Muscular System KIN202-M1

3 types of muscle

1. cardiac muscle

2. skeletal muscle

3. smooth muscle

musculotendinous unit

muscles attach to bones by tendons

type of tissue connected to the musculotendinous unit

tough fibrous connective tissue

bone to tissue in order

bone → tendon → muscle → tendon → tissue

3 other connective tissue

1. epimysium

2. endomysium

3. perimysium

function of connective tissue

stabilizes and supports many organizational levels of muscle

label: bone, tendon, epimysium, muscle fascicle, muscle fiber (cell), endomysium, permysium, blood vessels, body of muscle

label: tendon, epimysium, perimysium, skeletal muscle, endomysium, muscle fiber, endomysium, sarcolemma membrane, microfiber, actin myosin, sarcomere, fasciculus, muscle fibers covered with endomysium

sarcomere function

smallest most basic contractile unit of skeletal muscle that produces force and shortening

label: sarcomere, z disc, thin filament, thick filament, m line, H zone, A band, I band

triposmysin

tube shaped protein molecule wrapped around actin

troponin

3 regulatory proteins located along tropomyosin molecule

the 3 troponin molecule

1. troponin I (Tnl)

2. troponin T (TnT)

3. troponin C (TnC)

Troponin I function

holds tropomyosin - troponin to actin

troponin T function

holds troponin to tropomysin

troponin C function

affinity for calcium. KEY for muscle activation

label: globular head, hinged pivot, flexible fibrous tail, thick filament, M one, head groups of myosin molecules form cross bridge

label: covered active site, Tnl, TnC, TnT, tropomyosin, actin, head to tail overlap

The ____ ____ of the muscles (contraction) is preceded by ____ ____ that are dependent on an ____ ____

mechanical response, chemical changes, electrical stimulus

The electrical stimulus is provided via the ___ ___

motor unit

The motor unit is what kind of nerve?

single motor nerve

single motor nerve originates in what 3 locations?

1. brain

2. brainstem

3. spinal cord

the motor unit has all of what that does what?

all the muscle fibers that a single motor nerve innervates

label: ventral horn motor unit, motor unit, skeletal muscle fiber

label: alpha motor neuron (cell body), axon hillock, dendrites, direction of propagation of action potential, terminal branches, motor unit, motor end plate

label: motor neuron (2), muscle cells, to other muscle fibers (2) and function

allows for uniform activation as well as graduations in force production

What does an electromyography do (EMG)?

detects the electrical activity or motor unit/muscle

easier than detecting the mechanical activity

T Tubules

spread electrical impulse from motor unit

sarcoplasmic reticulum

storage of Ca²+

what percent of calcium in the body is unbound from bones?

1%

Adenosine Triphosphate (ATP)

the energy molecule that is produced from ADP and inorganic phosphate (Pi) and when broken down to ADP and Pi energy is released

energy needed to bound ADP and Pi obtained from (2)

aerobic metabolism and anaerobic metabolism

the 5 steps of muscle contraction

1. resting muscle

2. activated muscle

3. movement of the muscle

4. tightly bound

5. detachment

What happens during the first step of muscle contraction

active sites are covered, ADP and Pi are on the myosin head

What happens during the second step of muscle contraction

neural activities cause a release of Ca++ from the sarcoplasmic reticulum. Ca++ bind to troponin, altering its shape and causing tropomyosin to shift, exposing the active sites. Myosin filaments can now attach to actin

What happens during the third step of muscle contraction

the release of Pi results in high affinity binding of x-bridge head with the actin binding site

What happens during the fourth step of muscle contraction

the release of ADP occurs during the power stroke

What happens during the last step of muscle contraction

ATP binds to myosin head causing detachment from actin active site. ATPase breaks down ATP to ADP+Pi which repositions myosin head at 90 degrees position like in the first step. step1-5 are then repeated to produce further shortening

the type of contraction depends on the ___ ___ relative to the force produced by the ___

external force, muscle

concentric

occur during dynamic tasks where the muscles shorten (like bringing your arm up while doing bicep curls)

Isometric

occur in static situations, no movement

eccentric

occurs during dynamic tasks, muscle lengthening (like when you’re moving your arm down during bicep curls)

lengthening velocity and force are high

eccentric

shortening velocity is high and force is low

concentric

force is 0 and neither at lengthening or shortening velocity

isometric

to exert a high force you need a ___ ___

high load

muscle fiber typing

• biopsy to obtain muscle samples

• sectioned cross-sectionally

• pointed on glass slide

• stained for various enzymes to discriminate among fiber types

Henneman’s “size principle”

most force is generated by ST fibers at low intensity exercise, but as force needs increase, FT fibers begin to be recruited (stronger neural signal). at maximal effort, all types of fibers are utilized, but even at maximal effort 100% of muscle fibers are not activated to prevent injury and muscles or tendons won’t tear

smaller and lower threshold motor units are recruited before larger and higher threshold units. the force required determines the number of active motor units