Histology of Muscle

Question 1

What are the 4 classes of muscle?

Answer 1

• Cardiac
• Skeletal
• Smooth
• Myoepithelial

Question 2

How is myosin made? What does this form?

Answer 2

It is made as cells fuse together. The myoblast is made by the fusion of many cells and is therefore multi nucleated.

Question 3

What connects muscle to the tendon?

What connects muscle to bone?

Answer 3

Connective tissue

Tendons

Question 4

What is a myotendinous junction?

Answer 4

A site of connection between tendon and muscle. The epimysium merge with the dense collagenous connective tissue of the tendon.

Question 5

How do we recognise skeletal muscle under a microscope?

Answer 5

Peripheral nuclei of fibres
Multi nucleated
Endomysium separating individual fibres 
Blood vessels
Striations

Question 6

What is the correct name for a muscle cell?

What is this name made up of?

Answer 6

Myofibre

Made up of myofibrils

Question 7

Explain all the bands present in a sarcomere

Answer 7

A Band - overlap of myosin and actin
I band - actin filament]
H band - myosin filament
Sarcomeres divided by Z lines

Question 8

Where does a myofibre receive innervation from?
What is formed at a neuromuscular junction?
What does motor unit size dictate?

Answer 8

• one motoneuron
• a synapse
• the degree of muscle control (smaller ones in eyes for more control)

Question 9

Give a definition of a motor unit

Answer 9

The set of muscle fibres which are innervated by the axonal branches of a single motor neuron of the CNS

Question 10

What is found in white and red muscle fibres?

Answer 10

White = fast myosin isoform. They contain small amounts of myoglobin and contract rapidly, hence quickly fatigued.
Red = slow myosin isoform. is found in red muscle. They contract slowly (endurance) and contains a lot of myoglobin.

Question 11

Give details on satellite cells found in skeletal muscle including what they form and where they are found

Answer 11

Found on the surface of muscle fibres.
They are a population of stem cells.
Usually quiescent (not dividing)
Can be activated and enter the cell cycle to become myoblasts. The myoblasts can then differentiate and fuse to form new myofibres.
Satellite cells can renewq to maintain the stem cell population
Important for muscle growth after birth, muscle maintenance, muscle repair and regeneration.

Question 12

Give details on the nuclei of cardiac cells.

How do cardiac cells connect together?

Answer 12

• mono nucleated
• nuclei centrally located
• cells connect via intercalated discs
• cells have gap junctions to allow transmission of action potentials

Question 13

Cardiac tissue has functional syncytium. What is this?

Why does it form?

Answer 13

A single cell with multiple nuclei formed by the fusion of cells or nuclei division.
Forms due to intercalated discs between cells.

Question 14

Why is regeneration of cardiac muscle cells not possible?

Answer 14

There are no satellite cells

Question 15

What is the function of a desmosome and a gap junction during muscle contraction?

What does the last sarcomere have at the end instead of a Z - line?

Answer 15

Desmosome - holds the sarcomeres together when contracting
Gap junction - allows the calcium to flow

It has actin bound to the end.

Question 16

Why does the heart not rely on for contraction and why?

Answer 16

It does not rely on neurons to coordinate contraction because the muscle cells do this themselves due to conductive myocytes called Purkinje fibres. These fibres ensure that the atria contract from the top down and ventricles from the bottom up,

Question 17

Where is smooth muscle usually found? What formation is it found in?

Answer 17

Found in walls of the gut, blood vessels, respiratory tract

Usually found in rings

Question 18

Give details on the histology of smooth muscle fibres

Answer 18

• each cell surrounded by a basal lamina
• small amount of connective tissue between cells
• spindle - shaped cells
• no myofibrils so no striations

Question 19

What is in the cytoplasm of smooth muscle cells?
What allows electrical excitation to spread from cell to cell?
What is contraction controlled by?

Answer 19

Filaments of actin and some myosin but more actin

Gap junctions

Hormones or the balance between the sympathetic and parasympathetic system