Muscle Physiology

Question 1

Muscle 

Comprises ____ group of tissues in body 

Three types of muscle (reflective of function) 

Skeletal muscle  Makes up____t of the muscular system

Cardiac muscle  Found only in the ___t  About the size of the___

Smooth muscle  Appears throughout the body systems as components of__ __ and tubes

Classified in two different ways

 Striated or unstriated( __)  Striated: Cardiac and Skeletal

 Voluntary or involuntary(____)  Voluntary: Skeletal  Involuntary: Cardiac, Smooth  ANS

Answer 1

Muscle  Comprises largest group of tissues in body  Three types of muscle (reflective of function)  Skeletal muscle  Makes up most of the muscular system  Cardiac muscle  Found only in the heart  About the size of the fist  Smooth muscle  Appears throughout the body systems as components of hollow organs and tubes  Classified in two different ways  Striated or unstriated (form)  Striated: Cardiac and Skeletal  Voluntary or involuntary (function)  Voluntary: Skeletal  Involuntary: Cardiac, Smooth  ANS

Question 2

Categorization of Muscle

_______: “Sliding Filament”

Answer 2

Categorization of Muscle Cardiac and Skeletal: “Sliding Filament”

Question 3

Muscle 

Controlled muscle contraction allows 

_____ movement of the whole body or parts of the body 

We think about it as being voluntary but frequently there are ____ that occur at lower brain or spinal cord 

Very rapid reflexes that provide ____ benefit 

Never really reach our ___ ____

 Hand withdrawn from flame before we even think about it

 There are other fcns that occur thru the ____

 Not something that we concentrate on→ the way we walk

 “withdrawal”, “crossed extension”

 Manipulation of ___ ____ 

Primarily_____

 Sometimes involves extremely __ motor control 

A __ ____ nerves supplying a ____ number of muscle fibers

____ of contents through various ____ internal organs 

We think of this as ____ but if you have digestive upset you probably have thought about it

 ____ activity,___ ____

___ of contents of certain organs to ___ environment 

Most ____ but voluntary ____

 Voluntary control is learned thru use of sphincter

 When propulsion is too great, then no amount of mental activity will stop what is going to happen

Answer 3

Muscle  Controlled muscle contraction allows  Purposeful movement of the whole body or parts of the body  We think about it as being voluntary but frequently there are reflexes that occur at lower brain or spinal cord  Very rapid reflexes that provide protective benefit  Never really reach our cerebral levels.  Hand withdrawn from flame before we even think about it  There are other fcns that occur thru the cerebellum  Not something that we concentrate on→ the way we walk  “withdrawal”, “crossed extension”  Manipulation of external objects  Primarily voluntary  Sometimes involves extremely fine motor control  A lot more nerves supplying a smaller number of muscle fibers  Propulsion of contents through various hollow internal organs  We think of this as involuntary but if you have digestive upset you probably have thought about it  Glandular activity, gut motility  Emptying of contents of certain organs to external environment  Most involuntary but voluntary sphincter  Voluntary control is learned thru use of sphincter  When propulsion is too great, then no amount of mental activity will stop what is going to happen

Question 4

Myosin

 Component of____ filament

___ molecule consisting of __ ____subunits shaped somewhat like a ___ ___

Tail ends are ____d around each other 

Globular heads ____ out at one end  In____ directions

Tails oriented toward____r of filament and globular heads protrude____ at regular intervals 

Heads form ___ ___ between ___ and ___ ____.

 Cross bridge has two important sites critical to contraction

An__ ___ site 

A___ ___ (____ ___ ) site

Answer 4

Myosin  Component of thick filament  Protein molecule consisting of two identical subunits shaped somewhat like a golf club  Tail ends are intertwined around each other  Globular heads project out at one end  In different directions  Tails oriented toward center of filament and globular heads protrude outward at regular intervals  Heads form cross bridges between thick and thin filaments  Cross bridge has two important sites critical to contraction  An actin-binding site  A myosin ATPase (ATP-splitting) site

Question 5

Actin 

Primary structural component of ___ filaments

____ l in shape

Thin filament also has___ other proteins

____ and ____

 Determine level of____ to see amt of ____e that has been done

 Eac____ molecule has special binding site for attachment with___ ___ ___

 Binding results in____ of muscle fiber

Answer 5

Actin  Primary structural component of thin filaments  Spherical in shape  Thin filament also has two other proteins  Tropomyosin and troponin  Determine level of troponin to see amt of damage that has been done  Each actin molecule has special binding site for attachment with myosin cross bridge  Binding results in contraction of muscle fiber

Question 6

Comment! Actin and myosin are often called ___ ___s …but neither actually ___

Actin and myosin are __ ___to muscle cells, but are more___ and more highly ___d in muscle cells.

