chapter 11 anatomy and physiology

8/13/2019 Chapter 11 Anatomy and Physiology

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Muscular System

myo = Muscle endo = Within fasc = little

epi = above peri = around apo = above

pena = feather syn = together ant = against

ramus = branch sarco = flesh blast =precursor

1. There are three kinds of muscular tissue studied in Myology, or the study of muscles, they are

cardiac muscle, skeletal muscle and smooth muscle. All muscle cells exhibit characteristics of

excitability, conductivity, contractility, extensibility, and elasticity.

I. Responsiveness (Excitability) - Responsiveness to external stimuli is a normal

property of all living cells, muscle cells and nervous cells are very responsive.

Stimuli could be chemical, mechanical, electrical and other stimuli which elicits a

response in the cell.

II. Conductivity -Stimulation is not only locally emulated but is conducted along a

pathway to neighboring cells.

III. Contractility - The ability to shorten or contract which creates a tug on bones,

and organs.

IV. Extensibility - Refers to the ability of muscle cells in being stretched, such as the

smooth muscles that make up the stomach.

V. Elasticity - Is the ability of muscle cells in returning to their original shape after

stretching or contracting.

2. Skeletal muscles are voluntary, motion is initiated by motor neurons attached to muscle fibers at

synapse, they are striated and are usually attached bones, they can be 100 um to 30 cm long.

3. Smooth muscles are involuntary and are usually moved through the control of the autonomic

nervous system and are never attached to bones.

4. Skeletal muscles vary in size from micrometers to about 30 cm, and usually appear as strands

and due to this factor muscle cells are also known as muscle fibers or myofibers.

5. Muscular tissue has four key functions: Producing body heat, stabilizing body positions, moving

substances within the body, and generating heat.

6. Muscle fibers are covered by a number of

connective fibrous layers including the tendons,

which arent excitable, conductive, or contract to

produce motion. They are however can be

stretched and are elastic so they resume shape

after being stretched within limits.

7. Fascia covers the entire muscle including groups of

muscle, which which is continuous with epimysium


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that narrows and become a tendon or an insert. Fascia can be surrounding Below the

epimysium bundles of muscle fiber or muscle cell are perimysium which surrounds about

10-100 of the muscle fibers. Endomysium surrounds individual muscle cells.

8. When muscles are contracted and motion occurs, the usual course of action in the muscles is

that a muscle stays stationary while the other bone moves. The site at which usually the muscle

is anchored where by it regulates motion is called its origin and the other end of the muscle orinsertion is where the muscle is attached to moving bones. In most cases insertions are distal

to origin.

9. Myofiber is the cell, Myofibril is the individual rod like arrangement of myofilaments within the

muscle cell. Within the myofibril exits the myofilaments that are actin and myosin filaments.

Components of muscle

Layers that cover muscle (> 2 )

16.Muscle cells are called myofibers, muscle fibers which are

distinct from myofibrils which are protein fibers that make up

the contractile component of a cell, myofibrils are made up

myofilaments which are the individual protein chains or

filaments that make up the myofibril.

17. Filaments is a long chain of protein organized into long parallel

lines. In a muscle can be broken into three categories (more


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below) thick filaments which are made up of myosin molecules, thin filaments which are made

up of a protein called actin. The last category of myofilaments are made up of elastic filaments

that anchors the thick filament or myosin to the z disc, contributes to the elastic recoil and helps

center the fiber for effective movement.

18. Sarcolemma - is the plasma membrane of the muscle cells that is continuous with the

endomysium. Below the sarcolemma lies the multiple nuclei of the muscle cell.19. Sarcoplasm - The cytoplasm of muscle cells, contains a larger amounts of glycosomes

(glycogen storage units), myoglobin (O2 binding protein), larger amounts of mitochondria, and the

sarcoplasmic reticulum (smooth ER) is mostly used for calcium storage and pumping during

excitation.

20. Sarcoplasmic Reticulum - In muscle cells the endoplasmic reticulum is called the

sarcoplasmic reticulum and completely covers each myofibril, it functions as a calcium storage

unit.

