General Histology and Histotechnique (1st semester 2012-2013)

MUSCLE TISSUES Myology Functions of muscle movements: 1. Produce body movements Ex. Skeletal muscle – Pull bones - Muscle movements; walking, running - With the help of joints

2. Stabilize body positions - To sit, stand, balance position

3. Regulate organ volume - Due to smooth muscle Smooth muscle Location: Stomach – for temporary storage Uterine – Store temporarily the urine 4. Move substances within the body Ex. Cardiac muscle - blood will be pumped Smooth muscle – enzymes, food GIT Skeletal muscle – substances within the body; produces Lactic acid. 5. Produce heat - Body movement – Increases temperature Properties Contractility - To generate the pulling force - Ability of muscle to contract forcefully Excitability - Ability to respond to a certain stimuli to produce

electrical signals Extensibility - Ability to stretch without being destroyed Elasticity - Able to go back to its original shape/length

Similarities of Muscle Tissues - Cells of muscles: fibers Muscle contraction - Depends on two types of myofilaments (contractile

proteins)

Actin

Myosin

- Sarcolemma – plasma membrane - Sarcoplasm

SKELETAL MUSCLE - To move the bones of skeleton - It does not consists of single muscle fiber - It form multinucleated used muscle fiber - Form by diffusion of myoblast

Embryonic cells of skeletal muscle

General Histology and Histotechnique (1st semester 2012-2013)

- Striations are present - Nucleus is found at the Peripheral – at the sides - Attached to the bones I. Connective Tissue components of skeletal

muscle 1. Fascia – (Bandage) - Fibrous connective tissue that is deep to the skin - Surrounds muscles and other organs of the body.

2 types: a. Superficial fascia or the subcutaneous layer - separate muscles from skin Made up of: - Areolar connective tissue - Adipose tissue Functions:

1. It provides a pathway for nerves and Blood vessels to enter and exits muscles.

2. Stores most of the triglycerides 3. Serves as good insulating layer; reducing heat

loss – due to Connective tissue 4. Protects muscles from physical trauma

b. Deep fascia - A dense irregular connective tissue Functions: - Lines the body wall and limbs - Holds muscles together - Allows free movement of muscles - Carries Blood vessels, nerves, Lymphatic vessels - Fills the spaces between muscles 2. Three layers of connective tissue - Extend from the deep fascia to further protect and

strengthen skeletal muscle

a. Epimysium - Encircles the whole muscle/covers the muscle - Dense irregular connective tissue b. Perimysium

- Encircles bundles of muscles Wrapped by Fascicle

10-100 or more muscle;

Individual muscle fibers

Dense irregular connective

tissue

c. Endomysium

- 1 bundle of muscle

- Covers the individual muscle fiber

- Areolar tissue

- Separate muscle fibers from each others

Basic features of skeletal muscle

Nerves and blood vessels - Each skeletal muscle is supplied by branches of one

nerve, one artery, one or more veins - Nerves and vessels branch repeatedly - Smallest nerve branches serve

General Histology and Histotechnique (1st semester 2012-2013)

Individual muscle fibers Tissue sheaths – extend to from the tendon - attaches muscles to bone.

Neuromuscular junction - A place in the body where nerves meet a muscle. - A synapse the motor neuron and the muscle fiber. Muscle attachments - Most skeletal muscles run from one bone to

another - One bone will move – other bone remains fixed

Origin – less movable part of the bone

Insertion – more movable attachment

Microscopic organization and development

a. Embryonic development - Fusion of myoblasts into muscle fibers Myoblast – fused to form the muscle fibers - After fusion, still with satellite cell, immature

muscle fiber will lose their potential to divide hence, satellite cell retains it.

- It cannot have any cell division Satellite cell – forms the muscle Functions: - Acts as a reserved population of cells - Whenever skeletal muscle is in its normal state it is

inactive or quiescent; if it is injured it becomes active.

- It continues to divide in order to repair and grow more muscle fibers.

- Repair and maintenance of skeletal muscle

b. The sarcolemma of the fiber encloses sarcoplasm

and myofibrils which are striated c. A sac of sarcoplasm is reticulum wraps around

each myofibril - Composed of a triad: is a two terminal cisterns and

a T (transverse tubule).

