Physio - Muscle Unit

everything

fascicle

a bundle of fibers

epimysium (fascia)

tissue sheath surrounding the muscle

perimysium

tissue steath surrounding the fascicle

endomysium

surrounds a muscle cell (individual muscle fibers)

functions of the fibrous connective tissue layers surrounding muscle tissue

• maintains muscle structure

• provides support for nerves and vessels (neurovascular bundles)

• ensures equal distribution of muscle tension during contraction

• maintains elasticity of muscle (allows it to recoil to resting length after stretching or constricting)

• merge to form tendons

tendons

fibrous layers of connective tissue that form when they merge and reach the ends of a muscle

the “belly” of a muscle

-whole muscle and all of the connective tissue layers

-shortens during muscle contraction

1st class lever

-joint lies between muscle and load

-most efficient class

2nd class lever

-load lies between the joint and the pulling muscle

-operates in a wheelbarrow way

-ex: someone standing on their tippy toes

3rd class lever

-muscle lies between the joint and the load

-has poor mechanical advantage here

-greatest leverage

motor nerve

stimulates muscle fibers to contract

motor unit

a group of muscle cells that are attached to the axon branches of the same motor neuron

maximal muscle contractions

all muscle units are discharged

partial muscle contractions

only some of the motor units are discharged

facial muscles

-nerve to muscle ratio of 1:10

-finer/refined control on muscular effect

-selective degree of contraction

gluteus maximus

-nerve to muscle ratio of 1:1000

-no possibility of controlled, refined contractions from this muscle

-more branched

insertion bone

the bone that moves when a muscle contracts

origin bone

the bone that remains fixed in place during the same contraction

agonists (prime movers)

the muscle that is contracting to make a movement

antagonists

the muscle that opposes the agonist’s movement

synergists

muscles that help/support the agonist’s contraction

isotonic contraction (can be concentric or eccentric)

-muscles shorten or lengthen

-concentric = towards body

-eccentric = away from body

isometric contraction

-muscles contract and hold tension with constant length

-there is no movement

muscles never push…

they always pull

whatever one muscle does…

another muscle can undo

mechanically, the degree of muscular effort required to overcome resistance to movement at a joint (fulcrum)…

depends on the force of the resistance (weight), the relative distances from the anatomical fulcrum to the anatomical sites of muscular effort, and the anatomical sites of resistance

the fewer number of muscle cells in any motor unit…

the more selective and refined the degree of contraction of that skeletal muscle

Neuromuscular Junction

1. nerve stimulates muscle

2. Acetylcholine (Ach) release causes sodium ions to move into the muscle cell

3. sodium ions cause the cell to depolarize

4. voltage-gated calcium channels open to allow calcium ions to move into the cell

5. the sarcoplasmic reticulum releases stored calcium

sarcoplasmic reticulum

storage for calcium when its not in the muscle cell

Sliding Filament Theory of Muscle Contraction

1. Myosin binds to actin

2. Myosin pulls the actin

3. Myosin releases the actin

4. Reset

1. Myosin binds to actin

1. Calcium binds to troponin and causes it to change shape

2. troponin change causes tropomyosin to expose the myosin binding sites on the actin

   Note : the myosin head has an ATP molecule (ADP + P) attached to it

2. Myosin pulls the actin

1. energy from ATP powers the myosin to pull the actin towards the center of the sarcomere

2. ADP + phosphate are released

3. Myosin releases the actin

1. ATP attaches to myosin and the myosin head detaches from the actin

   Note: many reactions (millions) are occurring at once to produce movement

4. Reset

1. Proteins prepare to contract again

2. myosin head returns to the starting position

3. calcium binds to troponin again, etc.

Recruitment

increasing the number of individual motor units involved in a contraction in response to a higher demand

• note: more motor units = more force

Fast Twitch (white color)

-metabolize ATP faster

-can do anaerobic respiration

-fatigue quickly

Slow twitch (red color)

-redder due to myoglobin (oxygen storing protein)

-fatigue slowly

-ex. sitting up

the amount of tension a muscle can produce is the result of…

the amount of motor units (recruitment)

Factors that contribute to muscle growth

-micro stress to proteins in muscle cells (force regrowth of protein which increases size of muscle)

-rest

-diet —> protein = amino acids (for regrowth)

-genetic factors

atrophy

when structural proteins are lost and muscle mass decreases

sacropenia

-age related atrophy

-as muscles age, muscle fibers die, and they are replaced by fibrous connective tissue and adipose tissue

-other causes: reduction in motor units, less fast fibers and more slow fibers

“all or none” law of muscle contraction

muscles will contract completely or not at all

muscle twitch

electral stimuli →muscle response = muscle twitch (very quick movement)

muscle’s threshold of stimulation

weakest response

point of muscle overload

place where muscle cannot contract