THE AXIAL SKELETON

I) The Skull (general overview)

1) consists of 22 bones

2) The skull is divided into the cranial bones (the cranium)which encloses and protects the brain and provides a site for the attachment of the neck muscles and the facial bones which contain cavities for the special senses of sight, taste, and smell as well as securing the teeth, anchoring the facial muscles of expression, and providing the openings for passage of air and food.

3) All bones of the skull are flat bones except for the mandible.

4) All bones in the skull (except for the mandible) are attached by interlocking joints called sutures. 

5) The Cranium can be divided into the cranial vault which forms the superior, lateral, and posterior parts of the skull as well as the forehead and the cranial base which is divided into the anterior, middle, and posterior cranial fossae. The brain is said to occupy this entire region called the cranial cavity.

6) Other cavities within the brain include the middle and inner ear cavities, the nasal cavity and the orbits which house the eyeballs.  Sinus cavities filled with air also are found within certain of the bones of the skull.

7) Many openings are found in the skull ( foramen, canals, fissures) which provide passageways for the spinal cord, major blood vessels serving the brain, and the 12 pairs of cranial nerves. 

II) The eight bones of the cranium

1) The frontal bone (1)

a) forms anterior portion of the cranium                                b) most anterior portion called the frontal squama or forehead which ends inferiorly at the supraorbital margins, and then extends posteriorly to form  the superior walls of the orbits and most of the anterior cranial fossa. This fossa supports the frontal lobes of the brain.  Piercing each of the supraorbital margin  are the supraorbital foramen (notch), which allows the supraorbital artery and nerve to pass to the forehead.  The smooth part of the frontal bone between the orbits is called the glabella, and just inferior to this the frontal bone meets the nasal bones (facial bones) at the frontonasal suture. The areas lateral to the glabella contain the frontal sinuses.

1) The parietal bones(2)

a) Curved rectangular bones forming most of the superior and lateral aspects of the the cranium.

b) The four largest sutures are found where the parietal bones articulate with other cranial bones: the coronal suture, the sagittal suture, the lambdoid suture, and the squamosal suture.

2) The occipital bone(1) 

a) forms the skull's posterior wall and base and articulates with the parietal and temporal bones by way of the lambdoid and occipitomastoid sutures and joins with the sphenoid bone in the cranial floor by way of  the pharyngeal tubercle.                                                                     b) it forms the walls of the posterior cranial fossa  which supports the cerebellum of the brain                                         c) The foramen magnum is found in the base of the occipital bone which is an opening through which the inferior part of the brains connects with the spinal cord. The occipital condyles are found on either side of the foramen magnum inferior to the cranium and is the point where the skull articulates with the first vertebrate of the spinal column (the atlas), in such a way as to allow a nodding movement of the head (the condyles are rocker-like). The hypoglossal canals are found superior to each condyle for the passage of the cranial nerves by the same name.                                 d) External bone markings include the external occipital protuberance, the external occipital crest and the superior and inferior nuchal lines. These are points of attachment for muscles and ligaments. The external occipital crest secures the ligamentum nuchae (an elastic ligament attaching the skull to the vertebrate), while the others anchor back and neck muscles.

3) the temporal bone (2) 

a) they lie inferior to the parietal bones and meet them at the squamosal sutures                                                                 

b) they contain four major regions                                     `     

1) the squamous region which contains the zygomatic process which together form the zygomatic arch (you feel it as the projection of your cheek  There is a small mandibular fossa on the inferior surface of the zygomatic process that receives the condyle of the mandible forming the temporomandibular joint.                                                            

2) The tympanic region surrounds the external auditory  (acoustic) meatus, or external ear canal. The styloid is located  below the external auditory meatus which is the attachment point for several muscles of the tongue and the neck and for a ligament that secures the hyoid bone to the skull.                                                                                             

3) the mastoid region contains the mastoid process, which anchors some of our neck muscles. The stylomastoid mastoid foramen between the styloid and the mastoid process, allows the facial nerve to leave the skull                    

4) the petrous region looks like a mountain ridge which houses the middle and inner ear cavities. The large jugular foramen penetrate the petrous  region allowing passage of the internal jugular vein and three cranial nerves.  The carotid canal allows passage of the carotid artery to the brain ( the two carotid arteries supply blood to 80% of our cerebral hemispheres--their closeness to the inner ear cavities explains why we hear a rapid pulse in our head. The foramen lacerum appears as an opening in a dry skull, but is completely covered with cartilage in a living skull. The internal acoustic  (auditory) meatus, transmits the cranial nerves (VII and VIII).   

