IB 303- Muscles

Red vs white muscle

classification by color based on the amount of myoglobin

not used much anymore

red- contracts slowly, high endurance, lots myoglobin(dark meat)

white- low myoglobin, rapid, fatigue easily, quick reactions(white meat)

Somatic muscle

attach to bone or cartilage

Visceral muscle

attach to organs, vessels, and ducts

ex. stomach

voluntary muscle

under conscious control

involuntary muscle

muscles that are not consciously controlled

Smooth muscle

unstriated (filaments aligned in even rows) muscle

mononucleate(one nuclei), short and fusiform in shape

cells joined in sheets that wrap around organs(visceral and involuntary)

maintain force without fatigue

Cardiac Muscle

Striated, mononucleate muscles in the heart

short cells joined by intercalated disks

Skeletal Muscle

Voluntary, striated, multinucleate

elongate(up to 40mm) unbranched fibers from fusion of several cells

filled with sarcomeres

apart of urinary tract

Head of muscle

Origin of muscle that attached to the immobile bone

Insertion of the bone

“slip” attached to the mobile bone

Muscle Action

muscle can only pull(contraction)

often paired as antagonistic sets(opposite matching muscles, quad and ham)

synergistic (build on each other, pull in same direction, quad set)

Skeletal muscle structure

composed of muscle bundles

bundles contain multiple muscle cells

surrounded by epimysium

Tendons

connective tissue for muscle to bone

connect to periosteum

less energetically costly than muscle

Muscle Russian doll cell structure

packed together in bundles called Fascicles surrounded by Perimysium

endomysium surrounds each cell

cell packed of myofibrils

Myofibril Structure

Chain of repeating units called sarcomeres(unit of contraction), separated by z-bands(the black lines)

two types of overlapping filaments:

Myosin: thick filament with protruding head

Actin: thin filament with two other proteins attached

Resting State

no stimulation from nerves

muscle is soft, but shape is maintained by collagenous fibers

no force, can be stretched

Active state

nerve stimulation

contraction, generates tensile force

resistance to this is load

Muscle contraction

Sarcomeres shorten during contraction(the white region shortens, just actin)

actin shifts and overlies with myosin, this shortens sarcomere

thick filament(myosin) pulling on thin filament(actin)

Myosin Heads

composed of coiled subunits with protruding heads

little heads of myosin moving across actin

get ATP, release move and grab actin, phosphorylize, become ADP to release to then be released again

Velocity vs force

binding and unbinding of myosin heads takes time, so tradeoff to velocity and force

limitation

tonic fibers

sustained low force, postural

rare in mammals(only in eyes)

twitch fibers

found in all vertebrates

fast contraction/higher forces

can be divided into slow and fast

is all relative

fiber mechanics: control

myosin heavy chain- isoforms are often used to identify fiber types

slow twitch fibers- rely on ATP from aerobic respiration, looks red bc of myoglobin

fast twitch- relies on ATP from anaerobic respiration, looks white bc of less myoglobin

order to initiation:

-slow twitch activated→fatigue-resistant fast twitch turn on→ fatiguable-fast twitch activated for final push

Graded force

activation of muscle is all or none

Rate modulation controls the rate that nerve impulses are delivered to muscle

alters how many motor units (single neuron and the set of fibers it innervates) are activating

Cross sectional area

cross-sectional area- proportional to the total force a muscle can produce, length of muscle does nothing for force

• Morphological cross section of overall muscle

• Physiological sum of the cross-sectional area of the muscle fibers in muscle(what you want to look at)

Fiber orientation

parallel fibers- fibers lie along the line of force(with the muscle), lighter loads through long distance

pinnate fibers- fibers lie like arrow feathers to the force generation, insert on a common tendon, better for force generation bc more myofibers can fit, but cannot shorten as much, heavier loads a short distance

Total Tension

Active tension(from muscle) + Passive tension(from elastic tendons)= total tension

tendons help give power to muscle through elasticity

Low Gear Muscles

more force advantage, used to overcome inertia during initial movement

-synergistic muscles

High Gear muscles

more speed advantage to create rapid movements

-synergistic muscles

Types of contraction

concentric-muscle contracts(force+shortening)

isometric- contraction and no length change(force+ no motion)

eccentric- contraction with lengthening(extend+force)

Depressor mandibulae

depress the lower jaw

digastric muscle

depresses the lower jaw

Paraxial mesoderm

the embryonic tissue that arises the skeletal muscle

tissue is first divided into somites that further divides into other tissues

• the tissues for muscles are myotomes

Fish musculature

segmented structure, zigzag pattern, for flexion- myomeres

my-septa- the white “walls” between myomeres

horizontal septa- runs length of the body, splits axial muscle into epaxials(dorsal) and hypaxials(ventral)

Constrictor and adductor muscle in fish

constrictor- straightens the brachial arches in fish

adductor- bend the arches

the agnostic action of these together pump water over gills

mandibular arch

modified brachial arch

the muscle becomes the adductor mandibulae

the bite muscle

Jaw adductors

sharks developed a muscle that aids adductor called pre-orbitals

evolution: tetrapods adductor remains one big muscle

• the muscle changes and attaches to the cranium itself instead of a separate palatoquadrate bone(lost in tetrapods)

• adductor been seperated into two muscles: masseter and temporalis(synergistic)

Constrictor colli

facial muscles: constrictor colli

mammalian facial muscle

Branchial muscles

aid in gill-based respiration

reduced in tetrapods, contribute to larynx

some of the elevator muscle along the dorsal end become apart of the pectoral sling- holds anterior portion of the body up

Chronic overload

sustained muscle activity for training

working harder than normal

hypertrophy

term for the increase in tissue size/mass because of stimuli

muscle growth

more myofilaments are added, increasing cross-sectional area

Slow twitch: better for endurance

fast twitch: better for burst activity

there is evidence that type of activity can influence which twitch fibers grow

Duchenne Muscular dystrophy(DMD)

most common, generally fatal in the 20s

adverse affects on bone development too due to lower loads on bones

caused by a gene mutation on X chromosome that codes for dystrophin

discovery: dogs that have an up regulation of gene for cell repair can counteract the DMD, seeming normal

dystrophin

important protein complex that creates a mechanical link between myofilaments and signaling to muscle fibers

Becker

similar to DMD but later onset with slower progression

Steinerts disease

adult-onset that affects face and neck. prevents relaxation of muscles and can cause cataracts, sleepiness, and arrhythmia

congenital

early onset with variable progression, effects both males and females