Body Fluids and Circulation

LOCOMOTION AND MOVEMENT

Definitions and Key Concepts

**Movement** is the change in position or place of an organism or body part. It is one of the significant features of all living beings.

**Locomotion** is a specific type of voluntary movement that results in a change of place or location of the whole organism. Examples: walking, running, climbing, flying, swimming.

Key distinction: **All locomotions are movements, but all movements are not locomotions.** For example, chewing food is movement but not locomotion.

Movement occurs for several biological reasons:

Search for food

Finding shelter

Finding mates

Locating suitable breeding grounds

Seeking favorable climatic conditions

Escaping from enemies or predators

Structural and Functional Relationships

Locomotory structures are often multifunctional. The same structure may perform different functions:

**Cilia in Paramoecium**: Move food through cytopharynx AND facilitate locomotion

**Tentacles in Hydra**: Capture prey AND assist in locomotion

**Limbs in humans**: Change body posture AND enable locomotion

The mode of locomotion varies with:

Animal's habitat (aquatic, terrestrial, aerial)

Situational demands

Evolutionary adaptations

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TYPES OF MOVEMENT

Human cells exhibit **three main types of movement**:

1. Amoeboid Movement

**Definition**: Movement involving the formation of temporary cytoplasmic projections called **pseudopodia** (false feet), formed by streaming of protoplasm.

**Mechanism**:

Involves cytoskeletal elements, particularly **microfilaments** (actin and myosin)

Protoplasm flows from one end of the cell to the other

Temporary extensions of the cell membrane form pseudopodia

Cell body follows the pseudopodia

**Cells showing amoeboid movement**:

Leucocytes (white blood cells) in blood

Macrophages in connective tissues

Free-living amoebae (Amoeba proteus)

**Biological significance**:

Enables cell migration

White blood cells can reach infected areas

Important in immune response

2. Ciliary Movement

**Definition**: Movement caused by coordinated beating of hair-like structures called cilia projecting from the cell surface.

**Location in human body**:

Trachea and bronchi (respiratory tract)

Fallopian tubes (female reproductive tract)

Inner lining of ventricles of brain

Kidney tubules

**Mechanism**:

Cilia beat in coordinated waves

Each cilium has a power stroke and recovery stroke

Cilia are made of microtubules arranged in 9+2 pattern (as studied in Chapter 8)

**Biological functions**:

**In trachea**: Removes dust particles and foreign substances inhaled with air; protects lungs

**In female reproductive tract**: Facilitates passage of ovum toward uterus

**In brain ventricles**: Facilitates cerebrospinal fluid circulation

**In kidney tubules**: Assists in fluid movement

3. Muscular Movement

**Definition**: Movements caused by contraction and relaxation of muscles, a specialized contractile tissue.

**Characteristics of muscles**:

Specialized tissue of **mesodermal origin**

Contributes **40-50% of human body weight** in adults

Possess four major properties:

**Excitability**: Respond to neural stimulation

**Contractility**: Can shorten and develop tension

**Extensibility**: Can be stretched

**Elasticity**: Return to original length after stretching

**Functions**:

Locomotion

Changes in body postures

Movement of specific body parts (jaw, eyelids, tongue, limbs)

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MUSCLE

Classification of Muscles

Muscles are classified based on three criteria: **location, appearance, and regulation of activity**.

#### A. Skeletal (Striated Voluntary) Muscles

**Location**:

Attached to skeletal components (bones and cartilages)

Cover the external surface of the body

Form the musculature of limbs

**Appearance**:

Exhibit **striped or striated pattern** under microscope due to alternating light and dark bands

Pattern is due to regular arrangement of contractile proteins

**Regulation**:

Under **voluntary control** of the central nervous system (CNS)

Also called **voluntary muscles**

**Function**:

Primary role in locomotory actions

Changes in body posture

Precise, powerful movements

**Structure**:

Made of muscle fibers arranged in bundles

Each fiber is multinucleate (syncytium)

