Tissue Mechanics-Muscle content

epimysium

surrounds the entire muscle

-a tough layer that contains an abundance of collagen making it resistant to stress

perimysium

-surrounds the muscle fascicles, blood vessels and nerves lie in this layer

-relatively resistant to stretch

endomysium

-surrounds the individual muscle fibers. just outside of sarcolemma

-area of metabolic exchange btw the capillaries and muscle fibers

-transmit some of force to the tendon

basal lamina

-scaffolding that surround the muscle cell

muscle is __

multi-nucleated

what are found on the outside of basal lamina

satelite cells

satellite cells will

divide, and one daughter cell will enter the muscle while the other remains on the outside

mitochondria uses

aerobic metabolism

mitochondria generate

the main cellular energy moloecule ATP

-the density varies depending on the cellular processes of the muscle

cytoplasm allows for

ATP generation through anaerobic glyolysis

z line to z line =

one sacromere

H zone

-midline of sacromere

-only have one myosin

-whole region

A band

-same width all the time

-all of myosin and where actin is overlapping it

I band

just the actin goes into one sacromere to other

-this includes z line

-shrinks when contracting as actin is getting pulled

M line

-middle of myosin projecting out on both sides

-just midline

thin filament

actin

thick filament

myosin

-bigger protein

-think of hooks on both sides

titin

big protein in muscle

-helps maintain muscle

-M line to Z line

-ensures all parts are moving simultaneously

actin functions

-binds with myosin to generate force and shorten the sarcomere

tropomyosin

stabilizes the actin filament

troponin

-influences position or tropomyosin with a bond to Ca++

troponin/tropomyosin complex

-at rest (without Ca++) is covering up the binding site of myosin

Myosin fx

-heavy chain-molecular motor for muscle contraction

-light chain-influences the contraction velocity of the sarcomere; modulates the kinetics of cross bridge cycling

non-contractile proteins

-titin

-desmin

titin

-passive tension within the muscle fiber

desmin

stabilizes the alignment of adjacent sarcomeres

non-contractile proteins will

1. generate passive tension when stretched

2. povide internal and external support and alignment of muscle fibers

3. help transfer the active force of the muscle

muscle is an __ tissue

excitable

three types of protein channels

1. chemical dependent: opens only when a particular chemical NT fits into a very specific receptor

2. Voltage dependent channel: opens only when the charge differnce across the membrane becomes -50 mV

3. potassium channel: opens when a specifc chemical NT fits into a receptor on the outside of the membrane or when the inside voltage reaches +30 mV

Muscle contraction

1. release of Ca+2 from SR exposes binding sites on thin filament

2. Ca2+ binds to troponin complex

3. tropomyosin pulled aside

4. bind sites on actin filament exposed

Contraction cycle after the actin filament binding site is exposed

1. exposed binding sites on atin allow muscle contraction cycle to occur

2. cross-bridge binds actin to myosin

3. cross-bridge pulls actin filament (power stroke), ADP and (P) released from myosin

4. New ATP binds to myosin, causing linkage to release

5. ATP splits, which provides power to “cock” the myosin cross-bridge

muscle relaxation

active transport of Ca2+ into SR, which requires ATP makes myosin binding site unavailable

rate coding

process by which the nervous system controls the force output of a muscle by varying the rate at which motor neurons fire action potentials

Type I

1. slow twitch

2. high resistance to fatigue

3. aerobic

4. low force production

5. low glycolytic capacity

6. high oxidatie capacity

7. used in everyday ADLS

Type IIa

1. intermediate resistance to fatigue

2. long term aerobic

3. force production is high

4. oxidative capacity is high

5. glycolytic capacity is high

Type IIx

1. low restitance to fatigue

2. short term aerobic

3. force production is very high

4. low oxidative capacity

5. high glycolytic capacity

6. couch potato

increase force demands __

increase number of motor unit activated

what is muscle architecture

• arrangement of fibers relative to the axis of force generation

• fiber diameter is similar regardless of the muscle

Muscle mass

may not be directly related to any function aspect of the muscle

the entire muscle volume is __ a good estimate of the amount of muscle

not

the arrangment of those fibers is ___ critical part of understanding how to estimate the amount of force that is produced

MOST

Pennation angle

angle btw the tendon and the fiber orientation usually btw 0-30 degree

Factors that effect muscle force

• pennation angle

  • the force generated will be less along the tendon, but the design allows us to pack more muscle into the cross sectional area, so overall force production is greater than a fusiform muscle of equal size

• physiologic cross section area

  • the amount of active proteins available to produce a contraction

    • measured by perpendicularly cutting through the muscle fibers

    • proportional to the max force production

• fiber type

• training

fusiform

-the length of the fiber is generally closer to the length of the mscle compared to pennate muscles

-facilitates rapid muscle shortening

pennate muscles differ from fusiform fibers in three ways

• contains shorter fibers

• possess more individual fibers

• exhibit less ROM

• for force

Active =

• shortening concentric contraction

• the myosin and actin have optimal length

• if contracted too close it is referred to as active insufficiency

• shortening both ends

  • too many cross bridges or too close so runs out of cross bridges to form

passive =

• shortening eccentric

• connective tissues stretched similar to a rubber band

concentric contraction produce __

more force at slower speeds

eccentric contractions produce __

more force at higher speeds

• stretch shortening cycle

• more passive tension being built up in muscle to produce more force

0 velocity =

isometric

positive work

concentric contraction

negative work

eccentric contraction

• stores potential energy to produce more positive work

fusiform is made for __

velocity

pennate is made for __

force development

greater excusion (ROM)=

increased in rotational torque