Exercise Physio Chapter 1 Exam 1

Skeletal muscle

voluntary control

smooth muscle

involuntary control, could be controlled by pacemaker cells, hormones, or nervous system

cardiac muscle

involuntary control, could be controlled by pacemaker cells, hormones, or nervous system

entire muscle

-Surrounded by epimysium (around bundles)

-Made of many bundles (fasciculi)

Fasciculi

-surrounded by perimysium (around fascicles)

-made of individual muscle cells (muscle fibers)

muscle fiber

-surrounded by endomysium (around cells)

-made of myofibrils divided into sarcomeres

Myofiber

whole cell, with all the organelles, has nuclei

myofibril

many within each cell, contribute to function, must be in a bunch to work, built of protein, no nuclei

plasmalemma

cell membrane

fuses with tendon

conducts action potential

maintains homeostasis

satellite cells

involved in muscle growth and development

aids response to injury, immobilization, training

sarcoplasm

serves as cytoplasm of muscle cell

stores fuel (glycogen) and myoglobin (transports O2 through cell)

other muscle fuel sources

protein, fat (low and slow), carbs (fast and hot)

t tubules

tunnels that run from the surface to deep in the muscle, transferring action potential via ion exchange

t tubules in smooth muscle

smooth muscle does not use them

t tubules in cardiac muscle

wider than in skeletal muscles

sarcoplasmic reticulum (SR)

expands calcium along the length of fibers, working together with t tubules to flood muscle with calcium when time to contract

what does the SR do during relaxation

reuptakes calcium and stores

nerve signal to membrane ->

brings signal inside and SR releases stores Ca2+ -> contract -> relaxation (Ca2+ back to SR)

sarcomeres

basic contractile element of skeletal muscle

end to end for full myofibril length

do not over stretch or they tear

myofibrils

Muscle -> fasciculi -> muscle fiber -> myofibril

Hundreds to thousands per muscle fiber

protein filaments

1. actin and myosin

2. troponin and tropomyosin

3. titin

actin (thin)

show up lighter under microscopes

I-band contains only actin filaments

myosin (thick)

show up darker under microscope

a-band contains both actin and myosin filament

h-zone contains only myosin filaments

a-bands

dark stripes (mostly myosin)

I-bands

light stripes (mostly actin)

H-Zone

middle of a-band

m-line

middle of h-zone

common boundary structure

Z disk

actin is composed of

actin: contains myosin binding site

troponin (anchored to actin): moves tropomyosin

tropomyosin: covers active site at rest

titin and nebulin

contribute to function of force of structure, especially stretching

myosin thick filament

two intertwined filaments with globular heads, stabilized by titin

globular heads

-protrude 360 degrees from thick filament axis

-will interact with actin filaments for contraction

motor unit

consists of a single alpha motor neuron dn all fibers it innervates

more operating motor units=more contractile force

neuromuscular junction

consists of synapse between alpha motor neuron and muscle fiber

serves as site of communication between neuron and muscle

excitation-contraction coupling

1. action potential starts in the brain

2. AP arrives at axon terminal, releases acetylcholine

3. ACh crosses synapse, binds to ACh receptors on plasmalemma

4. AP travels down plasmalemma and t-tubules

5. Triggers calcium release from SR

6. Calcium enables sliding filament theory

Action Potential in SR

SR is sensitive to electrical charge

causes mass release of calcium into sarcoplasm

Calcium binding to troponin

at rest, tropomyosin covers myosin-binding site, blocking actin-myosin attraction

troponin calcium complex moves tropomyosin

myosin binds to actin and contraction can occur

sliding filament theory: relaxed state

No actin-myosin interaction at binding site

Myofilaments overlap a little

sliding filament theory: contracted state

Myosin head pulls actin toward sarcomere center (power stroke)

Filaments slide past each other

Sarcomeres, myofibrils, muscle fiber all shorten

sliding filament theory: after power stroke ends

Myosin detaches from active site

Myosin head rotates back to original position

Myosin attaches to another active site farther down

sliding filament theory: process continues until...

