Anatomy And Physiology I

The Skeletal System - The Axial skeleton

Kefah Zaben

BSN,MSN, PHD
 The Skeletal System

Divided into two divisions

 Axial skeleton : bones of the cranium, face, vertebral column, and bony

thorax.

 Appendicular skeleton : includes the bones of the pelvic girdles, the upper

extremities and lower extremities.

The Skeletal System
 The Skeletal System

The axial skeleton forms the upright axis of the body .

The axial skeleton is divided into the skull, auditory ossicles, hyoid

bone, vertebral column, and thoracic cage, or rib cage.

The axial skeleton protects the brain, the spinal cord, and the vital organs

housed within the thorax.

 The Axial Skeleton

• Forms the longitudinal part of the body

Divided into three parts

1. Skull

2. Vertebral column

3. Bony thorax
 The Skull (28 bones) (18 names)

 Sits on top of the vertebral column

 Two sets of bones

1. Cranium (8 bones)

2. Facial bones (14 bones)

 Bones are joined by sutures

 Only the mandible is attached by a freely movable joint

 The Cranium

 The Cranium : is the bony structure that encases and protects the brain.

 The Cranium consist of 8 bones

 Frontal bone (1) parietal bone (2) temporal bones (2)

Occipital bone(1) sphenoid bone (1) ethmoid bone (1)

 The 4 Major Sutures

Suture : The immovable joints of the skull

1. Lambdoid suture : Separates occipital from parietal bones

2. Coronal suture: Attaches frontal bone to parietal bones

3. Sagittal suture : Between the parietal bones .

4. Squamous suture :Form boundaries between temporal bones and parietal

bones
Major Sutures
The Cranium
The Cranium
Human Skull, Superior View
Human Skull, Inferior View
 The Cranium

1- Frontal Bone : forehead/upper part of the bony structure

surrounding the eyes.

2- Parietal Bone (2) :

upper sides of the head and the roof of the cranial cavity (top of the
head)
 The Cranium

3- Temporal Bones (2) : sides of the head, close to ears.

• Commonly called the temples

•Includes the external auditory meatus

• Opening for the ear

•Includes the zygomatic process

• Part of the cheekbone

 The Cranium

4- Occipital Bone : back and base of the cranium

•Includes the foramen magnum

•Foramen means hole

•Large hole for the brainstem/spinal cord

 The Cranium

5- Sphenoid Bone : forms sides of cranium and parts of orbits of the

eyes

Butterfly shaped

•Includes Sella Turcica (Turk’s Saddle)

•Where pituitary gland sits

 The Cranium

6- Ethmoid Bone : irregularly

shaped bone located between the eye

orbits

•Major supporting bone of the

nasal cavity
206 bones - 8 bones = 198
bones
 Facial Bones

 14 bones

 Most of these bones come in pairs

 Only the mandible and vomer are single bones

 Facial Bones

The facial bones support the organs of vision, smell, and taste.

 The Facial Bones provide attachment points for the muscles

involved in mastication (chewing), facial expression, and eye

movement.
 Facial Bones

 Mandible : the lower jaw bone

 Carries the lower teeth

 The anterior portion forms the chin

 Only freely movable joint in the skull

 Facial Bones

The mandible consists of two main parts:

the body and the ramus (branch).

The body and ramus join at the angle of the mandible

The superior end of the ramus has a mandibular condyle, which articulates with the

temporal bone, allowing movement of the mandible

The maxillae and mandible have alveolar processes with sockets for the attachment of the

teeth.
Facial Bones
 Facial Bones

• Maxilla (2) : Upper jaw

• Two bones fused together

• Roof of the mouth

• Form parts of the nasal cavity and eye orbits

 Facial Bones

•Palantine Bones (2) : form the posterior part of the hard palate and

the floor of the nasal cavity.

• Failure of the palatine and/or maxillary bones to fuse causes a

cleft palate.
 Facial Bones

•Zygomatic Bones (2) : the cheekbones

• Forms a part of the orbits of the eyes
Human Skull, Superior View
 Other Facial Bones

1. Lacrimal Bones (2) : inner wall of eye sockets

2. Nasal Bones (2) : bridge of nose

3. Vomer : nasal septum

4. Inferior Nasal Conchae (2)

198 bones - 14 bones =
184 bones
 Nasal Cavity
The nasal cavity is divided into right and left halves by a nasal septum .

