Exam 3
Cardiac Muscle Tissue
*found only in the heart *Involuntary *Striated *Is organized into sarcomeres *Are shorter than skeletal muscle fibers *Usually contain only one nucleus *Possess many mitochondria and myoglobin, as ATP is primarily produced through aerobic metabolism *Contain extensively branched muscle cells that are connected to one another at their ends by intercalated discs *It is relatively long action potentials in its fibers, having a sustained depolarization "plateau" *Unlike skeletal muscle, a large percentage of the calcium ions that initiates contraction in cardiac muscles comes from outside the cell rather than from the SR
Fast Oxidative (FO) Fibers
*have fast contractions *primarily use aerobic respiration, but because they may switch to anaerobic respiration, can fatigue more quickly than SO fibers
Hypertrophy
*increase in muscle size (mass)
How does the Skeletal Muscle function?
-Depends on the signaling from the to work properly
Complete Tetanus
-If stimulation frequency is high enough, relaxation phase is completely eliminated -Muscle is in continuous contraction, producing maximum tension
A triad is made of ___ t-tubule(s) and ____ terminal cisterna(e)
1, 2
The following are keywords for a metabolic pathway: 34 ATP, oxygen, Pyruvate enters the Mitochondria. These terms best describe which of the following
Aerobic Respiration
Aerobic respiration produces ______ as a byproduct during ATP production
Carbon dioxide and H20 (water)
The repeating functional units seen on the myofibrils are __________.
Sarcomeres
Myasthenia gravis occurs when which part of our body is attacked by antibodies?
The Neuromuscular Junction
sarcoplasmic reticulum (SR) of Skeletal Muscle
The specialized smooth endoplasmic reticulum that stores, releases, and retrieves calcium ions (CA2+)
Which of the following statements about muscle contraction is FALSE?
When Ca2+ binds to a myosin head, it triggers the formation of a cross-bridge between myosin and actin.
Autorhythmicity
a group of cells that is self-excitable and able to depolarize to threshold and fire action potential on their own
Gated Channels
a protein channel that opens under specific conditions, such as voltage change or physical deformation
Myotube
fusion of many myoblast cells
Atrophy of muscles
loss of structural proteins from muscle fibers
Fast Glycolytic (FG)
muscle fiber that primarily uses anaerobic glycolysis
Unique features of smooth muscles include which of the following?
plasticity
During moderate and peak exertion of skeletal muscles, the body experiences a higher temperature because of which of the following?
the reduction of energy captured by skeletal muscles as ATP during moderate and peak exertion
Given the following: 1. Ca2+ ions are actively transported back into sarcoplasmic reticulum 2. Troponin-tropomyosin complexes move to inhibit cross-bridge formation 3. Muscle fibers lengthen passively These events best describe:
the relaxation phase
Stimulus
the sensory functions of the nervous system register the presence of a change from homeostasis or a particular event in the environment, known as a stimulus
latent period
the time when a twitch does not produce contraction
electrical synapse
there is a direct connection between the 2 cells so that ions can pass directly from one cell to the next
For tropomyosin to be shifted off its position covering the active sites of G actin molecules, calcium ions must bind to which structure?
troponin
A-band (Sarcomere)
* the dark band where thick filaments are found *the area in the center of the sarcomere where thick and thin filaments overlap. *Stay the same during muscle contraction
Muscle fatigue
*A result of intense muscle activity *Occurs when a muscle can no longer contract in response to signals from the nervous system
Fascicle of Skeletal Muscles
*Are the muscle fibers organized into individual bundles in the skeletal muscles
Smooth Muscle Tissue
*Have no striations *Is present in the walls of hollow organs and passageways, in the tracts of the respiratory, urinary, and reproductive systems, in the eyes, and in the skin *The smooth muscle fibers are spindle-shaped and have a single nucleus *The smooth muscle fibers produce their own connective tissue, endomysium *Don't have sarcomeres *Contains actin and myosin contractile proteins and thin and thick filaments *The thin filaments are anchored by dense bodies *Does not contain troponin *Cross-bridge formation is not regulated by the troponin-tropomyosin complex but instead by the regulatory protein calmodulin. *In a smooth muscle fiber, external calcium ions passing through opened calcium channels in the sarcolemma, and additional calcium ions released from SR, bind to calmodulin *Have a smaller diameter *Is involuntary *Contain varicosity (a series of neurotransmitter-filled bulges that release neurotransmitters into the synaptic cleft). *Contain pacesetter cells that can spontaneously trigger action potentials and contractions in the muscle. *Is organized in 2 ways: as single-unit smooth muscle and as multiunit smooth muscle *Can undergo hypertrophy to increase in size *Can also divide to produce more cells, a process called hyperplasia
H-Zone (Sarcomere)
*Middle region of sarcomere that contains only thick filaments *Becomes smaller as the muscle contracts
The Sliding Filament Model of Contraction
*States that during contraction the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree *When signaled by a motor neuron, a skeletal muscle fiber contracts as the thin filaments are pulled and then slide past the thick filaments within the fiber's sarcomeres. *The sliding can only occur when myosin-binding sites on the actin filaments are exposed by a series of steps that begins with calcium ion entry into teh sarcoplasm
Smooth muscle is not found in which of the following organ systems:
*The nervous system Is found in the integumentary, circulatory, cardiovascular, and digestive system
Axons
*a part of a neuron that carries impulses away from the cell body *Transmit action potentials long distances *single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell
Where are skeletal muscles located?
