Muscles and Muscle Tissue Flashcards
What are the four general functions of the muscular system?
- Producing movement -
* skeletal - responsible for locomotion (movement of the body) and manipulation (movement of body parts)
* cardiac- beating helps blood course through your body
* smooth - maintains blood pressure and propel substances through organs & along the tract - Maintaining posture - skeletal system makes partial muscle contractions to counteract gravity
- Stabilizing joints - when pulling on bones for movement, they strengthen and stabilize the joints of the skeletons.
- Thermogensis (generate heat) - when muscle contracts they generate heat (when you exercise too.)
Classify the three types of muscle tissue (according to location, appearance, and type of nervous system control).
Skeletal - LONGEST MUSCLE CELLS, striated, VOLUNTARY
Cardiac - striated, involuntary, cardiac
Smooth - NONSTRAITED, involuntary, in walls of visceral organs
ex: dilates and constricts pupils , forms arrector pili muscles in hair follicles
Name and describe the four functional characteristics of muscle.
Excitability (responsiveness) - Ability of a cell to receive and respond to a stimulus by changing its membrane potential. (stimulus is usually chemical like a neurotransmitter released by a nerve cell.)
NERVOUS TISSUE IS MOST EXCITABLE
Contractibility - ONLY IN MUSCLES (the ability to forcibly shorten when adequately stimulated)
Extensibility- Ability to extend or stretch (when relaxed) *protective characteristic
Elasticity- The ability of a muscle cell to. recoil and resume its resting length after stretching *protective characteristic
Which of the above properties (#3) is muscle’s most distinguishing, or unique, characteristic?
contractibility
Which of the above properties (#3) are protective?
extensibility, elasticity
Describe the gross anatomy of a muscle, beginning with the myofibrils.
MUSCLE (covered by Epimysium)
- — fascicles (portion of the muscle) (covered by perimysium)
- —- made of…. muscle fibers (covered by endomysium)
- —– made of myofibrils
skeletal muscle also has:
rich nerve and blood supply
Name the CT sheath that surrounds individual muscle fibers. Of what type of CT is this sheath
composed?
endomysium , AREOLAR CT
. Name the CT sheath that surrounds a fascicle. Of what type of CT is this sheath
composed?
perimysium ; dense IR CT
Name the CT sheath that holds multiple fascicles together to create a muscle. Of what type of
CT is this sheath composed?
Epimysium ; dense CT
Describe the difference between indirect and direct muscle attachments
Direct (fleshy attachments) - binds directly to bone ; the epimysium of the muscle is fused to the periosteum or perichondrium
Indirect - Anchors muscle to the CT covering of a bone ; Muscle CT wrapping extends beyond muscle as either a tendon (ropelike) or aponeurosis (sheetlike)
Name and compare the two types of indirect muscle attachments.
tendon (ropelike)
aponeurosis (sheetlike)
Relative to muscle function, can you describe the significance of Sharpey’s fibers (i.e.,
perforating fibers)?
It connected tendons etc to the periosteum of bone
Name and describe the four arrangements of fascicles/fibers within skeletal muscles.
- circular, - arranged in concentric rings (close when contracting)
Ex: orbicularis muscles surrounding the eyes and the mouth
- convergent - its fascicles converge towards a single tendon of insertion (has a triangular tip)
- parallel- the length of the fascicles run parallel to the long axis of the muscle
- pennate - short and attach obliquely to a central tendon that runs the length of the muscle (all shaped differentl but have a blunt point)
What is the advantage of the parallel arrangement of fibers? of the pennate
arrangement? the convergent?
The more parallel the muscle arrangement is, the more the muscle can contract but not very powerful ;
pennate - they have more muscle fibers making them more powerful.
convergent - allow muscles to cover broad surfaces
What benefit is provided by a lever that operates at a mechanical advantage? at a
mechanical disadvantage?
Power levers, a large load is moved only a small distance but the effort required is small if the load is farther from the fulcrum and the fulcrum is closer to the effort then then thats a mechanical disadvantage because the effort has to be greater.
What is the most common class of lever system in the in the body? Where is the fulcrum with respect to the load and effort in this lever system?
The third class lever ; the effort (applied force) is between the load and the fulcrum.
when you flex with a weight and the effort does to your brachial not your antebrachiel or antecubital
What is the function of myoglobin?
stores and transfers O2 from the blood to the mitochondria.
