W1_Musculoskeletal System_2025_CKK_upload(3)

A meatus is a passage or channel, especially the opening of a canal, that is tube-like in structure.

• Sulcus: Narrow groove
• Fossa: Shallow depression

The acromioclavicular joints are associated with structures such as the capsule, articular disc, synovial membrane, acromion, coracoacromial ligament, coracoid process, trapezoid ligament, conoid ligament, and clavicle.

Hinge joints allow angular movement in one direction and in one plane, specifically flexion and extension.

Examples of hinge joints include the elbow joint, knee joint, ankle joint, and interphalangeal joints of the fingers.

A pivot joint allows rotary movement around a single axis, enabling rotation in one direction.

The proximal radioulnar joints are pivot joints that allow for the rotation of the radius around the ulna, facilitating movements such as pronation and supination of the forearm.

The movements associated with the shoulders are:

1. Protraction
2. Retraction
3. Elevation
4. Depression

The key movements of the arms include:

1. Flexion
2. Extension
3. Abduction
4. Adduction

The movements involved in the legs are:

1. Abduction
2. Adduction
3. External Rotation
4. Internal Rotation
5. Flexion
6. Extension

The movements of the feet include:

1. Dorsi Flexion
2. Plantar Flexion
3. Inversion
4. Eversion

The skeleton protects internal organs such as the brain, heart, and lungs.

The skeleton stores and releases fat, which serves as an energy reserve.

The skeleton produces blood cells, particularly in the bone marrow.

The skeleton stores and releases minerals such as calcium (Ca) and phosphate (PO), which are essential for various bodily functions.

The skeleton facilitates movement by providing a framework for muscles to act upon, allowing for locomotion and various physical activities.

The skeleton supports the body by providing structure and shape, allowing for upright posture and stability.

Tendons are fibrous connective tissues that attach muscle to bone, enabling movement.

Cartilage serves as soft, gel-like padding between bones, protecting joints and facilitating movement.

Ligaments are bands of tough elastic tissue that connect bone to bone around joints, providing support and limiting movement.

The axial skeleton has a total of 80 bones, while the appendicular skeleton has a total of 126 bones. This indicates that the appendicular skeleton contains significantly more bones than the axial skeleton, reflecting its role in facilitating movement and supporting limbs.

The bone matrix consists of:

1. Calcium hydroxyapatite (2/3 of the matrix):

   • Composed mainly of Ca3(PO4)2
   • Strong but inflexible

2. Collagen fibers (1/3 of the matrix):

   • Tough and flexible
   • Provides structural support

3. Ground substance:

   • A component that helps in the overall structure of the matrix.

The angle decreases as the ulna moves toward the humerus bone.

The transverse ligament is crucial for stabilizing the atlantoaxial joint, which allows for rotation of the head and neck while preventing excessive movement that could lead to injury.

The angle increases as the ulna moves away from the humerus bone.

The angle increases as the arms move posteriorly.

Lateral rotation of the shoulder involves a circular motion that rotates the forearms outward, away from the body. This movement is typically performed with the arms outstretched to the sides.

Medial rotation of the shoulder involves a circular motion that rotates the forearms inward, towards the body. This movement is often performed with the elbows bent and hands positioned in front of the body, palms facing upwards.

The angle at the palm of the hand and the anterior surface of the forearm decreases.

The angle between digits 2-5 and the palm decreases.

The fingers bend at the interphalangeal joints.

The angle at the palm of the hand and the anterior surface of the forearm increases.

The angle between digits 2-5 and the palm increases.

The fingers are straightened at the interphalangeal joints.

The angle between the femur and hip decreases as the thigh moves anteriorly.

The angle between the tibia and femur decreases.

Hip/thigh extension allows the thigh to move posteriorly. Extension past the anatomical position is referred to as hyperextension.

The angle between the tibia and femur increases.

During spine flexion, the angle between the spine and hip decreases as the individual bends forward at the waist.

In spine extension, the angle between the spine and hip increases as the individual stands straight, and the spine can extend beyond the anatomical position.

During neck flexion, the angle between the head and trunk decreases as the individual looks down.

The types of bone cells include:

The periosteum is a fibrous tissue that surrounds the outer surface of the bone (except at articular sites). Its inner layer is osteogenic, meaning it can differentiate into osteoblasts. Additionally, it is richly supplied with capillaries and nerves, which are essential for bone health and repair.

