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495 Cards in this Set

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Extensions of deep fascia are:
*Epimysium-covers a whole muscle *Perimysium-surrounds fascicles (bundles) of cells ("fibers") *Endomysium- arround individual cells (fibers)
True or False All of the (CT) deep fasia extentions coalesces at the end of the muscle continuous w/ the tendon
TRUE
Tendon
*dense regular CT *attaches muscle to perioseum
Skeletal Muscle Fiber Ultrastructure
*cells are long & thread-like, thus called FIBERS *typically 1-2" long; up to 12"long *only ~100umin diameter *multinucleated- post-miotic *many mitochondria *special terms: sarcoplasm & sacrolemma *sacroplasmis many myofibrils (arranged parallel) -> striated (banded)
Skeletal Muscle Hierachy
Skeletal muscle to fascicles to muscle fibers to myofibrils to myofilaments (filaments) to chain-like proteins (actin & myosin)
Three Types of Filaments
*thin *thick *elastic
True or False Elastic filaments are structural elements.
TRUE
True or False Thin & thick filaments are not involved in contraction.
FALSE
Thick filaments are:
~200 molecules of myosin
Thin filaments are:
actin tropnin tropomyosin
Muscle is a tissue that is specialized to do what?
Generate mechanical force that may or may not result in movement
Muscle has the machinery for what?
Energy transduction
Chemical E. (ATP) is converted to what?
Mechanical E. (force) that may result in movement
3 principle types of muscle
Skeletal, Cardiac, Smooth
What are the major differences in the 3 principle types of muscle?
Morphology (appearance) Method of activation
Describe skeletal muscle
Primarily attached to bone-striated--> alternating patter of light & dark bands-voluntary-->activation is under conscious control
Describe Cardiac Muscle
Muscle tissue of the heart -striated -involuntary-->activation is NOT consciously controlled instead heart initiates its own contraction (beats) (although it can be modified by outside influences)
What is automaticity of cardiac muscle?
Initiates its own contraction (beats)
Describe Smooth Muscle
Lines walls of hollow internal structures -non-striated (smooth) -involuntary
3 characteristics of all muscle
1. Excitable: stimulation produces an electrical impulse (action potential) 2. Contractility: can shorten to generate force 3. Elasticity: can be stretched
What % of total human body mass does skeletal muscle make up?
~40-50%
Skeletal muscle can increase the metabolic rate by how much?
10-15 fold
What do the terminal branches of motor neurons do?
Activate muscle
How do we know that skeletal muscle is highly vascular (what shows us)?
Each muscle cell is surrounded by a few capillaries & Reflects need for O2 and CO2 exchange
Muscle (organs) are make up largely of what?
Skeletal muscle tissue held together by CT.
What is a deep fascia in skeletal muscle tissue?
A fibrous membrane (dense irreg. CT) Covers, supports, & separates muscles Binds muscle but allows movement (normally)
What are the 3 extensions of deep fascia?
Epimysium Perimysium Endomysium
What is the function of the epimysium?
Covers a whole muscle
What is the function of the perimysium?
Surrounds fascicles(bundles) of cells ("fibers")
What is the function of the endomysium?
Surrounds each individual cell (fiber)
What is a fascicle?
Bundles of muscle cells or fibers
What does CT do at the ends of muscles?
Coalesces at the end of the muscle and continues on to form the muscle's tendons
What is a tendon?
Dense regular CT that attaches muscle to the periosteum
What shape do muscle cells take on?
Long and thread-like and thus are called fibers
What is the range of lengths of the muscle fibers found in the human body?
Typically 1-2 inches long but some are up to 12 inches or 1 foot long
What is the average diameter of a muscle fiber?
Usually only about 100 micrometers in diameter
When are muscle cells said to be multinucleated?
Post-mitotic
What amount of mitochondria can be found in skeletal muscle fiber? (none, few, several, many ?)
Many
What does the sarcoplasm of skeletal muscle tissue contain?
Many striated myofibrils arranged in parallel with one another
What is the Hierarchy of skeletal muscle?
Skeletal muscle is comprised of fascicles. Fascicles are comprised of muscle fibers. Muscle fibers are comprised of myofibrils. Myofibrils are comprised of myofilaments. Myofilaments are comprised of chain-like proteins called actin and myosin.
What are the 3 types of filaments of skeletal muscle tissue?
Thin Thick Elastic
What is the function of elastic filaments?
Structural elements
What is the function of thin and thick filaments?
Involved in contraction
What are thick filaments comprised of?
~200 molecules of myosin
What are thin filaments comprised of?
Actin Troponin Tropomyosin Contractile proteins Regulatory proteins
What gives skeletal muscle it's striations?
The pattern of overlapping of the thick and thin filaments
What are the 5 main areas within a myofibril?
A-band I-band H-zone M-line Z-disc (line)
What is the compartments within a myofibril where filaments are arranged called?
Sarcomere
What is a sarcomere?
The area between 2 z-discs which is an individual contractile unit within a striated muscle fiber.
What is a Z-disc in a sarcomere?
Thin area of very dense material (very dark)
What is the A-band in a sarcomere?
The dark area from one end of the thick filaments to the other end including the part of the thin filaments that overlap with the thick filaments
What is the I-band in a sarcomere?
The light area where thin filaments do not overlap (no thick filaments) with the Z-disc in its center. (Thus, an I-band is part of 2 adjacent sarcomeres)
What is the H-zone in a sarcomere?
The center of the A-band that contains only thick filaments. The rest of the A-band is called the "zone of overlap"
What is an M-line in a sarcomere?
The center of the H-zone where proteins connect adjacent thick filaments
What are the 2 elastic filaments of a sarcomere?
Connectin: protein at the Z-disc & Titin: which anchors the thick filaments to the Z-disc
What are the 3 organelles of skeletal muscle tissue?
Mitochondria Sarcoplasmic Reticulum (SR) Transverse Tubules
What is the sarcoplasmic reticulum of skeletal muscle and what is it's function?
SR is the network of cisterns and tubues that surround each myofibril and it releases and take up Ca++ through Ca++ release channels
Where is the sarcoplamic reticulum found in muscle fiber?
Surrounds each myofibril
What is the sarcoplamic reticulum's function?
Releases and takes up Ca++ through release channels for Ca++
What are transverse tubules and what are their functions?
T-tubules are minute channels or invaginations of the sarcolemma that are filled with ECF and they carry the electrical impulse deep to myofibrils in the center of the fiber
What molecules are needed for a muscle contraction?
ATP & Ca++
Myosin molecules have globular portions called what?
Myosin heads
What is the job of the myosin heads?
They attach to actin and using energy they swivel or pivot which creates a sliding movement of thin filaments sliding past thick filaments
What blocks the binding sites of actin from the myosin heads during rest?
Troponin-tropomyosin complex
Muscle contraction: What is Step 1?
An action potential (impulse) results in Ca++ release from SR. Ca++ binds to troponin causing a change in shape of the troponin-tropomyosin complex. This exposed the myosin-binding site on actin.
Muscle contraction: What is Step 2?
Attachment (binding) of the myosin head with actin occurs. This actin-myosin complex is called a cross-bridge.
Muscle contraction: What is Step 3?
When myosin attaches, swiveling (rotation) of the myosin head toward sarcomere's center occurs. This is referred to as the power stroke. Thus, the thick and thin filaments slide past one another.
Muscle contraction: What is Step 4?
During the pivot, myosin heads release ADP and Pi. Another ATP molecule can now bind to the myosin head. ATP binding causes the myosin head to detach from actin.
Muscle contraction: What is Step 5?
ATP is broken down. The myosin head is once again energized and is prepared for another cross-bridge cycle.
How often do the 5 steps of a muscle contraction occur during contraction?
The cycle is repeated over and over during a single muscle contraction.
What does a muscle contraction involve?
Interaction of actin and myosin, which slide past one another. Result--> Sarcomere length decreases and overall muscle shortens.
What is the process of the shortening of a sarcomere?
*Thin filaments slide toward M-line. *Width of I-band decreases. * Distance between 2 Z-lines decreases. *Width of H-zone decreases. *Zone of Overlap increases. *Width of A-band stays constant even under contraction.
