Histology 10

8/8/2019 Histology 10

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There are located at the peripheral of the muscle fiber or muscle cell. The

muscle fiber or muscle cells are tiny and thin. They have flat nuclei at the

peripheral, and long straight, they have the thin diameter from the beginning till

the end of the muscle and the show striation. And the contraction is on our will

(voluntary). And I forget to mention that they are red in color is attributed to the

present of myoglobin. Compare to the other globin in the body, hemoglobin.

Doc : What the function of myoglobin?

Student: storage.Doc: storage of what?

Doc didnt explain in detail.

Myoglobin can also carry oxygen but the function is not oxygenation as

hemoglobin in the blood do. As I mention muscle is a cell, so we talk about nuclei

and the have endoplasmic reticulum and they have plasma membrane but in the

muscle the ER it has a specific name called sarcoplasmic reticulum. And the

plasma membrane is called sarcolemma. And the cytoplasm we called it

sarcoplasm.

IN MUSCLE

ER: sarcoplasmic reticulum

Plasma membrane : sarcolemma


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Cytoplasm : sarcoplasm

We have two terms here. HYPERTROPHY and HYPERPLASIA..

Hypertrophy is increase the size of the cell and hyperplasia increase of the

number of the cell. Actually, both of them occur in the skeletal muscle fiber.

Weight lifting people and gymnastics their muscle fiber become hypertrophy like

the body builder. This is due to the hypertrophy (enlarge of single muscle fiber).

In addition, sometimes hyperplasia might happened which increase the number

the cell.

*take note about the different between hypertrophy and hyperplasia

If you take one muscle in the body like rectus femoris or the biceps, the whole

muscle is surrounded by a dense connective tissue capsule or capsule or just

dense connective tissue. This connective tissue that covers the whole musclefrom outside, if you remember in the nerve muscle it is called epineurium, but in

the skeletal muscle is called epimysium.

From the epimysium, thin septa of connective tissue extend inwards divide the

muscle into smaller group that we called muscle fascicle. The dense connective

tissue that surround the muscle fascicle we called it perimysium. In muscle

fascicle there are many muscle fibers. Each muscle fiber in the muscle fascicle is

surrounded by a loose connective tissue, basal lamina and may add to it

reticular fiber is called endomysium.


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What is the function of the three types or borders part of the muscle fiber? We

know that the action of single muscle fiber is contraction. I dont think that one

muscle fiber, that cant be seen by naked eyes, can do anything. So we need the

summation of the contraction of the whole muscle fiber to produce an action. The

connective tissues that surrounding either the single muscle fiber or the whole

muscle that will transmit or sum the contraction of all muscle to a single

contraction. And transmit to the tendon or the end of muscle. In addition, the

characteristic of the connective tissue is rich in blood supply. The blood

supply to the muscle itself is come from the connective tissue surrounding either

the single muscle fiber or the whole muscle group. It is for the nutrition or to

transmit the summation of the contraction of the single muscle fiber.


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This is in light microscope, we can see the striation but we cannot tell the name

of the striation. We cannot differentiate the lines and bands as in the electron

microscope.

If we look to a skeleton muscle fiber in the electron microscope, we can see two

dark lines. This dark lines we called it Z-line. So this muscle fiber runs in this

direction (Z-line direction).The dark lines separate the certain area of the muscle

fiber we called it sacromere. It is the contractile unit of the muscle fiber (the unit

function of contraction). Contraction happened in between the Z-lines(sacromere). The summation of all contractile unit comes together as a

contractive of a single muscle fiber. In the middle, you can identified a darker

area called A-band ( in between the two light areas). Surrounding the Z-lines

from both side, the lighter area, we called it I-band. This means that the Z-lines

bisect the I-band into two areas. The lighter zone in the middle of A-band we

called as H-band. In the middle of the H-band, there is darker line called M-

line.

As you see, in this muscle fiber that is only full of actin and myosin. This area is

made mainly from actin and myosin filament. It looks like the whole muscle ismade up of actins and myosin. But, in fact the other organelles are distributed

somewhere here and here [refer picture]. In the electron micrograph you can see

here and here which is constitute a part of the sarcoplasmic reticulum. This

diagram here, it shows the details structure of the actin filament. So we know that

here the thin filament is made mainly of actin and the thicker filament is made


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mainly of the myosin. This yellow round structure here constitute the actin

filament and attached to it here something that called tropomyosin [refer

picture]. Here troponin that consist of three parts [refer picture]. The thick

filament is consist of the myosin while the thin filament is consist of the actin,

tropomyosin and troponin. I dont want much detail, just remember the name.

