Ch 9 - muscle

The ____ of a scarcomere produces tension/force within a muscle

Shortening

Length-tension relationship

The sarcomere must be at an optimal length (not too long, not too short) for optimal muscle contraction.

Sources of ATP

Creatine phosphate, anaerobic respiration (fermentation), aerobic respiration

How is creatine phosphate used in muscle contraction?

Uses a high energy phosphate from extra ATP

Resting skeletal muscle

Low demand for ATP, abundant oxygen, extra ATP being produced which is used to build energy reserves

Energy reserves

Creatine phosphate, glycogen

Immediate energy

ATP and creatine phosphate are used, ~15 s

Short term energy

Anaerobic respiration

Creatine phosphate is depleted

Blood glucose and glycogen used in glycolysis

Lactic acid production due to low oxygen

long term energy

aerobic respiration

breathing rate increases

oxygen delivery increases

rate of ATP production is slower

oxygen debt

amount of oxygen needed to convert lactic acid to glucose

muscle fatigue

inability of muscle to maintain force of contraction after prolonged use

energy sources depleted

calcium released from SR into sarcoplasm reduced

not enough oxygen

lactic acid build up

reduced Ach release

motor unit

all the muscle fibers controlled by a single motor neuron

more precise control, less power

less muscle fibers in a motor unit

more powerful, less precise control

more muscle fibers in a motor unit

sensitivity to stimuli of a motor unit

fewer muscle fibers, more sensitive

more muscle fibers, less sensitive

what factors affect muscle contraction?

stimulus intensity/frequency

number of muscle fibers

amount of calcium in the sarcoplasm

temperature

pH

motor unit recruitment

increase in number of active motor units

start with the minimal number of motor units needed

if need more, recruit/activate larger, stronger motor units

types of contraction

twitch, wave summation, complete tetanus, incomplete tetanus, isometric, isotonic

twitch

contraction of all muscle fibers within motor unit in response to a SINGLE action potential

3 stages of a twitch

lag

contraction

relaxation

lag phase

the time it takes for the action potential to travel down the axon of the neuron

(ach released and calcium gates open in SR)

is a single twitch enough to perform work?

no

contraction phase

tension peak

calcium binds to troponin

crossbridge cycling

relaxation phase

SR reabsorbs calcium

crossbridge cycling stops

frequency of stimulation

rate of action potentials from neuron that arrives at NMJ, exciting the muscle fiber

wave summation

2nd action potential arrives before muscle fiber relaxes

produces a larger contraction than first

incomplete tetanus

increased frequency of AP (action potential)

muscle fibers PARTIALLY relax before next AP

complete tetanus

increased frequency of AP (action potential)

muscle fibers DO NOT RELAX

how can a muscle sustain contraction?

asynchronous motor unit recruitment

asynchronous motor unit recruitment

motor units are activated on a rotating basis

while some rest and recover, others contract

incomplete tetanus

prevents jerky movement

produces slightly less than maximal tension

muscle tone

the small amount of tension in muscle at rest

no movement

result of weak, involuntary contractions of motor units

how are muscle tone and BMR related?

greater the muscle tone, the higher the resting rate (direct relation)

isometric

muscle length is constant while tension increases

isotonic

tension is constant while muscle length shortens

how can muscle return to original length?

elastic forces (recoiling, pull of tendons)

opposing muscle

gravity

types of skeletal muscle fibers

slow oxidative (type 1)

fast oxidative glycolytic (type 2A)

fast glycolytic (type 2B)

characteristics of slow oxidative muscle fibers

slow contraction (small diameter)

more mitochondria

many capillaries (to transport O2)

aerobic metabolism

high levels of myoglobin

fatigue resistant

where are slow oxidative muscles most abundant?

postural muscles, lower limbs

characteristics of fast glycolytic muscle fibers

majority in body

most myofibrils (large diameter)

fast contractions

low myoglobin levels

few capillaries

few mitochondria

lots of glycogen

fatigue easily

where are fast glycolytic muscles most abundant?

upper limbs

characteristics of fast oxidative glycolytic muscle fibers

intermediate characteristics of both slow oxidative and fast glycolytic

white muscles

fast fibers more abundant

lack of myoglobin

red muscle

slow fibers more abundant

more myoglobin

how can the proportions of our muscle fiber types change?