What initiates contraction?
Ca++ in sarcoplasm So Regulation involves a change in Ca++.
Where is Ca++ sequestered?
SR
What membrane has active transport pumps?
SR
True/False. Muscles use energy while at rest.
True. At rest Ca++ is sequestered in SR which has active transport pumps.
What is the general mechanism of a muscle contraction?
1. Action potential occurs. 2. Opens Ca++ release channels in SR. 3.Ca++ is released into sarcoplasm. 4. Ca++ binds to troponin in thin filaments. 5.Troponin-tropomyosin complex changes shape. 6. Myosin binding sites on actin is exposed. 7. Actin and myosin interact. 8. Contraction takes place.
What are the 2 process of relaxation from contraction?
Motor neuron action potential ceases. Ca++ is pumped back into SR.
During relaxation from contraction what does the cessation of motor neuron action potential cause?
Ach release stops and Ach left in synaptic cleft if broken down by acetycholinsterase (AchE). Muscle action potential stops. SR Ca++ release channels close.
During relaxation from contraction what is the general process involved with pumping Ca++ back into SR?
Pumps can pump against an extreme (Ca++) gradient. Calsequestrin binds to Ca++ inside SR which reduces free Ca++ in solution. Thus more Ca++ can be pumped into SR.
What is a motor neuron?
Neuron (nerve cell) that activates skeletal muscle fiber. Most activate several muscle fiber simultaneously.
What is a motor unit?
Basic functional unit of skeletal muscle. It is a motor neuron and all of the muscle fibers that it intervates.
What determines extent of control over skeletal muscle?
The number of muscle fibers in the motor unit
How many fibers are in motor unit(s) in eye muscle?
1 fiber per MU. Since eye muscles must function with much greater precision, it contains much more nerve for a given amount of muscle.
How many fibers are in a motor unit of the thigh muscle?
2,000 fibers per MU
What is on way in which force is modulated?
By changing the number of MU's
What happens if muscle contains smaller MU's?
Increment in force is small.
Motor neurons and muscle fibers are not directly connected so the electrical impulse cannot flow from motor neuron to the muscle. What does the body produce to overcome this problem?
A chemical called a neurotransmitter is released from the motor neuron which diffuses across the synaptic cleft and attaches to the muscle fiber surface allowing the electrical signal to initiate the process of contraction.
What is the specialized region in which neurotransmitters are released between the motor neuron and the muscle fiber called?
The synapse
The synapse between the motor neuron and the muscle fiber is called what?
Neuromuscular Junction (NMJ)
Events at the NMJ involve a specialized region of the muscle membrane called what?
Motor Endplate
The motor neuron's axon branches into clusters of what?
Axon terminals
The neuromuscular junction includes what 2 things?
Axon terminals and Motor endplate
What are the basic steps in which an nerve impulse initiates a contraction?
*Nerve impulse travels down the axon. *Impulse arrives at the axon terminal which causes fusion of synaptic vesicles to the cell membrane. *Ach is released. *Ach binds to Ach receptors at motor endplate and triggers electrical impulse in muscle fiber which initiates contraction.
What is a twitch?
Single contraction resulting from a single motor neuron impulse (action potential)
How do motor units contract during each twitch?
MU's contract simultaneously and to the same extent (if conditions do not change)
What is the All-or-none Principle?
All of the fibers in a MU contract "completely" or not at all. (There is no partial contraction)
What is the latent period and how long does it last?
Time for the Ca++ to be released from SR. 2-3 milliseconds.
What is the contraction period and how long does it take to complete?
The actual contraction of the muscle. 10-100ms depending on fiber type.
What is the relaxation period and how long does it last?
The time that Ca++ is being pumped back into the SR. 10-100ms depending on the fiber type.
How are you able to increase force of a muscle contraction?
Recruiting or activating more MU's and Increasing the frequency of stimulation of each MU.
What is the recruitment (activation) of more MU's called?
Multiple motor unit summation
How does multiple motor unit summation work?
At low force levels: small MU's are added. At higher force levels: larger MU's are added.
What happens if a 2nd stimulus is applied to the MU before the muscle has relaxed from the 1st stimulus?
The 2 twitches will summate and have an additive effect on contraction.
What is the increase in muscle contraction that results when stimuli follow in rapid succession called?
Wave (temporal) summation.
Why is the force of a twitch "limited"?
There is enough Ca++ released to allow complete interaction HOWEVER, Ca++ is removed BEFORE force reaches its maximum and the muscle relaxes.
What does the decreasing of the time interval between twitches result in?
Greater summation of twitch force.
What is tetanus?
A condition where stimuli occur at a high enough frequency that they fuse together completely and a smooth sustained contraction is produced and represents the maximum force output of the MU.
Why is there a limit to how fast twitches in muscle can be generated?
Refractory period
What is the refractory period?
After the muscle action potential begins, there is a brief period of time during which no impulse can activate the muscle.
How long is a refractory period?
5 ms
What are voluntary contractions?
Short-term tetanic contractions
What do short-term tetanic contractions involve?
MU's firing asynchronously (not same time). Each MU may be firing at less than fusion frequency. But added together, contraction of the whole muscle is smooth. Thus by sharing work, each one experiences less fatigue.
What is the importance of muscle in terms of its influence on overall body metabolism?
1. There is a lot of it: ~40-50% of body mass on average. 2. Can increase metabolic rate 10-15 fold.
Cardiac output can increase from ~ ____ liters/min at rest to as much as____ liters/min during maximal exercise which is a ____ fold increase.
6, 30, 5
At rest ___% of the total blood flow (cardiac output) goes to _____ ______. During maximal exercise this increases to ___%.
15, skeletal muscle, 85
Skeletal muscle competes with the thermoregulatory system for _____ _____.
blood flow
Pulmonary ventilation increased from ~__ liters/min to ~ ___ liters/min.
5, 150
Muscle activity involves energy transduction from ________ energy into _______ energy with ______ energy as a by-product.
chemical, mechanical, thermal
Where is energy stored in molecules?
chemical bonds
Energy released in pathways of energy metabolism is used to make what?
ATP
Energy pathways involve many what?
chemical reactions
Energy transfer between chemicals in these pathways involves what?
"Coupling" of chemical reactions
Energy releasing reactions are coupled to what kind of other reactions?
energy absorbing reactions
Muscle contractions require ATP for what 2 functions?
Energize the myosin heads and to pump Ca++.
ATP is converted to what?
ADP + Pi + Energy
How much ATP is stored in the muscle?
Very little, thus ATP must be continuously be produced during activity
What are the 3 energy systems?
Phosphagen (ATP-PC) system. Lactic Acid system (anaerobic system). Aerobic system (cellular respiration).
How do the 3 energy systems differ?
Capacity (amount of E.) and Rate of E. release (power).
Describe the phosphagen system
Very simple=Two components: -ATP -Phosphocreatine (PC) or Creatine Phosphate (CP) Coupled reaction.
What system represents the most immediate source of energy for muscle contraction?
Phosphagen system
Where does all energy for muscle contraction ultimately come from?
The breakdown of food molecules
What are the high energy sources of food that are broken down for energy for muscle contraction?
Lipids, CHO (carbohydrates), Proteins, Ethanol.
Describe the lactic acid system
"Glycolysis that proceeds faster than the supply of O2
How many ATP's are produced by the lactic acid system during glycolysis?
2
Describe the process of glycolysis in a diagram
glucose(glycogen)------> several steps-------------> lactic acid + energy = 2 ATP's
Describe (diagram) how aerobic system works
glucose--->CO2+H2O+Energy= 36 ATP's
Describe how the phosphagen system works
PC ------creatine kinase------>creatine
Describe the process of the phosphagen system
Provides a very rapid E supply. Allows for quick powerful movements. Unfortunately, it is only a very limited E source. Provides E for a maximum of only 15 seconds.
When glucose is completely oxidized in the presence of O2, what percent of E is used to make ATP and where does the rest get lost at?
~40% used to make ATP. Rest is lost as heat.
