.

**Types of Synovial Joints (based on shape of articulating surfaces and range of motion):**
*   **Ball-and-Socket Joint:** Spherical head of one bone fits into a cup-like depression of another (e.g., shoulder, hip joint). Allows movement in all planes (multiaxial).
*   **Hinge Joint:** Convex surface of one bone fits into the concave surface of another (e.g., elbow, knee, interphalangeal joints). Allows movement in one plane (uniaxial) like a door hinge.
*   **Pivot Joint:** Rounded end of one bone fits into a ring formed by another bone and a ligament (e.g., atlas/axis joint, radioulnar joint). Allows rotation around a central axis (uniaxial).
*   **Condyloid (Ellipsoidal) Joint:** Oval-shaped condyle of one bone fits into an elliptical cavity of another (e.g., wrist joint, metacarpophalangeal joints). Allows movement in two planes (biaxial) – flexion/extension, abduction/adduction, circumduction.
*   **Saddle Joint:** Articular surfaces are saddle-shaped, with one concave and the other convex (e.g., carpometacarpal joint of the thumb). Allows movement in two planes (biaxial) – flexion/extension, abduction/adduction, circumduction.
*   **Gliding (Plane) Joint:** Flat or slightly curved surfaces slide over each other (e.g., intercarpal, intertarsal, acromioclavicular joints). Allows limited gliding movements (nonaxial).

**Function:** Synovial joints are crucial for locomotion and a wide range of body movements, providing flexibility and mobility.

Question 7

Q7. Differentiate between:
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle

Accepted Answer

### (a) Actin and Myosin

| Feature           | Actin (Thin Filament)                               | Myosin (Thick Filament)                               | | :---------------- | :-------------------------------------------------- | :---------------------------------------------------- | | **Composition**   | Primarily F-actin (polymer of G-actin), Tropomyosin, Troponin | Primarily Myosin protein                              | | **Structure**     | Double-helical strand of F-actin. Tropomyosin coils around F-actin. Troponin complex (TnI, TnT, TnC) attached to tropomyosin. | Each myosin molecule has a globular head (heavy meromyosin, HMM) and a tail (light meromyosin, LMM). Heads project outwards. | | **Location**      | Forms the I-band and extends into the A-band. Anchored to the Z-line. | Forms the A-band. Located in the center of the sarcomere. | | **Role in Contraction** | Provides binding sites for myosin heads. Slides past myosin filaments during contraction. | Myosin heads bind to actin, form cross-bridges, and pull actin filaments towards the M-line, using ATP hydrolysis. | | **ATP Binding**   | Does not directly bind ATP.                         | Myosin heads have ATP-binding sites and ATPase activity. | | **Regulatory Proteins** | Associated with regulatory proteins (tropomyosin and troponin) that control myosin binding. | No direct regulatory proteins associated with myosin itself, but its interaction with actin is regulated. | | **Size**          | Thinner (approx. 5-8 nm diameter).                  | Thicker (approx. 12-16 nm diameter).                  | | **Movement**      | Is pulled by myosin heads.                          | Pulls actin filaments.                                |

### (b) Red and White Muscles

### (c) Pectoral and Pelvic Girdle

| Feature           | Pectoral Girdle (Shoulder Girdle)                     | Pelvic Girdle (Hip Girdle)                              | | :---------------- | :---------------------------------------------------- | :------------------------------------------------------ | | **Components**    | Two halves, each consisting of a clavicle (collar bone) and a scapula (shoulder blade). | Two large hip bones (coxal bones), each formed by the fusion of ilium, ischium, and pubis. | | **Connection to Axial Skeleton** | Does not directly articulate with the vertebral column. Connected indirectly via muscles and ligaments. | Directly articulates with the sacrum (part of the vertebral column) posteriorly at the sacroiliac joints. | | **Stability**     | Less stable, designed for mobility.                   | Highly stable, designed for weight-bearing.             | | **Mobility**      | Highly mobile, allowing wide range of motion for the upper limb. | Less mobile, restricted range of motion for the lower limb. | | **Glenoid/Acetabulum** | Has a shallow glenoid cavity for articulation with the head of the humerus. | Has a deep acetabulum for articulation with the head of the femur. | | **Weight Bearing** | Not primarily involved in weight bearing.             | Primarily involved in transmitting body weight to the lower limbs. | | **Function**      | Connects upper limbs to the axial skeleton, provides attachment for upper limb muscles, facilitates movement. | Connects lower limbs to the axial skeleton, supports body weight, protects pelvic organs, provides attachment for lower limb and trunk muscles. | | **Bone Fusion**   | Bones (clavicle, scapula) remain separate.            | Three bones (ilium, ischium, pubis) fuse to form a single hip bone. |