4) The sphenoid bone(1)

a) butterfly shaped and consists of a central body and three pairs of processes the greater wings, the lesser wings,and the pterygoid processes. 

b) The sphenoid sinuses are found within the body and the superior surface of the body bears the sella turcica(meaning Turk's saddle) . In the middle of the sella turcica  (the saddle) is the hypophyseal fossa which encloses the pituitary gland. Also found here are the tuberculum sellae and the dorsum sellae, and the posterior clinoid processes. 

c) The greater wings project laterally from the body and the lesser wings form part of the floor of the anterior cranial fossa. Medially they both form the anterior clinoid processes which provide an anchoring site for securing the brain within the skull. 

d) The pterygoid processes anchor the pterygoid muscles important in chewing.

e) Openings in the sphenoid bone include the optic canals for the passage of the optic nerves, the superior orbital fissure allows passage of cranial nerves which control eye movements, the foramen rotundum  and the foramen ovale allow passageways for the maxillary and mandibular cranial nerves and the foramen spinosum allows passage for the middle meningeal artery . 

5) The ethmoid bone(1) 

a) forms bone between the nasal cavities and the orbits

b) The superior surface is called the cribriform plate forming the roof of the nasal cavity and the floor of the anterior cranial fossa.  It has many tiny holes called olfactory foramina that allows the olfactory nerves to pass into the brain. The crista galli is found on the cribriform plate which provides a place of attachment for the the dura mater ( the outermost covering of the brain). 

c) The perpendicular plate divides the nasal cavity into right and left halves. The ethmoid sinuses are found within the lateral masses ofthe ethmoid bone.

d) The superior and and middle nasal conchae  extend medially from the lateral masses. The lateral surfaces of the ethmoid's lateral masses are called the orbital plates.

***Sutural bones (Wormian bones) are bone clusters that appear within sutures (usually within the lambdoid sutures. They represent additional ossification centers that appeared when the skull was expanding very rapidly during fetal devlopment.

****The ear ossicles (malleus, incus and the stapes)(2 each) found in the middle ear cavity 

III The 14 Facial Bones

a) The mandible is the largest and strongest bone of the face. It consists of two parts: the body which forms the chin and two rami meeting the body posteriorly at a  mandibular angle. Located superior to each ramus is the anterior coronoid process ( an insertion point for the large temporalis muscle that elevates the jaw for chewing), and the posterior mandibular condyle which articulates with the manibular fossa of the  temporal bone forming the temporomandibular joint. The superior border of the body is called the alveolar margin which contains the sockets (alveoli) in which the teeth are found. The mandibular symphysis which indicates the fusion of the two mandibular bones during infancy is at the midline of the mandibular body. Mandibular foramina are on the medial surface of each ramus permiting the nerves responsible for tooth sensation to pass to the teeth in the lower jaw (dentists inject novacain into the foramen to numb the lower teeth), and the mental foramina on the lateral surfaces of the mandibular body allow blood vessels and nerves to pass to the skin of the chin.

b) The maxillary bones or maxillae are two fused bones (the anterior nasal spine marks the point at which they are fused)forming the upper jaw and the central portion of the facial skeleton. The maxillae provide a place for the upper teeth it their alveolar margins and the palatine processes fuse medially posteriorly to the alveolar margins forming  two thirds of the hard palate. The incisive fossa  a midline foramen  found posteriorly to the margins provides a passageway for blood vessels and nerves. The frontal processes extending superiorly form the bridge of the nose. On either side of the frontal processes are the maxillary sinuses ( the largest of the paranasal sinuses.) extending from the orbits to the upper teeth. The zygomatic processes are found laterally on each side of the maxilla where it articulates with the zygomatic bone. The infraorbital foramen are located on each side of the maxilla and allows the infraorbital nerve and artery to reach the face. The inferior orbital fissure is found at the junction of the maxilla  and the greater wing of the sphenoid and permits the zygomatic nerve, the maxillary nerve and blood vessels to pass to the face.

c) The zygomatic bones are called the cheekbones.

d) The nasal bones forms the bridge of the nose and attach to the cartilages which form the skeleton of the external nose.

e) The lacrimal bones forms part of the medial walls of the orbits, each containing the lacrimal fossa  which contains the lacrimal sac for tear production.

f) The palatine bones which are L shaped are formed from the horizontal and perpendicular bony plates and contain the pyramidal, sphenoidal, and orbital processes.  The horizontal plate completes the posterior portion of the hard palate while the perpendicular plate forms the walls of the nasal cavity and parts of the orbits.

g) The Vomer forms part of the nasal septum.

h) The inferior Nasal Conchae form parts of the lateral walls of the nasal cavity and are the largest of the three pair of conchae

***Sinuses that cluster around the nasal cavity are called the paranasal sinuses: the frontal sinuses, the sphenoid sinuses, the sphenoid sinuses, and the maxillary sinuses.

