Ch7 study guide. Skeletal System: Axial Skeleton Structure

Structure of the Skeletal System and Skeletal Cartilages

• The human body has ~206 bones and cartilage, forming the skeleton system.
• The skeleton is composed of bone groups that work together.
• The skeleton has two basic parts: the axial skeleton and the appendicular skeleton.

The Axial Skeleton

• The axial skeleton forms the body's longitudinal axis, encasing body cavities for organ protection.
• The axial skeleton includes the skull, vertebral column, and thoracic cage.

The Skull

• The skull consists of 22 bones: 8 cranial and 14 facial.
• The skull encases the brain and forms the face.

The Vertebral Column

• The vertebral column consists of 33 bones, with 24 individual vertebrae protecting the spinal cord.
• The remaining vertebrae fuse to form the sacrum and coccyx.

The Thoracic Cage

• The thoracic cage (rib cage) consists of 12 pairs of ribs, the sternum, and sections of the vertebral column.
• The thoracic cage encases and protects the lungs, heart, and other thoracic cavity contents.

The Appendicular Skeleton

• The appendicular skeleton includes the bones of the pectoral girdle, upper limb, pelvic girdle, and lower limb.
• The appendicular skeleton supports movement, support, and muscle attachment.

The Pectoral Girdle

• The pectoral girdle anchors the upper limb to the trunk
• The pectoral girdle is composed of the clavicle and scapula.

The Upper Limb

• The upper limb consists of the arm, forearm, wrist, and hand.
• The arm contains the humerus; the forearm contains the radius and ulna.
• The wrist and hand contain the carpals, metacarpals, and phalanges.

The Pelvic Girdle

• The pelvic girdle anchors the lower limb to the trunk.
• The pelvic girdle is composed of two pelvic bones and the sacrum, which are collectively called the pelvis.

The Lower Limb

• The lower limb includes the thigh (femur), leg (tibia and fibula), and ankle & foot (tarsals, metatarsals, and phalanges).

Bone Markings

• Bones have surface features used for depressions, openings, and projections.
• Depressions may provide pathways for blood vessels, nerves, articulations, or joints between bones.
• Openings enclose structures, allowing them to travel through bones.
• Projections provide sites where bones articulate or ligaments and tendons attach.

Overview of Skull Structure

• The skull has 22 bones, consisting of cranial and facial bones.

Cranial Bones

• The cranium is composed of eight bones.
• The four single cranial bones are the frontal, occipital, ethmoid, and sphenoid bones.
• The two paired cranial bones are the temporal and parietal bones.

Facial Bones

• The facial bones form the face and consist of 14 bones.
• The six paired facial bones are the maxillary, zygomatic, nasal, lacrimal, palatine, and inferior nasal conchae bones.
• The two single facial bones are the mandible and vomer.

Sutures

• Except for the mandible, skull bones are fused at immovable joints called sutures.

Cranial Cavity

• The cranial cavity surrounds the brain.
• The cranial cavity consists of orbits for eyeballs and the nasal cavity for smell.
• The oral cavity surrounds the teeth and tongue.
• Small cavities contain sense organs for hearing and balance.

Sinuses

• Skull bones contain membrane-lined spaces called sinuses.
• Four bones surrounding the nasal cavity consist of paranasal sinuses.

Cranial Vault and Base

• The cranial vault or calvarium is the superior portion of the cranial cavity.
• The inferior portion, called the cranial base, has anterior, middle, and posterior cranial fossae for the brain.

Cavities of the Skull

• Several small cavities are found within the skull.

Orbit

• The orbit is a complex anatomical structure formed by seven fused bones.
• The orbit encases the eyeball, lacrimal gland, blood vessels, muscles, and nerves: frontal, maxilla, zygomatic, sphenoid, ethmoid, lacrimal, and palatine bones.

Nasal Cavity

• The nasal cavity includes mucus membranes that form the walls of the respiratory tract's first part.

Paranasal Sinuses

• The paranasal sinuses are found within the frontal, sphenoid, ethmoid, and maxillary bones.
• The paranasal sinuses communicate with the nasal cavity through small openings.
• Mucous membranes in the sinuses filter, warm, and humidify inspired air, reduce skull weight, and enhance voice resonance.

