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Muscle

I). Muscle Twitch

A). Muscle twitch is the response of a muscle to a single brief threshold stimulus.

The strength of twitch depends on the number of motor units activated

B). Phases

1). Latent Period

Muscle tension is beginning.

2). Period of Contraction

Muscle fibers shorten.

3). Period of Relaxation

Ca++ renters the sarcoplasmic reticulum

II). Graded Response

A). Force depends on muscle units

Threshold

Maximal stimulus

B). All or none response:

A muscle fiber that is exposed to threshold stimulus will contract with a complete twitch.

C). Staircase Effect

D). Graded muscle response

i). Summation

If 2 stimuli are delivered in rapid succession the second twitch will be greater than the first.

This only occurs if repolarization is not complete.

ii). Incomplete Tetanus

The amount of Ca++ increases in the cytoplasm results in a quivering response

iii). Complete Tetanus

III). Isotonic & Isometric Contractions

A). Muscle tone

B). Isotonic contractions The muscle changes length and moves a load.

Isotonic contractions the thin actin filaments are sliding across the myosin

$\isometric$

C). Isometric contractions:

Tension in the muscle increases but the muscle neither shortens or lengthens.

Isometric contractions the cross bridges are forming and pulling but the actin filament is not moving

IV) The ability to move a load (Load = resistance) is dependent on:

A). The Force of Contraction

The degree of force is affected by:

1). The number of muscle fibers contracting.

2). The relative size of the muscle based on cross-section.

3). Series–elastic elements

4). Degree of muscle stretch.

Length tension relationship:

Too long: do not overlap & no cross bridges form

Too short: overlap too much shortening cannot occur

B). Contractile Velocity

1). Size of load

2). Recruitment of motor units.

3). Muscle fiber type:

slow fibers: fatigue resistant & aerobic endurance activities

fast fibers: fatigue fast both aerobic and anaerobic.

.

C). Contractile Duration

D). The points of attachment

Muscle & bone act as a lever:

A change in the insertion point of a muscle can greatly affect its ability to move a load.

(A load that is far from the joint takes a greater force to move)

E). Fascicle Arrangement

Types

1). Parallel: Strap-like

2). Convergent: Fan shaped

3). Circular or Sphinchteral

4). Pennate:

	Muscle & bone act as a lever:
	A change in the insertion point of a muscle can greatly affect its ability to move a load.