***The hydoid bone is the only bone that does not articulate with any other bone in the skeleton. It attaches by way of the stylohyoid ligament with the styloid processes of the temporal bone.  The hyoid body and greater horns are attachments for neck muscles that raise and lower the larynx during swallowing and speech.

IV) The Vertebral Column

1) general description

a) Consists of interlocking vertebrate. A typical vertebrate has an anterior thickened portion called a body or centrum which is the weight bearing region and a vertebral arch posteriorly. Together they enclose an opening called the vertebral foramen. Successive  vertebral foramen form the vertebral canal surrounding the spinal cord. Each vertebral arch consist of two pedicles and two laminae.Seven processes project from the vertebral arch: the spinous process and  a transverse process which are attachements for muscles that move the spinal column and for ligament which stabilize it. The paired superior and inferior articular processes  contain facets and are covered with hyaline cartilage. The inferior articular processses of each vertebra form moveable joints with the superior articular processes of the veterbrate below it. Notches are present on the pedicles at the superior and inferior borders providing lateral openings between adjacent vertebrate called intervertebral foramina through which the spinal nerves pass. 

b) Consist of 33 vertebrate in five divisions: the cervical vertebrate (C1-C7), the thoracic vertebrate (T1-T12), the lumbar vertebrate (L1-L5, the sacrum (5 fused vertebrate), and the coccyx (4 fused vertebrate).

c) Arrangement of vertebrate produce an S shaped or sinusoid shape producing the cervical, thoracic, and lumbar curvature giving the spine the ability to function like a spring, rather than a rod therefore making the spine more flexible and resilient.  Vertebrate size increases from top to bottom because the lower vertebrate have to support more weight.

2) The (7) cervical vertebrates (C1-C7)

a) smallest and the lightest vertebrate of the neck 

b) The first two are called the atlas (C1) and the axis C2). They have no intervertebral discs between them. The atlas has no body and no spinal processes and is nothing but a ring of bone consisting of  anterior and posterior arches and a lateral mass on each side. Articular facets are found on the superior and inferior surfaces of the body. The superior articular facets  receive the occipital condyles of the skull carrying the skull like Atlas supported the heavens and enable us to nod yes, while the inferior facets articulate with the axis  The axis has a body, spine and is like other cervical vertebrate except for a knoblike dens or odontoid process. The dens was the body of the atlas  , but fused with the axis during embryonic devlopment. The dens  allows you to rotate your head to say no.

c) The remaining cervical vertebrate (C3-C7) has the following distinguishing characteristics :

-----the body is oval -----                                                            ----the spinous process is short, projects directly back and is bifid or split at its tip except for the 7th vertebrate and is much larger and is visible through the skin (called the vertebra prominens making it a landmark for counting the vertebrate---                                                                                ---the vertebral foramen is large and generally triangular---                                                                                ----each transverse process contains a transverse foramen through which the vertebral arteries pass to service the brain------                            

3) The Thoracic Vertebrate(T1-T12)

a) all articulate with the ribs, increase in size from the first to the last; the first looks like C7 and the last four show a progression toward lumbar vertebrate.

b) Distinguishing characteristics include:

----a heart shaped body---two pairs of facets or demifacets (half facets) to articulate with the ribs (except for T10-T12 which have only a single facet to accept their ribs ----the vertebral foramen is circular---the spinous process is long and points sharply inferiorly--the superior and inferior articular facets lie mainly in the frontal plane(prevents flexion and extension but allows rotation in this region of the spine

4) The Lumbar Vertebrate (L1-L5) 

a) the small of the back, receives the most stress

b) Distinguishing characteristics include

---massive kidney shaped bodies---the pedicles and laminae are shorter and thicker----the spinous processes are short, flat and hatchet shaped to allow attachment for the large back muscles and are easily seen  when a person bends forward---the vertebral foramen is triangular--orientation of the facets lock the vertebrate together providing stability by preventing rotation of the lumbar spine while still allowing for flexion and extension--

