Smooth Muscle Tissue

Question 1

Describe the appearance of smooth muscle tissue cells.

Answer 1

They have a single nuclei with a central location in the cell. The nuclei follow the shape of the cell, which is elongated in this case.

Question 2

Where can smooth muscle tissues be found?

Answer 2

• Tunica media of vessels.
• Associated with capillaries in the form or single cells called pericytes.
• Digestive, respiratory, urinary and reproductive organs.

Question 3

What are the functions of smooth muscle tissue?

Answer 3

• Associated with peristaltic movement.
• Relevant in controlling respiratory systems.
• Regulating diameter of vessels.

Question 4

How are the functions of smooth muscle tissue regulated?

Answer 4

These functions are regulated by the involuntary nervous system.

Question 5

What structures can smooth muscle cells organise themselves in?

Answer 5

Smooth muscle cells can organise into the laminae of the tissue, as well as forming smooth muscles, e.g. arrector pili.

Or we can find isolated cells, like the myoepithelial cells which are responsible for the squeezing of the glandular tissue.

Question 6

Describe the appearance of smooth muscle cells under TEM.

Answer 6

The nuclei under TEM appear darker from staining, they are elongated and follow a spindle shape.

All the organelles in the cytoplasm are organised at the 2 sides of the nucleus.

The presence of mitochondria can be observed.

During contraction, the nucleus takes on a corkscrew shape. This can happen after fixation when the cells can contract a bit. This also changes the appearance of the cytoplasm.

Question 7

What is the size of smooth muscle cells?

Answer 7

Length 20-500 μm, thickness 1-3 μm

Question 8

Describe the organisation pattern of smooth muscle cells.

Answer 8

Groups of cells form laminae, the outer layer is longitudinal and the inner is oriented circularly.

The shape of the nucleus also represents the cell’s orientation. The longitudinal cells have an elongated nucleus, while the circular cells have a more round nucleus.

Question 9

What are small smooth muscle tissues? Where can they be found?

Answer 9

Small muscles made of smooth muscles can be found in the arrector pili, which is responsible for erecting the hair on our skin.

This type of tissue is also present in the ileus, which is the muscle responsible for constriction or dilation of the pupils.

Question 10

Where can isolated smooth muscle cells be found?

Answer 10

They can be found in the glands. Also in the male reproductive apparatus in the male seminiferous tubules.

Question 11

What are the functions of isolated smooth muscle cells?

Answer 11

By contracting, they squeeze the adenomeri of the gland.

Myoid cells help the seminiferous tubules to release the spermatozoa.

Question 12

What are the dark spots observed in the cytoplasm?

Answer 12

Several dark spots and plugs can be observed in the cytoplasm. These are attaching areas for the contracting apparatus, called cytoplasmic dense bodies and subsarcolemmal dense bodies. These are dense areas containing alpha actinin.

Question 13

What types of filaments are present in smooth muscle tissue?

Answer 13

Actin

Desmin /vimentin - intermediate filaments

Question 14

What are the differences between actin filaments in smooth muscle vs skeletal muscle?

Answer 14

The difference between actin filaments in smooth muscle cells vs skeletal muscle cells are the length, the smooth muscle tissue are longer than skeletal muscle.

The contracting apparatus also functions differently. The hydrolysis of ATP occurs slower in smooth muscle tissue, which allows the muscle to contract slower but for a longer period of time.

Myosin filaments of the smooth muscle cells are thinner than skeletal muscles, they are visible under appropriate conditions.

Question 15

What are the dark spots observed in the cytoplasm?

Answer 15

Several dark spots and plugs can be observed in the cytoplasm.

These are attaching areas for the contracting apparatus, called cytoplasmic dense bodies and subsarcolemmal dense bodies.

These are dense areas containing alpha actinin.

Question 16

What are caveulae?

Answer 16

Caveolae are observed on the sarcolemma, which is considered to have a similar function to t tubules in the skeletal muscle tissue.

Question 17

What type of junctions are present?

Answer 17

Gap junctions (nexus) are also present and they interconnect the cells.

Question 18

How are the proteins organised?

Answer 18

There are no proper sarcomeres, but the dense bodies represent attachment sites for the actin filaments. And the myosin chains interconnect.

The mechanism is the same as skeletal muscle tissue.

Question 19

How do the myosin chains appear in smooth muscle vs skeletal muscle?

Answer 19

The myosin chains are organized in side-polar filaments. While the bipolar filaments are the organisations found in the sarcomeres.

This allows a bidirectional sliding of filaments.

Question 20

How is Ca2+ released and regulated?

Answer 20

The signal to start contraction is Ca2+. with the influx of Ca2+ through calcium gated channels, though this is not enough and there is also Ca2+ released from the SER.

This is regulated in different ways, one of them is through the action of hormones. E.g. contraction of the uterus in labour.

Question 21

Describe the mechanism that phosphorylates myosin.

Answer 21

Ca2+ binds to a protein called calmodulin, this complex activates different enzymes.

For instance in muscle contraction, the calcium calmodulin complex binds to the MLCK which is responsible for the phosphorylation of the light chains of myosin.

This allows myosin to change conformation and be available for forming myosin myofilaments.

Question 22

What are the sifferent types of stimuli for muscle contraction?

Answer 22

Innervation of the autonomic nervous system (unitary and multi unitary).
Stimulating hormones
Chemical stimuli
Mechanical stimulation (stretching)
Independent properties to maintain a partial contraction (muscle tone).

Question 23

How does the innervation of smooth muscle cells occur?

Answer 23

The innervation of the smooth muscle tissue occurs through the formation of varicosity which contains the neurotransmitter.

Question 24

What happens in unitary innervations? (check)

Answer 24

In the unitary innervation, there is no total innervation of the whole sheet of cells, but contractions are transmitted through gap junctions.

Question 25

Describe the regenerative ability of smooth muscle cells.

Answer 25

Smooth muscle tissues have good regenerative capacity, they are proliferating cells.

Question 26

What kind of cells can contribute to the proliferation of smooth muscle cells?

Answer 26

Mesenchymal stem cells can also differentiate to smooth muscle cells.

While in the periphery muscles are pericytes, which are single cells with contracting ability. They retain a stemness and can differentiate and contribute to the tissue in case of damage.