the skeletal system

THE SKELETAL SYSTEM

General Considerations of Bones

Average adult skeleton has 206 bones (Figure 7.1)

Bones are paired or unpaired

Most anatomical terms used to describe the features of bones are based on the relationship between the bones and associated ligaments, muscles, joints, nerves, and blood vessels (Table 7.1) Processes

Surfaces

Holes

The skeleton is divided into the axial and appendicular skeletons

Fig 7.1

Tab. 7.1

Axial Skeleton

The axial skeleton forms the upright axis of the body

Consists of

Skull

Auditory ossicles

Hyoid bone

Vertebral column

Thoracic cage (rib cage)

Protects the brain, the spinal cord, and the vital organs housed within the thorax

Axial Skeleton Skull

Composed of 22 bones The braincase protects the brain Paired parietal and temporal bones, and the unpaired

frontal, occipital, sphenoid, and ethmoid bones

The facial bones protect the sensory organs of the head and serve as muscle attachment sites The 14 facial bones are the maxilla (2), zygomatic (2),

palatine (2), lacrimal (2), nasal (2), inferior nasal concha (2), mandible (1), and vomer (1) bones

The mandible and maxillae hold the teeth, and the auditory ossicles that function in hearing, are located inside the temporal bones

Axial Skeleton

Skull (External view)

Parietal bones Joined at the midline by the sagittal suture

Joined to the frontal bone by the coronal suture

Joined to the occipital bone by the lambdoid suture

Joined to the temporal bone by the squamous suture

The external occipital protuberance is an attachment site for an elastic ligament

Nuchal lines are the points of attachment for neck muscles

Fig 7.2

Fig 7.3

Axial Skeleton Skull (Lateral view)

The external acoustic meatus transmits sound waves toward the eardrum

Neck muscles attach to the mastoid process, which contains mastoid air cells

The temporal lines are attachment points of the temporalis muscle

The zygomatic arch, from the temporal and zygomatic bones forms a bridge across the side of the skull

The mandible articulates with the temporal bone

Fig 7.4

Fig 7.5

Axial Skeleton

Skull (Anterior view)

The orbits contain the eyes

The nasal cavity is divided by the nasal septum

Sinuses within bone are air-filled cavities The paranasal sinuses, which connect to the

nasal cavity, are the Frontal sinus

Sphenoidal sinus

Maxillary sinuses

Ethmoidal labyrinth

Fig 7.6

Fig 7.7

Fig 7.8

Fig 7.9

Fig 7.10

Axial Skeleton

Skull (Inferior surface)

Spinal cord and brain are connected through the foramen magnum

Occipital condyles are points of articulation between the skull and the vertebral column

Blood reaches the brain through the internal carotid arteries, which pass through the carotid canals, and the vertebral arteries, which pass through the foramen magnum

Axial Skeleton

Skull (Inferior surface)

Most blood leaves the brain through the internal jugular veins, which exit through the jugular foramina

Styloid processes provide attachment points for three muscles involved in movement of the tongue, hyoid bone, and pharynx

The hard palate separates the oral cavity from the nasal cavity

Fig 7.11

Axial Skeleton

Skull (Superior view inside the cranial cavity)

The crista galli is a point of attachment for one of the meninges

The olfactory nerves extend into the roof of the nasal cavity through the olfactory foramina of the cribriform plate

The sella turcica is occupied by the pituitary gland

Tab. 7.2

Tab. 7.3

Fig 7.12

Axial Skeleton

The hyoid bone, which floats in the neck, is the attachment site for throat and tongue muscles

Fig 7.13

Axial Skeleton

Vertebral Column

Provides flexible support and protects the spinal cord

The vertebral column has four major curvatures:

Cervical

Thoracic

Lumbar

Sacral/Coccygeal

Fig 7.14

Fig 7.15

Axial Skeleton

Vertebral Column (Vertebra) Consists of a body, a vertebral arch, and various

processes Part of the body and vertebral arch (pedicle and

lamina) form the vertebral foramen, which contains and protects the spinal cord

The transverse and spinous processes are points of muscle and ligament attachment

Vertebrae articulate with one another through the superior and inferior articular processes

Spinal nerves exit through the intervertebral foramina

Adjacent bodies are separated by intervertebral disks

Fig 7.16

Tab. 7.4

Axial Skeleton

Vertebral Column Components All seven cervical vertebrae have transverse

foramina, and most have bifid spinous processes The 12 thoracic vertebrae have attachment sites

for ribs and are characterized by long, downward-pointing spinous processes

The five lumbar vertebrae have thick, heavy bodies and processes. Their superior articular facets face medially and their inferior articular facets face laterally

The sacrum consists of five fused vertebrae and attaches to the coxal bones to form the pelvis

The coccyx consists of four fused vertebrae attached to the sacrum

Fig 7.17

Tab.

