The human skeleton has 206 bones that are divided into the axial skeleton (80 bones) and appendicular skeleton (126 bones). The axial skeleton includes bones such as the skull, vertebral column, ribs, and hyoid bone that form the central axis of the body. The appendicular skeleton includes the bones of the shoulders, pelvis, and limbs that attach to the axial skeleton. Bones provide structure and protection, allow movement through leveraging muscles, and store minerals. The skeleton enables vital functions and improves chances of survival.

1. Human
Skeleton

2. Skeleton is the supportive, hard frame work in/around the body & its study is
called Osteology.
In vertebrates it is divided into Exoskeleton & Endoskeleton.
Human endoskeleton has 206 bones.
Functions
Provides definite shape Protects internal organs
Provides surface for attachment of muscles
Acts as a system of levers helping in movement & locomotion.
Red bone marrow produces RBC’s & other blood cells (long bones & spongy bones)
Bones also act as a store house of Ca, P & Mg salts.
Human Skeleton
Axial Skeleton (80) Appendicular Skeleton (126)
Skull Vertebral
column
Girdles Limb bones
Hyoid
bone
Thoracic
cage

3. Axial Skeleton – Skull
Formed of 28 bones
Dicondylar (2 condyles at the base), immovable except mandibles.
Skull protects brain, provides sockets for eyes, ears & nasal chambers.
Provides proper shape to head & face.
Made up of Cranium, Facial bones & Ear Ossicles
Mandibles help in opening & closing of mouth.
Axial Skeleton – Vertebral Column
Also called as backbone /spine, forms central axis, has chain of 33 vertebrae.
In adults 5 Sacral & 4 Caudal vertebrae fuse to form Sacrum & Coccyx
respectively hence 26 bones in adults.
According to position the vertebrae are
7  Cervical 12  Thoracic 5  Lumbar 5  Sacral 4  Coccygeal
It shows 4 curvatures cervical, thoracic, lumbar & sacral (balance the erect posture).
Cervical, Lumbar -- directed forwards & Thoracic, Sacral – directed backwards

4. Axial Skeleton – Thoracic Cage
Formed of 12 thoracic vertebrae, 12 pairs of ribs & sternum
Ribs are articulated with thoracic vertebrae (12) dorsally & sternum ventrally.
Sternum is a long mid ventral, flat bone, of 15-17 cms. in length.
Divided into 3 parts Manubrium, Body & Xiphoid process.
The last two pairs are called floating ribs
Gives proper shape to thorax, helps in breathing (diaphragm & intercostal muscles).
Axial Skeleton – Hyoid bone
Horse shoe shaped bone just below the tongue to give proper support .

5. Appendicular Skeleton (126 bones)
Includes bones of girdles (Pectoral & Pelvic), limb bones.
Pectoral girdle is made up of two symmetrical halves (SCAPULA & CLAVICLE)
They are articulated anteriorly in midline by cartilagenous joint Pubic Symphysis.
Pelvic girdle consists of two large hip bones (innominate/coxal bones)
Each hip bone is made up ILIUM, ISCHIUM & PUBIS (os-innominate/os-coxal).
Each forelimb has 30 bones HUMERUS, RADIUS, ULNA, CARPELS, META
CARPELS & PHALANGES.
Each hindlimb has Femur, TIBIA, FIBULA, TARSELS, METATARSELS &
PHALANGES.

6. Locomotion
In humans there are two kinds of movements Internal Movements & Locomotion.
Internal movements
Includes Voluntary & Involuntary movements brought about by 3 types of muscles.
Peristatlic (digestive tract, constriction & dialation of blood vessels) – Smooth muscles.
Contraction & Relaxation of heart – Cardiac muscles.
Movements of limbs, head, trunk, eyeballs – Striated muscles
Significance of Movements
Maintains equilibrium against gravity.
Helps in food intake
Helps in breathing
Rhythmic movements of heart helps in circulation.

