THE SKELETAL SYSTEM

BY SANJAI
What is the human skeletal system?
The human skeleton is the internal
framework of the human body. It is
composed of around 270 bones at
birth – this total decreases to
around 206 bones by adulthood
after some bones get fused together.
The bone mass in the skeleton
reaches maximum density around
age 21.
Functions of the human skeleton:-

The skeletal system works as a

support structure for your body.
It gives the body its shape,
allows movement, makes blood
cells, provides protection for
organs and stores minerals. The
skeletal system is also called the
musculoskeletal system.
 Constituents of skeleton:-

The skeletal system is made up of

bones, cartilage, and ligaments. The
skeletal system has many important
functions in your body.

● Bones- Comprise the hard framework of

the body
● Cartilages- Supporting and connecting
structures
● Ligaments- Bind the bones together.
Bone:-

Bones of all shapes and sizes

support your body, protect
organs and tissues, store
calcium and fat and produce
blood cells. A bone's hard
outside shell surrounds a
spongy center. Bones provide
structure and form for your
body.
Classification of bones on the basis of shape:-

The bones of the body come in a variety

of sizes and shapes. The four principal
types of bones are long, short, flat and
irregular. Bones that are longer than
they are wide are called long bones.
They consist of a long shaft with two
bulky ends or extremities. They are
primarily compact bone but may have a
large amount of spongy bone at the
ends or extremities. Long bones include
bones of the thigh, leg, arm, and
forearm.
Long Bone:-

A long bone is a bone that has a shaft

and 2 ends and is longer than it is
wide. Long bones have a thick outside
layer of compact bone and an inner
medullary cavity containing bone
marrow. The epiphyseal line is a
remnant of an area that contained
hyaline cartilage that grew during
childhood to lengthen the bone.Ex:-
THIGH BONE.
Short bone:-

Short bones are shaped roughly

as a cube and contain mostly
spongy bone. The outside surface
is comprised of a thin layer of
compact bone. Short bones are
located in the hands and feet. The
patella (kneecap) is also
considered a short bone.
Flat bone:-

Flat bones are bones whose

principal function is either
extensive protection or the
provision of broad surfaces for
muscular attachment. ... The flat
bones are: the occipital, parietal,
frontal, nasal, lacrimal, vomer, hip
bone (coxal bone), sternum, ribs,
and scapulae.
Irregular bone:-

They consist of cancellous tissue

enclosed within a thin layer of
compact bone. The irregular bones
are: the vertebræ, sacrum, coccyx,
temporal, sphenoid, ethmoid,
zygomatic, maxilla, mandible,
palatine, inferior nasal concha,
and hyoid.
The Human Skeleton:-

The human skeleton has 2 main divisions :-

● The axial skeleton which

includes the basic
central framework of the
body.
● The appendicular
skeleton which includes
the bones of the limbs
and girdles.
AXIAL SKELETON:-

The axial skeleton is the part of the

skeleton that consists of the bones of the
head and trunk of a vertebrate. In the
human skeleton, it consists of 80 bones
and is composed of six parts; the skull (22
bones), also the ossicles of the middle ear,
the hyoid bone, the rib cage, sternum and
the vertebral column. Axial skeleton
consists of the skull, vertebral column, the
ribs and the sternum.
The Skull:-

The skull is a bone structure that forms

the head in vertebrates. It supports the
structures of the face and provides a
protective cavity for the brain. The
skull is composed of two parts: the
cranium and the mandible. ... In
humans these sensory structures are
part of the facial skeleton.
Vertebral column:-

The bones, muscles, tendons, and

other tissues that reach from the
base of the skull to the tailbone.
The vertebral column encloses the
spinal cord and the fluid
surrounding the spinal cord. Also
called backbone, spinal column,
and spine.
Structure of vertebrae:-

A typical vertebra consists of a body

and a vertebral arch. The arch is
formed by the paired pedicles and
paired laminae. Arising from the
vertebral arch are the transverse,
spinous, superior articular, and inferior
articular processes. The vertebral
foramen provides for passage of the
spinal cord.
Neck or cervical vertebrae:-

The first cervical vertebrae is

called the Atlas. The second
second vertebra is the axis.
The remaining five neck
vertebrae do not have any
special names.
Thoracic vertebrae:-

The thoracic vertebrae are a

group of twelve small bones that
form the vertebral spine in the
upper trunk. ... They form the
region of the spinal column
inferior to the cervical vertebrae
of the neck and superior to the
lumbar vertebrae of the lower
back.
Lumbar vertebrae:-

The lumbar spine contains 5

vertebrae, which progressively
increase in size going down the
lower back. The vertebrae are
connected with joints at the back
to enable bending and twisting
movements of the spine.
Sacrum:-