#### B. Visceral (Smooth Involuntary) Muscles

**Location**:

Inner walls of hollow visceral organs

Alimentary canal (esophagus, stomach, small intestine)

Reproductive tract

Blood vessels

Urinary bladder

**Appearance**:

Smooth, non-striated appearance under microscope

Also called **smooth muscles** or **non-striated muscles**

**Regulation**:

**NOT under voluntary control**

Controlled by autonomic nervous system

Also called **involuntary muscles**

**Function**:

Transportation of food through digestive tract (**peristalsis**)

Movement of gametes through reproductive tract

Regulation of blood vessel diameter

Movement of materials through ducts

**Structure**:

Fibers are uninucleate or binucleate

Spindle-shaped fibers

#### C. Cardiac Muscles

**Location**:

Heart walls exclusively

**Arrangement**:

Multiple cardiac muscle cells assemble in **branching patterns**

Connected by intercalated discs containing tight junctions

**Appearance**:

**Striated** (similar to skeletal muscles)

However, striations are less regular than skeletal muscles

**Regulation**:

**Involuntary** in nature

CNS does not directly control their activity

Possess autorhythmicity (can contract without external stimulus)

**Function**:

Pumping of blood throughout the body

Maintaining continuous circulation

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STRUCTURE OF SKELETAL MUSCLE

Hierarchical Organization

Skeletal muscles have a precise hierarchical organization from gross to microscopic level:

**Level 1: Whole Muscle**

Multiple muscle bundles held together by **fascia** (collagenous connective tissue sheath)

Fascia extends from the muscle to form tendons that attach to bones

**Level 2: Muscle Bundle (Fascicle)**

Bundle of muscle fibers

Surrounded by **perimysium** (connective tissue layer)

**Level 3: Muscle Fiber (Muscle Cell)**

Single elongated multinucleate cell

**Sarcolemma**: Plasma membrane surrounding the muscle fiber

**Sarcoplasm**: Cytoplasm of muscle fiber containing:

Multiple nuclei (syncytium)

Mitochondria

Sarcoplasmic reticulum (specialized endoplasmic reticulum)

Myofibrils (contractile filaments)

**Level 4: Myofibril (Myofilament)**

Parallel cylindrical structures within sarcoplasm

Made of thick and thin filaments

**Level 5: Sarcomere**

**Functional unit of muscle contraction**

Portion of myofibril between two successive Z-lines

Contains contractile proteins arranged in specific patterns

Banding Pattern of Myofibril

Under electron microscope, myofibrils show alternating dark and light bands due to overlapping arrangement of actin and myosin filaments:

**I-Band (Isotropic Band)**

Appears **light** in color

Contains only **thin (actin) filaments**

Bisected in the middle by an elastic fiber called **Z-line** or **Z-disc**

During muscle contraction, I-band length **decreases**

**A-Band (Anisotropic Band)**

Appears **dark** in color

Contains both **thick (myosin)** and **thin (actin) filaments**

Middle region of thick filaments held together by **M-line** (M-disc)

During muscle contraction, A-band length **remains constant**

**H-Zone**

Region within A-band containing only thick filaments

Located between edges of overlapping thin filaments

In resting state, central part of thick filaments is not overlapped

Decreases during contraction as thin filaments slide over thick filaments

**Z-Line (Z-Disc)**

Elastic protein structure

Bisects each I-band

Thin filaments attached to Z-lines on both sides

Z-lines move toward each other during contraction

**Sarcomere**: Region between two Z-lines; this is the **contractile unit**

Sarcoplasmic Reticulum and Calcium Storage

**Sarcoplasmic reticulum**: Specialized smooth endoplasmic reticulum in muscle fibers

Functions as the **main calcium ion (Ca²⁺) store** in muscle cells

Calcium is essential for initiating muscle contraction

Calcium release is triggered by action potential spreading through T-tubules

**T-tubules**: Invaginations of sarcolemma that penetrate deep into muscle fiber

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STRUCTURE OF CONTRACTILE PROTEINS

Actin (Thin Filaments)