Simply remember how this muscle will contract.

Firstly, the first event of the contraction of the skeletal muscle is the effect of

action potential from the motor in the plate, nerve impulse spread the action

potential. The action potential will cause the release of calcium(Ca2+) from the

smooth endoplasmic reticulum in the muscle. Calcium will come and attached

to a part of troponin called troponin-c. And that will lead to the changed of

geometry of the structure. This will change the confirmation of troponin. And

finally lead to contraction. DONT GO FOR DETAIL..that will be discussed more

detail in PHYSIOLOGY.

I forget to mention that the Z-lines are consist of a protein called alpha-actinin.

This is the myosin fiber and it concise of area from here to here. So the myosin

fiber arranged themselves into this line. And this is the middle of myosin fiber

here which concise of M-line. And this is the area where the secretine kinase is

localized. The secretine activity is concise within M-line area. As I mention

before that the sarcoplasmic reticulum (SR) is found in the muscle fiber in

addition to the actin and myosin.


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This is the sketch diagram of the muscle fiber. In the diagram you can see the Z-

lines, A-band, the darker zone, and I-band, the lighter zone[refer the picture].

The T-tubules represent the sacrolemma towards the plasma membrane. At

this location between A-band and I-band , at the junction of the A-band and I-

band, the plasma membrane will enter inside the cell. The part of sarcolemma

that enter the A-I junction is called T-tubules(transverse tubules). It called

transverse tubules because it come across or enter perpendicular to the direction

of muscle fiber. At this area, the SR will become dilated here and here. And this

is the biostructure of the SR[refer picture]. It forms cisternae or cavity here and

here. And you can see beside it the T-tubules. That means the SR is bisected by

the T-tubules. Now we have three part, T-tubules and two SR from the both site,

this will form a structure called triads(means three). So the skeletal muscle is

characterized by the present of triads. SR is the source of Ca2+. The T-tubules, it

ensures the action potential will spread very fast to all fibers inside the muscle.

You have a term called RIGOR MORTIS. I said Ca2+ will be release from the

cisternae of SR and cause contraction. For how long the contraction will stay? I

dont think you can sustain the contraction for hours. Then ATPase will be

release and cause the Ca2+ to return back into the SR. It is an active process. It

needs ATPase (ATP enzyme) to release the Ca2+ from the muscle and cause

relaxation. If ATP enzyme missing?? What will happened?? The static

contraction or the prolonged contraction will happen. The muscle will continue


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contracting and this is what we called as RIGOR MORTIS. And this is what

happened after death.

During contraction, the A-band will be same in length. I-band will get shorter.

H-band will also be the same (no change). BUT the Z-line is getting

closer.[refer picture]

The main innervation of the skeletal muscle fiber is myoneural junction. Other

name is motor end-plate. It is a synapse between two nerves or between the

nerve and muscle. A motor or axon terminal is full of mitochondria and

microtubules. And here we have presynaptic membrane, synaptic cleft, and

then we have the muscle. So this is the structure of the skeletal muscle fiberinnervations. Other innervations of the muscle fiber, you dont have to worry

about it. Im not going to talk about golgi tendon or the muscles spindles (type I

fibers & type II fibers). I only talk about myoneural junction. And you can see, one

nerve here supplying the muscle fiber. All of this, these whole nerves (any nerves

not specific) and with a number of skeletal muscle fibers with supply altogether


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are called motor unit. Mysthenia gravis is another disease affecting the skeletal

muscle fibers. For the muscle to contract what happen? There will be release of

acetylcholine from the end-plate and reach the muscle and cause the

polarization and the depolarization. When the acetylcholine not attached to the

receptor in the muscle, there will be no contraction. If the receptors are deficient,

there is no contraction. Mysthenia gravis is characterized by not completely

absent receptor, but we can tell the deficiency or decrease in the number of

receptors or they have the receptors in a number but they have some resistant

of acetylcholine. They cant use the acetylcholine for contraction. It could cause

the weakness in muscular system because of either the deficient amount of

receptor or resistance to acetylcholine at the receptors.

Sometimes this caused the autoimmunity diseases.

CARDIAC FIBER

More or less they are like skeletal muscle fiber, they are striated and they have

the Z line and they have actin and myosin and all these detail( refer slide).but in

cell they are short branching. The nuclei are single sometimes 2. They(nuclei)

are round and situated in the middle of the cell. In addition to skeletal muscle

they have this line called intercalated discs. Although it looks like a line but it is

a composite structure.Compare to the skeletal, in skeletal we have epimycium, endomycium and

perimycium. But theres no epimycium and peryimicum in cardiac muscle fiber ,

we only have endomycium,basal lamina and reticular fiber in cardiac

muscle.In the electron micrograph, we can see the 3 structure forming the

intercalated discs we have desmosome, macula adherence and fascia

adherence and lastly gap junction. The one with length of the length of muscle

fiber we call it gap junction. Those that are perpendicular to the muscle fiber is

called macula adherence and fascia adherence.