What is the most prevalent chemical compound (by weight) in muscle?
ATP
Describe how the following organelles are modified or adapted for function in skeletal
muscle tissue: nucleus; mitochondria; smooth endoplasmic reticulum.
Nucleus - Involved in regulating protein synthesis
Mitochondria - muscle contracts require a lot of ATP
smooth ER - forms a tubular network around individual myofibrils.
- regulated conc. of intracellular Ca2+ , send Ca2+ to sarcoplasm
What gives skeletal muscle fibers a striated appearance?
the thin and thick filaments overlapping each other
What causes each of the bands, zones, and lines in a myofibril?
LEFT TO RIGHT
Z disc - a single sarcomere extends from one Z to the next; marks the boundary between one sarcomere and the next
— composed of elastic filaments compounds that are made of TITIN (protein) ; they hold thick filaments in place and give them elasticity
I band - light area because its thin filaments only
A band - dark area because thats where the thin and thick filaments over lap
- —- H zone - thick filaments only
- —— M line in H zone (thick filaments linked by accessory proteins)
What is a sarcomere?
the contractile unit compounds of myofilaments
What is the function of the Z disc?
marks the boundary between one sarcomere and the next
Identify the two primary types of myofilaments found in myofibrils.
THICK - made of myosin
-rod like tail with a globular head
THIN - made of actin
- made of blueberry looking G actin made into a line called F actin and held together by regulatory proteins
Describe the structure of a myosin molecule. How are myosin arranged to make up a thick filament?
consists of a rod-like tail with a globular head , to forms a thick filament, the myosin molecules are packed together protrude at the opposite ends of the filament.
Identify the proteins which make up thin filaments.
Actin (small G actins make long F actin strands) , troponin and tropomyosin
Which of the proteins identified above in thin filaments is/are regulatory proteins and their functions?
troponin -attaches to a G protein (hold tropomyosin over active site ad positions it on actin)
- binds calcium ions
tropomyosin - reshaped protein
- polypeptide strands
- helps stiffen and stabilize
- prevents tick filament from binding to thin ones
Describe the structure of an actin molecule. How are individual actin monomers
arranged to make up a thin filament?
G actin - blueberry looking come together to form F actin that if held by tropomyosin and troponin attaches to the active site in the G actin
Which protein covers the active sites on the actin filament in a resting muscle fiber?
troponin
Describe the location of the sarcoplasmic reticulum (SR) with respect to the myofibrils.
It forms a tubular network around individual myofibrils
What is the function of the SR and the terminal cisternae?
regulate muscle contraction (intracellular levels of ionic calcium) ; it stores calcium and releases it on demand when the muscle fiber is stimulated to contract
What is the significance of the Ca2+-release channels and the Ca2+ active transport pumps
in the SR?
sends calcium to the sarcoplasm
What are the T tubules? Where are they located?
(transverse)-tunnel ;
tunnel-like invaginations (cavity or pouch) of the sarcolemma
at each A band-I band junction
What is the function of the T tubules?
They conduct impulses to the deepest regions of the muscle cell and every sarcomere.
These impulses trigger the release of calcium from the adjacent terminal cisterns.
Its like a messaging system that makes sure every myofibril contracts at the same time
Why is the triad of functional significance?
it is made of 1 T tubule and 2 terminal cisterna
has integral proteins that extend into the inter membrane space and acts as voltage sensors
proteins are also receptor that regulate the release of calcium from the SR
What causes Ca2+ to be released from the terminal cisternae?
action potential (electrical impulses that send signals around your body)
triggers voltage sensors
Muscle contraction is currently best described by the sliding filament theory. Why is this
name appropriate for the contraction process?
During contraction, the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree
What happens to the A band, I band, H zone, and Z discs during contraction? to
sarcomere length?
A band - doesn’t change its length because thick filaments determine its length.
I band - shortens
H zone- disappears because thats the space outside the m line, if the filaments pull in, it disappears.
Z Discis- distance between the two discs shorten
What is the role of Ca2+ and the regulatory proteins in the sliding filament mechanism?
calcium levels have to be elevated so that the nervous system can stimulate the muscle fibers (send nerve impulses/ action potential) , calcium binds to troponin changing the shape of tropomyosin and exposing the actin sites that myosin attaches to for muscle contraction.
