Anatomy - Muscular System

Front 1

Muscular System

Back 1

composed of muscles as organs
-blood vessels, nerve fibers, muscle tissue organized with connective tissue wrapping

-skeletal muscle system
-smooth muscle system
-cardiac muscle system

Front 2

Skeletal Muscle

Back 2

Organized with connective tissue wrappings
structural organization
-attached to structures in skeletal system
--bones, cartilage
-2 ways of attachment to structures
-direct attachment
-indirect attachment

Front 3

Indirect Attachment

Back 3

-the epimysium blends into a tendon, and the tendon attaches the skeletal muscle to bone
-most muscle attached to bone this way in human body
-2 advantages of indirect attachment
1) skeletal muscle is protected from the rough surface of bone to prevent tearing
2)the extension of the tendon to surface of the bone saves space
-> because tendon is "cord-like" and can fit into smaller spaces and the tendon occupies a smaller surface of the bone

Front 4

Direct Attachment

Back 4

-the skeletal muscle attaches directly to the periosteum of the bone(no tendons)
-ex. cranial bone muscle

Front 5

Skeletal Muscle Attachment Site

Back 5

referred to as an origin and an insertion

Front 6

Microscopic Anatomy of Skeletal Muscle Fiber

Back 6

-each fiber runs the entire length of the skeletal muscle(organ)
-each fiber is composed of rod-like structures called myofibrils
--these run the entire length of the skeletal muscle fiber
80% of the volume of skeletal muscle fibers = myofibrils

Front 7

Myofibril

Back 7

-contains 2 types of myofilaments
1)thin filaments
2)thick filaments
-these filaments are arranged in an alternating pattern resulting in striations in skeletal muscle

Front 8

Thin Filament

Back 8

composed of 3 types of proteins
-actin
-troponin
-tropomyosin

Front 9

Actin

Back 9

Forms the framework of the tin filaments

Front 10

Troponin

Back 10

regulatory protein composed of 3 subunits
-troponinT(TnT) - binds to tropomyosin
-troponinC(TnC) - binds calcium ions
-tropoinhibitory(TnI) - binds to actin

Front 11

Tropomyosin

Back 11

Regulatory protein, rod-like protein that spirals around the actin, blocking myosin binding sites on actin
-in relaxed skeletal muscle, the myosin binding sites are blocked by tropomyosin

Front 12

Z-Line

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-Each thin filament is bisected by a line called the z-line(z-disc)
-the distance between successive z-lines is referred to as a Sarcomere
-Z-lines anchor the thin filaments

Front 13

Sarcomere

Back 13

-called the structural units of skeletal muscle - smallest contractile unit

Front 14

Thick Filament

Back 14

-each is composed of protein called myosin
-the tails of the myosin molecules form the core of the thick filaments with their globular heads exposed on the surface

Front 15

Myosin heads

Back 15

-globular, have 2 binding sites
1)binding site for actin
2)binding site for ATP
-heads contain the enzyme ATPase which catalyzes the hydrolysis of ATP to ADP

Front 16

Thick filament Location

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-inside the sarcomeres, where they occupy the center of the sarcomere and are referred to as A-bands

Front 17

Structure of a Sarcomere

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-in the center is the A-band(thick filament)
-A-band overlaps with thin filaments
-region of thin filaments not overlapping A-band is the I-band
-I-band = thin filaments attached by z-lines
-region of A-band in center not overlapping thin filaments = H-zone
-the line bisecting the H-Zone = M-line, which anchors the A-bands in the sarcomere

Front 18

Sliding Filament Mechanism

Back 18

-skeletal muscle contraction occurs when the myosin heads attach to the binding sites on actin and cause the thin filaments to slide toward the M-line
-the slidingof the thin filaments brings the z-lines closer together - the distance is shortened
-the sarcomeres shorten, since they run the entire length of the skeletal muscle fiber, the fiber will also shorten
-skeletal muscle fibers run the entire length of the skeletal muscle so the skeletal muscle shortens/contracts

Front 19

Sliding filament mechanism

Back 19

-explained by the excitation-contraction
->a series of events that couples the activation of a motor neuron to the contraction of skeletal muscle
-Each skeletal muscle is innervated by a motor neuron
->gives several axon terminals which make contact with several skeletal muscle fibers in that skeletal muscle

