Term
| What features distinguish the three types of muscle tissue?1 |
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Definition
| Skeletal: Function of most skeletal muscles is to move bones of the skeleton. *striated *voluntary Cardiac: Only present in the heart *striated *involuntary *autorythmicity Smooth: located in the walls of hollow internal structures. (i.e. blood vessels, airways, most organs of the abdominopelvic cavity), also found in skin attached hair follicles. *nonstriated *involuntary |
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Term
| Summarize the functions of muscle tissue. |
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Definition
1) producing body movement
-integrated functioning of bones, joints, and skeletal muscle.
2) Stabilizing body positions (maintaining posture, stabilizing joints)
-contractions stabilize joints and help maintain body positions, such as standing or sitting
3) Regulating organ volume
-sphincters (valves) prevent the outflow of the contents of hollow organs.
4)moving substances within the body
-cardiac muscle contractions: movement of blood
-contraction and relaxation of smooth muscle in the wall of blood vessels:helps adjust their diameter and therefore, rate of blood flow.
5)producing heat |
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Term
| What are the four functional characteristics of muscle tissue? |
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Definition
1)electrical excitability(irritability): the ability to respond to certain stimuli by producing electrical signals. (action potentials)
2)contractiblity: the ability to contract (shorten) forcefully when stimulated by an action potential
3)extensibility: the ability to stretch without being damaged
4)elasticity: the ability of muscle tissue to return to its original length and shape after contraction or extension. |
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Term
| Why are skeletal muscle fibers multinucleated? |
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Definition
| They are myonucleated because during embryonic development, each skeletal muscle fiber arises from the fusion of myoblasts, which is how they form multinucleated muscle cells. |
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Term
| Describe the three types of fascia that cover skeletal muscles. |
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Definition
1)epimysium: outer most layer; encircles the whole muscle
-it is connected to the deep fascia
2)perimysium: surrounds groups of 10-100 individual muscle fibers; separates them into bundles called fasicles
-it contains blood vessels and nerves for the muscle fibers from one another
3)endomysium: separates individual muscle fibers from one another
-it contains a capillary network, satellite cells and nerve fibers controlling the muscle. |
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Term
| Why is a rich blood supply important to muscle contraction? |
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Definition
In general, each muscle is served by one nerve, one artery and one or several veins.
-Skeletal muscle is well supplied by capillaries so you have oxygen and energy. |
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Term
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Definition
Neurons that stimulate skeletal muscle to contract.
-each somatic motor neuron has an axon that extends from the brain or spinal cord to a group of skeletal muscle fibers. |
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Term
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Definition
| the plasma membrane of the skeletal muscle fiber. It has a characteristic transmembrane potential due to the unequal distribution of postive and negative charges across the membrane. |
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Term
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Definition
| tiny invaginations of the sarcolemma tunnel from the surface toward the center of each muscle fiber. They are open to the outside.They are filled with extracellular fluid and therefore have the same general properties of sacolemma. THE ACTION POTENTIALS ARE THE TIGGERS FOR MUSCLE FIBER CONTRACTIONS |
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Term
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Definition
the cytoplasm of a muscle fiber
-contains glycogen and myoglobin(a red pigment that stores oxygen within the muscle cell) |
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Term
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Definition
contactile elements of skeletal muscle.
