Anatomy Flashcards

Bone marrow
Terms Definitions
Gross Anatomy Basics: Axial
figure 7.1
a. the long axis of the body
b. protect, support, carry
c. consists of: skull, vertebral column, rib cage
Gross Anatomy Basics: Appendicular
a. everything else
b. movement, manipulation
c. consists of: upper and lower limbs, girdles (attach axial and appen)
Bones Classified by Shape: Long
figure 6.2

• longer than wide; elongated
• limb bones
Bones Classified by Shape: Short
• equally broad and long
o cube-like or roundish
• wrist and ankle bones
• patella
Bones Classified by Shape: Flat
• thin, flattened, usually curved
• sternum
• ribs
• skull bones
Bones Classified by Shape: Irregular
• none of the above
• vertebrae
• facial bones
Functions of the Skeleton: Protection
• skull protects the brain
• vertebrae protect the spinal cord
• rib cage protects thoracic viscera
o heart & lungs
Functions of the Skeleton: Support
a. bone
• pelvis supports lower abdominal viscera (bladder, lower colon)
• legs bear weight
b. cartilage
Functions of the Skeleton: Movement
• skeletal muscles attached by tendons
• joint
o formed where 2 or more bones come together
o also called “atriculations”
Functions of the Skeleton: Mineral Storage
• stored in matrix
• calcium and phosphate
Functions of the Skeleton: Blood Cell Production (hematopoiesis)
• produced in marrow cavities of certain bones
• “red marrow”
• Triglyceride storage
Skeletal Tissue: Bone
1. Bone
a. Compact
• dense
• found on outer surface of all bones
b. Spongy
• lighter
• found inside most bones
Skeletal Tissue: Hyaline Cartilage
a. Hyaline cartilage
figure 4.8g
1) slightly flexible, durable support
2) locations within skeleton
• embryonic skeleton, growth plate, costal cartilage, articular cartilage, nose, trachea, larynx
Skeletal Tissue: Elastic Cartilage
figure 4.8h
1) flexible, retains shape with repeated bending
2) locations within skeleton
• external ear, epiglottis (flap of skin in back of throat (swallowing))
Skeletal Tissue: Fibrocartilage
figure 4.8i
1) highly compressible; great tensile strength
2) locations within skeleton
• intervertebral disks
• articular disks
Skeletal Tissue: Other connective tissue
a. blood (red marrow)
b. adipose (yellow marrow)
c. dense irregular connective tissue (periosteum)
Bone Tissue Histology: Chemical Composition of Matrix: Organic: proteins
a. 1/3 of bone’s matrix
b. proteins
• prtoeoglycans & glycoproteins
o increase water content of bones
• collagen
Bone Tissue Histology: Chemical Composition of Matrix: Organic: resilience
• gives tensile strength
• ability to resist stretch and twist
Bone Tissue Histology: Chemical Composition of Matrix: Organic: "sacrificial bonds"
• collagen proteins have bonds between them
• with force, these bonds readily break
o dissipating energy
• like a car bumper on impact
• can re-establish bonds after impact
Bone Tissue Histology: Chemical Composition of Matrix: Inorganic
• 2/3 of bone’s matrix
• calcium phosphate salts
• hardness
Bone Tissue Histology: Cells: Osteogenic Cells
• stem cells for the osteoblasts
Bone Tissue Histology: Cells: Osteoblasts Cells
• lay down new bone
• primarily on the surfaces of the bone
Bone Tissue Histology: Cells: Osteocytes Cells
• maintain the matrix
• former osteoblasts now surrounded by bone matrix
Bone Tissue Histology: Cells: Osteoclasts Cells
• break down bone for remodeling
• primarily on the surfaces of bone
Bone Tissue Histology: Compact Bone
1. Dense, layered bone
2. Found on outside surface of all bones
3. Osteon (Haversian system)
a. cylinder of bone that is the structural unit of compact bone
Bone Tissue Histology: Compact Bone: Central Canal
• parallel to bone axis
• lined with endosteum
• contains blood vessels and nerves
Bone Tissue Histology: Compact Bone: Lamellae form concentric layers of bone
1) collagen fibers
2) calcium phosphate crystals
• align with the collagen fibers
• (run parallel but in opposite directions and that will add strength in one direction)
Bone Tissue Histology: Compact Bone: Osteocytes
1) located in lacunae between the lamellae
2) the lacunae are connected to each other via canaliculi
•the osteocytes connect to each other (gap junctions)
Bone Tissue Histology: Compact Bone: interstitial lamellae
• located in spaces between osteons
• (think inter=between)
Bone Tissue Histology: Compact Bone: circumferential lamellae
