Unit 4 the skeletal system

The Skeletal System
Dr. Faiza Munir Ch
Medical Officer
MINAS
dr.faizamunirch@gmail.com

At the completion of this unit, learners will be able
to:
• Define Skeletal system
• Discuss the structure, type and function of bone.
• List the function of skeletal system.
• Identify the bones of axial and appendicular skeleton.
• Describe the various marking on the surface of bones.

The Skeletal system
• The skeleton is the bony framework of the body. It forms the cavities
and fossae (depressions or hollows) that protect some structures,
forms the joints and gives attachment to muscles.
• The skeletal system is composed of 206 bones that, along with
cartilage, tendons, and ligaments, make up the framework or
skeleton of the body.

• There are two parts to the
skeleton:
• Axial skeleton – bones along the
axis of the body, including the skull,
vertebral column and ribcage.
• Appendicular skeleton –
appendages, such as the upper and
lower limbs, pelvic girdle and
shoulder girdle.
Dr. Faiza Munir Ch
Medical Officer
MINAS

Axial skeleton
• The axial skeleton consists of 80
bones.
• The primary bones of the axial
skeleton are the skull, spine, ribs
and sternum (thorax).

Appendicular skeleton
• The appendicular skeleton
consists of 126 bones.
• The primary bones of this
skeleton are the shoulder or
pectoral girdle, arms, hands,
pelvic girdle, legs and feet.
Dr. Faiza Munir Ch
Medical Officer
MINAS

Function of Skeletal system
1. Movement: Skeletal system provides points of attachment for muscles. Your legs
and arms move when the muscles pull on the bones.
2. Support: The backbone is the main support center for the upper body. It holds your
head up and protects your spinal cord.
3. Protection: The bones of your skull protect your brain. Your ribs protect your lungs
and heart from injury.
4. Makes Blood: Red and white blood cells are formed by tissue called marrow, which
is in the center of the bone.Blood-cell formation (haemopoiesis)
5. Storage: Bones store minerals, such as calcium and phosphorus, for use by
the body.

• Support and movement: Bones are a site of attachment for ligaments and tendons, providing a skeletal
framework that can produce movement through the coordinated use of levers, muscles, tendons and
ligaments. The bones act as levers, while the muscles generate the forces responsible for moving the bones.
• Protection: Bones provide protective boundaries for soft organs: the cranium around the brain, the vertebral
column surrounding the spinal cord, the ribcage containing the heart and lungs, and the pelvis protecting the
urogenital organs.
• Mineral homoeostasis: As the main reservoirs for minerals in the body, bones contain approximately 99% of
the body’s calcium, 85% of its phosphate and 50% of its magnesium . They are essential in maintaining
homoeostasis of minerals in the blood with minerals stored in the bone are released in response to the body’s
demands, with levels maintained and regulated by hormones, such as parathyroid hormone.
• Blood-cell formation (haemopoiesis): Blood cells are formed from haemopoietic stem cells present in red
bone marrow. Babies are born with only red bone marrow; over time this is replaced by yellow marrow due to
a decrease in erythropoietin, the hormone responsible for stimulating the production of erythrocytes (red
blood cells) in the bone marrow. By adulthood, the amount of red marrow has halved, and this reduces further
to around 30% in older age.
• Triglyceride storage: Yellow bone marrow acts as a potential energy reserve for the body; it consists largely
of adipose cells, which store triglycerides (a type of lipid that occurs naturally in the blood).

Classification of Bones
Dr. Faiza Munir Ch
Medical Officer
MINAS

Long bones include:
• Femur (thigh)
• Tibia (larger shin)
• Fibula (smaller shin bone)
• Humerus (upper arm)
• Radius (larger forearm)
• Ulna (smaller forearm).

Short bones include:
• the carpals of the wrist and
tarsals of the ankle.

Flat bones include:
• Skull,
• Sternum (breastbone),
• Scapula (shoulder bone).

Irregular bones include:
• The vertebrae (spine),
• pelvic.
• Sphenoid and hyoid

Sesamoid (Round)bones:
•Usually small and round.
• Embedded within tendons
adjacent to joints.
• Example: patella (knee cap)
Dr. Faiza Munir Ch
Medical Officer
MINAS

Structure of bones
Typical Four Layers:
• Periosteum: Covers Bones
• Compact Bone: Lies
beneath the periosteum
• Spongy Bone: Lies beneath
the compact bone
• Bone Marrow: Fills the gaps
between the spongy bone

Structure of bones
Epiphysis
• growing end
Diaphysis
• shaft
Periosteum
• outside covering
Medullary
• inner space containing bone marrow
Endosteum
• lining of medullary cavity

Structure of bones
• Bones are complex living structures that undergo growth and
development.
• A thin tough outer membrane covers the bone.
• Beneath the outer membrane is a layer of compact bone (hard and
dense, but not solid – it is filled with holes and has small canals for blood
vessels and nerves).
• Inside the compact bone is a layer of spongy bone.It has many small
spaces, is light weight, but strong.Spongy bone is also found at the ends
of bones.
Dr. Faiza Munir Ch
Medical Officer
MINAS

Structure of bones
• In the spaces of many bones there is a
soft connective tissue called marrow.
• Two types of Marrow:
 Red Marrow:
produces most of the body’s
blood cells.
 Yellow Marrow:
stores fat that can serve as an
energy reserve.