21. Transverse Tubule or T- tubules, the sarcolemma has deep infolds or invagination that

extend from outside the cell to the inside of the cell and wraps around myofibrils (bundle of

filaments).22. Triad - Each of the Transverse tubules are situated between two enlarged parts of the

sarcoplasmic reticulum called cisternae,so this structure with two cisternae with a transverse

tube in the middle is known as a Triad.

23. Fascicles - Perimysium surrounds fascicles which are bundles of muscle fibers numbering

anywhere from 10-100.

24. Muscle Fibers (Cells) - Long cylindrical cells covered by endomysium and sarcolemma, and

the nucleus is located near the edge of the cell immediately after the sarcolemma.

25. Myofibrils - Threadlike structures that make up the contractile portion or the functional portion ofthe cell. Composed of protein filaments and extend to the entire length of the cell.

Myofilaments

26.Myofibrils are made up of myofilaments and are the contractile organelle of the skeletal system,

they can be classified into three categories though there are more than three kinds of proteins


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that make up myofibrils. (above they are categorized into thick, thin and elastic, here they are

grouped by function) http://www.youtube.com/watch?v=Ct8AbZn_A8A

I. Contractile Proteins - Myosin and actin make up the contractile proteins in that their

combined function creates motion. Actin and myosin are contractile proteins in many

different cells in use in cellular transport, during meiosis and mitosis but they are

abundant in muscle cells and give the striated appearance to skeletal muscle. Myosin is a motor proteinthat it uses ATP to pull on structures to create

movement.

Myosin is organized into bundles of about 300 strands that combine to make up

the thick filament of the myofibril.

Projections of myosin called myosin headsextend outwards and become attached

to active sites on the thin filaments and propel themselves forward.

Actin molecules are arranged into spiralled filament (Helix) and have active siteswhere myosin heads can attach.

Actin molecules can be further broken down into F-actin which makes up the

chain of the molecule that makes the actin filament and G-actin makes up theactive sites where myosin head can attach.

II. Regulatory Proteins - Regulatory proteins help switch the muscle from active to

relaxed, they are both part of the actin helix. (thin filament)

Tropomyosin molecules are arranged into thin filaments that block the active sitesof actin in relaxed state.

Troponin molecules when combined with calcium ions change the tropomyosinso that the active sites are revealed so that myosin heads can attach to the

tropomyosin active sites.

(The cycle is described shortly...as soon as I understand it and not fall

asleep.hahah sleep, like I can fall asleep)

III. Structural Proteins - There are about 12 structural protein the sarcomere eachadding to the elasticity, extensibility, connect filaments and for the proper alignment of

molecules.

Nebulin - Limits the length of the thin filament. Titin the most plentiful after myosin and actin, because of its springy nature

connects M- line to the Z disc and can recoil after stretching aiding to elasticity of

the sarcomere and secures the sarcomere against overstretching.

- actinin makes up the z line of sarcomere and anchors titin molecules and
http://www.youtube.com/watch?v=Ct8AbZn_A8A


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actin filament that makes up the thin filament.

Dystrophin - (I am not sure whether if they are part of the regulatory protein, I

mean it doesnt sound like it.. but its on the book so here it goes) These

molecules transfer the contractile strength of the sarcomere

Myomesin - molecules that are lined up on the M-Line that are connected to thetitin molecules and keep the myosin molecules in a bundle.

Striations

27.The arrangement of myosin and actin fibers are organized in such way at a molecular level that

at a microscopic level it seems striated. The striations come from two alternating bands of dark

and light sections.

The A- Band is the middle part of the sarcomere and contains the entire lenghth of the

thick filament or myosin and thus appear darker in comparison to the I-Band I-Band where there are no thick filament or myosin and so it appears lighter, the center

of the I band is where each of the sarcomere ends. At the end of each sarcomere lies

proteins that anchor the filaments within the sarcomere.

28.Z- Disk is the center of each of the I-band where thin filaments are connected to them, they are

at the end of the each sarcomere and so each z-disk signal the end of a sarcomere.

29.A narrow part of the A-band contains thick filament but no thin filament this portion of the

sarcomere is called the H-Band, the center of which is the midline of a sarcomere and so its

called the M-Line.