What is NAD+ ?
A coenzyme that transfers electrons (e-) to other reactions as it carries e-'s as H atoms.
NAD+ is essential for what?
For glycolysis to continue
What are the 2 ways in which NAD+ is regenerated?
Electron transport chain and Lactic acid production.
What are the 3 components of the aerobic system (cellular respiration)?
Glycolysis. Krebs cycle (citric acid cycle). Electron transportation (ETC) and oxidation phosporylation.
What is oxidation phosphorylation?
Production of ATP using E from the ETC
How does NADH carry energy?
In the form of electrons
Describe the anaerobic (lactic acid) system
End product is a strong acid which dissociates into lactate(negative ion) and H+ H+ interferes with contraction thus maximal activity can only be supported for 1-2 minutes.
What does lactic acid do?
Allows glycolysis to continue when O2 is limited
Describe the aerobic system
Completely oxidizes glucose (also fats). Supplies much more E (more efficient). Can support muscle activity for unlimited amount of time. Involves dozens of reactions, so unfortunately E is supplied at a slow rate.
What is the definition of work?
Application of force through a distance. W=FxO
What is the definition of power?
Work per unit of time. P=W/T
Describe the efficiency of the phosphagen system
Extremely high power output for very short period with a very limited capacity
Describe the efficiency of the lactic acid system
Moderate power but still limited capacity
Describe the efficiency of the aerobic system
Limited power but unlimited capacity
What are the 2 types of skeletal muscles?
Slow-twitch and Fast-twitch
How is a muscle classified to be either slow-twitch or fast-twitch?
Based on the speed of contraction and relaxation during a single twitch
How do fast and slow twitch differ?
The difference in myosin ATP-ase activity (fast-twitch split ATP more rapidly) and Difference in Ca++ handling.
What are the characteristics of fast-twitch fibers?
Contraction speed = fast; Power output = high; Endurance = low; Aerobic enzymes = low; Anaerobic enzymes = high; Fatigue resistance = low.
What are the characteristics of slow-twitch fibers?
Contraction speed = slow; Power output = low; Endurance = high; Aerobic enzymes = high; Anaerobic enzymes = low; Fatigue resistance = high.
What are some other common names for slow-twitch fibers?
Red muscle, type I, oxidative fibers, fatigue-resistant muscle, tonic.
What are some other common names for fast-twitch fibers?
White muscle, type II, glycolytic fibers, fatigable muscle, phasic.
Can all muscle fibers perform under both aerobic and anaerobic conditions?
Yes
What are slow-twitch fibers better suited for?
Better equipped biochemically and physiologically to work aerobically
What are fast-twitch fibers better suited for?
Anaerobically equipped
In what order are each muscle fiber type activated and why?
Since the motor neuron of slow-twitch fibers is smaller in diameter, it is activated first. Slow motor units tend to have fewer numbers and smaller fibers. Thus, the motor units activated first do not add much force and they are equipped to resist fatigue.
What 6 factors influence muscle force?
1.Muscle environment. 2.Cross-sectional area. 3.Speed of contraction. 4.Muscle length (amount of stretch). 5.Lever system arrangement. 6.Muscle architecture.
How is muscle environment a factor which influences muscle force?
pH, temp., and available O2
How is cross-sectional area a factor which influences muscle force?
Muscle with greater cross-sectional area produce greater force due to more myofibrils in parallel
How is contraction speed a factor which influences muscle force?
Force and speed are inversely related: As speed of movement increases there is less time for cross-bridge formation, thus force must decrease.
How is muscle length a factor which influences muscle force?
Maximal force occurs at an optimal length that represents maximal overlap of actin and myosin
How is the lever system arrangement a factor which influences muscle force?
Most skeletal muscles attach to a limb very close to the point of rotation of the joint. For example: the biceps brachii operates at a 1:7 mechanical disadvantage so to lift 20 lbs. the muscle must generate 140 lbs. of force.
What are the 2 advantages to the lever system arrangement in the human body?
Big displacement (movement) for short amount of muscle shortening. Much faster speed of motion or contraction.
What are the 2 types of skeletal muscle architecture?
Parallel and Pennate
Describe parallel muscle architecture
Muscle fibers are arranged parallel to long axis and thus the line of action of the muscle. Advantage: all of the shortening goes toward movement.
Describe pennate muscle architecture
Muscle fibers are arranged at an angle to the long axis. Advantage: more fibers can be attached, thus more force is possible. Disadvantage: range of movement (shortening) and speed are compromised.
Describe cardiac muscle tissue
Tissue of the heart wall-striated-involuntary
How does cardiac muscle compare to skeletal muscle?
Cardiac: Fibers are much smaller, 1 or 2 central nuclei, Same striations and actin-myosin arrangement, Many more mitochondria.
Describe the structure of cardiac muscle
Fibers branch and form interconnections through intercalated discs. This allows electrical activity to spread from fiber to fiber. Thus, all of the fibers can work together as a pump.
What are the 4 physiological differences between cardiac and skeletal muscle?
1.Cardiac muscle relies almost solely on aerobic system for ATP. 2.Stimulation of cardiac muscles occurs via specialized fibers within the heart. 3.Cardiac muscle twitches last 10 times longer than those in skeletal muscles. 4.Cardiac muscle has a much longer refractory period.
Describe smooth muscle tissue
Tissue of hollow internal organs, Non-striated (smooth), Involuntary.
How does smooth muscle tissue compare to skeletal muscle?
Cells are very large, Each cell has only 1 central nucleus, There are no striations and no myofibrils, Cells are spindle-shaped.
Describe the structure of smooth muscle tissue
Thin and thick filaments are not arranged in an orderly manner. Thus, there are no sarcomeres. There are no Z-lines, instead, filaments attach to dense bodies
What are the 4 physiological differences between smooth and skeletal muscle?
1.Calcium comes mainly from the ECF. SR is very small. 2.The regulatory protein is calmodulin(not troponin). 3.Smooth muscle contracts much more slowly and each contraction lasts much longer. 4.Contraction can be initiated by factors within the muscle such as changes in certain hormones and ions.
Why does smooth muscle contract much more slowly and last much longer?
There are no T-tubules and Much different organization of fibers.
Muscle is a tissue that is specialized to do what?
To generate mechanical force.
What does the mechanical force gererated by muscle result in?
It may or may not result in movement.
Muscle has the machinery for…
energy transduction. Chemicat E. (ATP)-->converted-->Mechanical E. (force) --> may result in movement
Three Princeple Types of Muscle
*Skeletal, *Cardiac, *Smooth
Major Difference of the Muscles:
morphology (appearance), -method of activation.
Skeletal Muscle
*primarily attached to bone ; -striated -> alternating pattern of light & dark bands -voluntary -> activation is under conscious control *makes up ~40-50% of the total body mass *Can increase metabolic rate by 10-15 fold
Cardiac Muscle
*muscle tissue of the heart. -striated. involuntary -> activation is NOT consciously controlled instead automaticity
Define automaticality as referes the cardiac muscle.
Heart initiates its own contraction (beats) (although it can be modified by outside influences)
Smooth Muscle
*walls of hollow internal structures, -non-striated (smooth), -involuntary.
Characteristics of all muscle:
*Excitable: stimulation produces an electrical impulse (action potential) *Contractility: can shorten to generate force *Elasticity: can be stretched
True or False Skeletal muscle accounts for much of overall body metabolism
TRUE
Morphology of Skeletal Muscle
*The terminal branches of motor neurons are present:-these activate muscle; *Highly vascular: -each muscle cell is surrounded by a few capillaries -reflects need for O2 & CO2 exchange *Muscle (organs) are made up largely of skeletal muscle tissue held together by connective tissue
The connective tissue that holds together skeletal muscle tissue is called?
Deep Fascia
Deep Fascia is?