z-disk reaches myosin filaments or ap stops at calcium and gets pumped back into SR

Energy for muscle contraction

ATP is necessary

binds to myosin head, ATPase on myosin head

muscle relaxation

AP ends; electrica stimulation of SR stops

Calcium pumped back into SR and is stored until next AP arrives (requires ATP)

without calcium, troponin and tropomyosin return to resting conformation, cover myosin-binding site, prevent actin-myosin cross bridging

type I muscle fiber

50% of fibers in average muscle

peak tension is 110 ms SLOW TWITCH

type II muscle fiber

peak tension is 50 ms FAST TWITCH

Type IIA

Type IIX

Type IIB

Type IIA muscle fiber

25% of fibers in average muscle, smallest of the big, slowest fast twitch

type IIX muscle fiber

25% of fibers in an average muscle, middle size of big, middle speed of fast

type IIB muscle fiber

1-3% of fiber in average muscle, biggest of big, fastest of fast

slow oxidative fibers

contract slowly, have slow acting myosin ATPase, and are fatigue resistant, low intensity, endurance activities (sitting)

fast oxidative glycolytic fibers

combine high myosin-ATPase activity with high oxidative capacity and intermediate glycolytic capacity, resist fatigue,

fast anaerobic fibers

large, very strong contractions, fatigue quickly

myosin heavy chain isoforms

traditional fiber typing method

11 different isoforms

means a lot of fibers are hybrids

maybe better to think of fibers as mostly fast or mostly slow, not all only one

distribution of fiber types

Each person has unique ratios; each muscle has a typical distribution (soleus type I, humans dont have any all type II muscles)

Type I predominates in endurance athletes

Type II in power athletes.

Type I fibers during exercise

-Possess high aerobic endurance.

-due to high mitochondria number

-Can maintain exercise for prolonged periods.

-Require oxygen for ATP production.

-Recruited for low-intensity aerobic exercise and daily activities.

-Efficiently produce ATP from fat and carbohydrate.

-low and slow

type II fibers during exercise

- fatigue quickly (poor aerobic endurance)

- produce ATP anaerobically

type IIA fibers during exercise

produce more force, fatigue faster than type I

used for short, intense, endurance (1,600 m run)

Type IIx fibers during exercise

Seldom used for everyday activities

Short, explosive sprints (100 m)

genetic factors of fiber types

-Determine which a-motor neurons innervate fibers

-Fibers differentiate based on a-motor neuron

training factors of fiber types

differentiate endurance training, strength training, and detraining

trining can induce small change in fiber type, usually just towards mixed

aging factor of fiber type

loss of type II motor units, shift to more type I

motor unit recruitment

-Type II motor units = more force

-Type I motor units = less force

-Fewer small fibers versus more large fibers

Frequency of stimulation (rate coding)

twitch, summation, tetanus

size principle

Order of recruitment relates directly to size of alpha-motor neuron.

recruit minimum number of motor units needed

First: smallest (type I) motor units

Next: midsize (type IIa) motor units

Last: largest (type IIx) motor units

recruitment order

type I, type IIA, type IIX

same order each time

Method for altering force production

Less force production: fewer or smaller motor units

More force production: more or larger motor units

Type I motor units smaller than type II

static (isometric) contraction

Muscle produces force but does not change length

Joint angle does not change

Myosin cross-bridges form and recycle, no sliding

dynamic contraction

Muscle produces force and changes length

Joint movement produced

concentric contraction

Muscle shortens while producing force

Most familiar type of contraction

Sarcomere shortens, filaments slide toward center

eccentric contraction

Muscle lengthens while producing force

Cross-bridges form but sarcomere lengthens

Example: lowering heavy weight

force-velocity relationship

contraction force is dependent on contraction speed

velocity increase force decrease (less time form cross bridges)

slower speed there is more time for cross bridges to form allowing more force generation

passive forces from connective tissue contribute to total force