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A&P 1 > Muscular Tissue > Flashcards

Muscular Tissue Flashcards

1
Q

Properties of Muscular Tissue

A
  • properties that enable musce to function in movements and contribute to homeostasis
    1. excitability- ability to respond to stimuli
    2. extensibility-ability to stretch without being damaged
    3. elasticity- ability to return back to original length after stretching
    4. contractibility- ability to contract and generate force
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2
Q

Functions of Muscular Tissue

A
  1. producing body movments
    walking and running; talking and writing
  2. stabilizing body positions (posture)
  3. Moving substances within the body
    * heart muscle pumping blood
    * moving substances in digestive tract
  4. Generating Heat
    * contracting muscle; especially skeletal muscle,prodices heat
    * shivering increases heat production
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3
Q

Skeletal Muscle Tissue

A
  • named like that because most skeletal muscles move bones
  • skeletal muscle tissue is striated
  • skeletal muscle works mostly in a voluntary manner
  • skeltal muscle may also be controlled subsconsciously
    ex: diaphram rekaxes and contracts during breathing without conscious control
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4
Q

Smooth Muscle Tissue

A
  • located in walls of hollow internal structure
    -blood vessels, airways, GI viscera, bladder and many other organs
  • does not have striations like skeletal and cardiac muscle tissue
  • action is involuntary
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5
Q

Cardiac Muscle Tissue

A
  • found only in walls of heart
  • striated like skeletal muscle
  • action is involuntary
  • contraction and relaxation of the heart is not consciously controlled
  • contraction of the heart is initiated by SA node of modified muscle tissue called the the pacemaker
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6
Q

Skeletal Muscle Tissue: Connective Tissue Components
(fascia,epimysium,perimysium,endomysium,tendon,aponeurosis)

A

*Fascia- Dense sheet or broad band of irregular connective tissue that
surrounds muscles
*Epimysium-The outermost layer of fascia; immediately adjacent to skeletal muscle tissue
-surrounds numerous bundles called fascicles
*Perimysium-Separates muscle tissue into fascicles of 10-100 muscle fibers
*endomysium-Separates individual muscle fibers from one another
*Tendon-Cord that attach a muscle to a bone
*Aponeurosis-broad, flat tendon, flat tendon example on the abdomen. helps with stability

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7
Q

Skeletal Muscle Tissue-Nerve and Blood Supply

A

*Neurons that stimulate skeletal muscle to contract are somatic motor neurons (SMN)
*The axon of a somatic neuron typically branches out many times
-each branch extends to a different skeletal muscle fiber.The neuron branch and an individual muscle fiber form a neuromuscular junction. A SMN and all the muscle fibers it innervates is known as a motor unit
* Each muscle fiber is in close proximity to one or more capillaries

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8
Q

Skeletal Muscle Tissue: microscopic anatomy facts (hypertrophy, satellite cells)

A

*The number of skeletal muscle fibers you will have is set before you are born
-most of these cells last a lifetime
*muscle growth occurs by hypertrophy: an enlargement of existing muscle fibers
* Testosterone and human growth hormone stimulate hypertrophy
*Satellite cells- retain the capacity to regenerate damaged muscle fibers

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9
Q

Skeletal Muscle Tissue
Microscopic Anatomy
(Sarcolemma, Transverse (T) Tubules, Sarcoplasm)

A

*Sarcolemma-the plasma membrane of the cell
*Transverse(T) tubules- Tunnel in from the sarcolemma
-muscle impulses or action potentials (AP) travel through the T tubules to the interior of the cell
*Sarcoplasm- the cytoplasm of a muscle fiber
-sarcoplasm includes glycogen used for synthesis of ATP and a red protein called myoglobin which binds oxygen molecules
-Myoglobin releases oxygen when it is needed for ATP production

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10
Q

Skeletal Muscle Tissue
Microscopic Anatomy
(Myofibrils, Sarcoplasmic Reticulum(SR), Filaments, Sarcomeres

A

*Myofibrils-Thread-like structures-subunits-within a muscle fiber that have a contractile function. Their contraction-a shortenning-generates force
*Sarcoplasmic Reticulum-A cluster of membranous sacs that encircles each myofibril
-Stores calcium ions (Ca ++), which are released by the muscle
impulse
-Release of Ca ++ then triggers muscle contraction
*Filaments-Function in the contractile process
-two types of filaments(thick and thin)
-There are two thin filaments for every thick filament.
Sarcomeres-compartments of arranged filaments
-sarcomeres are the basic functional units of a myofibril

-

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11
Q

Myofibril

A

Myofibril-A bundle of protein myofilaments within a muscle fiber;
myofibrils collectively fill most of the cytoplasm. Each
surrounded by sarcoplasmic reticulum and mitochondria.
Has a banded (striated) appearance due to orderly overlap
of protein myofilaments

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12
Q

Sarcomere

A

A segment of myofibril from one Z disc to the next in the
fiber’s striation pattern. Hundreds of sarcomeres end to end
compose a myofibril. The functional, contractile unit of the
muscle fiber.