 Bones of Axial skeleton
• Composed of skull, vertebral column and ribcage.
• Mainly flat and irregular bones
• Serve to protect organs such as brain, heart, and lungs
• Also helps to support body along central axis (backbone).
Parts of Axial skeleton
• Skull – protects brain
• Vertebrae – protect spinal chord ;also serves to keep
skeleton upright
• Ribs – protect lungs and heart ; gives intercostal muscles
a hard surface to move against for breathing.

Skull
• The skull is made up of 22 bones
that articulate with each other.
• Skull is divided into 2 sets of bones
• Cranium – collection of 8 bones
which hold and protect brain.
• Facial bones – 14 bones that
make up the face; all but 2 are
paired.

 Cranium
• Frontal Bone (1) – makes up forehead,
eyebrows, and superior section of eye orbital
• Parietal Bone(2) – form most of the superior
and lateral walls of cranium
• Temporal bones (2)– lie inferior to parietal
bones
• Occipital bone (1) – forms back and floor of
cranium.
• Ethmoidal bone (1) -forms roof of nasal cavity
• Sphenoid bone (1)- where the pituitary gland
sits.

 Facial Bones
• Maxillary (2)
• Mandible (1)
• Conchae (2)
• Nasal (2)
• Vomer(1)
• Lacrimal (2)
• Zygomatic (2)
• Palatine (2)

Facial Bones
• Mandible- lower jaw bone
• Maxillary bones (maxillae) fuse
together to form upper jaw
• Palatine processes – directly
posterior to maxillae; forms rear
of hard palate
• Zygomatic bones – cheekbones
• Lacrimal bones – inferior section
of orbital bones; provides
passageway for tears

Facial Bones
• Nasal bones- form bridge of
nose.
• Vomer – divides nasal cavity in
half
• Inferior conchae- thin curved
bones which project from
interior of nasal cavity.
Dr. Faiza Munir Ch
Medical Officer
MINAS

function of skull:
• The various parts of the skull have specific and different
functions and are, in summary:
• protection of delicate structures including the brain, eyes and
inner ears.
• maintaining patency of the nasal passages enabling breathing.
• eating – the teeth are embedded in the mandible and maxilla;
and movement of the mandible allows chewing

Vertebral column:
This consists of 24 movable bones (vertebrae) plus the sacrum and
coccyx. The bodies of the bones are separated from each other by
intervertebral discs, consisting of fibrocartilage. The vertebral column is
described in five parts and the bones of each part are numbered from
above downwards:
• 7 cervical
• 12 thoracic
• 5 lumbar
• 1 sacrum (5 fused bones)
• 1 coccyx (4 fused bones).
The first cervical vertebra, called the atlas, forms a joint (articulates)
with the skull. Thereafter each vertebra forms a joint with the vertebrae
immediately above and below. More movement is possible in the
cervical and lumbar regions than in the thoracic region.

Vertebral column:
• The sacrum consists of five
vertebrae fused into one bone
that articulates with the fifth
lumbar vertebra above, the coccyx
below and pelvic or hip bone at
each side.
• The coccyx consists of the four
terminal vertebrae fused into a
small triangular bone that
articulates with the sacrum
above.
Dr. Faiza Munir Ch
Medical Officer
MINAS

Cervical curvature:
 Begins where skull meets spine
 Composed of 7 vertebrae
 Labeled C1-C7, starting at skull
 First two vertebrae (C1 and C2)are different
C1 And C2:
 Perform different jobs than other vertebrae
 C1 (atlas) has depressions that accept the
occipital codyles (“yes nod”)
 C2 (axis) acts as pivot point for skull (“no” head
shake)

Thoracic Curvature
 12 bones
 T1-T12
 Costal demifacet – point of
attachment of ribs
Dr. Faiza Munir Ch
Medical Officer
MINAS

Lumbar Vertebrae:
 5 vertebrae
 (L1-L5)
 Sturdiest because under the
most stress

Sacrum:
 1 bone composed of 5 fused
vertebrae
 “wing-like” alae connect
laterally with hip bones (forms
sacroiliac joints)
 Makes up posterior wall of
pelvis

Coccyx:
 1 bone formed by fusion of 3
vertebrae
 Tailbone
 Thought to be left over from
when our ancestors had tails

Spinal Curvatures
 Scoliosis- lateral curvature
 Lordosis- Apex towards anterior
(ie. Lumbar curvature)
 Kyphosis- Apex towards
posterior (Osteoporosis
patients)
Dr. Faiza Munir Ch
Medical Officer
MINAS

Functions
• The vertebral column has several important
functions:
• • it protects the spinal cord. In each vertebra
is a hole, the vertebral foramen, and
collectively the foramina form a canal in
which the spinal cord lies
• • adjacent vertebrae form openings
(intervertebral foramina), which protect the
spinal nerves as they pass from the spinal
cord .
• • in the thoracic region the ribs articulate
with the vertebrae forming joints that allow
movement of the ribcage during respiration.

