Muscular Tissue Flashcards
Properties of Muscular Tissue
- 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
Functions of Muscular Tissue
- producing body movments
walking and running; talking and writing - stabilizing body positions (posture)
- Moving substances within the body
* heart muscle pumping blood
* moving substances in digestive tract - Generating Heat
* contracting muscle; especially skeletal muscle,prodices heat
* shivering increases heat production
Skeletal Muscle Tissue
- 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
Smooth Muscle Tissue
- 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
Cardiac Muscle Tissue
- 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
Skeletal Muscle Tissue: Connective Tissue Components
(fascia,epimysium,perimysium,endomysium,tendon,aponeurosis)
*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
Skeletal Muscle Tissue-Nerve and Blood Supply
*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
Skeletal Muscle Tissue: microscopic anatomy facts (hypertrophy, satellite cells)
*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
Skeletal Muscle Tissue
Microscopic Anatomy
(Sarcolemma, Transverse (T) Tubules, Sarcoplasm)
*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
Skeletal Muscle Tissue
Microscopic Anatomy
(Myofibrils, Sarcoplasmic Reticulum(SR), Filaments, Sarcomeres
*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
-
Myofibril
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
Sarcomere
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.
Myofilaments
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.
Muscle Proteins
(3 proteins that make up Myofibrils)
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
Contractile Proteins (Myosin)
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
Contractile Proteins
(Actin)
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.
The Sliding Filament Mechanism
● 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.
The Contraction Cycle
● 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.
Contraction Cycle 4 steps
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.
Contraction and Relaxation of skeletal muscle
● 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.
Contraction and Relaxation of Skeletal Muscle: Review of Major Terms(The Motor Unit,Neuromuscular Junction, Synaptic Cleft)
- 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.
Contraction and Relaxation of Skeletal
Muscle: Review of Major Terms (Neurotransmitter, Synaptic Vesicles, Motor End Plate)
● 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.
Contraction and Relaxation of Skeletal
Muscle
● 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).
Botulinum toxin
● 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
Curare & Anticholinesterase (AChE)
*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.
Production of ATP in muscle fibers
*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
Creatine Phosphate
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
Glycolisis: Anaerobic(means without oxygen) Respiration
(aka fermentation) breakdown of glycogen
*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
Aerobic Respiration
*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
Muscle Fatigue
*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
Oxygen Consumption after exercise
(EPOC)
*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
Control of Muscle Tension Motor Units
*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
Control of Muscle Tension (Force)
*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
Control of Muscle Tension
*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)
Twitch Contraction
- 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**
Latent Period(2 msec), Contraction Period (10-100 msec)
*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
Relaxation Period and Refractory Period
*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
Summation of Contraction
● 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.
Control of Muscle Tension
Muscle Tone
● 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.
Types of Contractions
Isotonic and Isometric
* 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
Aging and Muscular Tissues
*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
