Lecture Exam 3 Review Flashcards
What are the functions of muscle tissue?
produce movement, stabilize body position/posture, regulate organ volume, generate heat, propel fluids and food matter through various body systems
What is the scientific study of muscles?
myology
Describe skeletal muscle tissue
moves bones of the skeleton, striated, mainly voluntary, controlled by somatic neurons
Describe cardiac muscle tissue
makes up most of the heart wall, striated, involuntary, autorhythmic, regulated by autonomic neurons and hormones
Describe smooth muscle tissue
located in the walls of hollow internal structures such as blood vessels, airways, and most organs in the abdominopelvic cavity, and in the skin attached to hair follicles, nonstriated, involuntary, autorhythmic in some digestive muscles, regulated by autonomic neurons and hormones
What are the properties of muscle tissue?
electrical excitability, contractility, extensibility, elasticity
What is electrical excitability?
the ability to respond to certain stimuli by producing electrical signals called action potentials
What is contractility?
the ability of muscular tissue to contract forcefully when stimulated by a nerve impulse
What is extensibility?
the ability of muscular tissue to stretch, within limits, without being damaged
What is elasticity?
the ability of muscular tissue to return to its original length and shape after contraction or extension
What are muscle cells called?
myocytes/muscle fibers
How does subcutaneous tissue relate to the muscles?
it separates muscle from skin, is composed of areolar connective tissue and adipose tissue, provides a pathway for nerves, blood vessels, lymphatic vessels to enter and exit muscles
What is fascia?
a dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body
What are the functions of fascia?
holds muscles with similar functions together, allows free movement; carries nerves, blood vessels, and lymphatic vessels; fills spaces between muscles
What are the 3 protective layers of connective tissues in muscles?
epimysium, perimysium, endomysium
What is the epimysium?
outer layer, encircling the entire muscle, dense irregular connective tissue
What is the perimysium?
dense irregular connective tissue, surrounds groups of 10-100+ muscle fibers separating them into fascicles
What is the endomysium?
penetrates the interior of each muscle fascicle and separates individual muscle fibers from one another; mostly reticular fibers
What is a tendon?
attaches a muscle to the periosteum of a bone
What is an aponeurosis?
when connective tissue elements extend as a broad, flat sheet
What is sarcolemma?
plasma membrane of a muscle fiber
What are T tubules?
tiny tube-shaped invaginations of the sarcolemma that tunnel in from the surface toward the center of each muscle fiber, filled with interstitial fluid
What is sarcoplasm?
the cytoplasm of a muscle fiber, includes a lot of glycogen
What is glycogen?
a large molecule composed of many glucose molecules that can be used for ATP synthesis
What is myoglobin?
inside the sarcoplasm, only in muscles, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid, releases oxygen when it is needed by the mitochondria for ATP production
What are myofibrils?
contractile organelles of skeletal muscle
What is the sarcoplasmic reticulum?
fluid-filled system of membranous sacs that encircle each myofibril
What are terminal cisterns?
dilated end sacs of SR that butt against the T tubule from both sides forming a triad; release of Ca2+ from the terminal cisterns triggers a muscle contraction
What are filaments?
smaller protein structures within myofibrils
What are thin filaments composed of?
actin
What are thick filaments composed of?
myosin
What are sarcomeres?
basic functional units of a myofibril
What 3 types of proteins form myofibrils?
contractile, regulatory, structural
What do contractile proteins do?
generate force during contraction; myosin and actin
What do regulatory proteins do?
help switch the contraction process on and off
What do structural proteins do?
keep the thick and thin filaments in the proper alignment, give the myofibrils elasticity and extensibility, and link the myofibrils to the sarcolemma and extracellular matrix
What do motor proteins do?
pull various cellular structures to achieve movement by converting the chemical energy in ATP to the mechanical energy of motion
What 2 binding sites are located on myosin heads?
actin and ATP
What is ATPase?
an enzyme that hydrolyzes ATP to generate energy for muscle contraction
What are Z discs?
narrow, plate-shaped regions of dense material that separate one sarcomere from the next
What is the A band?
dark, middle part of sarcomere that extends the entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments
What is the I band?
lighter, less dense area of sarcomere that contains remainder of thin filaments but no thick filaments; a Z disc passes through center of each I band
What is the H band?
