larry m. frolich, ph.d. biology department, yavapai college movement—muscle and bone muscle...

Larry M. Frolich, Ph.D.Biology Department, Yavapai College

Movement—muscle and bone• Muscle structure and contraction• Movement across joints• Bones


Overview• Neuron brings

impulse to synapse with muscle

• Muscle cells shorten by sliding protein filaments (actin-myosin units)

• Great in-depth molecular understanding of how muscle moves

• Movements at protein level cause whole muscle to rapidly shorten or contract


Muscle cell structure• Muscle cells are large

—visible with naked eye as “fibers of meat/chicken/fish

• Each cell contains hundreds of myofibrils

• Each myofibril contains actin/myosin filamentous proteins all lined up (gives striated appearance in microscope)


Parts of muscle cell

• Sarcolemma—muscle cell membrane (“excitable” membrane like neuron can generate action potential)

• Sarcoplasmic reticulum—endoplasmic reticulum in muscle (holds Ca+2 ions)

• T-tubules penetrate into cell and contact sarcoplasmic reticulum


Calcium release in muscle

• Motor neuron impulse arrives to axonal terminus• Neuro-muscular junction synapse passes

message on to muscle cell• Sarcolemma (muscle cell membrane) undergoes

action potential all along length of cell membrane and into T-tubule system

• Voltage change causes release of Ca+2 ions into muscle cell

• Calcium causes actin-myosin units (sarcomeres) to shorten


Sliding filament model• Thick

filaments (myosin) “row” or pull in thin filaments (actin)

• Molecular cross-bridges undergo cycling shape change in the presence of calcium


Muscle contraction requires energy

• Three sources of energy, all part of cellular respiration


• Muscle cells all lined up in skeletal muscle• Contaction of many cells makes whole muscle shorten bringing about body

movements• Movement happens across joints between skeletal elements

Shortening of actin-myosin units lead to whole muscle contraction


Movement—muscle and bone• Muscle structure and contraction

• Movement across joints• Bones


Joints

• Joints connect skeletal elements

• Synovial joints are lubricated, mobile joints

• Skeletal elements linked by synovial joints move when muscles pull on those skeletal elements

• This is how movement happens


Technical vocabulary for movement across joints—very specific


Movement—muscle and bone• Muscle structure and contraction• Movement across joints

• Bones


Structure of a bone

• Bone is alive• Has nerves, blood

supply, cells• Connective tissue

very organized in layers around blood vessels

• Cells make bone tissue, dissolve bone tissue, live inside bone tissue


Fetal bone formation

• Cartilage model forms first• Then bony tissue fills in around blood vessels• Final bone has three parts: central shaft (diaphysis) and two

ends (epiphyses)


Growth plate

• New bone tissue forms within cartilage• Bone growth occurs at cartilaginous growth plate

between diaphysis and epiphysis at either end of bone


• Inside of diaphysis is hollow tube called medullary cavity• In life filled with bone marrow, where blood cells form• Diameter of bone grows by bone formation around outside and

bone absorption on inside

Medullary cavity


Calcium regulation and bone• Bone also serves as

calcium storage• Calcium is needed

for many aspects of cell metabolism, but especially in muscle cells

• Calcium regulation is negative feedback mechanism

• Release of calcium by degrading bone can be contrary to support role of bone


Osteoporosis is result of calcium need outweighing bone support role

• Affects elderly, especially women• Bone resorption proceeds faster than deposition• Low estrogen levels implicated but estrogen replacement now

considered risky• Importance of calcium in diet???• Leads to fractures

– Compression fractures of vertebrae– Neck of femur

• Lifelong habit of weight-bearing activity is probably best remedy


Total Movement Picture• Neurons trigger

muscle to contract based on stimuli or sensory input

• Muscle contracts by sliding filaments

• Muscle pulls on bone to cause movement across joint


Movement—muscle and bone: Review• Muscle structure and contraction• Movement across joints• Bones