Muscle tissue

Department of Histology and Embryology Medical college in Three Gorges University

• Muscle tissue can be divided into three

types:

Skeletal muscle

Cardiac muscle

Smooth muscle

Skeletal muscles

• Skeletal muscle is composed of

extremely elongated, multinucleate

contractile cells, often described as

muscle fibres, bound together by

collagenous supporting tissue.

• The connective tissue associated with muscle is named according to its relationship with muscle fiber:

endomysium

perimysium

epimysium

• Endomysium the delicate layer of

reticular fibers that immediately

surrounds individual muscle fibers.

picture

• Perimysium is a thicker connective tissue

layer that surrounds a group of fibers to form a

bundle or fascicle.Fascicles are functional

units of muscle fibers that tend to work

together to perform a specific function.

• Epimysium is a thicker layer connective

tissue which invested the whole muscle

mass, large blood vessels and nerves enter

the epimysium and divide to ramify

throughout the muscle in the perimysium

and endomysium.

17 18

perimycium

endomycium

The histological features of skeletal

muscle fibres in longitudinal section:

1) extremely elongated, unbranched

cylindrical cells

2) with regular cross-striations

3) numerous flattened nuclei located at

fairly regular intervals just beneath the

sarcolemma (plasma membrane)..

the cross-striations result from the

arrangement of the contractile proteins.

Cross striation means alternating light and

dark bands in the longitudinal sectioned

skeletal muscle.

Tran

sverse section

perimycium

endomycium

This micrograph of skeletal muscle cut

in transverse section shows the extreme

peripheral location of the nuclei of

skeletal muscle fibres. In cross-section

muscle fibres appear polyhedral with

flattening of adjacent cells.The cell is

spherical, polyhedral or irregular shape.

Tran

sverse section

Myofibrils

Connective tissue

• Sarcomere : the part of a myofibril situated

between two consecutive Z-band is called

a sarcomere. Each of them is composed of

I ½+ A band + I ½. It is the stuacture and

function unit of myofibrils

• The sarcomere consists of two types of myofilaments, thick filaments and thin filaments.

Why do the myofibril display cross striation?

Myofilaments

Thick filaments

Thin filaments

• Each type remains constant in length

irrespective of the state of contraction of the

muscle. The thick filaments, which are

composed mainly of the protein myosin, are

maintained in register by their attachment to

a disc-like zone represented by the M line.

• Similarly the thin filaments, which are

composed mainly of the protein actin, are

attached to a disc-like zone represented by

the Z line. The I and H bands, both areas of

low electron density, represent areas where

the thick and thin filaments do not overlap

one another.

light band dark band

Z 线

H

M

肌节： 1/2I 带 + A 带 + 1/2I 带

Thick filaments Thin filaments

sacomere

Thick filaments: Myocin

Thin filaments: actin, tropomyosin and troponin

Thick filaments

Thin filaments

Myocin

actin ， tropomyocin ， troponin

• Transverse tubules :

These fingerlike invaginations of the sarcolemma form a complex anastomosing network of tubules that encircle the boundaries of the A-I bands of each sarcomere in every myofibrils.

Function: rapidly conduct impulse for contraction to every myofibrils in the muscle fiber.

Sarcoplasmic R

Transverse tubules

Triad Terminal cisterna

Sarcoplasmic reticulum:

• Sarcoplasmic reticulum is a specialized smooth endoplasmic reticulum. It forms extensive anastomosing network which runs between and around the myofibrils in a longitudinal direction. Adjacent to opposite sides of each T tubule are expanded terminal cisternae of the sarcoplasmic reticulum

• Triad:

• This specialized complex consist of a T

tubule with 2 lateral terminal cisternae of

sarcoplasmic reticulum is known as the

triad.

Cardiac muscle

• Cardiac muscle fibers are essentially short

cylindrical cells with one or at most two

nuclei, centrally located within the cell. The

ends of the fibers are split longitudinally

into a small number of branches.

Intercalated disc

disc

• Micrograph illustrates an extremely thin resin-embedded section at very high magnification. The branching cytoplasmic network is readily seen with prominent intercalated discs marking the intercellular boundaries. Note the typical cross-striations.

• Summing: Feature of cardiac muscle in LM

• 1. short cylindrical ,one or two nuclei, located

in the center of the cardiac muscle.

• 2. cross-striations of cardiac muscle , are not

very clear than that of the skeletal.

• 3.Intercalated disc闰盘 ,

• it is dark-staining transverse line that

cross the chains of cardiac muscle.

located between the ends of adjacent

cardiac muscle cells,which can cause the

adjacent cells to contract almost

simultaneously.

Feature of cardiac muscle in EM

• 1. myofibrils is less than that of SM

• 2. Tranverse tubules is thick

• 3. Sarcoplasmic reticulum is less

• 4. terminal cisternae is small,

• 5. mitochondria is aboundant

Mitochondria

Sarcoplasmic reticulum

Intercalated disc

desmosome

SR Terminal cisternaeT tubulesdyad

Triad

Sarcoplasmic R

T C

T tubules

dyad

Smooth muscle

• Smooth muscle is involuntary and

unstriated. They are often seen as

individual fibers or slender bundles or

fascicles, however they are predominantly

found lining the visceral organ and blood

vessels.

• Smooth muscle fibers are elongated, spindle-

shaped cells with tapered ends which may

occasionally be bifurcated. Smooth muscle fibers

are generally much shorter than skeletal muscle

fibers and contain only one nucleus which is

elongated and centrally located in the cytoplasm

at the widest part of the cell.

• Smooth muscle fibres are bound together in

irregular, branching fasciculi.Within the

fasciculi, individual muscle fibres are

arranged roughly parallel to one another

with the thickest part of one cell lying

against the thin parts of adjacent cells.

• The contractile proteins of smooth muscle

are not arranged in myofibrils as in skeletal

and cardiac muscle, and thus visceral

muscle cells are not striated.

•This micrograph illustrates smooth muscle cut in longitudinal section. At this magnification, the micrograph demonstrates the spindle-shaped and elongated central nuclei of smooth muscle cells.

• In this case, the fibres are arranged in a highly regular manner and packed so closely that it is difficult to identify individual cell outlines although cell shape can be deduced from that of the nuclei.