Physio Lab Exam 1 - Skeletal Muscle

smooth muscle

involuntary and non-striated

• in blood vessels and GI tract

• uni nucleated

skeletal muscle

voluntary and striated

• in the biceps and triceps

• multi nucleated

cardiac muscle

involuntary and striated

• uni or multinucleatic

how is the diaphragm a special case of skeletal muscle?

its important function of respiration is involuntary primarily but we can also take over if we want o

tendon

attaches muscle to bones

ligaments

attaches bone to bone

epimysium

connective tissue layers that surrounds a muscle group

perimysium

connective tissue layer that surrounds a fascicle

endomysium

connective tissue layer that surrounds muscle fiber/cell

organization of skeletal muscle?

muscle → fascicle → fiber/cell → myofibril → sarcomere

longtudinal section of skeletal muscle

• multinucleic nuclei sit at the edges of fiber unlike other cells!

• alternating light/dark bands

cross section of skeletal muscle

sarcomere

functional repeating segment units or most basic unit of a muscle that ultimately makes muscles move

• area from z-line to z-line

• myofibrils are in a muscle ___.

  • they are made of repeating segments aka ___.

  • they have ____ aka contractile proteins: actin and myosin

• cell

  • sarcomeres

  • myofilaments

what are the two protein filaments of myofibrils?

• thick/myosin

• thin/actin

troponin and tropomyosin

two additional proteins on the actin molecule

• small portion of muscle that help regulate contraction process

a band

region of myosin filaments and some overlapping actin

• dark region of the sarcomere

I band

region that contains only actin filaments

• light region of sarcomere

H zone

region in the center of each A band thats a portion of myosin filament w/o overlap of actin

Z line

how sarcomeres are divided from each other

• in the center of each I band

M line

in the center of each A band

sarcomere relaxation

• sarcomere at resting length

• all bands are visible

sarcomere contraction

• z disc are closer together

• I band and H zone disappear

• zone of overlap increases

• no change in size of A band

as muscle contracts, myosin ___ grab onto ___ → pull it ___ → 2 lines come closer together → sarcomere shorterns

• ACTIN AND MYOSIN DON’T SHORTEN; THEIR OVERLAP JUST INCREASES

• ___ and ___ bands get smaller

heads → actin → inwards

• I … H

peripheral nucleias are in sarcolemmas

true

importance of tubules of sarcoplasmic reticulum

• where calcium is stored until contraction signal

• extends into the interior of muscle fiber → helps depolarization reach every membrane

overall internal structure of skeletal muscle:

skeletal muscle → myofibril → sarcomere → filaments

what are the three parts of excitation-contraction coupling

electrical, chemical, and mechanical

what is excitation-contraction coupling

process that pairs depolarization of a neuron w/ depolarization of a muscle cell

• motor neuron - nerve cell that innervated muscle fibers

• NMJ - spot where nerve endings meats muscle fibers

electrical excitation contraction coupling:

1. ach is released at the ___ and binds to receptor site on the ___

2. ___ happens in the muscle membrane

3. ___ of T tubules causes ___ channels to open

1. NMJ

2. action potential

3. depolarization … calcium

chemical excitation contraction coupling

4. intracellular concentration of calcium ___

5. calcium binds to ___ on thin filaments

6. ___ moves to let myosin bind to actin

• increases

• troponin

• tropomyosin

mechanical excitation contraction coupling

7. ___ cycling begins and force is ___

8. calcium is ___ by the ___ → muscle relaxes

• cross-bridge … generated

• reaccumulated … SR

detailed excitation-contraction coupling:

1. AP is made in neuron → goes to axon → nerve impulse stimulated AcH release into synaptic cleft (released via exocytosis)

2. AcH released from synaptic vesicles of axon terminal → diffuses across cleft and attaches to receptors on sarcolemma → impulse made to excite the muscle cells

3. impulse propagates along sarcolemma and polarizes the T tubulus → calcium channels open → rise in intracellular concentration of calcium

• calcium is released from the sarcoplasmic reticulum and into the cytoplasm to bind to troponin for contraction

troponin

regulatory protein on thin filament that binds calcium to initiate contraction

• polypeptides w/ 3 subunits

TnI troponin and its significance

inhibitor subunit

• elevated lvls in a blood test → physiological indicator of cardiac damage

  • elevated lvls → sign of heart attack in a patient

TnT troponin

helps bind troponin and tropomyosin

TnC troponin

available calcium is cytoplasm that binds to TnC

• what calcium binds to to get tropo myosin to move

when calcium concentration is low what happens?

tropomyosin blocks the myosin binding site on actin → no contraction

when calcium concentration is high what happens?

