The Skeletal System


The Skeletal System

By Rafael Perez

Israel Torres

Khristopher Bandong

Skeletal System

• The human skeleton consists of 206 bones

• The skeleton is used as a barrier and defense to protect the vital organs. (Brains, heart, stomach, etc)

• Allows muscles to attach to

• It maintains balance and maintains the shape of the body.

• The most important function of the skeleton is to allow limbs to move

Bone Composition.

There are 4 different types of bones: long bones, short bones, flat bones, and irregular bones . Long bones work as levers. The short bones are the bones in the wrists and ankles. The flat bones are used for protection of organs or attachment of muscles, and the irregular bones are all the other bones, that do not fit into the other categories.

• Bones are composed of tissue that take one of two forms: Compact or Spongy bone.

Compact Bones are dense, hard, and forms the protective exterior of all bones.

– Spongy Bones occur in most bones, and are inside the contact bones.

Bone tissue is made of several types of bone cells, fused with a large amount of inorganic salts such as calcium and phosphorus, to give the bone strength, and collagenous fibers and ground substances to give the bone flexibility .

The Skull

• The skull is the biggest bone In your body, consisting of many parts. It is one of the most useful bones in your body because it protects the brain. Divided into two parts . Cranial and Facial Skull

• Usually made up of about 22 bones .

• The large bone that covers the backside of the brain is called the Parietal bone .

• The front bone that is connected to the parietal bone is called the Front bone

• The Hyoid bone connects to the tongue and causes the movement of it.

Spinal Cord

• Extends from the medulla oblongata.

• Divided into 31 segments , with motor nerve exiting the ventral, and nerve roots entering the dorsal

• Ventral and Dorsal roots later join to form paired spinal nerves.

• Seperated into 5 parts : The

Cervical, Thoracic, Lumbar,

Sacral, and Coccyx.

• Primary purpose is to send signals to the brain and back .

Works with the nervous system.

The Arm

The arm, or branchium, is the region between the shoulder and elbow.

• It consists of a single long bone called the humerus

The humerus is the longest bone in the upper body .

The head is large, smooth, and rounded and fits into the scapula in the shoulders.

• On the bottom of the humerus, are two depressions where the humerus connects to the ulna and radius of the forearm.

The radius is connected on the side away from the body and the ulna is connected to the side towards the body . Together the humerus and the ulna make up the elbow.

The bottom of the humerus protects the ulnar nerve, or otherwise known as the

“funny bone”

The forearm

• The forearm is the region between the elbow and the wrist . It is formed by the radius on the lateral side of the ulna. The ulna is longer than the radius and connected more to the firmly to the humerus.

• The radius contributes more to the movement of the wrist and hand then the ulna does.

• Both the ulna and the radius connects to the bottom of the humerus and the top of the bones in the hand.

The Hand

• Consists of the wrist, palm, and fingers. Has 27 bones .

• The wrist consists of 8 small bones called carpal bones ; lightly bound by ligaments.

The bones are arranged in two rows.

– The first row contains scaphoid, lunate, triquetral, and pisiform bones

– The second row contains trapezium, trapezoid, capitate, and hamate


• The palm (Metacarpas) consists of 5 metacarpal bones.

• The base of the metacarpal bones are connected to the wrist bone, and the head is connected to the bones in the finger. They form the knuckles in a clenched fist.

• The fingers are made up of 14 bones called “phalanges”. Each finger except the thumb has three phalanx. A proximal phalanx, a middle phalanx, and a distal phalax.

Rib Cage

• The primary function of the rib cage is to protect the heart, lungs, and major blood vessels.

• The sternum is a flat, dagger shaped bone located at the middle of the chest. Along with the ribs they form the rib cage. Consists of three parts.

– The manubrim, which located at the top of the sternum and slightly moves. Connects to the first two rows of ribs.

– The body, located at the middle of the sternum and connects the third to seventh ribs directly, and the eighth through tenth indirectly.

– The xiphoid Process, located at the bottom of the sternum, often cartilaginous.

• The ribs are thin, flat curved bones that form a cage around the organs in your body. Composed of 24 bones arranged in 12 pairs.