Oral Cavity

• The tongue, teeth, and salivary glands are found in the oral cavity, which is the first part of the digestive tract.
• The oral cavity roof is created by the hard palate.
• The maxilla and mandible makes the anterior and lateral walls of the cavity.
• The posterior wall and bony floor are absent

Fetal Skull

• Fetal skull bones are not fused like adult skulls.
• Soft spots called fontanels are membranous areas between fetal cranial bones.
• Fontanels and unfused sutures allow the skull to fit through the vaginal canal during birth.
• Fontanels are present until the child's cranial bones develop at 18–24 months consisting of the anterior, posterior, sphenoid, and mastoid fontanels.

Hyoid Bone

• The hyoid is a C-shaped bone.
• The hyoid bone is unique because it doesn't articulate with any other bone.
• Provides attachment points for swallowing and speech muscles.

Overview of the Vertebral Column

• The vertebral column (spine) has 33 bones called vertebrae.
• Vertebrae are classified by structure and location.

Intervertebral Foramen

• The intervertebral foramen is the space between movable vertebrae, viewed laterally.
• Each vertebra has a letter indicating its location and a number indicating its position.

Cervical Vertebrae

• 7 cervical vertebrae are in the neck (C4 is the fourth cervical vertebra).

Thoracic Vertebrae

• 12 thoracic vertebrae articulate with the ribs (T11 is the eleventh thoracic vertebra).

Lumbar Vertebrae

• 5 lumbar vertebrae are in the lower back (L3 is the third lumbar vertebra).

Sacral Vertebrae

• 5 fused sacral vertebrae form the sacrum, articulating with the pelvic bones.

Coccygeal Vertebrae

• 3-5 fused coccygeal vertebrae form the coccyx at the vertebral column's inferior end.

Spinal Curvatures

• Newborns have a C-shaped vertebral column that develops into S-shaped secondary curvatures as they grow.
• Secondary curvatures are the cervical and lumbar curvatures.
• Primary curvatures are the thoracic and sacral curvatures.
• Secondary curvatures develop after the fetal period, while primary curvatures are present at the fetal period.

Cervical Curvature

• The cervical curvature is concave.
• The cervical curvature extends from C2 to T2, developing as infants start to lift their heads and crawl.

Lumbar Curvature

• The lumbar curvature is concave.
• The lumbar curvature extends from T12 to L5, developing as children age and begin to walk.

Thoracic Curvature

• The thoracic curvature is convex.
• The thoracic curvature extends from T2 to T12.

Sacral Curvature

• The sacral curvature is convex.
• The sacral curvature extends from the lumbosacral junction to the coccyx.

Abnormal Spinal Curvatures

• Abnormal spinal curvatures include scoliosis, lordosis, and kyphosis.

Scoliosis

• Scoliosis is characterized by abnormal lateral curvatures in the vertebral column.

Lordosis

• Lordosis (swayback) is characterized by exaggerated cervical and lumbar curvatures.

Kyphosis

• Kyphosis is an exaggeration of the thoracic curvature, resulting in a hunchback appearance.

Structure of the Vertebrae

• Vertebrae share common structural features for spinal cord protection and head & neck support.
• The following outlines the common features of all vertebrae: the body, vertebral foramen, pedicles, laminae, vertebral arch, inferior vertebral notch, superior & inferior articular processes, transverse processes, and spinous process.

Body/Centrum

• The body (centrum) is the primary weight-bearing surface and the anterior aspect of the vertebra.
• Vertebral discs are between adjacent bodies to absorb shock.

Vertebral Foramen

• The vertebral foramen is the large opening through which the spinal cord and tissues travel.
• Foraminae together form the vertebral canal.

Pedicles

• Two pedicles border the vertebral foramen laterally.
• The pedicles project posteriorly from the body.

Laminae

• Two laminae merge with the pedicles and border the vertebral foramen posteriorly.

Vertebral Arch

• The pedicles and laminae form the vertebral arch together.

Inferior vertebral notch

• A deep inferior vertebral notch is found on the inferior side of each pedicle, while the superior vertebral notch is found on the superior side.
• Together successive notches form the intervertebral foramina.

Articular Processes

• Superior and inferior articular processes are at the junction of each pedicle and lamina.
• Facets on these processes form joints between vertebrae.

Transverse Processes

• Transverse processes project from the lateral sides of the vertebral arch.
• Transverse processes project providing attachment sites for muscles.

Spinous Process

• The spinous process projects from the posterior aspect of the vertebral arch.
• The spinous process provides attachment sites for muscles.

Intervertebral Discs

• An intervertebral disc (23 total) is a fibrocartilage pad between adjacent vertebrae bodies.
• Intervertebral discs absorb shock and bind the vertebral column together.