physical conditioning

anaerobic exercise

strength, speed, power

promotes hypertrophy

short, high-intensity workouts

fast glycolytic

O2 not required

aerobic exercise

prolonged activities

long, low intensity

fast glycolytic and fast oxidative glycolytic

O2 required

does not promote hypertrophy

which type of exercise can alter muscle fiber characteristics?

aerobic exercise can convert fast glycolytic to fast oxidative glycolytic

improves aerobic endurance

hypertrophy

muscle growth

increase in myofibrils and sarcomeres

muscles stronger

atrophy

decrease in muscle size

muscle fibers smaller

muscles weaker

Functions of the muscular system

body movement

stabilize body position

organ volume regulation

moving substances within the body

heat production

characteristics of skeletal muscle cells

very large muscle fibers

long and slender

multi-nucleated

striated

cardiocytes

cells of cardiac muscle

characteristics of cardiac muscle cells

shorter

striated

branched

intercalated disks

single nucleus

characteristic of smooth muscle cells

small

spindle-shaped

tapered oval nucleus

no striations

involuntary

properties of muscular tissue

excitability, contractility, extensibility, elasticity

excitability

ability to respond to stimuli, producing action potentials

contractility

contraction develops tension with or without shortening of sarcomere

extensibility

stretch without damage

elasticity

return to original shape and length

additional functions of the skeletal muscle specifically

support and protect soft tissue

guard entrances and exits

energy storage

connective tissue in muscle organization

subcutaneous layer (hypodermis)

fascia (sheet wrapping muscles and organs)

what type of connective tissue is fascia made of?

dense irregular

functions of fascia

holds groups of muscles of similar functions together

fills spaces between muscles

carries blood vessels and nerves with it

what are the 3 layers of connective tissue that extend from fascia?

epimysium, perimysium, endomysium

epimysium

wraps entire muscle organ

perimysium

wraps bundles of fibers (fascicles), contains blood and nerve supply

endomysium

wraps individual muscle fibers and contains myosatellite

myosatellite cell function

muscle repair, nonmitotic

aponeurosis

Sheet of connective tissue that attaches muscles to muscles

(ex: head)

somatic motor neurons

nerve cells that stimulate a group of skeletal muscle fibers

(CNS to PNS)

blood capllaries

bring in oxygen and nutrients through endomysium and removes heat and waste

sarcolemma

plasma membrane of muscle cell

T (Transverse) tubules

invaginations of sarcolemma

T tubule function

relay information of the transmembrane potential change to the inside of the cell (sarcoplasm)

sarcoplasm

cytoplasm of a muscle cell

myoglobin

red pigment that stores oxygen

myofibrils

protein fibers within skeletal muscle cells

sarcoplasmic reticulum (SR)

covers each myofibril

stores calcium (keeps calcium levels in cytoplasm low)

consists of terminal cisternae and triads

terminal cisternae

dilated ends against T tubules full of calcium

triad

a t tubule with 2 terminal cisternae that opens calcium voltage channel to trigger muscle contraction

actin

thin filaments

myosin

thick filaments

sarcomeres

contractile unit containing actin and myosin, structural and regulatory proteins

z disk

separates sarcomeres, where actin attaches

A band (dark)

consists of H-zone, M-line, and zone of overlap

entirety of myosin and zones where myosin interacts with actin

H zone

center of A band of ONLY myosin

M line

center of sarcomere/H zone

zone of overlap

where actin and myosin overlap

I band (lighter area)

contains z line, ONLY actin

components of actin

2 strands of actin, myosin binding site, tropomyosin, tropnin

tropomyosin

covers myosin binding sites on actin, when muscle is at rest

troponin

contains 3 binding sites: tropomyosin, calcium, and actin

cross-bridges

connection between actin and myosin during contraction

titin

strongest structural muscle protein in body

prevents overstretching

attaches myosin to z line

actinin

Structural protein that makes up Z line

attaches to titin and actin

Myoblasts

differentiate into myofibrils

myomesin

forms the M line

dystrophin

links thin filaments to integral membrane proteins of sarcolemma

sliding filament model

myosin heads pull on actin, sliding past toward the A band

neuromuscular junction (NMJ)

where communication between the nervous and muscular system occur