mechanisms of skeletal mm contraction

Question 1

what composes the parallel elastic component?

Answer 1

epimysium, perimysium, endomysium

Question 2

what is the series elastic components?

Answer 2

tendon

Question 3

what is the 1st phase of mm contraction?

Answer 3

isometric- elastic component stretches but there is no change in length of the mm itself

Question 4

what is the 2nd phase of mm contraction?

Answer 4

isotonic- continued shortening, mm fiber shortens, load is moved

Question 5

describe the active length-tension relationship

Answer 5

the length of the sarcomere (specifically the overlap of the thin and thick filaments) will affect the number of cross bridges that can be formed. the more cross bridges formed, the stronger the contraction

Question 6

what is the “ideal” overlap

Answer 6

2.25 um

Question 7

what is “preload” for mm contraction?

Answer 7

this is the passive tension, the amount that the parallel and series components are stretched prior to the actual mm contracting

Question 8

at what point is the mm activated?

Answer 8

at around 140% of resting length

Question 9

what is a motor unit?

Answer 9

a motor unit is all of the mm fibers that are stimulated by a single motor neuron

Question 10

discuss larger vs smaller motor units

Answer 10

smaller motor units allow for fine control

larger motor units allow for powerful mmt

Question 11

what is temporal summation?

Answer 11

stimuli from same source that are close together, Ca doesn’t have time to decrease, if stimuli continue, increased contraction and tetanus will result

Question 12

what is spatial summation?

Answer 12

stimuli from different sources act on the same mm to increase contraction

Question 13

what is the size principle?

Answer 13

small force needed- smaller motor units stimulated; as force needed increases, increasingly larger motor units are recruited

Question 14

describe type I mm fibers

Answer 14

slow oxidative
red
smaller size, least force

Question 15

describe type IIa mm fibers

Answer 15

fast oxidative

med size, med force

Question 16

describe type IIb mm fibers

Answer 16

fast glycolytic
white
large size, large force

Question 17

2 types of sensory receptors in mm

Answer 17

1- mm spindles

2- golgi tendon organ

Question 18

where are mm spindles located? function?

Answer 18

in the mm belly, but are not contractile “intrafusal”, send info to CNS and are involve in proprioception

Question 19

Describe the stretch “myotatic” reflex

Answer 19

muscle is stretched
signals to mm spindles
mm spindle sends info via sensory neuron to 2 places
1-excitatory- contracts the mm that was stretched
2- inhibitory- reciprocal inhibition to relax the mm antagonist
overall outcome is mm contraction

Question 20

where are golgi tendon organs? function?

Answer 20

located in tendon and ECM, will sense contraction

Question 21

describe the deep tendon reflex

Answer 21

muscle is contracted
signals to golgi tendon organ
GTO sends info via sensory neuron to 2 places
1- excitatory- reciprocal activation to contract the mm antagonist
2- inhibitory- relax the mm
overall outcome is mm relaxation

Question 22

example of DTR in patellar reflex

Answer 22

strike the patellar tendon = signals to GTO that quad is contracted, GTO signals to the quad to relax and to the hamstrings to contract

Question 23

example of the myotatic reflex in the arm

Answer 23

bicep is stretched = signals to the mm spindle that signals the bicep to contract and also inhibits the tricep from contracting

Question 24

golgi tendon organ responds to…

Answer 24

muscle contraction

Question 25

muscle spindle responds to…

Answer 25

muscle stretch