Specifically, how do troponin and tropomyosin help regulate the contraction process?
Once calcium levels get low, tropomyosin blocks the active sites on actin and troponin pulls tropomyosin off of the active site.
What is the role of ATP and the myosin head in the sliding filament mechanism?
atp causes the myosin head to cock and attach to the actin binding site
At what point in cross bridge cycling does ATP become hydrolyzed, and provide the energy
for activation of the myosin head?
step 4 (reactivation of the myosin head)
At what point (#42) does the power stroke occur?
step 2
When is the (ADP + Pi ) which fueled the power stroke released from the myosin head?
step 2
What causes myosin to detach from actin after the power stroke is completed?
step 3: crossbridge breaks
after ATP attaches to myosin, the link between myosin and actin weakness, and the myosin head detaches
Describe the structure of the neuromuscular junction.
the functional contact between axonal endings of an a-motor neuron and the muscle fiber it innervates
What specializations of the muscle fiber (at the motor end plate) enable it to respond to signals from the motor neuron?
contains many ACh receptors that are on ion-gated channels, acetocyoline (EACh) opens up the gated channels which allows sodium to flow in
What is the synaptic cleft?
Acetylcholinesterase (AChE) - diffuses across it to bind to ion gated Chanels and open them up, allowing sodium to flow out
What is acetylcholine? What role does it play at the neuromuscular junction?
compound in the nervous system ; it opens up the ion channels that let sodium through
Describe the process of signal transmission at the neuromuscular junction (i.e.,
communication of nerve AP to the muscle fiber).
step 1 : the muscle action potential opened up the voltage-sensitive tubules
step 2 : and triggers Ca2+ to flood out of the terminal cisternae (through calsequestrin) and into the sarcoplasm
step 3: calcium binds to troponin causing tropopmysin to change shape and exposes the actin sites for myosin to bind
CROSSBIDGE CYCLING
calcium levels fall and pumps separate it from the sarcoplasm and tropomyosin moves over the actin sites again
What prevents prolonged stimulation of the muscle fiber by acetylcholine (ACh)?
the enzyme acetylcholinesterase (AChE) breaks it down in the synaptic cleft which prevents continued muscle activation in the absence of additional nervous system activation
What two factors permit relaxation?
when calcium falls and actin becomes covered again
Describe the entire process of excitation-contraction coupling, beginning with a nerve
impulse in a motor neuron.
step 1: muscle action potential open ups the T - tubule and
step 2: triggers release of calcium from the terminal Cristina into the sarcoplasm (calsequestrin is bound to the channel calcium leaves through)
step 3: calcium binds to troponin and changes where tropomyosin to move and myosin head binds to the active site
steps 4-5 cross bridge cycling
step 6 : calcium falls so low that tropomyosin moves back to where it was
Identify the ways in which ATP is used to directly power muscle contraction events.
pumps Ca2+ from sarcoplasm to SR, detachment of ADP activates myosin head, ATP attaches to myosin head causing detachment
What is the relationship between the initial length of the sarcomere (or muscle fiber) and the
amount of tension it can produce?
the bulkier the stronger but longer muscles can contract more (not necessarily stronger)
Describe the relative positions of actin and myosin when the muscle is at its optimal length
for strength production.
at rest - the thick and thin filaments overlap slight at the end of the A band
optimal for length production - actions above the myosin head
What happens to force production in a muscle that is in extreme stretch or contraction?
reduces the amount of force (insufficient overlap of the myofilaments)
What is a motor unit?
a single motor neuron and all of the skeletal muscle fibers that it activates
What is a muscle twitch?
response of an isolate muscle or motor unit to a single, brief threshold stimulus
What is the latent period and what is taking place during the latent period?
period of time between stimulation and contraction
nothing is happening
like 2ml
What is taking place during the relaxation period?
contractile force is no longer generated and muscle tension is returning to his resting level (not there yet)
Explain the all-or-none law as it relates to skeletal muscle fibers. explain the all-or-none law as it
relates to motor units.
a single nerve impulse elicits a single contraction event in all of the muscle fibers in the motor unit
motor units vary in size and canoe the tension a muscle produces
(does not apply to to a whole muscle)
What are graded muscle responses? What are the two general ways of producing a graded
muscle response?
