Physiology Exam 1 Muscle Organization And Function

Front 1

Properties of muscle

Back 1

Contractility - ability to shorten

Excitability - capacity to receive/respond to stim

Extensibility - ability to stretch (passive)

Elasticity - ability to return to original shape

Front 2

Functions of muscle

Back 2

production of movement

Maintaining posture

stabilizing joints

Generating heat

Front 3

Epimysium

Back 3

connective tissue surrounding muscle

Front 4

Perimysium

Back 4

connective tissue surrounding muscle fascicles (muscle bundles

Front 5

Endomysium

Back 5

connective tissue surrounding muscle fibers

Front 6

Myofibril contractile proteins

Back 6

Generated force during contraction

Actin & Myosin

Front 7

Myofibril regulatory proteins

Back 7

initiate and terminate contraction

Troponin & tropomyosin

Front 8

Myofibril structural proteins

Back 8

maintain alignment, elastic & extensible

Titin, Myomesis, Dystrophin

Front 9

Type I muscle fibers

Back 9

Slow oxidative muscle fibers

small diameter

Lots of capillaries, mitochondria, myoglobin and fat

Not much glycogen and creatinine

Red meat

Aerobic ATP generation

Low contraction velocity

Primary function postural and endurance

Front 10

Type II A muscle fibers

Back 10

Fast Oxidative-Glycolytic

Lots of capillaries, mitochondria, myoglobin and fat

Somewhere in the middle for glycogen and creatinine

Middle ground for ATP

Aerobic and glycolysis to generate ATP

Primary function sprinting, walking

Front 11

Type II B muscle fibers

Back 11

Fast glycolytic

Large diameter

few capillaries, mitochondria, myoglobin, fat

Lots of glycogen and creatinine kinase

White meat

generate ATP via glycolysis

Use ATP quickly

Primary function short term work

Front 12

What is the sarcoplasmic reticulum?

Back 12

Only found in muscle cells

Wraps around the T tubules and is where Ca2+ stored and released from after action potential.

- 2 terminal cisternae + T tubule = triad

cisternae have Calesquestrin - sequestors of Ca2+

Front 13

Sarcomere anatomy

Back 13

Functional unit of muscle - region between two Z lines.

1. A band - composed of thick and thin myofilaments. H zone is only thick filaments, M line contains myomyesin. Titin anchors thick filaments to Z and M lines.

2. I band - composed of thin filaments

3. Z line - anchors thin filaments (Actinin and Nebulin).

Front 14

Myofilaments

Back 14

Thick: composed of myosin - tail (light meromyosin) and head and cross bridges (heacy meromyosin

Thin: composed of Actin (F&G), Troponin (TIC subunits) and Tropomyosin (wraps around F actin)

Front 15

Major differences between cardiac and skeletal muscle

Back 15

Fibers are enucleated, branched, and rich in mitochondria and lipids in cardiac.

Cardiac have intercalated discs with gap junctions (allows AP to travel between cells so act together) - functional syncytium

Cardiac muscle slower to contract than skeletal

Front 16

Major differences in smooth muscle

Back 16

Not striated b/c no myofibrils (actin and myosin loosely organized.

Slow prolonged contractions

No T-tubules, SR poorly developed so have special gated Ca2+ channels instead

Actin hooked into dense bodies

Can be multi unit (like skeletal with individual innervation; eye) or single units (like a sheet connected by gap junctions so AP rapidly propogated; GI)

Front 17

Anatomical muscle comparison of three types

Back 17

Front 18

Functional comparison of muscles

Back 18

Front 19

Describe excitation-contraction coupling

Back 19

1. Action potential propagates along sarcolemma and down the T tubules.

2. Depolarization opens up/conformational change in DHP receptor in T tubule

3. DHP opening linked/gated to opening of ryanodine receptor in SR.

4. Changes in ryanodine allow for Ca2+ to release from SR.

5. Ca2+ bind troponin > changes tropomyosin > active sites on actin exposed

6. Formation of cross bridges between myosin (ADP + Pi) and actin > Pi released > power stroke

7. Ca2+ removed back to SR

8. Tropomyosin block active sites on actin

Front 20

How does muscle length/tension relationship affect skeletal muscle contraction?

Back 20

The further the muscle was stretched or shortened from optimum resting length, the less tension it is capable of applying.

Optimum force can be applied when the most number of myosin heads can be in contact with actin filament. When stretched, fewer myosin heads will be in contact with actin filament. When contracted, actin filaments hit the z-line and can't be contracted anymore.

Front 21

How does the force/load -velocity relationship affect muscle contraction?

Back 21

With no load can contract quickly, with load will be slower b/c resistance. Load where V=0

Front 22

Isotonic contraction

Back 22

Muscle contracts and produces movement

e.g., push up

concentric - dec in muscle length (cross bridges formed btw actin and myosin)

-e.g., E2 of step cycle

eccentric - inc muscle length

-e.g., E3 of step cycle or walking down a steep incline controlling rate of elongation as stretching to next location

Front 23

Isometric contraction

Back 23

muscle contracts but produces no movement

e.g., holding a plank, postural muscles (maintain body position while opposing gravity)

Front 24

Treppe - wave sumamtion - tetanus

Back 24

1. Treppe: muscle stimulated 2nd time imm. after relaxation of 1st phase which inc tension b/c Ca2+ not fully sequestered by SR.

2. Summation: 2nd stim before complete relaxation, 2nd twitch causes greater tension b/c superimposed

3. Incomplete tetanus: individual twitches are distinguishable

4.Complete tetanus: individual twitches indistinguishable b/c no relaxation phase

Front 25

Describe myogenesis

Back 25

Front 26

How does nutrition impact muscle development?

Back 26

-All myofibers there from fetal 6 mos+, no new ones

-If decrease nutrition during secondary myogenesis (3-6 mths) see decreased myogenesis so fewer fibers for life.

-If adequate nutrition later can compensate a bit with muscle hypertrophy but no myogenesis

Front 27

Muscle hypertrophy

Back 27

Double muscling

Myostatin mutation so doesn't inhibit muscle hypertrophy and hyperplasia

Front 28

Neurogenic muscle atrophy

Back 28

denervation > lysosomal protein degradation > 50% dec muscle mass and EMG abnormalities

Fairly immediate compared to myogenic atrophy

e.g., Sweeney in horses

Front 29

Myogenic muscle atrophy

Back 29

malnutrition, cachexia (weight loss secondary to disease), corticosteroid excess

Slow progression, normal EMG (effects at level of muscle mass not innervation), atrophy only type II fibers

Front 30

Muscle necrosis or Rhabdomyolosis or tying up

Back 30

-Clinical features: muscle pain, contracture, high RR and sweating; high creatinine kinase & aspartate transaminase in serum, coffee coloured urine

-Causes: deficiency of Vit E and selenium, infectious, immune mediated, metabolic

Front 31

Muscular dystrophy

Back 31

deficiency in dystrophin which anchors sarcolemma to actin cytoskeleton - don't have anchors so muscle paresis