Lecture 17 9/20/23

Question 1

What is the term for a muscle cell?

Answer 1

muscle fiber

Question 2

What are the characteristics of muscle fibers?

Answer 2

-multiple nuclei
-many mitochondria and other organelles

Question 3

What is the sarcolemma?

Answer 3

-the outer membrane around the muscle fiber
-equivalent to the plasma membrane of other cells

Question 4

How many motor neurons innervate each muscle fiber?

Answer 4

one

Question 5

Why does each muscle fiber only have one innervation?

Answer 5

so that the muscle fiber can only be triggered to move in one direction at any one time

Question 6

What are the parts of a sarcomere?

Answer 6

-Z line
-I band
-A band
-H zone
-M line

Question 7

What is the Z line?

Answer 7

periphery of sarcomere where thin actin filaments attach

Question 8

What is the I band?

Answer 8

light area containing only actin

Question 9

What is the A band?

Answer 9

dark area where actin and myosin overlap

Question 10

What is the H zone?

Answer 10

center light zone with only myosin

Question 11

What is the M line?

Answer 11

middle of the sarcomere, within the H zone

Question 12

What are the characteristics of actin?

Answer 12

-thin protein filaments
-intertwines with tropomyosin
-intermittently bound troponin

Question 13

What are the characteristics of myosin?

Answer 13

-thick filaments
-intertwined helices with globular heads
-binds ATP and actin

Question 14

What are the characteristics of the sarcoplasmic reticulum?

Answer 14

-surrounds the myofibrils
-stores calcium at rest
-releases calcium rapidly during an action potential

Question 15

Why are the transverse tubules important?

Answer 15

they allow for better signal transmission and faster movement of Ca2+

Question 16

What are the steps of an action potential/muscle contraction?

Answer 16

-Ach released at NMJ
-nicotinic Ach receptors on sarcolemma activated
-voltage-gated Na+ channels opened
-action potentials spread
-Ca2 released from sarcoplasmic reticulum
-contraction initiated

Question 17

How is the DHP receptor involved with action potentials/muscle contraction?

Answer 17

-action potential in T-tubule alters DHP rec. conformation
-DHP rec. opens Ca2+ ion channels in SR, allowing Ca2+ to enter cytoplasm
-Ca2+ binds to troponin, allowing actin-myosin binding

Question 18

What are the characteristics of milk fever?

Answer 18

-semi-paralysis in dairy cows
-hypocalcemia
-less Ach released
-less depolarization of sarcolemma
-unable to contract muscles/too weak

Question 19

What are the characteristics of puerperal tetany?

Answer 19

-hypocalcemia after whelping (dogs)
-muscle rigidity
-hyper-contraction due to more permeable Na+ channels and hyper-depolarization

Question 20

What are the steps of excitation-contraction coupling?

Answer 20

-increased calcium in sarcoplasm
-additional calcium binds to troponin
-tropomyosin moves, exposing the myosin-binding site on actin

Question 21

What are the steps of shortening the sarcomere?

Answer 21

-ATP binds myosin head
-myosin no longer bind actin
-enzymes on myosin head hydrolyze ATP
-ADP and Pi change myosin’s conformation so it strongly binds actin again (cross-bridging)
-ADP and Pi released from myosin
-myosin head flexes, pulling actin towards center

Question 22

What are the characteristics of riger mortis?

Answer 22

-shortening of muscle fibers w/o action potentials
-not enough ATP to release myosin head from actin

Question 23

What are the characteristics of fast twitch/type II fibers?

Answer 23

-larger
-extensive SR/rapid Ca2+ release
-fewer mitochondria
-less extensive blood supply
-quick fatigue
-more powerful

Question 24

What are the characteristics of slow twitch/type I fibers?

Answer 24

-darker color due to more myoglobin
-rich blood supply
-more mitochondria
-more aerobic
-longer-lasting energy

Question 25

What are the two subdivisions of type II fibers?

Answer 25

-type IIA: intermediate between slow and fast twitch
-type IIB: traditional fast twitch

Question 26

How do muscle fibers differ between dogs?

Answer 26

-endurance athletes have more type 1 muscle fibers
-sprint athletes have more type II muscle fibers

Question 27

What nutrient supplies dogs’ muscles with energy?

Answer 27

fats