Question 8

Q8. Match the following:
(a) Smooth muscle	(i) Myoglobin
(b) Tropomyosin	(ii) Sutures
(c) Red muscle	(iii) Actin filament
(d) Skull		(iv) Involuntary
(e) Pectoral girdle	(v)

Accepted Answer

The correct matches are:
(a) Smooth muscle - (iv) Involuntary
(b) Tropomyosin - (iii) Actin filament
(c) Red muscle - (i) Myoglobin
(d) Skull - (ii) Sutures
(e) Pectoral girdle - (v) Glenoid cavity

Question 9

Q9. Discuss the important steps in muscle contraction.

Accepted Answer

Muscle contraction is a complex process explained by the **Sliding Filament Theory**, which states that muscle contraction occurs by the sliding of thin (actin) filaments over thick (myosin) filaments, without a change in the length of either filament. This process is initiated by a neural signal and requires ATP.

Here are the important steps in muscle contraction:

### 1. Neural Signal and Neurotransmitter Release
*   A motor neuron transmits an action potential (nerve impulse) to the neuromuscular junction (NMJ), which is the synapse between a motor neuron and a muscle fiber.
*   At the axon terminal of the motor neuron, the action potential causes the release of the neurotransmitter **acetylcholine (ACh)** into the synaptic cleft.

### 2. Muscle Fiber Excitation
*   ACh binds to specific receptors on the motor end plate of the muscle fiber membrane (sarcolemma).
*   This binding causes depolarization of the sarcolemma, generating an action potential in the muscle fiber.
*   The action potential propagates along the sarcolemma and into the muscle fiber's interior via the **T-tubules (transverse tubules)**.

### 3. Calcium Release from Sarcoplasmic Reticulum (SR)
*   The action potential traveling through the T-tubules triggers the release of calcium ions (Ca²⁺) from the **sarcoplasmic reticulum (SR)**, which is the muscle cell's specialized endoplasmic reticulum.
*   Ca²⁺ ions are released into the sarcoplasm (cytoplasm of the muscle fiber).

### 4. Actin-Myosin Binding (Cross-Bridge Formation)
*   In a resting muscle, the myosin-binding sites on the actin filaments are blocked by **tropomyosin**, which is held in place by the **troponin complex**.
*   When Ca²⁺ ions are released, they bind to the **troponin C subunit** of the troponin complex.
*   This binding causes a conformational change in troponin, which in turn pulls tropomyosin away from the myosin-binding sites on the actin filaments.
*   With the binding sites exposed, the **myosin heads** (which are already energized by ATP hydrolysis into ADP + Pi, and are in a 'cocked' position) can now bind to the exposed active sites on the actin filaments, forming **cross-bridges**.

### 5. Power Stroke
*   Upon formation of the cross-bridge, the stored energy in the myosin head is released, causing the myosin head to pivot or 'bend'. This movement is called the **power stroke**.
*   The power stroke pulls the attached actin filament towards the center of the sarcomere (M-line).
*   During the power stroke, ADP and Pi are released from the myosin head.

### 6. Cross-Bridge Detachment
*   A new ATP molecule binds to the myosin head.
*   The binding of ATP causes the myosin head to detach from the actin filament, breaking the cross-bridge.

### 7. Myosin Head Re-energization (Recovery Stroke)
*   The newly bound ATP is hydrolyzed by the myosin head's ATPase activity into ADP and Pi.
*   This hydrolysis re-energizes the myosin head, causing it to return to its original 'cocked' position, ready to bind to another active site on the actin filament further down.