-consist of bundles of myofilaments (protein filaments)
-within myofibrils are two types of filaments; thin filaments(primarily actin) and thick filaments(primarily myosin) |
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Term
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Definition
| fluid filled system of membranous sacs that encircles each myofibril |
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Term
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Definition
dilated end sacs of the sarcoplasmic reticulum; they butt against the T tubule from both sides
-located at the zones of overlap |
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Term
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Definition
formed by one transverse tubule and the 2 terminal cisterns on either side of it
*it stores ca++ and releases it on demand when the muscle fiber is stimulated to contract
*the release of calcium ions from the terminal cisterns of the SR triggers muscle contraction. |
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Term
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Definition
| A sarcomere contains thick filaments, thin filaments, stabilizing proteins for positions of thick and thin filaments and regulatory proteins. |
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Term
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Definition
separate one sarcomere from the next
*the Z lines consists of proteins (actinins) that interconnect thin filaments of adjacent sarcomeres
*each Z line is surrounded by a mesh of intermediate filaments that interconnect adjacent myofibrils |
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Term
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Definition
| extends the entire length of the thick filament |
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Term
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Definition
| (in the center of each A band) contains thick but no thin filamnets |
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Term
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Definition
| supporting proteins that hold the thick filaments together at the center of the H zone |
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Term
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Definition
| toward each end of the A band |
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Term
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Definition
contains the rest of the thin filaments, but no thick filaments
-a Z disc passes throough the center of each I band |
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Term
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Definition
| generate force during contraction |
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Term
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Definition
this contractile protein functions as a motor protein in all three types of muscle tissue
*forms the thick filaments |
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Term
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Definition
| points toward the M line in the center of the sarcomere |
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Term
| myosin heads(cross bridges) |
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Definition
| each head extends toward one of the 6 thin filaments that surrounds the thick filaments. It includes ATP binding sites and ATPase |
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Term
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Definition
main component of thin filaments
*individual actin molecules join to form an actin filament that is twisted into a helix: Active site (myosin binding site) site of myosin head attachment |
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Term
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Definition
help switch the contraction process on and off
-they regulate the interactions between the thick and thin filaments
-troponin and tropomyosin: part of thin filaments |
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Term
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Definition
1. Ca++ binding site
2. binding site for tropomyosin
3. binding site for actin |
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Term
| Structural (stabilizing) proteins |
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Definition
-keep the thick and thin filaments in proper alignment
-give the myofibril elasticity and extensibility
-link the myofibrils to the sarcolemma and extracellular matrix |
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Term
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Definition
each thick filament has a core of titin
*the portion of the titin strand exposed within the I band is elastic and will recoil after stretching
*in a resting muscle the titin strands are completely relaxed |
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Term
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Definition
| extend along the actin strand and hold them together. |
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Term
| Sliding Filament mechanism |
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Definition
Skeletal muscles shortens during contraction because the thick and thin filaments slide past one another.
-the length of the individual thick and thin filament do not change.
-shortening of the sarcomere causes shortening of the whole muscle fibers, and ultimately shortening of the entire muscle.
Since myofibrils are attached to the sarcolemma at each Z line, and at either end of the muscle fiber, the muscle fiber shortens too. |
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Term
| Excitation-contraction Coupling |
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Definition
| The series of events linking the electrical signals to contraction is known as excitation-contraction coupling: Excitation-contraction coupling is the sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments. THE FIRST STEP IN EXCITATION-CONTRACTION COUPLING IS THE RELEASE OF CALCIUM IONS FROM THE CISTERNEA OF THE SARCOPLASMIC RETICULUM FROM VOLTAGE GATED CALCIUM CHANNELS. |
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Term
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Definition
| the point of contact (synapse) between the motor neuron and the muscle fiber |
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Term
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Definition
| a region where communication occurs between 1)two neurons and 2)a neuron and a target cell |
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Term
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Definition
a small gap at synapses; it separates two cells.
*since the cells do not phyically touch, an action potential cannot jump from one cell to the other; instead the first cell communicates with the second cell indirectly by releasing a chemical called a neurotransmitter. |
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Term
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Definition
| at the neuromuscular junction the motor neuron axon terminal divides into a cluster of synaptic end bulbs. |
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Term
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Definition
| are suspended in the cytosol of synaptic bulbs. The neurotransmitter molecule acetycholine is present in the synaptic vesicles. |
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Term
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Definition
the region of the sarcolemma that is adjacent to the synaptic end bulb.
