biol 223 muscles 3

muscle performance

considered in terms of force and endurance

force

power and strength

maximum amount of tension produced by a muscle or muscle group

endurance

amount of time during which an individual can perform a particular activity

factors determining performance capabilities of a skeletal muscle

types of muscle fibers present in the muscle

physical conditioning or training

slow fibers (type I fibers)

slow twitch oxidative fibers

better for marathon runners

smaller diameter, darker color due to myoglobin; fatigue resistant, red

half the diameter of fast fibers

take three times as long to contract after stimulation

abundant mitochondria

• aerobic, oxidative metabolism

extensive capillary supply

high concentrations of myoglobin

• intracellular oxygen storage molecule

can contract for long periods of time

• fatigue-resistant

intermediate fibers (type II-A fibers)

fast twitch oxidative fibers

good at maintaining aerobic status

fast fibers that gain greater resistance to fatigue in response to aerobic endurance training

• additional capillary supply

• more mitochondria

• smaller in diameter

• not as dependent on anaerobic metabolism

fast fibers (type II-B fibers)

fast twitch glycolytic fibers

specialized to be better at glycolysis

better for sprinters

larger diameter, paler color; easily fatigued, white

large in diameter

contain densely packed myofibrils

large glycogen reserves

relatively few mitochondria

• anaerobic, glycolytic metabolism

produce rapid, powerful contractions of short duration

fatigue rapidly bc of lactic acid production

muscle performance and the distribution of muscle fibers

percentage of slow fibers and fast fibers genetically determined, can vary considerably among muscles

• pale (white) muscles - mostly fast fibers

• dark (red) muscles - dominated by slow fibers

training can change percentage of fast fibers that have intermediate properties

hypertrophy

increase in diameter of muscle

atrophy

decrease in diameter of a muscle

muscle hypertrophy and atrophy

change is due to increase or decrease in diameter of muscle fibers within the muscle

• number of muscle fibers (cells) does not change

change in diameter of muscle cells

increase or decrease depending on level of activity over time

increased activity leads to synthesis of more actin and myosin myofilaments

decreased activity leads to loss of actin and myosin myofilaments

long term disuse of muscles can lead to irreversible atrophy in muscle if muscle cells die

muscle fiber A is twice the diameter of muscle fiber B. muscle fiber A can produce greater tension than muscle fiber B because

A has more myosin to actin cross bridges forming during a contraction

A has more endoplasmic reticulum to store calcium ions

A has more sarcolemma and T tubules for action potential propagation

A has more mitochondria to produce ATP

A has more myosin to actin cross bridges forming during a contraction

anaerobic endurance

time period in which muscular contractions are sustained by glycolysis after depleting ATP/CP reserves

aerobic endurance

time period in which muscle can continue to contract while supported by mitochondrial activities after depleting ATP/CP reserves

improve anaerobic endurance

frequent brief, intensive workouts

increase muscle mass

increase ATP/CP reserves

increase glycogen reserves

increase ability to tolerate lactic acid buildup

improve aerobic endurance

sustained low levels of activity

increased blood supply to muscles

improve cardiovascular activity

aging and the muscular system

decrease in size, strength, and endurance of muscles

• reduction in size and strength due to decrease in number of myofibrils

• decrease in endurance due to less ATP, CP, glycogen, and myoglobin

skeletal muscle become less elastic

• develop increasing amounts of fibrous connective tissue (fibrosis)

tolerance for exercise decreases

• muscles fatigue more quickly

• reduction in thermoregulatory ability, thus are subject to overheating

ability to recover from muscular injuries decreases

• number of satellite cells decreases with age

  • repair capabilities become more limited, more scar tissue (fibrous tissue) formation occurs

the disease called tetanus, caused by the bacteria clostridium tetani

A. causes loss of voluntary muscle control by the nervous system

B. causes strong contractions in muscles

C. prevents contractions from occurring in muscles, causing them to be relaxed and flaccid

D. A and B

E. A and C

D. A and B

muscle disorders infection

myositis

necrotizing fascilitis

tetanus

trichinosis

fibromyalgia

muscle disorders trauma

hernias

compartment syndrome

bruises and tears

carpal tunnel syndrome

muscle disorders tumors

myomas

sarcomas

muscle disorders: secondary

nervous system: botulism, poliomyelitis

immune problems: myasthenia gravis

cardiovascular system: anemia, heart failure

metabolic problems: hypercalcemia, hypocalcemia

primary disorders

result from problems with the muscular system itself

• muscle trauma - ex. injury

• muscle nfections

• inherited disorders - ex. genetics

  • tumors - ex. sarcoma

secondary disorders

result of problems originating in other systems

• nervous system disorders that affect the coordination or control of muscle contraction

