BIO 201 Chapter 10, Part 2 Lecture
Transcript of BIO 201 Chapter 10, Part 2 Lecture
Chapter 10, Part 2:Muscular Tissue
Muscle Metabolism
Production of ATP in Muscle Fibers A huge amount of ATP is needed to:▪ Power the contraction cycle▪ Pump Ca++ into the SR
The ATP inside muscle fibers will power contraction for only a few seconds
ATP must be produced by the muscle fiber after reserves are used up
Muscle fibers have three ways to produce ATP▪ 1) From creatine phosphate▪ 2) By anaerobic cellular respiration▪ 3) By aerobic cellular respiration
Muscle Metabolism
Muscle Metabolism
Creatine Phosphate Excess ATP is used to synthesize
creatine phosphate▪ Energy-rich molecule
Creatine phosphate transfers its high energy phosphate group to ADP regenerating new ATP
Creatine phosphate and ATP provide enough energy for contraction for about 15 seconds
Muscle Metabolism
Anaerobic Respiration Series of ATP producing reactions that do not
require oxygen Glucose is used to generate ATP when the supply of
creatine phosphate is depleted Glucose is derived from the blood and from
glycogen stored in muscle fibers Glycolysis breaks down glucose into molecules of
pyruvic acid and produces two molecules of ATP If sufficient oxygen is present, pyruvic acid formed
by glycolysis enters aerobic respiration pathways producing a large amount of ATP
If oxygen levels are low, anaerobic reactions convert pyruvic acid to lactic acid which is carried away by the blood
Anaerobic respiration can provide enough energy for about 30 to 40 seconds of muscle activity
Muscle Metabolism
Aerobic Respiration Activity that lasts longer than half a minute depends on
aerobic respiration Pyruvic acid entering the mitochondria is completely
oxidized generating▪ ATP▪ carbon dioxide▪ Water▪ Heat
Each molecule of glucose yields about 36 molecules of ATP
Muscle tissue has two sources of oxygen▪ 1) Oxygen from hemoglobin in the blood▪ 2) Oxygen released by myoglobin in the muscle cell
Myoglobin and hemoglobin are oxygen-binding proteins Aerobic respiration supplies ATP for prolonged activity Aerobic respiration provides more than 90% of the
needed ATP in activities lasting more than 10 minutes
Muscle Metabolism
Muscle Fatigue Inability of muscle to maintain force of
contraction after prolonged activity Factors that contribute to muscle fatigue Inadequate release of calcium ions from
the SR Depletion of creatine phosphate Insufficient oxygen Depletion of glycogen and other
nutrients Buildup of lactic acid and ADP Failure of the motor neuron to release
enough acetylcholine
Muscle Metabolism
Oxygen Consumption After Exercise After exercise, heavy breathing
continues and oxygen consumption remains above the resting level
Oxygen debt▪ The added oxygen that is taken into the body
after exercise This added oxygen is used to restore
muscle cells to the resting level in three ways▪ 1) to convert lactic acid into glycogen▪ 2) to synthesize creatine phosphate and ATP▪ 3) to replace the oxygen removed from
myoglobin
Control of Muscle Tension The tension or force of muscle cell
contraction varies
Maximum Tension (force) is dependent on The rate at which nerve impulses arrive The amount of stretch before contraction The nutrient and oxygen availability The size of the motor unit
Control of Muscle Tension Motor Units
Consists of a motor neuron and the muscle fibers it stimulates
The axon of a motor neuron branches out forming neuromuscular junctions with different muscle fibers
A motor neuron makes contact with about 150 muscle fibers
Control of precise movements consist of many small motor units▪ Muscles that control voice production have 2 - 3 muscle
fibers per motor unit▪ Muscles controlling eye movements have 10 - 20 muscle
fibers per motor unit▪ Muscles in the arm and the leg have 2000 - 3000 muscle
fibers per motor unit The total strength of a contraction depends on the size of
the motor units and the number that are activated
Control of Muscle Tension
Control of Muscle TensionTwitch Contraction