Thoracic Cage

• The thoracic cage consists of the sternum, 12 pairs of ribs, and the thoracic vertebrae.
• The thoracic cage forms the protective peripheral boundary of the thoracic cavity.

Sternum

• The flattened sternum (breastbone) forms the thoracic cage's anterior section.
• The sternum has three portions: the manubrium, body, and xiphoid process.

Rib Cage

• The rib cage has 12 pairs of ribs and their costal cartilages, curved into a C-shape.
• Each rib attaches to a thoracic vertebra posteriorly.
• Intercostal spaces are the gaps between successive ribs that allow flexibility during movement and breathing.

True Ribs

• Based on anterior attachments, the ribs are grouped into true and false ribs.
• Ribs 1-7 are true ribs (vertebrosternal), attaching to the sternum via costal cartilages.

False Ribs

• Ribs 8-12 are false ribs, not directly attached to the sternum.
• Vertebrochondral ribs 8–10 attach to the cartilage of the seventh ribs.
• Ribs 11 and 12 are floating or vertebral ribs, not attached to the sternum.
• The costal margin is formed by the costal cartilage of ribs 7–10.

Rib Structure

• The following describes the structure of ribs 2–9.
• Ribs 1, 10–12 have slight variations.

Pectoral Girdle

• The pectoral girdle consists of the clavicle and scapula.
• The pectoral supports 30 bones of the upper limb, which are components of the appendicular skeleton.

Clavicle

• The clavicle (collarbone) is straight viewed anteriorly and S-shaped when viewed superiorly or inferiorly.

Scapula

• The triangular scapula sits on the posterosuperior rib cage between the second and seventh ribs.
• The body (largest section) has medial, lateral, and superior borders.

Coracoid Process

• The coracoid process is a hook-shaped projection on the scapula's anterior surface.

Glenoid Cavity

• The glenoid cavity is a shallow indentation on the lateral surface.
• The glenoid cavity articulates with the humerus in the shoulder joint.

Spine

• The spine is a ridge of bone posteriorly across the superior scapula.
• The spine terminates as the acromion at the acromioclavicular joint (AC).

Supraspinous and Infraspinous Fossa

• The supraspinous fossa is superior to the spine, while the infraspinous fossa is inferior.

Humerus

• The humerus is the largest and strongest bone of the upper limb.
• The humerus is found in the arm (brachium).
• This long bones consists of two epiphyses that articulate with other bones and a long diaphysis.

Humerus: Proximal Epiphysis

• The proximal epiphysis has a medially-oriented ball-shaped humeral head that articulates with the glenoid cavity at the shoulder joint.
• The anatomical neck surrounds the head while the surgical neck is found where the proximal epiphysis and diaphysis meet.

Humerus: Distal Epiphysis

• The distal epiphysis features medial and lateral epicondyles, which provide attachment sites for muscles.

Bones of Forearm

• Bones of the forearm (antebrachium) consist of the lateral radius and medial ulna, held together by the fibrous interosseous membrane.
• Both bones articulate proximally with the humerus and distally with the carpal bones, articulating with each other at proximal and distal radioulnar joints.

Carpals

• The wrist (carpus) has eight short bones collectively called carpals, arranged in two rows with four bones each.
• The four proximal carpal bones are the scaphoid, lunate, triquetrum, and pisiform (lateral to medial).
• The four distal carpal bones are the trapezium, trapezoid, capitate, and hamate (lateral to medial).

Metacarpals and Phalanges

• The hand (manus) has five long bones called metacarpals, numbered I–V (lateral to medial).
• The metacarpals articulate with distal carpal bones and the bones of the fingers.
• Each metacarpal has 3 parts: the base (proximal epiphysis), body (diaphysis), and head (distal epiphysis).
• The finger bones have 14 phalanges, each with a base, body, and head.
• Each finger consists of three bones: a proximal, middle, and distal phalanx.
• The thumb (pollex) consists of only a proximal and distal phalanx.

Pelvis and Bones of the Pelvic Girdle

• The pelvis and bones of the pelvic girdle and lower limb complete the appendicular skeleton.
• The hip bones (coxal bones) make up the pelvic girdle, which articulates with the sacrum (part of the axial skeleton).

Pelvis

• The bowl-shaped pelvis is composed of the sacrum and two coxal bones.
• The pelvis creates the boundary for the pelvic cavity.

Pelvis: Structures

• The pelvic inlet is an oval opening formed by the sacrum and pelvic girdle.
• The pelvic brim is the bony ridge surrounding the inlet.
• The greater (false) pelvis is superior to the pelvic brim.
• The lesser (true) pelvis is inferior to the brim.
• The pelvic outlet is the opening at the inferior boundary of the lesser pelvis.