7. Locomotion
Characteristic feature of animals, willful/voluntary act of displacement.
The change in locus of whole body of living organism from one place to another
place is called locomotion.
There are four basic types of locomotion in animal kingdom namely;
Amoeboid movements : psuedopodia (leucocytes)
Ciliary movements : cilia (ciliated epithelium)
Whorling movements : flagella (sperms)
Muscular movements : muscles (limbs)
It includes acts of walking, running, creeping, hopping, flying, leaping & jumping.
In higher animals locomotion is performed by skeletal muscles.
It is the result of combined action of bones, joints & skeletal muscles.
Bone serves as lever, joints as fulcrum & muscles generate force.
Significance
Escaping from predators, search of food, water& shelter, courtship & mating
Improves chances of survival & continuation of race.

8. Joints
A place where two or more bones get articulated with one another is called a
joint.
Study of structure and functions of various joints is called arthrology.
They maintain position & prevents dislocation
Ligaments are tough elastic fibrous connective tissue bands/threads connecting
bones.
Joints help in locomotion, desirable voluntary movements, also brings flexibility,
some joints are protective & act es shock absorbers.
Classification
Synarthrosis/Fibrous/
Fixed
Amphiarthrosis/Cartilagenous/
Slightly movable
Diarthrosis/Synovial/
Freely movable
Sutures
Syndesmosis
Gomphoses/
Peg & Socket
Synchondrosis
Symphysis
Intervertebral joints
Ball & Socket
Hinge
Gliding
Condyloid
Saddle
Pivot

9. Bones are united at joints by thin/dense layer of white fibrous connective tissue.
White fibres are made up of Collagen (do not permit any movement).
They are meant for growth & may permit moulding during childbirth, these joints
are the at the places of growth.
Line of fusion at the joint is called as suture
Synarthrosis/Fibrous/Fixed
Sutures
They are found in flat & curved roofing bones, also
called serrate joints(serrated margins).
Bones are repeatedly interlocked hence become
more fixed & protective.
Coronal suture – between Frontal & Parietal
Saggital suture – between Parietals
Lambdoidal suture – between Parietals & Occipitals
Lateral suture – between Temporal & Parietals
In young/newborns the roofing bones leave six gaps called FONTANELLES.
Fontanelles provide flexibility for parturition & brain growth.
Gaps are closed at about 2 years of age by ossification.

10. Syndesmosis
Fibrous connective tissue that
connects two bones eg. Tibia &
Fibula
Synarthrosis/Fibrous/Fixed contd…..
Gomphosis
In thecodont teeth roots of the teeth are
fixed in sockets(alveoli) of jaws.
Diphyodont – 2 sets, first set falls &
permanent teeth arise
Fibrous connections are many
periodontal ligaments.

11. They are neither fixed nor freely movable hence termed as amphiarthrosis.
Amphiarthrosis/Cartilagenous/Slightly movable
They allow some movements in response to compression, tension/twisting.
The line of fusion between articulating surfaces is called synchondrosis/symphysis.
Synchondrosis
Connecting material is hyaline cartilage,
soft & elastic with minimal strength.
Epiphyseal plate between epiphysis &
diaphysis of long bones represents
synchondrosis.
It is a temporary joint in children, gets
ossified in adults. Provides site for
growth & flexibility in children.

12. Amphiarthrosis/Cartilagenous/Slightly movable contd…
Symphysis
Connecting material is fibro
cartilage, opaque comparatively
strong but flexible, contains
numerous white fibres (Collagen).
Present between pubic bones of
pelvic girdle, they are connected
by fibro cartilagenous disc.
Allows slight movements as
twisting, bending, compression.
More flexible in females for easy
parturition.

13. Intervertebral Disc
Present between the centres of
adjacent vertebrae, connected by
fibro cartilagenous disc.
Absorb shocks, protects spinal
cord, makes vertebral column
flexible.
Amphiarthrosis/Cartilagenous/Slightly movable contd…

14. Diarthrosis/Synovial/Freely movable
These are perfect joints due to well developed structures required for free
movements.
TYPICAL SYNOVIAL JOINT
It consists of synovial membrane synovial cavity, synovial fluid, capsule, ligament
& articulating surfaces covered by hyaline cartilage.
Synovial membrane lines the cavity & forms the capsule,
it secretes synovial fluid.
Synovial fluid is clear, yellowish white, slimy, viscous fluid
similar to lymph .
It is viscous due to Hyaluronic acid secreted by cells of
synovial membrane.
It contains nutrients & mucus for nourishment (hyaline
cartilage) & lubrication.
It also contains phagocytes to remove microbes & cellular
debris, deficiency causes arthrosclerosis.
Hyaline cartilage covers the end of
articulating surfaces avoiding friction.
Capsular ligaments & accessory
ligaments(intra/extra capsular), avoids
dislocation
Synovial membrane
Synovial fluid
Cartilage Ligaments