Answer 6

Comment! Actin and myosin are often called contractile proteins …but neither actually contracts. Actin and myosin are not unique to muscle cells, but are more abundant and more highly organized in muscle cells.

Question 7

Tropomyosin and Troponin  Often called___ proteins

 Tropomyosin

 ___-like molecules that lie __ to ___ alongside___ of ___ ___

 In this position, it ___ ___ ___ blocking interaction that would lead to muscle contraction

 Troponin

 Made of ____polypeptide units 

One binds to ___  One binds to___  One can bind wit___

Answer 7

Tropomyosin and Troponin  Often called regulatory proteins  Tropomyosin  Thread-like molecules that lie end-to-end alongside groove of actin spiral  In this position, it covers actin sites blocking interaction that would lead to muscle contraction  Troponin  Made of three polypeptide units  One binds to tropomyosin  One binds to actin  One can bind with Ca2+

Question 8

Troponin 

When not bound to Ca2+, troponin stabilizes tropomyosin in a “___ ____” over actin’s cross-bridge binding sites

 When Ca2+ binds to troponin, then____ moves away from ___ ___

 With tropomyosin out of way___ and ___ bind, interact at cross-bridges to cause___ ____

Answer 8

Troponin  When not bound to Ca2+, troponin stabilizes tropomyosin in a “blocking position” over actin’s cross-bridge binding sites  When Ca2+ binds to troponin, then tropomyosin moves away from blocking position  With tropomyosin out of way, actin and myosin bind, interact at cross-bridges to cause muscle contraction

Question 9

Role of Calcium in Cross-Bridge Formation

Relaxed State: • Muscle Fiber relaxed • ___ cross bridge binding bc binding site on actin covered by ___________n complex

Excited State • Muscle Fiber Excited • ___ Ca binds with t_____n, pulling troponin-tropomyosin complex aside to ____ cross bridge binding site • Cross bridge binding occurs • Binding of actin and myosin at cross bridge triggers ___ _____ that pulls ____filament inward during contraction

Answer 9

Role of Calcium in Cross-Bridge Formation Relaxed State: • Muscle Fiber relaxed • No cross bridge binding bc binding site on actin covered by troponin/tropomyosin complex Excited State • Muscle Fiber Excited • Released Ca binds with troponin, pulling troponin-tropomyosin complex aside to expose cross bridge binding site • Cross bridge binding occurs • Binding of actin and myosin at cross bridge triggers power stroke that pulls thin filament inward during contraction

Question 10

The Theory & Mechanism

___ ___ ____ between actin and myosin brings about muscle contraction by means of the “___ ____” mechanism.

Answer 10

The Theory & Mechanism Cross-bridge interaction between actin and myosin brings about muscle contraction by means of the “Sliding Filament” mechanism.

Question 11

“Sliding Filament Mechanism”

____ in ___ initiates filament sliding 

____ in _____ turns off sliding process 

____ filaments on each side of ____ slide ____ over____ ____filaments toward center of ___ band during contraction 

As thin filaments slide inward, they pull __ ___ closer together …thus causing the sarcomere to ____

 Sarcomere is measured from__ to ___

Answer 11

“Sliding Filament Mechanism”  Increase in Ca2+ initiates filament sliding  Decrease in Ca2+ turns off sliding process  Thin filaments on each side of sarcomere slide inward over stationary thick filaments toward center of A band during contraction  As thin filaments slide inward, they pull Z lines closer together …thus causing the sarcomere to shorten  Sarcomere is measured from Z to Z

Question 12

“Sliding Filament Mechanism” 

All sarcomeres throughout muscle fiber’s length___ ____

 We have excitation going over the____

 Contraction is accomplished by___ ___ s from___ ___s of each sarcomere sliding____r together ____ thick filaments

Answer 12

“Sliding Filament Mechanism”  All sarcomeres throughout muscle fiber’s length shorten simultaneously  We have excitation going over the membrane  Contraction is accomplished by thin filaments from opposite sides of each sarcomere sliding closer together between thick filaments

Question 13

The Steps toward the “Power Stroke” 

____ cross bridge___ twd ___ of ____ flilament, “___” in ___ filament to which it is attached 

___ ____ releases Ca into ____

____ ___ bind to actin

 Myosin heads swivel toward center of sarcomere (the “power stroke”)

