Module 3: Muscular System Flashcards
Muscular System Functions
- Movement
- Maintain posture
- Stabilize Joints
- Production of body heat
- Respiration and Heart Beat
- Communication
- Contraction of organs and vessels
Properties of Muscles
Contractility
Excitability
Extensibility
Elasticity
the ability of muscle to shorten forcefully, or contract
Contractility
the capacity of muscle to respond to a stimulus
Excitability
the ability to be stretched beyond it normal resting length and still be able to contract
Extensibility
the ability of the muscle to recoil to its original resting length after it has been stretched
Elasticity
Types of Muscles
Skeletal
Cardiac
Smooth
*attached to bones
*striated
*voluntarily controlled
Skeletal
*located in the heart
*striated
*involuntarily controlled
Cardiac
*Located in blood vessels, hollow organs
*Non-striated; visceral
*involuntarily controlled
Smooth
Each skeletal muscle is surrounded by a connective tissue sheath called the _____________.
epimysium
A skeletal muscle is subdivided into groups of muscle cells termed __________
fascicles
Each fascicle is surrounded by a connective tissue covering, termed the _____________.
perimysium
Each skeletal muscle cell (fiber) is surrounded by a connective tissue covering, termed the ______________.
endomysium
is a single cylindrical cell, with several nuclei located at its periphery.
Muscle fiber
Muscle fibers range in length _____ to _____ and are generally ______ in diameter.
1 cm ; 30 cm ; 0.15 mm
Skeletal muscle fibers contain several ______ that are located at the ____________________.
nuclei ; periphery of the fiber
The _______________ (cell membrane) has many tubelike inward folds, called ________________, or ______________.
sarcolemma ; transverse tubules ; T tubules.
T tubules occur at _______________ along the _____________ and extend into the __________________________.
regular intervals ; muscle fiber ; center of the muscle fiber
The T tubules are associated with enlarged portions of the smooth endoplasmic reticulum called the ____________________.
sarcoplasmic reticulum
The enlarged portions are called _____________.
terminal cisternae
T tubules connect the ______________ to the ____________________ to form a _______________.
sarcolemma ; terminal cisternae ; muscle triad
The sarcoplasmic reticulum has a relatively high concentration of _________ , which plays a major role in __________________.
Ca2 + ; muscle contraction
The cytoplasm of a muscle fiber is called the ______________, which contains many bundles of protein filaments.
sarcoplasm
Bundles of protein filaments are called __________.
myofibrils
Myofibrils consist of the:
myofilaments
actin
myosin
A __________consists of hundreds to thousands of muscle cells, plus connective tissue wrappings, blood vessels, and nerve fibers.
Muscle (organ)
Muscle is covered externally by the ___________
epimysium
A _______ is a discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath.
Fascicle (a portion of the muscle)
Fascicle is surrounded by _____________
perimysium
A _____________ is an elongated multinucleate cell; it has a banded (striated) appearance.
Muscle fiber
Muscle fiber is surrounded by ____________
endomysium
___________ are rodlike contractile elements that occupy most of the muscle cell volume. Composed of sarcomeres arranged end to end, they appear banded, and bands of adjacent myofibrils are aligned.
Myofibril (complex organelle composed of bundles of myofilaments)
A ____________ is the contractile unit, composed of myofilaments made up of contractile proteins.
Sarcomere (a segment of a myofibril)
Thin (_____) filament Thick (_______) filament
actin ; myosin
Contractile myofilaments are of two types- thick and thin.
Myofilament, or filament (extended macromolecular structure)
__________________ contain bundled myosin molecules
Thick filaments
_______________ contain actin molecules (plus other proteins).
Thin filaments
The sliding of the thin filaments past the thick filaments produces ________________. Elastic filaments provide elastic recoil when tension is released and help maintain _____________ organization.
muscle shortening ; myofilament
The _____________ is the basic structural and functional unit of a skeletal muscle because it is the smallest portion of a skeletal muscle capable of contracting.
sarcomere
_________ form a network of protein fibers that both serve as an anchor for actin myofilaments and separate one sarcomere from the next.
Z disks
A sarcomere extends from one ______ to the next _______.
Z disk ; Z disk
Light bands, consist only of actin, and are called _________ that extends toward the center of the sarcomere to the ends of the myosin myofilaments.
I bands
Dark staining bands are called _________, that extend the length of the myosin myofilaments.
A bands
Actin and myosin myofilaments overlap for some distance on both ends of the ________; this overlap causes the ___________.
A band ; contraction
Actin myofilaments are made up of three components:
actin
troponin
tropomyosin
________ is a protein that forms the structural framework of muscle fibers. It is involved in the sliding filament theory of muscle contraction, where _____ filaments slide past myosin filaments, leading to muscle contraction.