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13
Q

Myofilaments

A

Fibrous protein strands that carry out the contraction
process. Two types: thick myofilaments composed mainly of
myosin, and thin myofilaments composed mainly of actin.
Thick and thin myofilaments slide over each other to shorten
each sarcomere. Shortening of end-to-end sarcomeres
shortens the entire muscle.

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14
Q

Muscle Proteins
(3 proteins that make up Myofibrils)

A

Myofibrils are built from three kinds of proteins.
● 1) Contractile proteins- generate force during contraction.
● 2) Regulatory proteins- Switch the contraction process on and off
● 3) Structural proteins-Align the thick and thin filaments properly
-Provide elasticity and extensibility
- Link the myofibrils to the sarcolemma

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15
Q

Contractile Proteins (Myosin)

A

Myosin
-Thick filament
- Functions as a motor protein which can achieve
motion
- Also acts as an ATPase to convert potential energy of
ATP to kinetic energy of motion
-Projections of each myosin molecule protrude
outward: These are the myosin heads

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16
Q

Contractile Proteins
(Actin)

A

Actin
-Thin filament
- Actin molecules provide a site where a myosin head can attach.
- Tropomyosin and troponin are also part of the thin filament.
- In relaxed muscle, myosin is blocked from binding to actin
because strands of tropomyosin cover the myosin-binding sites.
- Calcium ion binding to troponin moves tropomyosin away from
myosin-binding sites.
- Calcium thus allows muscle contraction to begin as myosin binds to
actin.

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17
Q

The Sliding Filament Mechanism

A

● Myosin heads attach to and “walk” along the thin filaments at both ends of a sarcomere.
● Myosin pulls the thin filaments toward the center of the sarcomere.
● Z discs (Z lines) come closer together and the
sarcomere shortens.
● For an isotonic contraction, this leads to shortening of the entire muscle.

18
Q

The Contraction Cycle

A

● Contraction begins with the SR releasing calcium
ions into the muscle cell after stimulation with an
action potential.
● Calcium ions bind to actin, exposing the myosin
binding sites.

19
Q

Contraction Cycle 4 steps

A

1) ATP hydrolysis
- Hydrolysis of ATP reorients and energizes the
myosin head.
● 2) Formation of crossbridges
● Myosin head attaches to the myosin-binding site on
actin
3) Power stroke
● During the power stroke, the crossbridge rotates,
sliding the filaments toward the middle of the
sarcomere.
● 4) Detachment of myosin from actin
● As the next ATP binds to the myosin head, the myosin
head detaches from actin.
● The contraction cycle repeats as long as ATP is
available and the Ca ++ level is sufficiently high.
● Continuing cycles apply the force that shortens the
sarcomere.

20
Q

Contraction and Relaxation of skeletal muscle

A

● Excitation–Contraction Coupling
*Action potentials causes Ca ++ to be released from the SR into
the muscle cell. An increase in Ca ++ concentration in the muscle
starts contraction.
* Ca++ moves tropomyosin away from the myosin-binding sites
on actin allowing cross-bridges to form.
*The muscle cell contains calcium pumps to return Ca ++ back to
the SR quickly. Calcium ion levels decrease.
* As the Ca++ level in the cell drops, myosin-binding sites are covered and the muscle relaxes.

21
Q

Contraction and Relaxation of Skeletal Muscle: Review of Major Terms(The Motor Unit,Neuromuscular Junction, Synaptic Cleft)

A
  • The Motor Unit-Motor neurons have a threadlike, highly branched axon that extends from the brain or spinal cord to a group of muscle fibers.
  • Neuromuscular junction (NMJ)- The NMJ is the interface of a motor neuron’s axon
    terminal and a muscle fiber.
  • Synaptic cleft- Gap that separates the nerve and muscle cells.
22
Q

Contraction and Relaxation of Skeletal
Muscle: Review of Major Terms (Neurotransmitter, Synaptic Vesicles, Motor End Plate)

A

● Neurotransmitter- Chemical released by the initial cell communicating with
the second cell.
● Synaptic vesicles-Sacs suspended within the synaptic end bulb containing
molecules of the neurotransmitter: acetylcholine (ACh)
● Motor end plate-The region of the sarcolemma (muscle cell membrane)
opposite the synaptic end bulbs
-The motor end plate contains acetylcholine receptors.