The main components of a long bone include:

1. Compact bone: Dense, solid mass with closely packed and well-aligned osteons, forming the outer surface layer of all bones.

2. Spongy bone: Lighter and less dense than compact bone, with bones arranged in trabeculae (irregularly-aligned osteons) and irregular cavities containing red bone marrow.

Red bone marrow contains hematopoietic stem cells that can differentiate into red blood cells (RBC), white blood cells (WBC), and platelets.

Red bone marrow is present in all bones before age 5 and gradually transforms into yellow bone marrow as a person ages. In adults, red bone marrow mainly persists in the central skeleton and the ends of long bones.

Yellow bone marrow is located in the cavities of long bones and contains adipose (fat) tissues and mesenchymal stem cells that can develop into cartilage, bone, fat, or muscle cells if needed.

Long bones are tubular in shape and are primarily found in the limbs. They serve as levers for muscles, facilitating movement and support.

Short bones are cubical in shape and provide support and stability with little or no movement, making them essential for maintaining structure in areas like the wrist and ankle.

Flat bones have a flat surface that facilitates muscular attachment and provides protection to underlying soft tissues, such as the sternum protecting the heart.

Sesamoid bones are small and resemble sesame seeds; they develop inside tendons and help to reduce friction and increase leverage during movement, such as the patella in the knee.

Irregular bones have an irregular or mixed shape and cannot be categorized into a particular type. They serve various functions, often providing support and protection in complex areas like the vertebrae.

A process is a projection or bump on a bone.

A ramus is an extension of a bone that forms an angle with the rest of the structure.

A sinus is a chamber within a bone, normally filled with air.

A foramen is a rounded passageway (hole) for blood vessels and/or nerves.

A fissure is a deep furrow, cleft, or slit in a bone.

Joints are articulations where two or more bones meet. Their characteristic structure determines the type and range of movement possible at the joint.

Joints can be classified according to their:

1. Anatomical aspects (regions)
2. Functional aspects (degree of mobility)
3. Structural aspects (tissues that separate the joints)

1. Immovable (Synarthrosis)
2. Slightly movable (Amphiarthrosis)
3. Freely movable (Diarthrosis)

1. Fibrous (joint separated by fibrous tissues)
2. Cartilages (joint separated by cartilages)
3. Synovial (joints separated by fluid-filled cavity; within a fibrous capsule)

Costochondral joints are immobile joints between the rib and its costal cartilage.

The joint characterized by a suture line in the skull is an immovable joint (Synarthrosis), connected by dense fibrous connective tissue.

Synovial joints are the most common type of joints in the body, allowing a wide range of movement, classified as diarthrosis.

The six types of synovial joints are:

1. Pivot joint - between C1 and C2 vertebrae
2. Hinge joint - elbow
3. Saddle joint - between trapezium carpal bone and 1st metacarpal bone
4. Plane joint - between tarsal bones
5. Condyloid joint - between radius and carpal bones of wrist
6. Ball-and-socket joint - hip joint

The articular capsule consists of:

1. Outer fibrous capsule - continuous with the periosteum.
2. Inner synovial membrane - secretes synovial fluid for lubrication, shock absorption, and joint nourishment.
3. Articular cartilages - provide a wear-resistant, low-friction surface on the bone.
4. Fibrocartilage (meniscus) - located between the articular bones to smooth movement and reduce friction.

Bursae are sacs filled with synovial fluid that provide cushioning around a joint. They are located between the bones and the muscles and tendons crossing the joint, helping to reduce friction and facilitate smooth movement.

Bursae usually form where tendons and ligaments rub against other tissues, such as bone. This positioning helps to minimize friction and protect the surrounding structures during movement.

The types of synovial joints include:

1. Hinge Joint: Allows movement in one plane (e.g., elbow).
2. Pivot Joint: A cylindrical bone rotates within a ring (e.g., between C1 and C2 vertebrae).
3. Condylar Joint: An oval condyle fits into an elliptical cavity (e.g., between radius and carpal bones).
4. Saddle Joint: Both bones have concave and convex areas, allowing a wide range of movement (e.g., between trapezium carpal bone and first metacarpal bone).
5. Plane Joint: Flat surfaces glide over each other (e.g., between tarsal bones).
6. Ball-and-Socket Joint: A spherical head fits into a cup-like socket, allowing movement in multiple axes (e.g., hip joint).