____ binds to myosin head and detaches it from ____

Answer 13

The Steps toward the “Power Stroke”  Activated cross bridge bends toward center of thick filament, “rowing” in thin filament to which it is attached  Sarcoplasmic reticulum releases Ca2+ into sarcoplasm  Myosin heads bind to actin  Myosin heads swivel toward center of sarcomere (the “power stroke”)  ATP binds to myosin head and detaches it from actin

Question 14

Key Determinants of The Power Stroke

____ of ___ transfers ____ to myosin head and____ it 

Contraction continues IF (1) ___ is available and (2) ___ level in ____ is high

Answer 14

Key Determinants of The Power Stroke  Hydrolysis of ATP transfers energy to myosin head and reorients it  Contraction continues IF (1) ATP is available and (2) Ca2+ level in sarcoplasm is high

Question 15

Determinants of “Relaxation”

Depends on____ of Ca2+ into___ ____

_____e breaks down ___ at ___ ____

 Muscle fiber action potential stops and when th____ action potential is no longer present, Ca2+ moves back into sarcoplasmic reticulum to wait for next depolarization

Answer 15

Determinants of “Relaxation”  Depends on reuptake of Ca2+ into sarcoplasmic reticulum (SR)  Acetylcholinesterase breaks down ACh at neuromuscular junction  Muscle fiber action potential stops and when the local action potential is no longer present, Ca2+ moves back into sarcoplasmic reticulum to wait for next depolarization

Question 16

Calcium Release in Excitation-Contraction Coupling

* Note “Clockwise Story of Events

1) Ach released by ___ of ____ neuron crosses cleft and binds to ___ /___ on ___ ___ ___
2) ___ ____ generated in response to binding of and subsequent end plate potential is propagated across ____ membrane and down ___ ____ of muscle cell
3) Action potential in T tubule triggers ___ ____ from sarcoplasmic reticulum
4) Ca ions released from___ ____ bind to ___ on actin filaments; leads to_____ being physically moved aside to uncover cross-bridge binding sites on actin
5) _____ cross bridges attach to actin and ____, pulling actin filaments twd center of sarcomere; powered by energy provided by ____
6) Ca actively ___ ____ by SR when there is no longer local an ___ ___
7) With Ca no longer bound to troponin, _____slips back to its ___ ___ over binding sites on actin; actin slides back to ___ ____

Answer 16

Calcium Release in Excitation-Contraction Coupling * Note “Clockwise Story of Events 1) Ach released by axon of motor neuron crosses cleft and binds to receptors/channels on motor end plate 2) Action potential generated in response to binding of Ach and subsequent end plate potential is propagated across surface membrane and down T tubules of muscle cell 3) Action potential in T tubule triggers Ca release from sarcoplasmic reticulum 4) Ca ions released from lateral sacs bind to troponin on actin filaments; leads to tropomyosin being physically moved aside to uncover cross-bridge binding sites on actin 5) Myosin cross bridges attach to actin and bend, pulling actin filaments twd center of sarcomere; powered by energy provided by ATP 6) Ca actively taken up by SR when there is no longer local action potential 7) With Ca no longer bound to troponin, tropomyosin slips back to its blocking position over binding sites on actin; actin slides back to resting position

Question 17

Sarcoplasmic Reticulum 

Modified endoplasmic reticulum 

Consists of fine network of ____ ____that surround each _____

Not ____ but encircles ____ throughout its length 

Segments are wrapped around each ___ band and each __ band

 Ends of segments expand to form_____ regions – ___ ___(AKA “___ ____”)

Answer 17

Sarcoplasmic Reticulum  Modified endoplasmic reticulum  Consists of fine network of interconnected compartments that surround each myofibril  Not continuous but encircles myofibril throughout its length  Segments are wrapped around each A band and each I band  Ends of segments expand to form saclike regions – lateral sacs (AKA “terminal cisternae”)

Question 18

____ Tubules 

T tubules 

Run____ from surface of muscle cell membrane into central portions of the muscle fiber

Plunging in to inner portion of muscle fiber 

____ of ____ from the surface of the cell so they carry ____ deep into the tissue

 Since membrane is continuous with surface membrane – action potential on surface membrane also spreads down into T-tubule

 Spread of action potential down a T tubule trigger ___ of ___ from sarcoplasmic reticulum into cytosol

Answer 18

Transverse Tubules  T tubules  Run perpendicularly from surface of muscle cell membrane into central portions of the muscle fiber  Plunging in to inner portion of muscle fiber  Protrusion of membrane from the surface of the cell so they carry excitations deep into the tissue  Since membrane is continuous with surface membrane – action potential on surface membrane also spreads down into T-tubule  Spread of action potential down a T tubule triggers release of Ca2+ from sarcoplasmic reticulum into cytosol

