Exam 3 BIOL 2251

Functions of the skeletal system

Support, protection, movement (leverage), mineral storage (Ca2+, phosphate), blood cell formation (hemopoiesis), fat storage

Osteogenic cells

Stem cells that divide to produce osteoblasts; found in periosteum and endosteum

Osteoblasts

Bone-forming cells; secrete osteoid (organic matrix)

Osteocytes

Mature bone cells; maintain bone matrix and communicate via canaliculi

Osteoclasts

Large multinucleated cells that break down bone (resorption)

Compact bone histology

Dense bone organized into osteons (Haversian systems)

Spongy bone histology

Trabeculae network with red marrow spaces; no osteons

Osteon (Haversian system)

Structural unit of compact bone with concentric lamellae around a central canal (A)

Central (Haversian) canal

Contains blood vessels and nerves

Lamellae

Concentric layers/rings of calcified bone matrix (D)

Lacunae

Small spaces housing osteocytes

Canaliculi

Tiny channels connecting osteocytes for nutrient/waste exchange

Organic bone component

Osteoid (collagen fibers); provides flexibility and tensile strength

Inorganic bone component

Hydroxyapatite (calcium phosphate salts); provides hardness and compressive strength

Red bone marrow

Produces blood cells; found in spongy bone of flat bones and epiphyses

Yellow bone marrow

Stores fat; found in medullary cavity of long bones

Hemopoiesis

The process of creating a wide variety of blood and bone marrow cells, namely erythrocytes, platelets, granulocytes, lymphocytes, and monocytes.

Diaphysis

Shaft of a long bone

Epiphysis

Ends of a long bone; contains spongy bone

Metaphysis

Region between diaphysis and epiphysis; contains growth plate

Articular cartilage

Hyaline cartilage covering bone ends; reduces friction

Periosteum

Outer fibrous covering of bone; contains blood vessels and nerves

Endosteum

Inner lining of medullary cavity

Medullary cavity

Hollow cavity in diaphysis containing marrow

Bone remodeling

Ongoing replacement of old bone with new bone

Purpose of remodeling

Maintains strength, repairs damage, regulates calcium levels

Cells in remodeling

Osteoclasts (resorption) and osteoblasts (formation)

Bone homeostasis

Maintenance of bone density via hormones, minerals, and mechanical stress

Role of calcium

Essential for bone strength and signaling

Role of vitamin D

Increases calcium absorption from intestines

Role of protein

Provides collagen for bone matrix

Parathyroid hormone (PTH) source

Parathyroid glands

PTH stimulus

Low blood calcium levels

PTH target

Bones, kidneys, intestines (indirect)

PTH effect

Increases blood calcium (bone resorption, Ca2+ reabsorption, activates vitamin D)

Calcitonin source

Thyroid gland (C cells)

Calcitonin stimulus

High blood calcium levels

Calcitonin target

Bones

Calcitonin effect

Decreases blood calcium (inhibits osteoclasts)

Calcitriol source

Kidneys (activated vitamin D)

Calcitriol effect

Increases calcium absorption in intestines

Calcitonin vs PTH

Calcitonin lowers blood Ca2+; PTH raises blood Ca2+

Low PTH effect

Bone overgrowth, low blood calcium

High PTH effect

Excess bone loss (weak bones)

PTH and calcitriol relationship

PTH stimulates calcitriol production to increase calcium absorption

Stress fracture

Small crack from repetitive force

Comminuted fracture

Bone breaks into 3 or more pieces

Greenstick fracture

Incomplete break; one side bends, the other breaks

Transverse fracture

Break is a straight line across the bone

Oblique fracture

Break is at a diagonal angle

Open fracture and closed fracture

Open: bone pierces the skin

Closed: bone breaks but doesn’t pierce the skin

Pathological fracture

Break due to disease (e.g., osteoporosis)

Fracture repair phases

Hematoma → granulation tissue → bony callus → remodeling

Functions of muscular system

Movement, posture, heat production, joint stabilization

Skeletal muscle

Long, cylindrical, striated, voluntary; attached to bones

Cardiac muscle

Branching, striated, involuntary; found in heart

Smooth muscle

Spindle-shaped, nonstriated, involuntary; found in organs

Muscle repair ability

Skeletal: limited; Cardiac: none; Smooth: good

Muscle control

Skeletal: voluntary; Cardiac & Smooth: involuntary

Epimysium

Connective tissue around whole muscle

Perimysium

Connective tissue around fascicles

Endomysium

Connective tissue around muscle fibers

Origin

Attachment site that remains relatively stationary

Insertion

Attachment site that moves during contraction

Muscle fiber cell

Long multinucleated cell

Myofibrils

Contractile rods within muscle fiber

Sarcoplasmic reticulum

Stores and releases calcium

T-tubules

Transmit electrical signals into fiber

Sarcomere

Functional contractile unit of muscle

Z disc

Boundary of sarcomere

A band

Dark band; length of myosin

I band

Light band; actin only

H zone

Region with only myosin

Actin (thin filament)

Anchored to Z disc

Myosin (thick filament)

Contains heads that bind actin

Sliding filament mechanism

Myosin pulls actin inward to shorten sarcomere

Troponin

Binds calcium and shifts tropomyosin

Tropomyosin

Blocks myosin-binding sites on actin

Neuromuscular junction (NMJ)

Synapse between motor neuron and muscle fiber

Acetylcholine (ACh)

Neurotransmitter that stimulates muscle contraction

Excitation-contraction coupling

Process linking electrical signal to contraction via Ca2+ release

Muscle relaxation

Calcium pumped back into SR; cross-bridges detach

Motor unit

Motor neuron + all muscle fibers it controls

Motor unit recruitment

More units = stronger contraction

Muscle twitch

Single contraction cycle

Latent phase

Time before contraction begins

Contraction phase

Muscle shortens

Relaxation phase

Muscle returns to resting state

Treppe

Staircase increase in contraction strength

Incomplete tetanus

Sustained contraction with partial relaxation

Isometric contraction

Tension without muscle length change

Isotonic contraction

Muscle changes length (concentric or eccentric)

Aerobic metabolism

Uses oxygen; produces more ATP

Anaerobic metabolism

No oxygen; produces lactic acid

Creatine phosphate

Quick ATP regeneration source

Myoglobin

Stores oxygen in muscle cells

Prime mover (agonist)

Main muscle causing movement

Antagonist

Muscle opposing movement

Synergist

Assists prime mover

Fixator

Stabilizes origin of muscle