### 8. Repetitive Cycling and Sarcomere Shortening
*   Steps 4-7 (cross-bridge formation, power stroke, detachment, and re-energization) repeat as long as Ca²⁺ ions are present and ATP is available.
*   This continuous cycling of myosin heads pulling on actin filaments causes the actin filaments to slide past the myosin filaments, leading to the shortening of the sarcomeres.
*   The shortening of many sarcomeres collectively results in the contraction of the entire muscle fiber and ultimately the whole muscle.

### 9. Relaxation
*   When the neural signal stops, acetylcholine is rapidly broken down by acetylcholinesterase in the synaptic cleft.
*   This stops the generation of action potentials in the muscle fiber.
*   Ca²⁺ ions are actively pumped back into the sarcoplasmic reticulum by Ca²⁺-ATPase pumps, requiring ATP.
*   The decrease in sarcoplasmic Ca²⁺ concentration causes Ca²⁺ to detach from troponin.
*   Tropomyosin then moves back to block the myosin-binding sites on actin.
*   Myosin heads can no longer form cross-bridges, and the muscle relaxes, returning to its original length.

Question 10

Q10. Name the type of joint between the following:
(a) Atlas/axis
(b) Carpal/metacarpal of thumb
(c) Phalanges
(d) Femur/acetabulum
(e) Cranial bones
(f) Between vertebrae

Accepted Answer

(a) **Atlas/axis:** Pivot joint (or Atlanto-axial joint)
(b) **Carpal/metacarpal of thumb:** Saddle joint
(c) **Phalanges:** Hinge joint (Interphalangeal joints)
(d) **Femur/acetabulum:** Ball and socket joint (Hip joint)
(e) **Cranial bones:** Fibrous joint / Sutures
(f) **Between vertebrae:** Cartilaginous joint (Symphysis) / Gliding joint (between articular processes)

Question 11

Q11. Write notes on the following:
(a) Humerus
(b) Pelvic girdle
(c) Synovial joint

Accepted Answer

### (a) Humerus

The humerus is the longest and largest bone of the upper arm, extending from the shoulder to the elbow. It is a typical long bone, characterized by a shaft (diaphysis) and two expanded ends (epiphyses).

**Key Features:**

1.  **Proximal End:**
    *   **Head:** A large, smooth, rounded structure that articulates with the glenoid cavity of the scapula to form the shoulder joint (a ball-and-socket joint).
    *   **Anatomical Neck:** A slight constriction inferior to the head.
    *   **Greater and Lesser Tubercles:** Prominences for muscle attachment (rotator cuff muscles).
    *   **Intertubercular (Bicipital) Groove:** A furrow between the tubercles, housing the tendon of the long head of the biceps brachii muscle.
    *   **Surgical Neck:** A common site for fractures, located inferior to the tubercles.

2.  **Shaft (Body):**
    *   **Deltoid Tuberosity:** A V-shaped roughened area on the lateral aspect, serving as the insertion point for the deltoid muscle.
    *   **Radial Groove (Spiral Groove):** Runs obliquely down the posterior surface, transmitting the radial nerve and profunda brachii artery.

3.  **Distal End:**
    *   **Medial and Lateral Epicondyles:** Bony projections on either side, providing attachment for forearm muscles and ligaments.
    *   **Trochlea:** A spool-shaped medial condyle that articulates with the trochlear notch of the ulna.
    *   **Capitulum:** A rounded lateral condyle that articulates with the head of the radius.
    *   **Fossae:** Three depressions:
        *   **Coronoid Fossa:** Anteriorly, superior to the trochlea, receives the coronoid process of the ulna during elbow flexion.
        *   **Radial Fossa:** Anteriorly, superior to the capitulum, receives the head of the radius during elbow flexion.
        *   **Olecranon Fossa:** Posteriorly, superior to the trochlea, receives the olecranon process of the ulna during elbow extension.

**Function:** The humerus provides attachment for numerous muscles of the shoulder and arm, and forms part of the highly mobile shoulder joint and the hinge-like elbow joint, facilitating a wide range of movements of the upper limb.

### (b) Pelvic Girdle

The pelvic girdle is part of the appendicular skeleton that connects the axial skeleton (vertebral column) to the lower limbs. It is a strong, basin-shaped structure that provides support for the weight of the upper body, protects pelvic organs, and serves as an attachment point for muscles of the lower limbs and trunk.