*attached to bones *Located throughout the body at the openings of internal tracts to control the movement of various substances
Z lines/Z-discs (sarcomere)
*boundaries of each sarcomere *where the actin myofilaments are anchored *move toward each other during contraction responsible for striated nature of skeletal and cardiac muscles)
Dendrite
*branches off from the soma (cell body) *are responsible for receiving most of the input from other regions *one of many branchlike processes that extends from the neuron cell body and functions as a contract for incoming signals (synapses) from other neurons or sensory cells
Slow Oxidative (SO) Fibers
*contract relatively slow *use aerobic respiration (oxygen and glucose) to produce ATP
Pacemaker cells
*control heart rate *contractions of the heart are controlled by these specialized cardiac muscle cells
Absolute Refractory Period
*during this phase, another action potential will not start because of the inactivation gate of the voltage-gated Na+ channel. Once that channel is back to its resting conformation (less than -55 mV), a new action potential could be started, but only by a stronger stimulus than the one that initiated the current action potential. This is because of the flow of K+ out of the cell. *time during an action period when another action potential cannot be generated because the voltage-gated Na+ channel is inactivated
Endomysium of Skeletal Muscle
*encloses a single muscle fiber *allows muscle to contract and move powerfully while maintaining its structural integrity *separates muscle from other tissues and organs in the area, allowing the muscle to move independently
Thermoreceptor
*found in the skin of your fingers or toes *a type of sensory receptor that is sensitive to temperature *when you place your hand under the shower, the cell membrane of the thermoreceptors changes its electrical state (voltage)
M-Line (Sarcomere)
*mid-line of sarcomere *the attachment site for thick filaments *stays the same during muscle contraction
Cross-bridge Cycle
*sequence of events between binding of a cross-bridge to actin, its release, and reattachment during muscle contraction *In order for thin filaments to continue to slide past thick filaments during muscle contraction, myosin heads must pull the actin at the binding sites, detach, re-cock, attach to more binding sites, pull, detach, re-cock, etc. This repeated movement is know as the cross-bridge cycle. *Each cycle requires energy
I-Band (Sarcomere)
*the light band between the ends of thick filaments *Contains only thin actin filaments *Shortens during muscle contractions
Atrophy
*where the number of sarcomeres and myofibrils disappear *(of body tissue or an organ) waste away, especially as a result of the degeneration of cells, or become vestigial during evolution.
Resting membrane is approximately ____ mV. Before an action potential can be initiated, a graded potential must reach _________ value.
-70; threshold
Functions of Skeletal Muscle
-Allows for body move -Help stop movement, such as resisting gravity to maintain posture -Prevent excess movement of the bones and joints -Prevents skeletal structure damage or deformation -Contribute to the maintenance of homeostasis by generating body heat -Allow functions such as swallowing, urination, and defecation, to be under voluntary control -Protects internal organs -Supports the weight of the internal organs
Relaxation of a Skeletal Muscle
-Begins when the motor neuron stops releasing its chemical signal (ACh) into the synapse at the NMJ -The muscle fiber will repolarize, which closes the gates in the SR where calcium ions was being released. -ATP-driven pumps will move calcium ions out of the sarcoplasm back into the SR. This results in the "reshielding" of the actin-binding sites on the thin filaments -Without the ability to form cross-bridges between the thin and thick filaments, the muscle fiber loses its tension and relaxes
What are the 2 types of channels of the voltage-gated Na+ channel?