**Composition**:

Two **F-actin** (filamentous actin) molecules wound helically around each other

Each F-actin is a polymer of monomeric **G-actin** (globular actin) subunits

Diameter: approximately 7 nm

**Associated Proteins**:

**Tropomyosin**: Two protein molecules run along the length of F-actin

Thin rod-like structure

Covers the myosin-binding sites on actin in resting state

**Troponin**: Complex regulatory protein

Distributed at regular intervals (approximately every 40 nm) on tropomyosin

Three subunits:

**TnC (Troponin C)**: Binds calcium ions

**TnI (Troponin I)**: Inhibitory subunit; masks binding site

**TnT (Troponin T)**: Binds to tropomyosin

In resting state: TnI subunit masks active binding sites for myosin on actin

**Function of Actin**:

Provides binding sites for myosin heads

Forms cross-bridges with myosin during contraction

Thin appearance compared to myosin filaments

Myosin (Thick Filaments)

**Basic Unit: Meromyosin**

Monomeric protein unit making up thick filaments

Approximately 110 nm in length

Two distinct regions:

**1. Heavy Meromyosin (HMM)**

Comprises approximately 50% of meromyosin

**Globular head**:

Spherical structure projecting outward

Acts as **active ATPase enzyme**

Has two critical sites:

**ATP-binding site**: Binds ATP molecules for energy

**Actin-binding site** (active site): Binds to exposed sites on actin filaments

Projects outward at regular intervals and angles from filament surface

**Short arm**: Connects head to tail; provides flexibility for power stroke

**2. Light Meromyosin (LMM)**

Forms the rod-like tail

Structural protein

Anchors myosin monomers together to form thick filament

**Thick Filament Structure**:

Formed by polymerization of hundreds of meromyosin molecules

Myosin heads project outward at angles (approximately 65° to 70°)

Two myosin head clusters at each end oriented in opposite directions

Provides bipolarity to thick filament

Diameter: approximately 15 nm

**Functions of Myosin**:

Catalyzes ATP hydrolysis to provide energy for contraction

Forms cross-bridges with actin

Causes sliding of thin filaments

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MECHANISM OF MUSCLE CONTRACTION

Sliding Filament Theory

**Definition**: **Muscle contraction is brought about by the sliding of thin filaments over the thick filaments without the filaments themselves changing length.**

Proposed by: H.E. Huxley and others (1950s)

**Key Evidence**:

During contraction, I-bands shorten but A-bands remain the same length

Sarcomere length decreases as Z-lines move closer

Thin and thick filaments overlap more

Step-by-Step Mechanism of Contraction

#### Step 1: Neural Signal and Neuromuscular Junction

**Motor Unit**: One motor neuron + all muscle fibers it innervates

**Neuromuscular Junction (Motor End Plate)**:

Point of contact between axon terminal of motor neuron and sarcolemma

Presynaptic membrane: Axon terminal

Synaptic cleft: 50 nm gap

Postsynaptic membrane: Sarcolemma with receptors

**Process**:

Action potential travels along motor neuron axon

Reaches axon terminal

Triggers release of neurotransmitter

#### Step 2: Neurotransmitter Release

**Neurotransmitter**: **Acetylcholine (ACh)**

Released from synaptic vesicles in axon terminal

Diffuses across synaptic cleft (50 nm)

Binds to **acetylcholine receptors** on sarcolemma

These are ligand-gated ion channels

#### Step 3: Generation of Action Potential

ACh binding causes conformational change in receptors

Sodium (Na⁺) ions enter the muscle fiber

**Depolarization** of sarcolemma

Action potential is generated

Action potential spreads across entire sarcolemma and down T-tubules

#### Step 4: Calcium Ion Release

**Location**: Sarcoplasmic reticulum (calcium store)

**Process**:

Action potential travels down T-tubules

Triggers opening of voltage-sensitive calcium channels in sarcoplasmic reticulum

**Calcium ions (Ca²⁺) flood into sarcoplasm**

Increase in intracellular Ca²⁺ concentration (from ~0.1 μM to ~1-10 μM)