*a fibrous membrane (dense irregular CT) *covers, supports, & seperates muscles *binds muscles but allows mov't (normally)
Extensions of deep fascia are:
*Epimysium-covers a whole muscle *Perimysium-surrounds fascicles (bundles) of cells ("fibers") *Endomysium- arround individual cells (fibers)
True or False All of the (CT) deep fasia extentions coalesces at the end of the muscle continuous w/ the tendon
TRUE
Tendon
*dense regular CT *attaches muscle to perioseum
Skeletal Muscle Fiber Ultrastructure
*cells are long & thread-like, thus called FIBERS *typically 1-2" long; up to 12"long *only ~100umin diameter *multinucleated- post-miotic *many mitochondria *special terms: sarcoplasm & sacrolemma *sacroplasmis many myofibrils (arranged parallel) -> striated (banded)
Skeletal Muscle Hierachy
Skeletal muscle to fascicles to muscle fibers to myofibrils to myofilaments (filaments) to chain-like proteins (actin & myosin)
Three Types of Filaments
*thin *thick *elastic
True or False Elastic filaments are structural elements.
TRUE
True or False Thin & thick filaments are not involved in contraction.
FALSE
Thick filaments are:
~200 molecules of myosin
Thin filaments are:
actin tropnin tropomyosin
Regulatory proteins are:
troponin tropomyosin
Contractile proteins are:
myosin actin
Areas w/in a myofibril:
*A-band *I-band *H-zone M-line *Z-disc (line)
Filaments are arranged into compartments called a:
Sarcomere
A sarcomere is
>an individual contractile unit w/in a striated muscle fiber >area between two z-discs
Z-disc is
thin area of very dense material (very dark)
A-band is
>dark area >from one end of the thick filaments to the other >includes the part of the thin filaments that overlap w/ thick
I-band is
>light area >area where thin filaments do not overlap (no thick) >a Z-disc is in the center (thus, an I-band is part of 2 adjacent sarcomeres)
H-zone is
>center of the A-band >contains only thick filaments >the rest of the A-band is called the "zone of overlap"
M-line is
>center of the H-zone >proteins connect adjacent thick filaments
"zone of overlap" is
the rest of the A-band that doesn't contain the center and the area where only thick filaments are found.
Elastic filaments are:
connectin titin
Connectin is
protein at the Z-disc
Titin
anchors the thick filaments to the Z-disc
Skeletal Muscle Organelles
*Mitochondria *Sarcoplasmic Reticulum *Transverse tubules
Sarcoplasmic Reticulum
> abbreviated SR >network of cisterns & tubules >surround each myofibril >releases & takes up Ca++ - thru Ca++ release channels
Transverse tubules
>(t-tubules; t-tubular system) >minute channels >invaginations of sarcolemna - filled w/ ECF >carry the electrical impulse deep to myofibrils in the center of the fiber
Muscle contraction involves:
>interaction of actin & myosin, which slide past one another. (Myosin is in a thick filament; actin is part of the thim filament.) -> result - sacromere lengths decreases -thus overall, the muscle shortens
When a sacromere shortens:
^thin filaments slide toward the M-line (can actually slide past it) ^the width of the I-band decreases ^the distances between two Z-lines decreases ^the width of the H-zone decreases ^the zone of overlap increases ^the width of the A-band stays the same ^***the length of filaments do not change
True or False the length of filaments shortens with muscle contraction
FALSE
Contraction Regulations
>calcium (Ca2+) in the sarcoplasm initiates contraction >thus, regulation involves a change in [Ca2+]
When a muscle is at rest where is Ca2+ sequestered?
Sarcoplasmic Reticulum
How does the Sarcoplasmic Reticulum move the Ca2+ back into itself?
By the use of active transport pumps. Thus, muscle uses energy even at rest.
Explain how action potential initiates muscle contraction.
action potential (impulse) -> opens Ca2+ release channels in SR -> Ca2+ is released into sarcoplasm -> Ca2+ binds to tropnin in the thin filaments -> troponin-tropomyosin complex changes shape -> myosin binding site on action is exposed -> actin & myosin interact -> contraction
What are the molecules needed for muscle contraction?
*Calcium *ATP
Myosin molecules have globular portions called:
myosin heads
What can myosin heads do?
They can attach to actin & using energy they can swivel (pivot)- this creates a sliding movement (thin filamenets slide past thick filaments).
Actin has a binding site for myosin heads that are blocked at rest by…
the troponin-tropomyosin complex
The steps that make up the sliding filament mechanism are:
*ATP binds to myosin ATPase, an enzyme located on the myosin head. ATP is broken down. ATP<=ADP +Pi+Energy Energy is transferred to the myosin (step 5) *An action potential (impulse) results in Ca++ release from the S.R. Ca++ binds to troponin causing a change in shape of the troponin-tropomyosin complex. This exposes the myosin-binding site on actin (step 1). *Attachment (binding) of the myosin head w/ actin occurs (step 2). This actin-myosin complex is called a cross-bridge (union). * When myosin attaches, swiveling (rotation) of the myosin head toward the center of the sarcomere occurs. This is referred to as the power stroke (step 3). #Thus, the thick & thin filaments slide past one another.# *During the pivot, the myosin heads release ADP & pi. Another ATP molecule can now bind to the myosin head. #ATP binding causes the myosin head to detach from actin. (step 4)*ATP is broken down. The myosin head is once again energized & is prepared for another cross-bridge cycle (step 5). ##This cycle is repeated over & over during a single muscle contraction ##.
The two processes involved in relaxation of a contraction
*motor neuron action potential ceases *Ca2+ is pumped back into SR
What is involved in the motor neuron action potential ceasation?
*Ach (acetylcholine) releases stops *Ach in synaptic cleft is broken down. (by acetylcholinesterase- AchE) *muscle action-potential stops *SR Ca2+ release channels close
What is involved in Ca2+ being pumped back into SR??
*pumps can pump against an extreme [Ca2+] gradient. (~400 fold difference b/n inside & outside) *aided by calseqestrin -> binds to Ca2+ inside SR -> this reduces free [Ca2+] in solution. -> #thus, more Ca2+ can be pumped into SR
Neuron (nerve cell) that activates skeletal muscle fiber:
Motor neuron
How many muscle fibers does a motor neuron activate in the skeletal muscle?
Most motor neurons activate several muscle fibers simultaneously
What is a motor unit?
A motor neuron & all of the muscle fibers that it innervates. *Basic functional unit of skeletal muscle.
What is the significance of the # of fibers/M.U.?
*the # of fibers/M.U. determines the extent of control: i.e., eye muscle -> 1 fiber/M.U., thigh muscle -> 2000 fibers/M.U.*since eye muscles must function w greater precision much more nerve is needed for a given amount of muscle.
How is force modulated?
One way it's modulated is by changing the # of M.U., if you add smaller M.U's -> increment in force is small
True or False: Motor neurons & muscle fibers are not directly connected.
TRUE
How is the electrical impulse transferred from the M.N. to the muscle fiber surface?
Sense the electrical impulse cannot flow from M.N to muscle instead a chemical, the neurotransmitter is released from the M.N. which diffuses across small space (synaptic cleft) and attaches to muscle fiber surface.
What is the name of the region where the neurotransmitter attaches to muscle fiber surface?
Synapse
What is the synapse b/n the M.N. & the muscle fiber called?
Neuromuscular junction (NMJ)
What is a motor endplate?
It is a specialized region of muscle membrane where NMJ events occur.
The MJN includes…
axon terminals & the motor endplate. The M.N.'s axon branches into clusters of axon terminals.
In general, what are the steps that occur in a muscle contraction?
*nerve impulse travels down axon *arrives @ axon terminal causes fusion of synaptic vesicles to cell membrane *the neurotransmitter, acetylchlorine (Ach) is released *Ach binds to Ach receptors @ motor endplate **triggers electrical impulse in the muscle fiber which initiates the contraction (positive feedback loop)
Define twitch.
a single contraction resulting from a single motor neuron impulse (action potential).
To what extent does amuscle contract each twitch?
**muscle fibers in a motor unit (MU) contract simultaneously, & to the same extent during each twitch (if conditions do not change).
Define the All-or-None Principle.
All of the fibers in a MU contract "completely" or not at all. (There is no such thing as a partial contraction.)
True or False: A single muscle twitch has three phases.
TRUE
What are the phases in a single muscle twitch?
