a&p - bones bones

axial skeleton

• skull

• hyoid

• vertebrae

• ribs and sternum

appendicular system

• clavicle and scapula - pectoral girdle

• upper limb

• os coxae - pelvic girdle

• lower limb

role of cranial bones

• protect brain

• attachment site for head/neck muscles

• intramembranous ossification is how its formed

facial bone role

• form the framework of face

• hold the teeth

• anchor muscles of the face

sutures

• immobile joints

• filled with dense connective tissue + ECF then calcifies over time

• wide and flexible during infancy

  • easier passage through birth canal

  • allows for brain growth

• interdigitate as cranial bones grow

• fuse over time

• four levels from open to complete obliteration

vertebral column numbers

26 vertebrae

• 7 cervical

• 12 thoracic

• 5 lumbar

• 5 sacral (will fuse into 1)

• 4 coccyx (will fuse into 1)

function of spinous/transverse processes

muscle or ligament attachment sites

atlas role

atlanto-occipital joint → head flexion/extension

axis role

atlas-axis joint → head L/R rotation

costal facets

articulate with ribs

• feature unique to thoracic vertebrae

• superior/inferior and transverse forms of this

intervertebral discs

• fibrocartilage with gel like center - tough and durable

• join vertebrae into column

• allow for mobility

• cushion and absorb force

true ribs

ribs 1-7

• attach to sternum by costal cartilages

false ribs

ribs 8-10

• attached via shared cartilage

floating ribs

ribs 11 and 12

thoracic cage

• protect underlying organs

• attachment site for respiratory muscles

• all ribs attach to thoracic vertebrae posteriorly

rib structure

• body/shaft

• head and tubercle

• angle

• costal groove

how does the clavicle form?

only long bone that forms through intramembranous ossification

scapula

• part of pectoral girdle

• acromion articulates with clavicle

• glenoid fossa articulates iwth humerous

• other fossae - muscle attachment sites

humerus bone

• articulations

  • proximal - scapula

  • distal - radius, ulna

• fossae - articulate with ulna

• tubercles/tuberosities - muscle attachments

ulna + radius

• has interosseous membrane of dense connective tissue allowing for rotation while maintaining spatial relationships

• ulna has the olecranon forms majority of elbow

• radius has a head that allows for rotation

• styloid processes - ligament attachment sites

What is another name for the os coxae?

Innominate bones (also called pelvic or hip bones)

How do the three bones of the os coxa develop?

Each develops from its own ossification center in the fetus, and they're fused into one bone by birth

What does the ischial tuberosity do?

It holds your body weight when you're sitting

what is the pubic symphysis

• The anterior joint where the two pubic bones meet

• It's a cartilaginous joint

• Pregnancy hormones make it more flexible to help with childbirth

what is the acetabulum

The socket on the lateral os coxa where the head of the femur fits, forming the hip joint. It's where the ilium, ischium, and pubis all come together

how does the female pelvis differ from the male pelvis?

It's wider and shallower, with a wider, more oval pelvic outlet, a sacrum tilted more posteriorly, and a larger subpubic angle. These differences make childbirth easier, and forensic scientists use them to estimate the sex of skeletal remains

what forms the pelvic girdle

The two os coxae plus the sacrum. The os coxae meet anteriorly at the pubic symphysis and connect posteriorly with the sacrum

femur key facts

• It's the longest and strongest bone in the body

• It articulates proximally with the acetabulum and distally with the tibia and patella

Why does the femur have such large trochanters and epicondyles?

Wolff's law: the big thigh muscles (quadriceps in front, hamstrings in back) put a lot of stress on the bone, so more bone is deposited at their attachment sites

where does the femur often fracture and why?

At the neck. The neck carries the weight of the whole upper body and is filled with less dense spongy (cancellous) bone

what type of bone is the patella and what are its key facts?

• the largest sesamoid bone in the body

• forms inside a tendon (the quadriceps femoris tendon)

• Its base is superior and its apex is inferior

• It's cartilage at birth and ossifies around ages 3–6, which is why people say babies don't have kneecaps

• It's anchored to the rectus femoris proximally and the tibia distally, but it is NOT attached to the femur

What bone pattern do the upper and lower limbs share?

One bone in the upper segment (humerus or femur), then two bones in the lower segment (radius and ulna, or tibia and fibula)

What are the key facts about the tibia?

