lab 7

The Human Skeletal System

Learning Objectives:

 Be able to recognize and label the major bones of the skeletal system (both the axial and appendicular skeleton)

 Be able to list the functions of the skeletal system

 Know how bones are classified and be able to give examples of: o Long bones o Short bones o Irregular bones and o Flat bones

 Know the difference between bone and cartilage.

 Know what a fontanelle and sutures are.

 Know that ossification is the natural process of bone development.

 Know that ligaments are responsible for connecting bones to other bones while tendons connect muscles to bones at joints (articulation).

 Know that an adult human skeleton contains an average of 206 bones

 Know what the foramen magnum is and why its position is crucial for human’s ability to walk upright.

 Know what osteoporosis is and how it can be prevented.

The Skeletal System

The skeleton is a framework of bones and cartilage. Bone is a living tissue that is constantly being formed and broken down. The two major types of connective tissue that form the skeletal system are bone and cartilage. Ligaments which help join the bones together are also important components of the skeletal system, and they are

made up of fibrous connective tissue.

Functions of the Skeleton

The skeleton performs the following functions:

 Support – provides a rigid framework that supports the soft tissues of the body. The leg bones and spine hold the body in an upright position, while the pelvic girdle supports the organs in the abdominal cavity.

 Movement- along with the muscles allows us flexible movement as it provides places for muscle attachment and the contraction of muscles allows the bones to move at the joints.

 Protection- shields the soft internal organs. The skull protects the brain and the rib cage helps protect the heart and lungs. The vertebrae in your spine protect the nerves in the spinal cord.

 Storage of Minerals- the bones store important minerals like calcium and phosphorous so that they can be released into the body when needed.

 Storage of Fat- fat is used for long term energy storage in the body. It is found in the yellow bone marrow where it can be metabolized into energy when needed.

 Production of red blood cells- blood cells are produced in the red bone marrow of certain bones in the adult, but all bones in the fetus contain red bone marrow

that produces blood cells.

Bone Growth and Development

Ossification is the term given to bone formation. An osteocyte is a bone cell. An osteoblast is a cell that forms or builds up bone, and an osteoclast is a type of bone cell that breaks down bone.

When a baby is born, its skeleton consists of between 270 to 350 “bones” with an average of about 300. An adult human has 206 bones. The extra “bones” in a baby give its skeleton flexibility and aid in the journey through the birth canal, and these bones are really composed of cartilage. .As the baby grows, the cartilage will ossify and fuse

together.

The skull of an infant contains both bone and areas of cartilage called fontanelles. This allows the brain to grow and develop as the child grows. Eventually, after the brain is fully developed, these fontanelles will ossify (turn to bone), and fuse together forming sutures.

Your bones to continue to grow as you age. Bone is constantly being built up (anabolism) and broken down (catabolism). The rate of bone formation from birth to adolescence is greater than the amount of bone being broken down. Then it slows down so that as an adult, the rate of bone formation equals the rate of bone reabsorption, but as you continue to age, the rate of bone reabsorption becomes greater than bone formation. Osteoporosis is a disease condition that causes the bones to become thinner and weak and happens as you age. This makes a person more prone to fractures. A proper diet that includes calcium, boron, zinc and manganese and weight/load bearing

exercise can prevent this from occurring,

Anatomy of a Long Bone

There are four types of bones that form the skeleton:

· Long bones (humerus, radius, ulna; (arm bones), femur, tibia, fibula; (leg bones) and phalanges (fingers and toes)

· Short bones (wrist and ankle) · Flat bones (ribs, sternum and skull) · Irregular bones (bones of the pelvic and pectoral girdle)

