Musculoskeletal system: Bones and Structure

• The musculoskeletal system is the focus of lectures 02-03.
• The goal is to identify skeletal organization, parts of the system, bone types, the skull structure, the vertebral column and its types, bones of the shoulder, upper and lower extremities and girdles, different joints, and different muscles.

Bone Function

• Bones provide support, protection, and movement for the body.
• Bones support the body's weight and protect organs like the lungs, while interacting with muscles to allow movement.
• Bones store inorganic salts like calcium, phosphate, magnesium, sodium, and potassium.
• Red marrow in bones is responsible for blood cell formation.

Skeletal Structure and Organization

• The axial skeleton forms the body's long axis, containing 80 bones in the skull, vertebral column, and bony thorax (ribs and sternum).
• The appendicular skeleton includes bones of the upper and lower extremities and girdles, with 126 bones split into shoulder and pelvic girdles, upper and lower extremities.
• The axial skeleton consists of the skull, vertebral column, and thoracic cage.
• The appendicular skeleton consists of the upper and lower limbs, as well as the pectoral and pelvic girdles.

Parts of the Skeletal System

• The skeletal system consists of bones (skeleton), joints, cartilages, ligaments (bone to bone), and tendons (bone to muscle).

Bone types and the Skull

• Bone types include flat, irregular, long and short.
• The skull has two sets of bones: cranium and facial bones (sense capsules and jaws).
• Skull bones are joined by sutures, except for the mandible, which has a freely movable joint.
• There are 8 cranial bones: frontal (1), parietal (2), sphenoid (1), temporal (2), occipital (1), and ethmoid (1).
• The skull includes 14 facial bones including the maxilla(2), palatine(2), nasal(2), lacrimal(2), zygomatic(2), inferior nasal conchae(2), mandible(1), and vomer(1).

The Bony Thorax

• The bony thorax consists of the sternum, ribs & costal cartilages, and thoracic vertebrae.
• All ribs attach to the vertebral column posteriorly.
• True ribs (1-7) attach to the sternum in the front and are known as true or sternal ribs.
• False ribs (8-12) do not directly connect to the sternum.
• The upper three false ribs connect to the costal cartilages just above them.
• The last two false ribs (11-12) have no ventral attachment and are called floating, fluctuating, or vertebral ribs.

The Vertebral Column

• The vertebral column consists of 26 irregular bones in adults and provides axial support for the trunk.
• The vertebral column: -Transmits weight to the lower limbs. -Protects the spinal cord. -Provides an attachment site for ribs and muscles.
• The vertebral column is separated by intervertebral discs, with 24 vertebrae, a sacrum (5 fused), and a coccyx (4 fused).

Regional Characteristics of the Vertebrae

• Cervical vertebrae (C1-C7) are in the neck and allow movement.
• Thoracic vertebrae (T1-T12) connect to the rib cage and have limited movement.
• Lumbar vertebrae (L1-L5) are in the low back and allow movement.
• The sacral vertebrae (5 fused) join the pelvis.
• The coccyx (4 fused) is the terminus.
• Cervical and lumbar curvatures are concave.
• Thoracic and sacral curvatures are convex.
• Primary curvatures are thoracic and sacral.
• Secondary curvatures are cervical and lumbar.
• The vertebral arch is formed by the spinous processes, transverse processes, pedicles, lamina, and articular processes.

Differences Between Vertebrae

• Cervical vertebrae (3-7) have a small wide body with kidney shaped sides, short bifid spinous processes, a triangular vertebral foramen, and contain foramina.
• Thoracic vertebrae have heart shaped bodies larger than cervical, long sharp and inferiorly shaped spinous processes, circular vertebral foramen, and bear facets for ribs (except T11-T12).
• Lumbar vertebrae has kidney shaped bodies. blunt spinous processes projecting directly posteriorly, triangular vertebral foramen, and thin tapered processes.
• The atlas is C1
• The axis is C2

Sacrum

• The sacrum contains has a sacral promontory, superior articular process, auricular surface, sacral canal, ala, median sacral crest, lateral sacral crest, posterior sacral foramina, anterior sacral foramina, sacral hiatus, coccyx

The Shoulder Girdle

• The shoulder girdle includes the scapula and clavicle.
• The glenoid cavity articulates with the humerus.
• The acromion articulates with the clavicle.
• The coracoid process projects anteriorly.

