sys phys exam 2 lectures 1-2 (set 1)

3 types of muscle

skeletal, cardiac, smooth

Which muscles are striated?

skeletal and cardiac

which muscles are involuntary?

smooth and cardiac

smooth muscle location

lining hollow organs ie arterioles, GI tract, airways

skeletal msucle mechanical roles (2)

actuate movement
produce force

what types of movement do skeletal muscles allow

maintenance of posture
purposeful movement
manipulation of external objects

physiological roles of skeletal muscles (3)

regulate water balance (intracellular muscle water redistributed outside cell during periods of dehydration)

store ingested glucose

maintain body temp.

skeletal muscle cellular structure

myocyte/fiber: muscle cell
fascicle: hundreds of fibers
muscle: many fascicles

skeletal muscle structure (organ level)

muscle = organ of contraction
tendons connecting to bones
muscle or tendon crosses a joint

tendon function (4)

1. allow transmission of force
2. reducing mass at joint
3. elastic energy storage and release, 4. reduces energy cost of movement

myocyte structure

nuclei, mitochondria (to meet energy demands), organelles
80% composed of myofibrils (contractile protein strands)

myofibrils

contractile protein strands to give striated pattern

skeletal muscle structure molecular level

thin (actin) and thick (myosin) filaments

A band

stack of thick filaments along with thin filaments that overlap

THICK FILAMENTS LIE ONLY IN THE A BAND

H zone

where thin filaments don't reach and where there are no myosin heads

M line

system of supporting proteins that hold the thick filaments together vertically with each stack

I band

remaining portion of the thin filaments that do not project into the A band

Z line

end of sarcomere

sarcomere

functional unit of skeletalmuscle contraction

structure of thin and thick filaments

each think filament surrounded by 3 thick filaments

myosin structure

form thick filament
2 polypeptide chains
4 light chains that make heads that have ATP and actin binding site

thin filament

actin, troponin, tropomyosin

actin structure

has binding site for myosin

tropomyosin

threadlike, lies alongside groove between actins

troponin

3 part protein that can bind to tropomyosin and ca

what are the contractile proteins

actin and myosin

what are the regulatory proteins

troponin and tropomyosin

what are the structural proteins

m and z lines, titin

titin

adds elasticity, signaling

sarcoplasmic reticulum

stores Ca

transverse proteins

where excitation events spread

excitation

synaptic transmission of neuromuscular junction
AP propagation down muscle cell membrane

excitation-contraction Coupling

APs travel down membrane and into transverse tubules
SR releases Ca

Contraction

myosin and actin produce force
sarcomere shortens due to rise in intracellular Ca

where does the command to contract come from

motor neuron

excitation steps (7)

1. AP propogates down motor neuron axon
2. Ca channels open, Ca enters
3. vesicles dock to pre synaptic membrane and fuse, AcH enters
4. ACh binds to receptors on muscle
5. membrane depolarizes
6. Na, K channels generate APs
7. AP's propagate along cell membrane and into transverse tubules

neuromuscular transmission termination

ACh splits
diffused away and taken up by motor neuron
repackaged into vesicles

key event in excitation-contraction coupling

rise in intracellular Ca from sarcoplasmic reticulum

sliding filament theory

muscle contraction occurs via relative movement of thick and thin filaments
length doesnt change, only position

cross bridge cycling (6 steps)

1. troponin binds to Ca
2. troponin undergoes conf. change
3. tropomyosin unblocks myosin binding site on actin
4. cross bridge can now bid and undergo power stroke
5. thin filaments pulled inward
6. ATP binds, Ca pumped back into SR, muscle relaxes

repeated cross bridge cycles

shortening and force production

rigor mortis

muscle stiffness occuring after death because there is no ATP to detach cross bridges

motor unit

alpha motor neuron and the muscle fibers it innervates

motor unit recruitment

activating more motor units to increase tension

proceeds from fatigue resistant units to fatigue sensitive units

rate coding

changing force per motor unit
changes stimulation frequency via summation
AP is much shorter than the corresponding contraction (twitch)

twitch

muscle contraction from single AP

twitch phases (3)

latent: period from the AP to onset of contraction due to E-C coupling

contraction: time that the tension is developing due to cross bridge cycling

relaxation: tension decreasing due to amount of time to sequester Ca

force @ high vs. low freq.

low freq: force relaxes completely btwn twitches

high freq: force does not recover completely and will sum

tetanus

contraction of max. tension resulting from high levels of intracellular Ca

isometric contraction

constant length

isotonic concentric contraction

muscle shortens
+ velocity

isotonic eccentric

muscle lengthens
- velocity

shortening contraction fx on cross bridge stress

1. proportion of cross bridges = lower
2. rate of ADP release from XB limits rate
3. mechanical stress on xb reduced

so. shortening contraction reduces stress on XB. ADP rate of release elevated (inversely related), cross bridges detach at higher rate

lengthening contraction fx on cross bridge stress

higher rate of cross bridge attachment

metabolic reactions that synthesize ATP

creatine kinase
anaerobic glycolysis
oxidative phosphorylation

creatine kinase rxn

1st pathway for ATP synth.
creatine catalyses rxn that makes ATP from ADP and phosphocreatine

anaerobic glycolysis

2nd pathway
hydrolysis of glucose from blood or glycogen to pyruvate forms ATP

oxidative phosphorylation

3rd pathway for ATP resynthesis
krebs cycle, ETC

what is activating metabolic rxns

muscle contractions (rise of Ca triggers metabolism) and increases in ADP and Pi (increases metabolic rates)

what inhibits muscle contraction

1. ADP and P (causes muscle fatigue)
2. decrease in pH (not lactic acid accumulation)
3. rise in extracellular K+
4. central fatigue
5. depletion of glycogen

motor unit types

slow oxidative (type 1)
fast oxidative glycolytic (type 2a)
fast glycolytic (type 2x)

Neutriceuticals

food used for medicine

antagonistic muscles

actuate a lever
work in pairs, but muscle works against the other