sustained contractions at varied intensities
changing the frequency and strength of stimulus
What happens to the strength of contraction when two or more identical stimuli are
delivered to the muscle in rapid succession (i.e., before complete relaxation occurs)? What is
this phenomenon called?
wave summation
What is the difference between unfused tetanus and complete tetanus? How is
complete tetanus achieved in a muscle fiber?
unfused - similar to wave summation where stimulation is is frequent and muscle is not allowed to relax. however, tension reaches its peak and stays consistent ish
complete- stimulation occupes so frequently that relation phase is eliminated ( looks stgnant)
What role does complete tetanus play in voluntary movements?
helps muscle reach maximum tension and sustain contractions
What is recruitment (i.e., multiple motor unit summation)?
controls the force of contraction more precisely. (greater external force is achieved by activating more motor units.)
is delivered by stimuli of increasing voltage calling more muscle fibers into play
What is muscle tone, and why is it important?
sustained , partial contraction in relaxed muscle
helps hold up our bodies when we are sitting and standing (keeps the muscles firm, healthy and ready to respond to stimulus)
What type of tension does a muscle develop when it is acting as an agonist?
concentric (isotonic contraction)
lengthens with tension but once the resistance is overcome , the muscle shortens and the tension remains constant for the rest of contraction
What type of tension is being produced when internal tension is being developed, but no
movement occurs?
isometric contraction
What type of tension is being produced when the overall length of the muscle is
increasing while the muscle is functioning?
eccentric contractions
Name and describe the muscle fiber’s three avenues of ATP production.
slow oxidative (slow twitch) - ENDURANCE TRAINING best suited for maintaining posture, stabilizing bones and joints, running marathons
fast oxidative glycolytic (FOG) fibers (fast twitch fatigue resistant fibers) - contribute during moderate intensity activity (sprinting, walking rapidly)
fast glycolytic fibers (FG) (fast twitch) - RESISTANCE TRAINING
contribute to intense/ powerful movements of short duration (lifting a heavy weight , throwing a ball)
Which of the above sources (#72) of ATP are produced anaerobically? Which are produced
aerobically?
anaerobic - fast glycolytic
aerobic - slow and fast OXIDATIVE
Which of the above sources (#72) provides energy to fuel prolonged, submaximal activity?
fast oxidative
hich of the above sources (#72) provides energy to fuel brief, high-intensity activity?
fast glycolytic fiber
Where is most of the cell’s ATP produced?
mitochondria
What happens to pyruvic acid when there is not enough O2 present to completely hydrolyze it?
it will undergo lactic acid fermentation - becomes lactic acid
What is muscle fatigue?
a state of physiological inability to contract even if the muscle is receiving stimuli
What 4 factors contribute to the onset of muscle fatigue?
- ionic imbalances - as AP is transmitted, potassium is lost which disturbs the membrane potential of muscle cells.
- Also reduces the size of the AP which reduces movement of the voltage-sensitive proteins in the T tubules and reduces 4th amount of calcium released from the SR - increased inorganic phosphate - can interfere with calcium release and with the release of P from myosin and thus creating power strokes
- decreased ATP and increased magnesium - atp binds magnesium to the cell so that when atp drops, mg rise but these can act on voltage sensitive proteins and decrease calcium release
- Decreased glycogen
What is meant by the term excess post-exercise oxygen consumption (EPOC), which was formerly
called “oxygen debt”? What accounts for EPOC?
a muscle returning to its pre-exercise state after vigorously exercising
What 4 factors influence the amount of force that a muscle generates during contraction?
- frequency of stimulation
- number of fibers activated (number of motor units recruited)
- The size of the muscle fibers and muscle recruited
- muscle and sarcomere length at onset of contraction
When does a muscle begin to develop (or exert) external tension?
when tension is exerted against the bone at the muscle attachment site ( if external tension is great enough , the muscle contraction will cause movement)
How does the size of a motor unit influence the strength of contraction and the control of a
movement?
the smaller it is, the easier to recruit and the more motor units = greater external force
Classify each muscle fiber type with respect to its predominant pathway for ATP synthesis, the
amount of myoglobin present, and the activity of its myosin ATPase.
in table
Which fiber type receives the richest blood supply?
slow oxidative
Which fiber type has the fastest contraction speed? the slowest?
fast oxidative an fast glycolic ; slow oxidative
What is the effect of load and recruitment on the duration of a muscle contraction?