15. Diarthrosis/Synovial/Freely movable contd..
Ball & Socket
Spherical head of one bone fits in a cup shaped socket of other bone, prone to
dislocation.
They are of different types on the basis of structures, function, movements &
articulating bones viz;
They show multiaxial movements; shoulder joint shows rotatory/circular movements
(3600), & hip joint shows straight movements.
Head of the humerus fits in glenoid cavity of pectoral girdle & head of the femur fits
in the acetabulum of pelvic girdle

16. Diarthrosis/Synovial/Freely movable contd..
Hinge
Spoon shaped surface of one bone fits into concave cavity of other bone.
There are strong colateral ligaments resisting dislocation.
Provide uniaxial movements (1800)
Elbow joint, Knee joint are the examples of hinge joint.

17. Diarthrosis/Synovial/Freely movable contd..
Gliding joint
Articulating bones are permitted for gliding,
show non axial movements.
Intercarpellar joint, intertarsal joints are the
examples.
Condyloid joint
Oval shaped condyle of one bone fits into
elliptical cavity of other bone.
They allow biaxial movements (forward--
backward)
Radius carpel, Metacarpo – phalangeal joints
are the examples.

18. Pivot joint
Articular surfaces comprises of central bony pivot
(dense) surrounded by osteo-ligamentous ring.
Allows uniaxial movements Atlas moves along
the skull around the odontoid process of axis.
Saddle joint
Articulating surfaces are saddle shaped,
each surface has convex & concave area.
Similar to condyloid but provides more
freedom.
Edges of metacarpel & carpel of thumb.
This joint has a great evolutionary
significance.
Diarthrosis/Synovial/Freely movable contd..

19. Muscular Movements
Muscular tissue has the property of contractility, extensibility, elasticity, flexibility&
conductivity.
Cells of this tissue are highly elongated, modified & are called as muscle fibres.
There are 3 types of muscles namely ; striated, unstriated & cardiac
Striated muscles are voluntary (control under will), while unstriated & cardiac are
involuntary.
Striated muscle cells are cylindrical, unbranched, multinucleated with cross
striations.
Muscle cells are covered by modified cell membrane named as sarcolemma
(electrically charged), basement membrane & reticular connective tissue.
Contractile Proteins
Voluntary Muscles (under control of will/wish)
Muscle fibres show many myofibrils, each myofibril has proteinaceous
myofilaments (actin & myosin). Contractile unit is called as sarcomere.
Actin filament is thin & filamentous made up of ‘F’ proteins , polymer of globular
(G) actins .

20. Contractile Proteins
Muscle fibres show many myofibrils, each myofibril has proteinaceous
myofilaments (actin & myosin). Contractile unit is called as sarcomere.
Actin filament is thin & filamentous made up of ‘F’ proteins , polymer of globular
(G) actins .
Muscular Movements contd…
Myosin filaments are thick & made up of many meromyosins. Each meromyosin
has globular head with short arm Heavy meromyosin (HMM) & a tail called light
meromyosin (LMM).
Head shows active ATPase & has binding sites for ATP & active sites for actin.
Mechanism of muscle contraction (Sliding filament theory)
Sliding filament theory suggests sliding of thin filaments over the thick filaments.
Nerve endings of motor neurons innervate muscles, junction between motor
neuron & sarcolemma of muscle fibre is called motor end plate.
At the axonic ends acetylcholine is released because of CNS.
It generates action potential in sarcolemma, causing release of Ca++ with troponin
on actin filament & removes masking of active site of actin filament which are
present between myosin filaments.