• It's the medial leg bone, and it bears weight. It articulates proximally with the femur, patella, and head of the fibula, and distally with the fibula and talus

• Its medial surface sits just under the skin, and that part is your shin

fibula key facts

• It's the lateral leg bone

• It is NOT weight bearing because the femur doesn't touch it. Its job is to stabilize the ankle. It articulates with the tibia at both ends and with the talus

what do the medial and lateral malleoli do?

• The medial malleolus (on the tibia) and the lateral malleolus (on the fibula) sit on either side of the talus to form the ankle joint

• They're the bumps you can feel on either side of your ankle

what connects the tibia and fibula

The interosseous membrane, just like the one between the radius and ulna

how many carpals are there, and which one do you need to know

There are 8, in two rows of 4. You only need to know the pisiform and the scaphoid

what is the pisiform

a sesamoid bone at the base of the pinky, inside the tendon of the flexor carpi ulnaris muscle. It's cartilage at birth and ossifies around age 12

what is the scaphoid known for?

It's the most frequently fractured carpal. It usually breaks from a FOOSH injury (fall on outstretched hand), when the end of the radius bangs into it

which tarsals do you need to know?

• The calcaneus and the talus

• Purpose of having many small bones in the wrist and ankle is mobility

what are the key facts about the calcaneus

• It's the largest tarsal and forms most of the heel

• It's where the Achilles tendon (from the calf muscles) attaches

how is body weight carried through the ankle and foot?

Weight goes from the tibia to the talus, then from the talus to the calcaneus. The talus and calcaneus hold most of your body weight when standing

key facts about metacarpals and metatarsals

• There are 5 of each, numbered I–V in Roman numerals to match the digits

• They articulate proximally with the carpals or tarsals and distally with the phalanges

• The 1st metatarsal (big toe, medial side) is the largest and most robust, and it helps the talus and calcaneus bear weight

how many phalanges does each digit have?

Most digits have 3: proximal, middle, and distal. The thumb and big toe have only 2: proximal and distal

what is a joint and what are its two functions

A place where two or more bones meet, also called an articulation. Joints provide support and movement

what are the three structural classes of joints?

• Fibrous (immobile)

• Cartilaginous (slightly mobile)

• Synovial (freely mobile)

Fibrous joints

• Bones joined by dense connective tissue

• Its collagen fibers give tensile strength (resistance to stretch), which holds the bones tightly together

• Immobile

• Examples are sutures and teeth in the mandible and maxilla

Why are cranial sutures flexible in babies?

They haven't fully ossified yet. This lets the head pass through the birth canal and leaves room for the brain to grow after birth. It's also why a baby's skull can flatten if they lie on their back too much

cartilaginous joints

• Bones joined by hyaline cartilage or fibrocartilage

• They're slightly mobile but still stable enough to hold body weight

• Examples are the pubic symphysis and the costochondral joints (where the ribs meet the sternum

synovial joints

• Joints with a joint cavity enclosed by a joint capsule, with articular cartilage on the bone ends

• They're freely mobile and make up most joints in the body

• They're the most structurally complex type of joint, and they allow locomotion

what are the two layers of the joint capsule

• fibrous outer layer

• synovial deeper layer

fibrous layer of joint capsule

• outer layer made of dense connective tissue

• blends into the periosteum, ligaments, and tendens

synovial layer of joint capsule

• inner layer

• secretes synovial fluid

synovial fluid

liquid that fills joint cavity and lubricates the joint, letting the bones glide past with almost no friction

what do ligaments do in the synovial joint?

• strengthen the joint

• They're made of dense regular connective tissue joining the bones together

what is articular cartilage

• Hyaline cartilage covering the bone ends. It cushions the joint

• It's left over from the cartilage model the bone developed from

• It's smooth and slippery, so it helps movement and absorbs force

what joints are most likely to get injured?

The more mobile a joint is, the more likely it is to be injured

flexion

Decreasing the angle of a joint

For example, bending the elbow brings the forearm toward the arm, and bending the knee brings the back of the leg toward the back of the thigh

extension

Straightening a joint back to the neutral position. In anatomical position, joints are extended but not hyperextended

hyperextension

Extending a joint past neutral, like lifting your leg behind you at the hip or tilting your head back. Only a small number of joints can hyperextend

abduction

moves a limb away from the midline in the frontal plane - aliens abducting you

adduction

moves a limb back to the midline - hyperadduction is moving past the midline like crossing your legs

How do abduction and adduction work in the fingers?

The reference point is the middle finger, not the body midline. Spreading the fingers is abduction, bringing them together is adduction, and crossing them is hyperadduction. This movement happens where the proximal phalanges meet the metacarpals.

pronation and supination

A special kind of rotation at the elbow, done by the proximal radioulnar joint. In supination, the radius is parallel to the ulna. In pronation, the radius crosses over the ulna

What are inversion and eversion?