Muscle contracts faster when the load is smaller , the higher the recruitment of motor units, the faster and more prolonged the contraction can be
What is the effect of load on the velocity of contraction?
Muscle contracts faster when the load is smaller
What changes are induced in skeletal muscle in response to a program of endurance (i.e.,
“cardio”) exercise training? Which muscle fiber type is most responsive to endurance
training?
more blood flow , slow: speed of contraction , myosin ATPase activity, rate of fatigue, low: glycogen stores, high myoglobin content ; slow oxidative
What changes are induced in skeletal muscle in response to a program of resistance exercise
training? Which muscle fiber types seem to be especially responsive to endurance training?
fast: speed of contraction , myosin ATPase activity, rate of fatigue, low: myoglobin content, high :glycogen store
fast glycolic
Describe the 6 major structural and functional differences between smooth and skeletal muscle.
- smooth muscle fibers are smaller
- smooth has no perimysium or epimysium, just endomysium and centrally locate nucleus
- smooth muscle has a network of dense bodies and intermediate filaments that makes cytoskeleton
- smooth doesnt have neuromuscular junctions (diffuse junctions) have diffuse junction
- gap junctions - no T tubules or terminal cisternae in smooth muscle
(contains cavolae) - thick and thin filaments are not formed into myofibrils or sarcomeres
- thin filaments have tropmysin but not troponin
active sites are always open
What structures anchor smooth muscle fibers and transmit the tension they develop?
dense bodies and intermediate filaments
What are the sources of the sarcoplasmic Ca2+ which triggers smooth muscle
contraction? Which of these is the main source?
the extracellular fluid
Describe the steps of excitation-contraction coupling in smooth muscle.
- draw out*
Identify the regulatory protein in smooth muscle which binds to Ca2+ to activate the
contraction process.
calmodulin - then activated MLCK which helps myosin head binds to tropomyosin / crossbridge cycling
What is the role of myosin light chain kinase (MLCK)?
MLCK phosphorylates the myosin head, activating it and leading to crossbridge formation -
which helps myosin head binds to tropomyosin / crossbridge cycling
Which contracts more quickly –smooth or skeletal muscle? Which is most fatigue-
resistant?
skeletal ; smooth
How is smooth muscle contraction regulated?
neural contraction - through neurotransmitters (norepinephrine)
hormones and local chemical factors that enhance or inhibit calcium (histamine, low ph, excess carbon dioxide)
hormone gastrin stimulates smooth muscle to contract so it can churn foodstuffs more efficiently.
Describe the relationship between resting length and tension development in smooth muscle.
smooth muscle spontaneously contracts when stretched (can move substances along an internal tract , however it only persists briefly before the muscle adapts to the length and relaxes while still being able to contract on demand)
Describe the stress-relaxation response.
allows a hollow organ to fill or expand slowly to accommodate a greater volume without causing contraction that will expel its contents (helps stomachs store their food for long, bladder )
Smooth muscle can be categorized as single-unit smooth muscle (which Marieb calls “unitary
smooth muscle) or multi-unit smooth muscle. Describe the ways in which these two types of
smooth muscle differ.
unitary (visceral muscle) - in the walls of hollow organs except the heart
- cells are arranged in opposing sheets
- filled with a bunch of automatic nerve fibers and often show rhythmic spontaneous action potentials
- are electrically coupled by gap junctions and so contract as a unit (NOT ONLY THEM)
- respond to various chemical stimuli
muli-unit -NO GAP JUNCTIONS , OR SPONTANEOUS DEPOLARIZATIONS
large airways in the lungs and large arteries, arrector pili , internal eye muscles that adjust pupil size and allow the eye to focus
- muscle fibers are independent of each other
- lots of nerve endings that throe a motor unit with a number of muscle fibers
- responds to neural stimulation with graded contractions that involve recruitment
Where is each type of smooth muscle located?
unitary (visceral muscle) - in the walls of hollow organs except the heart
multi- large airways in the lungs and large arteries, arrector pili , internal eye muscles that adjust pupil size and allow the eye to focus
What is the role of gap junctions and pacemaker cells in single-unit smooth muscle?
gap junctions - allow excitation impulses to spread rapidly through the entire sheet
pace maker - set the rhythmic pattern of contraction
Which type of smooth muscle exhibits rhythmicity and self-excitation?
single unit smooth muscle