23
Q

Contraction and Relaxation of Skeletal
Muscle

A

● 1) Release of acetylcholine
● Nerve impulse arriving at the synaptic end bulbs causes many
synaptic vesicles to release ACh into the synaptic cleft.
● 2) Activation of ACh receptors
● Binding of ACh to the receptor on the motor end plate opens an
ion channel.
● Channel allows flow of Na + to the inside of the muscle cell.
● 3) Production of muscle action potential
● The inflow of Na + makes the inside of the muscle fiber more
positively charged, triggering a muscle action potential
● The muscle action potential then propagates along the
sarcolemma to the SR to release its stored Ca ++.
● 4) Termination of ACh activity
● ACh effects last only briefly because it is rapidly broken down
by acetylcholinesterase (AChE).

24
Q

Botulinum toxin

A

● Blocks release of ACh from synaptic vesicles
● May be found in improperly canned foods
- A tiny amount can cause death by paralyzing respiratory
muscles.
● Used as a medicine (Botox®)
● Strabismus (crossed eyes)
● Blepharospasm (uncontrollable blinking)
● Spasms of the vocal cords that interfere with speech
● Alleviates chronic back pain due to muscle spasms in the
lumbar region
● Cosmetic treatment to relax muscles that cause facial
wrinkles

25
Q

Curare & Anticholinesterase (AChE)

A

*Curare
-A plant poison used by South American Indians on arrows and
blowgun darts
-Causes muscle paralysis by blocking ACh receptors. This prevents
Na+ ion channels from opening.
-Derivatives of curare are used during surgery to relax skeletal
muscles.
*Anticholinestarase (AChE)
-Retards removal of ACh from NMJ
-By increasing available ACh, AChE strengthens muscle
contractions.
-Anticholinesterase is a treatment for myasthenia gravis and antidote
for curare.

26
Q

Production of ATP in muscle fibers

A

*a large amount of atp is needed to
-power the contraction cycle
-pump Ca++ into the sarcoplasmic reticulum via active transport
*the ATP thats inside muscle cells will only power contraction for a few seconds
ATP must be rapidly produced by the muscle fiber to keep up with demand
*muscle fibers have 3 ways to produce ATP
1) from creatine phosphate
2) by aneorobic fermentation
3) by aerobic cellular respiration

27
Q

Creatine Phosphate

A

Creatine phosphate
-excess atp is used to synthesize(make) energy-rich creatine phosphate
-creatine phosphate transfers its high energy phosphate group to ADP to rapidly regenerate new ATP
-pre-existing creatine phosphate and ATP provide enough energy for contraction for about 15 seconds during moderate exersice

28
Q

Glycolisis: Anaerobic(means without oxygen) Respiration
(aka fermentation) breakdown of glycogen

A

*series of ATP producing reactions that do not require oxygen and that continues after oxygen within muscle fibers is depleted
*glucose is used to generate ATP when the supply of creatine phosphate is depleted
*glucose is derived from the blood and from glycogen stored in muscle fibers
*glycolysis breaks down glucose into molecules of pyruvic acid and produces two molecules of ATP in the process
*if suuficient oxygen is present, pyruvic acid formed by glycolises enters aerobic respiration pathways as acetyl CoA, producing relatively large amount of ATP
*if oxygen levels are low, anaerobic reactions convert pyruvic acid to lactid acid,which is carried by the blood
*anaerobic respiration can provide enough energy for 30 to 40 seconds of moderate exercise. Ex. a short race

29
Q

Aerobic Respiration

A

*moderate physical activity that lasts longer than about half a minute depends on aerobic respiration
*pyruvic acid entering the mitochondria , when completely oxidized, generates
-ATP
-Carbon Dioxide
-Water
-Heat
*muscle tissue has two sources of oxygen:
1) oxygen from hemoglobin in the blood
2) oxygen released by myoglobin in the musce cell
*myoglobin and hemoglobin are oxygen bonding proteins
* aerobic exercises supplies ATP for prolonged activity
* aerobic repiration provides more than 90% of the needed ATP in activities lasting more than 10 minutes. Ex: a marathon

30
Q

Muscle Fatigue

A

*muscle fatigue-inability to maintain force of contraction after prolonged physical activity or short-duration strenous activity due to diminished atp
*factors that contribute to muscle fatigue:
-inadequate release of calcium ions from the SR
depletion of creatin phosphate
-insufficient oxygen within the muscle fibers
depletion of glycogen and other nutrients(“hitting the wall” in long distance race)
buildup of lactic acid and ADP
-failure of motor neuron to release enough acetylcholine

31
Q

Oxygen Consumption after exercise
(EPOC)

