Structure of Skeletal, Cardiac and Smooth Muscle

Question 1

How is the muscle attached to bone?

Answer 1

By tendons

Question 2

What creates muscle sections?

Answer 2

extensive connective tissue coverings that support nerves and capillaries

Question 3

What is the name for a bundle of muscle fibre?

Answer 3

A fascicle

Question 4

What are fascicles wrapped in?

Answer 4

Perimysium

Question 5

What is epimysium?

Answer 5

dense collagenous sheath that surrounds gross muscle

Question 6

What is perimysium?

Answer 6

loose collagenous connective tissue that surrounds fascicle

Question 7

What is endomysium?

Answer 7

connective tissue that separates the muscle fibres

Question 8

What is a fascicle?

Answer 8

grouping of elongated bundles of muscle fibres (cells)

Question 9

What structures allow you to recognise skeletal muscle?

Answer 9

Nuclei, striations and clear muscle fibre

Question 10

What structures allow you to recognise cardiac muscle?

Answer 10

Branching cells, prominent nuclei, striations and intercalated discs

Question 11

What structures allow you to recognise smooth muscle?

Answer 11

The presence of a ton of muscle cells with nuclei that are seemingly disordered and layered

Question 12

When considering the histology of skeletal muscle, which structure is barely visible

Answer 12

The endomysium

Question 13

What may one use to take a histology of skeletal muscle?

Answer 13

Medium Power transverse section Haemotoxylin and Eosin (H&E)

Question 14

Describe Haemotoxylin and Eosin (H&E) dyes

Answer 14

Eosinis anacidicdye.It stains basic (oracidophilic) structures red or pink.
Haematoxylincan be considered as abasicdye. It stains acidic (orbasophilic) structures a purplish blue

Question 15

What defining characteristics does a skeletal muscle cell (fibre) have?

Answer 15

• multinucleated
• contains many mitochondria
• has special structures called Transverse tubules (T tubules)
• has repeating structure of sarcomeres and myofibrils
• has specific terms for some of its intracellular structures
• also called voluntary muscle or striated muscle
• attached to bone by tendons
• under voluntary and reflexive control

Question 16

What specific terms can be used when describing the intracellular structures of the skeletal muscle fibres?

Answer 16

Lotsa sarcos
Sarcolemma = Plasma membrane
Sarcoplasm = Cytoplasm
Sarcoplasmic reticulum = Smooth ER

Question 17

What can be used to identify a skeletal muscle fibre in longitudinal section histology?

Answer 17

Elongated, unbranched, cylindrical cells with numerous flattened nuclei just beneath thesarcolemma.

Question 18

Describe the structure of skeletal muscle cells

Answer 18

Made if alternating broad light I bands (isotropic in polarised light) and dark (anisotropic) A bands
Z lines(Zwischenscheiben) bisect the I bands
Nucleus at the periphery of the cell.

Question 19

Describe the sarcoplasm of the skeletal muscle cells

Answer 19

Sarcoplasm filled with myofibrils My oriented parallel to the long axis of the cell
Sarcoplasm containing rows of mitochondriaMtin a similar orientation
Z bands are the most electron-dense and divide each myofibril into numerous contractile units called sarcomeres

Question 20

Describe sacromere structure

Answer 20

At junction of theAandIbands (and depending on the state of contraction) are tubular triadseach comprising a central flattened tubule of the tubule systemand a pair of terminal cisternaeof the sarcoplasmic reticulum.
Within the bands there are tubular elements of the sarcoplasmic reticulumconnecting the terminal cisternae.
Similarly, within the I bands, less regular longitudinal tubular profiles of sarcoplasmic reticulum.
Note the distribution of mitochondria, regularly arranged between the sarcomeres within the I bands in immediate association with those parts of the actin and myosin filaments which interact during the process of contraction.

Question 21

Describe the structure of the sarcoplasmic reticulum

Answer 21

Sarcoplasmic reticulum in the spaces between the myofibrils

Longitudinal system paralleling the myofibrils

there are tubules that lead to the exterior of the fibre membrane

Important for conducting the electrical signal into the centre of the muscle fibre

Question 22

Describe the structure of cardiac muscle

Answer 22

Cardiac muscle cells have one nuclei, centrally located
Cardiac muscle is striated and uses the sliding filament mechanism to contract
Mechanical connection between adjacent cardiac muscle cells - desmosome (structural)
Electrical connection between adjacent cardiac muscle cells – Gap Junctions (functional)

Question 23

Describe the histology of cardiac muscle

Answer 23

Cardiac muscle fibres form an interconnecting network

There are intercalated discs

Question 24

What do the intercalated discs do?

Answer 24

Intercalated Discs provide both mechanical and electrophysiological coupling, allowing the cardiac myocytes to act as a functional syncytium. The cells possess central nuclei and regular cytoplasmic cross-striations

More simply:
Intercalated discs bind the cells, transmit forces of contraction and provide areas of low electrical resistance for the rapid spread of excitation throughout the myocardium.