The brief contraction of the muscle fibers in a motor unit in response to an action potential
Twitches last from 20 to 200 msec Latent period (2 msec)▪ A brief delay between the stimulus and
muscular contraction▪ The action potential sweeps over the
sarcolemma and Ca++ is released from the SR Contraction period (10–100 msec)▪ Ca++ binds to troponin▪ Myosin-binding sites on actin are exposed▪ Cross-bridges form
Control of Muscle Tension
Relaxation period (10–100 msec)▪ Ca++ is transported into the SR▪ Myosin-binding sites are covered by
tropomyosin▪ Myosin heads detach from actin▪ Muscle fibers that move the eyes have contraction
periods lasting 10 msec▪ Muscle fibers that move the legs have contraction
periods lasting 100 msec Refractory period▪ When a muscle fiber contracts, it temporarily
cannot respond to another action potential▪ Skeletal muscle has a refractory period of 5
milliseconds▪ Cardiac muscle has a refractory period of 300
milliseconds
Control of Muscle Tension
Control of Muscle Tension
Control of Muscle TensionMuscle Tone
A small amount of tension in the muscle due to weak contractions of motor units
Small groups of motor units are alternatively active and inactive in a constantly shifting pattern to sustain muscle tone
Muscle tone keeps skeletal muscles firm Keep the head from slumping forward on
the chest
Control of Muscle TensionTypes of Contractions
Isotonic contraction▪ The tension developed remains constant
while the muscle changes its length▪ Used for body movements and for moving
objects▪ Picking a book up off a table
Isometric contraction▪ The tension generated is not enough for the
object to be moved and the muscle does not change its length▪ Holding a book steady using an outstretched
arm
Control of Muscle Tension
Types of Skeletal Muscle Fibers Muscle fibers vary in their content of
myoglobin Red muscle fibers▪ Have a high myoglobin content▪ Appear darker (dark meat in chicken legs and
thighs)▪ Contain more mitochondria▪ Supplied by more blood capillaries
White muscle fibers▪ Have a low content of myoglobin▪ Appear lighter (white meat in chicken
breasts)
Types of Skeletal Muscle Fibers Muscle fibers contract at different speeds,
and vary in how quickly they fatigue Muscle fibers are classified into three main
types 1) Slow oxidative fibers 2) Fast oxidative-glycolytic fibers 3) Fast glycolytic fibers
Types of Skeletal Muscle Fibers Slow Oxidative Fibers (SO fibers)
Smallest in diameter Least powerful type of muscle fibers Appear dark red (more myoglobin) Generate ATP mainly by aerobic cellular
respiration Have a slow speed of contraction▪ Twitch contractions last from 100 to 200 msec
Very resistant to fatigue Capable of prolonged, sustained contractions
for many hours Adapted for maintaining posture and for
aerobic, endurance-type activities such as running a marathon
Types of Skeletal Muscle Fibers Fast Oxidative–Glycolytic Fibers (FOG
fibers) Intermediate in diameter between the other
two types of fibers Contain large amounts of myoglobin and many
blood capillaries Have a dark red appearance Generate considerable ATP by aerobic cellular
respiration Moderately high resistance to fatigue Generate some ATP by anaerobic glycolysis Speed of contraction faster▪ Twitch contractions last less than 100 msec
Contribute to activities such as walking and sprinting
Types of Skeletal Muscle Fibers Fast Glycolytic Fibers (FG fibers)
Largest in diameter Generate the most powerful contractions Have low myoglobin content Relatively few blood capillaries Few mitochondria Appear white in color Generate ATP mainly by glycolysis Fibers contract strongly and quickly Fatigue quickly Adapted for intense anaerobic movements of
short duration▪ Weight lifting or throwing a ball
Types of Skeletal Muscle Fibers
Types of Skeletal Muscle FibersDistribution and Recruitment of
Different Types of Fibers Most muscles are a mixture of all three
types of muscle fibers Proportions vary, depending on the