5) The Sacrum (S1-S5)

a) formed by 5 fused vertebrate

b) articulates superiorly with L5 by way of the superior articular processes, inferiorly with the coccyx, and laterally with the two hip bones via its auricular surfaces to form the sacroiliac joints of the pelvis 

c) transverse lines mark the points of fusion of the vertebrate

d) the ventral sacral foramina penetrate the sacrum at the lateral ends of the transverse lines or ridges and carry blood vessels and nerves

e) the median sacral crest represents the fused spinous processes of the sacral vertebrate and flanked by the dorsal sacral foramina and the lateral sacral crests which are the remnants of the transverse processes

f) The vertebral canal continues inside the sacrum as the sacral canal 

g) The sacral hiatus is an enlarged external opening at the inferior end of the sacral canal since the lamina of the fifth and sometimes the fourth vertebrate do not fuse medially

6) The coccyx

a) the tailbone

b) consists of four (or three or five) vertebrate fused together

c) nearly a useless bone except for the slight support that the coccyx gives our pelvic organs

V) The Bony Thorax

1) The Sternum

a) the breastbone formed by the fusion of three bones: the most superior of which is the manubrium which articulates via its clavicular notches with the clavicles or collarbones and articulating laterally with the first two pair of ribs; the body which is notched where it articulates with the cartilages of the second to seventh ribs; the xiphoid process on the inferior end of the sternum only serves as a point of attachment for some abdominal muscles.

2) The ribs 

a) twelve pairs of ribs

b) The true or vertebrosternal ribs are the first seven pairs of ribs that attach directly to the sternum by individual costal (hyaline) cartilages.

c) The false ribs are the remaining five pairs of ribs and attach either indirectly to the sternum or lack a sternal attachment.  Ribs 8-10 attach to the sternum indirectly and are called the vertebrochondral ribs.  Ribs 11 and 12 are called the floating ribs because they have no attachments.

d) A rib is typically a bowed flat bone. The shaft which is the bulk of a rib is smooth on its superior surface, by its inferior border is sharp and smooth and has a costal groove on its inner surface that provides o path for the intercostal nerves and blood vessels.

e) Each rib also has a head, neck, and tubercle.  The head is the posteriormost  end and articulates with the vertebral bodies by two facets: one joins the body of the same numbered thoracic vertebra, the other articulates with the body of the vertebra immediately superior. The neck is the constricted portion of the rib just beyond the head and lateral to this the knoblike tubercle articulates with the transverse process of the same numbered thoracic vertebrae. 

THE APPENDICULAR SKELETON

I) The Pectoral (shoulder) Girdle

a) consists of the clavicle (collarbone) and the scapula (shoulder blades)

b) provide a point of attachment for the upper limbs

c) The clavicles have two ends: a cone shaped sternal end that attaches to the sternum at the manubrium and the flattened lateral end called the acromial end which artiticulates with the scapula.  The clavicles act as braces holding the scapula and arm out laterally (a broken collarbone causes the entire shoulder region to collapse medially. They also transmit compression forces from the upper limbs to the axial skeleton when we push on something. The outward convex shape of the clavicle assures that when it will fracture anteriorly away from the subclavian artery.

d) The scapulae located on the dorsal surface of the rib cage are triangularly shaped flat bones having three borders: the superior, medial, and lateral borders. The lateral or axillary border contains a shallow fossa called the glenoid cavity which articulates with the humerus of the arm forming the shoulder joint. The glenoid cavity is shallow and poorly reinforced so that it does not restrict the movement of the humerus which is good for flexibility, but bad for stability making shoulder locations fairly common. Three angles form the scapula as it does in a triangle. The superior angle, the lateral angle, and the inferior angle. The inferior angle moves extensively as the arm is raised and lowered, an important landmark for studying scapular movements. The costal surface is concave and featureless. The posterior surface contains a spine which ends laterally with the acromion which articulates with the acromial ends of the clavicle, formingthe acromioclavicular joint. The corocoid process helps to anchor the biceps muscle and is bound by the suprascapular notch which is a nerve passage. Fossae include the infraspinous, superaspinous and the subscapular fossa.