Latent period (resting phase) Contraction (phase) Relaxation (phase)
How long does a single muscle twitch latent period last?
A time for Ca+ to be released from S.R. (2-3 ms)
How long does a single muscle contraction phase take to occur?
10-100 ms depending on the fiber type
How long does a single muscle relaxation phase take to occur?
10-100 ms depending on the fiber type -> during this time Ca+ is being pumped back into the S.R.
How are you able to increase force of a muscle contraction?
*recruiting (activating) more MU's *increasing the frequency of stimulation of each MU
Recruiting (activating) more MU's is also known as what?.
Multiple Motor Unit Summation
What is multiple motor unit summation?
*@ low force levels: small MU's are added *@ higher force levels: larger MU's are added
How do you increse the frequency of stimulation of each MU?
if a second stimulus is applied to the MU before the muscle has relaxed from the first: THE TWO TWITCHES WILL SUMMATE (have an additive effect).
When two twitches summate they are referred to as:
WAVE (temporal) SUMMATION
Define Wave Summation.
the increase in muscle contraction that results when stimuli follow in rapid succession.
Why is the force of a twitch "limited"?
*there is enough Ca+ released to allow complete interaction. HOWEVER, Ca+ is emoved before force reaches its maximum & the muscle relaxes. *decreasing the time interval b/n twitches results in greater summation of twitch forces.
What is tetanus?
*The more stimuli the more force.If the stimuli occur @ a high enough frequency, the twitches will completely fuse together. *A smooth sustained contraction produced by a series of very rapid stimuli; this represents the maximum force output of the MU.
There is a limit to how fast twitches in muscle can be generated, why?
Refractory period
Define refractory period.
Is a brief period of time after the muscle action potential begins, during which no impulse can activate the muscle (5 ms)
True or False: Most of our muscle contractions are short-term tetanic contractions.
TRUE
Voluntary contractions are…
short-term tetanic contractions
Voluntary contractions involve…
*MU's firing asynchronously (not @ same time) *Each MU may be firing @ less than fusion frequency but, when added together, contraction of the whole muscle is smooth. ** Thus, by sharing the work, each one experiences less fatique.
What is the importance of muscle in terms of its influence on overall body metabolism?
1. there is a lot of it; 40-50% of body mass on average 2. can increase metabolic rate 10- to 15-fold
True or False: Skeletal muscle places large demands on most other systems of the body
TRUE
What body systems does skeletal muscle places large demands on & how?
*Cardiac output increases from ~6 liters/min at rest to as much as 30 liters/min during maximal exercise. (5-fold increase) *At rest 15% of the total blood flow (cardiac output) goes to skeletal muscle. During maximal exercise (whole body exercise) this increases to 85%.*Skeletal muscle competes w/ the thermoregulatory system for blood flow.*Pulmonary ventilation increased from ~5 L/min to ~150 L/min (30-fold increase)
Muscle activity involves energy transduction: What is energy transduction?
Chemical energy -> Mechanical energy
What is a by-product of energy transduction?
Thermal (heat) energy
Where is energy stored?
In chemical bonds of (food) molecules
Energy released in pathways of energy metabolism is used to make what?
ATP
Energy pathways involve many chemical reactions. Energy transfer between chemicals in these pathways involves what?
"coupling" of chemical reactions
Energy releasing reactions are coupled to what?
energy absorbing reactions (i.e., some reactions drive other reactions)
Muscle contraction requires…
ATP
ATP does what in performing muscle contraction?
*energizes the myosin heads (during one twitch the myosin heads will cycle through several notions to move the thin filaments closer to the M-line).*to pump Ca++
What is the formula for the breakdown & regeneration of ATP?
ATP<-->ADP + Pi + Energy
How much ATP is stored in muscle?
Very little, ATP must be continuously produced during activity.
Name 3 Energy Sysytems
*Phosphogen (ATP-PC) System *Lactic Acid System (Anaerobic System)*Aerobic System (Cellular Respiration)
How do these systems differ?
*in capacity (amount of energy)*rate of energy release -> power
What is the phosphagen system?
*very simple *two components
What are the two components of the phosphagen system?
*ATP *Phosphocreatine (PC) [or creatinephosphate (CP)] -> "high-energy phosphates"
What is the formula for the phosphagen system regenerating ATP from ADP?
ADP------------>ATP (coupled reactions) PC---------->creatine
True or False: The Phosphagen System represents the most immediate source of energy for muscle contraction.
TRUE
True or False: All energy for muscle contraction ultimately comes from breakdown of food molecules.
TRUE
What food molecules provide energy for muscle contractions?
*lipids (fats) *CHO (carbohydrates) in the form of glucose *protein *ethanol
What is the formula for glucose breakdown in the presence of oxygen?
Glucose -->CO2 + H2O + Energy
Lactic Acid System
"glyclysis that proceeds faster than the supply of oxygen." (Glycolysis is always anaerobic) glucose --several steps--> lactic acid + energy ~2 ATP
Aerobic System formula
glucose --> CO2 + H2O + Energy ~36 ATP
True or False: The phosphagen system provides a very rapid supply of energy.
TRUE
The Phosphagen System allows for quick powerful movements. Why?
Only involves 2 coupled reactions. Unfortunately, it's a very limited energy source - max. of 15 seconds.
What % of energy is used to make ATP when glucose is completely oxidized?
~40%
What is the formula for glucose breakdown in the presence of oxygen? Explain where the electron loses are and the electron gains occur.
C6H12O6 + 6O2----> 6CO2 + 6H2O + Energy. C6H12O6 (glucose) loses H to make 6CO2. 6O2 gains H to make 6H2O.
What is a NAD+?
It is a (carrier) coenzyme that transfers electrons (e-) to other reactions. It gets reduced during the process of converting glucose in the presence of O2 into CO2,H2O & Energy. ***It carries e- as H atoms. NAD+<--+2H--> NADH
How many e-'s worth of energy does a NADH carry?
two
NAD+ is essential for what?
Glycolysis
How can NAD+ be regenerated?
In 2 ways: 1. electron transport chain 2. lactic acid production
Formula for how the Anaerobic System works
Glucose---(10 steps where NAD is converted to NADH)--> Pyruvic acid---(NADH is converted to NAD)---> Lactic acid
Name the 3 components of the Aerobic System.
*glycolysis *Kreb's cycle (citric acid cycle) *Electron transportation (ETC) & oxidative phosphorylation
Which sysytem produces the most energy Anaerobic or Aerobic?
Aerobic
What is oxidative phosphorylation?
production of ATP using energy from the ETC
What is the end product of the Anaerobic System?
Lactic acid which is a strong acid that dissociates into lactate- & H+ where the H+ interferes w/ contractions.
How long can maximal activity be supported using the Anaerobic System?
1 to 2 minutes
Lactic acid formation does what?
It allows glycolysis to continue when O2 is limited.
Name three things about the Aerobic System where energy production is concerned.
*completely oxidizes glucose (also fats)- supplies much more energy *can support muscle activity for an unlimited amount of time *involves dozens of reactions, so unfortunately energy is supplied at a slower rate.
Factors which influence muscle force: muscle environment
pH, temperature, O2
Factors which influence muscle force: cross-sectional area
muscle w/ greater cross-sectional area produce greater force- more myofibrils in parallel
Factors which influence muscle force: speed of contraction
Force & speed are inversely elated: As speed of movement increases there is less time for cross-bridge formulation; thus, force must decrease.
Factors which influence muscle force: lever system arrangement
Most skeletal muscles attach to the limb very close to the point of rotation of the joint.
What is the ratio of mechanical disadvantage that the biceps brachii operates at?
0.046527778
What is the advantages to the lever system arrangement?
1. Much larger amount of pull out of a shorter contraction. 2. Much faster speed of motion (movement) for given contraction.
Factors which influence muscle force: muscle architecture
*Parallel *Pennate
What is parallel muscle architecture?
muscle fibers are arranged parallel to long axis & thus the line of action of the muscle (e.g., biceps). Advantage: all of the shortening goes toward movement
What is pennate muscle architecture?
muscle fibers are arranged at an angle to the long axis. Advantage: more fibers can be attached, thus more force is possible. Disadvantage: range of movement (shortening) & speed are compromised.