The bony part of the nasal septum consists :

The Vomer ( shaped like a plowshare) inferiorly

 The perpendicular plate of the Ethmoid (sieve-shaped) bone superiorly.

 The anterior part of the nasal septum is formed by hyaline cartilage called septal cartilage

 The external part of the nose has some bone but is mostly hyaline cartilage which is absent in

the dried skeleton.

 Paranasal Sinuses
Functions of paranasal sinuses
 Air filled cavities
 Lighten the skull
 Give resonance and amplification to voice
 The Fetal Skull
• The fetal skull is large compared to the infants

total body length

Fontanelles : fibrous membranes connecting the

cranial bones

Function : Allow the brain to grow

Convert to bone within 24 months after birth

 The Hyoid Bone

• The Hyoid Bone is U shaped

• Found in the upper neck

• The only bone that does not articulate with

another bone

• Serves as a moveable base for the tongue

 The Hyoid Bone
The hyoid bone:

 No direct bony attachment to the skull.

 Muscles and ligaments attach it to the skull.

The hyoid “floats” in the superior aspect of the neck, just below the mandible.

The hyoid bone provides

an attachment point for some tongue muscles, and it is an attachment point for important

neck muscles that elevate the larynx during speech or swallowing.

The Hyoid Bone
 Middle Ear
Three tiny bones : transmit vibrations
All derived from Latin words

1. Malleus (hammer): attached to the eardrum.

2. Incus (anvil) : in the middle of the chain of

bones.

3. Stapes (stirrup): attached to the membrane -

that connects the middle ear with the inner
ear and the smallest bone in the body
Middle Ear and Hyoid Bones

184 bones - 4 bones = 180

bones
 The Vertebral Column

The backbone or spine

 Consists of 26 bones called vertebrae

 The Vertebral Column
Major Functions of the Vertebral Column:

1. It supports the weight of the head and trunk

2. It protects the spinal cord

3. It allows spinal nerves to exit the spinal cord

4. It provides a site for muscle attachment

5. It permits movement of the head and trunk.

 Abnormal Spinal Curvatures

Lordosis : is an exaggeration of the concave curve of the lumbar region, resulting

in a swayback condition.

Kyphosis : is an exaggeration of the convex curve of the thoracic region,

resulting in a hunchback condition.

Scoliosis : is an abnormal lateral and rotational curvature of the vertebral

column, which is often accompanied by secondary abnormal curvatures, such as

kyphosis.
Spinal curvatures
The Vertebral Column

 Vertebrae separated by intervertebral discs

(act as shock absorbers)

 The spine has a normal curvature

 Each vertebrae is given a name according

to its location
 The Vertebral Column

 C1-C7 : in the neck region

 7 cervical vertebrae

 T1-T12 : located in the chest region

 12 thoracic vertebrae

 L1-L5 : located in the lower back

 5 lumbar vertebrae
 The Vertebral Column

• Sacrum : curved bone of the lower back

(posterior wall of the pelvis)

• fused sacral vertebrae

• 5 vertebrae at birth

• Coccyx : the tailbone

• 4 vertebrae at birth
 The Vertebral Column

• The vertebrae become larger as the

vertebral column descends…..WHY?
• Vertebral foramen : opening for spinal
cord.
• What is the opening for the spinal cord in
the skull called?
The Vertebral Arch
 Anatomy of Vertebra

Body : Disk-shaped;the largest part with flat surfaces directed superiorly and

inferiorly; forms the anterior wall of the vertebral foramen

intervertebral disks : are located between the bodies

Vertebral foramen : Hole in each vertebra through which the spinal cord passes;

adjacent vertebral foramina form the vertebral canal

 Anatomy of Vertebra

Vertebral arch :

Pedicle Foot : of the arch with one on each side; forms the lateral walls

of the vertebral foramen

Lamina: Posterior part of the arch; forms the posterior wall of the

vertebral foramen
The Vertebral Arch
 Anatomy of Vertebra

 Transverse process :

Process projecting laterally from the junction of the lamina and pedicle; a site of

muscle attachment

 Spinous process :

Process projecting posteriorly at the point where the two lamina join; a site of

muscle attachment; strengthens the vertebral column and allows for movement
The Vertebral Arch
 Anatomy of Vertebra
• Articular processes :

Superior and inferior projections containing articular facets where vertebrae

articulate with each other; strength the vertebral column and allow for

movement

• Intervertebral foramina which spinal nerves exit the vertebral canal

 Spinal Bifida

Sometimes vertebral lamina partly or completely fail to fuse during fetal

development resulting in a condition called spinal bifida .