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The Nerve Muscle Relationship

30.Muscles contract only in response to electrical signals, and those signals are delivered throughthe somatic nervous system.

31.Each of the muscle fiber is connected to one corresponding neuron, but one neuron can be

connected to a thousand muscle fiber as it is in the calf, or for highly specialized movement

such as it is is in the eye only 3-6 muscle cells are connected to a neuron. On average about

200 muscle fibers are connected to a neuron.

32.Neuronal connection is vital for neurons, with a severed nerve the muscle no longer function and

as a result it denervation atrophy.

33.Somatic motor neurons make up the activation pathways for skeletal muscle, they are located

in the CNS with their axons reaching the individual muscle cells. Once the neuron fires sending

electrical signal to the target cell, the signal travels to the end of the neuron where the fibersbranch off and connect anywhere from a few muscle cells to about a 1000 muscle cells at the

neuromuscular junction (NMJ).

34.At the Neuromuscular Junction the ends of neuron called the axon terminal divides into

cluster of synaptic bulbs (or synaptic knob). The synaptic knob and the depression in the

sarcolemma where communication occurs does not have direct contact. Communication is

carried out through synaptic vesicles with corresponding receptors in the muscle.


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35.The space between the synaptic bulbs and the receptors is called the synaptic cleft, and can

have as many as 50 million active sites for transmitters (30 - 40 million norm) . The depression

on the sarcolemma has junctional folds which increases the amount of surface area available for

receptors.

36.When neurons communicate with other cells or themselves neurotransmitters are used, a

specialized molecule that are released in vesicles to the receptor site of the target cell. Inneuron-muscle communication the neurotransmitter used is called Acetylcholine (ACh).

37.A motor unit- consists of one motor neuron and its associated muscle fibers. A motor unit could

be spread through the group of muscle.

Fibers in motion

38. The sliding filament model is the representation of the movement of the thick and thin filament

which does not change in size but slide past each other.

The thin filaments move towards the center, as this occurs the H-zones and the I bands

narrow and the Z lines become closer together. The combined mechanism of the molecules in the sarcomere add towards shortening

the length of the sarcomere.

39. All or nothing Muscle fibers of a motor unit moves in unison to stimuli, the force of

concentration for a motor unit remains the same for all contractions. The variations of strength

for muscle movement is achieved through the activation of only some of the motor unit in the

same muscle group. Muscle groups are spread throughout the muscle and so the activation of

just a fraction of a muscle can contract a muscle without having to use all of its contractile

strength.

40. Electrophysiology and excitability of cells

In a electrically polarized cell (cells that have different voltage outside the cell than the

outside) there are more negative charges (anions) within the cells than outside the cell,

this is mostly due to the negatively charged protein, nucleic acids and proteins.

Within the cells there are more K+ ions and outside the cell (ICG) there is an excess of

Na+.

Electric Potential refers to the the difference in voltage between two points, in musclecells this difference is about -90 millivolts referred to as the resting membrane

potential (RMP). This charge difference is maintained through the sodium potassium

pump.

When a stimulus triggers the cell to open its ion gates the sodium ions in the ICF rushes

in while the positive potassium ions within the cells partly due to the positive sodium and

partly due to the its own concentration gradient (there are less k+in ICF) rushes out of the

cell as the sodium rushes in. This change progresses in a steady stream of action as

one action triggers another is called action potential.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__

action_potentials_and_muscle_contraction.html
http://www.google.com/url?q=http%3A%2F%2Fhighered.mcgraw-hill.com%2Fsites%2F0072495855%2Fstudent_view0%2Fchapter10%2Fanimation__action_potentials_and_muscle_contraction.html&sa=D&sntz=1&usg=AFQjCNEbWZ_OD2Sg5K7XXgdsUu05Dnqumwhttp://www.google.com/url?q=http%3A%2F%2Fhighered.mcgraw-hill.com%2Fsites%2F0072495855%2Fstudent_view0%2Fchapter10%2Fanimation__action_potentials_and_muscle_contraction.html&sa=D&sntz=1&usg=AFQjCNEbWZ_OD2Sg5K7XXgdsUu05Dnqumw


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41. Muscle movement andcross bridge cycling:

I. The signal, the nerve impulse initiated at the central nervous system is carried to the

target cell through axons and arrives at the synapse.