Inversion tilts the sole of the foot to face medially. Eversion tilts it to face laterally. These happen at the intertarsal joints.

circumduction

Moving a joint in a full circle. Some ball-and-socket joints can do this

atlantoaxial joint movement

It's the joint between C1 (atlas) and C2 (axis), a pivot joint that rotates the head left and right. The dens of C2 rests against the anterior arch of C1, held in place by the transverse ligament

what does the atlanto-occipital joint do?

It's the joint between C1 and the occipital condyles of the skull, and it allows flexion and extension of the head (nodding)

What is range of motion (ROM), and what determines it?

ROM is the number of degrees a joint can move through. It depends on three things: the shape of the articular surfaces, the structure and tension of the ligaments and joint capsule, and the action of the muscles and tendons

what is a plane (gliding) joint?

• Flat surfaces that slide over each other, allowing multidirectional movement

• The movement is often limited by soft tissue

• Examples are the carpals, tarsals, and vertebral articular processes

• The wrist moves more than the ankle because of differences in soft tissue

hinge joint

A convex end of one bone fits into a C-shaped depression in another. It allows only flexion and extension, in one plane

• Examples are the elbow, the interphalangeal joints (knuckles), and the ankle

pivot joint

• A rounded part of one bone is partially enclosed by a ligament and rotates inside it

• ie atlantoaxial joint and the proximal radioulnar joint

ball and socket joint

A round head fits into a cup-shaped depression. Unlike a hinge, both surfaces are spherical. It allows multidirectional movement, the greatest range of motion of any joint: flexion and extension, abduction and adduction, medial and lateral rotation, and circumduction

• shoulder and hip

shoulder joint

Another name is the glenohumeral joint. It's a ball-and-socket joint, the most mobile type of joint

shoulder joint anatomy

• Formed between the glenoid fossa (scapula) and the head of the humerus

• The glenoid fossa is a very shallow depression, and the glenoid labrum is a ring of cartilage that deepens it

Why does the shoulder dislocate so easily?

It's mainly supported by muscles, and the shallow glenoid fossa allows little bony contact

shoulder discloation

• Detachment of the humeral head from the glenoid fossa, usually from a superior blow. Inferior displacement is most common

• symptoms: Visible deformity, intense pain, and inability to move the joint

• Surrounding soft tissue is frequently damaged too, so recovery will likely include muscle rehab

• repeated dislocations are likely because of the original injury’s strain

elbow

Formed among the humerus, radius, and ulna. Made up of the humeroulnar, humeroradial, and radioulnar joints

Elbow hinge joint

the humeroulnar and humeroradial joints together form a hinge joint, which produces flexion and extension

elbow pivot joint

the radioulnar joint is a pivot joint. The head of the radius sits in the radial notch of the ulna, held by the annular ligament

when the forearm is supinated what does it look like?

Radius is parallel to the ulna, and the palm faces anteriorly

when the forearm is pronated what does it look like?

Radius is crossed over the ulna, and the palm faces posteriorly.

shoulder v hip

Both are ball-and-socket joints. The shoulder is built for mobility, and the hip is built for stability

shoulder features

Shallow glenoid fossa and loose muscular connections. Less bony contact means more movement

hip features

Deep acetabulum and strong ligament connections, which means less mobility.

what is another word for the hip joint?

coxial joint - a ball and socket one

hip anatomy

Formed between the head of the femur and the acetabulum. The acetabular labrum deepens the acetabulum, and the ligamentum teres carries an artery to the head of the femur

why are hip dislocations rare?

The hip is tightly bound by ligaments. A force strong enough to dislocate it would normally cause a fracture instead

knee

Formed between the femur and tibia. It mainly acts like a hinge joint and is supported by several ligaments

knee movement

It can rotate slightly when flexed and can "lock" when fully extended

why does the knee lock

So the bones hold more of the weight instead of the muscles

menisci

Cushion and stabilize the knee

knee ligaments

Medial and lateral collateral ligaments, anterior cruciate ligament (ACL), and posterior cruciate ligament (PCL)

role of medial and lateral collateral ligaments role

Prevent lateral deviation (stop lateral movement)

ACL role

prevents hyperextension

PCL role

Prevents posterior displacement of the tibia.

ankle joint

Another name is the talocrural joint. It's formed among the tibia, fibula, and talus

ankle hinge joint

The talotibial and talofibular joints together form a hinge joint