Muscle

• ~640 pieces of muscles

• Working as antagonistic

pairs through a joint of the

skeletal system

• ~320 pairs

• How many types of muscle?—Based on morphological and

functional differences.

Three:

• Skeletal muscle

• Cardiac muscle

• Smooth

1. Skeletal Muscle –

composed of bundles of very long cylindrical

multinucleated cells that have cross –

striations.

Their contraction is quick, forceful and usually

under voluntary control.

2. Cardiac Muscle composed of elongated or branched

individual cells that run parallel to each other. At sites of end to end contact are the

intercalated disks. Also have cross – striations. Contraction is involuntary, vigorous and

rhythmic.

3. Smooth Muscle

consists of collections of fusiform cells,

no cross – striations.

Contraction is slow and involuntary.

• How many types of skeletal

muscle?—Based on color or

oxidative capacity.

Three; white (anaerobic), pink or

red (aerobic).

Why farmers prefer to plough the land with a cow instead of a pig?

Beef Pork

Marathon runner versus sprinter?

There are different types of muscle with different ATPase activity and differing speeds of contraction :

Fast Muscle low oxidation

Fast Muscle high oxidation

Slow Muscle high oxidation

1. 2. 3.

very low mitochondria

Many mitochondria Many mitochondria

white or pink, few

oxidative enzymes no myoglobin

darker pink oxidative

enzymes low myoglobin

dark red oxidative

enzymes high myoglobin

uses only glucose uses glucose, fat

and protein uses glucose, fat

and protein

easily fatigued lactic acid formed

easily fatigued lactic acid formed

long lasting little lactic acid

Fast ATPase Intermediate ATPase

Slow ATPase

Tetanus tensions

a)

b)

c)

d)

e)

f)

time

Tension Tension

time time

Tension

RED

White

Skeletal muscle http://www.youtube.com/watch?v=KG1JHW_q2VA

• What constitute the thin filaments?

• What is the function of the G-actin

and F-actin?

Z-line

Binding site for

myosin head

Change position after binging with Ca++

• What constitute the thick filaments?

• What is the function of the myosin

head?

HMM

S1

LMM

HMM

S2

M-line

ATPase

• How do thick and thin filaments

organized into functional units of

skeletal muscle?

• What is a sarcomere?

Storage of Ca++ Transmission of

action potential

Sliding of filaments

Sarcomeres – Thin and thick filaments overlap in two

regions of each sarcomere

– Each thick filament is surrounded by six thin

filaments

– Three-dimensional organization of thin and

thick filaments is maintained by other proteins

• Nebulin

– Along length of thin filament

• Titin

– Keeps thick filament centered in sarcomere

– Attaches thick filament to Z-disk

Sarcomeres

Figure 5.17

Three-Dimensional Structure of Sarcomere

Figure 5.18

6 thin: 1 thick

• What are the advantages of having

many units of short sarcomeres

instead of one long units which

covers the whole length of the

muscle?

At Z – line, thin filaments do not run

straight through, but terminate.

?

“Cocked” Thick

filament

Thin

filament

?

“Cocked”

“Rotated”

Thick

filament

Thin

filament

?

“Cocked”

“Rotated”

Thick

filament

Thin

filament

?

•Why would the muscle exhibit constant

volume contraction?

Relaxed contracted

Z-line

• Since skeletal muscle is voluntary,

how is skeletal muscle contraction

controlled?

Sliding,

myosin

binding site

uncovered.

Relaxed;

myosin

binding site

covered.

• What is the role of calcium in muscle contraction?

• How does it work together with troponin and affect tropomyocin?

Very low in Ca++

conc. at resting

Very high in Ca++

conc. at resting

Upon

depolarization, Ca++

channels open,

releasing Ca++ into myofibriles

(Dihydropyridine receptor )

Graded

signal All-or-none

signal

• How does sliding occur between thick and thin filaments?

Cocked position

ready for binding

rotated position,

sliding occurs

Video on control of muscle contraction

http://www.youtube.com/watch?v=WRxsOMenNQM

During shortening of the sarcomere,

there are no changes in the lengths

of the thick and thin filaments.

Constant Shortened

Constant

length

Constant

length

• What are the roles of ATP in muscle

contraction? Link with this week’s practical.

Structure of ATP

The bonds between the phosphate groups of ATP

are unstable and can be broken by hydrolysis.

If no ATP is available

to bind to the myosin

head, the actiomyosin

complex will not

dissociation—Rigor

Mortis after death

So, what are the roles of ATP in the contraction and relaxation of skeletal muscle contraction?

• Myosin head conformational change

• Dissociation of actomyosin complex

• Active transport of Ca++

• Maintenance of Na+ and K+ gradients

Production of heat (shivering)

What is the relationship between the degree of overlap between thick and thin

filaments and the tension build up?