narrow region in center of each A band that contains thick filaments but no thin filaments
What is the M line?
region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere
What is actin?
main component of thin filaments, on each actin molecule is a myosin-binding site where a myosin head can attach
What are the two regulatory proteins in muscles?
troponin and tropomyosin
What is tropomyosin?
a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin
What is troponin?
component of thin filament; when calcium ions binds to troponin, it changes shape, this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds on actin
What is titin?
a structural protein that connects Z disc to M line of sarcomere, thereby helping stabilize thick filament position; it can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils
What is α-actinin?
structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules
What is myomesin?
structural protein that forms M line of sarcomere; binds to titin molecules and connects adjacent thick filaments to one another
What is nebulin?
structural protein that wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development
What is dystrophin?
structural protein that links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons
Define skeletal muscle
organ made up of muscle fascicles that contain muscle fibers, blood vessels and nerves; wrapped in epimysium
Define muscle fascicle
bundle of muscle fibers wrapped in perimysium
Define muscle fiber
long cylindrical cell covered by endomysium and sarcolemma; contains sarcoplasm, myofibrils, many peripherally located nuclei, mitochondria, T tubules, sarcoplasmic reticulum, and terminal cisterns; has a striated appearance
Define myofibril
threadlike contractile elements within sarcoplasm of muscle fiber that extend entire length of fiber; composed of filaments
Define filaments/myofilaments
contractile proteins within myofibrils that are of two types: thick filaments composed of myosin and thin filaments composed of actin, tropomyosin, and troponin; sliding of thin filaments past thick filaments produces muscle shortening
What is the sliding filament mechanism?
the process of skeletal muscle shortening during contraction by thick and thin filaments sliding past one another
What is the contraction cycle?
repeating sequence of events that causes the filaments to slide
What is step 1 of the contraction cycle?
ATP hydrolysis- myosin head hydrolyzes ATP and becomes energized and oriented
What is step 2 of the contraction cycle?
attachment of myosin to actin- myosin head binds to actin, forming a cross-bridge
What is step 3 of the contraction cycle?
power stroke- myosin head pivots, pulling the thin filament past the thick filament toward the center of the sarcomere
What is step 4 of the contraction cycle?
detachment of myosin from actin- as myosin head binds ATP, the cross-bridge detaches from actin
Where is calcium stored?
sarcoplasmic reticulum
What are voltage-gated Ca2+ channels?
located in the T tubule membrane; arranged in tetrads; serve as voltage sensors that trigger the opening of the Ca2+ release channels
What are Ca2+ release channels?
release calcium from the SR for muscle contraction
What is the length-tension relationship?
forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins
What is the neuromuscular junction (NMJ)?
the synapse between a somatic motor neuron and a skeletal muscle fiber; includes all synaptic end bulbs on one side of synaptic cleft, the synaptic cleft, motor end plate of muscle fiber on the other side
synapse
a region where communication occurs between 2 neurons or between a neuron and a target cell
synaptic cleft
a small gap that separates the 2 cells at most synapses
neurotransmitter
chemical messenger that allows the cells to communicate across the gap
axon terminal
end of a motor neuron
synaptic end bulbs
in clusters, neural part of NMJ
synaptic vesicles
membrane-enclosed sacs suspended in the cytosol within each synaptic end bulb, contains thousands of molecules of acetylcholine
acetylcholine (ACh)
neurotransmitter released at the NMJ
motor end plate
region of the sarcolemma opposite the synaptic end bulbs, muscular part of NMJ, contains ACh receptors
acetylcholine receptors
integral transmembrane proteins to which ACh specifically binds, abundant in junctional folds
junctional folds
deep grooves in the motor end plate that provide a large surface area for ACh
what type of channel are ACh receptors?
ligand-gated ion channels
What is step 1 of generating a muscle action potential?
nerve impulse stimulates voltage-gated channels to open and release Ca2+, synaptic vesicles release ACh into the synaptic cleft
What is step 2 of generating a muscle action potential?