Front 20

Motor Unit

Back 20

-Made up of a motor neuron and the skeletal muscle fibers it innervates in a skeletal muscle
-they have different sizes
-small motor unit - neuron makes contact with a few muscle fibers
-medium motor unit - more contact with skeletal muscle fibers than small motor unit ~50
-large motor unit - contact with many skeletal muscle fibers - at least 100

Front 21

Neuromuscular Junction

Back 21

Point of close contact between the axon terminal and the skeletal muscle fiber

Front 22

Neuromuscular Cleft

Back 22

The narrow space between the axon terminal and the sarcolema of the skeletal muscle fiber

Front 23

Motor End Plate

Back 23

Area of the sarcolema involved in forming the neuromuscular junction
-highly folded
-has increased surface area to accomodate more acetylcholine receptors which are located on the surface of the sarcolema or motor end plate

Front 24

Excitation-Contraction Coupling
1-3

Back 24

1)motor neuron activated - generates and transmits action potentials
2)action potential causes release of neurotransmitter from axon terminal - acetylcholine released into neuromuscular cleft
3)acetylcholine binds to its receptors on surface of motor end plate - stimulates the generation and transmission of action potentials which spread across entire sarcolema including t-tubules in triads

Front 25

Excitation-Contraction Coupling
4-6

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4)The action potential in t tubules stimulates the release of calcium ions from the sarcoplasmic reticulum by depolarization of the terminal cisterne(expanded ends of SR in triads)
5)Calcium ions bind to TnC which causes a conformational change in the troponin-tropomyosin complex via TnT -> this ends the blockade of tropomyosin which exposes myosin binding sites on actin
6)activated myoin heads can now bind to their sites on actin

Front 26

activated myosin head

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-ATPase splits ATP into ADP and inorganic phosphate
-a myosin head with ADP and inorganic phosphate attached is considered active

Front 27

Excitation-Contraction Coupling
7-9

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7)activated myosin head binds to its site on actin at right angles - an upright position
8)The attached myosin heads are called crossbridges
- the ADP + Pi dissociate from the crossbridges
Theres a change in orientation from upright to oblique referred to as the power stroke - results in sliding of thin filaments into the H-zone toward the M-line
9)crossbridge detachment requires binding of new ATP to myosin heads

Front 28

Rigor Mortis

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Cross bridge detachment does not occur becuase of total lack of ATP in dead people - muscles stay contracted

Front 29

Muscle Fatigue

Back 29

physiological fatigue
-inability of skeletal muscle to contract and relax due to ATP deficit
-person is alive, but demand for ATP outpaces rate of ATP production

Front 30

Sources of ATP in skeletal muscle fibers 1-2

Back 30

supports skeletal muscle contraction
1)stored ATP - minimum amount of ATP is directly stored - can support less than 5 seconds of skeletal muscle activity
2)creatin phosphate stored in skeletal muscle fibers (cp) -> cp = creatin + Pi
cp + ADP -> creatin + ATP
CP is unique to skeletal muscle fiber and cardiac muscle cells
increase in creatin output in urine may be an indication of skeletal muscle or cardiac muscle breakdown

Front 31

Sources of ATP in skeletal muscle fibers 3-4

Back 31

3)Anaerobic catabolism of glucose ->glycolysis
-a molecule of glucose yields a net of 2ATP molecules via glycolysis. since oxygen is absent, pyruvic acid produced at end of glycolysis will be converted into lactuic acid which lowers pH. This decreased pH interferes with the actions of enzymes reserved for skeletal muscle contraction resulting in muscle fatigue
4)Aerobic catabolism of glucose
-glycolysis -> krebs cycle -> electron transport chain yields 38 ATP per glucose molecule - muscle fatigue doesn't occur

anaerobic is faster but less efficient, aerobic is efficient but longer process

Front 32

How a contracted muscle relaxes

Back 32

1)motor neuron is no longer activated
2)cross-bridge detachment - new ATP required
3)sequestration of calcium ions back into the sarcoplasmic reticulum
-calcium sequestration is an active transport that requires ATP input

Front 33

Factors of force generated by skeletal muscle contraction

Back 33

1)size of the motor units activated
2)number of motor units activated - recruitment of motor units
3)frequency of the motor neuron innervating the skeletal muscle
4)length of the sarcomere prior to contraction