**Composition:**

The pelvic girdle is formed by two large, irregularly shaped **coxal bones** (also known as hip bones or innominate bones), which articulate anteriorly at the pubic symphysis and posteriorly with the sacrum (part of the axial skeleton) at the sacroiliac joints.

Each coxal bone is formed by the fusion of three separate bones during adolescence:

1.  **Ilium:** The largest and most superior part of the coxal bone. It forms the superior two-fifths of the acetabulum. Its prominent features include the iliac crest (the superior border), anterior and posterior superior/inferior iliac spines, and the greater sciatic notch.
2.  **Ischium:** The posteroinferior part of the coxal bone. It forms the posterior two-fifths of the acetabulum. Key features include the ischial tuberosity (the bony prominence you sit on) and the ischial spine.
3.  **Pubis:** The anteroinferior part of the coxal bone. It forms the anterior one-fifth of the acetabulum. The two pubic bones meet anteriorly at the pubic symphysis, a cartilaginous joint.

**Key Features of the Pelvic Girdle:**

*   **Acetabulum:** A deep, cup-shaped socket formed by the fusion of the ilium, ischium, and pubis. It articulates with the head of the femur to form the hip joint (a ball-and-socket joint).
*   **Obturator Foramen:** A large opening in the anterior part of the coxal bone, partially closed by a membrane, allowing passage for nerves and blood vessels.
*   **Pubic Symphysis:** A cartilaginous joint (symphysis) connecting the two pubic bones anteriorly.
*   **Sacroiliac Joints:** Strong, partially movable joints where the ilium articulates with the sacrum posteriorly.

**Function:**

*   Transmits the weight of the upper body to the lower limbs.
*   Provides a strong, stable base for the trunk.
*   Protects the organs of the pelvic cavity (e.g., bladder, reproductive organs, parts of the large intestine).
*   Serves as an extensive attachment site for muscles of the abdomen, back, and lower limbs.

### (c) Synovial Joint

Synovial joints are the most common type of joint in the human body and are characterized by the presence of a fluid-filled synovial cavity between the articulating bones. They are highly movable joints, allowing for a wide range of motion, which is crucial for locomotion and various body movements.

**Structural Components:**

1.  **Articular Cartilage:** The ends of the articulating bones are covered by a layer of smooth, slippery hyaline cartilage. This cartilage reduces friction between bones during movement and absorbs shock.
2.  **Articular Capsule:** A two-layered capsule that encloses the synovial cavity and unites the articulating bones.
    *   **Fibrous Capsule (Outer Layer):** Composed of dense irregular connective tissue, continuous with the periosteum of the bones. It provides strength and prevents dislocation.
    *   **Synovial Membrane (Inner Layer):** Lines the fibrous capsule internally (except over the articular cartilage). It secretes synovial fluid.
3.  **Synovial Cavity:** The space between the articulating bones, filled with synovial fluid.
4.  **Synovial Fluid:** A viscous, clear or pale yellow fluid secreted by the synovial membrane. Its functions include:
    *   **Lubrication:** Reduces friction between articular cartilages.
    *   **Nutrient Distribution:** Supplies nutrients to and removes wastes from the articular cartilage (which is avascular).
    *   **Shock Absorption:** Distributes pressure evenly across the articular surfaces.
5.  **Ligaments:** Bands of dense regular connective tissue that reinforce the joint capsule, connecting bone to bone and preventing excessive or undesirable movements. They can be intrinsic (part of the capsule), extrinsic (outside the capsule), or intracapsular (within the capsule).
6.  **Accessory Structures (Optional):** Some synovial joints may have additional structures:
    *   **Articular Discs (Menisci):** Pads of fibrocartilage (e.g., in the knee joint) that improve the fit between bones, absorb shock, and distribute weight.
    *   **Bursae:** Fluid-filled sacs located at friction points (e.g., between tendons and bones) to reduce friction.
    *   **Tendon Sheaths:** Elongated bursae that wrap around tendons, reducing friction where tendons pass over bones.

