lecture 13

Question 1

what does muscle tension depend on?

Answer 1

muscle tension depends on the sarcomere length

Question 2

what is the optimal resting length? whats the length um?

Answer 2

optimal resting length means maximum tension because of maximum cross bridge formation. its 1.6 to 2.6 um optimal resting length

Question 3

what happens when the muscle is too stretched and compressed?

Answer 3

If the muscle is too stretched → theres fewer cross bridge interactions → fewer tension
If the muscle is too compressed → filaments overlap → less tension
,C`

Question 4

what is a myogram? what can it be used to compare? what is a twitch?

Answer 4

Myogram is a graph showing muscle tension over time
- it can be used to compare different types of muscles tension over time
- for example, the eye muscle, gastrocnemius, and deep muscle of the calf are all on a myogram to compare how quickly tension is relieved over time

Twitch = A muscle twitch is a single contraction relaxation cycle from one stimulus (one quick muscle contraction and then relaxation caused by one signal)

Question 5

do different muscles repsond to the same stimulation differently?

Answer 5

yes, different muscles can respond quicker or slower

Question 6

what is the latent, contraction, and relaxation phase of a myograph/muscle twitch

Answer 6

1. Latent period
   - the action potential spreads along sarcolemma, Ca2+ is released from the SR, theres no tension yet though
2. Contraction phase
   - ca2+ binds to troponin, cross bridge cycling begins, and tension rises to peak
3. Relaxation phase
   - Ca2+ decrease, cross bridge detach, active sites covered, muscles return to resting tension and is a 25ms duration from peak to end of the twitch

Question 7

what are the two main factors that tension depends on?

Answer 7

1. Frequency of stimulation, so how often a muscle is stimulated. There are three types of frequency of stimulation
2. number of muscle fibers activated. more fibers = more force

so: how often theres stimuli AND the number of muscle fibers

Question 8

what are the three types of frequency of stimulation

Answer 8

1. Frequency of stimulation, so how often a muscle is stimulated. There are three types of frequency of stimulation:

a. Treppe (staircase effect) which is repeated stimuli to a gradual increase in tension
(Muscle relaxes each time, but gets stronger with each contraction)

b. Wave summation → stimuli arrive before full relaxation so tension builds on previous contraction
(New signal comes before the muscle fully relaxes)

c. tetanus which is continuous stimulation leading to sustained contraction

• incomplete tetanus is partial relaxation between stimuli
• complete tetanus is no relaxation so theres maximum sustained tension (doesnt happen in skeletal muscle)

Question 9

whats the difference between incomplete tetanus and wave summation ?

Answer 9

Wave summation = noticeable partial relaxation
Incomplete tetanus = very little relaxation (almost fused)

Question 10

what is a motor unit

Answer 10

A motor unit = one motor neuron and all the muscle fibers it controls

Question 11

what is motor unit recruitment?

Answer 11

Motor unit recruitment = increasing number of active motor units means more tension
For example, light objects have few motor units needed to carry, heavy objects need many motor units to cary

Question 12

what is asynchronous motor unit summation

Answer 12

Asynchronous motor unit summation
This is when motor units take turn to contract and prevents fatigue, also allowing sustained contraction

Question 13

what is muscle tone?

Answer 13

Muscle tone is when there is constant, low level contraction at rest / resting tension in a skeletal muscle

Question 14

what is isontonic contraction? give its two examples

Answer 14

1. Isotonic contraction is when muscle changes length. Theres two explanations:
   - concentric is when the muscle shortens, so when lifting a weight
   - eccentric is when the muscle lengthens while contracting, like lowering a weight

Question 15

what is isometric contraction

Answer 15

2. Isometric contractions
   - muscle tension increases, there’s no change in length. For example, a weight still at 90 degrees during a curl. Muscle is producing tension, but not moving

Question 16

isotonic vs isometric

Answer 16

isoTONIC = movement (concentric vs ecentric)
(think sweat and TONIC for movement)
isoMETRIC = no movement

Question 17

what are the four fascicle patterns of skeletal muscles

Answer 17

1. parallel, 2. convergent, 3. pennate, 4. circular

Question 18

what are parallel muscles and examples

Answer 18

1. Parallel muscles
   - these are fibers that run parallel to long axis
   - muscle shortens 30%
   - has a central body
   - examples are biceps brachii

Question 19

what are convergent muscles and examples

Answer 19

2. Convergent muscles
   - fibers are spread out and converge to one tendon
   - can pull in many directions
   - less force than parallel (Does not pull as hard on attachment as parallel
   muscles)
   - example is pectoralis major

Question 20

what are pennate muscles and examples

Answer 20

• fibers at an angle to tendon
• there is unipennate((extensor digitorium), bipennate(rectus femoris), and multipennate(deltoid)
• contain more myofibrils than parallel muscles and develop more tension than parallel muscles BUT does not move as far as parallel muscles

Question 21

what are circular muscles and examples

Answer 21

4. Circular muscles
   - fibers arranged in rings
   - control openings like sphincters
   - its function is contraction and then closes opening
   - examples are orbiculatis oris

Question 22

what are he three classes of levers? what do they depend on the relationship between?

Answer 22

Mechanically, each bone is a lever and each joint is a fulcrum. Muscle provide applied force (AF) which is needed to overcome Load (L)

There are three classes of levers:
1. First class lever
2. Second class lever
3. Third class lever

All depend on relationship between:
- effort (muscle force)
- load (resistance)
- fulcrum (joint)

Question 23

what is a first class lever? how does it work? give examples

Answer 23

First class lever is when a fulcrum (F, Joint) is between the applied force (AF) and the load (L)
- it acts like a pry bar
- distance moved
- depends on size of force and load, and how far each is from fulcrum
(think of the joint/fulcrum in the middle and the order is force → fulcrum → load)
- you apply force on one side, the laid is on the other side and the joint/fulcrum is between and helps movement
- think of a seesaw or pry bar and it depends on how strong the force is, how heavy the load is and how far each is from fulcrum

Question 24

what is a second class lever? give examples

Answer 24

This is when the load is between the applied force and the fulcrum
- it acts like a wheelbarrow. The force is farther from fulcrum than the load
- small force moves large load, increased effective force, but moves it slowly and short distances.

think of second meaning load is SECOND

Question 25

what is a third class lever? give examples

Answer 25

This is when applied force is in the middle between the load and fulcrum - most common lever in the body - BBQ tongs as an example and doing a bicep curl with the AF being biceps, the load being the weight, and the fulcrum being the elbow - speed/distance travelled are increased at expense of force (meaning less force = faster speed and distance)

Question 26

summarize first, second, and third levers

Answer 26

first = AF --> Fulcrum --> Load (like a seesaw, first = first grade seesaw time) second = Fulcrum --> load -> AF think of a wheel barrow (load is closer to AF) third = Fulcrum --> AF --> load think of third grade youre big and strong to do bicep curls and cook with tongs

Question 27

origin vs insertion vs action

Answer 27

The origin is where the muscle attaches to a fixed point and does not move. The insertion is where the muscle attaches to the part that moves and is pulled toward the origin during contraction. (usually bones) The action is the movement the muscle produces, such as bending or straightening a joint.

Question 28

agonist, antagonist, synergist, fixator meaning

Answer 28

The agonist is the main muscle responsible for a movement (prime mover), such as the biceps brachii during a curl. The antagonist opposes that movement of the agonist, such as the triceps brachii. A synergist helps the agonist by adding extra force or stabilizing it, such as the brachioradialis. A fixator is a type of synergist that prevents movement at another joint to assist