Plane joints permit gliding movement only.

The vertebral joints are commonly referred to as facet joints.

The main bones involved in the sacroiliac joints are the sacrum and ilium.

The intercarpal joints are classified as plane joints that allow gliding movements between the carpal bones of the wrist.

A condylar (ellipsoid) joint is a type of biaxial joint characterized by an oval-shaped head fitting into an elliptical cavity. It allows for the following movements:

• Flexion/Extension
• Abduction/Adduction
• Circumduction

A saddle joint is characterized by the articular surfaces of each bone being concave in one direction and convex in another. This unique structure allows for a wide range of movement, including flexion, extension, abduction, and adduction, making it highly functional in areas such as the thumb and sternoclavicular joint.

Ball and socket joints allow angular movement in all directions and a pivot movement.

The main ligaments associated with the shoulder joint include:

• Coracoclavicular ligament: Connects the coracoid process of the scapula to the clavicle.
• Acromioclavicular ligament: Connects the acromion of the scapula to the clavicle.
• Glenohumeral ligaments: A group of ligaments that stabilize the glenohumeral joint (shoulder joint).
• Transverse humeral ligament: Holds the tendon of the biceps brachii in the bicipital groove of the humerus.

Intracapsular ligaments are localized thickenings of fibrous connective tissue that help reinforce the joint capsule. Examples include the Anterior and Posterior cruciate ligaments.

Accessory ligaments are separate from the joint capsule and help to reinforce the joint by attaching the bones together. Examples include the Medial and Lateral collateral ligaments.

Ligaments join bones together and stabilize the joints, ensuring proper function and movement.

• Absorbing shock
• Reducing friction
• Supporting structures

Hyaline cartilage is primarily found in the rib cage, trachea, and nasal structures.

Fibrocartilage is strong and resilient, commonly found in intervertebral discs and the pubic symphysis.

Elastic cartilage contains elastic fibers, allowing it to maintain shape while being flexible, found in structures like the epiglottis and larynx.

The three main types of muscle tissue are:

1. Skeletal Muscle - Voluntary muscle that moves bones and is under conscious control.
2. Smooth Muscle - Involuntary muscle found in walls of hollow organs, such as the intestines and blood vessels.
3. Cardiac Muscle - Involuntary muscle that makes up the heart and is responsible for pumping blood.

The primary functions of skeletal muscles include:

1. Generate movement
2. Maintain posture and body position
3. Support soft tissue
4. Control of body openings and passages
5. Regulate body temperature
6. Store nutrients

The hierarchical structure of muscle organization includes the following levels:

1. Bone
2. Tendon
3. Fascia (covering muscle)
4. Epimysium
5. Muscle
6. Fascicles
7. Muscle fibers (cells)
8. Myofibrils
9. Perimysium
10. Endomysium
11. Thick and thin filaments

Additional important structures include:

• Nucleus
• Sarcoplasmic reticulum
• Axon of motor neuron
• Blood vessel
• Sarcolemma

A sarcomere is the repeating unit within muscle fibers that is responsible for contraction. It contains organized arrangements of actin (thin filaments) and myosin (thick filaments) that interact to produce muscle contraction.

During muscle contraction, the actin filaments are pulled further into the myosin filaments, resulting in a shorter muscle fiber length compared to the relaxed state. This interaction between actin and myosin is crucial for muscle contraction.

Tendons are composed of tough, dense fibrous connective tissue that has high tensile strength. They synthesize extracellular matrix (ECM) containing collagen and proteoglycans. The primary function of tendons is to attach muscles to bones and transmit forces generated by muscles to the bones, facilitating movement.

Tendons play a crucial role in movement by:

1. Attaching muscles to bones
2. Transmitting forces generated by muscle contractions to the bones
3. Enabling the elaboration of movement through the skeletal system.

Fusiform muscles have fascicles that are nearly parallel to the longitudinal axis of the muscle and taper towards the tendons.

In parallel muscles, the fascicles are parallel to the longitudinal axis of the muscle and terminate at either end in a flat tendon.

Convergent muscles have fascicles that spread over a broad area and converge at a thick central tendon, giving the muscle a triangular appearance.

Circular muscles have fascicles arranged in concentric circles to form a sphincter or opening.