The Upper Limb

• The arm is formed by the humerus, which articulates with the glenoid cavity of the axial skeleton
• The forearm has two bones, the ulna and radius,
• The hand includes carpal bones (wrist), metacarpals (palm), and phalanges (fingers).
• Supination of the palm faces upwards
• Pronation has the Palm facing downwards
• The radioulnar joint is involved in pronation and supination

The Pelvis

• The bony pelvis consists of two hip bones, the sacrum, and the coccyx.
• There are four articulations within the pelvis: sacroiliac joints, sacrococcygeal symphysis, and pubic symphysis.
• The hip bones consist of the ilium, ischium and pubis

The Lower Limb

• The thigh contains one bone that is the femur
• The leg has two bones, the tibia and fibula.
• The foot includes tarsus (ankle), metatarsals (sole), and phalanges (toes).

Joints

• Joints are articulations of bones that allow for mobility and hold bones together.
• Functionally, joints are classified as immovable, slightly movable, or freely movable.
• Structurally, joints are classified as fibrous (generally immovable), cartilaginous (immovable or slightly moveable), or synovial (freely moveable).
• Joints include hinge, pivot, gliding, condyloid, saddle and ball and socket joints

Introduction to the Muscular System

• Muscles are tissues that can contract to enable movement.
• Muscle cells are called myocytes.
• Functions of the muscular system include attaching to bones of the skeletal system, moving food through the digestive system, passing blood through the circulatory system, and expelling fluids through the excretory system.

Types of Muscle Tissue

• There are three types of muscle tissue: skeletal, smooth, and cardiac.

Skeletal Muscle

• Skeletal muscles produce movements of the skeleton and are voluntary.
• Skeletal muscles are made of striped ms. fibers and have at least two attachments: origin and insertion.
• The fleshy part of the muscle is called the belly.
• The ends of ms. are attached to bones, cartilage, or ligaments.
• The attachment of ms. to bone may take one of the following shapes: tendon (cord of fibrous T) or aponeurosis (strong sheet of fibrous T).
• Another form of muscle attachment is via raphe (interdigitation of tendinous ends of fibers of flat muscles)
• Based on the direction of ms. fibers, skeletal muscles are classified as parallel and oblique types

Parallel Muscles

• Parallel muscles have ms. fibers that are parallel to the long axis of muscle and include strap like muscles such as sartorius, fusiform e.g. Biceps brachii, Digastric, Quadrilateral e.g. Quadratus lumborum.

Oblique Muscles

• Oblique muscles have muscle fibers that run obliquely like Pennate muscles, which are further classified as:
  • Unipennate
  • Bipennate
  • Multipennate

Terms of Movement

• Flexion and Extension: Movements that occur in the sagittal plane, referring to decreasing (flexion) or increasing (extension) the angle between two body parts.
• Abduction and Adduction: Abduction is a movement away from the midline, while adduction is a movement towards the midline.
• Medial and Lateral Rotation: Movements describing the rotation of limbs around their long axis, with medial rotation being towards the midline and lateral rotation away from the midline.

Skeletal Muscle Action

• Prime mover: The chief muscle or muscle group responsible for a particular movement.
• Antagonist: A muscle that opposes the action of the prime mover.
• Synergist: A muscle that assists the prime mover by stabilizing intermediate joints and preventing unwanted movements when the prime mover crosses multiple joints.
• A nerve trunk to a muscle is a mixed nerve containing: motor fibers (60%), sensory fibers (40%) and some sympathetic fibers
• Motor point is located where the motor nerve enters the muscle and is most electrically excitable.
• Naming of skeletal muscles is according to: shape, size, heads, position, depth, attachments or actions.
• Muscle Tone: A slight unconscious continuous contraction in the skeletal muscle.

Smooth Muscles

• Smooth muscles are involuntary.
• Smooth muscles are found in the GIT, blood and lymph vessel walls, and in various hollow organs like the stomach.

Cardiac Muscles

• Cardiac muscles attach to the heart, and are responsible for moving the blood through the heart's chambers and pumping it to all parts of the body.
• Cardiac muscles are involuntary.