The sacrum is a shield-shaped bony

structure that is located at the base of
the lumbar vertebrae and that is
connected to the pelvis. The sacrum
forms the posterior pelvic wall and
strengthens and stabilizes the pelvis. ...
The coccyx provides slight support for
the pelvic organs but actually is a
bone of little use.
Coccyx:-

The coccyx is the very bottom portion of

the spine. It represents a vestigial tail
(hence the common term "tailbone")
and consists of four or more very small
bones that are fused together. The
coccyx articulates with the sacrum
above it through a vestigial disc, and is
also connected to the sacrum with
ligaments.
Sternum:-

Your sternum is a bone that's

located in the middle of your chest.
It's also sometimes referred to as
the breastbone. Your sternum
protects the organs of your torso
from injury and also serves as a
connection point for other bones
and muscles.
Ribs:-

The ribs are the bony framework of the

thoracic cavity. The ribs form the main
structure of the thoracic cage
protecting the thoracic organs, however
their main function is to aid
respiration. There are twelve pairs of
ribs. Each rib articulates posteriorly
with two thoracic vertebrae by the
costovertebral joint.
APPENDICULAR SKELETON:-

The appendicular skeleton is the

portion of the skeleton of vertebrates
consisting of the bones that support
the appendages. There are 126 bones.
The appendicular skeleton includes
the skeletal elements within the limbs,
as well as supporting shoulder girdle
and pelvic girdle.
Bones of the Limbs:-

Like the upper limb, the lower limb is

divided into three regions. The lower
limb contains 30 bones. These are the
femur, patella, tibia, fibula, tarsal
bones, metatarsal bones, and
phalanges. The femur is the single
bone of the thigh. The patella is the
kneecap and articulates with the distal
femur.
Girdles:-

Your body is comprised of joints,

muscles, and structures that connect
one bone to the next. A pectoral
girdle, also referred to as the
shoulder girdle, connects your
upper limbs to the bones along the
axis of your body. You have two
pectoral girdles in your body.
Joints:-

A joint is the part of the body where

two or more bones meet to allow
movement. Generally speaking, the
greater the range of movement, the
higher the risk of injury because the
strength of the joint is reduced. The
six types of freely movable joint
include ball and socket, saddle,
hinge, condyloid, pivot and gliding.
Immovable Joints:-

An immovable joint connects the ends

of the bones by a tough fibrous tissue.
Examples of immovable joints are
sutures found between the bones of the
skull, syndesmosis between long bones
of the body, and gomphosis between the
root of a tooth and the sockets in the
maxilla or mandible. Synonyms:
fibrous joint.
Partially movable joints:-

Slightly movable joints are called

amphiarthroses. The singular form
is amphiarthrosis. In this type of
joint, the bones are connected by
hyaline cartilage or fibrocartilage.
The ribs connected to the sternum
by costal cartilages are slightly
movable joints connected by
hyaline cartilage.
Freely Movable Joints:-

● There are six types of freely movable

diarthrosis (synovial) joints:
● Ball and socket joint. Permitting
movement in all directions, the ball and
socket joint features the rounded head of
one bone sitting in the cup of another
bone. ...
● Hinge joint. ...
● Condyloid joint. ...
● Pivot joint. ...
● Gliding joint. ...
● Saddle joint.
Synovial Joints:-

A synovial joint, also known as

diarthrosis, joins bones or cartilage
with a fibrous joint capsule that is
continuous with the periosteum of the
joined bones, constitutes the outer
boundary of a synovial cavity, and
surrounds the bones' articulating
surfaces.
Muscles:-

There are about 600 muscles in

the human body. The three main
types of muscle include skeletal,
smooth and cardiac. The brain,
nerves and skeletal muscles work
together to cause movement –
this is collectively known as the
neuromuscular system.
Voluntary Muscles:-

Voluntary muscles are the muscles

that are under conscious control and
can be controlled at will or we can
choose when to use them. They are
also known as skeletal muscles as
they are attached to the bones.
Voluntary muscles are responsible for
the movement of body parts and the
locomotion.
Involuntary Muscles:-
Involuntary muscles are the muscles
that contract or move without
conscious control. The autonomic
nervous system controls involuntary
muscle movement. These muscles are
generally associated with the viscera
or internal organs that exhibit regular,
slow contractions and involuntary
actions.
Cardiac Muscles:-

Cardiac muscle (also called heart

muscle or myocardium) is one of
three types of vertebrate muscle
tissue, with the other two being
skeletal muscle and smooth
muscle. It is involuntary, striated
muscle that constitutes the main
tissue of the wall of the heart.
LEVER MECHANISMS IN HUMAN BODY:-

A lever is a rigid rod (usually a

length of bone) that turns about a
pivot (usually a joint). ... In our
bodies bones act as lever arms,
joints act as pivots, and muscles
provide the effort forces to move
loads. There are four parts to a
lever – lever arm, pivot, effort and
load.
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