The electrical signal (action potential) causes voltage gated calcium channels to open,

this causes calcium to enter the synaptic knob. The newly released calcium channels initiates the exocytosis of the vesicles containing

acetylcholine.

The Neuromuscular Junctions are slightly apart from the muscle (60-100 nm wide), and

are covered by Schwann Cells (same cells that cover the axons).

The sarcolemma is covered with ACh receptors which bind to the ACh released from the

nerve. The ACh receptors are specially concentrated in the high infolds directly beneath

the neuromuscular junction called Junctional Folds.

The ligand gated ACh receptors channels open letting in sodium ions which causes

potassium channel to leak out. As the sodium rushes in the resting potential of the cell

which was -90 mV jumps to +75, but once the potassium leaves the cell membrane itgoes back down to a level closer to its resting potential.

II. Acetylcholine

Acetylcholinerase (AChE) is an enzyme in the muscles basal lamina that breaks down

acetylcholine after the muscle has been exited. It allows the muscle to relax after

excitation, although ACh molecules can leave the ACh receptors the procedure is

expedited by AChE.

Toxins that interfere with the procedure of AChE causes muscle paralysis, such as

spastic paralysis. Other conditions such as that brought on by the bacterium Clostridium

Tetaniblocks the production of glycine, which is inhibitory protein produced in the spine to

prevent unwanted muscle contractions.III. Gates open Once Acetylcholine binds to the Acetylcholine receptors, the receptors are

ligand gated ion channels and once they open sodium ions rush in followed by potassium

ions leaking out.

The sudden change in voltage change continues through the muscle and within the

muscle this change is almost instantaneous and throughout because of the transverse

tubules and its webbed network.

As the action potential travels through the transverse tubules in the triad it signals voltage

sensitive tubule proteins in the cisternae to open releasing stored up calcium into the

muscle cell.

IV. Calcium ions and actin

Once calcium is released into the cell, the calcium binds to the troponin, which alters the

shape of troponin which in turn changes the shape of tropomyosin.

Tropomyosin covers the binding site of actin (G actin) preventing myosin heads from

being attached to them, but the change in shape of troponin alters the tropomyosin and

moves them out of the binding site.


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V. Myosin and ATP

Myosin is in its cocked position when an ATP is hydrolyzed to form ADP and inorganic

phosphate.

The activated myosin head binds to a G protein as the tropomyosin moves away.

After the connection has been made between the myosin and actin the inorganic

phosphate leaves the myosin head strengthening the bond between the two proteins.VI. Power stroke

After the inorganic phosphate leaves the myosin and the bond is made stronger, the

myosin head moves backward propelling the actin filament toward the M line, thus

narrowing the H zone (bare zone with no actin filament) and I zone.

As the thin filaments are pulled closer to each other the space between the actin

filaments shorten which shorten the length of a sarcomere and as a result the combined

effort of many sarcomeres produce contraction.

At maximal contraction the actin filaments not only get closer to each other but can

overlap one another.

As the thin filaments are pulled toward the midline, a protein structure called dystrophin

translates the force to ECf and to the endomysium which pulls on the connective tissues

including and eventually the tendons producing motion or force.

VII. Myosin becomes detached

After the myosin has exerted its force on the actin filament, the myosin remains attached

to the actin until it binds to another ATP molecule.

Once ATP binds to the myosin head the bond between actin and myosin becomes

weaker and the two separates.

VIII. ATP Splits ATP is hydrolyzed forming ATP and inorganic phosphate and the cycle begins all over

again.

The myosin head attaches and detaches about five times per second as long the G-

actin sites remain open.

Myosin heads in their state of relaxations stays with an unhydrolyzed ATP molecule, and

in the extended (not cocked) position.


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IX. Acetylcholine stops.

