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Prepared By: S. Ehtesham Al Hanif (Hridoy) [0510035

BIO (BIO-MEDICAL) ENGINEERING MUSCLE

ME 471- BIO-ENGINEERING / BIO-MEDICAL

TOPICS: MUSCLE

Prepared By,

S. EHTESHAM AL HANIF (HRIDOY)

STUDENT ID: 0510035

E-MAIL: [email protected]

MOBILE: 88-01670839383

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Thin filament

Thick f ilament

Attached crossbridge, no

force (spring not stretched)

Attached crossbridge has

changed shape to stretch

spring, force but no sliding

2

3

Skeletal Muscle Basics:

y Muscle to tendon then tendon to bone

y Movement done by muscle

y Dependence of isometric force on sarcomere lengthy Force is proportional to filament overlap: important evidence for sliding filaments

What causes the filament sliding?

y Myosin heads bind to actin, then go through a cycle of events the cross bridge cycle

y Overall effect is force generation and ATP hydrolysis

y As all myosin molecules are identical, can reduce problem to considering just a single myosin head interacting

with actin

y Force in Isometric contraction: no sliding (bond will break down if hydrolysis happened)

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Cross-bridge Cycle: Key Features

1) ATP is used in each cycle to provide the energy

a. Rigor mortis occurs if ATP concentration = 0

2) Direction of filament force and sliding (if sliding occurs) is one-way (thin filament moves toward M-line at the

centre of the sarcomere)

3) Step size is small: sliding produced by one cycle is only about 1% of the sarcomere length

a.M

any cycles occur in succession to cause large movements (as in running, walking, etc)

Why so complicated?

y Some constraints due to muscle properties

What is isometric contraction?

y Muscles are active (=contracting) producing isometric force

y The muscle force resists gravity and prevents the arm and book falling

y Isometric means the muscle length is constant

Contraction with shortening (concentric)

y Biceps contracts and its shortening flexes the elbow

y Biceps does work lifting the book

y POWER is the rate at which work is done

Antagonistic muscles

y Active (contracting) muscle can shorten (pull towards its center)

y BUT it cannot elongate (push away from its center)

y Therefore, antagonistic muscles are required

y Example: Rotation around the elbow

Rotation around the elbow: Flexion

Rotation around the elbow: Extension

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Series & Parallel structures (How the arrangement of structures affects force and length change):

Structures in Series:

y Force at A and B are equal.

y For structures in series, forces do NOT add up

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yF

or structures in parallel, forces add upLength changes

For structures in series, length changes add up

For structures in parallel, length changes do NOT add up

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Contractile and Elastic Structures

In series and in parallel

A muscle-tendon complex (MTC):

Because muscle and tendon are in series:

Both experience the same force at each moment.

An observed length change of MTC could be due to either component

Tendon can only be stretched when muscle is active Muscle cannot move bones without first stretching tendon

Elasticity also in parallel:

The parallel element:

Can exert force when CC is relaxed.

Adds its force to that of muscle when CC is active.

More complicated connections can switch elasticity between series and parallel.

Where and what are the SEC and PEC relative to the crossbridges?

Tendon (collagen) series

Aponeuroses (collagen) series Epimysium (collagen) parallel

Filaments (titin) parallel

Filaments (myosin, actin) series

Arrangement of fibres withmuscle

y How the arrangement of structures affect force and length change

y Arrangement of muscle fibres: some examples

parallel fusiform triangular unipennate multipennate

bipennate

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Arrangement of fibres within muscle:

Pennation increases muscle force

y Volumes equal and line of muscle force is the same

y Each fibre in pennate muscle is half the length of the fibres in the parallel muscle and at angleU to the line

of muscle force;

y force along line of muscle (F) = cosU * force along line of fibre (f)

y ForU = 30o

, cosU = 0.87y But there are twice as many fibres in the pennate muscle as in the parallel muscle

y Net effect: pennate muscle produces 2 * 0.87 = 1.74 times more force than the

parallel muscle

Pennation reduces muscle shortening velocity

y In each unit of time

y the cos rule means that muscle shortening is cos * fibre shortening.

y also each fibre in the pennate muscle only shortens half as far as each

fibre in the parallel muscle.

y Net effect: pennate muscle shortening is only 0.5 * 0.87 = 0.41 times as much as the

parallel muscle per unit time

Force-velocity relation, also power

Muscle Force

Muscle length

time(Lever movement)

Bef

e st

l

t

f t

e

scle st

t st

l

t

f t

e

scle

Isometric phasemuscle force toosmall to lift weight

Muscle Force

Muscle length

time

(Lever movement)

Stim

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Velocity

0.0 0.5 1.0

Power

0.0

0.1

0.2

Velocity

0.0 0.5 1.0 1.5

Force

0.0

0.5

1.0

During stimul

tion, muscle forceenough tolift weight

Muscle Force

Muscle length

ti

e

(Lever ove ent)

Sti

Isotonic shortening:constant force

during shortening

Muscle Force

Muscle length

ti

e(Lever

ove

ent)

Before stimul!

tionof themuscle

Largerweight

During stimulationof the muscle

time

Muscle Force

Muscle length

(Lever movement)

Stim

Isometric phasemuscle force toosmall to lift weight

D" # $ %

& '

(

$ ) " 0

1

(

2

%

2

3

(

4

5

) "

'

6

5

Muscle Force

Muscle length

time

(Lever movement)

Stim

Isotonic shortening:constant forceduring shortening

Larger force &

slower velocity

Inverse relation between force and velocity of shortening.The Force Velocity Curve

y Power = work rate

= (force x (length ) / (time

= force x ((length / (time)

= force x velocity

Contraction with lengthening (eccentric)

y The book is lowered in a slow, controlled movement.

y Biceps is acting as a brake.

y Biceps is producing force, EMG, etc, (=contracting)

y The elbow extends as the length of biceps increases due to the book & gravity. Work is done on biceps.

y Force during isovelocity stretch of active muscle

o Force-Velocity relation for Stretch

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Stretch of active muscle

Occurs during normal every-day activities

Contracting muscle fibres act as a brake

Large forces can be produced

But not much fuel (ATP) is used

Forces can be large enough to cause damage

Not covered in many standard textbooks

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