II) The Upper Limb

a) The humerus is the only bone of the arm. The head is located at the proximal end and articulates with the glenoid cavity of the scapula.  Inferior to the head is the anatomical neck followed by the lateral greater tubercle, and a medial lesser tubercle (sites of muscle attachments) separated by the intertubercular or bicipital groove which guides a tendon of the biceps muscle to its attachment point at the rim of the glenoid cavity. Distal to the tubercles is the surgical neck (so named because it is the most frequently fractured  part of the humerus).  The deltoid tuberosity  is a V shaped roughened area serves as a point of attachment for the deltoid muscle of the shoulder. The radial groove forms a path for the radial nerve.  Two condyles are found at the distal end of the humerus. These are the trochlea and the capitulum which articulate with the ulna and the radius  respectively. Muscle attachment sites called the medial and lateral epicondyles are on either side of the condyles, and above the epicondyles are are the supracondylar ridges. The ulnar nerve runs behind the medial epicondyle (responsible for the "funny bone" sensation). The coronoid fossa (on the anterior surface) and the olecranon fossa ( on the posterior surface) allow the corresponding processes of the ulna to move freely when flexing and extending the elbow. The radial fossa receives the head of the radius when the elbow is flexed.

b) The forearm is formed by the radius and ulna which articulate with each other at the radioulnar joints, and are connected with each other over their entire length by the interosseous membrane.                                                         

c)The ulna is longer than the radius and forms the elbow joint as it articulates with the humerus. On the proximal end are the olcranon and coronoid processes separated by the trochlear notch (which grip the trochlea of the humerus forming a hinge joint). The radial notch is on the lateral surface of the coronoid process where the ulna articulates with the head of the radius. A knob like head is found distally and medial to the head is a styloid process from which a ligament funs to the wrist.

d) The head of the radius shaped like the head of  a nail and articulates with the capitulum and the humerus. Medially the head articulates with the radial notch at the ulna. The radial tuberosity which is inferior to the head anchors the biceps muscle. The ulnar notch found distally articulates with the ulna and a lateral styloid process which is an anchoring  site for ligaments that run to the wrist.  The ulna contributes more to the elbow joint, while the radius contributes more to the wrist joint (when the radius moves, the hand moves with it). 

e) The hand  is formed from the carpals (wrist bones), the metacarpals (bones of the palms) and the phalanges (the bones of the fingers)

f) The carpals are arranged in two irregular rows of four bones each. In the proximal row are the scaphoid, lunate, triquetral and psiform bones (only the scaphoid and the lunate articulate with the radius to form the wrist joint). In the distal row are the trapezium, trapezoid, capitate, and hamate bones.  To recall the bones easilly use this phrase: Sally left the party to take Cathy home.

g) The metacarpal bones have no names, but are numbered from 1 to 5 from the thumb to the little finger . The bases articulate with the carpals proximally and with each other medially and laterally. Their heads articulate with with the proximal phalanges; the heads of the metacarpals are your knuckles when you clinch your fist.

h) The fingers or digits contain small bones called phalanges (14 in each hand). Except for the thumb each finger has three phalanges: a distal, middle, and a proximal phalanges. Each set of phalanges are numbered 1 to 5 beginning with the thumb or pollex.

III) The Pelvic (Hip) girdle

a) It attaches the lower limbs to the axial skeleton, transmits the weight of the upper body to the lower limbs and supports the visceral organs of the pelvis. 

b) It is formed by a pair of hip bones or coxial bones, each uniting with the sacrum posteriorly and with each other anteriorly at the pubic symphysis.

c) Each hip bone or pelvis consists of three bones the ilium, ischium and pubis which become permanently fused in the adult.  At the point of fusion of these three bones is the acetabulum, a socket that receives the head of femur or thigh bone.

d) The  ilium is the most superior coxial bone and consists of a body and a superior winglike portion called the ala. The thickened superior margins of the ala are called the iliac crests (this is where you rest your hands on your hips). The iliac crests are thickest at the tubercle of the iliac crest. Anteriorly, each iliac crest ends as the blunt anterior superior iliac spine and posteriorly as the sharp posterior superior iliac spine. The anterior and posterior inferior iliac spines are located below. The greater sciatic notch is a passage for the sciatic nerve, and the gluteal muscles attach to the posterior, anterior, and inferior gluteal lines. The iliac fossa is found on the internal surface of the ala, and the auricular surface  articulates with the sacrum to form the sacroiliac joints. The arcuate line helps define the pelvic brim, the superior margin of the true pelvis.

