Greenstick Fracture

Anatomy lecture notes, Chapter 6

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In 2011, South Carolina photographer Kathleen Robbins spent time documenting the complex histories of cotton farms in the Mississippi Delta in a series entitled In Cotton.

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Types of Muscle Tissue

Skeletal (more direct control, aka voluntary control, striated)

Cardiac (involuntary, striated)

Smooth 

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Major Functions of the Muscular System

Prime mover

Stabilizes skeleton in position: erector spinae

Store and move substances in the body (calcium= skeletal muscle contraction, sugar, oxygen (which is a macronutrient))

Skeletal muscles generate heat in thermogenesis

Maintains proper temperature for function of enzymes

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Structure of Thin Filaments of Skeletal Muscle

THIN FILAMENT (fig 10.4):

Myosin heads

Wrapped in tropomyosin

Calcium ions bind to troponin and move it away from myosin binding cells

***CROSS BRIDGES****

Shortening of sarcomere, z discs coming closer together, is CONTRACTING

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Structure of Skeletal Muscle

Epimysium: surrounds entire muscle fascicle

Perimysium: surrounds 10-100 groups of muscle fibers

Endomysium: around individual cells

(329)

Aponuerosis

MUSCLE CELLS

Same parts as typical eukaryotic cell, with new names

FASCICLE: skeletal muscle cell

Plasma membrane: SARCOLEMMA: covers entire muscle cell

When sarcolemma attaches to a nerve, nueromuscular junction, embedded in sarcolemma

Synaptic bulb releases ACH into synaptic cleft, embedded in sarcolemma

Neurotransmitter: ACH

SARCOPLASMIC RETICULUM (SR) fig. 10.2, (330-331):

Releases Ca2+

Terminal cisterns

Triads: where ends of sarcoplasmic reticulum are invaded by T-tubles

Sodium, calcium, THEN ACH

SARCOMERE: unit of skeletal muscle contraction, how you generate force in skeletal muscles (334)

Can be arranged in serial or paralell

Sarcomeres have many types of protein:

Myosin (big) and actin (small): (contractile proteins)

Tropomyosin, troponin, chitin: (regulatory proteins)

Ends of sarcomere are Z discs (zed discs): THICK filaments (myosin) on top of THIN (actin) filaments

Thin filaments by themselves: I BAND

Overlap between thick and thin filaments: A BAND

Thick filaments only: H ZONE

Middle of sarcomere: M LINE

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Flexion: decreases angle of bones of a joint

Extension: increases angle of bones of a joint

Circumduction: distal end moves in a circle from point of origin

Adduction: movement toward midline

Abduction: movement away from midline

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3 Types of Joints

Fibrous joints are connected by dense connective tissue, consisting mainly of collagen.

sutures, gomphoses, and syndesmose

Suture only in skull

Cartilaginous joints are connected entirely by cartilage (fibrocartilage or hyaline).[1] Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. 

synchondroses and symphyses

pubic symphysis:

Mandibular symphysis:

A Synovial joint, also known as a diarthrosis, is the most common and most movable type of joint in the body of a mammal.

main structural differences between synovial and fibrous joints are the existence of articular cartilage/ synovial membranes surrounding the articulating surfaces of a synovial joint and the presence of lubricating synovial fluid within those capsules (synovial cavities).

knee

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Calcitonin Decreases Blood Calcium

stimulates osteoblasts, who make bone, decreasing Ca2+ available in blood

Secreted by thryoid gland

inhibits osteoclasts

makes blood more acidic

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Negative Feedback Loop: Parathyroid Hormone and Low Blood Calcium

Parathyroid hormone (PTH) is secreted by parathyroid glands and works via a negative feedback loop to respond to LOW levels of blood calcium, which will give you respitory arrest

a) Parathyroid glands: receptor

increase synthesis and secretion of PTH and calcitriol, activated vitamin D, which causes GI tract to absorb more calcium 

b) PTH gene: control center

c) Kidneys and osteoclasts: effector

PTH increases bone resorption by activating osteoclasts, which start dissolving bone to add Ca2+ to blood