• layers along the outer circumference of the bone
Bone Tissue Histology: Compact Bone: Perforating canal (Volkmann’s canal)
• perpendicular to axis of bone
• bring blood vessels and nerves from outside of bone to osteons
Bone Tissue Histology: Spongy Bone: Purpose
• lighter than compact bone
o more weight to move if bones entirely compact bone
• shock absorption
• if present, always interior
Bone Tissue Histology: Spongy Bone: trabeculae
• interconnecting rods or plates of bones
• oriented in direction of stress/force
Bone Tissue Histology: Spongy Bone: no osteons
a. irregular lamellae arranged concentrically in trabeculae
b. osteocytes in lacunae between layers
c. no central blood vessel
•osteocytes connected to each other via canaliculi
•nutrients gained through canaliculi
Typical Bone Structure: Anatomy of a Long Bone: Diaphysis
o collar of compact bone
o medullary cavity (hollow core) or fat (yellow marrow)
Typical Bone Structure: Anatomy of a Long Bone: Epiphyses (sing., epiphysis)
• ends
• structure
o shell of compact bone
o interior of spongy bone
Typical Bone Structure: Anatomy of a Long Bone: Growth Plate / Epiphyseal Line
a. located in long bones between diaphysis and epiphysis
b. “growth plate”; allows lengthening of bone; hyaline cartilage
c. epiphyseal line
• cone tissue replacement of growth plate
Typical Bone Structure: Anatomy of a Long Bone: Periosteum
a. connective tissue covering outside of bone
b. structure
1) outer layer
• dense, irregular connective tissue
• entry point for blood vessels and nerves
• attachment point for tendons and ligaments
2) inner layer
• osteoblasts-form bone
• osteoclasts-break bone down
Typical Bone Structure: Anatomy of a Long Bone: Endosteum
• connective tissue lining inside of bone
• contains osteoblasts and osteoclasts
Typical Bone Structure: Anatomy of a Long Bone: Articular Cartilage
• hyaline cartilage cap
• flexible, durable support
• located at joint
Typical Bone Structure: Anatomy of a Long Bone: Hematopoietic tissue (red marrow)
a. newborn
• found in medullary cavities and spongy bone
b. adult
• spongy bone of flat and irregular bones
o sternum, pelvic bones
• medullary cavity of epiphysis
o only in head of femur and humerus
Typical Bone Structure: Basic Anatomy of Short, Irregular, and Flat bones
figure 6.5
• periosteum
• compact bone
• spongy bone and endosteum
• compact bone
• periosteum
Bone Development (Osteogenesis): Intramembranous Ossification: Overview
a. occurs during fetal life in the mandible, clavicle and cranial bones (frontal, parietal occipital, temporal)
b. bone grows within fibrous membranes
c. begins in middle of bone, moves towards edges
Bone Development (Osteogenesis): Intramembranous Ossification: process
a. clustered mesenchymal cells secrete matrix of collagen fibers
b. formation of ossification center
1) crystallization of calcium salts
2) some mesenchymal cells differentiate into osteoblasts
c. osteoblasts become enclosed in matrix, become osteocytes
d. outward growth of bone matrix (osteoid) not uniform, but forms trabeculae
• interconnected network of trabeculae
• trabeculae thicken over time
• mesenchyme outside matrix develops into periosteum
e at edge of bone structure, compact bone tissue produced
f. red marrow formed within spaces of spongy bone
Bone Development (Osteogenesis): Endochondral Ossification: Overview
1. begins during fetal life
2. bone replaces hyaline cartilage models of most bones
• most bones below the base of the skull this way
Bone Development (Osteogenesis): Endochondral Ossification: Primary ossification: ossification of shaft
1) 1° ossification center: formation of calcified cartilage
• interior chondrocytes enlarge
• matrix becomes calcified
2) formation of bone collar (calcifying of cartilage)
• perichondrium cells become osteoblasts
• formation of compact bone at surface of cartilage (the bone collar)
3) hollowing of cartilage shaft to form medullary cavity
• chondrocytes die, leaving the lacunae within calcified matrix
4) spongy bone formation along edge of medullary cavity
a) osteoblasts from periosteum move to interior of bone
• replace calcified cartilage into spongy bone
b) osteoclasts from periosteum move to interior of bone
• hollow out medullary cavity
• other cells form red bone marrow within cavity
Bone Development (Osteogenesis): Endochondral Ossification:Secondary ossification: ossification at one or both ends