7.4(Cont

d.)

Tab. 7.5

Axial Skeleton Thoracic Cage The thoracic cage (consisting of the ribs, their

associated costal cartilages, and the sternum) protects the thoracic organs and changes volume during respiration

Twelve pairs of ribs attach to the thoracic vertebrae Seven pairs of true ribs

Five pairs of false ribs Two pairs of false ribs are floating

The sternum is composed of the Manubrium

Body

Xiphoid process

Fig 7.19

Fig 7.20

Appendicular Skeleton

Consists of the bones of the upper and lower limbs and the girdles by which they are attached to the body

Pectoral girdle: upper limbs

Pelvic girdle: lower limbs


Pectoral Girdle/Shoulder Girdle

scapulae and clavicles

Scapula

Flat, triangular

3 fossae: arm muscles

Glenoid fossa: head of humerus

Acromion process: clavicle

Spine: posterior surface of scapula

Coracoid process: arm and chest muscles Attachment site for shoulder, back and arm muscles

Fig 7.22


Clavicle Proximal end: attached to the

sternum

Holds the shoulder away from the body and allows movement of the scapula, resulting in free movement of the arm

Fig 7.23


Upper Limb

Arm bone: humerus Head: glenoid cavity of scapula

Anatomical neck

Surgical neck

Tubercles: hold humerus to scapula

Deltoid tuberosity

Epicondyle: forearm muscles; medial and lateral

Capitulum: radius

Trochlea: ulna

Fig 7.25


Upper Limb

Forearm bone: Ulna (medial) Trochlear notch: proximal end; elbow

joint

Olecranon process: point of the elbow

Coronoid process: grip with humerus

Styloid process: wrist ligaments

Head: posterior ulnar side of wrist


Upper Limb

Forearm bone: Radius (lateral) Head: rotates against humerus & ulna

Radial tuberosity: biceps brachii

Styloid process: wrist ligaments


Upper Limb

Eight carpal, or wrist, bones are arranged in two rows

five metacarpal bones (bony framework)

The phalanges are digital bones. Each finger has three phalanges, and the thumb has two phalanges

Proximal, middle, distal


Pelvic Girdle

2 coxal (hip) bones + sacrum

Pelvis: pelvic girdle + coccyx

Coxal bone

Ilium: most superior

Ischium: inferior and posterior

Pubis: inferior and anterior

Iliac crest: superior margin


Pelvic Girdle

Anterior superior iliac spine: landmark

Pubic symphysis: anterior

Sacroiliac joint: posterior

Acetabulum: socket

Obturator foramen

Pelvic (Hip) Girdle

Basin-like pelvis is formed by two hip bones (pelvic girdle) + sacrum and coccyx

False (greater) pelvis: broad region superior to pelvic brim; contains abdominal organs

True (lesser) pelvis: small region inferior to pelvic brim; contains urinary bladder + internal reproductive organs


Lower Limb

Femur (thigh): between hip and knee

Head: acetabulum of coxa

Condyles (medial and lateral): tibia

Epicondyles (medial and lateral): ligament attachment

Neck

Trochanters (Greater and lesser)


Lower Limb

Leg (between knee and ankle)

Tibia (shinbone): major weight-bearing bone; medial

Condyles (medial and lateral): articulates with the condyles of the femur

Tibial tuberosity

Medial malleous


Lower Limb

Fibula (lateral)

Longest and thinnest bone

Does not articulate with femur

Head articulates with tibia

Lateral malleolus

Right Femur

Right Tibia and Fibula

Ankle and Foot Tarsus (ankle) has 7 bones Large talus (ankle bone) and

Calcaneus (heel bone)

Metatarsals (foot bones) Numbered 1 to 5 from medial to lateral

Phalanges (toe bones) Big toe has proximal and distal phalanges while

others have proximal, medial and distal phalanges. Numbered like metatarsals from 1-5

Right Foot

the skeletal system

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