Skeletal Muscle Fiber Orientation / Microscopic Anatomy

Question 1

What are muscle fibers organized into?

Answer 1

fascicles

Question 2

four patterns of muscle fascicle arrangements

Answer 2

circular: mouth and eyes
parallel: ab muscle
convergent: pec muscle
pennate: (unipennate, bipennate, multipennate)

Question 3

sarcolemma

Answer 3

cell membrane of a muscle fiber

Question 4

sarcoplasm

Answer 4

cytoplasm of a muscle fiber

Question 5

transverse tubules (t-tubules)

Answer 5

deep invagination’s of the sarcolemma that extend into the sarcoplasm

transport electric currents

carry impulses from sarcolemma to help stimulate muscle contraction

Question 6

sarcoplasmic reticulum

Answer 6

internal membrane complex

adjacent to t-tubules

stores calcium

Question 7

myofibrils

Answer 7

cylindrical structures within muscle fibers that run the length of the cell (80% of fiber volume)

ability to shorten, resulting in contraction

myofilaments (thick and thin)

Question 8

myofilaments - thick filaments

Answer 8

• bundles of myosin
• myosin heads: able to move or pivot

Question 9

myofilaments - thin filaments

Answer 9

• mainly actin
• tropomyosin: ropelike protein, at rest, covers binding sites
• troponin: attaches to tropomyosin, binding site for calcium (lock)
  – holds tropomyosin in place at rest

Question 10

sarcomere

Answer 10

functional unit within a myofibril
- arranged in series
- contain overlapping thick and thin filaments
- one sarcomere spans from one Z disc to the next

Question 11

I band

Answer 11

region that contains only thin filaments (lighter bands)

Question 12

A band

Answer 12

anywhere we have thick filaments even if there’s overlap

Question 13

H zone

Answer 13

no overlap, only thick filamet

Question 14

M line

Answer 14

center of the H zone

Question 15

Z discs…

Answer 15

slide toward each other