The Skeletomuscular System

1
The Skeletomuscular System Bone- brief anatomy,
bone formation, disorders Muscular
system skeletal- structure, contraction,
control smooth muscle cardiac
muscle Innervation of muscle
2
Functions of bone (skeleton) Support and
protection Blood cell formation Mineral storage
(calcium especially) Site for muscle
attachment?body movement
3
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)
4
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
5
(No Transcript)
6
Prenatal development skeleton is mostly
cartilaginous Cartilage cells and then
osteoblasts start to deposit minerals Cartilagin
ous disk (epiphyseal disk) remains in
epiphysis Cells eventually stop dividing
7
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? osteocytes
8
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
9
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)
10
Joints Immovable (synarthoses) bones sutured
together by connective tissue skull Slightly
movable (amphiarthoses) connected
by fibrocartilage or hyaline cartilage vertebra
e, rib/sternum joint, pubic symphysis Freely
movable (diarthroses)- separated ligaments- hold
bones together tendons- muscle to bone lined by
synovial membrane
11
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
12
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
13
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 easily
14
Skeleton and other systems Skin makes vitamin D
which enhances calcium absorption 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)
15
(No Transcript)
16
(No Transcript)
17
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 childhood?gigantism In adulthood-
acromegaly. Bones cant grow but soft tissue can
18
(No Transcript)
19
(No Transcript)
20
When muscle contracts, it shortens and
causes movement 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
21
(No Transcript)
22
(No Transcript)
23
Skeletal muscle structure Connective tissue
divides muscle tissue into fascicles ? muscle
fibers (myofibers) ? myofibrils ? myofilaments
(actin and myosin) Each myofiber is formed from
several myoblast cells myofiber cells have
multiple nuclei
24
(No Transcript)
25
(No Transcript)
26
Muscles appear striated A, I and Z bands appear
to change position relative to each other when
muscle contracts Each muscle fiber is
stimulated by a single axon terminal from a
somatic motor neuron Neuromuscular junction-
neuron releases acetylcholine at the motor end
plate in the sarcolemma
27
(No Transcript)
28
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
29
(No Transcript)
30
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
31
Sliding filament theory of contraction A bands
do not decrease in length I bands do Thin
filaments slide past thick filaments How? Cross
bridges extending from myosin to actin
32
(No Transcript)
33
(No Transcript)
34
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 decompose
35
Regulation of contraction Actin filament
associates with troponin and tropomyosin Tropom
yosin blocks the attachment sites in actin for
the cross bridges when muscle is realxed To move
tropomyosin, troponin interacts with calcium
36
(No Transcript)
37
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.
38
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.
39
(No Transcript)
40
Relaxation of muscle sarcoplasmic reticulum
actively accumulates calcium process involves
hydrolysis of ATP (Note muscle activity
requires a lot of ATP)
41
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 tetanus Isometric- muscle
exerts tension without shortening Isotonic-
shortening does occur
42
Series-elastic component Tendons have
elasticity Elastic recoil helps muscles return to
resting length Length-tension muscle is at
optimum length for contraction when it is at
resting length
43
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 reticulum (i.e., for
contraction AND relaxation)
44
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
45
Oxygen debt- oxygen stores in hemoglobin, myoglob
in depleted How is oxygen debt repaid? Phosphoc
reatine helps produce more ATP A lot more
phosphocreatine than ATP in muscle cells
46
(No Transcript)
47
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
48
A given motor neuron stimulates one type of
fiber. Muscles used routinely are mostly
smaller with slow-twitch fibers Fatigue accumul
ation of K reduces action potential accumulatio
n of lactic acid lowers pH increased H
concentration may interfere with other processes?
49
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
50
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
51
Upper motor neurons act on descending
motor tract 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
52
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
53
Summary

• 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

54
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 fibers physical training affects the
aspects of these fibers