1) occurs after birth in the epiphyses
2) process similar to primary ossification, except:
a) no medullary cavity
b) instead, spongy bone retained
Comparison of Intramembranous and Endochondral Ossification
1. original matrix
a. intramembranous ossification
• within the mesenchyme
• doesn’t replace, just grows within
b. endochondral ossification
• hyaline cartilage
• replaced
2. direction
a. intramembranous ossification
• is simple
• inside → out
b. endochondral ossification
• is complicated
• primarily is outside → in
Developmental Growth: Appositional Growth
a. osteons added to outer surface by osteoblasts of periosteum
b. bone destroyed on inner surface by osteoclasts of endosteum
Developmental Growth: Elongation of long bones
a. epiphyseal plates
• growth only occurs here
• cartilage proliferation pushes outward
b. bone formation similar to original ossification
• “older” cartilage near bone is calcified, chondrocytes die
• osteoblasts form bone matrix
• osteocytes expand medullary cavity
Developmental Growth: Hormonal regulation
a. childhood
1) growth hormone
• from anterior pituitary
• simulates cartilage growth in epiphyseal plate
2) thyroid hormones
• from thyroid
• regulate growth hormone actions
b. adolescence
1) steroid hormones
• male, primarily testosterone
• female, primarily estrogen
2) actions
• initially stimulate chondrocytes
• sex-specific skeletal characteristics
o thicker bones in males
o “opening” of pelvis in females
3) cessation of growth
a) ossification (“closing”) of epiphyseal plates
b) hormone levels do not decrease
Developmental Growth: X-rays
• can tell If growth is still possible by presence of growth place
• cartilage does not show up in x-rays
• dangerous break if it occurs at growth plate
o can prevent further bone growth
o difficult to detect a break at growth plate-both appear as line in x-ray
Bone Homeostasis: Remodeling: Continuous
• response to functional requirements
o muscle tone
o impact
o lifting/compression forces
• must occur as bone lengthens
• addition and subtraction of bone matrix generally balanced in healthy adults
Bone Homeostasis: Process
a. occurs both at periosteal and endosteal surfaces
b. osteoblasts
• deposit bone matrix
• thickens bone surface
c. osteoclasts (think “cut”)
• degrades organic matrix
• secrete lysosomal enzymes
• secrete acid
Bone Homeostasis: Hormonal control
a. Regulation of blood calcium
1) importance
• nerve activity
• muscle activity
2) bone acts as calcium “bank”
• movement of calcium from/to bank
b. Increase in blood calcium
• secretion of calcitonin
• calcitonin stimulates activity of osteoblasts
• calcitonin inhibits activity of osteoclasts
c. Decrease in blood calcium
• secretion of parathyroid hormone (PTH)
• PTH stimulates activity of osteoclasts
• PTH inhibits activity of osteoblasts
d. negative feedback
• high calcium→ stimulate release of calcitonin & inhibit release of PTH→ low calcium → inhibit release of calcitonin & stimulate release of PTH
Bone Homeostasis: Effects of mechanical stress
a. bone thickest where it experiences most stress
• usually center
• point of muscle (tendon) attachment
• in curved bones, area of curve
b. stress generally exerted by muscles
• weight-lifting increases bone mass
• exercises should have some impact
Bone Homeostasis: Repair of Fractures
1. Break
2. Hematoma
3. Fibrocartilaginous Callus Formation
• clot broken down by cells transported in by new blood vessels
• callus formed between ends of broken bones
• fibrobalsts produced collagen
• chondrocytes secrete cartilage matrix
4. Bony Callus Formation
• osteoclasts and osteoclasts convert internal callus to spongy bone
5. Remodeling of bone
• spongy bone→compact bone
• restoration to original form (typically takes about 2 months)
Homeostatic Imbalances of Bone: Osteoporosis
1. Bone matrix degraded faster than laid down
• matrix composition still normal
2. Increased incidence of fractures
• vertebrae
• neck of femur
3. Post-menopausal women
• reduced estrogen results in reduced bone matrix formation
4. Treatment
• estrogen supplements
• calcium and citamin D
• exercise
Homeostatic Imbalances of Bone: Osteomalacia (“soft bones”)
1. Bone matrix is mineral-deficient
• weaker
• cones generally deformed, ay break
2. Rickets in children
• usually vitamin D deficiency