• nutritional or metabolic problems that affect electrolyte concentrations or the energy supply available to the muscles

  • cardiovascular disorders that restrict or reduce blood flow to skeletal muscles

muscle spasm (cramp)

strong, sudden, usually painful, unwanted contraction

muscle spasticity

excessive muscle tone

muscle flaccidity

very low muscle tone

muscle atrophy

deterioration or wasting due to disuse, immobility, or interference with normal motor neuron innervation

myositis

muscle inflammation

• ex. polymyositis and dermatomyositis - autoimmune (immune systems attacking tissues nearby)

strain

tears in muscle tissue

sprain

tears in ligament or tendon or joint capsule

paralysis

loss of voluntary motor control

• flaccid (unable to control) or spastic (so contracted, you are paralyzed)

nervous system disorders that affect the coordination or control os muscle contraction

blockage of release of acetylcholine (e.g. botulism)

• flaccid paralysis

interference with binding of ACh to receptors

• flaccid paralysis

interference with ACh Esterase activity

• spastic paralysis - organophosphates, nerve gas, insecticides, neostigmine

loss of motor neuron (e.g. polio-attacks+destroys nerves)

• flaccid paralysis - increased branching of remaining motor neurons

loss of motor neuron axon - peripheral nerve damage-direct nerve injury

• flaccid paralysis

excessive stimulation of motor neuron (e.g. tetanus)

• spastic paralysis

inherited disorders

primary

muscular dystrophies

• duchenne’s MD - gene on X chromosome

• early onset

myotonic dystrophy

• chromosome 19 disorder

• typical onset is after puberty

  • bc producing new muscles to greater extent

• less severe

muscle trauma

minor trauma such as damage to myofibrils, sarcolemma from excessive activity

major trauma such as laceration, crushing, deep bruise, muscle tear (strain)

new muscle cell production from satellite cells - limited ability

scar tissue formation

compartment syndrome

compartment syndrome

1. swelling

2. increased pressure

3. veins collapse

4. no blood in or out

5. O2 decrease, CO2 increase, pH decrease

nutritional or metabolic problems

can affect the energy supply available to the muscles (e.g. starvation)

can affect electrolyte concentration (e.g. dehydration, kidney disease)

• hyper or hypokalemia (K+)

• hyper or hyponatremia (Na+)

  • hyper or hypocalcemia (Ca2+)

in comparison to muscle cells dependent on anaerobic metabolism, cells using primarily aerobic metabolism would have

A. more mitochondria, less myoglobin, fewer capillaries, more oxidative enzymes

B. more mitochondria, more myoglobin, more capillaries, more oxidative enzymes

C. fewer mitochondria, less myoglobin, fewer capillaries, more glycolytic enzymes

D. fewer mitochondria, more myoglobin, more capillaries, more glycolytic enzymes

B. more mitochondria, more myoglobin, more capillaries, more oxidative enzymes

skeletal muscle tissue

attached to bone

striated voluntary muscle

cells are long, cylindrical, striated and multinucleate

locations: combined with connective tissues and neural tissue in skeletal muscles

functions: moves or stabilizes the position of the skeleton; guards entrances and exits to the digestive, respiratory, and urinary tracts; generates heat; protects internal organs

cardiac muscle tissue

form the walls of the heart

striated involuntary muscle, has sarcomeres

cells are short, branched, and striated, usually with a single nucleus; cells are interconnected by intercalated discs

location: heart

functions: circulates blood; maintains blood pressure

smooth muscle tissue

forms the walls of most hollow internal organs

non-striated involuntary muscle, no sarcomeres

cells are short, spindle shaped, and non striated, with a single, central nucleus

locations: found in the walls of blood vessels and in digestive, respiratory, urinary, and reproductive organs

functions: moves food, urine, and reproductive tract secretions; controls diameter of respiratory passageways; regulates diameter of blood vessels

smooth muscle

present in almost all organ systems

• integument - blood vessels, arrestor pili muscles

• cardiovascular - encircle blood vessels, control distribution of blood, help regulate blood pressure

