014 muscle histology

Question 1

what are the 3 connective tissue sheets on muscle?

Answer 1

• epimysium = outside of muscle
• perimysium = around each muscle bundle/fasicle
• endomysium = around each individual muscle fibre/cell

Question 2

what does the epimysium cover?

Answer 2

• outside of muscle

Question 3

what does the perimysium cover?

Answer 3

• each muscle bundle/fascicle

Question 4

what does the endomysium cover?

Answer 4

• each individual muscle cell/fiber

Question 5

what is the breakdown of the structure of skeletal muscle?

Answer 5

• myofilaments (actin, myosin) —>
• sarcomere —>
• myofibril —>
• muscle cell/fibre —>
• muscle fascicle —>
• skeletal muscle

Question 6

give 7 key features of skeletal muscle cells

Answer 6

• 1 muscle cell = 1 muscle fibre
• very wide, 100 micrometers diameter
• very long 30cm
• many nuclei on periphery
• no special junctions between cells
• many mitochondria
• sarcolemma, sarcoplasm, sarcoplasmic retitculum

Question 7

where are the nuclei in skeletal muscle?

Answer 7

• on periphery of muscle cells

Question 8

what does this transmssion electron micrograph (TEM) show?

Answer 8

• skeletal muscle fibres
• you can see the sarcomeres Sa
• SR = sarcoplasmic reticulum
• ZL = Z line
• A = dark A band = myosin and actin overlap
• I = light I band = actin
• Hzone = myosin only

Question 9

what happens to the sarcomere during contraction?

Answer 9

• myosin pulls the actin filaments towards each either
• Z lines get closer together
• light I band shortens
• dark A band = same
• sarcomere shortens
• sliding filament theory

Question 10

what is A?

Answer 10

sarcolemma

Question 11

what is b?

Answer 11

terminal cisternae

Question 12

what is c?

Answer 12

transverse tubules / T-tubules

Question 13

what is d?

Answer 13

sarcoplasmic reticulum

Question 14

what is e?

Answer 14

mitochondria

Question 15

what is f?

Answer 15

myofibrils

Question 16

what is g?

Answer 16

• dark A band myosin

Question 17

what is h?

Answer 17

• light I band actin

Question 18

what is i?

Answer 18

• Z line

Question 19

what is j?

Answer 19

• nucleus

Question 20

what is the triad in skeletal muscle?

Answer 20

• 1 T tubule and 2 terminal cisternae

Question 21

what are the 2 different muscle fibre types?

Answer 21

• type 1 = slow
• type 2 = fast

Question 22

what colour do type 1 muscle fibres appear?

Answer 22

• red = rich in myoglobin

Question 23

what colour do type 2 muscle fibres appear?

Answer 23

• white = rich in glycogen, less myoglobin

Question 24

what are type 1 muscle fibers used for?

Answer 24

• small, slow, aerobic exercise
• e.g. marathon
• related to continuous weak contractions e.g. postural muscles

Question 25

what are type 2 muscle fibres used for?

Answer 25

- large fast anaerobic exercise - e.g. sprint - related to intense sporadic contraction, e.g. biceps

Question 26

what does this image show?

Answer 26

- neuromuscular junction - motor unit with multiple motor end plates on different myofibrils

Question 27

what does this image demonstrate?

Answer 27

- muscle spindles

Question 28

what do muscle spindles detect?

Answer 28

stretch

Question 29

what do golgi tendon organs detect?

Answer 29

tension

Question 30

what is myasthenia gravis and what is its pathophysiology?

Answer 30

- rare autoimmune disease that causes weakness of muscles - caused by auto-anitbodies attacking ACh receptors on post-synaptic membrane of muscle - also flattens junctional folds = weaker less frequent nerve transmission = wealer muscle contractions

Question 31

what is Duchenne's muscular dystrophy?

Answer 31

- genetic disorder characterized by progressive muscle degeneration and weakness due to the alterations of a protein called dystrophin that helps keep muscle cells intact

Question 32

what is Duchenne's muscular dystrophy caused by?

Answer 32

- mutation in dystrophin gene which is responsible for connecting cytoskeleton of each muscle fibre to the basal lamina - when dystrophin is mutated, excess Ca can penetrate the sarcolemma = excess water entry = cells burst and die = muscles waste away

Question 33

what does this picture show in terms of Duchenne muscular dystrophy?

Answer 33

dystrophin immunofluorescence stain shows absence of functional dystrophin in muscle membrane in MD

Question 34

what are satellite cells?

Answer 34

- stem cells of the muscle = proliferate to form new muscle fibres or replace damaged muscle fibres

Question 35

where are satellite cells found in muscle?

Answer 35

- on the outside of skeletal muscle cells/fibres

Question 36

what are satellite cells activated/stimulated by?

Answer 36

- muscle cells breaking/over stretching

Question 37

what is this a picture of ?

Answer 37

satellite cell