Long bone is formed of an outer layer of compact bone and an inner layer of spongy bone which can contain red bone marrow. They are called long bones because they longer than they are wide. The ends of the bone are called the epiphysis and the shaft or main portion of the bone is called the diaphysis. The diaphysis contains a large medullary cavity with walls composed of compact bone. The medullary cavity is lined with a thin, vascular membrane called the endosteum and is packed with yellow bone marrow. Branches of blood vessels can be found throughout this cavity. The epiphysis is made up of mostly spongy bone containing red bone marrow. Bone elongation takes place at the epiphysis while increases in bone diameter occur in the diaphysis. The epiphysis is covered by a thin layer of hyaline cartilage called articular cartilage because it is found at a joint while a long bone is covered by the periosteum except at the ends. The periosteum is a layer of fibrous connective tissue that contains blood vessels, lymphatic vessels and nerves and is continuous with the ligaments and tendons that are connected to a bone.

Bone Types

Compact bone, which is very dense with few internal spaces, forms most of the shaft of long bones (arms and legs, etc.) and is composed of cylindrical structures called osteons. Osteocytes are bone cells and these are located inside the lacunae which are arranged in concentric circles around the central canal. The space between the rows of lacunae is filled with matrix. Canaliculi, which are minute canals, run through the matrix. Cytoplasmic connections which extend into the canaliculi help the cells remain in contact with each other. Nutrients and wastes are exchanged by diffusion in the osteocytes through blood vessels located in the central canal. Those osteocytes located further away from the central canal obtain nutrients and exchange wastes with the help of cells that pass on these materials via the gap junctions.

Spongy bone is porous and loosely packed with a honey comb appearance and is found at the ends and inner surfaces of long bones. While spongy bone is lighter than and not as dense as compact bone, it is still extremely strong. Spongy bone contains support structures known as trabeculae that help strengthen this type of bone. They enable bone to absorb force from a multitude of directions and for this reason, are located at the ends of long bones. In some types of bones, the spaces located between the trabeculae contain red bone marrow, the specialized tissue that produces red blood cells. The osteocytes of spongy bone, which occur in irregular intervals within the

trabeculae, are supplied with nutrients from the red bone marrow by the canaliculi.

Cartilage

Cartilage is a type of connective tissue with specialized cells called chondrocytes that produce a firm gelatinous matrix containing collagen and elastic protein fibers for strength. While cartilage does not possess the strength of bone, it makes up for this in increased flexibility. The role of cartilage is to provide structure and support to the other tissues in your body without being as inflexible as bone. It also helps provide padding

and cushioning in the joints and is found in many other areas of the body including the ears, nose, rib cage and intervertebral discs.

Unlike other types of connective tissue, cartilage is avascular meaning that it does not contain any blood vessels, so it must rely on obtaining required nutrients from neighboring tissues through the process of diffusion. As a result, when any damage

occurs to this type of tissue, it requires a much longer time to heal and repair itself.

There are three different types of cartilage and each one differs in the types and arrangements of fibers in the matrix. The three types of cartilage are:

1. Hyaline cartilage

 Found in nose, larynx, trachea and at ends of long bones

 Matrix contains numerous collagen fibers and is firm and glossy. 2. Fibrocartilage

 Found in the intervertebral discs and the cartilage of the knee

 Matrix contains wide rows of thick collagen fibers and 3. Elastic cartilage

 Found in the ears and epiglottis

 Matrix contains primarily elastin fibers

Fibrous Connective Tissue

The cells that produce fibers and other substances in connective tissue are called fibroblasts. Fibrous connective tissue is composed of many rows of these types of cells separated by bundles of collagenous fibers. It is this type of tissue that is found in tendons and ligaments. Ligaments are responsible for connecting bones to other bones

while tendons connect muscles to bones at joints (articulation).

Bones of the Axial Skeleton

The axial skeleton is made up of 80 different bones that support the head and trunk of the body. The five parts that make up the axial skeleton are: the skull, the spine (vertebral column), ribs and breastbone (sternum), and hyoid bone.

