BME101 Quiz 4

muscle & cell mechanics

fascicles

small bundles that divide the muscle belly

fibers

muscle belly composition; muscle cells that produce the contraction & the epimysium

epimysium

connective tissue encasing the muscle fibers

skeletal muscle fiber

a long, cylindrical, multinucleated cell that is filled with smaller units of filaments

myofibril

the largest of the filaments; composed of subunits called sarcomeres

sarcomere

contains filaments called myofilaments

actin & myosin

types of myofilaments

myosin protein molecules

thicker

actin protein molecules

thinner

concentric contraction

shortens muscle while generating force, e.g. lifting weight in a bicep curl

what is an eccentric contraction

occurs when the muscle lengthens while under tension due to a greater opposing force

isometric contractions

generate force without changing the length of the muscle

agonist muscle

contracts to produce movement; known as the prime mover

antagonist muscle

opposes the prime mover; the action of this muscle is opposite to the prime mover

protrusion of the leading edge

1st stage of cell migration

adhesion to the matrix

2nd stage of cell migration

contraction

3rd stage of cell migration

release of the rear attachments

4th stage of cell migration

cytoskeleton

gives the cell body shape & internal organization; provides mechanical support that allows cells to carry out essential functions like division & movement

force-application techniques

applies a force to the cell; records the cell’s biochemical/mechanical response to the applied force

force-sensing techniques

measure the forces produced by cells during development, contraction, migration, etc.

why must the skull be over-designed?

to protect the brain from a monotonic failure

compression, tension, shear

bone strength from highest to lowest

periosteum

outer cortical membrane (long bone)

endosteum

inner cortical membrane (long bone)

stress

force per cross-sectional area

F/A

stress equation

displacement/original length

strain

stiffness

the slope of the elastic portion of the curve

osteoclasts

large cells that dissolve the bone; come from the bone marrow & are related to WBC

osteoblasts

cells that form new bone; from the bone marrow & found on the surface of new bone

osteocytes

cells inside the bone

bone response to stress

dependent on the direction of the applied load

long axis

where bone is strongest

wood & composites

anisotropic material examples

before permanent deformation

when brittle materials FAIL

before failure

when ductile material DEFORMS

bone fractures sooner when

load is applied *slowly*

stress depends on

strain & rate of strain

rate of strain

the history of strain

longitudinal growth: **epiphyseal** (growth) plate

bone growth location

longitudinal growth: **diaphyseal** side of the plate

bone cell production site

ages 18-25

**longitudinal growth** stops & plate *ossifies*

circumferential bone growth

continues throughout lifespan

circumferential growth: internal layer of the periosteum

bone cell production site (by **osteoblasts**)

circumferential growth: around the circumference of the medullary cavity

concurrently bone is resorbed here by the **osteoclasts**

wolff’s law

bone grows & remodels in response to the forces that are placed upon it

shape of bone

reflects its function

dominant arm

has thicker & stronger bone

curved bones

are thickest where they are most likely to buckle

trabeculae

forms trusses along lines of stress

large bone projections

observed where heavy active muscles attach

response to regular activity

regular exercise provides stimulation to maintain bone throughout the body

lack of mechanical stress

Ca levels decrease & is removed through blood via kidneys (increases chance of kidney stones)

weightless effects

astronauts use exercise routines to provide stimulus from muscle tension

in adults: bone length

little change

in adults: density

the most change; lack of use decreases density

density

strength of bone

in adults: increased activity

leads to increased diameter, density, cortical width, & Ca

osteoporosis

(porous bone) occurs when there is an imbalance between new bone formation & old bone resorption