physio exam 3

functions of controlled muscle contractions

* purposeful movement of the whole body or parts of the body
* manipulation of external objects
* propulsion of contents through carious hollow internal organs
* emptying of contents of certain organs to external environment

skeletal muscle

striated, voluntary, multi nucleated

attached to bones of skeleton (movement of body in relation to external environment)

cardiac muscle

striated, involuntary, intercalated disc

wall of heart (pumping blood out)

smooth muscle

unstriated, involuntary, spindle-shaped

walls of hallow organs (movement of contents with hollow organs)

mesenchymal cells

multipotent stem cells

important for making and repairing skeletal muscles

myoblasts

embryonic precursor of myocytes

myotube

developmental stage of a muscle fiber composted of a syncytium formed by fusion of myoblasts

myocyte

unit of muscle tissue that contains bundles of myofibrils

myofibril

contain sarcomeres connected in a series

1 um in diameter, make up 80% of the muscle fiber

sarcomere

the smallest functional (contractile) unit of skeletal muscle fiber and is a highly organized arrangement of contractile, regulatory, and structural proteins

muscle fiber

long, cylindrical, 10-100um in diameter and 750,000 um (2.5 ft in length)

thick filaments

special assemblies of the protein myosin

thin filaments

smaller filament size and made up of the protein actin

A band

dark, stacked set of thick filaments

thin filaments overlap in this region

H zone

the lighter region of the A band, this region does not contain the filament oveerlap

M line

support proteins that hold the thick filaments together vertically

I band

contain thin filaments that do not go into the A band

Z line

a dense vertical cytoskeletal disc that defines the boundaries of the sarcomere. anchors thin and titin filaments

titin

highly elastic protein. providing parallel stability, elasticity, and signal transduction

scaffold

sarcomere stability

along with M line proteins (vertical stability), titin helps stabilize the position of thick filaments in relation to thin filaments (parallel stability)

elastic spring

titin acts as a recoil spring

when a muscle is stretched, titin helps the muscle recoil back to its rest position

Signal Transduction

titin is involved in the muscle enlargement pathway in response to weight lifting

myosin

protein consisting of two identical golf club-like subunits (intertwined tails, two globular heads, two hinges)

forming cross-bridges

the heads contains an actin binding site and a myosin ATP site

actin

primary structural component

spherical in shape, they contain binding sites for the myosin

they are arranged in two twisted strands (actin helix)

tropomyosin

thread-like proteins that lie end to end on the actin helix, covering the actin sites at rest

troponin

a complex made of three polypeptide units, binding to: tropomyosin, actin, and Ca2+

Relaxed

1. no excitation
2. no cross-bridge binding because cross-bridge binding site on actin is physically covered by troponin-tropomyosin complex
3. muscle fiber is relaxed

excited

2. muscle fiber is excited and Ca2+ is released
3. released Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site
4. cross-bridge binding occurs
5. binding of actin and myosin cross bridge triggers power stroke that pulls thin filament inward during contraction

Power Stroke Steps

1. binding
2. power stroke
3. detachment
4. binding

SERCA Pump

* actively transport Ca2+ from cytosol to lateral sacs
* this allows the troponin-tropomyosin complex slip back into its blocking position

latent period

excitation-contraction coupling must occur before cross-bridge activityc

contraction time

time from contraction onset to peak tension (15-50ms) this cannot end until the Ca2+ has been removed

Relaxation time

time from peak tension to relaxation (15-50ms)

skeletal muscle biomechanics

applying physics to study mechanical principles of biological systems. transforming chemical energy to mechanical energyt

tendon

tough, elastic, connective tissue that connects whole muscle groups to bones

muscle tension

the tension produced in the muscle that is applied on bones via tendon

contractile component

when the sarcomeres shorted, due to cross-bridge cycling, this tension is only within the muscle itself

series-elastic component

refers to the elastic, non-contractile tendons

shortening of the sarcomeres stretches the series-elastic component, transferring muscle tension to the bone

origin

the muscle attached to the more stationary bone

insertion

muscle attached to the bone that is moving

isotionic

constant tension

concentric isotonic

if the force the muscle produces is greater than the opposing force, the muscle shortens

eccentric isotonic

if the force the muscle produces is less than the opposing force, the muscle lengthens

isometric

constant length

isokinetic

constant velocity

work

force multiplied by distance

force

the muscle tension required to overcome the load (weight of the object)