-The activation gate: opens when the membrane potential crosses -50mV *when the threshold is reached, the activate gate opens, allowing sodium ions to rush into the cell. -Inactivation gate: closes after a specific period of time
Thin filaments (actin)
-double strand of actin -troponin -tropomyosin -the thin strands of actin and its troponin-tropomyosin complex projecting from the Z-discs towards the center of the sarcomere
Characteristics of Skeletal Muscle
-striated, voluntary, multinucleated -Include fibers, blood vessels, nerve fibers, and connective tissues -Each skeletal muscle has 3 layers of connective tissue called "mysia" -Each skeletal muscle is wrapped in a dense, irregular connective tissue called the epimysium -Are richly supplied by blood vessels for nourishment, oxygen delivery, and waste removal -Every muscle fiber in a skeletal muscle is supplied by the axon branch of a somatic motor neuron, which signals the fiber to contract -The skeletal muscle cells/muscle fibers are long and cylindrical
List the events of excitation in order:
1-ACh binds to receptors on motor end plate 2-action potentials travel down T-tubules 3-calcium enters the synaptic bulb and triggers release of vesicles 4-depolarization of sarcolemma 5-Na+ ion channels open Answer: 3, 1, 5, 4, 2
Steps of Muscle Contraction (Sliding Filament Theory)
1-Calcium ions bind to troponin so that tropomyosin can slide away from the binding sites on the actin strands. This allows the myosin heads to bind to these exposed binding sites and form-cross bridges 2- The thin filaments are pulled by the myosin heads to slide past the thick filaments toward the center of a sarcomere *Each head can only pull a very short distance before it has reached its limit and must be re-cocked before it can pull again, a step that requires ATP
Skeletal Muscle Contraction
1-The active site on actin is exposed as calcium binds to troponin 2-The myosin head is attracted to actin, and myosin binds actin at its actin-binding site, forming the cross-bridge 3-During the power stroke, ADP and PI are released. This results in the myosin head pivoting toward the center of the sarcomere, after which the attached ADP and phosphate group are released. 4-A new molecule of ATP attaches to the myosin head, causing the cross-bridge to detach 5-The myosin head hydrolyzes ATP to ADP and phosphate, which returns the myosin to the cocked position
When Jennifer looks through the microscope at skeletal and cardiac muscles, she sees striations. What are these striations?
A bands and I bands
Contraction of a muscle fiber
A cross-bridge forms between actin and the myosin heads triggering contraction. As long as Ca++ ions remain in the sarcoplasm to bind to troponin, and as long as ATP is available, the muscle fiber will continue to shorten.
Isotonic Contraction
A muscle contraction where the tension in the muscle stays constant, a load is moved as the length of the muscle changes (shortens). *There are 2 types
Myoblast
A muscle-forming stem cell that migrates to different regions in the body and then fuses to form a syncytium, or myotube
Tropomyosin
A protein that winds around the chains of the actin filament and covers the myosin-binding sites to prevent actin from binding to myosin -Binds to troponin to form a troponin-tropomyosin complex. This prevents the myosin "heads" from binding to the active sites on the actin microfilaments *To initiate muscle contraction, tropomyosin has to expose the myosin-binding site on an actin filament to allow cross-bridge formation between the actin and myosin microfilaments
Twitch
A single action potential from a motor neuron will produce a single contraction in the muscle fibers of its motor unit. This isolated contraction is called a twitch.
Aponeurosis of Skeletal Muscle
A tendon-like sheet
Endomysium
A thin connective tissue layer of collagen and reticular fibers found inside each fascicle *contains the extracellular fluid and nutrients to support the muscle fiber. These nutrient are supplied via blood to the muscle tissue
Axon
A threadlike extension of a neuron that carries nerve impulses away from the cell body. *the fiber that connect a neuron with its target
Which of the following is the dark band seen on myofibrils?
A-band
Name the neurotransmitter that is found in a neuromuscular junction (NMJ)?
Acetycholine
Recruitment
Activation of multiple motor units
Which energy pathway does not require oxygen and can supply ATP for 30-60 seconds during maximum activity?
Anaerobic (glycosis)
Motor End-Plate and Innervation
At the NMJ, the axon terminal releases ACh. The motor end-plate is the location of the ACh-receptors in the muscle fiber in the muscle fiber sarcolemma. When ACh molecules are released, they diffuse across a minute space called the synaptic cleft and bind to the receptors.
Where is the action potential initiated?
At the beginning of the axon. *The action potential is propagated while it goes down the length of the axon because more voltage-gated sodium channels are opened as the depolarization spreads
Relaxation of a Muscle Fiber
Ca++ ions are pumped back into the SR, which causes the tropomyosin to reshield the binding sites on the actin strands. A muscle may also stop contracting when it runs out of ATP and becomes fatigued.
What must bind to troponin in order to expose the active sites on actin?
Calcium ions
If a stimulus is a continuously reapplied to a muscle fiber before each relaxation phase begins, tension will steadily increase in a process known as:
Complete Tetanus
In a twitch, what is the phase in which tension rises to a peak?
Contraction phase
These are all properties of cardiac muscle tissue except:
Correct Answer: Non-striated Other answers: involuntary, autorhythmic, moconucleated
What is the name of the molecule that is involved in immediate, short term ATP production?