ACh binds to the ACh receptor in a junctional fold, ion channel opens which allows Na+ to flow across the membrane
What is step 3 of generating a muscle action potential?
inflow of Na+ makes the inside of the muscle fiber more positively charged, change in membrane potential triggers a muscle action potential which propagates along the sarcolemma into the system of T tubules, SR releases stored Ca2+ into the sarcoplasm and the muscle fiber contracts
What 3 ways can muscle fibers produce ATP?
creatine phosphate, anaerobic glycolysis, and aerobic respiration
How does creatine phosphate produce ATP?
formed from ATP while the muscle is relaxed, transfers a high-energy phosphate group to ADP, forming ATP during muscle contraction
How long does energy produced from creatine phosphate last?
15 seconds
How does anaerobic glycolysis produce ATP?
breakdown of muscle glycogen into glucose and production of pyruvic acid from glucose via glycolysis produce both ATP and lactic acid; because no oxygen is needed, this is an anaerobic pathway
How does aerobic respiration produce ATP?
within the mitochondria, pyruvic acid, fatty acids, and amino acids are used to produce ATP via aerobic respiration, an oxygen-requiring set of reactions
How long does the energy produced from anaerobic glycolysis last?
2 minutes
How long does the energy produced from aerobic respiration last?
several minutes to hours
What two ways does muscle tissue receive oxygen?
diffused from the blood or released from myoglobin
What is muscle fatigue?
the inability of a muscle to maintain force of contraction after prolonged activity
What are some potential causes of muscle fatigue?
inadequate release of calcium ions from SR, depletion of creatine phosphate, insufficient oxygen, depletion of glycogen and other nutrients, buildup of lactic acid and ADP, failure of action potentials in the motor neuron to release enough ACh
What is oxygen debt/recovery oxygen uptake?
added oxygen, over and above, the resting oxygen consumption, that is taken back into the body after exercise
frequency of stimulation
number of nerve impulses per second
motor unit
a somatic motor neuron plus all of the skeletal muscle fibers it stimulates
twitch contraction
the brief contraction of all muscle fibers in a motor unit in response to a single action potential in its motor neuron
myogram
record of a muscle contraction
latent period
brief delay between application of stimulus and the beginning of contraction
What happens during the latent period?
the muscle action potential sweeps over the sarcolemma and Ca2+ is released from the SR
What happens during the contraction period?
Ca2+ binds to troponin, myosin-binding sites on actin are exposed, cross-bridges form, peak tension develops in the muscle fiber
What happens during the relaxation period?
Ca2+ is actively transported back into the SR, myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, tension in muscle fiber decreases
refractory period
a characteristic of all muscle and nerve cells where there is lost excitability
wave summation
stimuli arriving at different times causes larger contractions, second contraction stronger than the first
unfused tetanus
skeletal muscle fiber is stimulated between 20-30 times per second and only partially relaxes between contractions
fused tetanus
skeletal muscle fiber is stimulated between 80-100 times per second and does not relax at all; a sustained contraction in which individual twitches cannot be detected
motor unit recruitment
process in which the number of active motor units increases; weakest motor units recruited first, with progressively stronger motor units added if the task requires more force
muscle tone
a small amount of tautness or tension in the muscle at rest due to weak, involuntary contractions of its motor units
flaccid
state of limpness in which muscle tone is lost
isotonic contraction
the tension developed in the muscle remains almost constant while the muscle changes its length
concentric isotonic conctraction
if the tension generated is great enough to overcome, the resistance of the object to be moved, the muscle shortens and pulls on another structure such as a tendon, to produce movement and reduce the angle at a joint
eccentric isotonic contraction
the tension exerted by the myosin cross-bridges resists movement of a load and slows the lengthening process
isometric contraction
the tension generated is not enough to exceed the resistance of the object to be moved and the muscle does not change in length
mesoderm
what the muscles of the body are derived from
somites
columns of mesoderm that have undergone segmentation into a series of cube-shaped structures
myotome
forms the skeletal muscles of the trunk and limbs
dermatomal mesenchyme
forms the connective tissues including the dermis of the skin and subcutaneous tissue
schlerotome
gives rise to the vertebrae and ribs
intercalated discs
irregular transverse thickenings of the sarcolemma that connect the ends of cardiac muscle fibers to one another
hypertrophy
enlargement of existing cells
hyperplasia
increase in the number of fibers