• permanent deformities
Joint Basics: Functions
• While they are the Weakest point of skeleton, they do absorb shock and injury, protects the bones
• Mobility
• Hold bones together
Synarthrosis Joints
• Immovable
• Primarily between axial bones
ex: sutures between bones in skull
Amphiarthrosis Joints
• Slightly movable
• Primarily between axial bones
ex: articulation between tibia and fibula
Diarthrosis Joints
• Freely movable
• Most joints in body, especially limbs
• (Probably what most commonly comes to mind when we think of “joint”/Contains lubricated joint cavity)
Structural Classification: Criteria for Joints
• Connective material binding the bones together
• Presence/absence of joint cavity
Structural Classification: Fibrous Joints: description
•Bones held together by fibrous connective tissue
•No joint cavity
•Synarthrosis and amphiarthrosis
Structural Classification: Fibrous Joints: Suture
•Location: skull
o“seams” of bones
•Short fibers
o Fibers are longer during childhood, allowing growth of bones
• immovable
Fibrous Joints: Syndesmosis (pl., syndesmoses)
longer fibers; ligaments
2) slightly movable; some joints have more mobility than others
example: tibia and fibula→has little “give” but not very movable
example: radius and ulna→freely moves
Fibrous Joints: Gomphosis (pl., gomphoses)
• Pegs held in sockets
• Collagenous connective tissue
• Mostly immovable
o Ex: teeth within mandible and maxilla
Cartilaginous Joints: description
•joints held together by cartilage
•(there are two types of Cartilaginous Joints)
Cartilaginous Joints: Synchondrosis (pl., synchondroses)
1) hyaline cartilage
2) many are replaced by bone (but not all are)
example: epiphyseal plate between epiphysis and shaft of long bone
Don’t normally think of this as a joint!!!
Note: this is also immovable
example: manubrosternal synchondrosis
Manubrium and body of sternum
Slightly movable– helps thorax to move during inspiration and expiration
Cartilaginous Joints: Symphysis (pl., symphyses)
• allows restricted movement
• can act as shock absorber
2) examples: pubis symphasis
Synovial Joints: description
• most common
• lots of movement
• joint cavity present
• lined with lubricating synovial membrane
Synovial Joints: Types: planes (gliding)
• surfaces are flat, allow short non-axial movement, in between carpals (hand)
Synovial Joints: Types: hinge
• cylindrical end of bone (elbow joint) motion along single plane
Synovial Joints: Types: pivot
• proximal radioulnar joint (shake your head no) only una-axial movement
Synovial Joints: Types: condyloid (ellipsoid)
• condyloid joint (metacarpophalangial joint) further out on fingers (allow angular)
Synovial Joints: Types: saddle
• carpometacarpal join of thumb, both surfaces have concave and convex surface (twiddling thumbs)
Synovial Joints: Types: ball-and-socket
• spherical, shoulder joint
Types of Movements: Cause
• Muscle contraction
• Generally, the further out a muscle/bone is, the more movement is possible
Types of Movements: According to Axis: nonaxial
slipping or gliding movement
example: hands and feet and vertebrae
Types of Movements: According to Axis: uniaxial
movement in one plate
examples. In between fingers and toes (interphalangal), and atlantoaxial joint
Types of Movements: According to Axis: biaxial
movement in 2 planes
examples: wrist: between radius and carpals, can move side to side (minor) or front to
Types of Movements: According to Axis: multiaxial
a. movement in all 3 planes of space, around several axes
b. example: shoulder and hip: coxal joint
Angular movements
• Angular
• Circular
• Special
Flexion: bending
• Decreasing bone angle
o Generally in the anterior or ventral direction
o Exception: knee moves leg in posterior direction
Flexion: plantar flexion
• Movement of foot toward plantar surface
• Plantar: sole of foot
• “tiptoe”
• By definition, all leg muscles that pass behind ankles and insert on foot
Flexion: dorsiflexion
• Movement of foot towards the anterior crest of tibia (shin)
• Walking on heels
• All leg muscles that pass in front of ankles and insert on foot
Extension: straightening
• Increasing bone angle
• Generally in posterior or dorsal direction
Extension: hyperextension
• Movement past a 180o joint
• Demonstrate with shoulder joint
• Have students demonstrate hyperextension of head/neck
Extension: Abduction