Define energy
capacity to perform work
Define work
application of force thru a distance W=F*D
What is the formula to calculate power?
work/unit of time P=W/T
Name three sources of power.
*Phosphagen *Lactic acid *Aerobic system
Rank Phosphagen, Lactic acid, & Aerobic system by the least to most amounts of power they offer to muscles.
1. Aerobic system: limited power 2. Lactic acid: moderate power 3. Phosphagen: extremely high power output for a very short period
Rank Phosphagen, Lactic acid, & Aerobic system by the least to most amounts of capcity they offer to muscles.
1. Phosphagen (very limited capacity) 2. Lactic acid (limited capacity) 3. Aerobic system (unlimited capacity)
Skeletal muscle fibers are referred to as…
slow-twitch or fast-twitch
How are skeletal muscle fibers classified as slow-twitch & fast-twitch?
>based on the speed of contraction & reaxation during a single twitch >due to difference in myosin ATP-ase activity (fast-twitch split ATP more rapidly) >also differ inCa++ handling
Major characteristics of fast-twich & slow-twitch muscle fibers
Variable Fast-twitch Slow-twitch Contraction speed Fast Slow Power output High Low Endurance Low High Aerobic enzymes Low High Anaerobic enzymes High Low Fatigue resistance Low High
Slow-twitch fibers are also called:
red muscle, type I, oxidative fibers, fatique-resistant muscle, tonic
Fast-twitch fibers are also called:
white muscle, type II, glycolytic fibers, fatigable muscles, phasic
True or False: All muscle fibers can perform under both aerobic & anaerobic conditions.
TRUE
True or False: Slow-twitch are better equipped biochemically & physiologically to work aerobically.
TRUE
True or False: fast-twitch are better equipped biochemically & physiologically to work anaerobically .
TRUE
Which type of fibers is activated first slow- or fast-twitch? Why?
Since the motor neuron of slow-twitch fibers is smaller in diameter, it is activated first.
The motor units activated first do not add much force & they are better equipped to resist fatigue. Why?
Slow motor units tend to have fewer numbers & smaler fibers.
Define cardiac muscle tissue
*Tissue of the heart wall *striated & involuntary
Compare cardiac muscle to skeletal muscle.
>Fibers are much smaller >1 or 2 central nuclei >Same striations & actin-myosin arrangement >Many more mitochondria
What is the structure of cardiac muscle tissue?
Fibers branch & form interconnections through intercalated discs. This allows electrical activity to spread from fiber to fiber. Thus, all of the fibers can work together as a pump.
Physiological differences between cardiac & skeletalmuscle:
1. Cardiac muscle relies almost solely on the aerobic system for ATP. 2. Stimulation of cardiac muscles occurs via specialized fibers w/in the heart. 3. Cardiac muscle twitches last 10 times longer than those in skeletal muscle. Ca stays in the sarcoplasm longer. 4. Cardiac muscle has a much longer refractory period (30ms-cardiac; 2-5ms skeletal)
Why does cardiac muscle have a longer refractory period?
to give the heart time to refill w/ blood
Define smooth muscle tissue
*Muscle tissue of hollow internal organs (e.g., blood vessels, lungs & intestines) *Non-striated (smooth) & involuntary
Compare smoth muscle to skeletal muscle.
>cells are very small >each cell has only one central nucleus >there are no striations & no myofils >cells are spindle-shaped
What is the structure of smooth muscle tissue?
Thin & thick filaments are not arranged in any orderly manner. Thus, there are no sacromeres. There are no z-lines; instead, filaments attach to dense bodies.
Physiological differences between cardiac & skeletalmuscle:
1.Ca comes mainly from the ECF, SR is very small. 2. The regulatory protein is calmodulin (not troponin) 3. smooth muscle contracts much more slowly & each cotraction lasts much longer 4. contraction can be initiated by factors w/in the muscle such as changes in certain hormones & iron
Why are smooth muscle contraction so slow?
>there are no t-tubules (don't get signal into cell quickly) >much different organization
3 Types of Muscle Tissue
Skeletal, Cardiac, Smooth
What is the function of skeletal muscle?
Attaches to bone and causes movement of the body
What are 2 other names often used for skeletal muscle and why?
Striated muscle because of its banding pattern under microscope and Voluntary because muscle contraction can be consciously controlled
Describe Cardiac Muscle
Function: responsible for the rhythmic contraction of the heart. Involuntary: generates its own stimuli to initiate muscle contraction.
Where is smooth muscle found?
Lines the walls of hollow organs. Examples include the walls of blood vessels and the walls of the digestive tract where it serves to advance the movement of substances
Describe Smooth Muscle Contractions
Relatively slow and involuntary
Skeletal muscle consists of what?
Numerous muscle cells called muscle fibers and 3 layers of CT that surround these fibers to form a muscle
Endomysium
The CT that surrounds each muscle fiber (cell level).
Perimysium
CT that encircles a group of muscle fibers forming a fascicle
Epimysium
CT that encircles all the fascicles to form a complete muscle
Tendon
Cordlike extension of the 3 layers (edomysium, perimysium, epimysium) or linings that extend beyond the muscle tissue to connect the muscle to a bone or to other muscles
Aponeurosis
Flat broad extension of the 3 muscle linings and serves same function as a tendon
Describe the deep fascia of muscle tissue.
Surrounds the perimysium and encloses or lines other nearby structures such as blood vessels, nerves, and the body wall
Describe the superficial fascia of muscle tissue.
(Hypodermis or subcutaneous layer) lies immediately below the skin and merges with the deep fascia where the surfaces of the skin meet
Sarcolemma
Another name for the plasma membrane of the muscle cell
What is it that highly invaginates the sarcolemma (plasma membrane) of muscle cells?
Transverse tubules (T-tubules) that permeate the cell
T-tubules or T-tubes
Transverse tubules
Sarcoplasm
Cytoplasm of the muscle cell
Sarcoplasmic Reticulum (SR)
The specialized endoplasmic reticulum of a muscle cell
What does the sarcoplasm of muscle tissue contain?
Calcium is stored in SR
Thin myofibril filaments consist of 2 strands of what?
2 strands of the globular protein called actin
What gives skeletal muscle its striated appearance?
Within a myofibril, actin and myosin filaments are parallel and arranged side by side. The overlapping filaments produce a repeating pattern that appear as bands
Thin filaments of myofibrils consist of 2 strands of actin that are arranged in what fashion?
Double helix
How are actin and myosin filaments arranged within a myofibril?
Parallel and arranged side by side in an overlapping pattern which gives skeletal muscle its striated appearance
Myofibrils consist of 2 types of what?
Filaments. Thick and thin.
What does each myosin filament form at one end?
A protruding head
Name the 2 types of filaments that comprise myofibrils.
Thick filaments and thin filaments
Each myosin filament forms a protruding head at one end. What does an array of myosin filaments possess?
Protruding heads at numerous positions at both ends
Where are the nuclei of striated muscle cells located or found?
Along the periphery of the cell, forming swellings visible through the sarcolemma
What do thick filaments of myofibrils consist of?
Groups of filamentous protein called myosin
What are actin filaments attached to within a sarcomere?
The Z discs on each side of the sarcomere
Nearly the entire volume of a muscle cell is filled with what?
Numerous long myofibrils
What is myosin?
Groups of filamentous protein in the thick filaments of myofibrils
Describe, in short, the location of myosin filaments with their protruding heads within a sarcomere.
They float between the actin, unattached to the Z disc
What is stored in Sarcoplasmic reticulum?
Calcium used for muscle contraction
What is found/located along the length of the double helix of globular protein (actin)?
Troponin and tropomyosin molecules
Each repeating unit of the actin and myosin filaments in skeletal muscle is called what?
A sarcomere
What type of muscle cells are multinucleated?
Striated muscle cells
What do troponin and tropomyosin molecules cover along the actin double helix?
Special binding sites
Each repeating unit of the pattern, called a sarcomere, is separated by a border called what?