**Types of Synovial Joints (based on shape of articulating surfaces and movement allowed):**

*   **Ball-and-Socket Joint:** Allows movement in all planes (e.g., shoulder, hip).
*   **Hinge Joint:** Allows movement in one plane (flexion/extension) (e.g., elbow, knee, ankle, interphalangeal).
*   **Pivot Joint:** Allows rotation around a central axis (e.g., atlanto-axial joint, radioulnar joint).
*   **Condyloid (Ellipsoidal) Joint:** Allows movement in two planes (flexion/extension, abduction/adduction, circumduction) but no rotation (e.g., wrist joint, metacarpophalangeal joints).
*   **Saddle Joint:** A modified condyloid joint, allows greater freedom of movement than condyloid (e.g., carpometacarpal joint of the thumb).
*   **Plane (Gliding) Joint:** Allows limited gliding movements (e.g., intercarpal, intertarsal joints, acromioclavicular joint).

**Function:** Synovial joints are essential for the body's mobility, enabling complex movements like walking, running, grasping, and precise manipulation.

Question 12

Q12. Give an account of the types of movement and their examples.

Accepted Answer

Movement is a fundamental characteristic of living organisms, essential for various biological processes and interaction with the environment. In humans, movement occurs at cellular, tissue, organ, and whole-body levels. These movements are primarily facilitated by specialized cells and tissues.

Based on the cellular structures involved and the mechanism, human body exhibits four main types of movement:

### 1. Amoeboid Movement

*   **Mechanism:** This type of movement is characterized by the streaming of protoplasm (cytoplasmic streaming) and the formation of temporary cytoplasmic extensions called **pseudopodia** (false feet). The movement involves the polymerization and depolymerization of actin microfilaments, which push the cell membrane forward.
*   **Involved Structures:** Primarily **microfilaments** (actin filaments) are responsible for generating the force required for pseudopodia formation and cytoplasmic flow.
*   **Examples:**
    *   **Macrophages and Leukocytes (white blood cells):** These immune cells move through tissues to engulf pathogens (phagocytosis) or reach sites of infection.
    *   **Amoeba:** A single-celled protozoan that uses amoeboid movement for locomotion and feeding.
    *   **Cytoskeletal streaming:** Within cells, organelles and cytoplasm can move via amoeboid-like mechanisms.

### 2. Ciliary Movement

*   **Mechanism:** Ciliary movement involves the coordinated, rhythmic beating of hair-like projections called **cilia**. Cilia are short, numerous appendages that extend from the surface of certain cells. Their beating creates a current that moves fluid or particles across the cell surface or propels the cell itself.
*   **Involved Structures:** **Cilia** are composed of microtubules arranged in a '9+2' array (nine peripheral doublets and two central single microtubules), powered by the motor protein dynein.
*   **Examples:**
    *   **Trachea (windpipe):** Ciliated epithelial cells lining the trachea sweep mucus, dust particles, and foreign substances upwards towards the pharynx, preventing them from entering the lungs.
    *   **Fallopian Tubes (Oviducts):** Cilia in the lining of the fallopian tubes help to propel the ovum (egg cell) from the ovary towards the uterus.
    *   **Ependymal Cells:** Cilia on ependymal cells lining the ventricles of the brain help circulate cerebrospinal fluid.

### 3. Flagellar Movement

*   **Mechanism:** Flagellar movement is characterized by the whip-like or undulating motion of longer, fewer appendages called **flagella**. Flagella are structurally similar to cilia (also '9+2' microtubule arrangement) but are typically much longer and generate movement by their undulating wave-like propagation.
*   **Involved Structures:** **Flagella** are the primary structures, driven by dynein motor proteins.
*   **Examples:**
    *   **Spermatozoa (sperm cells):** The tail of a sperm is a flagellum that propels the sperm through the female reproductive tract to reach the ovum.
    *   **Some Protozoans:** Certain single-celled organisms, like Euglena, use flagella for locomotion.