Question 19

Skeletal Muscle Mechanics 

Muscle consists of groups of ___ ___ bundled together and attached to ___s

___ ____ covering muscle divides muscle internally into bundles 

Connective tissue (That covers the muscle) extends beyond ends of muscle to form____

Tendons attach___ to ____

 Some muscles can be so strong that in ER situations, muscles become tense so much that you can___ tendon off

 Conn tissue that covers muscle can be quite constrictive  We think of muscles being pretty much constant in volume and size but they can become ___ with ____ from an inflammatory process or _____

 Two examples

 People come into ER having been in a crushed situation. One of 2 things happened. There were without blood flow to that area for an extended period of time where there was _____ of those tissues bc it wasn’t well nourished. There wasn’t good vascular supply. During that time, there was an ____ process that sets in. As tissue is on its way to dying. That leads to an increased ____ of the tissue and the ___ ___ that are in the blood stream start leaking out of the tissues. When they get into the interstitial spaces of those tissues…Plasma proteins were in the blood stream and they typically stay in there and they are typically described as __ ___, that is they help retain fluid in the circulation as well so if you start losing plasma proteins out of blood and into interstitial spaces, they will carry ____ with them. Outcome is going to be ____. Muscles start ____and they are entrapped in the ___ ____, It won’t be long before the accumulation of fluid will ____ the continue of circulation. Even though they’ve been rescused and are in ER, their tissues are swelling and they are trapped in this muscle sheath. Frequently they do a ____. They will cut down the fascial sheets aroung the muscle so the muscle can survive. They will leave those open during the acute phase to make sure they can survive okay. 

Some profession athletes develop such massive muscles. When they tense those muscles on the line in football, muscles become ___ with ____. BB pump up their muscles. Blood rushes into muscle mass. This can ____ circulation. They may end up having impaired muscular FCN. Will do ____ so muscles don’t get trapped.

Answer 19

Skeletal Muscle Mechanics  Muscle consists of groups of muscle fibers bundled together and attached to bones  Connective tissue covering muscle divides muscle internally into bundles  Connective tissue (That covers the muscle) extends beyond ends of muscle to form tendons  Tendons attach muscle to bone  Some muscles can be so strong that in ER situations, muscles become tense so much that you can rip tendon off  Conn tissue that covers muscle can be quite constrictive  We think of muscles being pretty much constant in volume and size but they can become engorged with fluid from an inflammatory process or blood.  Two examples  People come into ER having been in a crushed situation. One of 2 things happened. There were without blood fry process thlow to that area for an extended period of time where there was deterioration of those tissues bc it wasn’t well nourished. There wasn’t good vascular supply. During that time, there was an inflammatoat sets in. As tissue is on its way to dying. That leads to an increased permeability of the tissue and the plasma proteins that are in the blood stream start leaking out of the tissues. When they get into the interstitial spaces of those tissues…Plasma proteins were in the blood stream and they typically stay in there and they are typically described as osmotically active, that is they help retain fluid in the circulation as well so if you start losing plasma proteins out of blood and into interstitial spaces, they will carry water with them. Outcome is going to be edema. Muscles start swelling and they are entrapped in the CT sheath. It won’t be long before the accumulation of fluid will impair the continue of circulation. Even though they’ve been rescused and are in ER, their tissues are swelling and they are trapped in this muscle sheath. Frequently they do a faciotomy. They will cut down the fascial sheets aroung the muscle so the muscle can survive. They will leave those open during the acute phase to make sure they can survive okay.  Some profession athletes develop such massive muscles. When they tense those muscles on the line in football, muscles become engorged with blood. BB pump up their muscles. Blood rushes into muscle mass. This can impair circulation. They may end up having impaired muscular FCN. Will do fasciotomy so muscles don’t get trapped.

Question 20

Muscle Contractions 

Contractions of whole muscle can be of varying ____

 “Twitch”

___, ____ contraction which is not useful to normal muscle FCN 

Produced from ____ action potential

 Typically does not__ ___ in body

 Can be elicited by direct___ ___n to a muscle

Used to ____ what is going on electrically  It’s a research term

 You may experience it if you have been exercising and get a____c state in a particular muscle group bc it was impaired circulation and you really worked really hard or you hadn’t done cool down afterwards and got accumulation of ___ ___and ____ in the tissues.

You might see what we call _____.

