Osteo-genesis
• Bones develop through a process called Osteogenesis or Ossification.
In embryo, primitive Skeleton is composed of either fibrous
membranes or hyaline cartilage.
• Bones can form either by intra-membranous method or by
intracartilaginous/endo-chondral method.
Intra-membranous Ossification
• In Intra-membranous bone formation, primitive mesenchyme can
give rise directly to bone.
Mesenchyme is embryonic connective tissue that is derived from the
mesoderm and that differentiates into hematopoietic and connective
tissue.
The mesoderm is one of the three primary germ layers in the embryo.
The other two layers are the ectoderm (outside layer) and endoderm
(inside layer), with the mesoderm as the middle layer between them.
MesodermMesenchymeOsteoblastBone
What is Cartilage?
• Strong but slightly flexible connective tissue. It is found around and in
between some bones. It is made up of cells(chondrocytes) suspended
in an Extra-cellular matrix.
Cartilage is of three types
• Hyaline(glass-like on appearance)
• Fibrous
• Elastic
Location
• Hyaline Cartilage is the most common type. It is present in
• Skeleton of Embryo
• Articular(articular=related to Joints) Cartilage
• Larynx, Trachea, Bronchi
• Costal Cartilages (connecting Ribs to Sternum)
• Inferior Part of Nose
• Fibro-cartilage is found in
• Intervertebral Discs
• Pubic Symphysis
• Menisci of Knee Joint
Elastic Cartilage is found in
Pinna of ear
Auditory Tube
Epiglottis of Larynx
Endochondral Classification
Classification of Joints
• 1. Synarthroses or Solid Joints
• 2. Diarthroses or Cavitated Joints
• Solid joints are further divided into Fibrous Joints and Cartilaginous
Joints.
• Fibrous Joints are mainly immovable. They include Sutures,
Syndesmoses(Interosseous membranes) and Gomphoses(teeth)
• Cartilaginous Joints are classified as Primary and Secondary
Cartilaginous Joints. Primary are also called Synchondroses, while
secondary are called Symphyses(singular is Symphysis). Primary
Cartilaginous joints are temporary, and play a role in growth of bones
by endochondral method. They consist of Hyaline Cartilage between
two growing bones. Secondary Joints are permanent and consist of
fibrocartilage between bones.
Synovial Joints? (Cavitated Joints)
• Articular Cartilage, Fibrous Capsule, Ligaments, Synovial Membrane,
Synovial Fluid.
• Menisci: Crescent-shaped wedge of fibro-cartilage.
Nervous System
• Central Nervous System: Brain and Spinal Cord
• Peripheral Nervous System: Nerves and
Ganglia(group/collection/bundle of neurons)
• Peripheral Nervous System or PNS(12 pairs of Cranial Nerves, 31 pairs
of spinal nerves)
• PNS is further divided into Somatic and Visceral Nervous System.
Somatic means related to body, Visceral means related to
Organs/Viscera.
• Somatic Nervous System has a sensory and a motor part. Sensory part
receives input from skin, skeletal muscles, tendons, joints, tongue,
eyes and ears. Motor Part brings information or output from Central
Nervous System to skin, skeletal muscles, tendons, joints, tongue,
eyes and ears.
• Visceral system also has sensory and motor part. The input is from
organs of digestive, respiratory, cardiovascular, urinary and
reproductive system.
• Afferent/sensory, Efferent/Motor.
Typical Spinal Nerve
Typical Neuron
Autonomic Nervous System
• It is part of motor section of Visceral PNS. It is exclusively the motor
system controlling the activity of cardiac muscle, smooth muscles and
glands.
• It has two components. Sympathetic System and Para-Sympathetic
System. Sympathetic system is activated during fight, flight or fright.
Parasympathetic system is like the default/background setting.
• Both systems have two sets of neurons in their pathway. The first
neuron, that is usually located in CNS is called pre-ganglionic neuron.
It synapses at a ganglion. Then there is the second neuron, the cellbody of which is located in ganglion. It is called post-ganglionic
neuron.
Line of Pull?
• A description of the direction of force exerted by a muscle, depending
on the orientation of its fibers, its skeletal attachments, the
disposition of its tendons, and the axis of movement of any joints
affected.
Skin
• Skin is the largest organ in the body. It covers all external free
surfaces.
• Skin has two main layers, the Epidermis is outer layer consisting of
Stratified Squamous epithelium. Dermis is a thicker layer of
connective tissue.
• Layers of Epidermis(From Below upwards) Stratum Basale, Stratum
Spinosum, Stratum Granulosum, Stratum Lucidum, Stratum Corneum.