Thoracic cage
The thoracic cage is formed by:
• 12 thoracic vertebrae
• 12 pairs of ribs
• 1 sternum or breast bone.
Dr. Faiza Munir Ch
Medical Officer
MINAS

Functions
The thoracic cage:
• protects the contents of the thorax including the heart, lungs and
large blood vessels
• forms joints between the upper limbs and the axial skeleton. The
upper part of the sternum, the manubrium, articulates with the
clavicles forming the only joints between the upper limbs and the
axial skeleton
• gives attachment to the muscles of respiration:
– intercostal muscles occupy the spaces between the ribs and when
they contract the ribs move upwards and outwards, increasing the
capacity of the thoracic cage, and inspiration occurs.– the
diaphragm is a dome-shaped muscle which separates the thoracic
and abdominal cavities; when it contracts it assists with inspiration.
• enables breathing to take place.

Ribs:
 12 pairs of ribs, each connects
to a thoracic vertebrae
 First 7 pairs = true ribs; attach
directly to sternum
 Last 5 pairs = false ribs; indirect
or no attachment; last two are
floating (no sternal attachment)

Sternum:
 Fusion of three bones
 1) Manubrium (top)
 2) Body (middle)
 3) Xiphoid Process (bottom)
 Location for rib attachment
 Surrounded by costal cartilage

 Bones of Appendicular skeleton:
The appendicular skeleton
consists of the shoulder girdles
and upper limbs, and the pelvic
girdle and lower limbs
The shoulder girdles
• Each shoulder girdle consists of a
clavicle and a scapula.

Clavicle:
 Collar bone
 Double-curved
 Attaches medially to manubrium of sternum
 Attaches laterally to scapula
 Acts as a brace, keeping arm away from
thorax
 Also prevents shoulder dislocation.

Scapula:
 Shoulder Blade
 Main function is attachment of shoulder
 Major point of muscle attachment for
movement of arms
 Weakly attached to thorax, so moves easily
 1)Acromion – extends from spine of
scapulae
 Point of attachment of clavicle
2)Coracoid- main site of arm muscle
attachment.
 Socket of arm
joint

Upper Limb:
Each upper limb comprises:
• 1 humerus
• 1 radius
• 1 ulna
• 8 carpal bones
• 5 metacarpal bones
• 14 phalanges.
Dr. Faiza Munir Ch
Medical Officer
MINAS

Humerus
 Simple long bone
 Greater and lesser tubercle
allow for muscle attachment
 Deltoid tuberosity-place of
attachment for deltoid muscle.

Attachment to the forearm
 Trochlea articulates against
bones of forearm
 Olecranon fossa shaped like
spoon
Dr. Faiza Munir Ch
Medical Officer
MINAS

Forearm bones
 Ulna – pinkie-side of forearm
 Radius – Thumb side of forearm
 Olecranon process attaches to
humerus at olecranon fossa
 Allows for articulation between
upper and lower arm

Dr. Faiza Munir Ch
Medical Officer
MINAS

The pelvic girdle and lower limbs.:
The bones of the pelvic girdle are the two hip bones and
the sacrum.
Pelvis:
• Juncture point for axial skeleton and
lower body
• Holds internal organs
• Distributes weight down legs
• 3 fused bones
• Obturator foramen- large hole
through which nerves and muscles
pass

Pelvis:
• The pelvis is the lower portion of
the trunk of the body.
• The hip bones, sacrum, and coccyx
form the pelvic basin.
• The male pelvis is shaped like a
funnel and is heavier and stronger
than the female. The female pelvis
is oval to round, and wider than the
male.

Bones of the Pelvis
•Ilium
•Ischium
•Pubis

Lower Limb:
Each lower limb consists of:
• 1 femur
• 1 tibia
• 1 fibula
• 1 patella
• 7 tarsal bones
Dr. Faiza Munir Ch
Medical Officer
MINAS

Foot:
•7 Tarsal , 5 metatarsal
bones
• 14 phalanges.

Function of Appendicular skeleton:
The appendicular skeleton has two main functions.
• Voluntary movement. The bones, muscles and joints of the limbs are
involved in movement of the skeleton.
• This ranges from very fine finger movements needed for writing to the
coordinated movement of all the limbs associated with running and
jumping
• Protection of blood vessels and nerves. These delicate structures along
the length of bones of the limbs and are protected from injury by the
associated muscles and skin. They are most vulnerable where they cross
joints and where bones can be felt immediately below the skin.

Assignment:
• Define Skeletal system
• Discuss the structure, type and function of bone.
• List the function of skeletal system.
• Identify the bones of axial and appendicular skeleton.
• Describe the various marking on the surface of bones.

Unit 4 the skeletal system

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