Once the motor neuron stops firing, the release of Acetylcholine ceases, some of the

ACh leaves through diffusion but most of them are broken down through

Acetylcholinerase into acetic acid and choline, Choline is absorbed back into the synaptic

knob.

Active transport pumps calcium back into the cisternae from the cytosol, calcium isstored attached to proteins called calsequestrin.

As calcium leaves the cytosol they dissociate from troponin which alters the shape of

tropomyosin and the active sites for myosin binding is closed.

X. Summary

A motor neuron releases Acetylcholine which triggers an action potential, which is carried

through the T-tubules and that releases calcium ions from SR.

Calcium ions bind to troponin, tropomyosin changes shape and myosin attaches to actin.

The myosin heads power-strokes toward the center pullin actin, which produces force

that translates to muscle contractions.

When acetylcholine is no longer released from the neuromuscular junction it is absorbedback into the sarcoplasmic reticulum, and trpomyosin reverts back to covering the actin

sites.

42. The length tension relationship

Overly Contracted - When a muscle is overly contracted the length of the

sarcomere is the length of the myosin filament, and any force produced

would act against the z disk and no force would be produced.

Optimum resting length - The optimum level for contraction is when

the fibers are set in a way where all of the myosin heads can

make contact and there is room for the filaments so thatmaximum motion can take place.

Overly stretched - When a muscle is overly stretched only a

fraction of the myosin heads can generate force and so the

force produced will also be a fraction of the total possible generatable force.

43. Threshold Latent period and Twitch (The twitch and the latent period between twitches are

achieved through activation of muscle fibers rather than nerve fibers, thus the twitch here does

not reflect the usual course of action in a muscle but rather

characteristics of muscle as studied in a laboratory through

stimulation and the resulting myogram )

Muscle contractions are initiated only when sufficient

electric activity brings forth an action potential wave,

the minimum amount of stimulation necessary for

muscle movement is called the threshold.

Once the stimulus is received from the nerve there is a

delay of about 2 milliseconds before the electric

stimulus becomes muscle contraction, this period is known as the Latent Period. This


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period is also includes the time in which the muscles becomes taught and the internal

tension becomes stronger in order to overcome the elastic properties of muscle.

The muscle and connective tissue would have to contract more than the amount that it

can stretch so that it can act upon the tendons and bones to produce movement

At stimulus that produces a muscle potential equalling or higher amount of action

potential causes a Twitch, which is a quick cycle of contraction followed by relaxation. Between two twitches there exists a latent period where the muscle does not contract

because time is required for excitation and excitation-contraction coupling.

Contraction Phase is when the components of myofibers have gone through theirelasticity and sarcomere contraction takes place, which is soon followed by relaxation

phase, where the calcium is pumped back into the sarcoplasm.

44.Muscle tonerefers to the bodys tendency to maintain optimum resting length of

sarcomeres for optimum production of force. This is achieved through partial contraction

of fibers in the muscle and through connective tissues that maintain elasticity.

45. Contraction Strength of Twitches Muscle cells when stimulated at nerves rather than the muscle produce stronger force,

because they stimulate more of the muscle fibers, the process of adding more motor

units in order to produce a stronger contractile strength is called Recruitment or

multiple motor unit summation.

Twitch Sudden excitation followed by relaxation, where the muscle produces strength ofequal degree.

TreppeA phenomenon exhibited by muscle to series of stimuli at the same strength,since not all calcium is absorbed back their strength becomes increasingly stronger, but

the muscle relaxes even if for a short time between excitation.

Incomplete Tetanus is achieved when a muscle is not allowed to completely relaxbetween stimuli. (20-40 stimuli / sec), in incomplete tetanus there is so small an interval

of time between stimulus that complete relaxation of the muscle never takes place.

Complete Tetanus is achieved when no relaxation at all takes place between stimuli.(40-50 stimuli/ sec), where the muscle never goes into relaxation but soon fatigues after

continues after complete tetanus.

The neuron rarely stimulates at rates higher than 25 stimuli/ second, the above noted

characteristics are observed in laboratory.

If a muscle is exited before it is allowed to relax then the two waves of excitation

combines together forming a larger wave of excitation.