Front 34

Sarcomere Length

Back 34

~optimum length is between 2.2-2.6 microns - generates maximum contractile force -overlap b/w thin filaments and A-band with sufficient H-zone to accommodate inward sliding of the thin filaments
~shortened sarcomere length - 1.2 microns - increased overlap b/w thin filaments and A-band - H-zone is decreased - limited inward sliding of thin filaments - decreased contractile force generated
~overstretched sarcomeres - little or no overlap b/w thin filaments and A-band - large H-zone - myosin heads can't reach actin binding sites - no inward sliding - no shortening of sarcomere - no force generated

Front 35

Slow oxidative skeletal muscle fibers

Back 35

have highest myoglobin content
-appear reddish - "red fibers"

Front 36

Fast glycolytic skeletal muscle fibers

Back 36

have very low myoglobin levels
-appear whitish - "white fibers"

Front 37

Fast oxidative skeletal muscle fibers

Back 37

"intermediate fibers"

Front 38

Smooth Muscle (organ)

Back 38

Msooth muscle + endomysium + blood vessels + nerve fibers -> autonomic nerve fiber

Front 39

Autonomic Nerve Fiber

Back 39

2 types
-sympathetic fibers
-parasympathetic fibers

Front 40

Smooth muscle cell

Back 40

-2-5 micron diameter - is 20 times less than diameter of skeletal muscle cell
-100-400 micron length - at least 1000 times less than length of skeletal muscle cell
-"smooth" - striations are absent
-thin/thick filaments are present but arranged in diagonal fashion - do NOT alternate
-Z-lines absent - sarcomeres absent

Front 41

Smooth Muscle Cell Components

Back 41

-Dense bodies to anchor thin filaments
-troponin absent - calcium ions bind to Calmodulin(because TnC absent)
-tropomyosin present to support actor in filament - tropomyosin doesn't block myosin binding site on actin - myosin binding sites on actin are always accessible
-t tubules are absent - triads are absent
-sarcoplasmic reticulum present but poorly developed - stores less calcium ions compared to skeletal muscle SR
-caveolae are present in sarcolemma of cells - contain calcium rich extracellular fluid
-contain intermediate filaments b/c smooth muscle is subjected to stress - they resist the stress/tension, and are absent from skeletal muscle fibers
-innervated by autonomic fibers - skeletal muscle is innervated by motor neurons

Front 42

Excitation - Contraction Coupling of Smooth Muscles

Back 42

3 ways
1) B pacemaker cells intrinsic to the smooth muscle can contract w/o external innervation(ie w/o nervous system)
2)smooth contraction can be cause by chemicals like hormones - epinephrine stimulates smooth muscle + blood vessels to contraact
-can be stimulated to relax by chemicals - epinephrine stimulates smooth muscle in bronchioles to relax
3)Activation of the autonomic nervous system may stimulate smooth muscle to contract or relax
-activation of sympathetic fibers stimulates smooth muscle in walls of blood vessels to contract
-parasympathetic innervation of smooth muscle in walls of blood vessels is sparse -> inhibition of sympathetic fiber activity -> relaxation of the smooth muscle

Front 43

Autonomic innervation of smooth muscle in walls of bronchioles

Back 43

-activation of sympathetic fibers causes smooth muscle in bronchioles to relax
-activation of parasympathetic fibers stimulates smooth muscle in the walls os bronchioles to contract

Front 44

Diffuse Junctions

Back 44

junctions b/w smooth muscle cells in the smooth muscle and the varicosities of the autonomic fibers

Front 45

Varicosities

Back 45

bulbous ends of the autonomic fiber in the vicinity of the smooth muscle cells
-can make contact w/ more than one smooth muscle - different than skeletal muscle

Front 46

Excitation- Contraction Coupling in SMOOTH MUSCLE

Back 46

Smooth muscle can be stimulated to contract by…
Pace maker activity
Chemicals
Activator of the autonomic nervous system
-some chemicals and autonomic activation can result in smooth muscle relaxation

Front 47

Excitation- Contraction Coupling in SMOOTH MUSCLE
B

Back 47

Calcium channels on the sacrolemma of smooth muscle cells open in response to the above stimuli

-Ca2+ ions move down the concentration gradient from the extracellular fluid in the caveolae into the sacroplasm of the smooth muscle cells

Front 48

Excitation- Contraction Coupling in SMOOTH MUSCLE
C

Back 48

Ca2+ binds to a regulatory protein called CALMODULIN to form a Ca2+ calmodulin complex