– The true ribs, which are the first 14 bones, connected to the spine and sternum. Are made of coastal cartilage.

– The false ribs, which are the next 6 bones. These are slightly shorter and are connected to the spine, but not to the sternum, instead to the lowest true rib.

– The floating ribs which are the 4 last bones. They are the smallest and are attached to the spine, but to nothing in the front.

• One very important use of the ribcage is when you inhale the muscles in between the rib cage lift up, allowing the lungs to expand. When you exhale, the rib cage moves back down, squeezing air back out.

Lower Body


– Is a ring of bones in the lower trunk of the body, protecting abdominal organs like the bladder, rectum and for the woman which is the uterus.

• Ischium – supports the body’s weight in the sitting position.


– The thigh bone, which is the longest bone of the body.

• Femur head – Top of the femur that fits into the socket of the pelvis that forms the hip joint


– Technical name for the kneecap, triangular shape bone at the bone of the knee joint, also connected to the tibia which is the shin.

Obturator Foramen

– Large opening of the Ischium, formed by the rami and the ischium together with the pubis.

– This creates an opening that allows the passage of the major blood vessels and the nerves to the legs and feet .

Lower Body cont.


– Is the inner and thicker of the two long bones in the lower leg, bigger shin bone.

– Upper end is divided into two sections : Medial and Lateral Condyles which attaches to the femur.

– At the ankle, there is medial malleolus which is the inside of the ankle of the large bony prominence of the table.

– Lateral malleolus which is the protrusion of the outside ankle. Common area of ankle sprains.

• Fibula – Is the outer and thinner of the two long bones in the lower leg, smaller skin bone

– Upper end doesn’t reach the knee

– Lower end descended below the shin and also a part of the ankle


– The phalanges are the small bones that make up the skeleton of the fingers, thumbs, and toes. Each finger and smaller toe has three phalanges; The big toe each have two. The phalange nearest the body of the hand or foot is called the

Proximal phalange; the one at the end of each digit is the distal phalange. And of course there are three, the middle one is called the middle phalange.

Tarsal Bones.

Tarsal Bones- The foot consists of an ankle, an instep, and five toes. The ankle is composed of seven tarsal bones forming a group called the Tarsus. These bones are arranged so that one of them, the Talus, can move freely where it joins the tibia and fibula (lower leg bones.). This is known as the head of the Talus.

The remaining tarsal bones are bound firmly together, forming a mass on which the talus rests. The other bones which compose the tarsus are the Calcaneus, the largest of the ankle bones.

The talus, the navicular, the cubiod, the lateral cuneiform, the intermediate cuneiform, and the medial cuneiform.

• The calcaneus, or “heel bone”, is located below the talus where it projects backward to form the base of the heel. It helps to support weight of the body and provides an attachment for muscles that move the foot.

• Metatarsal – The metatarsal is one of the five long, cylindrical bones in the foot. The bones make up the central skeleton of the foot and are held in an arch formation by surrounding ligaments. The metatarsal bones are joined to the toe at the metatarsophatangeal joint; a fancy name for the knuckles on the toes.

Tarsal Bone

Ligaments (Lower Body)


– Is a band of tissue, used to connect the bones, hold organs in place, and more.

• Iliofemoral Ligaments – A Y-shape band of very strong fibers that connect the lower front iliac spine of the coxal bone to the bony line.

• Pubofemoral Ligaments – Bone that extends between upper portion of the pubis and the iliofemoral ligaments . Its fiber also blends with fibers of the joint capsule of the hip joints.

Obturator Membrane

– A portion of the pubis passes down and in the back to join an ischium. Between the bodies of these bones, on either side, there is a gap, called the obturator foramen in the skeleton.

• Patellar Ligament – Is the center of the common tendon, which continues from the patella to the tibia. Allows muscle and tissue to pass through from the femur.

Tibial Collateral Ligament

– Flat band of tissue that connects the medial condyle of the femur to the medial condyle of the tibia at the knee joint.

• Fibular Collateral Ligament – Consists strong, round cord located between the lateral condyle of the femur and the head of the fibula at the knee joint.

Interosseous Membrane

– Layer of tissue that separates the space between the joints or bones.