SKeletal muscle part 2

Principles of Muscle Mechanics

1. how a single muscle fiber contracts are mostly the same as for how an entire skeletal muscle contracts, even though the whole muscle has many cells.

2. Muscle tension is the force a muscle creates when it contracts, and the load is the force from the weight of the object the muscle is trying to move.

3. contracting muscles dont always shorten and move the load

4. A skeletal muscle contracts with different strength and for different times depending on how often and how strong the stimuli are.

Motor Unit:

Muscle Twitch

Myogram:

• motor neuron and all the muscle fibers it act upon

• respone of a motor unit to a action potential of its motor neuron

• graphic of contractile activity

Phases of Muscle Twitch

Latent period: excitation/ contraction coupling

Period of Contraction: cross bridges are active

Period of Relaxation: Ca2+ reenters the SR

2 types of graded muscle response?

changing frequency of stimultion & strength of stimulus

Stimulation Frequency

• Wave Summation

• Incomplete Tetanus

• Complete Tetanus

• If two stimuli are delievered in rapid succession, second twitch will be stronger

• sustained but quivering contraction

• smooth, sustained contraction plateau (coordinated movement)

Strength of STimulus

• Multiple Motor Unit Summation

  • Thershold STimulus

  • Maximal STimulus

• (recruitment) delievering shocks of increasing voltage to muscle, calling more muscle fibers

  • enough voltage to ignite 1 motor unit

  • ignites every unit to contract

What is the recruitment look like for a smaller motor unit (size principle)?

they have a low threshold for activation and are recruited first, then when more force larger ones are recruited

Treppe:

Muscle tone helps…

Muscle tone does not produce ____

Muscle tone is due to ____ _____

(staircase) warmup muscle contraction going to tense more than a cold one (more Ca2+)

• stabilize joints, posture, health, ready to respond

• spinal reflexes

CONTRACTIONS

Isotonic (Dynamic) Contractions:

Isometric Contractions:

1. Concentric: shorterning muscle while moving load (flexing)

2. Eccentric: muscle is lengthing while its contracting (unflexing)

Muscle is not moving, to gain strength (wall sits,planks)