____ nerves firing off a muscle and seeing little twitches of the muscle itself but not any type of ___ ____

Key factors which determine gradations of (whole) muscle tension

____ of ___ ___ contracting within a muscle 

____ developed by each ___ ___

Answer 20

Muscle Contractions  Contractions of whole muscle can be of varying strength  “Twitch”  Brief, weak contraction which is not useful to normal muscle FCN  Produced from single action potential  Typically does not take place in body  Can be elicited by direct electrical stimulation to a muscle  Used to analyze what is going on electrically  It’s a research term  You may experience it if you have been exercising and get a hypoxic state in a particular muscle group bc it was impaired circulation and you really worked really hard or you hadn’t done cool down afterwards and got accumulation of lactic acid and CO2 in the tissues. You might see what we call fasiculations. Indiv nerves firing off a muscle and seeing little twitches of the muscle itself but not any type of organized contraction  Key factors which determine gradations of (whole) muscle tension  Number of muscle fibers contracting within a muscle  Tension developed by each contracting fiber

Question 21

Types of Muscle Contraction 

Two primary types

 ___”→ Same _____

. It remains constant 

Muscle ____ remains constant as muscle ___ ____

___ contractions or movements

 Two types

 _____” contractions  Muscle shortens

_____ ” contractions  Muscle lengthens

____” → Same____

 Muscle is prevented from shortening

____ state

___ develops at ___ muscle length 

Typically in sports, they will do some isometric contractions 

Like pushing against immovable object 

Applying Force to wall but your muscles are not shortening 

That is like lifting very heavy weights

Answer 21

Types of Muscle Contraction  Two primary types  “Isotonic”→ Same tension. It remains constant  Muscle tension remains constant as muscle changes length  Smooth contractions or movements  Two types  “Concentric” contractions  Muscle shortens  “Eccentric” contractions  Muscle lengthens  “Isometric” → Same length  Muscle is prevented from shortening  Experimental state  Tension develops at constant muscle length  Typically in sports, they will do some isometric contractions  Like pushing against immovable object  Applying Force to wall but your muscles are not shortening  That is like lifting very heavy weights

Question 22

Cardiac Muscle 

Found only in walls of heart 

Striated  Cells are interconnected by “__ ___” 

Fibers are joined in ____ network 

Innervated by ___ ___ ____

 These cells are branching with blunt ends on them and they have what are called ___ ____

 Under these conditions the impulse is ideally distributed over the heart

___ ___ gives rise to a depolarization and before you know it, it spreads in a wave over the heart bc the ____ in the cells afford that opportunity for greater faster spreading involving all the cells in the chamber of the heart

__ ____ beat

 If it was going slower, the heart would be more apt to____ blood around in the chambers and not have these explosive kinds of ejections that are critical to the normal fcn of the heart. 

____ nerve is a prime nerve that goes to the ___ node of the heart.

Its process of ____ the heart rate is that it _____s those membranes.

Hyperpolarize→ moving further from threshold.

Pumping that resting membrane potential down even lower.

Greater distance that membrane has to leak up to, to reach threshold and then have spontaneous discharge that we call Action Potential.

Answer 22

Cardiac Muscle  Found only in walls of heart  Striated  Cells are interconnected by “gap junctions”  Fibers are joined in branching network  Innervated by autonomic nervous system  These cells are branching with blunt ends on them and they have what are called intercalated disks  Under these conditions the impulse is ideally distributed over the heart  SA node gives rise to a depolarization and before you know it, it spreads in a wave over the heart bc the branches in the cells afford that opportunity for greater faster spreading involving all the cells in the chamber of the heart  Rapid coordinated beat  If it was going slower, the heart would be more apt to churn blood around in the chambers and not have these explosive kinds of ejections that are critical to the normal fcn of the heart.  Vagus nerve is a prime nerve that goes to the SA node of the heart. Its process of depressing the heart rate is that it hyperpolarizes those membranes. Hyperpolarize→ moving further from threshold. Pumping that resting membrane potential down even lower. Greater distance that membrane has to leak up to, to reach threshold and then have spontaneous discharge that we call Action Potential.

Question 23

Cardiac Muscle Fibers

 Interconnected by____ ___ and form ___ ____

 Syncytium: behaving as if its___ ___l

When impulse starts it spreads over everywhere 

Within intercalated discs – two kinds of membrane junctions

____

___ ____

 These allow the____ over those spaces

Answer 23

Cardiac Muscle Fibers  Interconnected by intercalated discs and form “functional syncytium”  Syncytium: behaving as if its one cell  When impulse starts it spreads over everywhere  Within intercalated discs – two kinds of membrane junctions  Desmosomes  “Gap junctions”  These allow the conduction over those spaces