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The Skeletomuscular System Bone- brief anatomy, bone formation, disorders Muscular system skeletal- structure, contract PowerPoint Presentation
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The Skeletomuscular System Bone- brief anatomy, bone formation, disorders Muscular system skeletal- structure, contraction, control smooth muscle cardiac muscle Innervation of muscle. Functions of bone (skeleton) Support and protection Blood cell formation

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The Skeletomuscular System

Bone- brief anatomy, bone formation, disorders

Muscular system

skeletal- structure, contraction, control

smooth muscle

cardiac muscle

Innervation of muscle


Functions of bone (skeleton)

Support and protection

Blood cell formation

Mineral storage (calcium especially)

Site for muscle attachmentbody movement


Bones classified by shape: long, short, flat,

irregular, round

Bone enclosed in periosteum, which is continuous

with tendons and ligaments

blood vessels in periosteum

Epiphysis- ends

spongy bone contains red marrow

compact bone, articular cartilage

Diaphysis- middle

compact bone

medullary cavity- contains yellow marrow (fat)

lined with endosteum (squamous epithelium)


Compact bone

osteocytes within lacunae

arranged in concentric circles called lamellae

This surrounds a central canal; complex is called

Haversian system

Canaliculi connect osteocytes to central canal and

to each other


Prenatal development

skeleton is mostly cartilaginous

Cartilage cells and then osteoblasts start to

deposit minerals

Cartilaginous disk (epiphyseal disk) remains

in epiphysis

Cells eventually stop dividing


Adults continually break down and build up bone

Osteoclasts remove damaged cells and release

calcium into blood

Osteoblasts remove calcium from blood and build

new matrix. They become trapped



Fracture repair

Hematoma- blood clot in space between edges

of break

Fibrocartilage callus- begins tissue repair

Bony callus- osteoblasts produce trabeculae

(structural supprt) of spongy bone and

replace fibrocartilage

Remodeling- osteoblasts build new compact bone,

osteoclasts build new medullary cavity


Axial skeleton

skull (cranium and facial bones)

hyoid bone (anchors tongue and muscles

associated with swallowing)

vertebral column (vertebrae and disks)

thoracic cage (ribs and sternum)

Appendicular skeleton

pectoral girdle (clavicles and scapulae)

upper limbs (arms)

pelvic girdle (coxal bones, sacrum, coccyx)

lower limbs (legs)



Immovable (synarthoses) bones sutured together

by connective tissue: skull

Slightly movable (amphiarthoses) connected by

fibrocartilage or hyaline cartilage:

vertebrae, rib/sternum joint, pubic


Freely movable (diarthroses)- separated

ligaments- hold bones together

tendons- muscle to bone

lined by synovial membrane


Types of freely movable joints

Saddle: carpal and metacarpal bones of thumb

Ball and socket: shoulder and hip joints

Pivot- rotation only: proximal end of radius and ulna

Hinge- up and own movement in one plane:

knee and elbow

Gliding- sliding and twisting: wrist and ankle

Condyloid- movement in different planes but not

rotations: btw metacarpals and phalanges


Types of movement and examples (with muscles)

flexion- move lower leg toward upper

extension- straightening the leg

abduction- moving leg away from body

adduction- movong leg toward the body

rotation- around its axis

supination- rotation of arm to palm-up position

pronation- palm down

circumduction- swinging arms in circles

inversion- turning foot so sole is inward

eversion- sole is out


Elevation and depression- raising body part up

or down

Aging and bones

both bone and cartilage tend to deteriorate

cartilage: chondrocytes die, cartilage

becomes calcified

osteoporosis; bone is broken down faster

than it can be built

bones get weak and brittle; tend to fracture



Skeleton and other systems

Skin makes vitamin D which enhances calcium


Skeleton stores calcium for muscle contraction,

nervous stimulation, blood clot formation

Red marrow- site of blood cell formation

Calcium levels regulated by

parathyroid hormone and calcitonin

kidneys (can help provide vitamin D)

digestive system (can release calcium

into blood)


Growth hormone regulates skeletal growth

stimulates cell division in epiphyseal disks

in long bones

Growth stops when epiphyseal disks are

converted to bone

When excess growth hormone is produced in


In adulthood- acromegaly. Bones can’t grow

but soft tissue can


When muscle contracts, it shortens and causes


Skeletal muscles attached to bones by tendons

Insertion- attachment to more movable bone

Origin- less movable

Refer to slide 13. Flexors and extensors act on

the same joint to produce opposite actions


Skeletal muscle structure

Connective tissue divides muscle tissue into


muscle fibers (myofibers)


myofilaments (actin and myosin)

Each myofiber is formed from several myoblast

cells; myofiber cells have multiple nuclei


Muscles appear striated

A, I and Z bands appear to change position

relative to each other when muscle


Each muscle fiber is stimulated by a single

axon terminal from a somatic motor


Neuromuscular junction- neuron releases

acetylcholine at the motor end plate

in the sarcolemma


A single somatic motor neuron can produce

an axon with several terminal branches.

Each stimulates a different muscle fiber.