Summary: Muscle structure and function http://www.youtube.com/watch?v=ren_IQPOhJc

• What is a muscle twitch, and

what is tetany (muscle cramp)?

Reading assignment on muscle cramp:

http://www.medicinenet.com/muscle_cramps/article.htm

The mechanical response of a muscle fiber to a

single action potential is known as a twitch.

A maintained contraction in response to repetitive

stimulation is known as a tetanus.

Muscle cramp (tetany)

• Mineral imbalance (Na+, K+, Ca++, Mg++,)

• Inadequate blood supply (temp, dehydration,

• Nerve compression

(age, dehydration, pregnancy, medical conditions.)

Tetanus disease Clostridium tetani

• What is a motor unit?

• Is it good to have large motor units

or small motor units?

Connection between motor neuron and skeletal muscle:

Neuromuscular junction and motor unit:

http://www.youtube.com/watch?v=hzXVe4RS8-A (8:50min).

The details of muscle contraction: http://www.youtube.com/watch?v=f0mDFP7qn1Y&feature=related

Size of motor units—delicate or powerful movement?

The motor neurons to a given muscle fire in an

asynchronous pattern.

Thus some motor units will be contracting while

others are relaxing.

This asynchrony has the advantages of:

1. Preventing fatigue of the muscle.

Some units are resting at all times.

2. Maintaining a nearly constant tension in the

muscle. If all were firing in synchrony,

movement would be jerky series of

contractions and relaxations. This type of

movements is associated with certain

diseases such as Parkinson’s disease and

also the normal shivering responses to cold.

Both inhibition of the subcortical centers in

the dominated by local feed back loops from

stretch receptors which tend to become

synchronous and thus oscillatory.

What happens to your muscles as you

aged?

http://images.google.com/imgres?imgurl=http://www.fall-prevention-institute.org/images/wastedleg.jpg&imgrefurl=http://www.fall-prevention-institute.org/muscleloss.html&usg=__YLSBli2KA1mda24Ysp9Y8uQyzMc=&h=332&w=295&sz=14&hl=en&start=2&tbnid=3PMOg_PwX_Z_dM:&tbnh=119&tbnw=106&prev=/images%3Fq%3Daging%2Bmuscle%26gbv%3D2%26hl%3Den

• What happens to your muscles

as you aged?

Weaker and Weaker!

Do exercise!!!

EXERCISE AND MUSCLES

Moderate exercise increases the diameter of muscle

cells, thus enlarging and strengthening the gross

muscle being exercised.

If the exercise involves movement, as in weight

lifting. It is said to be isotonic, for though a muscle

does shorten during such exercise, its tension does

not greatly increase. If one exercise, by pushing

against an immovable object, or by opposing

antagonistic muscle to each other, the resulting

contraction does not actually shorten the muscle.

This is called isometric exercise.

• What is isometric contraction?

• What is isotonic contraction?

Note: isotonic exercise involves

both isometric and isotonic

contraction in a muscle.

Antagonistic pair of muscles Red= contract

Blue=relax

Isotonic vs isometric contraction:

http://www.youtube.com/watch?v=pbXML3m2hSE

Isotonic

contraction

Isometric

contraction

Isotonic= constant tension Isometric= constant length

• Although muscle fibers enlarge with body growth,

they do not normally increase in number, so that

as they die they cannot be replaced (under

normal circumstances). However, vigorous and

continual exercise may lead to hypertrophy (i.e.

increase in myofibril number).

• Thus, without exercise, the number of muscle

cells in all muscles drastically decreases in old

age.

• Part of this decrease is no doubt due to minor

injuries that occur in the course of a life time.

Muscle stem cells can help to repair major muscle injuries (would you consider doing stem cell

research?)

What is muscle soreness?

How to deal with it?

• What kind of lever system

does the arm represent?

• What is its mechanical

advantage? Why?

Skeletal muscles produce forces which

need to work with the skeletal systems

(bones and joints)!

Class 1 Class 2 Class 3

Types of levers

• Third type lever

• Disadvantage:

Low mechanical

advantage Advantage

:You can touch your nose!!!

• What kind of lever system

does other parts of the body

have?

• Any joint exhibit high

mechanical advantage (MA)?

Mechanical advantage http://www.youtube.com/watch?v=eTa2EFd3JF0

Low MA

High flexibility

High MA

Low

flexibility

Why can deer run faster than human? How to

improve both mechanical advantage and flexibility?

• Why would a person fall?

• Where is the center of mass

in your body?

• Is it in a constant position?

• How high can you jump?

• What is the relationship

between the center of mass

and high jump?

• How to improve the method of

high jump?

= center of mass

Center of mass is

outside the body

An athlete use physics to break the world record in

high jump! (Always think about application!!)

End