Musculoskeletal System

What are the 3 types of muscle?

1. skeletal

2. cardiac

3. smooth

muscle fiber

long cylindrical cell in muscle

What are the components/features of muscle fiber?

• multinucleate

• myofibrils

• sarcolemma

• sarcoplasmic reticulum (SR)

• T-tubules

• filaments

What is the storage location for Ca²⁺?

sarcoplasmic reticulum

What are myofibrils composed of?

thick & thin filaments

What are two features of thick and thin filaments?

• highly organized proteins

• striated

What are the two kinds of filaments?

1. thick filament

2. thin filament

What makes up thick filament?

~ 350 myosins

• head

• flexible hinge region

• tail

What makes up thin filament?

2 strands of actin + 2 regulatory proteins

• tropomyosin

• troposin

• actin subunit

Where is the binding site for myosin?

actin subunit

What is the basic unit of contraction?

sarcomere

sarcomere

overlapping thin & thick filaments

100s of sarcomeres end-to-end =

myofibril

In a sarcomere, thin filaments are attached to…

Z line

In a sarcomere, thick filaments are anchored to…

M line

draw a sarcomere

What do thin and thick filaments do during contraction?

make & break connections;

“slide” past each other and increase overlap

What shortens during contractions?

the sarcomere NOT the length of filaments

How does the sarcomere shorten during contractions?

the distance between the Z lines shorten

Does the sarcomere shorten during contractions?

yes

Does the overlap increase during contractions?

yes

Do the thin filaments shorten during contractions?

no

Do the thick filaments shorten during contractions?

no

When the muscle fiber is at rest, myosin binding sites are blocked by…

tropomyosin

SEQ the process of a motor neuron transmitting a message

• AP arrives at junction

• acetylcholine released into synaptic cleft

• acetylcholine binds to receptors on muscle fiber

• Na⁺ channels open

• AP in sarcolemma of muscle fiber

• AP down T-tubules

• Ca²⁺ channels in SR open

• Ca²⁺ released into cytoplasm

SEQ muscle contraction

• myosin head is bound to ADP +P_i = high energy state

• Ca²⁺ binds to troponin

  • changes shape

  • tropomyosin moves away from myosin-binding sites

  • myosin binds & forms cross-bridge

• ADP + P_i released

  • myosin head goes to low energy state

  • pulls thin filament toward center of sarcomere = “power stroke”

• ATP attaches to myosin & myosin head detaches

  • breaks cross-bridge

  • head in low energy state

• myosin is a ATPase

  • ATP → ADP + P_i

• myosin head changes shape → now in high energy state

What is needed to break cross-bridges?

ATP

What is the difference between ATP and creatine phosphate?

ATP = not stockpiled

creatine phosphate = stockpiled → contractions for ~ 15 seconds

What are the two kinds of glucose metabolism?

1. aerobic = cellular respiration

2. anaerobic = lactic acid fermentation

cardiac muscle

• walls of the heart

• striated & branched

• autorhythmic

• intercalated disks

What makes cardiac muscle autorhythmic?

pacemaker cells respond to autonomic nervous system to control rate

What do intercalated disks do?

• allow ions to pass between cells

• AP can pass quickly to all cells

• contract simultaneously

smooth muscle

• not attached

• not striated

• no T-tubules

• SR less developed

• less efficient

• long, slow contractions

• walls of digestive tract, bladder, uterus, & blood vessels

What are the functions of skeletons?

• support

• protect organs

• movement (force from muscle contractions)

What are the 3 types of skeletons?

1. hydrostatic skeleton

2. exoskeleton

3. endoskeleton

hydrostatic skeleton

• coelom

  • muscle contracts → force on fluid → shape change

• soft-bodied invertebrates

  • cnidarians, nematodes, annelids

exoskeleton

external, non-living tissue → protection

• mollusks

  • CaCO₃ shell secreted by mantle

  • enlarges at outer edge

• arthropods

  • chitin

  • ecdysis

endoskeleton

internal, living tissue → growth

• echinoderms & chordates

What are the two kinds of endoskeletons that chordates can have?

1. cartilage

   1. chondrocytes → collagen

2. bone

   1. osteoblasts → collagen

   2. hydroxyapatite (Ca & P)

ligaments

connects bone to bone

joints

junctions between 2 or more bones;

flexibility & movement