Motor unit- a motor neuron and the muscle

fibers it innervates


How muscles contract

A bands- thick filaments- myosin

I bands- thin filaments- actin

“Edges” of A band are darker because thin and

thick filaments overlap there

H bands- center of A band; lighter because

thin filaments do NOT extend there

Z bands (disks) define boundaries of the functional

unit, or sarcomere


Sliding filament theory of contraction

A bands do not decrease in length;

I bands do

Thin filaments slide past thick filaments


Cross bridges extending from myosin to actin


Detachment of a cross bridge from actin at

end of a power stroke requires a new

ATP to bind to myosin ATPase.

Rigor mortis at death: no ATP is available

ADP remains bound to cross bridges (and thus

actin to myosin)

Muscles remain stiff until they begin to



Regulation of contraction

Actin filament associates with troponin and


Tropomyosin blocks the attachment sites in actin

for the cross bridges when muscle is realxed

To move tropomyosin, troponin interacts with



When Ca 2+ binds

troponin, the complex

shifts. The cross

bridges can now bind

to actin. Contraction

can continue as long

as calcium is bound

to troponin.


How is calcium level in cells regulated?

Calcium is stored in sarcoplasmic reticulum

Released from terminal cisternae by stimulus

from motor neuron

Transverse tubules are continuous with plasma

membrane (sarcolemma). Help conduct

action potentials into the muscle fiber.


Relaxation of muscle

sarcoplasmic reticulum actively

accumulates calcium

process involves hydrolysis of ATP

(Note: muscle activity requires a lot of ATP)


Movement of skeletal muscles

Twitch-rapid contraction and relaxation of fibers

Muscle can twitch is response to a single pulse

stronger the shock, stronger the twitch

graded contraction of whole muscle-

depends on number of fibers contracting

Summation of twitches- if rapid enough produces


Isometric- muscle exerts tension without


Isotonic- shortening does occur


Series-elastic component

Tendons have elasticity

Elastic recoil helps muscles return to resting



muscle is at optimum length for contraction

when it is at resting length


Energy requirements of skeletal muscles

At rest, most energy obtained from fatty acids

Exercise: glycogen and glucose also used

ATP is used for: movement of cross bridges

pumping of calcium into sarcoplasmic


(i.e., for contraction AND relaxation)


Capacity for aerobic exercise

Maximal oxygen uptake (VO2 max)

varies by age, size and sex

Lactate threshold- percentage of maximal oxygen

uptake at which significant increase in lactate

is seen (usually 50-70%; higher in athletes)

Light exercise: most energy derived from fatty acids

At lactate threshold: fatty acids and glucose equally

Heavy exercise: over 60% glucose


Oxygen debt- oxygen stores in hemoglobin,

myoglobin depleted

How is oxygen debt “repaid”?

Phosphocreatine helps produce more ATP

A lot more phosphocreatine than ATP in

muscle cells


Not all muscles have the same contraction speed

Slow-twitch- red fibers; lots of myoglobin and

blood supply

Fast-twitch- fewer capillaries and less myoglobin

(white fibers)- anaerobic activity

Intermediate fibers- fast twitch but with high

oxidative capacity. Resistant to fatigue


A given motor neuron stimulates one type of


Muscles used routinely are mostly smaller

with slow-twitch fibers


accumulation of K+ reduces action


accumulation of lactic acid lowers pH

increased H+ concentration may

interfere with other processes?


Effect of endurance training on muscles

Increased ability to obtain energy from fatty

acids (spare glycogen)

Increased myoglobin, mitochondria

Lactate threshold is raised

Does NOT increase size of muscle (anaerobic

training does)

e.g., weightlifting- increases thickness of myofibrils

and helps build new ones


Alpha and gamma motoneurons can be

stimulated simultaneously by upper

motor neurons

Gamma motoneurons help maintain muscle tone

Reflexes- unconscious reaction to muscle stretch

(by contraction)

monosynaptic- one synapse within CNS

Golgi tendon organs- disynaptic reflex

monitor tension in tendon

Reciprocal innervation- agonist is stimulated,

antagonist is inhibited


Upper motor neurons act on descending motor


Alpha motoneuronsextrafusal fibers

bigger and more numerous than intrafusal

myofibrils all along length

this causes muscle contraction

Gamma motoneurons intrafusal fibers

tightens spindles

enhances sensitivity of spindles


Upper motoneurons usually stimulate both

simultaneously (coactivation)

Alpha motoneurons promote muscle contracting

Gamma motoneurons help maintain muscle tone

Reflexes are produced as an unconscious

response to particular stimuli

Can be simple or complex

Golgi tendon organs monitor tension

  • Skeletomuscular system provides support for the body
  • Bones provide structure; also important for calcium homeostasis and production of blood cells
  • Skeletal muscles are attached to bones by tendons
  • Muscles are innervated by motor units

Summary, continued

Functional unit of muscle cell is myofibril

“Sliding filament” mechanism requires ATP

and calcium

calcium influx regulated by nervous system

aerobic and anaerobic respiration supply

ATP for muscle contraction

regulated by different types of muscle


physical training affects the aspects

of these fibers