histology of muscle tissues

Question 1

what are four types of muscle?

Answer 1

skeletal
cardiac
smooth
myoepithelial

Question 2

how does muscle originate?

Answer 2

-originate from myogenic precursor cells (myoblasts) that originate in the embryo
- myosin is made as cells fuse together to form multinucleated sacs (myofibres)
-results in myosin and actin banding patterns = striations
when fibres are damaged satellite cells can from daughter cells which result in new muscle cells

Question 3

cardiac muscle - what type of cells and nucleus location?

Answer 3

made of mono or bi nuclear cells that are located in the centre of the cell
- cells are smaller than skeletal fibres

Question 4

cardiac muscle - striation?

Answer 4

yes - actin and myosin banding present

Question 5

cardiac muscle - connective tissue present?

Answer 5

yes abundant CT (more than skeletal muscle) with blood vessels present too
- only aerobic resp takes place here

Question 6

cardiac muscle - regeneration?

Answer 6

no- no satellite cells present

Question 7

cardiac muscle - purkinje cells?

Answer 7

present
part of conducting system
modified myocytes that lack T tubules
intercalated discs still present

Question 8

cardiac muscle - cell fusion?

Answer 8

no - but there is functional syncytium with some side branching - thanks to intercalated discs only found in cardiac muscle

Question 9

cardiac muscle - intercalated discs function?

Answer 9

junctions between cardiac muscle cells that allow all the muscles to contract together when electrically excites
function as - gap junctions: allow Ca transmission between cells like T tubules, adherens junctions and desmosomes
found in same position as Z discs

Question 10

where is smooth muscle found?

Answer 10

walls of gut, blood vessels, resp tract and urinogenital system

Question 11

smooth muscle - cells?

Answer 11

• single nucleus
• spindle- shaped
• diam 5um and length varies from 20-500 um
• each cell surrounded by basal lamina, with small amount of CT between ells - which allows for passage of nerve tracts and blood vessels
• often found in layers and arranged into fibres

Question 12

smooth muscle - cytoplasm of cells?

Answer 12

filled with filaments of actin (lesser amount of myosin)

- not striated as there is less order

Question 13

smooth muscle - type of contraction?

Answer 13

involuntary - controlled by hormones or balance between symp and parasymp

• weak contraction force
• does not fatigue easily and contracts slowly

Question 14

smooth muscle -how does electrical excitation spread?

Answer 14

spread cell to cell via gap junctions

Question 15

skeletal muscle - what are striations?

Answer 15

alternating light and dark bands that appear across the length of the fibre

Question 16

skeletal muscle - what causes striations?

Answer 16

organisation of thick and thin filaments and division into sarcomeres

Question 17

skeletal muscle -what protein filaments do myofibrils contain?

Answer 17

thick - myosin

thin - actin

Question 18

skeletal muscle -what are sarcomeres?

Answer 18

contractile units

Question 19

skeletal muscle - what is A band

Answer 19

thick myosin filaments located within the dark stripes of the sarcomere

Question 20

skeletal muscle - what is the I band

Answer 20

thin actin filaments occur in the light region

Question 21

skeletal muscle - rest of sarcomere structure

Answer 21

centre - portion with no overlap known as H band
delimited by Z lines
each sarcomere has a complete A band and two half I bands

Question 22

what are satellite cells?

Answer 22

resident adult muscle stem cells

Question 23

what do satellite cells do?

Answer 23

can be activated
become myoblasts
myoblasts proliferate and differentiate to provide new myonuclei fro existing muscle fibres or fuse together to generate new myofibres
also they self renew to maintain the stem cell population