The Skull

The cranium of the skull protects the brain. In adults, it is composed of 8 bones that are joined tightly together. Newborns must have room for their brain to continue to grow so the cranial bones are not completely formed. These bones are joined by soft, cartilaginous membranes called fontanels which will close usually by the age of 16 months. These will ossify and fuse together forming sutures when development is complete. The sinuses, which are cavities of air lined by a mucus membrane, are contained within some of the bones of the cranium and help to reduce the overall weight of the skull. They are also responsible for giving a resonant sound to your voice. The

two mastoid sinuses drain into the middle ear. They can sometimes get infected and inflamed resulting in a medical condition called mastoiditis which can cause deafness.

One of the most significant features of the skull is the large opening in the base called the foramen magnum. It is through this opening that your vertebral column passes and becomes the brain stem. In humans it is located in the center of the base of

the skull and this positioning allows us to walk in the upright position.

Skull (22)

 Cranial Bones (8) o Parietal (2) o Temporal (2) o Frontal (1) o Occipital (1) o Ethmoid (1) o Sphenoid (1)

 Facial Bones (14) o Maxilla (2) o Zygomatic (2) o Mandible (1) o Nasal (2) o Palatine (2) o Inferior nasal concha (2) o Lacrimal (2) o Vomer (1)

The mandible, or lower jaw, is the only moveable part of the skull and forms the chin. The grinding action of the mandible and maxillae are responsible for being able to chew food. The lips and cheeks are composed of a core of skeletal muscle. The cheekbones are created by the zygomatic bones while the nasal bones form the bridge of the nose. The lacrimal bones contain the openings for the nasolacrimal canal which forms the tear ducts. Some portion of your face is formed by cartilage, not bone as are the outside of your ears and the tip of your nose. The eye sockets are called orbits because you can

rotate/roll your eyes.

Hyoid Bone

The Hyoid bone is a u-shape bone located in the neck that anchors the tongue and is associated with swallowing. It is the only bone in your body that does not articulate with

another bone.

Vertebral column

Vertebral Column (33)

 Cervical vertebrae (7) - in the neck region form the cervical curvature  Thoracic vertebrae (12) - form the thoracic curvature. The ribs are attached here.  Lumbar vertebrae (5) - in the small of the back form the lumbar curvature.  Sacrum (5) (fused) form the pelvic curvature.  Coccyx (4) (fused, varies between 3-5 bones) - form the tailbone.

Your spine has an S shaped curve to it. The four curvatures of the spine provide more strength and resilience for our upright posture than a straight column could provide. Scoliosis is an abnormal curvature of the spine. Kyphosis is another spinal abnormality in the posterior curvature that results in a hunchback appearance while lordosis is an abnormal anterior curvature of the spine resulting in a swayback

appearance.

The vertebral canal is located in the center of the spinal column and the spinal cord passes through this canal. There are holes or openings, called intervertebral foramina that are found on either side of the column through which the spinal nerves pass and branch out to various locations throughout your body. The spinal nerves function in assisting muscle contractions and many other functions. Injuries to the vertebrae and spinal nerves can result in paralysis and possible death depending on where the injury occurs. The names of the different vertebrae correspond to their position or location in

the vertebral column.

The first cervical vertebra is called the atlas and is responsible for holding up your head. The second one is called axis. Thoracic vertebrae have long, thin, spinous processes and articular facets to facilitate the attachment of the ribs. Lumbar vertebrae have much larger bodies and thicker processes. The coccyx usually contains 4 fused vertebrae, but may contain from 3 -5 depending on the individual. Intervertebral discs are the shock absorbers between the vertebrae, and also allow more flexibility of

movement.

The Rib Cage

Thoracic cage (25) - protects the heart and lungs, but swings outward and upward to allow for the increased flexibility which is needed for breathing.

 Sternum (1)- or breastbone which helps protect the heart and lungs. It is a flat bone that is actually composed of three separate bones (the manubrium, body and xiphoid process, which serve as an attachment for the diaphragm).