fulcrum

elbow joint

power arm

distance between fulcrum and the insertion

load arm

entire arm from fulcrum to hand

lever ration

power arm : load arm

distance and velocity

muscle shortening / lever ratio

force

weight of object / lever ration

no summation

if a muscle fiber is restimulated after it has completely relaxed, the second twitch is the same magnitude as the first twitch

twitch summation

if a muscle fiber is restimulated before it has completely relaxed, the second twitch is added on to the first twitch

tetanus

if a muscle fiber is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, a maximal sustained contrtraction

somatic reflex responses

no conscious effort, automatic

volunatry movements

goal-directed movements initiated and terminated at will

rhythmic movements

patterned movements

central pattern generators

biological neural circuits that autonomously bring about patterned movements

ATP production

1. creatine phosphate
2. oxidative phosphorylation
3. glycolysis

creatine phosphate

* first energy source tapped at the onset of muscle contractions
* has a high-energy phosphate group that can be donated to ADP to form ATP and creatine
* reversible reaction
* pools in your muscles
* short bursts of high intensity can deplete the pools in 5-10 seconds

creatine supplement

* side effects: high blood pressure, dehydration, upset stomach, muscle cramps
* make mania worse in bipolar disorder
* make kidney disease worse
* associated with a faster rate of parkinson’s progression

glycogen

glucose is delivered to the muscles via the blood and is stored as chains of glucose

live stores excess

oxidative phosphorylation

* utilizes glycogen and oxygen
* many enzymatic steps
* aerobic activity
* light exercise - walking, light jog, playing in the pool
* \

mechanisms to increase O2

1. increase breathing
2. increase o2 storage/diffusion

hemoglobin

4 globulins each with a hemes and iron

a1 a2 b2 b1

myoglobin

able to bind and release o2 depending on o2 concentration and increases oxygen diffusion (whales have more of this)

limitations to o2 delivery

lungs can only take in so much O2 and blood can only deliver so much

near maximal contractions also close blood vessels, limiting O2 supply

glycolysis

occurs in absence of oxygen

its faster

muscle fatigue

occurs when an exercising muscle can no longer respond to stimulation with the same degree of contractile active

it’s a defense mechanism to prevent the total loss of ATP

cause of muscle fatigue

unclear but:

* could be due to a local increase in inorganic phosphate
* SERCA Ca2+ pump leakage - protease activation
* depleted glycogen stores

central fatigue

when the CNS no longer activates the motor neurons supplying the muscle

poorly understood

filaments in smooth muscle

1. thick myosin
2. thin actin
3. intermediate filaments

intermediate filaments

binds to dense bodies to provide structural support for actin and myosin in smooth muscle

smooth muscle thin filament

no troponin

tropomyosin is not covering the myosin binding site on the actin

smooth muscle contraction

regulated by ANS through varicosities

single unit smooth muscle

fibers connect as one through a syncytium via gap junctions

ex: visceral muscle

multi unit

fibers act independently of each other

pupillary muscles

pacemaker potentials

spontaneous potentials that always reach threshold

depolarization is induced by Ca2+ (not Na2+) and use L-type voltage-fated Ca2+ channels

repolarization L-type voltage-gated K+ channels

slow wave potentials

constant depolarizations and repolarizations that do not necessarily reach threshold

largely unknown how this occurs

stress-relaxation response

enables smooth muscle to exist in a variety of lengths with little change in tension

circulatory system

the bodies system of transport

heart

establishes a pressure gradient

blood vessels

passageways for transport

blood

transport medium

pulmonary circulation

heart to lungs

systemic circulaton

heart to body systems

heart

hollow organ about the size of a fist

lies left in the thoracic cavity

right side of heart

deoxygenated

serves pulmonary circuit

left side of heart

serves systemic circuit

oxygenated

superior/inferior vena cava

right side vessels leading blood to the atria

pulmonary veins

left side vessels leading blood to the atria

pulmonary trunk

right side vessels leading blood away from ventricles

aorta

left side vessel leading blood away from ventricles

pressure

the force on the vessel walls from the heart pumping the blood into themr

resistance

friction between the blood and the vessel wall

chordae tendineae

tendinous tissue connecting the valve to the papillary muscle

papillary muscle

nipple

contracts with a ventricle contraction