Movement toward the midline (like “add”ing them together)
Circular movements: Rotation (general)
turning of structure around its long axis
Circular movements: medial rotation
• Turning into the middle
• Demonstrate using the shoulder joint
Circular movements: lateral rotation
• Turning toward the “outside”
• Demonstrate using the shoulder joint
• Also works with hip joint
Circular movements: upward rotation
• Specifically refers to movement of the scapula
• Defined according to movement of scapula’s lateral edge
• Result: lateral spine moves up, medial spine moves down
o Movement will allow full abduction of shoulder
Circular movements: downward rotation
• Specifically refers to movement of the scapula
• Defined according to movement of scapula’s lateral edge
• Result: lateral spine moves down, medial spine moves up
Circular movements: Pronation
• Only used to describe specific action of forearm
• Rotation of palm to face down
o Prone: lying face down
o Demonstrate
o Pronation of foot is an entirely different phenomenon; it refers to the “rolling inward” motion as the foot steps down and pressure transfers from heel to metatarsus. This helps to absorb the energy from impact. Over-pronation of the foot “rolls” the foot too much
Circular movements: Supination
• Only used to describe specific action of forearm
• Rotation of palm to face up
o Supine: lying face up
o Demonstrate: have students hold out left arm in pronated position, switch to supined position and them have them touch elbow; repeat pronation and supination. Note that the ulna does not move– only radius!
Circular movements: Circumduction
• Combination of flexion, extension, abduction and adduction
o Forming a cone
• Demonstrate at shoulder
o Can also be done with hip and thumb
• Lifting a body part superiorly
• Demonstrate scapular elevation
• Lowering a body part inferiorly
• Have students demonstrate scapular elevation and depression
• Have the students demonstrate mandibular depression and elevation
• Moving a body part anteriorly
• Demonstrate scapular protraction
• Moving a body part posteriorly
• Have the students demonstrate scapular protraction and retraction
• Have the students demonstrate mandibular protraction and retraction
• Only used to describe specific action of the thumb and another finger
• Thumb and another finger brought together
• Only used to describe specific action of the thumb and another finger
• Thumb and finger brought back to original position
• Have students hold up right hand and demonstrate opposition, then reposition
• Only used to describe specific action of the foot
• Plantar surface turned medially
• Only used to describe specific action of the foot
• Plantar surface turned laterally
Shoulder Joint (glenohumeral joint)
1. most flexible, mobile joint in body
2. strength and stability sacrificed
a. glenoid fossa of scapula
1) shallow articular socket
2) glenoid labrum
• Fibrocartilage ring around edge of glenoid fossa
• Slightly deepens socket
• Doesn’t increase stability
b. dislocation
c. shoulder separation
Shoulder joint: Acromioclavicular joint
Torn ligament causes should to sag
Shoulder joint: ligaments
a. increase stability
b. primarily located on the anterior and superior joint surface
• Leaves shoulder vulnerable from inferior direction
Shoulder joint: coracohumeral ligament
anterior and superior
Shoulder joint: glenohumeral ligament
• anterior
• three ligaments
• weak, may even be absent
Shoulder joint: muscle tendons
a. greatly increase stability
b. tendon of biceps brachii (long head)
• passes through articular capsule (intertubercular groove)
• attaches to upper rim of glenoid fossa
• pulls humerus against glenoid fossa of scapula
c. tendons of “rotator cuff” muscles
• tendons insert onto superior portion of humerus
• humerus pulled superiorly and medially against scapula
• vigorous circumduction can result in injury
Elbow Joint
1. two joints
2. humerus-ulna
a. main joint
• extension and flexion
• hinge joint
b. strong ligaments restrict side-to-side movements
3. ulna-radius
• not truly the elbow joint
• rotational movement
Hip Joint (coxal joint)
1. fairly flexible and mobile
2. greater stability than shoulder
a. structure of joint
1) deep articular socket formed by acetabulum
2) acetabular labrum
3) iliofemoral ligament
• anterior surface
• support body weight when standing in relaxed position (very strong!)