#### Step 5: Removal of Inhibition

**Initial state (resting muscle)**:

TnI subunit of troponin masks the myosin-binding site on actin

Tropomyosin blocks access to binding site

**Upon Ca²⁺ binding**:

Ca²⁺ binds to **TnC (Troponin C)** subunit

Conformational change in troponin complex

Troponin moves, pulling tropomyosin aside

**Myosin-binding sites on actin become exposed**

#### Step 6: Cross-Bridge Formation

**Process**:

Myosin heads, already activated by ATP hydrolysis (containing ADP + Pi), attach to exposed binding sites on actin

Forms **cross-bridge** between thick and thin filaments

Myosin head is in high-energy state

Power stroke is about to occur

#### Step 7: Power Stroke (Ratcheting)

**Process**:

Myosin head pivots on its short arm

Pulls actin filament toward center of A-band

Z-lines attached to actin move inward

**Sarcomere shortens** (approximately 10 nm movement per power stroke)

ADP and Pi are released from myosin head

Myosin head moves to low-energy state

**Effects**:

**I-bands decrease in length** (thin filaments slide over thick filaments)

**A-bands remain constant** in length

**H-zone decreases** (thin filaments extend further)

#### Step 8: Cross-Bridge Breaking (Rigor State)

**Trigger**: New ATP molecule binds to myosin head

**Process**:

ATP binding causes conformational change

Myosin head releases from actin (cross-bridge breaks)

Muscle fiber enters **rigor state** (maximum force) if no ATP available

**Significance**: This is why muscles become rigid after death (**rigor mortis**) when ATP production stops

#### Step 9: ATP Hydrolysis and Re-activation

**Process**:

ATPase activity of myosin head hydrolyzes ATP

ATP → ADP + Pi + Energy

Energy is stored in myosin head

Myosin head returns to high-energy conformation

Myosin head moves back to original position (without binding to actin) ready for next power stroke

#### Step 10: Relaxation

**Trigger**: Calcium ions are pumped back to sarcoplasmic reticulum

**Process**:

Neural signal stops

Acetylcholine release stops

Ca²⁺ levels in sarcoplasm decrease

Ca²⁺ is removed from TnC

Tropomyosin returns to blocking position

Myosin-binding sites on actin are masked again

Myosin heads cannot bind

Z-lines return to original position

**Muscle relaxes**

**Energy requirement**: ATP needed for muscle relaxation to pump Ca²⁺ (via Ca²⁺-ATPase pumps)

Muscle Contraction Cycle Summary

**In rapidly contracting muscle**:

Cross-bridge formation, power stroke, and cross-bridge breaking occur continuously

Multiple myosin heads engage sequentially

One myosin head completes cycle while others are binding or generating power strokes

Sliding continues until Ca²⁺ is removed

**Number of cross-bridges**:

Only about 50% of myosin heads engaged at any given moment in active contraction

Rotation of myosin heads can drag actin filaments several micrometers

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MUSCLE FIBER TYPES

Red Fibers (Slow-Twitch, Type I Fibers)

**Appearance**: Reddish color

**Pigment**: High content of **myoglobin**

Oxygen-binding pigment

Similar structure to hemoglobin

Stores oxygen for prolonged use

**Mitochondrial Content**: Abundant mitochondria

**Metabolic Pathway**: **Aerobic respiration** (use oxygen)

Produce ATP efficiently

Can sustain contraction for long periods

**Energy Source**: Oxidative phosphorylation

Break down glucose and fatty acids with oxygen

**Contraction Speed**: Slow (slow-twitch)

**Fatigue Resistance**: Very resistant to fatigue

**Function**: Postural muscles, endurance activities (long-distance running, holding posture)

**Location**: Postural muscles of neck and back

**ATPase Activity**: Low

White Fibers (Fast-Twitch, Type II Fibers)