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46. Isometric and Isotonic Contractions

Isometric contraction is when a muscle develops tension but is unable to producemovement. (pushing against an object producing no movement)

Isotonic contraction is where the as a result of contraction produces movement, if themovement is achieved through shortening of the muscle then its Isotonic concentric

contraction and if the motion is when the muscle lengthen under tension its calledeccentric contraction.

Isometric, no movement, isotonic movement, concentric shorter muscle, and eccentric

is when the muscle lengthen under tension.

Muscle Metabolism

47. ATP sources , muscle requires a continuous source of ATP to function, which can be produced

from organic compounds such as glucose, fatty acids, glycogen and other molecules. It can be

produced by one of three mechanism : (1) Creatine Phosphate (2) anaerobic cellular

respiration and (3) aerobic cellular respiration. (Production of ATP through creatine phosphate isunique to muscle)

48. Immediate Energy - Immediate energy requirements of the skeletal system, about six seconds

of intense activity or a minute of brisk walking, until aerobic metabolic processes act to produce

ATP. Myokinase and creatine kinasewithin the muscle provide for this type of energy. Myokinase - Transfers phosphate group from an ADP to another ADP forming an ATP.[ ADP +ADP + Myokinase = ATP + AMP + Myokinase]

Creatine kinase - Creatine Phosphate molecules are energy storing molecules with aphosphate groups that are synthesized during energy surplus. This energy storage unit

transfers a phosphate group to form ATP. ATP is used in times of abundant ATP to form

creatine phosphate so that the creatine phosphate can be used in times of need.

[ ADP + Creatine Phosphate + Creatine kinase = ATP +Creatine + Creatine kinase]


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Slow Oxidative Fibers, these fibers are rich in myoglobin and capillaries and are thesmallest of the fibers, they are fatigue resistance but are not able to deliver large

amounts of force. They are mostly components of muscle used for posture and aerobic,

endurance type activities.

Fast Oxidative - Glycolytic Fibers - Like slow oxidative fibers they can produce ATPaerobically, they are medium sized and faster in comparison to slow oxidative fibers interms of the rate of hydrolysis of ATP in myosin heads. These fibers also known as type

II B are rare in human body and are prevalent only in people with endurance training.

Fast Glycolytic Fibers - They are the largest of the three and contain the most amountof myofibrils and generate the greatest amount of force. They generate ATP mainly

through glycolysis and so they fatigue faster.

A major cause for distinction is the rate at which ATP is hydrolyzed in the myosin head ofeach of the fibers.

Most skeletal muscle are a combination of the three fibers, depending whether they are

used for posture (SO fibers), for generating force (upper limbs) or a combination of two

(legs). The amount of fibers present in an

individual is largely dependent on genetic

predisposition but FOG can become FG or

vise versa to accommodate physical

activity over time.

The textbook used for class onlymentions two of the three fibers since

fast-glycolytic fibers or intermediate

fibers are rare in human body and are

only abundant in trained athletes. Thetable below shows just the two muscle

fibers.

54. Muscle Strength and Conditioning Many factors affect the efficiency of muscle such as the

size of the muscle, fascicle arrangement (pennate muscles are stronger in comparison to

parallel muscle which in turn is stronger than ocular muscle). Size of motor unit, multiple motor

unit summation, temporal summation (delivery rate by the neuron, stronger the rate=stronger

force), optimum length of muscle and fatigue.

Elasticity of a muscle changes largely due to connective tissues that surrounds each

muscle.

55. Resistance Exercise is weight training where by increasing the size of the muscle, which

makes them stronger, Endurance (aerobic) Exercise makes the muscle fibers less subject to

fatigue. A combination of the two known as Cross trainingwhich is a combination of the two.

56. Delayed onset muscle soreness results from microtrauma to the muscle.

57. Cramps are initiated by the central nervous system, they are painful spasmodic contractions

that are usually the result of extreme cold, heavy exercise, lack of blood supply, electrolyte

depletion, dehydration and low blood glucose.