e) The ischium has a thick body joining the ilium and a thinner ischial ramus joining the pubis. The ischial spine provides a point of attachment for the sacrospinous ligament from the sacrum.  The lesser sciatic notch allows passage for nerves and blood vessels supplying the anogenital area. The ischial tuberosity are the strongest part of our hip bones and when we sit our weight is borne entirely be these tuberosities. A massive ligament runs from the sacrum to each ischial tuberosity called the sacrotuberous ligament which helps hold the pelvis together.

f) The pubis is V-shaped with superior and inferior rami attached to a flattend medial body. The anterior border is thickened to form the pubic crest, and at the lateral end of the pubic crest is the pubic tubercle (one of the attachments for the inguinal ligament). The obturator foramen is a large opening through which blood vessels and nerves pass. The pubic symphysis is the point of attachment of the bodies of the two pubic bones join by way of a fibrocartilage disc. At this point where the two rami angle laterally we have formed the pubic arch.

IV) The Lower Limb

a) The femur or thigh bone is the largest strongest bone of the body. They course medially as they descend toward the knee causing the knee joints to be closer to the bodies center of gravity for better balance. The medial course of the two femurs is more pronounced in women because of their wider pelvis.  The head of the femur has a small central pit called the fovea capitis from which a short ligament the ligamentum teres attaches the femur to the acetabulum. The head is carried on the neck which is the weakest part of the femur and is often fractured which is called a broken hip.  The lesser and greater trochanter  serve as sites of attachment for thigh and buttock muscles and are connected by the intertrochanteric line anteriorly and the intertrochanteric crest  posteriorly.  The gluteal tuberosity is found inferior to the intertrochanteric crest  on the posterior shaft and blends into the linea aspera all of which are sites of muscle attachments. The lateral and medial condyles articulate with the tibia of the leg, and flanked by the medial and lateral epicondyles. The adductor tubercle is found on the medial epicondyle. The patellar surface articulates with the kneecap. The intercondylar notch is found between the condyles.  The patella is a sesamoid bone  enclosed in the quadriceps tendon that secures the anterior thigh muscles to the tibia. It protects the knee joint and improves the leverage of the thigh muscles acting across the knee.

b) The leg is formed by the tibia and the fibula which are connected by and interosseous membrane  and articulate with each other proximally and distally. The tibia articulates with the femur to form the hinge joint of the knee, while the fibula only helps stabilize the ankle joint. The tibia or shinbone contains the concave medial and lateral condyles which articulate with the femur and are separated by an irregular projection called the intercondylar eminence. The pateller ligament attaches to the tibial tuberosity. The anterior border of the tibial shaft contains the anterior crest (the shin). The medial malleolus forms the medial bulge of the ankle and the fibular notch on the lateral surface of the tibia helps form the distal tibiofibular joint.  The fibula has a proximal head and a distal lateral malleolus (which forms the lateral ankle bulge). 

c) The foot includes the tarsus (ankle bones), the metatarsus  (bones of the foot), and the phalanges (toe bones). The tarsus consists of seven tarsal bones that form the postererior half of the foot. The two largest bones are the talus (articulating with the tibia and the fibula) and the calcaneus (heel bone) which carries the talus on its superior surface. The achilles tendon of the calf muscle attaches to the posterior surface of the calcanus. The remaining tarsal bones include the lateral cuboid, the medial navicular,and the anterior meidial, intermediate, andlateral cuneiform bones.  The metatarsus consists of five bones numbered 1 to 5 beginning with the toe. The 14 phalanges (toes) are smaller than those of the fingers. Three phalanges (distal, middle, and proximal, except for the great toe or hallus which has only two, proximal and distal.  

JOINTS (can be functionally classified as being synarthroses joints (immovable joints), amphiarthroses joints (slightly moveable), or diarthroses joints (freely movable)

Types of Joints based upon structure binding the joints together:

I) FIBROUS JOINTS - no joint cavity present and bones joined by fibrous tissue

a) Sutures occur only between the bones of the skull. The fibrous tissue is continuous with the periosteum and is present during youth to allow for growth of the skull bones to grow.  During middle age the fibrous tissue ossifies and the sutures are called synostoses  which prevents movement of the cranial bones that may damage the brain.Sutures are classified functionally as synarthrosis or immovable joints.

b) Syndesmoses involves joints formed by a ligament. An example would be the ligament connecting the distal ends of the tibia and the fibula. This joint only allows slightly more movement than a suture and is also classified as an immovable joint or synarthrosis.  Other syndesmoses do allow some movement and are classified as amphiarthrosis. 

c) Gomphoses joints are a peg-in-socket fibrous joint. The only example is the articulation of a tooth with its bony alveolar socket. The fibrous connection here consists of a short periodontal ligment. 