21. It results in shortening of sarcomere by reducing I band Myosin reduces ADP &
becomes relaxed.
Muscular Movements contd…
Again the whole process repeats causing further sliding, this continues till Ca++
ions are pumped.
When the Ca ++ ions are pumped back, the masking of actin filaments takes
place.
Repeated activation of muscles leads to accumulation of lactic acid due to
anaerobic breakdown of glycogen causing muscle fatigue.
They are packed in to two bundles, (altogether 640 muscles) . Each muscle
contains many fasciculi & each fasciculus contains bundle of muscle fibres.
Muscles are joined to skeleton by tendons, they are elastic, thick bands of white
fibrous connective tissue.

22. At any joint there are two types of bones stationary & movable.
Location& Structure-- Striated muscles
The end of the muscle attached to stationary bone is called origin, the opposite
end is called as insertion, the middle thick part is called as belly.
All the fibres are not from end to end but concentrated in the middle hence
fusiform.
Types of Muscles
On the basis of movements muscles are Prime movers (agonist) – initial
movement, (Biceps) Antagonists -- opposite to prime movers (Triceps) &
Synergists – assist prime movers (Brachialis).
Prime movers (agonist) – initial movement, (Biceps)
Antagonists -- opposite to prime movers (Triceps)
Synergists – assist prime movers (Brachialis).

23. Work in pair & produce opposite action (Biceps & Triceps)
Working
One in the pair is always stronger than the other eg. Biceps are much stronger
than triceps,
Fundamental characteristic of muscles is contraction hence muscles can only pull
& not push the bone.
Action of striated muscles are quick hence prone to fatigue, they are neurogenic.
Important antagonistic muscles
Flexor & Extensor – Biceps & Triceps
Abductor & Adductor – deltoid & Latissimus (shoulder -- towards & away)
Pronator & Supinator – downwards & backwards, upwards & forward (palm)
Levator & Depressor – Raises & lowers body parts.
Protractor & Retractor – move forward & backward
Sphincters – closure & opening (circular muscles in Stomach, anus).

24. Not under the control of will/wish but autonomic nervous system i.e. neurogenic.
Involuntary Movements (Not under the control of will/wish)
Present in the walls of visceral organs.
Cells are elongated/spindle shaped, non-striated, uninucleate & involuntary.
Arranged in longitudinal/circular layers .
They are not easily fatigued because they contract slowly & for longer duration.
Movement of Cardiac Muscles
Elongated, cylindrical, striated, uninucleate, involuntary, branched & show
intercalated discs, present in the wall of heart.
Movement of Smooth Muscles
They are myogenic & show rhythmic movements, may get fatigued due to longer
duration of contraction & relaxation.

25. Muscular dystrophy
Skeletal disorders
Inherited muscle destroying disease, degeneration of muscle fibres.
Leads to progressive atrophy of skeletal muscles.
Usually the skeletal muscles are weakened internally & externally but diaphragm
is not affected.
Duchenne type is the most common.
Osteoporosis
In women after menopause oestrogen becomes less, causing loss of calcium
hence the bones become porous, skeleton fails to withstand stress,
Deficiency of Ca, vitamin D, sex hormones & calcitonin are also the other causes.
Arthritis
Inflammation of joints,pain & stiffness.
Gouty arthritis – excessive accumulation of uric acid, due to excessive production
or inability to excrete. Deposited in joints resulting in pain.
Osteoarthritis – degeneration of cartilage, knees/hands/spine are usually affected.
Rheumatoid arthritis – inflammation of synovial membrane, it thickens, fluid
increases causes pain, abnormal granules – pannus from membrane cause
erosion of cartilage.

26. Myasthenia gravis
Skeletal disorders
Autoimmune condition of unknown origin
Antibodies produced bind to the acetylcholine receptors of neuromuscular
junction.
Transmission is thus blocked, causes progressive muscle weakness.
May effect movement of eyelids/eye/facial expression & swallowing.
Degree of weakness varies from local to general.
Eyelid muscles – ptosis (drooping of eyelids), diplopia (double vision) difficulty in
swallowinf/speech/chewing.
Tetany
Impulses arrive in rapid succession resulting in summation of action potential.
Reduced activity of parathyroids, causes low serum levels of calcium which is a
cause for tetany,
Person exhibits persistant contractions of skeletal muscles.