 Ribs (24) 12 pairs of ribs which connect directly to the thoracic vertebrae in the back. The upper 7 pairs are called the true ribs and these attach directly to the sternum (breastbone). The next three pairs are called the false ribs which are connected to the sternum by cartilage. The last two pairs are the floating ribs that

do not attach to the sternum at all.

Bones of the Appendicular Skeleton

The Appendicular skeleton is made up of 126 bones within the pectoral and pelvic girdle and their attached limbs. These bones make movement possible as well as

protect the excretory, digestive and reproductive organs.

The appendicular skeleton has four major regions:

 Pectoral or shoulder girdles - (4 bones)  Upper Limbs (60 bones) – humerus, radius, ulna, carpels, metacarpals and

phalanges  Pelvic or hip girdle (2 bones) – coxal bones (ilium, pubis and ischium)  Lower Limbs (60 bones) – femur, tibia, fibula, tarsals, metatarsals and phalanges

The pectoral girdle and the bones of the upper limbs are specialized for flexibility while

those of the pelvic girdle and lower limbs are specialized for strength.

The Pectoral Girdle and Upper Limb

There are a pair of pectoral girdles one each for the right and left sides of your body. Each one contains a scapula or shoulder blade, and a clavicle or collarbone. The clavicle, which is a flat bone that has a double curve, connects the arm to the body. It acts as a support beam to help hold the scapula in place so that the arm can move freely. The scapula is a flat, irregular bone that connects the humerus (arm) to the clavicle. Muscles of the chest and arm attach to the scapula. The glenoid cavity at the top of the scapula forms the socket of the shoulder joint into which the humerus (single, long arm bone) fits. Ligaments and tendons help stabilize this joint. The rotator cuff is the term given to the group of four small muscles and tendons that help stabilize the shoulder. The lower part of forearm is made up of two bones – the radius and ulna. The bones of the hand include the carpals, metacarpals and phalanges which help increase its flexibility. The wrist contains eight carpal bones. The metacarpals form the framework of the palm while the phalanges are the bones of your fingers and thumb

(digits).

The Pelvic Girdle and Lower Limb

The pelvic girdle (the hip girdle) is composed of two large and very heavy bones called the coxal bones. Your pelvis is made up of the pelvic girdle, the sacrum and the coccyx and functions to protect the digestive and reproductive organs as well as to serve as a place of attachment for your legs. Each coxal bone is made up of three parts:

the ilium, pubis and ischium. The hip socket or acetabulum is located where these three bones converge. The ilium is the largest part of the coxal bone. The ischium is the lower and back part of your hip bone that supports your weight when you sit down and the pubis is the anterior portion of the coxal bone.

You can identify a male skeleton from a female one by the hip bones. Females have wider and shorter pelvic cavities and the iliac bones are more flared. The sacrum is shorter and more triangular in females as well. In males, the pelvic inlet is more heart

shaped.

The femur or thigh bone is the longest and strongest bone in the human body. Thigh muscles, buttock muscles and hip flexors are attached to the femur by the greater and lesser trochanters at the top of the femur. The tibia (shin bone) and fibula are the two bones of the lower leg. The tibia carries all the body’s weight. Your kneecap is called the patella which is held in place by a tendon (quadriceps). The fibula acts as a stabilizer and does not support much weight. Each of your two feet has an ankle, an instep, and five toes. Again, the foot like the hand also has many bones to give it more flexibility. The ankle is made up of seven tarsal bones. One of these bones, the talus, is capable of moving freely at the point where it joins the tibia and fibula. The heel bone or calcaneus is also considered to be part of the ankle. Both the talus and the calcaneus support the boy’s weight.

Five elongated metatarsal bones comprise the instep of the foot, with the ends farthest away forming the ball of the foot. The bones of the toes like the fingers are also called phalanges although the bones of the toes are much shorter and wider for

strength.