Front 49

Excitation- Contraction Coupling in SMOOTH MUSCLE
D

Back 49

Ca2+ Calmodulin activates an enzyme called myosin- light chain kinase (MLCK)

Front 50

Excitation- Contraction Coupling in SMOOTH MUSCLE
E

Back 50

Activated MLCK removes inorganic phosphate (Pi) from ATP; the inorganic phosphate is attached to the myosin heads, THIS ACTIVATES THE MYOSIN HEADS

Front 51

Excitation- Contraction Coupling in SMOOTH MUSCLE
F

Back 51

The activated myosin heads bind to their sites on actin (myosin binding sites on actin is always accessible in smooth muscle cells)= to form cross bridges

Front 52

Excitation- Contraction Coupling in SMOOTH MUSCLE
G

Back 52

The cross bridges (activated myosin heads bound to actin) undergo a change in orientation which will result in sliding of the thin filaments alongside the thick filaments which will result in SHORTENING (contraction) of smooth muscle.

Front 53

Excitation- Contraction Coupling in SMOOTH MUSCLE
H

Back 53

For the smooth muscle to relax (after contraction)..
-Crossbridge detachment which occurs when an enzyme called PHOSPHORYLASE removes the inorganic phosphate (Pi) from the myosin heads(myosin heads are deactivated)
-Ca2+ must be pumped out into the extracellular fluid; Ca2+ ions must be pumped back into the SR
-The stimuli must be turned off/ removed
--Pacemaker activity is halted
--Chemical stimuli are inactivated
--Inhibition of the autonomic division causing the smooth muscle to contract

Front 54

Types of Smooth muscle

Back 54

2 types
-Single-Unit Smooth Muscle
-Multiunit Smooth Muscle

Front 55

Single-Unit Smooth Muscle

Back 55

-Gap junctions
-All the smooth muscle cells in the smooth muscle contract as a single unit

Front 56

Multiunit Smooth Muscle

Back 56

A.Individual smooth cells that contract independently
B.Appear to be a blend of skeletal and smooth muscle
C.Ex: arrector pili muscle
D.Skeletal muscle characteristics
-No gap junctions
-Smooth muscle cells are independent of each other that contract independently
-Exhibit motor unit arrangement with the autonomic nerve fibers
E.Mulitunit has similarities with the single-unit smooth muscle
-Both can be stimulated to contract by chemical and autonomic fibers
-Both are NOT attached to skeletal structures

Front 57

Cardiac Muscle Composition

Back 57

-Cardiac Tissue
-Connective tissue coverings
-Blood Vessels
-Autonomic fibers

-Only located in the myocardium (middle layer) of the heart wall

Front 58

Cardiac Muscle Structure

Back 58

Structurally, the cardiac muscle is similar to skeletal muscle
--Cardiac muscle cells appear striated= alternating pattern of thick and thin filaments which means sacromeres are present

Front 59

Cardiac Muscle similarities with single-unit smooth muscle

*Important

Back 59

Cardiac muscle has the ability to respond to the same three stimuli that stimulate single-unit smooth muscle contraction
>Pacemaker activity
>Chemicals
>Activation of the autonomic nervous system
Cardiac muscle is similar to single-unit smooth muscle by the present of gap junctions, which cause the cells to be depolarized at the same time and hence, the cardiac muscle (single-unit smooth muscle) to contract as a single unit
Both are under involuntary control

Front 60

Which of the muscle types will be affected by altering the extracellular calcium concentration?

Back 60

Smooth muscle will be affected
>In smooth muscle contraction, calcium ions enter from the extracellular fluid to trigger more calcium release from the poorly developed SR
>Calcium channel blockers will obliterate smooth muscle contraction
Cardiac muscle will be affected
>In cardiac muscle, calcium ion entry systems the plateau phase of cardiac muscle contraction to allow for the heart to pump blood. Hence, calcium channel blockers reduce the contractile force of the cardiac muscle = so heart becomes less effective as a pump
---So some people with high blood pressure will be given calcium channel blockers to lower their blood pressure

Front 61

isometric contraction

Back 61

force(tension) generated by the muscle is increasing at a constant muscle length ( “isometric” = same length); occurs when the weight exceeds the force generated by the muscle

Front 62

isotonic contraction

Back 62

muscle shortens at a relatively constant force
( isotonic = same force); force generated by skeletal muscle exceeds the weight so the skeletal muscle contracts and work is done, such as lifting the weight