Creatine Phosphate
Which of the following is not a phase of a twitch?
Delay
Which phase of an action potential is characterized by the opening of Na+ channels followed by a change in voltage from negative to positive:
Depolarization
Sarcomere
Each packet of the microfilaments (actin and myosin) and their regulatory proteins, troponin and tropomyosin.
Which of the following statements about muscle fatigue and the recovery period is FALSE?
Elevated oxygen demand in muscle tissue stops as soon as exercise activities cease.
After acetylcholine binds to receptors on the motor end plate of the NMJ, it creates a localized depolarization called:
End Plate Potential
Which connective tissue layer wraps the entire muscle?
Epimysium
Which of the following produces ATP from glucose anaerobically?
Glycosis
The part of the sarcomere that contains thick filaments but no thin filaments is the __________.
H-band
Which exercise would be considered Anaerobic and would utilized mostly Type II muscle fibers:
Heavy weightlifting
During _________ of an ATP molecule, energy is released and ADP + Pi is formed.
Hydrolosis
Key point
If a positive charge moves out of a cell, the cell becomes more negative; if a negative charge enters the cell, the same thing happens
During motor unit recruitment, activating more motor units (neurons and their muscle fibers) will cause muscle tension/force to _______.
Increase
Neurons
Individual cells in the nervous system that receive, integrate, and transmit information. *cells and therefore have a soma, or cell body, but they also have extensions of the cell; each extension is generally referred to as a process
Which of the following best describes Cardiac muscle:
Involuntary and Striated
Dense Body
Is analogous to the Z-discs of skeletal and cardiac muscle fibers and is fastened to the sarcolemma.
The Plateau
Is produced by calcium ions entry through voltage-gated calcium channels in the sarcolemma of cardiac muscle fibers
What is the type of contraction in which the muscle does NOT change length and the contraction does NOT produce tension that exceeds the load?
Isometric
Which type of muscle contraction develops muscle tension without a change in length of the muscle?
Isometric
What does the action potential demonstrate?
It demonstrates how changes in the membrane can constitute a signal
What happens to the sarcomere during contraction?
It shortens *The Z lines move closer together *The I band becomes smaller *The A band stays the same width *At full contraction, the thin and thick filaments overlap completely
What happens when a signal reaches the end bulbs?
It triggers the release of neurotransmitters
Latch-bridges in Smooth Muscles
Keep the thick and thin filaments linked together for a prolonged period, and without the need from ATP
This condition would be found within the leg muscle cells of a good sprinter:
Large deposits of glycogen
All the muscle fibers and the single motor neuron that innervates them are called a __________.
Motor unit
Which of the following best describes smooth muscle:
Multiple types of stimuli can cause contraction
We would expect to find smooth muscle in all of the following EXCEPT:
Myocardial tissue
The sarcoplasm (cytoplasm) of Muscle fibers contain large amounts of long proteins called _______. These proteins are can be broken down into smaller contractile proteins called ________.
Myofibrils; Myofilaments
Once the active sites on Actin have been exposed, which protein binds to actin and forms cross bridges?
Myosin
Which of the following is NOT found in a thin filament?
Myosin
Thick filaments (myosin)
Myosin myofilament with heads that bind to actin by reaching up and ratcheting forward *The thick myosin strands and their multiple heads projecting from the center of the sarcomere toward, but not all to way to, the Z-discs
Graded Muscle Response
Normal muscle contraction is more sustained, and it can be modified by input from the nervous system to produce varying amounts of force
Isometric contraction
Occurs as the muscle produces tension without changing the angle of a skeletal joint -Involve sarcomere shortening and increasing muscle tension, but do not move a load, as the force produced cannot overcome the resistance provided by the load -Help maintain posture and maintaining bone and joint stability Example: If one attempts to lift a hand weight that is too heavy, there will be sarcomere activation and shortening to a point, and ever-increasing muscle tension, but no change in the angle of the elbow joint
During resting potential (RMP), Na+ is primarily located ________ and K+ is primarily located __________.
Outside the cell; Inside the cell
Which of the following does NOT happen when the action potential reaches the synaptic terminal?
Potassium ions flood into the intercellular space
Repolarization
Return of the cell to resting state, caused by reentry of potassium into the cell while sodium exits the cell. *the membrane voltage moves back toward the -70mV value of the resting membrane potential *returns the membrane potential to the -70mV value that indicates the resting potential, but it actually overshoots that value.
The distance from one Z line to the next Z line is called the ____ and it ____ during contraction.
Sarcomere, shortens
Type I muscle fibers are ______ compared to Type II; Type I muscle fibers are _____ to fatigue compared to Type II.