Actin ; Actin
is a complex of three protein subunits
Troponin
Three protein subunits of Troponin
Troponin C
Troponin I
Troponin T
___________ molecules have binding sites for Ca2 +
Troponin C
__________ is located on the actin filament and is essential for muscle contraction.
T. Troponin
___________ inhibits the interaction between actin and myosin, preventing contraction in the absence of calcium.
Troponin I
____________ is a long protein strand that is wrapped around actin filaments in muscle cells
Tropomyosin
In a relaxed muscle ___________ filaments block the myosin myofilament binding sites on the actin myofilaments.
Tropomyosin
___________________ resemble bundles of tiny golf clubs.
Myosin myofilaments
Myosin heads have _____ binding sites, ATPase and attachment spots for actin
ATP
The electrical charge difference across the cell membrane of an unstimulated cell is called the ____________________________.
resting membrane potential
Muscle cells (fibers) have a resting membrane potential, but can also perform _________________.
action potentials
The resting membrane potential is due to the inside of the membrane being __________ charged in comparison to the outside of the membrane being ___________ charged.
negatively ; positively
Action potentials are due to the membrane having ______________.
gated channels
The resting membrane potential exists because of:
The concentration of K+ being higher on the inside of the cell membrane and the concentration of Na+ being higher on the outside
The presence of many negatively charged molecules, such as proteins, inside the cell that are too large to exit the cell
The presence of leak protein channels in the membrane that are more permeable to K+ than it is to Na+
____ tends to diffuse into the cell and ___ tends to diffuse out.
Na+ ; K+
In order to maintain the resting membrane potential, the sodium potassium pump recreates the Na+ and K+ ion gradient by pumping _____ out of the cell and ____ into the cell.
Na+ ; K+
Resting membrane potential. Na+ channels (pink) and some, but not all, K+ channels (purple) are ____.
_____ diffuses down its concentration gradient through the open K channels, making the inside (yellow) of the cell membrane ___________ charged compared to the outside.
closed ; K+ ; negatively
To initiate a muscle contraction, the resting membrane potential must be changed to an _____________.
action potential
Changes in the resting membrane potential occur when _____________________________ open.
gated cell membrane channels
In a skeletal muscle fiber, a nerve impulse triggers gated ___ channels to open and ____ diffuses into the cell down its concentration gradient and toward the negative charges inside the cell.
Na+ ; Na+
The entry of Na+ causes the inside of the cell membrane to become more __________ than when the cell is at resting membrane potential.
positive
This increase in positive charge inside the cell membrane is called ______________.
depolarization
If the depolarization changes the membrane potential to a value called ____________, an action potential is triggered.
threshold
An action potential is a _____________ in charge across the cell membrane.
rapid change
_____________ during the action potential is when the inside of the cell membrane becomes more positively charged than the outside of the cell membrane.
Depolarization
Near the end of depolarization, the positive charge causes gated ____ channels to close and gated ____ channels to open.
Na+ ; K+
Opening of gated K+ channels starts _____________ of the cell membrane.
repolarization
____________ is due to the exit of K+ from the cell.
Repolarization
The outward diffusion of _____ returns the cell to its resting membrane conditions and the action potential ends.
K+
In a muscle fiber, an action potential results in ___________+.
muscle contraction
A _____ neuron is a nerve cell stimulates muscle cells.
motor
A ___________________ is a synapse where a the fiber of a nerve connects with a muscle fiber.
neuromuscular junction
A _______ refers to the cell-to-cell junction between a nerve cell and either another nerve cell or an effector cell, such as in a muscle or a gland.
synapse
A _________ is a group of muscle fibers that a motor neuron stimulates.
motor unit
A ______________ is the end of a neuron cell axon fiber.
presynaptic terminal
A ______________ is the space between the presynaptic terminal and postsynaptic membrane.
synaptic cleft
The ________________ is the muscle fiber membrane (sarcolemma).
postsynaptic membrane
A ______________ is a vesicle in the presynaptic terminal that stores and releases neurotransmitter chemicals.
synaptic vesicle
______________ are chemicals that stimulate or inhibit postsynaptic cells.
Neurotransmitters
______________ is the neurotransmitter that stimulates skeletal muscles.
Acetylcholine
Muscle Contraction Cycle 1
An action potential travels down motor neuron to presynaptic terminal causing Ca2+ channels to open.
Ca2+ causes synaptic vesicles to release acetylcholine into synaptic cleft.
Acetylcholine binds to receptor sites on Na+ channels, Na+ channels open, and Na+ rushes into postsynaptic terminal (depolarization).
Muscle Contraction Cycle 2
Na+ causes sarcolemma and t-tubules to increase the permeability of sarcoplasmic reticulum which releases stored calcium.
Ca2+ binds to troponin which is attached to actin.
Ca2+ binding to troponin causes tropomyosin to move exposing attachment sites for myosin.
Myosin heads bind to actin.
Muscle Contraction Cycle 3
ATP is released from myosin heads and heads bend toward center of sarcomere.
