Histology

Muscular Tissue

Muscular Tissue


It is responsible for body movements, it mainly derived from mesoderm except the iris muscle of eye which is ectoderm in origin,

There are 3 types of muscles 1. Smooth muscle 2. Skeletal muscle 3- Cardiac muscle

There are basic similarities between the three types of muscles:-


1- They are all mesodermally derived. 2- They are elongated, parallel to their axis of contraction. 3- They have numerous mitochondria to accommodate their high-energy. 4-They contain contractile elements called myofilaments, contain proteins in the form of actin and myosin


1. Smooth muscle (involuntary muscle, Non-striated muscular tissue) they are also known as visceral muscles. These tissues, being very simple in structure, the muscle cells of this tissue are involuntary since their contraction and relaxation are not under voluntary control.



The muscle fibers are spindle-shaped with oval nucleus lies in the middle wide portion surrounded by cytoplasm called sarcoplasm which contain mitochondria, endoplasmic reticulum & Golgi complex, the sarcoplasm contain a number of longitudinal myofibrils which give longitudinal striation to the fiber,


The muscle cell surround by cell membrane called plasmalemma(sarcolemma) which is formed of two layers protein &lipid, The contraction of these muscles is slow and is retained for a longer time. Hence they do not get fatigued soon. This tissue is found in the walls of visceral organs such as stomach, lungs, bladder, blood vessels etc.


2. Skeletal muscle (voluntary muscles, the contraction of these muscles is under voluntary control).


It is called skeletal muscle because it is attached to the skeleton, it is also known as striated muscular tissue they are formed of muscle fibers or cells which are multinucleated cylindrical in shape arranged parallel to each other, they contain cytoplasm & surrounded by sarcolemma, the nuclei are periphery located under the sarcolemma.


The muscle fibers are not branched, Skeletal muscles are surrounded by c.t. called epimysium from the epimysium thin septa of looser C. T extends between the bundles of muscle fibers is called perimysium each muscle fiber is itself surrounded by a delicate layer of C. T called the endomysium.

Microscopically features of skeletal muscles:-

As observed with the light Microscope , longitudinally section of muscle cells show transverse (cross) striations of alternating dark areas (bands) called Anisotropic area ( A- band ) are birefringent in polarized light & light areas called Isotropic ( I- band ) do not polarized light . The A-band is formed of both Actin & Myosin while, the I-band is formed of Actin only. A thin membrane called (Z-band) runs transversely.



This Krause's membrane (Z-band) passes through the centre of all I-bands in a single horizontal line along the width of the muscle fiber. Sarcomere is the smallest repetitive subunit of the contractile apparatus extends from Z line to Z line contain A and I bands. The Sarcomere is the structural and functional unit of a muscle fiber.

Z line

Types of skeletal muscle fibers:


Red and white muscles It is classified into 3 types; 1. Red muscle fibers: they characterized by a- they are small in diameter. b- They have a high content of myoglobin & cytochrome which are responsible for the dark red color.


c- They contain great number of mitochondria. d- They contract slower than the white fibers. These fibers are in the breast muscle of migrating birds & mammalian limbs.


2- White fibers: they characterized by: a- they are larger in diameter. b- They have a low content of myoglobin & cytochrome. c- They have fewer mitochondria. d- They contract rapidly. These fibers are in the breast muscle of chicken & turkeys.


3- Intermediate fibers: they have characteristics between the two types Above. In human the skeletal muscles composed of mixture of these three types of fibers.

3- Cardiac muscle (involuntary):

This is also striated muscle which have cross striation in addition to longitudinal striation but the striation are less clear than the striations of skeletal muscle, The muscle fibers are branch & anastomose, each Muscle fiber consist of several muscle cells joined end to end by intercalated discs which are heavy transverse line across the fiber ,


their function is to aid transmit of impulses from one cell to another , each muscle contain one or two nuclei . The sarcoplasm is abundant; its function is to pump blood through the circulatory system by contraction.

Voluntary

Fast
Involuntar

Fast

No disks
Intercalated disks
No disks 
Disks?
Nucleus peripheral
Nucleus central
Nucleus central
Nucleus location
Not branched
Branched
Not branched
Branched
Cylindrical
Cylindrical
Spindle-shaped


Striated
Striated
Not striated
Striated
Skeletal
Cardiac
Smooth