The three types of pennate muscle arrangements are:

1. Unipennate - fascicles arranged on one side of the tendon.
2. Bipennate - fascicles arranged on both sides of a centrally positioned tendon.
3. Multipennate - fascicles attached obliquely from many directions to several tendons.

The myotendinous junction is the point at which a tendon attaches to muscles.

The osteotendinous junction is the point at which a tendon attaches to bone.

The origin is the attachment site that does not move during contraction (usually proximal), while the insertion is the attachment site that moves when the muscle contracts (usually distal).

The functional unit of skeletal muscle is defined as a motor unit, which consists of a motor neuron and the muscle fibers it innervates.

A motor neuron may control between 13 to 20 muscle fibers in some muscles, while in larger muscles, it can control up to 2000 muscle fibers.

Muscle tone refers to a low level of contraction in skeletal muscles, maintained by small groups of motor units that are constantly active and inactive even at rest. This tone keeps the skeletal muscle firm without producing movement.

• Size & Color: Thin, bright red
• Capillary Network: Highest
• Metabolism: Aerobic (uses O2 and myoglobin)
• Mitochondria: High
• Fiber Recruitment: 1st
• Contraction Speed: Slow
• Contraction Force: Low
• Fatigue Resistance: High

• Size & Color: Thicker, pale red
• Capillary Network: Intermediate
• Metabolism: Aerobic/anaerobic (O2 present)
• Mitochondria: High
• Fiber Recruitment: 2nd
• Contraction Speed: Intermediate
• Contraction Force: Intermediate
• Fatigue Resistance: Intermediate

• Size & Color: Thickest, pale pink
• Capillary Network: Lowest
• Metabolism: Anaerobic (uses O2 and glycogen storage)
• Mitochondria: Low
• Fiber Recruitment: 3rd
• Contraction Speed: Fast
• Contraction Force: Highest
• Fatigue Resistance: Low

ATPase levels directly correlate with contraction speed; higher ATPase levels result in faster contraction speeds in muscle fibers.

Flexor muscles decrease the angle between two bones at a joint when they contract.

Extensor muscles increase the angle between two bones at a joint when they contract.

An agonist is the primary muscle that, when contracted, produces a specific movement in a given direction.

An antagonist opposes the action of the agonist by relaxing or lengthening during movement.

The primary movements of the torso include:

1. Flexion
2. Extension
3. Lateral Flexion
4. Rotation

The angle decreases as the arms move anteriorly.

In neck extension, the angle between the head and trunk increases as the individual looks up, and some anatomists define movement past the anatomical position as hyperextension.

Abduction is the movement of a limb or body part away from the midline of the body. For example, raising the arm or leg sideways away from the body.

Adduction is the movement of a limb or body part towards the midline of the body, contrasting with abduction. For instance, bringing the arm or leg back towards the body after being raised.

The movements of the thumb include:

1. Abduction - Moving the thumb away from the hand.
2. Adduction - Moving the thumb towards the hand.
3. Extension - Straightening the thumb.
4. Flexion - Bending the thumb inward.
5. Opposition - Touching the tip of the thumb to the tip of the little finger.
6. Reposition - Returning the thumb to its neutral position.

Pronation refers to the rotation of the forearm or hand so that the palm faces downward (or inward), while supination is the rotation that turns the palm upward (or outward).

Arm circumduction is a circular movement of the arm that involves moving the arm in a circular path while keeping it extended. This movement can be performed by standing with the arm extended to the side and tracing a circular motion, typically in a clockwise or counterclockwise direction.

Leg circumduction involves moving the leg in a circular motion while keeping it extended. To perform this movement, one stands and lifts the leg to the side, then traces a circular path with the leg, similar to the motion of a windmill.

Finger circumduction refers to the circular motion of the finger, particularly the index finger. This movement is executed by pointing the finger and rotating it in a circular path, allowing for a range of motion that combines flexion, extension, abduction, and adduction.

Dorsiflexion is the movement where the toes point upwards towards the shin, decreasing the angle between the foot and the leg.

Plantarflexion is the movement where the toes point downwards away from the shin, increasing the angle between the foot and the leg.

Eversion is the movement where the sole of the foot turns outwards away from the midline of the body.

Inversion is the movement where the sole of the foot turns inwards towards the midline of the body.