Question 25

Describe the histology of cardiac muscle in relation to blood supply

Answer 25

Extensive and intimate capillary network between the myocardial fibres Vessels in this section are distended with red blood cells High level of vascularity is a reflection of the high and constant oxygen demand of the myocardium

Question 26

Describe the physiology of cardiac muscles

Answer 26

Have one nuclei, centrally located Striated and use the sliding filament mechanism to contract Branching cells with intercalated discs with desmosomes and gap junctions Nodal cells stimulate their own action potentials - automaticity or auto-rhythmicity Absolute refractory period is about 250ms

Question 27

Why are gap junctions important in cardiac muscle?

Answer 27

gap junctions are critical to the heart’s ability to be electrically coupled

Question 28

What is the benefit of the cardiac muscle having an absolute refractory period of around 250ms?

Answer 28

prevents tetanic contractions which would interfere with the heart’s ability to pump

Question 29

Where can intercalated discs be found?

Answer 29

Intercalated discs are specialised transverse junctions between cardiac muscle cells at sites where they meet end to end; they always coincide with the Z lines.

Question 30

What kind of junction is the intercalated disc?

Answer 30

An interdigitating junction and consists of three types of membrane-to-membrane contact. The predominant type of contact, the fascia adherens, resembles the zonula adherens of epithelial junctional complexes but is more extensive and less regular. The actin filaments at the ends of terminal sarcomeres insert into the fasciae adherentes and thereby transmit contractile forces from cell to cell. Desmosomes occur less frequently and provide anchorage for intermediate filaments of the cytoskeleton. Gap (nexus) junctions are present mainly in the longitudinal portions of the interdigitations and are sites of low electrical resistance through which excitation passes from cell to cell

Question 31

What are gap junctions?

Answer 31

Constructed from a hexagonal array of protein subunits – connexins Act as communicating channels – connexon Gap junction formed from two connexons stacked end to end Sites of low electrical resistance between cells Central pore of 1.4 nm diameter Small molecules (1 kDa, ions & glucose size) pass through

Question 32

What do gap junctions do?

Answer 32

Link adjacent myocytes | Provide pathway for direct electrical and chemical communications

Question 33

How can one measure current through a gap junction?

Answer 33

Can measure current through gap junction using whole-cell patch clamp Current flows from cell 1 to cell 2 current recorded are mirror images

Question 34

Describe the structure of smooth muscle

Answer 34

Contains actin and myosin filaments, however not aligned by Z discs so no visible striations Actin and myosin filaments aligned along long axis of cells Filaments anchored at dense bodies (α-actinin-rich) scattered throughout sarcoplasm Contractile arrays anchored to sarcolemma by dense plaques Smooth muscle cells connected by focal adhesions (adherens junctions)

Question 35

Describe the histology of smooth muscles

Answer 35

Elongated, spindle-shaped cells with tapered ends which may occasionally be bifurcated. Shorter than skeletal muscle fibres containing only one nucleus which is elongated and centrally located. Individual muscle fibres are arranged roughly parallel to one another.

Question 36

How are the contractile proteins of smooth muscle arranged?

Answer 36

The contractile proteins of smooth muscle are not arranged in myofibrils, as in skeletal and cardiac muscle, and thus visceral muscle cells are not striated.

Question 37

What may be found between the individual muscle fibres and fascicle in smooth muscle?

Answer 37

A network of supporting collagenous tissue

Question 38

Describe the physiology of smooth muscle

Answer 38

Small cells, fusiform shape with a single central nucleus Involuntary, autonomic innervation Surrounding network of collagen No striations, myofibril meshwork anchored to dense bodies Different mechanism of muscle contraction compared to skeletal and cardiac muscle contraction Cells shorten and broaden on contraction Surround blood vessels, GI tract, bronchial airways

Question 39

Provide a summary of skeletal muscle

Answer 39

Large, elongated multinucleated cells, may be up to 1 m in length Multiple peripherally situated nuclei Voluntary muscle, innervated by alpha motor neurones Arranged in fascicles with endomysium, perimysium and epimysium Cross-striations due to organisation of myofibrils Sliding filament mechanism of contraction

Question 40

Provide a summary of smooth muscle

Answer 40

``` Small cells, fusiform shape Single central nucleus Involuntary, autonomic innervation Surrounding network of collagen No striations, myofibril meshwork anchored to dense bodies Cells shorten and broaden on contraction ```

Question 41

Provide a summary of cardiac muscle

Answer 41

Elongated branching cells, joined by intercalated discs Single central nucleus typical, some cells binucleate Involuntary muscle, spontaneously contractile, autonomic modulation Branching interconnected cells, functional syncytium Cross-striations due to organisation of myofibrils Sliding filament mechanism of contraction

Question 42

In skeletal muscle what contractile protein may be found prominently in I bands?

Answer 42

Actin

Question 43

In skeletal muscle what contractile protein may be found prominently in A bands?

Answer 43

Myosin

Question 44

Where is calcium stored in skeletal muscle?

Answer 44

Sarcoplasmic reticulum

Question 45

How does a connexon form?

Answer 45

From 6 connexins