Smaller; slower
The binding of ACh to the motor end plate causes a change in membrane permeability to __________.
Sodium
What is the role of acetylcholine in calcium release?
Stimulates cellular contraction by opening voltage-gated ion channels
Action potentials must travel along which structure internal to the sarcolemma to cause the release of calcium ions from the sarcoplasmic reticulum?
T-Tubule
Which structure in a muscle fiber or muscle cell is continuous with the sarcolemma and carries the signal to contract deep into the muscle cells?
T-tubules
Which of the following descriptions of sarcomere components is FALSE?
The I band contains the zone of overlap at its center.
What is the sarcomere bundled within?
The Myofibril that runs the entire length of the muscle fiber and attaches to the sarcolemma at its end
What is the membranous network that surrounds each myofibril?
The Sarcoplasmic Reticulum
What causes the striated appearance of skeletal muscle fibers?
The arrangement of the myofilaments of actin and myosin in sequential order from one end of the muscle fiber to the other
aerobic respiration
The breakdown of glucose or other nutrients in the presence of oxygen to produce carbon dioxide, water, and ATP. *takes place in mitochondria
Fascia of Skeletal Muscle
The connective tissue found between skin and bones
Sarcoplasm of Skeletal Muscle
The cytoplasm of muscle fibers
Axon terminal
The endpoint of a neuron where neurotransmitters are stored *where there are usually several branches extending toward the target cell
How can you get an electrical signal started?
The membrane potential has to change. This starts with a channel opening for sodium ions in the membrane. Because the concentration of sodium ions is higher outside the cell than inside the cell by a factor of 10, ions will rush into the cell that is driven largely by the concentration gradient.
Hyperpolarization
The movement of the membrane potential of a cell away from rest potential in a more negative direction.
Sarcolemma of Skeletal Muscle
The plasma membrane of muscle fibers
membrane potential (Vm)
The potential difference across a cell membrane (always inside relative to outside) *a distribution of charge across the cell membrane, based on the charges of ions *measured in millivolts (mV)
Depolarization
The process during the action potential when sodium is rushing into the cell causing the interior to become more positive. *When a membrane potential of the muscle fiber becomes less negative (closer to zero)
Muscle Fiber Contraction
The sequence of events that result in the contraction of an individual muscle fiber begins with a signal (the neurotransmitter, ACh) from the motor neuron innervating that fiber. The local membrane of the fiber will depolarize as positively charged sodium ions enter, triggering an action potential that spreads to the rest of the membrane will depolarize, including the T-tubules. This triggers the release of calcium ions from storage in the SR. The calcium ions initiate contraction, which is sustained by ATP. As long as calcium ions remain in the sarcoplasm to bind to troponin, which keeps the actin-binding sites "unshielded", and as long as ATP is available to drive the cross-bridge cycling and the pulling of actin strands by myosin, the muscle fiber will continue to shorten to an anatomical limit. Muscle contraction usually stops when signaling from the motor neuron ends, which repolarizes the sarcolemma and T-tubules, and closes the voltage-gated calcium channels in the SR. Ca++ are then pumped back into the SR, which causes the tropomyosin to reshield (or recover) the binding sites on the actin strands. A muscle also can stop contracting when it runs out of ATP and becomes fatigued.
Neuromuscular Junction
The site where a motor neuron's terminal meets the muscle fiber *where the muscle fiber first responds to signaling by the motor neuron
Mysia of Skeletal Muscle
The three layers of connective tissue in skeletal muscles that enclose it and provide structure to the muscle as a whole and also compartmentalize the muscle fibers within the muscle
What do all muscle tissues have in common?
They all exhibit a quality called excitabilitiy as their plasma membranes can change their electrical states and send an electrical wave called an action potential along the entire length of the membrane
What do both the cardiac and smooth muscle have in common?
They both respond to other stimuli such as hormones and local stimuli
The command to contract is conducted throughout the muscle fiber by the __________.
Transverse Tubules
Which protein binds to calcium ions?
Troponin
Smooth muscle does not contain which of the following?
Troponin Does have an SR, actin, and myosin
Length-Tension Range of a Sarcomere
When a skeletal muscle fiber contracts, myosin heads attach to actin to form cross-bridges followed by the thin filaments sliding over the thick filaments as the heads pull the actin, and this results in sarcomere shortening, creating the tension of the muscle contraction. The cross-bridges can only form where thin and thick filaments already overlap, so that the length of the sarcomere has a direct influence on the force generated when the sarcomere shortens. This is called the length-tension relationship.