• respiratory - contraction or relaxation alters diameters of respiratory passageways

• digestive system - control movement of materials through digestive system

• urinary system - urinary bladder, ureters, kidney blood vessels

  • reproductive tract - uterus, etc.

skeletal size

diameter: 100 micrometers

length: up to 30 cm

cardiac size

diameter: 10-20 micrometers

length - 50-100 micrometers

smooth size

diameter: 5-10 micrometers

length: 30-200 micrometers

skeletal muscle syncytium

not syncytium (fused mass of cells)

multinucleate cells formed by fusion of many myoblasts during embryogenesis

cells linked by connective tissue layers that fuse to form tendons

cardiac muscle syncytium

yes syncytium

cells linked by gap junctions and desmosomes into functional syncytium

(cardiac)

smooth muscle syncytium

yes syncytium

cells linked by gap junctions and dense bodies into functional syncytium

(smooth)

cardiac muscle intercalated discs

desmosomes provide structural attachment

• integral membrane proteins and proteoglycans link opposing cell membranes

• myofibrils are anchored to desmosomes

gap junctions hold cells together with membrane channel proteins

• form narrow passageways between cytoplasms of both cells

  • create electrical connections

skeletal filament organizations

striated - actin and myosin fibers arranged in sarcomeres (skeletal)

cardiac filament organization

striated - actin and myosin fibers arranged in sarcomeres (cardiac)

smooth filament organization

non-striated - actin and myosin fibers not organized in sarcomeress

smooth muscle myofilament organization

thick filaments scattered through out sarcoplasm

thin filaments attached to dense bodies

• some dense bodies at intersections of cytoskeletal framework

• some dense bodies firmly attached to plasma membrane

• dense bodies can link adjacent muscle cells

sliding of thick and thin filaments causes cell to shorten and twist

smooth muscle contraction

length-tension relationship

• does not matter

• tension development and resting length not directly related

• plasticity - stretched muscle adapts to new length and retains ability to contract and produce tension bc no sarcomeres

• contractions can be just as powerful as those of skeletal muscles

  • can undergo sustained tetanic contractions

skeletal contraction type

tetanic contractions produce greatest tension

summation of tension as stimulus frequency increases

(skeletal)

cardiac contraction type

twitch contractions only

smooth contraction type

tetanic contractions produce greatest tension

summation of tension as action potential frequency increases

(smooth)

skeletal control mechanisms

voluntary muscle

controlled by motor neurons of voluntary nervous system

motor unit - motor neuron branches to synapse on several muscle cells

cardiac control mechanisms

involuntary muscle

controlled by pacemaker cells, autonomic nervous system

smooth control mechanisms

involuntary muscle

controlled by pacesetter cells, hormones, autonomic nervous system

cardiac muscle control of contraction

automaticity - can contract without neural stimulation

timing of contractions determined by specialized pacemaker muscle cells

rate of pacemaker cells and amount of tension can be modified

• innervated by motor neurons of autonomic nervous system (sympathetic, parasympathetic)

smooth muscle control of contraction

visceral smooth muscle cells

• connected by gap junctions into large syncytia arranged in sheets or layers

• automaticity - pacesetter cells can trigger rhythmic contractions

• stimuli from autonomic nervous system can control contraction frequency

multi-unit smooth muscle cells

• not connected by gap junctions

  • each cell innervated by one or more motor neurons of the autonomic nervous system

skeletal energy source

aerobic metabolism at moderate activity, anaerobic metabolism during peak activity

cardiac energy source

aerobic metabolism

• myoglobin and mitochondria content is high

smooth energy source

aerobic metabolism at moderate activity (typical), anaerobic metabolism during peak activity (rare, ex. during childbirth)

organophosphate insecticides block acetylcholine esterase (AChE). the effects of organophosphate poisoning are

A. more ACh in the synaptic gap, more AP in the muscle cells, flaccid paralysis

B. more ACh in the synaptic gap, fewer AP in the muscle cells, spastic paralysis

C. less ACh in the synaptic gap, fewer AP in the muscle cells, flaccid paralysis

D. more ACh in the synaptic gap, more AP in the muscle cells, spastic paralysis

E. less ACh in the synaptic gap, more AP in the muscle cells, flaccid paralysis

D. more ACh in the synaptic gap, more AP in the muscle cells, spastic paralysis