**Appearance**: Pale or whitish color

**Pigment**: Very low myoglobin content

**Mitochondrial Content**: Few mitochondria

**Sarcoplasmic Reticulum**: High amount (stores calcium)

**Metabolic Pathway**: **Anaerobic respiration** (without oxygen)

Depend on glycolysis

Rapid but less efficient ATP production

Produce lactic acid as byproduct

**Energy Source**:

Breakdown of glycogen and glucose

Creatine phosphate (quick energy source)

**Contraction Speed**: Fast (fast-twitch)

**Contraction Force**: Generate high force initially

**Fatigue**: Fatigue quickly due to lactic acid accumulation

**Function**: Rapid, powerful movements (sprinting, jumping, weight lifting)

**Location**: Limb muscles involved in movement

**ATPase Activity**: High

Muscle Fatigue

**Definition**: Decreased ability of muscle to maintain force of contraction

**Causes**:

1. **Accumulation of lactic acid**: Anaerobic metabolism produces lactate ions that lower pH

2. **Depletion of glycogen stores**: Reduced substrate for ATP production

3. **Accumulation of Pi (inorganic phosphate)**: Inhibits cross-bridge formation and power stroke

4. **Reduced Ca²⁺ release**: Sarcoplasmic reticulum Ca²⁺ stores become depleted

5. **Central nervous fatigue**: Reduced neural drive

6. **Accumulation of K⁺ outside cells**: Affects action potential generation

**Recovery**: Lactic acid is metabolized, oxygen is supplied, energy stores are replenished

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SKELETAL SYSTEM

Overview

**Definition**: The skeletal system is a framework of bones and cartilages that supports the body and enables movement.

**Composition in humans**:

**206 bones** (in adults; newborns have ~270, many fuse during development)

**Cartilages**: Smaller number in specific locations

**Components**: Bone and cartilage are specialized connective tissues

Bone vs. Cartilage

| Feature | Bone | Cartilage |

|---------|------|-----------|

| Matrix | Hard, rigid | Slightly pliable (flexible) |

| Mineral composition | Rich in calcium salts | Contains chondroitin salts |

| Rigidity | Very hard and strong | Flexible and slightly compressible |

| Vascularity | Well-vascularized | Avascular (no blood vessels) |

| Function | Support, protection, movement | Reduces friction, provides support |

**Chondroitin salts**: Provide elasticity and flexibility to cartilage

Divisions of Skeletal System

#### A. AXIAL SKELETON

**Definition**: Bones distributed along the main axis of the body

**Total bones**: 80 bones

**Components**:

1. **Skull**

2. **Vertebral column**

3. **Sternum**

4. **Ribs**

##### 1. SKULL

**Total bones**: 22 bones + 3 ear ossicles

**Composition**:

**Cranial bones**: 8 bones forming cranium

Frontal bone (1): Forms forehead

Parietal bones (2): Sides and roof of cranium

Temporal bones (2): Sides of cranium; contain ear canal

Occipital bone (1): Back and base of cranium; contains foramen magnum (opening for spinal cord)

Sphenoid bone (1): Forms base of cranium; contains pituitary gland fossa

Ethmoid bone (1): Between eye sockets; forms part of nasal septum

**Facial bones**: 14 bones forming front of skull

Maxilla (2): Upper jaw; fused to form single structure

Mandible (1): Lower jaw; single bone

Nasal bones (2): Form nose bridge

Lacrimal bones (2): Inner corners of eye sockets; contain lacrimal glands

Zygomatic bones (2): Cheekbones

Vomer (1): Nasal septum

Palatine bones (2): Roof of mouth

Inferior nasal conchae (2): Nasal passages

**Special Bones**:

**Hyoid bone**: U-shaped bone at base of buccal cavity; only unpaired facial bone

**Ear Ossicles**: Three tiny bones in each middle ear (6 total)

**Malleus** (hammer): Connected to tympanum

**Incus** (anvil): Middle position

**Stapes** (stirrup): Connected to inner ear

Function: Transmit vibrations from eardrum to inner ear

**Articulation with Vertebral Column**:

Skull articulates with first vertebra (atlas) via **occipital condyles**

**Two occipital condyles**: Makes human skull dicondylic (two points of articulation)

Allows forward and backward nodding movements

##### 2. VERTEBRAL COLUMN

**Definition**: Series of serially arranged bones (vertebrae) forming the backbone

**Position**: Dorsally placed (along the back)

**Total vertebrae**: 26 in adults (some are fused)

**Extension**: From base of skull to end of vertebral column

**Functions**:

Protects spinal cord (which runs through neural canal)