Neurotransmitter Release
When an action potential reaches the axon terminals, voltage-gated Ca 2+ channels in the membrane of the synaptic end bulb open. The concentration of Ca 2+ increases inside the end bulb, and the Ca 2+ ion associates with proteins in the outer surface of neurotransmitter vesicles. The Ca 2+ facilitates the merging of the vesicle with the presynaptic membrane so that the neurotransmitter is released through exocytosis into the synaptic cleft. Once in the synaptic cleft, the neurotransmitter diffuses the short distance to the postsynaptic membrane and can interact with neurotransmitter receptors. Once neurotransmitter binds to its receptor and will not bind to receptors for other neurotransmitters, making the binding a specific chemical event.
Somites
a block of cells that give rise to myoblasts
Sodium/Potassium Pump
a carrier protein that moves sodium ions (Na+) out of a cell and potassium ions (K+) into a cell, thus regulating ion concentration on both sides of the cell membrane *requires energy in the form of adenosine triphosphate (ATP) or ATPase *The concentration of sodium ions is higher outside the cell than inside, and the concentration of ions is higher inside the cell than outside
voltage-gated channels
a channel that responds to changes in the electrical properties of the membrane in which it is embedded. *When the voltage of the inner portion of the membrane becomes less negative, the channel begins to allow ions to cross the membrane.
Chemical synapse
a chemical signal is released from one cell and its affects the other
Synaptic cleft
a gap into which neurotransmitters are released from the axon terminal
Satellitle cells
a type of stem cells that facilitate the protein synthesis is required for repair and growth
Extensibility of Muscle Tissue
ability to extend/ lengthen of muscle tissue
Contractility
ability to shorten forcibly when stimulated
Hypertonia
abnormally high muscle tone
The neurotransmitter required to trigger skeletal muscle contraction is __________.
acetylcholine (ACh)
Power Stroke
action of myosin pulling actin inward (toward the M line)
Which of the following represents the correct sequence of events in a contraction cycle?
active-site exposure, cross-bridge attachment, pivoting, cross-bridge detachment, myosin reactivation
Contractility of Muscle Tissue
allows muscle tissue to pull on its attachment points and shorten with force
intercalated discs of cardiac muscle
allows the cardiac muscle cells to contract in a wave-like pattern so that the heart can work as a pump *are part of the sarcolemma *Contain 2 structures important in cardiac muscle contraction: gap junctions and desmosomes
Oxygen Debt
amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction
In __________ contraction, the peak tension developed is less than the resistance, and the muscle elongates as a result of the contraction of another muscle or the pull of gravity.
an eccentric
Pushing against a locked door is an example of __________.
an isometric contraction
Glycosis
anaerobic breakdown of glucose to ATP
The length of time muscular contraction can be supported by glycolysis is called __________.
anaerobic endurance
What is the term for the ability of cardiac muscle cells to contract without neural stimulation?
automaticity
Fascicle
bundle of muscle fibers within a skeletal muscle
Excitable membrane
cell membrane that regulates the movement of ions so that an electrical signal can be generated
Desmosome
cell structure that anchors the ends of cardiac muscle fibers to allow contraction to occur so that they do not pull apart during the stress of individual fibers contracting
Action potential
change in voltage of a cell membrane in response to a stimulus that results in the Fatransmission of an electrical signal; unique to neurons and muscle fiber
Neurotransmitter
chemical signal that is released from the synaptic end bulb of a neuron to cause a change in the target cell
Perimysium
connective tissue that bundles skeletal muscle fibers into fascicles within a skeletal muscle
Cell Body (soma)
contains the nucleus and most of the major organelles
Which of the following events in a muscle contraction marks the beginning of the relaxation of the muscle cell?
detachment of cross-bridges
What is the term for the ability to function over a wide range of lengths?
elasticity/plasticity
ATPase
enzyme that hydrolyzes ATP to ADP
The perimysium surrounds a bundle of muscle fibers called a __________.
fascicle
Which type of muscle fiber allows for extremely quick contractions but fatigues quickly?
fast fiber
When energy reserves in a muscle are exhausted and lactic acid levels increase, __________ occurs.
fatigue
A gap junction
forms channels between adjacent cardiac muscle fibers that allow the depolarizing current produced by cations to flow from one cardiac muscle cell to the next
At peak levels of muscle exertion, mitochondrial activity can provide about only one-third of the ATP needed. The remainder is provided through __________.
glycosis
G protein
guanosine triphosphate (GTP) hydrolase that physically moves from the receptor protein to the effector protein to activate the latter *hydrolyzes GTP *physically moves from the receptor protein to the effector protein to activate the latter
Voluntary control over swallowing, defecation, and urination is provided by muscles that __________.
guard entrances and exits
What human muscles contain ONLY fast fibers?