Histological features

General Histology and Histotechnique (1st semester 2012-2013)

Structure of a skeletal muscle fiber

Sarcoplasmic reticulo Triad 1. Sarcolemma - Muscle fibers plasma membrane which is

perforated with thousands of tiny invagination called triad.

Two terminal sisters: a. Terminal cisterns - Structure madeup of two strands on either strands

of T tubule. b. T tubules - These are tunnels from the surface towards the

center of each muscle fiber. Function of Triad: To ensure that all parts of the muscle fiber become excited by an action potential virtually simultaneously. 2. Sarcoplasm

- The cytoplasm of muscle fibers - Contains a substantial amount of glycogen and

myoglobin Oxygen binding protein which is red colored

globins and found only in muscle fibers. 3. Myofibrils - Contractile element of muscles - Contains overlapping thick and thin filaments - With prominent striations

Alternating line and dark bands 4. Sarcoplasmic Reticulum - Fluid-filled system of membranous sacs that

encircles each myofibrils Function: - Releases Calcium ions to trigger muscle contraction 5. Sarcomere - Basic functional unit of myofibril - Compartment of filaments inside the myofibrils 6. Filaments - Within the myofibrils of two types:

a. Thin filaments

- 8 nm in diameter - Protein: Myosin b. Thick filaments

- 16 nm in diameter - Protein: Actin 7. Mitochondria - Small and less numerous skeletal muscle fiber - For cell respiration - Powerhouse of the cell - For the synthesis of ATP Zones and bands of sarcomere: 1. A-band – anisotropic - Darker middle portion - Where thick filaments (myosin) are located - Toward the end of the A band is a zone of overlap:

where thick and thin filaments lie side by side

General Histology and Histotechnique (1st semester 2012-2013)

2. I-band – isotropic - Lighter dense area - Where thin filaments (actin) extend - No thick filaments 3. Z-line - Distinct dark line running down the middle of the I-

band - Where thin filaments are attached end to end - Zone of apposition (increase in diameter) of actin

filaments belonging to two neighboring sarcomeres 4. M-line - So named because it is at the middle of sarcomere - Where thick filaments are attached end-to-end in

the center of the A-band - Band of connections between myosin filaments - Supporting proteins that hold thick filaments

together at the center of H-zone. 5. H-band - Appears along the middle of A-band, between the

free ends of the thin filaments when muscles are stretched.

- Zone of myosin filaments only (no overlap with actin filaments) within the A-band

CARDIAC MUSCLE

II. Cardiac muscle tissue - Principal muscular tissue in the heart wall - Shorter in length and larger in diameter - Exhibit branching which gives an individual fiber and

y-shaped appearance - Nucleus centrally located

General Histology and Histotechnique (1st semester 2012-2013)

Histological parts: 1. Sarcolemma - Plasma membrane surrounding the cardiac muscle 2. Sarcoplasm - The cytoplasm 3. Mitochondria - Larger and more numerous 4. T-tubules - Wider and less abundant and there is only one T-

tubule per sarcomere located at the Z-disc. 5. Sarcoplasmic reticulum - Few, has limited intracellular reserved of Calcium

ions. 6. Myofibril - Contractile unit 7. Sarcomeres - Functional unit, same zones, bands and lines as the

skeletal muscle. SMOOTH MUSCLE

III. Smooth muscle tissue Two types: 1. Visceral smooth muscle tissue - Also known as the single unit smooth muscle tissue

- Found in wrap around sheets that form part of the walls of smaller arteries and veins and hollow viscera such as the stomach, intestines, uterus, and urinary bladder.

2. Multiunit smooth muscle tissue - Consists of individual fibers, each with its own

motor neuron terminals and with few gap junctions between neighboring fibers

- Found in the walls of large arteries, in airways to the lungs, in arrector pili muscle that attaches to hair follicles and muscles of iris that adjust pupil diameter

Histological features: 1. Endomysium - Surrounds the smooth muscle fiber 2. Have a single centrally located oval nucleus 3. Sarcoplasm - Contains both thick and thin filaments 4. There is no sarcomere 5. Contains intermediate filaments 6. Have a sarcoplasmic reticulum which is scanty 7. Do not have T-tubules 8. Gap junction in visceral smooth muscles is present

but not in multiunit smooth muscle.