Human Skeletal System

Previous post was all about locomotion and movement. In this post we will study at length about the Human Skeletal System.

Skeletal system is a system of external and internal, living or dead, hardened structures which forms the supportive, protective and jointed framework of the body.

Hard or flexible, internal and external structures of the animal body such as bone and cartilage constitutes the skeleton. The skeleton system is responsible for movement or locomotion of various body parts.

TYPES OF SKELETAL SYSTEM

1. Exoskeletal system

• The skeleton which is external.
• It is rigid, protective and supportive covering present outside the body.

2. Endoskeletal system

• The skeletal system present inside the body.
• The endoskeleton in case of vertebrates is made up of bones and cartilage.

SKELETAL SYSTEM IN HUMAN

1. Axial Skeleton
2. Appendicular Skeleton

A. Axial skeleton

• It runs along the middle longitudanal axis of the body.
• It comprises 80 bones which distribute along the main axis and form four structures such as Skull, vertebral column, sternum and ribs.

 SKULL

• the skeleton of the head is called skull.
• it rest on the upper end of vertebral column and bony structure consists of four parts such as cranium, facial bones, hyoid and ear ossicles.

1.CRANIUM

• it is hollow and nearly rounded bony structure that protects the brain. it is made up of 8 bones called cranial bones. These bones fuse together to form sutures.
• Base of skull is has a large opening called foramen magnum through which brain communicates with spinal cord. There are two facets called occipital.condyles on both sides; hence, called dicondylic.

2.EAR OSSICLES-

The middle ear has 3 bones which helps in amplification of sound. These bones are

• Malleus ( hammer shaped)
• Incus (anvil shaped )
• Stapes (stirrup shaped )

3. FACIAL BONE-

• It constitutes the front part of skull, skeleton of lower jaw, hard palate and nose.

4. HYOID BONE-

It is U shaped bone which is present at the base of buccal cavity. the hyoid bone together with tongue forms the hyoid apparatus.

FUNCTIONS OF SKULL

• It protects the brain.
• The skull bears jaw which helps in cutting and mastication of food.
• Ear bones helps in amplification of sound.
• It protects and supports the special sense organs.

VERTEBRAL COLUMN

• It is known as backbone. It lies in mid dorsal region of the neck and trunk is made up of 26 serially arranged units called vertebrae.
• The vertebral column extends from base of the skull and constitute the main framework of the trunk.
• There are  pads or discs made up of cartilage present  between the vertebrae are called invertebral discs.
• A hollow central position occurs in each vertebrae which together forms a structure through which the spinal cord passes.

Functions of Vertebral Column

• it protects the spinal cord, supports the head and serves as the point of attachment for the ribs and musculature of the back.
• it carries weight  of the body during motion as well as in standing position.
• thealtlas and axis vertebrae of the vertebral column allows the movement of head in different directions.

STERNUM

It is a flat bone present on the ventral midline of the thorax. It is present just under the skin in the middle of the chest. It forms the protective covering which protects the internal organs present in the thoracic region.

RIBS

These are thin flat bone which is dorsally connected to vertebral column and ventrally to the sternum. There are 12 pair of ribs.

• True ribs– the first 7 pairs are known as true ribs. They are dorsally attached to thoracic vertebrae and are ventrally connected to sternum with help of hyaline cartilage.
• False ribs– the three pairsi.e 8th, 9th, 10th pair do not directly articulate with sternum rather it joins 7th pair of ribs and hence called false ribs.
• Floating ribs – the 11th and 12th  pair of ribs are called as floating ribs because one end of the rib is attached to the vertebral volumn and other end is free. They play an important role in protection of kidneys.

 • APPENDICULAR SKELETON

• It includes the skeleton of limbs, the pectoral and pelvic girdle which supports and suspend the skeleton of the limbs from the vertebral column.
• The girdle which supports the forelimb is called pectoral girdle and the girdle which supports the hindlimbs is called pelvic girdle.

PECTORAL GIRDLE:

It is a bony complex which occurs between the forelimbs and axial skeleton. It consists of two halves-right & left. Each half consists of two bones – clavicle and scapula.

• SCAPULA – it is thin, curved triangular bone which extends on the backside of thorax between 2nd and 7th rib.  It consists of a sharp ridge, spine and triangular body.
• CLAVICLE- Also, called as collar bone. It is thin elongated bone which curves at two places.

Functions:

• It provides glenoid cavity which articulates with head of humerus.
• It is also  meant for attachment of the arm muscles which protects the delicate internal organs present in these areas.

 PELVIC GIRDLE

• It is an irregular trough-shaped,supporting bone.
• it occurs between the hindlimbs and the axial skeleton. The pelvic girdle is attached posteriorly to sacrum. The sacrum and coccyx form the basin- shaped pelvis.
• The pelvic girdle consists of two coxal bones. The two halves meet ventrally to form a pubicsymphysis. Each coxal bone is formed of three bones i.e upper ilium inner pubis, ischium below the pubis. These three bones fuse to form the hip bone. The point at which three bones meet, a cupshaped hollow cavity is present called acetabulum. The thigh bone or femur articulates with acetabulum.

Functions:

• It is the site for attachment of leg muscles.
• It provides strength to sacral region.
• It transfers weight of whole body on the hindlimbs.

LIMB BONES

There are two pairs of limbs present in our body- forelimbs and hindlimbs. Both the limbs contains 30 bones each.

FORELIMBS:

• In humans, a pair of forelimbs arepresent. Each forelimb has 30 bones.
• The single long bone of the upper arm is called humerus. The two bones present at lower arm are ulna and radius. The radius is shorter than ulna.
• The hand has 27 bones where 8 bones are present in wrist region, 5 bones are present in palm region and 14 bones are present in fingers. The 8 bones of the wrist are called carpals, the 5 bones of the palm are called metacarpals and the 14 bones of fingers are called phalanges.

