Skeletal Muscle Properties

Question 1

what is a sarcomere

Answer 1

muscle functional contractile unit

Question 2

what is a myofibril

Answer 2

bundles of contractile and elastic proteins (series of sarcomeres)

Question 3

the physically independent processes that affect active tension

Answer 3

1. number of cross bridges formed
2. force produced at each cross bridge
3. velocity of cross bridge motion

Question 4

regulatory proteins of myofibrils are

Answer 4

troponin and tropomyosin

Question 5

accessory proteins of myofibrils are and their function is

Answer 5

Titin: provides elasticity
Nebulin: helps align actin filaments

Question 6

what allows for large simultaneous ACh release at the motor end plate?

Answer 6

there are many contact points of the motor neuron to the muscle fibre!

Question 7

what happens to strength of post synaptic potential as it travels away from the motor end plate? what is the cause of this? What shape does the current create? What does the membrane as act?

Answer 7

decreases in strength due to leakiness of the muscle fibre membrane; travels in a circuit; membrane acts as a capacitor

Question 8

what are T-tubules for?

Answer 8

they allow the AP to travel deep into the muscle so all muscle fibres are stimulated simultaneously

Question 9

where are DHP receptors located

Answer 9

in t-tubules

Question 10

what to DHP receptors do?

Answer 10

react with ryanodine channels, which stimulate SR to release calcium into muscle cell

Question 11

steps in an AP in muscle to calcium release

Answer 11

ACh release from MN –> ligand gated Na/K channels open –> voltage gated Na channels open –> EPP –> moves across membrane and town t tubules –> stimulate DHP receptors –> ryanodine receptor activated –> SR stimulated to release calcium

Question 12

what is the latent period is contraction

Answer 12

the time between Ca being released and contraction actually occurring, takes times for Ca to difuse over filaments of the myofibril - so AP electrical stimulation has occurred, and then a lag between that and actual muscular contraction

Question 13

force generating capacity of a muscle changes with

Answer 13

muscle length and velocity

Question 14

two characteristics of muscles

Answer 14

contractile and visco elastic

Question 15

increased pennation does what

Answer 15

increases muscles fibres per given area, allowing more force production, but decreases muscle fibres length for it decreases shortening velocity

Question 16

what is muscle viscosity

Answer 16

related to contractile elements
characterized by force-length and force-velocity relationships of muscle
actin-myosin related
more viscous = more resistance to flow

Question 17

what is muscle elasticity according the the hill muscle model

Answer 17

corresponds to passive effects of tissue on CE
- series element = Titin
-parallel element = connective tissue and cytoskeleton
provides passive force that combines with active force (cross-bridge activity)
passive properties contribute to force more as muscle lengthens

Question 18

passive force in muscle is from

Answer 18

connective tissue and titin

Question 19

active force in muscle is from

Answer 19

cross bridge activity

Question 20

length tension relationship - what does the sliding filament theory say

Answer 20

tension varies directly with number of cross bridges

Question 21

what is the optimal sarcomere length for force production? what happens if they are too long or too short?

Answer 21

2-2.5um
too long = not enough overall
too short = limited cross bridge formation

Question 22

force velocity relationship

describe (2)

Answer 22

increase velocity of lengthening = increase force

increase velocity of shortening = force decline

Question 23

frequency force relationship

Answer 23

increase Hz = increase force
increase is Ca release
summation

Question 24

what is minimum discharge rate for max force production

Answer 24

50-60Hz

Question 25

what happens if multiple action potential come to the fibres at short intervals?

Answer 25

• mechanical effects may superimpose

- peak force is increased

Question 26

three factors that affect muscle history

Answer 26

temperature, stretching, previous contractions

Question 27

how does temperature affect muscle history

Answer 27

Contractile effects
-increase conduction velocity in nerves and muscle
-improved blood flow to muscle
-enhanced metabolic reactions (enzyme action)
Passive muscle properties
-decrease muscle viscosity
Increase extensibility of connective tissue

Question 28

effects of temperature on contractile properties

Answer 28

increase in torque-velocity, increase power, increase MVC, force production, ATP consumption

Question 29

what is muscle thixotropy?

Answer 29

decrease in resistance in a tissue offers to stretch due to prior activity
property of gels:
-gels become more fluid with use
-when gels sit then set
-inactivity = greater stiffness
-in muscles = related to bonding between actin and myosin filaments
Thixotropy affected by both temperature and stretch to the muscle

Question 30

effect of stretch on force production

Answer 30

repeated stretch leads to muscle elongation

steady decrease of force exerted with successive identical stretches

Question 31

post activation potentiation is (PAP)

Answer 31

short lasting increase in contractile performance

Question 32

what are the 2 mechanisms that make PAP

Answer 32

altered phosphorylation of myosin regulatory light chains

actin-myosin binding more sensitive to Ca release from SR

Question 33

what type of muscle fibres is most affected by PAP

Answer 33

Type II

Question 34

what is tendon creep

Answer 34

when tendon length increases with constant load and remains lengthened even when load is released

Question 35

what is hysteresis

Answer 35

during unloading there is less torque produced by the muscle