Muscle Cells and Related Sturctures

Question 1

Structure of a Sarcolemma

Answer 1

T tubules and sarcoplasmic reticulum

T tubules invaginate toward the SR cisternae
form triads

Question 2

Slide filament mechanism: all the steps

Answer 2

a) AP arrives at synapse terminal
b) calcium channels bring in Ca2+, cause vesicle fusion
c) neurotransmitter release into synapse
d) AcC binds to ligand gated channel
e) end plate depolarization
f) action potential occurs down sarcolemma
g) AP carries down t Tubule
h) AP causes conformation change in DHP receptors
i) DHP causes conformation change in Ryanodine ion channels
j) ryanodine receptors release calcium from SR
k) calcium binds to troponin
l) tropomyosin allows actin to bind to myosin
m) power stroke
n) calcium uptake carriers in SR and sarcolemma pump Ca out of cell

Question 3

Where are the t tubules in relation to the actin and myosin

Answer 3

they invaginate the sarcolemma at the I-A band, form “triads” with cisternae

two per sarcomere

Question 4

DHP

Answer 4

dihydropyridine receptors

voltage sensitive l type calcium channels arranged in quadruplets

located on the sarcolemma t tubules

cause a conformational change in the ryanodine receptors

a minute amount of calcium flows intot the cytosol via these channels

Question 5

RyRs

Answer 5

Ca+2 release channels

open in response to conformation change in DHP receptors

Question 6

How do muscle cells return calcium once it has been released by RyR from the SR?

Answer 6

atp dependent pumps

calsequestrin: monitors and maintains optimal calcium concentration gradient

SERCA

Sarcoplasmic Reticulum Calcium ATPase

Question 7

Sarcomere Lengths (Maximum tension to Maximum Extension)

Answer 7

SR max tension between (1.6-2.2)micrometers

“Resting” length is 2 mic.m

beyond 2.2 there’s no tension, and below 1.6 mic.m there’s no tension

Question 8

ATP in skeletal muscle: where and why

Answer 8

ATP used for powerstroke

ATP used for pumping calcium back into SR

ATP used for Na/K pump

Question 9

Concentration of calcium in muscle fibers

Answer 9

4 mmol, enough for 1-2 sec contractions

Question 10

energy sources in skeletal muscles

Answer 10

a. phosphocreatine (reconstitutes ATP), rapid release, sustains 5-8 second contractions
b. glycolysis, sustains up to 1 minute contractions
c. Oxidative metabolism, 95% of energy needs met for long term contraction

Question 11

Isometric contraction

Answer 11

increase in tension but not in length

Question 12

Isotonic contraction

Answer 12

eccentric and concentric

eccentric occurs when the muscle lengthens

concentric occurs when the muscle shortens

Question 13

White vs Red fibers

Answer 13

Categorized based on endurance

White is fast, contains less mitochondria, myoglobin, and relies on mainly anaerobic respiration (lactic acid/pyruvate build up), and lots of ATPase

Red is slower, has more mitochondria, aerobically based, has more myoglobin, smaller concentration of ATPase

Question 14

Myofibers

Answer 14

cannot be increased after birth

myofibrils CAN be increased, so mass can be increased but not number

Question 15

Lost muscle will be replaced by

Answer 15

scar tissue (fibrous connective tissue

Question 16

Myofiber type

Answer 16

dark fibers (myofiber) (soleus)
light fibers (myofibers) (gastrocnemius

Question 17

the “motor unit” consists of the

Answer 17

a single nerve cell may innervate from a few to several hundred myofibers

a) motorunit consists of the myofibers and the neuron

all or none

Question 18

Summation

Answer 18

electrical events occur faster than mechanical events

additional “spike” ca cause MORE calcium to add to a previous cycle, total Ca2+ increases, causing increased muscle tension

the spikes are additive (sum)

Question 19

Tetany

Answer 19

no relaxation between “spikes” of calcium influx, muscle remains at maximum contraction

Question 20

Machines transmit forces from one place to another. What are the forces involved? By what means?

Answer 20

Force applied TO the machine (in force)
Force applied FROM the machine (out force)

the system of levers muscle and bones create

Question 21

Architecture of the Lever

Answer 21

Distance between point of force on the lever arm and fulcrum (joint or pivot) is the “in lever arm”

distance from the lever to the out force is the out lever arm

Question 22

Mi = FiLi

Answer 22

M = moment; F = force; L = lever arm

Mo=FoLo

Question 23

At equilibrium, the muscle lever equation reads

Answer 23

FiLi=FoLo

Question 24

Which muscle activates the lever system?

Answer 24

biceps

Question 25

Classification of levers is based on

Answer 25

the position of the fulcrum to the in force/out force

Question 26

Types of levers

Answer 26

1st class: fulcrum is in the middle
a. in force equals out force move in opposite
directions

2nd class: resistence (out-force) is in the middle
a. fulcrum = ball of the foot if you elevated yourself using your toes
b. both in and out forces are on the same side of the
fulcrum

3rd class: effort (in force) is in the middle
(lifting a weight in the palm of your hand)