HINDLIMBS:

• In humans, a pair of hind limbs arepresent. Each hind limb has 30 bones.
• The single longest and strongest bone each forelimb has 30 bone present in thigh is called femur. The two bonepresent in shank region are tibia and fibula. The 7 bones of the ankle are called tarsal, the 5 bones of the sole are called metatarsal and the 14 bones that form the toes are called phalanges.

JOINTS

Joints are structural arrangement where two bones articulate. The joints are essential for movement of different skeletal structures i.e all the bones present in the body produce movement due to the movement of these joints.

On the basis of movability, joints are classified into three major joints.

A. FIBROUS OR IMOVABLE OR FIXED JOINT:

These joints do not allow any movement because the bones are firmly fixed together by strong collagen fibre. These joints in the skull are called sutures. The attachment of tooth with socket in jaw is also an example of fixed joints.

B. CARTILAGINOUS OR IMPERFECT OR SLIGHTLY MOVABLE JOINTS:

In these joints, two bones are joined together with help of a disc or white fibrous cartilage. The disc of cartilage restricts the movement in these joints due to which these joints show limited or slight movement. They are present in sternum ribs, pubisymphysis etc.

C. SYNOVIAL OR FREE MOVABLE JOINTS:

They are freely movable joint which allow movement in one or more directions. The bones of these joints are covered by a membane called synovial membane. Inside the membrane and between the two articulating surfaces of the bone, synovial cavity is present. The cavity is filled with synovial fluid that acts as a lubricant which nourishes the bone with nutrients and also acts as a shock absorber.

• According to shape and movement performed by synovial joints six different types of synovial joints are:
• BALL AND SOCKET JOINT– it is most free of all joints. It shows movement in different directions. The articulate end of one bone is in shape of ball whereas the end of other bone is in shape of cup. Example: shoulder joint and hip joint.
• HINGE JOINT– it allows movement in only one plane. In this joint, the end of one bone is deep convex in shape and in the end of other is deep concave in shape. Example: elbow joint, knee joint.
• PIVOT JOINT– this joint allows moveemnt in one plane. theprimary movement at the pivot joint is rotation. two bones articulates with each othee where end of one bone is rounded or pointed which fits into a shallow depression of the other bone. example: joint betwween the radius and ulna just below the elbow and between atlas and axis.
• GLIDING JOINT– the articulate ends of bth the bones are flat or slightly curved so that the bones can easily glide oe slide over each other. This joint allows movement only in one direction i.e  side to side movement, no twisting or rotational movement is possible because the bones are packed closely or held in place by ligaments. Example: tarsal and carpals.
• SADDLE JOINT– a joint in which one ball or convex head of one bone fixes into saddle like depression of other bone. It allows the movement in many directions. Example: between carpals and metacarpals of human thumb.
• ANGULAR OR ELLIPSOID JOINT– a joint in which articulate end of one bone is oval and convex and articulate end of other is elliptical or concave. It allows movement in two directions. Example: joint between radius and carpal.

DISORDERS

• MYASTHENIA GRAVIS:

It is an autoimmune disorder in which the antibodies produced in the body starts attacking its own body cells.The antibodies start attacking the acetyl choline receptors present on the sarcolemma, due to which neurotransmitter could not bind to its receptors and hence could not initiate nerve transmission. The skeletal muscle in patients become weak and leads to paralysis.

• MUSCULAR DYSTROPHY:

It is genetic disorder in which  aproteindystrophin is not formed. It is essential for contraction of muscle.

• TETANY:

It is rapid spasm in muscle due to lesser Ca2+ in body fluid.

• ARTHRITIS:

It is disorder in which inflamation of the joints occur. It is characterised by pain, swelling, redness, heat.

• GOUT:

 It is type of arthritis where inflammation of joints occur due to accumulation of uric acid crystals. In the patients of gout, there is an error in the uric acid metabolism due to which over secretion of uric acid occurs.

• OSTEOPOROSIS:

It is a skeletal disorder where bone loses its minerals  andfibres from its matrix. The loss of minerals and fibres decreases the bone mass causing osteoporosis. It is an age related disorder which is caused due to many factors such as imbalance of hormones like calcitonin and parathormone. As bone mass decreases the bone become more prone to fractures.

• OSTEOMALACIA AND RICKETS:

 It occurs in childhood, in this disorder the bones contains insufficient amount of calcium and phosphorus. The cause of kidney disease , vitamin d deficiency, an inherited defect.

• DISLOCATION:

It is a displacement of articular surface of a joint, it usually involves a damage to ligaments surrounding the joint.  Syptoms of dislocation includes  swelling, pain, and loss of motion.

• SPRAIN AND STRAINS:

 A sprain is twisting of a joint without dislocating it. Such an injury causes damage to ligaments and also often damaged tendons, muscle, blood vessels and nerves.

In contrast to sprain, a strain is a less severe stretching or twisting of a joint. Muscle and tendons may be stretched and became somewhat painful but minor damage is done to the tissue of the joint.

FRACTURE

It is bone breakage either complete or incomplete.

TYPES:

• SIMPLE FRACTURE– breaking into two fully separateparts with little damage.
• GREEN STICK FRACTURE– breaking of bone is formod crack only with broken parts still holding together.
• COMMINUTED FRACTURE– breaking of bone into more than two fragments with some of fragments losing any connection with blood circulation
• COMPOUND FRACTURE– the broken ends of fractured bone protrude through skin.

If you wish to read about axial skeleton and appendicular skeleton in detail, click on the link. Happy Reading 🙂