A

*after strenous exercise heavy breathing and elevated heart rate continue and oxygen consumption remains above resting level
*oxygen debt(excessive post-exercise exygen consumption: EPOC)
-oxygen debt is the added oxygen taken into the body after exercise

*this added oxygen is used to restore muscle cells to the resting level in three ways
1) to convert lactic acid into oxygen
2) to re-synthesize creatine phosphate and ATP
3) to replace the oxygen removed from myoglobin

32
Q

Control of Muscle Tension Motor Units

A

*consist of a motor neuron and the muscle fibers it stimulates
*the axon of a motor neuron branches out,forming neuromuscular junctions with different muscle fibers
*a motor neuron makes contact with about 150 muscle fibers

33
Q

Control of Muscle Tension (Force)

A

*control of fine (precise) movements require many small motor units
-muscle that control voice production have 2-3 muscle fibers per motor unit
-muscle fibers controlling motor units have 10-20 muscle fibers per motor unit
-by contrast, muscles in the arm and the leg which produce gross movements,have 2000-3000 muscle fibers per motor unit

34
Q

Control of Muscle Tension

A

*the total strength of a contraction depends on the size of the motor units and the number that are activated at any given time
*the graded principle (recruitment) : the greater the stimulus strength, the more motor units will be bought into simoltaneous contraction. (this applies to a whole muscle; motor unit is all-or-none)

35
Q

Twitch Contraction

A
  • a twitch is a brief contraction of the muscle fibers in a motor unit in response to an action potential. The least voltage required to elicit a contraction is the threshold stimulus
    *** twitches last from 20-200 msec
  • Most are in the 100-200 msec range**
36
Q

Latent Period(2 msec), Contraction Period (10-100 msec)

A

*latent period-brief delay between the stimulus and muscular contraction
-during the latent period the action potential sweeps over the sarcolemma and down the t-tubules. result is Ca++ is released from the SR
*contraction period(10-200 msec)
-Ca++ bings to troponon
-myosin binding sites on actin are exposed
crossbridges form and sarcomeres shorten
-muscle fibers that move the eyes have contraction periods lasting 10 msec
-muscle fibers that move lower limbs have contraction periods lasting 100 msec

37
Q

Relaxation Period and Refractory Period

A

*relaxation period (10-100 msec)
-Ca++ is transported back into the SR
-myosin binding sights are covered with tropomyosin
-mysoin heads detach from actin and sarcomere lenghthens
*refractory period- when a muscle fiber contracts, it temporarely cannot respond to another action potential (toilet flush analogy)
-skeletal muscle fibers have a refractory period of <5 milliseconds, allowing 100 contractions-sec
-cardiac muscle has a refractory period of 250-300 milliseconds, allowing - 75 contractions/ min

38
Q

Summation of Contraction

A

● If a second stimulus is applied to a muscle before it has completed its
contraction-relaxation cycle, a second, stronger contraction will occur. This
adding together of twitches is known as summation of contraction or
wave summation.
● When the muscle is stimulated so often that the relaxation period is
interrupted, it results in incomplete summation, or when sustained,
incomplete tetanic contraction (incomplete or unfused tetanus).
● When the muscle is stimulated so often that the contraction period is
interrupted, it results in complete summation, or when sustained,
complete tetanic contraction (complete or fused tetanus).
● This is the norm in skeletal muscle physiology. Stimulus frequencies that
produce complete tetanus are on the order of 100 per sec.

39
Q

Control of Muscle Tension
Muscle Tone

A

● Muscle Tone
● Muscle tone is continuous, involuntary tension in the muscle due
to a small number of active motor units. Contractile force is
relatively weak.
● Small groups of motor units are alternatively active and inactive in
a constantly shifting pattern to sustain muscle tone. This is
explained by asynchronous volleys of motor neuron impulses.
● Muscle tone keeps skeletal muscles firm with no voluntary effort.
● Muscle tone maintains posture: postural muscle tone.
Example: While sitting, the head is kept from slumping forward
on the chest. (During sleep, the number of active motor units is reduced and muscle tone is diminished.

40
Q

Types of Contractions
Isotonic and Isometric

A

* Isotonic contraction
- The tension developed remains constant while the muscle changes its length.
- Used for body movements and for moving objects
Example: Picking a book off a table
** Isometric contraction**
-The tension generated is not enough for the object to be moved and the muscle does not change its length.
Ex. Holding a book steady using an outstretched
arm

41
Q

Aging and Muscular Tissues

A

*aging
-brings a progrssive loss of skeletal mass
-a decrease in maximal strength
-a slowing of muscle reflexes
-a loss of flexibility
* aerobic activities and strength training can slow the decline in muscular performance

A&P 1 (4 decks)

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