Z disc or Z line
What kind of model is used to describe muscle contraction?
Sliding-filament model
What happens when attachment sites on the actin double helix are exposed?
The myosin heads bind to actin to form cross-bridges
When a new ATP molecule attaches to the myosin head and breaks the cross-bridge between the myosin and actin filaments what happens to the myosin head?
Returns to its unattached position
During 1st step of muscle contraction: ATP binds to a myosin head and forms what?
ATP + Pi
What happens after the myosin heads bind to actin forming cross-bridges?
ADP and Pi are released, and sliding motion of actin results
Without the addition of a new ATP molecule, what happens to the cross-bridge?
Remains attached to the actin/myosin filaments
What is a polarity change of a neuron (nerve cell) called?
Action potential
Stimulation of a muscle contraction: what is the 3rd step occurring during a muscle contraction?
Sarcoplasmic reticulum (SR) released Ca++ as a result of the action potential's traveling throughout the T tubules
Refractory period
The time immediately following a stimulus during which the muscle fiber will not respond to a 2nd stimulus
What stimulates a neuron (nerve cell)?
When the polarity across its plasma membrane changes
Stimulation of a muscle contraction: what is the 2nd step during a muscle contraction?
Action potential is generated on the motor end plate and throughout the T tubules.
What 7 factors contribute to the strength and maximum duration of a muscle contraction?
1. Frequency of stimuli 2. Strength of stimulus 3. Length of muscle fiber contraction 4. Type of contraction 5. Muscle fiber type 6. Muscle tone 7. Muscle fatigue
Ca++ binds to the troponin molecule causing what?
Causing tropomyosin to expose positions on the actin filament for the attachment of myosin heads
What are the basic actions of a power stroke?
The pulling of a sarcomere's Z discs towards each other when the myosin head's shape change is stimulated by the release of ADP and Pi when the cross-bridges between actin and myosin form
Ca++ binds to the troponin molecule causing tropomyosin to expose positions on the actin filament for the attachment of myosin heads. What happens next in the sequence?
Cross-bridges between myosin heads and actin filaments form
What causes the cross-bridges between myosin and actin to unbind?
A new ATP molecule attaches to the myosin head
Stimulation of a muscle contraction: what is the 1st step during muscle contraction?
Action potential generates release of acetylcholine (Ach) which diffuses across the synaptic cleft
Relaxation Period
The time during which Ca++ is returned to the SR by active transport
What is a neuromuscular junction?
The specialized synapse (synaptic cleft) of a motor neuron that is specialized for it's function of muscular stimulation
Contraction period
The time during actual muscle contraction
What exposes the binding sites on the actin filaments?
Ca++ (calcium)
When the cross-bridges between myosin and actin cause the release of ADP and Pi, which in turn causes a change in shape of the myosin head, what is generated?
Sliding movement of the actin filament towards the center of the sarcomere
How does Ca++ expose the binding sites of the actin filaments of a sarcomere during muscle contraction?
Ca++ binds to the troponin molecules causing tropomyosin to expose positions on the actin filament for the attachment of myosin heads
When ADP and Pi causes a change in shape of the myosin head and generates a sliding movement of actin towards the sarcomere center, what does the sliding movement cause?
Pulls the 2 Z discs together, effectively contracting the muscle fiber to produce a power stroke
What is the difference between a synapse of a motor neuron and the synapse of other neurons of the body?
Motor neuron's synapse is specialized for motor function and is called a neuromuscular junction
Latent period
The time required for the release of Ca++
What is a motor neuron (MN)?
Any neuron that stimulates a muscle
Myogram
A graph of muscle strength (tension) with time
During 1st step of muscle contraction: What does ATP do?
Binds to a myosin head and forms ATP+Pi
The attachment of cross-bridges between myosin and actin causes what?
The release of ADP and Pi
What causes a corpse to become stiff with rigor mortis?
The cross-bridge between myosin and actin filaments remains intact due to the lack of availability of new ATP molecules. The muscle contracts and does not relax and all of the opposing muscle contractions against each other hold the body in a stiff rigid state.
During 1st step of muscle contraction: ATP binds to a myosin head and forms ATP+Pi which is then converted to what?
ADP and Pi, which remains attached to the myosin head
The release of ADP and Pi causes what?
A change in shape of the myosin head, which generates a sliding movement of the actin towards the center of the sarcomere.
Neurons
Nerve Cells
What separates a neuron from a muscle cell or another neuron?
A very small gap called a synapse or a synaptic cleft
Twitch contraction
A muscle contraction in response to a single nerve action potential
Describe the effects of frequency of stimuli to the quality of a muscle contraction.
If stimuli are repeatedly applied to muscle fiber, Ca++ may not be completely transported back into SR before next stimulus occurs. Depending upon the frequency of stimuli, Ca++ may accumulate. Extra Ca++ results in more power strokes and a stronger contraction.
Stimulation of a muscle contraction: what is the 4th step of a muscle contraction?
Myosin cross-bridges form. Ca++ released by SR binds to troponin molecules on the actin helix prompting tropomyosin molecules to expose binding sites for myosin cross-bridge formation. If ATP is available, the physical contraction begins
How does the polarity (action potential) travel in/on a neuron?
Along the neuron from one end down the neuron until it reaches the end at the synaptic cleft
If each successive stimulus occurs after the relaxation period of the previous stimulus, what effect is produced?
Staircase effect or treppe
Describe how incomplete (unfused) tetanus occurs.
When frequency of stimuli increases, successive muscle contractions begin to blend, almost appearing as a single large contraction
Does the movement between myosin cross-bridges and actin imply that shortening of the muscle actually occurs? Why or why not?
No, as a result there are 2 kinds of muscle contractions defined: 1. Isotonic contractions 2. Isometric contractions
What is the function of muscle tone or firmness in muscle tissue?
To maintain body posture and increase muscle readiness
What occurs if consecutive stimuli are applied during the relaxation period of each preceding contraction?
Wave (temporal) summation effect
Muscle contraction implies that movement occurs where within it's structure?
Between myosin cross-bridges and actin filaments
What is muscle tone or muscle firmness?
In any relaxed skeletal muscle, a small number of contractions continuously occur. Observed as firmness in a muscle, these contractions maintain body posture and increase muscle readiness
Why or how do muscle contractions intensify?
More motor neurons stimulate more muscle fibers
Define isotonic contraction
Occurs when muscles change length during a contraction. Like picking up an object.
What is lactic acid?
Byproduct of ATP production in the absence of O2
Describe how/when complete (fused) tetanus occurs.
Frequency of stimuli increase still further than in incomplete (unfused) tetanus. In this case, individual muscle contractions completely fuse to produce one large muscle contraction
What are the 2 types of skeletal muscle contractions?
Isotonic and Isometric contractions
What 3 factors contribute to muscle fatigue?
1. Lack of O2 and glycogen 2. Accumulation of Lactic Acid 3. Lack of available ATP
What is responsible for fine motor coordination?
Muscle contractions intensify when more motor neurons stimulate more muscle fibers. This effect (recruitment or multiple motor unit summation) is also responsible for fine motor coordination because by continually varying stimulation of specific muscle fibers, smooth body movements are maintained.
Muscle fibers are classified into how many groups?
2: Slow (slow twitch) and Fast (fast twitch)
What is recruitment or multiple motor unit summation?
Intensity of a muscle contraction is increased due to more motor neurons stimulating more muscle fibers
Define isometric contraction
Occurs when a force is applied but muscle length does not change during contraction. Like holding an object in midair, force is applied but no movement in muscle length occurs
Muscle contraction is restricted to lengths that are between 60-175 % of length that produces optimal strength. What does this range of muscle length limit?
Limits myosin cross-bridges and actin only to positions where they overlap and thus can generate contraction.
Describe fast fiber (fast twitch) within muscle tissue.
1. Contract rapidly 2. Fatigues rapidly 3. Appear white due to limited blood supply 4. Generate considerable strength 5. Used for short-term explosive type movement
What are the restricted lengths of muscle contraction?
