Muscle

Question 1

endomysium

Answer 1

endomysium

• most internal muscle layer (of 3 layers)
• type III collagen
• delicate layer that surrounds each individual myofiber and contains reticular fibers

Question 2

epimysium

Answer 2

Epimysium

• external muscle surface; most outer muscle layer of 3 layers
• dense connective tissue sheath (type I collagen)
• also known as deep fascia
• continuous with tendons (attach muscle to bones)

Question 3

External lamina

Answer 3

External lamina in muscle is equivalent to the basal lamina of epithelial cells
* helps muscle attach to extracellular connective tissue
* insulate the adjacent electrical active muscle cells
→ no shorting out of signals

Question 4

A-band

Answer 4

A (anisotropic) bands

overlap of thick (myosin) filaments + thin (actin) filaments: dark

Question 5

Fast-twitch fibers

Answer 5

white (fast-twitch) fibers

* fewer mitochondria, rely more on anaerobic metabolism; fatigue quickly (ex. muscles for sprinting)

Question 6

Golgi tendon organ

Answer 6

Golgi tendon organ

• proprioceptive info re: muscle tendons, ex. when a skeletal muscle is stretched too far

Question 7

H-band

Answer 7

H-band
o H bands: thick bands; these lie in the central region of the A bands (lighter part of the A band) (no thin filaments); only in relaxed muscle

Question 8

I-band

Answer 8

I-band 
o	I (isotropic) bands: thin (actin) filaments: light bands (outer) – doesn’t finish at the end of the sarcomere – continues to the next A band

Question 9

Intercalated disc

Answer 9

Intercalated disc
• forms specialized end-to-end junctions between cells (cardiac muscles); these include macula adherens and fascia adherens junctions; these exist in addition to gap junctions in cardiac muscle

Question 10

M-line

Answer 10

M line

* supporting proteins to thick filaments in the middle

Question 11

Motor unit

Answer 11

Motor unit
* # muscle fibers innervated by a single motor neuron; 1 motor neuron controls a few muscle cells; less muscles per neuron is greater fine control of contraction

Question 12

Muscle spindles

Answer 12

muscle spindle
* specialized muscle fiber within muscle → stretch detection
o ex. patellar tendon reflex

Question 13

Myofiber

Answer 13

• skeletal myofiber: 1 muscle cell
• cardiac myofiber: many individual cardiac myocytes joined end to end with specialized junctions
• there is no such thing as smooth myofiber
• the myofiber cytoplasm is filled with many striated myofibrils containing the contractile proteins organized as sarcomeres

Question 14

Myofibril

Answer 14

Myofibril
o cylindrical, include thin or thick filaments = contractile proteins (actin/myosin)
o longitudinal section: alternating light and dark bands
o cross section: punctate densities

Question 15

actin

Answer 15

actin
* major thin filament protein
* anchored to Z disc on outside, twisted into helix
• each has a myosin binding site for myosin head during contraction

Question 16

regulatory proteins in muscle contraction

Answer 16

regulatory proteins in muscle contraction
o tropomyosin: regulates when a muscle contracts
o troponin (C, I, T): hold tropomyosin in place
•

Question 17

myosin

Answer 17

myosin is the major protein of thick filaments

• heads and tails, point towards M line

Question 18

sarcomere

Answer 18

sarcomere

• structured repeating units that make up myofibril
• skeletal and cardiac only: responsible for striations
• contractile proteins organized here; muscle unit – shortens during contraction

Question 19

Perimysium

Answer 19

Perimysium
• middle muscle layer (2 of 3): The perimysium (type I collagen) surrounds groups of fibers and organizes them into fascicles

Question 20

Purkinje fibers

Answer 20

Purkinje fibers are a type of cardiac cell
• wide diameter
• cardiac muscle fiber conduction; end of impulse conduction pathway, deep to endocardial surface
Often have glycogen (poorly preserved); large empty spaces; more resistant to ischemia

Question 21

Sarcoplasmic reticulum

Answer 21

Sarcoplasmic reticulum
* extracellular interstitial space (electrical
Sac around microfibers: sarcoplasmic reticulum
• Neighboring myofibrils are separated by sarcoplasmic reticulum (specialized smooth endoplasmic reticulum) (TEM)

Question 22

Sarcolemma

Answer 22

Sarcolemma: the muscle’s equivalent of smooth ER

Question 23

Slow-twitch muscle

Answer 23

Slow-twitch muscle
• Red - slow twitch fibers: many mitochondria and oxidative enzymes; slow to fatigue, used when muscular contraction is constant (ex. back postural muscles); lots of myoglobin

Question 24

Syncytium

Answer 24

Syncytium

• multinucleated cell formed by the secondary union of originally separate cells

Question 25

Terminal cisternae

Answer 25

Terminal cisternae

sarcoplasmic reticulum is dilated at ends, which are terminal cisternae

Question 26

T tubule

Answer 26

T tubule
* Hollow pipes that wrap around the myofibrils are T tubules – have interstitial fluid for electrical current/action potential

Question 27

Triad zone

Answer 27

• Where 2 terminal cisternae contact T tubules = triad zone, important to allow action potential to go across T tubule into fibrils

Question 28

Z-disk

Answer 28

Z-disk

• Z lines/discs: dense material that separates sarcomere; anchor the thin actin filaments
• at the center of each I band; separate halves of I bands