Coxal Bones

• Each coxal bone has three fused bones: the ilium, ischium, and pubis.
• The ilium, ischium, and pubis contribute to the acetabulum (a deep socket on the coxal bone's lateral aspect).
• The ilium forms the superior portion of the coxal bone.

Ischium

• The ischium (ischial body and ramus) forms the coxal bone's C-shaped posteroinferior portion.
• Notable markings on the ischium include the ischial spine and ischial tuberosity.

Pubis

• The pubis is the smallest coxal bone with three parts in a C-shape: superior pubic ramus, pubic body, and inferior pubic ramus.
• The pubic symphysis is the joint where the two pubic bodies are separated by a fibrocartilaginous pad.
• The pubic arch is the angle formed by the two pubic bodies that differs between genders.

Gender Determination

• Female and male pelvises (skeletal structures) determine gender.
• The female pelvis (adapted for childbirth) is wider and shallower than its male counterpart.

Gender Determination: Greater pelvis Shape

• The female pelvis is wider with flared iliac crests, increasing the distance between anterior superior iliac spines.

Gender Determination: Coccyx and Sacrum

• The female sacrum is shorter while the female coccyx is more flexible.
• The female coccyx is oriented more posteriorly than the male equivalent.

Gender Determination: Pelvic Inlet & Outlet

• The female inlet is wider and oval-shaped, while the male inlet is narrow and heart-shaped.
• The female outlet is wider than the male equivalent.

Gender Determination: Acetabula

• Acetabula in females are farther apart and pointed more anteriorly than the male counterpart.

Gender Determination: Pubic Arch

• The female pubic arch measures between 90°–100°, and the male arch measures between 60°-70°.

Gender Determination: Ischial Tuberosities

• Ischial tuberosities in females point laterally, while males point more medially.

Gender Determination: General

• The female pelvis is lighter and less robust than its male equivalent because males have greater muscle mass and body weight.

Femur and Patella

• The femur is the largest and strongest bone in the body.
• The femur is the only bone in the thigh.

Femur and Patella: Proximal Epiphysis

• The proximal epiphysis features a spherical head articulating with the acetabulum at the hip joint.
• The fovea capitis is a small pit in the head's center where a small ligament attaches.
• The neck is distal to the head, with the lateral greater trochanter.
• The lesser trochanter is medial and distal to the greater trochanter.
• Trochanters connect by a bony ridge on the anterior side (intertrochanteric line) that continues posteriorly as the intertrochanteric crest.

Femoral Shaft

• The femoral diaphysis (shaft) exhibits different features.

Patella

• The triangular patella (kneecap) articulates with the patellar surface on the femur.

Tibia and Fibula

• The tibia and fibula make up the bones of the leg.
• These bones connect via an interosseous membrane and articulate with one another at the proximal and distal tibiofibular joints.

Tibia

• The tibia is the larger medial bone of the leg that bears the weight of the body.
• Two concave depressions (medial and lateral condyles) are at the tibia's proximal end, articulating with the medial and lateral condyles of the femur in the knee joint.

Fibula

• The fibula is the smaller lateral bone of the leg, bearing 1/6 of the tibia's weight.
• The head of the fibula articulates with the lateral tibia proximally.
• The fibula expands into the palpable lateral malleolus that stabilizes the ankle joint distal to the distal tibiofibular joint and articulates with the lateral talus.

Tarsals, Metatarsals, and Phalanges

• The structure of the foot and ankle is similar to that of the hand and wrist.
• The tarsals are the seven short bones that make up the ankle region that connects the leg to the foot.
• The proximal tarsals include the talus, calcaneus, and navicular.
• The distal tarsals include the medial cuneiform, intermediate cuneiform, lateral cuneiform, and cuboid.
• The metatarsals (numbered I–V from medial to lateral) have a proximal base, middle shaft, and distal head.

Phalanges

• Fourteen phalanges are found in the toes, where toes II–V have proximal, middle, and distal phalanges, and the great toe (hallux) has only a proximal and distal phalanx.

Arches of Foot

• The bones of the foot are arched instead of flat on the ground.
• The arches support and distribute body weight during movement.
• The following three arches stabilize with ligaments muscles: the medial longitudinal arch (calcaneus to metatarsals I-III), the lateral longitudinal arch (lateral calcaneus to metatarsals IV–V), and the transverse arch (middle of the foot involving distal tarsals and all five metatarsals).