Biomechanics of the Muscular System

sprain

sprain

ligaments reinforcing the joint are stretched and possibly torn

1st degree sprain

minor tear or stretch

2nd degree sprain

tear, followed by pain and swelling

3rd degree sprain

complete ligamentous rupture

4th degree sprain

complete rupture, along with some small bones

subluxation

partial dislocation of a joint

dislocation (luxation)

total malalignment of joint

• Usually requires medical treatment to reduce

plica

a flap of cartilage left over from fetal development

plica syndrome

• When a plica gets irritated and painful

• It is treated with rest, NSAIDs, physical therapy and as a last resort, surgery to remove the plica.

BEAR technique

• Bridge Enhanced ACL Repair

• Uses stem cells to repair ACL

• Still only done in children, and only in select hospitals

bursitis

inflammation of the bursae

arthritis

inflammation of the joint

osteoarthritis

wear and tear arthritis

• Single joint specific, not systemic

rheumatoid arthritis

autoimmune disorder in which the immune system attacks synovial joints (diarthroses)

gout

uric acid crystalizes in the joints

• The crystals are sharp and very irritating to the joint capsule

• Distal joints are the most affected

epimysium

surrounds entire muscle

perimysium

surrounds each fascicle

endomysium

surrounds each muscle cell

connective tissue sheaths

are continuous with tendons

contractibility

ability to shorten to generate force

excitability

ability to react to a stimulus (i.e. electrical nerve impulse)

extensibility

Ability to be stretched

elasticity

ability to recoil after being stretched

hyperplasia

increase in fiber number

hypertrophy

appears to represent an increase in fiber diameter

birds and amphibians

can grow new muscle fibers

sarcomere

The basic unit of contraction of skeletal muscle

thin (actin) filaments

extend from Z disc toward the center of the sarcomere

thick (myosin) filaments

located in the center of the sarcomere

• overlap inner ends of the thin filaments

elastic (titin) filaments

located between the myosin filament and the end of the sarcomere

• Function to hold the myosin in place in the center of the sarcomere

z disc (z line)

boundaries of each sarcomere

A bands

full length of the thick filament

• Includes inner end of thin filaments

• Red stripe

H zone

center part of A band where no thin filaments occur

M line

center of the H-zone

• contains tiny rods that hold thick filaments together

I band

region with only thin filaments

• lies within two adjacent sarcomeres

• white stripe

sarcoplasmic reticulum

An elaborate smooth endoplasmic reticulum made of interconnecting tubules

•Contains calcium ions – released when muscle is stimulated to contract

•Calcium ions diffuse through cytoplasm

•Trigger the sliding filament mechanism

interconnecting tubules

• surround each myofibril

• Most run longitudinally along the myofibril

terminal cisternae

tubules that form form larger ^ cross-channels between the A and I bands

• occur in pairs on either side of a T tubule

muscle contraction

• Ultimately controlled by nerve-generated impulse

• Impulse travels along the sarcolemma of the muscle cell

• Impulses further conducted by T tubules

t tubule

a deep invagination of the sarcolemma

myosin heads

• attach to actin in the thin filaments (i.e. form crossbridges)

• then pivot to pull thin filaments inward toward the center of the sarcomere

motor unit

A single motor neuron and all fibers it innervates comprised of:

• The cell body of the alpha efferent neuron

• The axon

• All muscle fibers innervated by the axon

motor units

# of fibers in the MU depends on how precise/powerful the movements are that the muscle normally does

• are confined to 1 muscle

quads, gastroc, hamstrings

> 1500 fibers/ mu

hand muscles

< 100 fibers/mu

twitch-type

responds to a single stimulus

tonic-type

need multiple stimuli to contract

• eye muscles

summation

building tension in an additive fashion in response to repeated stimulation

• section B

tetanus

state of sustained max tension resulting from repetitive stimulation

• all myosin are bonded so no more force

skeletal muscle fibers categorized by

• How they manufacture energy

• How quickly they contract

3 classes of skeletal muscle fibers

• Slow oxidative fibers (type I)

• Fast oxidative glycolytic fibers (type IIA)

• Fast glycolytic fibers (Type IIB)- white meat

type 1

slow twitch muscle fibers

• usually aerobic; you can do for a very long time

type IIA

moderate fast-twitch muscle fibers

• almost all the compound exercises, pushups, pull-ups, squats, and dips

type IIB

sprints, pylometrics, heavy lifting, weight calisthenics, and hard bodyweight variations