action of the muscle, the person ’s training regimen, and genetic factors▪ Postural muscles of the neck, back, and legs
have a high proportion of SO fibers▪ Muscles of the shoulders and arms have a
high proportion of FG fibers▪ Leg muscles have large numbers of both SO
and FOG fibers
Exercise and Skeletal Muscle Tissue
Ratios of fast glycolytic and slow oxidative fibers are genetically determined Individuals with a higher proportion of
FG fibers▪ Excel in intense activity (weight lifting,
sprinting) Individuals with higher percentages of
SO fibers▪ Excel in endurance activities (long-distance
running)
Exercise and Skeletal Muscle Tissue
Various types of exercises can induce changes in muscle fibers Aerobic exercise transforms some FG
fibers into FOG fibers▪ Endurance exercises do not increase muscle
mass Exercises that require short bursts of
strength produce an increase in the size of FG fibers▪ Muscle enlargement (hypertrophy) due to
increased synthesis of thick and thin filaments
Cardiac Muscle Tissue
Principal tissue in the heart wall Intercalated discs connect the ends of cardiac muscle
fibers to one another▪ Allow muscle action potentials to spread from one cardiac
muscle fiber to another Cardiac muscle tissue contracts when stimulated by its
own autorhythmic muscle fibers▪ Continuous, rhythmic activity is a major physiological
difference between cardiac and skeletal muscle tissue Contractions lasts longer than a skeletal muscle twitch Have the same arrangement of actin and myosin as
skeletal muscle fibers Mitochondria are large and numerous Depends on aerobic respiration to generate ATP▪ Requires a constant supply of oxygen▪ Able to use lactic acid produced by skeletal muscle fibers to
make ATP
Smooth Muscle Tissue
Usually activated involuntarily Action potentials are spread through the
fibers by gap junctions Fibers are stimulated by certain
neurotransmitter, hormone, or autorhythmic signals
Found in the▪ Walls of arteries and veins▪ Walls of hollow organs▪ Walls of airways to the lungs▪ Muscles that attach to hair follicles▪ Muscles that adjust pupil diameter▪ Muscles that adjust focus of the lens in the eye
Smooth Muscle Tissue
Smooth Muscle Tissue
Microscopic Anatomy of Smooth Muscle Contains both thick filaments and thin
filaments▪ Not arranged in orderly sarcomeres
No regular pattern of overlap thus not striated
Contain only a small amount of stored Ca++
Filaments attach to dense bodies and stretch from one dense body to another
Dense bodies▪ Function in the same way as Z discs▪ During contraction the filaments pull on the dense
bodies causing a shortening of the muscle fiber
Smooth Muscle Tissue
Physiology of Smooth Muscle Contraction lasts longer than skeletal muscle
contraction Contractions are initiated by Ca++ flow primarily
from the interstitial fluid Ca++ move slowly out of the muscle fiber
delaying relaxation Able to sustain long-term muscle tone▪ Prolonged presence of Ca++ in the cell provides for a
state of continued partial contraction▪ Important in the:▪ Gastrointestinal tract where a steady pressure is
maintained on the contents of the tract▪ In the walls of blood vessels which maintain a steady
pressure on blood
Smooth Muscle Tissue
Physiology of Smooth Muscle Most smooth muscle fibers contract or
relax in response to:▪ Action potentials from the autonomic nervous
system▪ Pupil constriction due to increased light energy
▪ In response to stretching▪ Food in digestive tract stretches intestinal walls
initiating peristalsis▪ Hormones▪ Epinephrine causes relaxation of smooth muscle in
the air-ways and in some blood vessel walls▪ Changes in pH, oxygen and carbon dioxide
levels
Smooth Muscle Tissue
Aging and Muscular Tissue Aging
Brings a progressive loss of skeletal muscle mass
A decrease in maximal strength A slowing of muscle reflexes A loss of flexibility
With aging, the relative number of slow oxidative fibers appears to increase
Aerobic activities and strength training can slow the decline in muscular performance
End of Chapter 10, Part 2