Supports head

Provides attachment points for ribs and back musculature

Provides structure to trunk

Allows movement of trunk

**Regions** (from skull downward):

1. **Cervical vertebrae**: 7

Smallest vertebrae

Located in neck region

**Atlas (C1)**: First cervical vertebra; articulates with occipital condyles

**Axis (C2)**: Second cervical vertebra; contains dens (odontoid process) for rotation

**Interesting fact**: All mammals (including giraffes and humans) have 7 cervical vertebrae

Allow head rotation and movement

2. **Thoracic vertebrae**: 12

Located in chest region

Articulate with ribs

Have facets for rib articulation

Heart and lungs lie at level of thoracic vertebrae

3. **Lumbar vertebrae**: 5

Located in lower back region

Largest vertebrae (bear more weight)

Support most body weight

4. **Sacral vertebrae**: 5 (fused into one **sacrum**)

Fused together in adults

Forms triangular bone

Forms part of pelvic girdle

Articulates with coccyx below

5. **Coccygeal vertebrae**: 4 (fused into one **coccyx**)

Tail bone in humans

Vestigial structure (no functional tail in humans)

Reduced size

**Intervertebral Discs**:

Fibrocartilage structure between adjacent vertebrae

Contain **nucleus pulposus** (gel-like center)

Absorb shock and allow limited movement

Can herniate if damaged ("slipped disc")

**Typical Vertebra Structure**:

**Vertebral body**: Main load-bearing part

**Vertebral arch**: Forms neural canal (spinal cord passage)

**Neural canal**: Central hollow region; passage for spinal cord

**Spinous process**: Posterior projection (felt along spine)

**Transverse processes**: Lateral projections

**Facets**: Articulating surfaces with adjacent vertebrae

##### 3. STERNUM (Breastbone)

**Description**: Flat bone on ventral midline of thorax

**Position**: Front and center of rib cage

**Function**: Articulation point for ribs; protection of heart and lungs

**Divisions**: Three parts

**Manubrium**: Upper part

**Body**: Middle part

**Xiphoid process**: Lower part (may become ossified)

##### 4. RIBS

**Total**: 12 pairs (24 ribs)

**Attachment**:

**Dorsally**: Connected to thoracic vertebrae

**Ventrally**: Connected to sternum (directly or indirectly)

**Structure**:

Thin, flat bones

Have two articulation surfaces on dorsal end

Called **bicephalic ribs** (two-headed)

**Classification**:

1. **True ribs (Vertebrosternal ribs)**: 1st-7th pairs (7 pairs)

Articulate directly with sternum via hyaline cartilage

Fully connect thoracic vertebrae to sternum

2. **False ribs (Vertebrochondral ribs)**: 8th-10th pairs (3 pairs)

Do NOT articulate directly with sternum

Connect to 7th rib via hyaline cartilage

Indirectly attach to sternum

3. **Floating ribs**: 11th-12th pairs (2 pairs)

No ventral attachment to sternum

Only attached to thoracic vertebrae dorsally

Free anteriorly

**Rib Cage**:

Structure formed by: Thoracic vertebrae + ribs + sternum + costal cartilages

Function: Protects heart, lungs, and other thoracic organs

Involved in respiration (movement allows breathing)