II) CARTILAGINOUS JOINTS (articulating bones are united by cartilage, and lack a joint cavity)

a) Synchondroses are types of joints in which a bar or plate of hyaline cartilage fuses two bones together. The are virtually immoveable and are therefore classified as synarthrosis joints. Examples of this joint type is the epiphyseal plate connecting the diaphysis and the epiphysis in long bones in children and the immovable joint between the costal cartilage of the first rib and the manubrium of the sternum.The epiphyseal plates are temporary joints and eventually become synostoses like the sutures of the skull.

b) Symphyses involves a joint in which the articular surfaces are covered with hyaline cartilage and fused to an intervening plate of fibrocartilage.  The fibrocarilage is compressible and resilient and acts as a shock absorber and prevent a limited amount of movement. Symphyses are are amphiarthrotic joints designed for strength and flexiblity. Examples include the intervertebral joints and the pubic symphysis of the pelvis.

III) SYNOVIAL JOINTS ( joints in which the articulating surfaces are separated by a fluid containing joint cavity, allowing for freedom of movement so that all synovial joints are diarthroses and includes all the joints of the limbs and most joints of our body)

a) Synovial joints have five distinguishing features:

1) Opposing bone surfaces are covered with smooth articular (hyaline) cartilage which absorb compression between the bones and prevent them from being crushed.

2) A joint cavity or synovial cavity is a potential space between the bones that contains a small amount of synovial fluid. 

3) The joint cavity is enclosed by a articular (joint) capsule. It has an external layer consists of a fibrous capsule composed of dense irregular connective tissue continuous with the periostea of the articulating bones that strengthens the joint so that the bones cannot be pulled apart.  The inner layer is the synovial membrane composed of loose connective tissue which lines the fibrous capsule internally and all internal joint surfaces that are not hyaline cartilage.

4) Synovial fluid is present in all free spaces within the joint. Synovial fluid enters into the joint cavity from the bloodstream as it is filtered out of the capillaries present in the synovial membrane. Synovial fluid is a very viscous fluid with an "egg white" consistency due to the presence of hyaluronic acid secreted by cells in the synovial membrane.  It becomes thinner and less viscous as it warms during joint activity. Synovial fluid is also found within the articular cartilage  and acts as a lubricant to reduce friction between the cartilages. Synovial fluid seeps back into the articular cartilage and can be released again when the cartilages are compressed, a mechanism called weeping lubrication. Phagocytic cells are also present within the synovial fluid to rid the joint cavity of microbes and cell fragments.

5) Reinforcing ligaments strengthen the synovial joints. The ligaments are either intrinisic or capsular in that they are thickend parts of the fibrous capsules, or they are distinct from the fibrous capsule and are found either outside the capsule (extracapsular ligaments) or deep to it  (intracapsular ligaments).  Extracapsular ligaments are covered with the synovial membrane and therefore do not lie directly within the joint cavity.

***Special features of synovial joints include fatty pads  between the fibrous capsule and the synovial membrane or bone as found in our knee and hip joints while others have discs or wedges of fibrocartilage separating the articular surfaces (articular discs or menisci) and divide the synovial cavity in two. Articular discs improve the fit  between articulating bone ends making the joint more stable and minimizing wear and tera on the joint surfaces. Articular discs are found in the knee and the jaw.

***Bursae and tendon sheaths are found within many synovial joints.  Bursae are flattened fibrous sacks of lubricants that reduce friction between joints by acting like ball bearings.An enlarged bursa or a bunion can form at the base of the big toe swollen from rubbing of a tight or poorly fitting shoe. Bursititis is an inflamation of the bursa within the shoulder joint. A tendon sheath is an elongated bursa that wraps completely around a tendon subjected to friction (like a bun around a hot dog) and acts to reduce friction as the bursa does acting like ball bearings. Bursae and tendon sheaths are typically found within knee, shoulder and elbow joints.

b) Movements allowed by synovial joints include:

1) Gliding movements are the simplest joint movements which involve the sliding of one flat bone surface over another. Gliding movements occur at the intercarpal and intertarsal joints as well as between the articular processes of the vertebrate.

2) Angular movements increase or decrease the angles between two bones and may occur in any plane of the body and include the following:

---flexion: a bending movement that decrease the angle of the joint bringing the articular bones closer together usually occurring along the saggital plane. Examples include bending the head forward on the chest and bending the body  trunk or the knee from a straight to an angled position.