hand muscles
Treppe (staircase effect)
increased contraction in response to multiple stimuli of the same strength *The muscle tension increases in a graded manner that to some looks like a set of stairs *a condition where muscle contractions become more efficient
What is the name of the structure that contains gap junctions and desmosomes and joins the plasma membranes of two cardiac muscle cells together?
intercalated discs
Which of the following features is found in cardiac muscle cells but NOT in skeletal and smooth muscle cells?
intercalated discs
isotonic concentric contraction
involves the muscle shortening to move a load Examples: the biceps brachii muscle contracting when a hand weight is brought upward with increasing muscle tension. As the biceps brachii contract, the angle of the elbow joint decreases as the forearm is brought toward the body. Here, the muscle fibers are shortening and cross bridges form; the myosin heads pull the actin
Nonspecific Channels
ion channels that are selective for charge but not necessary for size. *these channels allow cations to cross the membrane, but exclude anions
When glycolysis produces pyruvic acid faster than it can be used by the mitochondria, pyruvic acid is converted to __________, which lowers the pH of body fluids.
lactic acid
When pyruvic acid is produced by anaerobic metabolism faster than it can be utilized, the surplus is converted to __________.
lactic acid
Phases of a muscle twitch: 3 phases
latent period, contraction phase, relaxation phase *The first phase is the latent period, during which the action potential is being propagated along the sarcolemma and calcium ions are released from the SR. This is the phase during which excitation and contraction are being coupled but contraction has yet to occur *The second phase is the contraction phase, during the calcium ions in the SR have bound to troponin, tropomyosin has shifted away from actin-binding sites, cross-bridges formed, and sarcomeres are actively shortening to the point of peak tension. *The third phase is the relaxation phase, when tension decreases as contraction stops. Calcium ions are pumped out of the sarcoplasm in to the SR, and cross-bridge cycling stops, returning the muscle fibers to their resting state.
Graded Potentials
localized changes in membrane potential *are usually associated with the dendrites of a neuron *the amount of change in the membrane potential is determined by the size of the stimulus that causes it *Can be of 2 sorts: either hyperpolarizing or depolarizing *For a membrane at the resting potential, a graded potential represents a change in that voltage either above -70mV or below -70mV *Depolarizing graded potentials are often the result of Na+ or Ca 2+ entering the cell *Hyperpolarizing graded potentials can be caused by K+ (potassium ions) leaving the cell or Cl- entering the cell.
Myofibril
long, cylindrical organelle that runs parallel within the muscle fiber and contains the sarcomeres
Heat released from contracting muscles functions to __________.
maintain body temperature
Skeletal muscle functions in __________.
maintaining body temperature
Z lines __________.
mark the boundary between adjacent sarcomeres
Voltage-gated sodium channels
membrane proteins that open sodium channels in response to a sufficient voltage change, and initiate and transmit the action potential as Na+ enters through the channel
What happens when the myosin head splits ATP into ADP and a phosphate group?
myosin reactivation
Synapses
narrow junction across which a chemical signal passes from neuron to the next, initiating a new electrical signal in the target cell
The junction between a muscle cell and the neuron innervating that cell is the __________
neuromuscular junction
Acetylcholine (ACh)
neurotransmitter that binds at a motor end-plate to trigger depolarization
Eccentric contraction
occurs as the muscle tension diminishes and the muscle lengthens *Are also used for movement and balance of the body
glial cells
one of the various types of neural tissue cells responsible for maintenance of the tissue, and largely responsible for supporting neurons
Ligand-gated channel (ionotrophic receptor)
opens because a signaling molecule, a ligand, binds to the extracellular region of the channel *when the ligand binds to the protein, ions cross the membrane changing its charge *when the ligand bind to a specific location on the extracellular surface of the channel protein, the pore opens to allow select ions through.
Mechanically gated channels
opens because of a physical distortion of the cell membrane *when a mechanical change occurs in the surrounding tissue, such as pressure or touch, the channel is physically opened. *ion channel that opens when a physical event directly affects the structure of the protein
Creatine Phosphate
phosphagen used to store energy from ATP and transfer it to muscle
Which of the following is NOT a characteristic of smooth muscle tissue?
presence of striations
Lactic acid
product of anaerobic metabolism, especially in muscle
Pyruvic Acid
product of glycolysis that can be used in aerobic respiration or converted to lactic acid
Skeletal muscle is responsible for all of the following EXCEPT __________.
production of Vitamin D
Actin
protein that makes up most of the thin myofilaments in a sarcomere muscle fiber
Leakage Channels
randomly gated, meaning that is open and closes at random, hence the reference to leaking. *has an intrinsic rate of switching between the open and closed states. *contribute to the resting transmembrane voltage of the excitable membrane *allow sodium ions to move slowly into the cell or K+ to slowly move out, and the sodium-potassium pump restores them.