 Spinal Bifida defect is most common in the lumbar region.

 If the defect is severe and involves the spinal cord , it may interfere with

normal nerve function below the point of the defect.

 Herniated, or Ruptured, Intervertebral Disk

A herniated, or ruptured, disk results from the breakage of the annulus

fibrous with a partial or complete release of the nucleus pulpous .

The herniated part of the disk may push against and compress the spinal cord,

Caudal equina, or spinal nerves, compromising their normal function and

producing pain.

Herniation of the inferior lumbar intervertebral disks is most common,

 Anatomy of vertebra
The cervical vertebrae all have a transverse foramen in each transverse
process through which the vertebral arteries extend toward the head.

The first cervical vertebra is called the atlas

 The atlas has no body

 The atlas has large superior articular facets where it articulates with the
occipital condyles on the base of the skull.

This joint allows the head to move in a “yes” motion or to tilt from side to side.
Anatomy of vertebra
 Anatomy of vertebra

The second cervical vertebra is called the axis

 it has a projection around which the atlas rotates to produce a “no”

motion of the head.

The projection is called the dens process. (dens, tooth shaped),

• Vertebral Column

180 bones - 26 vertebral column bones =

154 bones
 The Bony Thorax (Thoracic Cage)

• The chest region

• Forms a cage to protect major organs

• Composed of sternum, ribs and thoracic

vertebrae.
 Thoracic Cage

Sternum : breastbone.

 Dagger - shaped bone located along

the midline of the anterior chest.

 Anatomy of the Sternum

1. The manubrium

2. The sternal body

3. The xiphoid process

 Anatomy of the Sternum

1. The manubrium:
• The superior portion of sternum

• Broad, triangular shape

• Articulates with collarbones (clavicles)

• Articulates with cartilages of 1st rib pair

• Has a jugular notch between clavicular articulations

 Anatomy of the Sternum

2. The sternal body:

•is tongue-shaped

•attaches to the manubrium

•attaches to costal cartilages of ribs 2–7

 Anatomy of the Sternum

3. The xiphoid process:

• Is the smallest part of the sternum

• Attaches to the sternal body

• Attaches to diaphragm and rectus abdominis

muscles
 Anatomy of the Sternum

At the superior end of the sternum, a depression, called the jugular

notch, is located between the ends of the clavicles where they articulate with

the manubrium of the sternum.

The jugular notch can easily be found at the base of the neck.

The sternal angle, can be felt at the junction of the manubrium and the body

of the sternum.
 Clinical Importance of the Sternum
The sternal angle is important clinically because the second rib is found lateral to
it and can be used as a starting point for counting the other ribs.

Counting ribs is important because they are landmarks used to locate structures
in the thorax, such as areas of the heart.

The sternum is used as a site for taking red bone marrow samples because it is
readily accessible.

the xiphoid process of the sternum is attached only at its superior end, it may be
broken during cardiopulmonary resuscitation (CPR) and then may lacerate the
underlying liver.
 Functions of Ribs

• Ribs:

1. are flexible

2. are mobile

3. can absorb shock

 Thoracic Cage

•Ribs : 12 pairs of ribs attach posteriorly

to the thoracic vertebrae

• True ribs : first 7 pair

• False ribs : last 5 pairs

 Anatomy of ribs
The true ribs attach directly through their costal cartilages to the sternum.

 The superior seven pairs of ribs are true ribs.

 The false ribs do not attach to the sternum.

The inferior five pairs of ribs are false ribs. On each side, the three superior false ribs

are joined by a common cartilage to the costal cartilage of the seventh true rib, which in turn is

attached to the sternum.

The two inferior pairs of false ribs are also called floating ribs because they do not

attach to the sternum.

 Anatomy of ribs
Most ribs have two points of articulation with the thoracic vertebrae

First, the head articulates with the bodies of two adjacent vertebrae and

the intervertebral disk between them.

The head of each rib articulates with the inferior articular facet of the

superior vertebra and the superior articular facet of the inferior vertebra.
 Anatomy of ribs

Second, the tubercle articulates with the transverse process of the inferior

vertebra.

The neck : is between the head and tubercle,

The body,: or shaft, is the main part of the rib.

The angle: of the rib is located just lateral to the tubercle and is the point of

greatest curvature.
154 bones - 24 ribs -1 sternum = 129
bones