Because muscle is attached to bone, muscle contraction is restricted to lengths that are between 60-175% of the length that will produce optimal strength
Describe a slow fiber (slow twitch) of muscle tissue.
1. Contracts slowly 2. Has high endurance 3. Appear red due to rich blood supply 4. Do not produce much strength 5. Used during long term events (endurance)
What are the important pathways by which ATP is obtained from energy-rich molecules via cellular respiration?
1. Glycolsis 2. Anaerobic respiration 3. Aerobic respiration
What must be available in the muscle fiber for contraction?
ATP
What are the 2 disadvantages of aerobic respiration?
1. Relatively slow 2. Requires O2
What is glycolysis?
Glucose is broken down into pyruvic acid, which generates 2 ATP molecules. Because no O2 is used this is called and anaerobic process.
What are the various sources of ATP for muscle fiber contraction? (4)
1. Within the cell 2. Creatine phosphate 3. Glucose stored in cells 4. Glucose and fatty acids from bloodstream
What is the general process (in steps) of energy production for/during muscle contraction?
1.ATP from creatine phosphate 2. Depletion forces anaerobic resp. to begin and lasts ~30 sec. 3. After ~30 sec. aerobic resp. begins and continues with O2 availability 4. O2 depletion stops aerobic resp. 5. Anaerobic resp. may still support some further contraction 6. Ultimately, lactic acid buildup (anaerobic resp.) and resource depletion (ATP,O2, Glycogen) lead to muscle fatigue and contraction stops.
Describe anaerobic respiration.
Pyruvic acid (from glycolysis) is converted to lactic acid. No ATP is generated and no O2 is required. The importance of this process is that it generates coenzymes necessary for glycolysis to continue. Thus, in the absence of O2, anaerobic respiration is directly responsible for the production of 2 ATP's (during glycolysis)
What is creatine phosphate?
High-energy molecule stored in muscle cells
What is the structure of cardiac muscle?
Although striated, cardiac differs from skeletal in that it is highly branched with cells connected by overlapping projections of the sarcolemma called intercalated discs. Cardiac is also autorhythmic and generates its own action potential, which spreads rapidly throughout tissue by electrical synapses across the gap junctions.
What are 2 advantages of anaerobic respiration?
1. Relatively rapid 2. Requires no O2
How is ATP obtained from creatine phosphate for muscle contraction?
Transfers it's high-energy phosphate group to ADP to form ATP.
What do the intercalated discs of cardiac muscle tissue contain?
Desmosomes and gap junctions
What are 5 disadvantages of anaerobic respiration?
1. Only generates 2 ATP's 2. Lactic acid is produced 3. Most lactic acid diffuses out of cell into bloodstream and is absorbed by liver 4. Some lactic acid remains in muscle fibers contributing to fatigue 5. Liver and muscle fibers must convert lactic acid back to pyruvic acid when O2 becomes available which is said to produce O2 debt
The creatine phosphate in muscle cells is able to generate enough ATP to maintain muscle contraction for about how long?
About 15 seconds
Describe the process of aerobic respiration.
Pyruvic acid (from glycolysis) and fatty acids (from bloodstream) are broken down producing H2O, CO2, and regenerating the coenzymes for glycolysis. A total of 36 ATP's are produced (including 2 from glycolysis). However, O2 is required.
How is ATP derived from glucose stored within muscle fibers?
Through the metabolic process of glycogenolysis where glycogen is broken down to release glucose. ATP is then generated from glucose by cellular respiration.
How many ATP's are produced through aerobic respiration?
36
What metabolic process is responsible for the breakdown of glycogen into glucose for the production of ATP?
Cellular respiration
Advantage of aerobic over anaerobic respiration.
Aerobic generate a large amount (36) ATP's
What is the process of ATP production from glucose and fatty acids from the bloodstream?
When energy requirements are high, glucose from glycogen stored in liver and fatty acids from fat stored in adipose cells and liver are released into bloodstream. Glucose and fatty acids are then absorbed from bloodstream by muscle cells. ATP is then generated from these energy-rich molecules by cellular respiration
Describe the structure of smooth muscle
Does not have striated appearance. Sarcolemma does not form a system of T-tubules. Contraction is controlled and relatively slow. Has thick myosin and thin actin filaments. Possess noncontracting intermediate filaments which attach to dense bodies scattered through sarcoplasm and attached to sarcolemma. During contraction myosin and actin movement is transferred to intermediate fibers which pull on the dense bodies to pull cell together. Dense bodies function similarly to Z discs in striated muscles.
What is a muscle origin?
The muscle end that attaches to the stationary structure, usually bone.
Examples of muscle names classified according to their origin or insertion.
Sternocleidomastoid: Sterno = sternum (origin) Cleido = clavicle (origin) Mastoid = mastoid process of temporal bone (insertion)
In anaerobic respiration ______ ______ accumulates and leads to muscle fatigue.
Lactic acid
What is a muscle insertion?
The muscle end that attaches to the moving structure
Examples of muscle names classified according to its location.
Temporalis: Muscle that covers the temporal bone
True/False. Fast-twitch fibers contract rapidly, fatigue rapidly, and are highly vascularized.
False. Fast-twitch fibers have an almost white appearance due to lack of high vascularization.
What is the belly of the muscle?
The part of the muscle between origin and insertion
Example of muscle names classified according to the shape of the muscle.
Deltoid = Delta = triangle Trapezius = Trapezoid Serratus = Saw-toothed Rhomboideus Major = Rhomboid
Which of the following is true of glycolysis? A. Pyruvic acid is broken down to produce ATP B. Cellular resp. primarily utilized in a 100m dash C. Is the slowest form of cellular resp. D. Produces O2 debt E. O2 is vital for this type of cellular resp.
B. Cellular respiration primarily utilized in a 100m dash
What is a prime mover?
The muscle that is most responsible for the movement
Examples of muscle name classifications according to the direction of the muscle's fibers with respect to the midline of the body.
Rectus = Parallel Transverse = Perpendicular Oblique = At an angle
True/False. In muscle contractions, the length of the muscle is always shortened.
False. Isometric contractions do not shorten muscle fibers.
What is a synergist?
The other muscle(s) that assist the prime mover. Synergists may stabilize nearby bones or refine the movement of a prime mover.
The ____ ____ is the time immediately following a stimulus where the muscle will not respond to a second stimulus.
Refractory period
What is an antagonist?
The muscle that causes a movement opposite to that of the prime mover. If the prime mover raises an arm, then it's antagonist pulls the arm down. Generally attached to the opposite side of the joint to which the prime mover is attached.
What does the muscular system consist of?
Skeletal muscles and their associated CT. It does not include cardiac or smooth muscle. Those types of muscles are associated and classified according to the body systems in which they appear.
Skeletal muscles are often named after what characteristics? (7)
1. # of origins 2. Location of origin/insertion 3. Location of muscle 4. Shape of muscle 5. Direction that muscle fibers lay 6.Size of muscle 7. Action of muscle
What is the function of skeletal muscle?
May attach a bone to another bone (often across a joint) or a bone to another structure, such as skin. When the muscle contracts, one of the structures usually remains stationary, while the other moves.
Example of muscle names classified by their number of origins.
Biceps = Bi = 2 origins Triceps = Tri = 3 origins Quadriceps = Quad = 4 origins
What determines the strength and range of movement of a muscle?
The length of a mucle's fibers
What does the increase in the number of muscle fibers effect?
Increases the strength of muscle contraction .
Describe parallel fascicles
1. Their long axes are parallel to each other 2. Can be flat 3. Can be straplike 4. Can bulge at their bellies and be spindle shaped 5. Fusiform
Describe circular fascicles
Arranged in concentric rings. Muscles with this pattern form sphincter muscles that control the opening and closing of orifices.
Describe pennate fascicles
Short and attach obliquely to a long tendon that extends across the entire muscle. In a unipennate pattern, the muscle resembles 1/2 of a feather (the tendon is represented by the shaft of the feather).
Describe a bipennate muscle
Resembles a complete feather with fascicles attached to both sides of a central tendon.
Describe a multipennate pattern of fascicles
Resembles 3 or more feathers attached at their bases.