slow twitch muscle fibers
red muscle fibers that are fatigue resistant but have a slow contraction speed and a lower capacity for tension; usually recruited for endurance activities *Type 1 Fibers *Contain a large amount of mitochondria *Have a small diameter *Don't produce a large amount of tension *Are extensively supplied with blood capillaries to supply oxygen from the red blood cells in the bloodstream *Possess Myoglobin *Help maintain posture, producing isometric contractions, stabilizing bones and joints, and making small movements that happen often but do not require large amount of energy
Calmodulin
regulatory protein that facilitates contraction in smooth muscles
FIbrosis
replacement of damaged cells with scar tissue
What is the functional unit of the muscle fiber?
sarcomere
exicitation-contraction coupling
sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber's sarcomeres
excitation-contraction coupling
sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber's sarcomeres *For a muscle fiber to contract, its membrane must first be "excited (be stimulated to fire an action potential). The muscle fiber action potential, which sweeps along the sarcolemma as a wave, is "coupled" to the actual contraction through the release of calcium ions (CA 2+) from the SR. Once released, the calcium interacts with the shielding proteins, forcing them to move aside so that the actin-binding sites are available for attachment by myosin heads. The myosin then pulls the actin filaments toward the center, shortening the muscle fiber.
What muscle fiber type contains abundant myoglobin and is specialized to contract for extended periods of time?
slow fiber
Which type of muscle fiber is supplied by extensive blood vessels?
slow fibers
synaptic cleft
space between a nerve (axon) terminal and a motor end-plate
Pericyte
stem cell that regenerates smooth muscle cells *found in some small blood vessels
Synaptic End Bulb
swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse
ACh is released from what structure?
synaptic terminal
Elasticity
the ability for a muscle to return to its original length when relaxed because of the elastic fibers.
Motor unit
the actual group of muscle fibers in a muscle innervated by a single motor neuron *A smaller motor unit is an arrangement where a single motor neuron supplies a small number of muscle fibers in a muscle. They allows very motor control of the muscle. *A larger motor unit is an arrangement where a single motor neuron supplies a large number of muscle fibers in a muscle.
Graded potential
the amount of change dependent on the strength of the stimulus *change in the membrane potential that varies in size, depending on the size of the stimulus that elicits it *if the stimulus is strong, the voltage of the cell membrane will change enough to generate an electrical signal that will travel down the axon
Triad
the arrangement of a T-tubule with the membranes of SR on either side is called a triad. The triad surrounds the cylindrical structure called a myofibril, which contains actin and myosin
What does a ligand-gated channel require in order to open?
the binding of a neurotransmitter
chemical gradient
the concentration gradient of an ion or molecule
electrical gradient
the difference in electrical charges between the inside and outside of the cell *the electrical potential that acts on an ion to drive the movement of the ion in one or another direction
Muscle tension
the force generated by the contraction of the muscle (or shortening of the sarcomeres)
What is a Sarcomere?
the functional unit of a skeletal muscle fiber
Threshold
the voltage at which a signal is generated *membrane voltage at which an action potential is initiated *voltage-gated Na+ channels open upon reaching this state
Wave Summation
this occurs when a second stimulus is received before the muscle fiber has relaxed, creating a second contraction that is stronger than the first
Depolarization must reach this value in a cell to trigger an action potential?
threshold
relative refractory period
time during the refractory period when a new action potential can only be initiated by a stronger stimulus than the current action potential because voltage-gated K+ channels are not closed
What is muscle strength related to?
to the amount of myofibrils and sarcomeres within each fiber
Contraction phase
twitch contraction phase when tension increases
The resting state of the membrane
when the cell is at rest, and the ion channels are closed, ions are distributed across the membrane in a very predictable way. The concentration Na+ outside the cell is 10x greater than the concentration inside. Also, the concentration of K+ inside the cell is greater than outside.
Tetanus
when the stimulus frequency is so high that the relaxation phase disappears completely, the contractions become continuous
Refractory period
while an action potential is in progress, another one cannot be initiated
fast twitch muscle fibers
white muscle fibers that contract rapidly and forcefully but fatigue quickly; usually recruited for actions requiring strength, power, or speed *Type 2 Fibers *Have a large diameter *Also called intermediate muscle fibers *Produce ATP relatively quickly *Produce a high amount of tension *Don't possess significant myoglobin *Possess high amount of glycogen *Produce rapid, forceful contractions to make quick, powerful movements
Resting membrane Potential (RMP)
with the ions distributed across the membrane at these concentrations, the difference in charge is measured at -70 mV, the value described as the resting membrane potential. -the steady-state of the cell
In which part of the sarcomere are myosin heads able to form cross-bridges with actin?
zone of overlap