### 4. Muscular Movement

*   **Mechanism:** Muscular movement is the most common and diverse type of movement in multicellular animals. It involves the contraction and relaxation of specialized muscle cells (muscle fibers) due to the interaction of contractile proteins (actin and myosin). This mechanism is explained by the sliding filament theory.
*   **Involved Structures:** **Muscles** (skeletal, smooth, and cardiac) are the primary organs responsible. Muscle fibers contain myofibrils, which are composed of actin (thin) and myosin (thick) filaments.
*   **Examples:**
    *   **Locomotion:** Walking, running, jumping, swimming, flying – all involve coordinated contraction of skeletal muscles.
    *   **Movement of Limbs:** Lifting an arm, bending a knee, grasping objects.
    *   **Jaw Movement:** Chewing and speaking.
    *   **Heartbeat:** The rhythmic contraction of cardiac muscle pumps blood throughout the body.
    *   **Peristalsis:** Wave-like contractions of smooth muscles in the walls of the digestive tract move food along.
    *   **Diaphragm Movement:** Contraction and relaxation of the diaphragm and intercostal muscles facilitate breathing.

These various types of movements, from the microscopic cellular level to the macroscopic whole-body level, are crucial for survival, reproduction, and interaction with the environment in humans and other organisms.

Question 13

Q13. Write short notes on:
(a) Humerus
(b) Malleus
(c) Atlas
(d) Pectoral girdle
(e) Pelvic girdle

Accepted Answer

(a) **Humerus**:
The humerus is the single long bone of the upper arm, extending from the shoulder to the elbow. It is the longest and largest bone of the upper limb. Proximally, its rounded head articulates with the glenoid cavity of the scapula to form the shoulder joint. Distally, it articulates with the radius and ulna at the elbow joint. Key features include the greater and lesser tubercles (for muscle attachment), the deltoid tuberosity (for deltoid muscle insertion), and the trochlea and capitulum (which articulate with the ulna and radius, respectively). The olecranon fossa, coronoid fossa, and radial fossa are depressions on the distal end that accommodate parts of the ulna and radius during elbow movements.

(b) **Malleus**:
The malleus is the largest of the three auditory ossicles (malleus, incus, stapes) located in the middle ear. It is hammer-shaped and is firmly attached to the inner surface of the tympanic membrane (eardrum). The malleus receives sound vibrations from the tympanic membrane and transmits them to the incus, which in turn passes them to the stapes. This chain of ossicles amplifies and transmits sound vibrations from the air-filled middle ear to the fluid-filled inner ear.

(c) **Atlas**:
The atlas is the first cervical vertebra (C1) and is unique among vertebrae. It is ring-shaped and lacks a vertebral body and a spinous process. Instead, it has two lateral masses connected by anterior and posterior arches. The superior articular facets of the atlas articulate with the occipital condyles of the skull, forming the atlanto-occipital joint, which allows for the 'nodding' movement of the head. The atlas also articulates with the dens (odontoid process) of the axis (C2) through its anterior arch, forming the atlanto-axial joint, which permits the 'shaking' or rotational movement of the head.

(d) **Pectoral Girdle**:
The pectoral girdle, also known as the shoulder girdle, connects the upper limbs to the axial skeleton. Each half of the pectoral girdle consists of two bones: the clavicle (collar bone) and the scapula (shoulder blade). The scapula is a large, triangular flat bone situated on the dorsal part of the thorax between the second and seventh ribs. It has a prominent ridge called the spine, which projects as a flat, expanded process called the acromion. Below the acromion is the glenoid cavity, which articulates with the head of the humerus to form the shoulder joint. The clavicle is a long, slender bone with two curvatures, articulating with the acromion process of the scapula and the manubrium of the sternum. The pectoral girdle provides flexibility and a wide range of motion for the upper limbs.

(e) **Pelvic Girdle**:
The pelvic girdle connects the lower limbs to the axial skeleton. It is formed by two large coxal bones (hip bones), which are fused ventrally at the pubic symphysis. Each coxal bone is formed by the fusion of three bones: the ilium, ischium, and pubis. At the point of fusion of these three bones, there is a deep socket called the acetabulum, which articulates with the head of the femur (thigh bone) to form the hip joint. The ilium is the largest and uppermost part, the ischium forms the posterior and inferior part, and the pubis forms the anterior part. The pelvic girdle provides strong support for the body's weight, protects pelvic organs, and serves as an attachment point for muscles of the lower limbs and trunk.

Chapter 20: Locomotion and Movement