calcium binds to troponin complex (TnC) → tropomyosin allows myosin to bind to actin → contraction

sliding filament theory

• filaments dont shorten, they slide

• the sarcomere shortens

• the muscle fiber shortens

process results in shortening of muscle and force generation

sliding filament theory process:

1. cocked: ATP is ___into ___ and ___→ myosin heads ___to ___conformation

2. cross bridge: myosin head binds to ___ monomer, making a ___bridge

3. power stroke: ___ P is released → myosin heads ___ ____ (like a bicep curl) → filament slide past each other → myosin drags ____ inward along w/ a zlines → how sarcomere shorterns

4. attached: ___ released but myosin is still ___ to actin (___state)

0. release: ___ binds to myosin → ___ of actin-myosin complex

1. hydrolyzed … ADP … P … returns … resting

2. actin … cross

3. P … change formation … actin

4. ADP … still … contracted

0. ATP … dissociation

motor unit

comprises a single motor neuron and the muscle fibers it innervates

• varies in size

small motor units

motor units involved w/ pecise motor activites

large motor units

units involved with large motor activites

recruitment of motor units

process where motor units are recruited from smallest to largest

• our bodies always use the minimum force necessary before recruiting more

  • a pianist’s finger muscle have motor units of 3-5 → ultra-precise

  • quadriceps motor unit have 1k+ fibers → built for power not precision

Isometric action

muscle contracts but length stays the same; the force generated is insufficient to overcome the load

• contracted but still losing energy

isotonic action

the contraction tension stays constant but the muscle changes in length and moves the load

• 2 types: concentric and eccentric

concentric action

type of isotonic action where muscle contracts and shortens

eccentric action

type of isotonic action where the muscle contracts and lengthens

agonist

primary mover

• i.e bicep

syngergistic

muscles that assist the agonist (primary mover) group

• i.e brachioradialis

antagonistic

muscles that oppose the agonist

• i.e tricep

structural and histological features determine the type of fibers based on ___

size, diameter, and myoglobin

myoglobin

oxygen binding molecules that facilitates oxygen transport into myocytes

slow twitch (T1)

what endurance athletes use → have smaller cross sectional layer

• myoglobin rich

• lots of oxidative enzymes

• high mitochondrial volume

• surrounded by dense capillary networks

• fatigue resistant

• slower maximal shortening velocity

• highly efficient

cells make a lot of energy for aerobic respiration

fast twitch IIX

What rapid-movement athletes use like basketball players

• small amount of mitochondria

• less resistant to fatigue

• rich in glycolytic enzymes

• generate the highest power input

• power/speed

• less efficient

twitch IIA

• intermediate fibers

• mixture of both Type 1 and Type IIX

  • i.e 800m runner → fibers are not purely aerobic → fatigue but can stil generate force to sustain pace -

• mixture and intermediate power/speed

• less efficient

hypertrophy

an increase in muscle fiber diamter due to myfibril size increase

• phyiolgoical adapatations because of strength training are result in increase in muscle size not number

muscle soreness

result of microscopic injury/tears to the muscle fibers

• DOMS

• not result of lactic acid accumulation

delayed onset muscle soreness (doms)

inujury occurs → 24-48 hrs peak soreness → resolution

sex differences

• men are stronger regarding absolute strength but relative strength per unit muscle mass is similiar

  • testosternone directly stimulates muscle growth

is it true that theres research that female m. is more fatigue resistant?

yes bc women recruit more muscle for a given task which distributes work load

according to the journal of applied physio, women have ___ less upper body strength and ___ less lower body strength

40% … 33%

rigor mortis

postmortem muscle stiffness resulting from rigid cross bridges in the absence of ATP

• helpful for estimating time of death 12 hrs after

• dying cells dont have proper ability to exlude calcium → leaking → calcium floods cytoplasm → calcium binds troponin and tropomyosin moves out the way … locked in contraction state

sarcopenia

Age related decline in muscle mass begins around age 25 and occurs across the lifetime.

slow phase sarcopenia

10% of muscle mass is lost from 25 to 50 years

rapid phase sarcopenia

An additional 40% of muscle mass is lost from 50 to 80 years

● Generally, see in a shift in fiber type (heavy loss of fast twitch, increase of slow

twitch).

muscular dystrophy

group of hereditary muscle diseases that weaken skeletal muscle characterized by defects in muscle proteins/lack of dystrophin protein that results in a progressive muscle weakness and a loss of muscle fibers

• bad prognosis w/ no cure and short lifespan bc the diaphragm is affect which can cause respiratory failure

why are men more affected by muscular dystrophy compared to women?

bc its a mutated gene expressed on the X chromosome, which men only have one of

thin filaments

filaments made of actin along w/ regulatory proteins troponin and tropomyosin

tropomysosin

regulatory protein that blocks the myosin-binding site on actin when calcium lvls are low