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Cardiac Muscle

58. Cardiac Muscle fibers share much in common with skeletal muscle tissue in that they both

have the same zones, sarcomere structure but differ in that the ends of the cardiac muscles are

joined to one another through Intercalated Disks which are unique to cardiac muscle fibers. In response to action potential

cardiac muscles contract 10-15

times longer for effective emptying

of chambers.

The ends of cardiac cells are

irregular shaped (intercalated

disks) with desmosomes for better

protection against stress and gap

junction gap junction to facilitate

transfer of materials. They have larger mitochondria and

more of it since it relies on constant

and abundant amount of ATP

almost exclusively from aerobic

respiration. (2% mitochondrial

volume in muscle, 25 % in cardiac

cells.

59.Cardiac cells can contract without action potential from the nervous system, that is they are

autorhythmic in that they have their own pacemakers that set the rate at which they beat.

Smooth Muscle

60.Smooth muscle have single centrally located nucleus with no visible striations since the

myofilaments (actin, myosin) are thinner in comparison and are randomly distributed. They lack

T-tubules and their sarcoplasmic reticulum is not as functional or developed as skeletal muscle

or cardiac muscle.

61.Some smooth muscles are not

innervated instead and communicate

with each other through gap junction,

pressure or other stimuli. When a nerve

is connected to them they are periodic

swelling that contains


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neurotransmitters, norepinephrine from the sympathetic fibers and acetylcholine from the

parasympathetic nervous system. A single nerve can have up to 20,000 swellings and

innervates large number of smooth muscle cells.

62.Smooth muscles layers of hollow organs can be formed from a single layer or from many layers,

such as small arteries with only one layer of cells to multilevel and layered stomach formation

with smooth muscle. (piloerector muscle is made up smooth muscle )63. Excitation of Smooth Muscles: Excitation of smooth muscle can take place from a number of

different stimuli specific to function unlike the skeletal muscle which is stimulated by the somatic

nervous system.

Autonomic nerve fibers and neurotransmitters, parasympathetic = acetylcholine,sympathetic = norepinephrine,

Chemicals, chemicals can be anything from hormones, carbon dioxide, low pH, nitricoxide to oxytocin during labor contractions.

Temperature, some of the smooth musclesin response to cold contract and dilate inresponse to heat.

Stretch Mechanically gated ion channels open in response to physical stress as in thestomach and bladder.

Autorhythmicity periodic contraction contribute to peristalsis.64. Two types of smooth muscle are

Single unit (visceral)smooth muscle where all of the smooth muscle are connected to

each other through gap junctions so that the activation of a smooth

muscle travels downwards activating other muscles. They are

usually found in smooth muscle of hollow organs.

Multi unit smooth muscle major difference between the two isthat the activation of a muscle stimulates just the muscle that was

stimulated. Makes up the smooth muscle of large arteries,piloerector muscle, muscle of the eye that focuses and adjusts the

size of the pupil.

65. Contraction of the smooth muscle, Smooth muscles contract through similar mechanisms as

skeletal muscle.

Smooth muscle excitation open calcium channels, the entering

calcium binds to calmodulin which starts a reaction that adds a

phosphate group to the head of myosin which makes it attracted

to G-actin of the thin filament.

Actin molecules are attached to dense bodies which are

connected to intermediate filaments that form the cytoskeleton of

the smooth muscle cells, and so as a result of contraction the

entire muscle contracts and becomes smaller.

Smooth muscle has a prolonged latent period of about 50-100

milliseconds due to slow absorption of calcium ions, and to a

mechanism called Latch mechanism (even after the phosphate

group is removed through calcium resorption crossbridge


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continues), these contribute to smooth muscle using less ATP and being less

susceptible to fatigue.

66. Response to stretch, peristalsi and bladder functions are maintained through the

stress-relaxation response, that is the smooth muscle builds up tension in response to stretch

(stress) but soon relaxes in order to accommodate the increasing stress.67. Smooth muscles maintain the ability to contract without the issue of optimum length due to the

fact there are no z-disks, there are myosin heads throughout the thick filament and so there is no

H-zone or bare zone. The sarcomeres are arranged in all directions so that despite formation the

muscle can contract.


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68.

chapter 11 anatomy and physiology

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