Biology, Musculoskeletal System

Raven Biology 13th Edition, CH45

Types of Skeletal Systems, Changes in movement occur because muscles pull against a support structure

zoologists recognize three types: hydrostatic skeletons, exoskeletons, and endoskeletons

Exoskeletons, Surrounds the body as a rigid hard case composed of chitin in arthropods

provides protection for internal organs and a site for muscle attachment; must be periodically shed for growth

Exoskeletons, Not as strong as a bony skeleton

respiratory system sets limit on body size; muscles cannot enlarge in size and power

Endoskeletons, Rigid internal skeletons that form the body's framework and offer surfaces for muscle attachment

echinoderms have calcite skeletons (calcium carbonate); vertebrate bone is made of calcium phosphate

Vertebrate Endoskeletons, Vertebrate endoskeletons have bone and/or cartilage

bone is much stronger and less flexible than cartilage; bone and cartilage are living tissues that can change and remodel

Bone Structure, Bone is a hard but resilient connective tissue unique to vertebrates

long bone covered by periosteum; shaft is diaphysis, ends are epiphyses; bone elongates at growth plates

Compact bone, Compact bone is the outer dense layer

extracellular matrix of calcium phosphate and collagen provides strength and support in the skeleton

Spongy (medullary) bone, Forms the epiphyses inside a thick shell of compact bone arranged in trabeculae

has porous appearance; medullary cavity houses bone marrow to produce blood cells

Microscopic Structure, Osteocytes (mature bone cells) found in lacunae in compact bone

osteocytes exchange nutrients through canaliculi; functional unit is osteon (Haversian system); spongy bone lacks osteons

Bone development types, Two types of bone development

intramembranous development (bones form within connective tissue) and endochondral development (begin as cartilaginous model)

Intramembranous Development, Osteoblasts initiate bone development

some cells become trapped in bone matrix; osteoclasts break down bone matrix

Endochondral Development, Typically bones deeper in the body begin as tiny cartilaginous models

bone development adds bone to outside of cartilaginous model while replacing interior cartilage with bone

Bone Remodeling, Bone is a dynamic tissue that can change

mechanical stress can remodel bone during embryonic development and after birth; weight-lifting is one osteoporosis treatment

Joints (Articulations), Locations where one bone meets another

four basic joint movement patterns: ball-and-socket (all directions), hinge (one plane), gliding (sliding), and combination joints

Skeletal Muscle Movement, Skeletal muscles produce movement of the skeleton contracting across a joint

origin remains stationary; insertion moves when muscle contracts; muscles can be antagonistic

Muscle contraction, Each skeletal muscle contains numerous muscle fibers

each muscle fiber encloses 4-20 myofibrils; each myofibril composed of thick and thin myofilaments; myofibrils have alternating dark and light bands (striated)

Components of a Sarcomere, A bands are stacked thick and thin myofilaments (dark bands)

I bands consist only of thin myofilaments (light bands) divided by Z line; sarcomere is distance between two Z lines (smallest subunit of contraction)

Skeletal Muscle Contraction, Muscle contracts because myofibrils contract and shorten

myofilaments themselves do not shorten; thick and thin filaments slide relative to each other (sliding filament mechanism)

Thick and Thin Filaments, Thick filament composed of myosin subunits with globular heads

thin filament composed of two chains of actin proteins twisted together in a helix

Cross-Bridge Cycle, Hydrolysis of ATP by myosin activates the head

myosin binds to actin forming cross-bridge; power stroke releases ADP and Pi; ATP binding releases actin

Requirements for Contraction, When muscle is relaxed, myosin heads cannot bind to actin because tropomyosin blocks attachment sites

for contraction, tropomyosin must be removed by troponin, regulated by Ca2+ levels

Calcium and Contraction, In low Ca2+ levels, tropomyosin inhibits cross-bridge formation

in high Ca2+ levels, Ca2+ binds to troponin, displacing tropomyosin and allowing actin-myosin cross-bridges

Stimulus for Contraction, Muscle fiber stimulated by motor neurons secreting acetylcholine at neuromuscular junction

depolarization conducted down T tubules stimulates Ca2+ release from sarcoplasmic reticulum (excitation-contraction coupling)

Motor Units and Contraction, Motor unit is a motor neuron and all muscle fibers it innervates

precise control muscles have smaller motor units; force muscles have larger motor units; recruitment increases contraction strength

Speed of Contraction, A single electric shock produces a twitch

summation of closely spaced twitches; tetanus is sustained contraction with no relaxation; muscles divided into slow-twitch (type I) and fast-twitch (type II) fibers

Two Types of Muscle Fibers, Slow-twitch (type I) fibers are rich in capillaries, mitochondria, and myoglobin (red fibers)

sustain action for long periods; fast-twitch (type II) fibers are poor in these (white fibers), adapted for rapid power generation and anaerobic respiration

Energy Use, Skeletal muscles at rest obtain most energy from aerobic respiration of fatty acids

during use, energy comes from glycogen and glucose; muscle fatigue correlated with lactic acid production

Modes of Animal Locomotion, Locomotion involves appendicular locomotion (appendages that oscillate) and axial locomotion (bodies that undulate)

physical constraints of gravity and frictional drag occur in every environment

Locomotion in Water, Water's buoyancy reduces effect of gravity

primary force retarding forward movement is frictional drag; swimming involves using body or appendages to push against water

Terrestrial Vertebrates, Many terrestrial tetrapod vertebrates can swim through limb movement

birds that swim use hind legs (often webbed feet); animals that swim with forelegs have modified flippers

Locomotion on Land, Terrestrial locomotion deals mainly with gravity

vertebrates and arthropods move by pushing against ground with jointed appendages (legs); vertebrates are tetrapods; arthropods have at least six limbs

Basic Walking Patterns, Basic walking pattern of quadrupeds generates diagonal pattern of foot falls

left hind leg, right foreleg, right hind leg, left foreleg; allows running by leaps

Locomotion in Air, Flight has evolved four times among animals

insects, pterosaurs, birds, and bats (convergent evolution); all three vertebrate fliers modified forelimb into wing but did so differentl