#### B. APPENDICULAR SKELETON

**Definition**: Bones of limbs and their girdles

**Total bones**: 126 bones (4 limbs + 2 girdles)

**Components**:

1. Pectoral girdle (shoulder girdle) + upper limbs

2. Pelvic girdle + lower limbs

##### PECTORAL GIRDLE (Shoulder Girdle)

**Function**: Articulates upper limbs with axial skeleton

**Bones**: Two halves, each containing 2 bones

**Per side**:

1. **Clavicle** (collar bone)

Long, slender bone with two curvatures

Articulates with scapula laterally and sternum medially

Readily breaks due to its position and structure

Provides attachment for muscles

2. **Scapula** (shoulder blade)

Large, triangular flat bone

Located dorsally on thorax

Between 2nd and 7th ribs

Has three borders: superior, lateral, medial

Spine: Ridge on posterior surface

**Acromion**: Flat, expanded process at apex of spine

**Clavicle articulates with acromion**

**Glenoid cavity**: Cup-shaped depression on lateral surface

**Head of humerus articulates with glenoid cavity** forming shoulder joint

**Coracoid process**: Beak-like projection; attachment for muscles and ligaments

##### UPPER LIMB BONES (Forelimb)

**Each upper limb**: 30 bones

**Regions** (from shoulder to fingertips):

1. **Humerus** (upper arm bone)

Long bone (largest bone of upper limb)

Has spherical head that articulates with glenoid cavity

**Deltoid tuberosity**: Rough area for muscle attachment

Articulates with radius and ulna at elbow

2. **Radius** (lateral forearm bone, thumb side)

Shorter than ulna

Has disc-shaped head articulating with humerus

**Radial tuberosity**: Attachment for biceps muscle

Allows rotation (supination and pronation)

3. **Ulna** (medial forearm bone, pinky side)

Longer than radius

**Olecranon process**: Posterior projection forming elbow prominence

**Coronoid process**: Anterior projection

Forms hinge joint with humerus

Articulates with radius

4. **Carpals** (wrist bones)

8 small bones arranged in two rows

Provide flexibility to wrist

Named: Scaphoid, Lunate, Triquetrum, Pisiform (proximal row); Trapezium, Trapezoid, Capitate, Hamate (distal row)

Allow wrist flexion, extension, and rotation

5. **Metacarpals** (palm bones)

5 elongated bones

Numbered 1-5 from thumb to pinky

Form structure of palm

Articulate with carpals and phalanges

6. **Phalanges** (fingers/digits bones)

14 bones total

**Thumb**: 2 phalanges (proximal, distal)

**Each finger**: 3 phalanges (proximal, middle, distal)

Smallest bones of upper limb

##### PELVIC GIRDLE

**Function**: Articulates lower limbs with axial skeleton; provides support

**Structure**: Two halves meeting ventrally

**Bones per side**: Each coxal bone formed by fusion of three bones

**Components of each coxal bone**:

1. **Ilium** (upper and largest)

Forms wing-like structure

Iliac crest: Upper border; palpable (can be felt)

**Acetabulum**: Deep cup-shaped cavity formed by fusion point of three bones

**Femoral head articulates with acetabulum**

2. **Ischium** (lower and posterior)

Forms lower and back part of pelvis

**Ischial tuberosities**: Points on which we sit

**Ischial spine**: Projection pointing inward

3. **Pubis** (anterior and medial)

Forms pubic bone anteriorly

**Pubic symphysis**: Cartilaginous joint between two pubic bones ventrally

Contains fibrous cartilage providing limited movement

Widens during pregnancy to facilitate childbirth

**Acetabulum**:

Deep socket where femur articulates

Formed by fusion of ilium, ischium, and pubis

Provides stable articulation for hip joint

Deeper and more enclosed than glenoid cavity

**Pelvic Structure and Sexual Dimorphism**:

**Female pelvis**: Wider, larger pelvic inlet, wider subpubic angle (facilitates childbirth)

**Male pelvis**: Narrower, deeper, smaller pelvic inlet

##### LOWER LIMB BONES (Hind limb)

**Each lower limb**: 30 bones

**Regions** (from hip to toes):

1. **Femur** (thigh bone)

**Longest and strongest bone**