b. muscular stabilization
• not as important as joint structure
Synovial Joints: Synovial Fluid
1. located in joint cavity
2. production and circulation
a. produced by synovial membrane
1) plasma
2) hyaluronic acid
• Produced by synovial fluid
• Hyaluronic acid increases viscosity
b. held within cartilage matrix reservoir
c. squeezed out of cartilage when cartilage is compressed during movement
d. reabsorbed by synovial membrane after movement
Synovial Joints: Synovial Fluid: function
Weeping Lubrication
a. provides nutrients for chondrocytes
• Cartilage is non-vascular
• Synovial fluid absorbed by hyaline cartilage matrix
b. compression releases synovial fluid for lubrication
c. after compression, new synovial fluid pulled into cartilage
Effects of exercise: decreases viscosity of synovial fluid
• More easily absorbed by cartilage
• Cartilage actually thicker, more effective cushion
• Benefits of warm-up period before exercise
Effects of exercise: increases synovial fluid circulation
• At rest, very little new synovial fluid enters and exits cartilage matrix
• Exercise keeps cartilage healthy!
Effects of exercise: excessive stress
• Over time, cartilage can break down
• Friction develop as bone contacts bone
General Structure of a Synovial Joint: Joint Capsule (Articular Capsule): fibrous capsule
1) tough, outer layer of joint capsule
• Dense irregular connective tissue
• Lots of collagen
• Contains blood vessels and nerves
2) continuous with fibrous layer of periosteum
3) portions may thicken to form ligaments
4) strengthens joint
• Holds the bones together
General Structure of a Synovial Joint: Joint Capsule (Articular Capsule): synovial membrane
1) inner layer of joint capsule
• Areolar connective tissue
• May have some folds to increase surface area
• May be separated from fibrous capsule by areolar tissue or adipose
2) lines joint cavity except over articular cartilage
3) produces synovial fluid
• Filtered from blood
• Fills the synovial joint cavity
Articular (hyaline) cartilage
a. covers articular surface
• 1-2 mm
• In children, can be 5-7 mm in large joints
b. reduces friction
• Smooth
c. absorbs compression
• Spongy
• Incorporates synovial fluid into its matrix
• Small space compressed
o bones very close together
• Filled with synovial fluid
Reinforcing Ligaments
a. give joint strength and flexibility
• Limit movement
b. intrinsic ligaments
• Continuous with fibrous capsule
o Join and thicken capsule
c. extrinsic ligaments
• Some outside and some inside fibrous capsule
Articular Discs (menisci)
a. pads of fibrocartilage between bone ends
• Extend into joint cavity and form attachments to capsule
• Divide synovial cavity in two
b. Stabilize the joint
• Improve “fit” between the two bone articulating surfaces
c. examples
• Knee and jaw
Bursae and Tendon Sheaths
a. bursa: flattened fibrous sac lined with synovial membrane, contain synovial fluid
• but do not surround a joint-lie near the joint
b. tendon sheath: elongated bursa that wraps around a tendon
c. reduce friction
• found in areas subject to repeated friction with bone (tendon, ligament, muscle, bone)
• separate potentially rubbing surfaces
• inflammation of a bursa
o happens with some repetitive movements
• bunion: an enlarged bursa at base of big toe, typically from rubbing against show
Fatty Pad
• may be found between fibrous membrane and synovial membranes or bone
• cushions
• found in hip and knee joint
Stability: Importance
• joints are used for movement
• needs to allow some movements and disallow others
• failure to regulate movement can result in dislocation
• also a need ( in some joints) to maintain posture
Stability: Articular surfaces
• many shallow
• non-complementary surfaces
b. exception: ball and deep socket joint
Stability: Muscle Tone!!!
b. constant, low level muscle contraction
• keeps tendons under tension
• tendons primarily stabilizing factor of joints
c. stretch of articular capsule and ligaments
• reflex contraction of muscle
• allows stabilization during movement
d. muscle training
1) particularly important in shallow joints
2) forceful or rapid movements
• could easily force joint to move in direction of movement
• need strong muscles holding back in place
3) need to have…balanced muscle strength
Stability: Ligaments
a. the more ligaments in a joint, the stronger it is
b. unfortunately, ligaments can be stretched
• not elastic, do not return to original state
• joint becomes less stable
• if ligaments further stretched, may snap
c. a joint that primarily depends on ligaments will be less stable than other joints
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