Kidneys absorb more calcium so less is lost in urine

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Calcium Homeostasis in Bone

9-11 mg/dl blood CALCIUM is needed for:

blood clotting

muscle contraction

nerve function

enzyme activity

HYPOCALCEMIA

low blood calcium concentration

respitory arrest

HYPERCALCEMIA

high blood calcium concentration

cardiac arrest

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Factors that Affect Bone Growth

1. MINERALS

Calcium and phosphate for new bone in childhood

Vitamin C, K, B12 for collagen fiber synthesis

Vitamin A increases osteoblast activity

2. HORMONES

hGH (human growth hormone) promotes release of insulinlike growth factors (IGF) from liver, which stimulate osteoblasts and promote mitosis at epiphyseal growth plate

Estrogen promotes bone growth by causing apoptosis in osteoclasts

Higher levels of estrogen in women remodel pelvic bones during puberty

Estrogen closes epiphyseal growth plate

Testosterone stimulates osteoblasts and synthesis of bone matrix

Thyroid hormones (T3 and T4) increase osteoblast activity

Insulin= synthesis of bone protein

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Five Common Bone Fractures

1. Compound (Open) Fracture

A fracture that ruptures the skin, exposing bone, causes serious soft tissue injury and risk of infection.

2. Comminuted 

A fracture with several breaks in the bone, creating numerous bone fragments

3. Greenstick Fracture

A fracture that occurs partly across a bone, commonly caused from a bending or crushing impact

Children get this: bones flexible/ not fully calcified

4) Impacted Fracture

Boxing

compression of spongy/trabecular bone with two fragments jammed tightly together.

5. Spiral Fracture

A fracture that occurs around the axis of a bone, commonly caused by a twisting motion 

Combined:

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Four Stages of Bone Remodeling

BONE REMODELING:

1. Formation of HEMATOMA (blood clot)

2. Fibrocartilaginous Callus Formation

always visible later

callus fills with cartilage, which ossifies

3. Bony Callus Formation

4. Bone Remodeling

Phases of fracture healing

There are three major phases of fracture healing, two of which can be further sub-divided to make a total of five phases;

1. Reactive Phase

i. Fracture and inflammatory phase

ii. Granulation tissue formation (hematoma)

2. Reparative Phase

iii. Fibrocartilaginous Callus formation

iv. Lamellar bone deposition

3. Remodeling Phase

v. Remodeling to original bone contour

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Types of Bone Growth

Interstitial Bone Growth

LONGER

For example, endochondral ossification of epiphyseal growth plate

Appositional Bone Growth

THICKER

Osteoblasts in periosteum secrete calcified ridges that fuse around periosteal blood vessels; periosteum becomes endosteum, forming a central haversian canal

Osteoclasts carve out medullary cavity

During fracture healing, cartilage is often formed and is called callus. This cartilage ultimately develops into new bone tissue through the process of endochondral ossification.

Fibrocartilage callus is a temporary formation of collagen fibers (from fibroblasts) and fibrocartilage (from chondroblasts) which forms at the area of a bone fracture as the bone attempts to heal 

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Epiphyseal Growth Plate: Cartilage Zones

1) Zone of Resting Cartilage: scattered chondrocytes in lacunae surrounded by hyaline cartilage matrix

Chondroblasts near perichondrium continuously secrete the cartilaginous matrix

2) Zone of Proliferating Cartilage: Rapid cell division makes chondrocytes appear stacked like coins, hormones promote rapid cell division

ZONE WHERE INTERSTITIAL GROWTH OCCURS

3) Zone of Hypertrophying Cartilage: cells getting larger, maturing cells are arranged in columns but not actively dividing

4) Zone of Calcifying Cartilage: only a few cells thick; chondrocytes die in calcifying matrix, some lacunae empty, invasion of capillaries from the diaphysis stimulates endochondral ossification

Hyaline cartilage of epiphyseal growth plate calcifies totally in adults, becoming the epiphyseal line

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The false ribs, are the five sets of ribs below the top seven true ribs. A rib is considered to be "false" if it has no direct attachment to the sternum, also known as the breast bone. Of these: the last two (eleventh rib and twelfth rib) are free at their anterior extremities and are termed floating ribs or vertebral ribs because they connect neither with the sternum nor with another rib. [1]. These ribs are relatively small and delicate, and are capped by a cartilaginous tip.[2]

http://en.wikipedia.org/wiki/False_ribs