Muscle

Question 1

What are the functions of muscle tissue?

Answer 1

Movement
Maintenance of posture
Joint stabilisation

Question 2

What are the two main types of muscles?

Answer 2

Striated muscle
Smooth muscle

Question 3

What are the types of striated muscle tissue?

Answer 3

Skeletal muscle - attached to bone, responsible for motor movement.
Cardiac muscle - found in the wall of the heart, and in the base of the large veins that empty into the heart.

Question 4

What are the characteristics of skeletal muscle?

Answer 4

Attach to and move skeleton
Fibres - multinucleate cells
Have obvious striations in cells
Contractions are voluntary

Question 5

What are the characteristics of cardiac muscle?

Answer 5

Only in the wall of the heart.
Contractions are involuntary

Question 6

What are the characteristics of smooth muscle?

Answer 6

Lack striations
Cells are fusiform spindle shaped.
There is one central nucleus.
They are grouped into sheets perpendicular to one another.

Question 7

What are the structures of the skeletal muscle?

Answer 7

Consists of muscle fibres which are long, cylindrical multinucleated cells.
Epimysium
Perimysium
Endomysium

Question 8

What does epi mean?

Answer 8

Outside

Question 9

What does endo mean?

Answer 9

Inside

Question 10

What does peri mean?

Answer 10

Surrounding

Question 11

What is epimysium?

Answer 11

Dense connective tissue sheath
Surrounds the whole muscle externally

Question 12

What is perimysium?

Answer 12

Connective tissue septa
Subdivides the muscle internally into fascicles, each containing several nerve fibres.
Nerves and blood vessels penetrate.

Question 13

What is endomysium?

Answer 13

A more delicate, looser connective tissue - surrounds individual muscle fibres.

Question 14

What does skeletal muscle look like?

Answer 14

see image

Question 15

What is the muscle fibre?

Answer 15

Each muscle fibre is the cell of the skeletal muscle.
It consists of myofibrils, which each have thick and thin actin and myosin myofilaments.

Question 16

What is a sarcomere?

Answer 16

The units of contraction.
Contains actin and myosin.
Dark, transverse Z bands mark the ends of each sarcomere and anchor the thin filaments.
Titin protein binds the thick filament to the Z disc.

Question 17

What is the structure of myofibrils?

Answer 17

Myofibrils has alternating light and dark filaments.
Light filaments are actin containing I bands.
Dark filaments are myosin containing A bands along its length.

Question 18

What is the H zone?

Answer 18

In the centre of each A band.
It is lighter because it is not overlapped by thin filaments.
It is then bisected by a thin, dark M band.

Question 19

What is the sarcoplasmic reticulum?

Answer 19

The SR is smooth ER.
Invagination of the cell membrane are T-tubules which surround the myofibrils.
Two terminal cisternae of SR surround each T-tubule to form a triad.

Question 20

What do SR cisternae do?

Answer 20

Cisternae store Ca2+ and release when the muscle is stimulated to contract.

Question 21

How is there simultaneous contraction?

Answer 21

The T tubules are continuous with the sarcolemma (cell membrane) so the whole muscle contracts simultaneously.

Question 22

How does muscle contraction occur?

Answer 22

The depolarisation of the T tubule membrane triggers the release of Ca2+ from terminal cisternae.
This initiates muscle contraction by binding to the troponin-tropomyosin complex.
This causes horizontal sliding of thin filaments on thick filaments, which shortens the muscle.

Question 23

How does muscle relaxation occur?

Answer 23

Results from the decrease of cytosolic free Ca2+ concentration.

Question 24

What is cardiac muscle?

Answer 24

Branched and striated.
It consists of individual cylindrical cells, each containing one or more central nuclei, and linked by adherens and gap junctions.

Question 25

Where are the nuclei in skeletal muscle?

Answer 25

Peripheral in the cell

Question 26

What are intercalated discs?

Answer 26

Adjacent cardiac cells are joined to each other by intercalated discs. These are highly specialised adhesion junctions containing fascia adherens, gap junctions and desmosomes. Found only in cardiac muscle.

Question 27

How does contraction occur in cardiac muscle?

Answer 27

Purkinje fibres exhibit a spontaneous rhythmic contraction. They generate and rapidly transmit action potentials to various parts of the myocardium. It is regulated by the autonomic nervous system.

Question 28

How are cisternae arranged in cardiac muscle?

Answer 28

Terminal cisternae are much smaller than in skeletal muscle. One terminal cisterna and T tubules form diads located at the level of the Z line, with one in each sarcomere.

Question 29

What is the structure of smooth muscle?

Answer 29

Dense bodies are the main unit of contraction. Thin filaments attach to dense bodies using a-actinin, located at the cell membrane and deep in the cytoplasm. Dense bodies at the membrane are also attachment sites for intermediate filaments and adhesive junctions between cells.

Question 30

What are the contractions of smooth muscle?

Answer 30

Contractions are involuntary, slow, sustained and resistant to fatigue. Does not always require a nervous signal - can be stimulated by stretching or hormones.

Question 31

Where is smooth muscle found?

Answer 31

The walls of hollow organs - digestive organs. Also found in the respiratory, urinary and reproductive tracts, and are a major component of blood vessels.

Question 32

How is smooth muscle adapted?

Answer 32

The arrangement of the cytoskeleton and contractile apparatus allows the multicellular tissue to contract as a unit, which provides better efficiency and force.

Question 33

How does contraction occur in smooth muscle?

Answer 33

Actin-myosin binding occurs with myosin phosphorylation by myosin light chain kinase (MLCK). This is triggered when calmodulin binds Ca2+.

Question 34

How is skeletal muscle repaired?

Answer 34

There is a sparse population of satellite cells. Limited regeneration capcity. After injury, inactive reserve myoblasts become activated, proliferate and fuse to form new skeletal muscle.

Question 35

How is cardiac muscle repaired?

Answer 35

Lacks satellite cells. Shows very little regenerative capacity. Damaged heart muscle is replaced by fibroblasts and growth of connective tissue, this causes scarring.

Question 36

How is smooth muscle repaired?

Answer 36

Has similar mononucleated cells. Has active regenerative capacity. After injury, smooth muscle cells undergo mitosis and replace the damaged tissue.