---extension: a reverse of flexion and occurs at the same joints it involves movement along the saggital plane  that increases the angle between the articulating bones, such as straightening a flexed neck, body trunk, elbow, or knee. Hyperextension involves bending the body part (such as the neck) beyond its straight (upright) position.

---Dorsiflexion and Plantar Flexion of the Foot: Lifting the foot so that its superior surface approaches the shin is called dorsiflexion, whereas depressing the foot (pointing the toes) is called plantar flexion . Flexion and extension are terms used for the corresponding movements of the wrist.

---Abduction: movement of a limb away from the midline or median plane of the body, along the frontal plane. Raising the thigh, or arm laterally is an example. Spreading the fingers or toes apart are another example in which case the midline beginning referred to is the longest digit ( the third finger or the second toe). The lateral bending of the trunk away from the body midline in the frontal plane is called lateral flexion, not abduction.

---Adduction: movment of  a limb toward the midline of the body or in the case of the digits toward the midline of the hand or foot.

---Circumduction: movement of a limb so that it describes a cone in space. The distal end of the limb moves in a circle while the point of the cone (shoulder or hip joint for example) is stationary. Examples include a pitcher winding up to throw a ball (circumduction is occurring  with his pitching arm).  This complex movement actually involves flexion, abduction, extension and adduction acting in succession at the hip or shoulder joint.

  3) Rotation is the turning of a bone around its own long axis. It is the only movement allowed between the first two cervical vertebrae and is common at the hip and shoulder joint. Two types of rotation include medial rotation (the anterior surface of the femur moving toward the midline of the body and lateral rotation (the movement of the femur in the opposite direction). 

4) Special movements include...

---Supination (turning backward)  and pronation turning forward) refers to the movements of the radius around the ulna. Rotating the forearm laterally  so that the palm faces anteriorly or superiorly is supination. The hand is supinated when in the anatomical position.  In pronation the forearm is rotated  and the palm faces posteriorly.  Pronation moves the distal end of the radius across the ulna so that the two bones form an X. A basketball player pronates his or her forearm to dribble  the ball.

---Inversion and Eversion are special movements of the foot. In inversion, the sole of the foot turns medially and in eversion the sole of the foot faces laterally.

---Protraction and Retraction consists of non angular anterior (protraction)  and posterior (retraction) movements in a transverse plane.  The mandible is protracted when you jut out your jaw and retracted when you move it back to its original position.

---Elevation and Depression. Elevation occurs when a body part is lifted superiorly (the scapulae is elevated when you shrug your shoulder), and depression occurs when an elevated part is moved inferiorly. During chewing, the mandible is alternately elevated and depressed.

---Opposition  is the movement of a body part opposing the movement of another body part. The opposing thumb of humans is an example involving the movement to occur between the saddle joint between metacarpal 1 and the carpals.  Touching your thumb to the tips of your finger is an example

c) Types of Synovial Joints:

1) Plane Joints involve joints in which the articular surfaces are flat and allow only short or gliding movements. Examples include the intercarpal and the intertarsal joints, and the joints between the vertebral articular processes. Gliding joints are the only examples of nonaxial joints  (meaning they do not rotate around any axis. Only gliding joints are nonaxial.

2) Hinge joints involves motion along a single plane, resembles that of a mechanical hinge, and permits flexion and extension only. Examples include bending and straightening the elbow, along with the inter phalangeal joints of the fingers and toes.

3) Pivot joints occurs when the rounded end of one bone protrudes into "sleeve" or ring of another.  The only movement allowed is uniaxial rotation (movement in one plane) of one bone around its own axis. An example is the joint between the atlas and dens of the axis which allows you to move your head from side to side to indicate "no". Another example includes the proximal radioulnar joint where the head of the radius rotates within a ringlike ligament secured to the ulna.

4) Condyloid joints or ellipsoidal joints occur when thte oval articular surface of one bone fits into a complementary depression in another. Both articular surfaces are oval and allows all angular motions (flexion, extension, abduction, adduction) and are considered to be biaxial (movement in two planes). Typical condyloid joints include the radiocarpal or wrist joints and knuckle joints or metacarpophalangeal joints.

5) Saddle joints include joints in which one has a convex surface and the other a concave surface. The carpometacarpal joints of the thumb, and movements allowed by these joints are shown when you twiddle your thumbs.