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Fascia adherence is to ensure the adherence(attachment) of actin filaments

from both sides. And macula adherence is for the tonofilaments. And the gap

junction is junction between three openings. This will ensure when ca2+ ion

when released to reach to all muscle fiber in ventricle or atrium to allow them to

contract the muscle at one time. We need the contraction of the muscle fiber as a

whole in one time not like the skeletal muscle fiber .in skeletal muscle fiber, if youwant to carry 1kg we only need to contract 10% of the muscle fiber will contract,

if you want to carry 2kg another 20% and so on. If you want to carry a very heavy

object, all the skeletal muscles will contract. In cardiac muscle in any time all the

muscle in atrium and ventricle will contract at the same time. Theres no 10% or

20% contraction in these muscles.

In skeletal muscle we have triad. In cardiac muscle the t-tubular system is

more profound(more) than the skeletal muscle. Why? To bring the action

potential faster because its need for the contraction in ventricle and atrium so we

have more t-tubule. The location of t-tubule is at the Z-line . On the other hand,we have SR only at one side(less profound). And they form diad. (ER+T-tubule)

so we have triad in skeletal muscle and diad at cardiac muscle.

The other thing to compare, I need more energy for the contraction of cardiac

muscle than the skeletal muscle so the mitochondria is more. So 40% of the cell

is filled with mitochondria compare to 2% in the skeletal muscle.

Lipofuscin pigment is found in the cardiac muscle but not in skeletal muscle.

Also there are more fat exist in the cardiac muscle because I need them as fuel.

But in skeletal muscle we have glycogen and also from Krebs cycle as fuel.

We can find cardiac muscle cell at the ventricle and the atrium. In atrium there

are certain muscle fiber that are different in morphology. They do not contract,

they become an endocrine cell, they secret a hormone called atrial natriuretic

factor which affect the kidney tubule and cause the opposite effect of


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aldesterone of the suprarenal gland. They increase the loss of Na and H2O in

the joint.

SMOOTH MUSCLE FIBERWe call it smooth because they do not have striation, and they have fusiform in

shape. They have straight fiber with thin diameter . In cardiac they are branched

but here it is fusiform .They are scattering at the end and they have a dilatation

in the middle and taper towards the end. They have nucleus single in the middle

that is ovoid in structure. When we say it is not striated doesnt mean that they

dont have actin and myosin filament actually, there are actin and myosin

filament in smooth muscle fiber but they are not arranged in the sacromere

fashion.

The contraction on smooth muscle depends on the sliding of the actinover

myosin. The same principle applies, but the ca2+ will come to the place of

myosin by a carrying protein called Caldomulin. Caldomulin is a calcium-

carrying protein that brings the actin to the myosin.

In addition there are certain small masses that are attached to the cell wall or

plasma membrane from inside side or distributed in the cytoplasm. All this small

masses we call them dense bodies. All of the dense bodies are attached

together by the actin filament. Once the actin filament is contracted it will bring


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together these dense bodies. So the dense bodies are very important in the

contraction of the smooth muscle fiber. They also contain intermediate filament

called skeletin or desmin.

Whats left is only the continuation of the characteristics of the smooth muscle

fiber.

The smooth muscle fiber consists of two types:

1. VISCERAL smooth muscle fiber

Large number of muscle fiber they are found in hollow visceral in the body for

example intestine, stomach, uterus, urinary bladder, gall bladder. They are

characterized by large muscle fiber and they contain skeletin or desmin

intermediate filament. Nerve supply for both side in bulk smooth muscle fiber

at uterus or intestine. One nerve supplies a bulk of smooth muscle fiber

because we need the stomach or uterus to contract as a whole.

2. Multiunit

Small in size,

they have additional intermediate filament called Vimentin

Example is in iris of the eye.

In iris all nerve, supply a single muscle fiber for a precise

movement, while in the stomach to contract as a whole.

The other 2 slides were not discussed.

Thank you very much.

We tried our best to write this lecture. We apologize for any mistakes. Do refer to

the books and slides. All the best in our exams.

Done by: Fifi Rafiza, Fatin Akmal and khalisah liyana (5/11/09)

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Histology 10