Bending forces actin to slide over myosin.
Acetylcholinesterase (enzyme breaks down acetylcholine) is released, Na+ channels close, and muscle contraction stops.
Skeletal Muscle Excitation Cycle 1
- An action potential travels along an axon membrane to a neuromuscular junction.
- Ca2+ channels open and Ca2+ enters the presynaptic terminal.
- Acetylcholine is released from presynaptic vesicles.
Skeletal Muscle Excitation Cycle 2
- Acetylcholine stimulates Na+ channels on the postsynaptic membrane to open.
- Na+ diffuses into the muscle fiber, initiating an action potential that travels along the sarcolemma and T tubule membranes.
- Action potentials in the T tubules cause the sarcoplasmic reticulum to release Ca2+
Skeletal Muscle Excitation Cycle 3
- On the actin, Ca2+ binds to troponin, which moves tropomyosin and exposes myosin attachment sites.
- ATP molecules are broken down to ADP and P, which releases energy needed to move the myosin heads.
- The heads of the myosin myofilaments bend, causing the actin to slide past the myosin. As long as Ca2+ is present, the cycle repeats.
Energy for muscle contractions is supplied by ____
ATP
Energy is released as ATP → ________
ADP + P
ATP is stored in ___________
myosin heads
ATP help form cross-bridge formation between _______ and _____
myosin ; actin
New ATP must bind to _______ before cross-bridge is released
myosin
___________ will occur when a person dies and no ATP is available to release cross-bridges
Rigor mortis
A _____________ is a single contraction of a muscle fiber in response to a stimulus.
muscle twitch
A muscle twitch has three phases:
latent phase,
contraction phase
relaxation phase
The __________ is the time between the application of a stimulus and the beginning of contraction.
latent phase
The _____________is the time during which the muscle contracts
contraction phase
The ___________ is the time during which the muscle relaxes.
relaxation phase
In ___________, individual muscles contract more forcefully.
summation
__________ is a sustained contraction that occurs when the frequency of stimulation is so rapid that no relaxation occurs.
Tetanus
_____________ is the stimulation of several motor units.
Recruitment
Skeletal Muscle Fiber Types
Slow twitch fibers
Fast twitch fibers
contract slowly
fatigue slowly
have a considerable amount of myoglobin
use aerobic respiration
are dark in color
used by long distance runners
Slow twitch fibers
contract quickly
fatigue quickly
use anaerobic respiration
energy from glycogen
light color
used by sprinters
Fast twitch fibers
____________ are very energy-demanding cells whether at rest or during any form of exercise.
Muscle fibers
Energy of Muscle fibers comes from either:
aerobic (with O2) or
anaerobic (without O2) ATP production
ATP is derived from four processes in skeletal muscle.
Aerobic production of ATP during most exercise and normal conditions.
Anaerobic production of ATP during intensive short-term work
Conversion of a molecule called creatine phosphate to ATP
Conversion of two ADP to one ATP and one AMP (adenosine monophosphate) during heavy exercise
Mechanisms of fatigue include:
Acidosis and ATP depletion due to either an increased ATP consumption or a decreased ATP production
Oxidative stress, which is characterized by the buildup of excess reactive oxygen species (ROS; free radicals)
Local inflammatory reactions
There are two types of muscle contractions:
Isometric
Isotonic
The ____________________ has an increase in muscle tension, but no change in length.
isometric contraction
The _____________________ has a change in muscle length with no change in tension.
isotonic contraction
_____________________are isotonic contractions in which muscle tension increases as the muscle shortens.
Concentric contractions
______________ are isotonic contractions in which tension is maintained in a muscle, but the opposing resistance causes the muscle to lengthen.
Eccentric contractions
___________ is the constant tension produced by body muscles over long periods of time.
Muscle tone
____________ is responsible for keeping the back and legs straight, the head in an upright position, and the abdomen from bulging.
Muscle tone
___________ depends on a small percentage of all the motor units in a muscle being stimulated at any point in time, causing their muscle fibers to contract tetanically and out of phase with one another
Muscle tone
_______________ cells are non-striated small, spindle-shaped muscle cells, usually with one nucleus per cell.
Smooth muscle
The _____________ are not organized into sarcomeres.
myofilaments
The cells comprise organs controlled involuntarily, except the _______.
heart
___________________ substances, __________, and other substances can stimulate smooth muscle.
Neurotransmitter ; hormones
______________ cells are long, striated, and branching, with usually only one nucleus per cell.
Cardiac muscle
______________ is striated as a result of the sarcomere arrangement.
Cardiac muscle
Cardiac muscle contraction is __________________.
autorhythmic
Cardiac muscle cells are connected to one another by specialized structures that include desmosomes and gap junctions called ____________
intercalated disks
Cardiac muscle cells function as a ___________ in that action potential in one cardiac muscle cell can stimulate action potentials in ______________.
single unit ; adjacent cells