*the motor end plate contains receptors for acetylcholine (gated ion channels)
*the motor end plate is highly folded(junctional folds) |
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Term
| Leakage channels(passive) |
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Definition
*always open
-plasma membranes have many more K+ leakage channels than Na+ leakage channels |
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Term
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Definition
*open and close in response to a stimulus
-the presence of gated ion channels in the plasma membranes of neurons and muscle fibers gives these cells their property of electrical excitability |
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Term
| What are the three types of gated ion channels present in excitable cells? |
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Definition
1)voltage-gated
2)ligand-gated(chemically gated)
3)mechanically gated |
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Term
| Voltage-gated ion channel |
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Definition
-opens in response to a change in membrane potential
-used in the generation and conduction of action potentials
-found on the membranes of excitable cells:
*axons of unipolar and multipolar neurons
*sarcolemma and T tubules of skeletal muscle fibers
*cardiac cells |
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Term
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Definition
-opens and closes in response to a specific chemical stimulus(i.e neurotransmitters, hormones, ions)
-found greatly on dendrites and cell body of neurons |
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Term
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Definition
| -opens and closes in response to mechanical stimulation (i.e vibration, pressure, tissue stretching) |
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Term
| 5 steps of a nerve impulse |
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Definition
1)an action potential arrives at the synaptic end bulbs of a somatic motor neuron.
2)ACh is released from synaptic vesicles
3)Ach binds to it receptors
4)muscle action potential is produced
5)Ach is broken down by acetylcholinesterase. |
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Term
Contraction cycle:
Active site exposure |
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Definition
At the onset of contraction:
-the sarcoplasmic reticulum releases calcium ions
-the Ca++ binds to troponin and cause troponin-tropomyosin complexes to move away from the myosin-binding sites on actin. |
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Term
Contraction Cycle:
Cross bridge attachment |
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Definition
attachment of myosin to actin to form cross bridges:
-the activated myosin heads(high energy configuration) are strongly attracted to the exposed binding sites on actin
-ADP and inorganic phosphate are attached to the myosin head
-in resting sarcomere, each myosin head is already energized. |
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Term
Contraction Cycle:
Pivoting (swiveling) of myosin head |
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Definition
(The working power stroke) the releases of the phosphate group triggers the power stroke of contraction
*the myosin head generates force as it rotates toward the center of the sarcomere, sliding the thin filamnt past the thick filament toward the M line. |
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Term
Contraction Cycle:
Cross bridge detachment |
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Definition
Detachment of myosin from actin
-at the end of the power stroke, the myosin head remains firmly attached to actin until it binds another molecule of ATP.
-As a new ATP molecule binds to the ATP binding pocket on the myosin head, the myosin head detaches from actin.
-the active site on actin is once again exposed, and it can form another cross bridge. |
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Term
Contraction Cycle:
ATP Hydrolysis/Myosin reactivation |
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Definition
-the hydrolysis of ATP (to ADP and Pi) by the myosin head energizes the myosin head
-the products of hydrolysis remain attached to myosin head |
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Term
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Definition
The duration of skeletal muscle contraction depends on:
1. duration of stimulation at the neuromuscular junction.
2. presence of free calcium ions in the sarcoplasm
3. ATP availability
- the return to resting length after a contraction can involve elastic forces, the contractions of opposing muscle groups and gravity. |
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Term
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Definition
The force of muscle contraction is affected by:
1. the number of muscle fibers contracting
*the more motor units that are recruited, the greater the muscle force
2. the relative size of the muscle
*the bulkier the muscle, the more tension it can develop and therefore, the greater its strength
3. the degree of muscle stretch
*the optimal resting length for muscle fibers is the length at which they can generate maximum force. |
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Term
| Tension produced by muscle fibers |
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Definition
The total tension that a single fiber can produce depends:
1. mainly on the rate at which nerve impulses arrive at the neuromuscular junction
*FREQUENCY OF STIMULATION
2)nutrient and oxygen availability
3)the amount of stretch prior to contraction (LENGTH-TENSION RELATIONSHIP) |
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Term
| Length-tension relationship |
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Definition
The forcefulness of muscle contraction depends on the length of the sarcomere within a muscle before contraction begins.
-The amount of tension generated during a contraction depends on the number of pivoting cross bridges in all the sarcomere along all the myofibrils.
*the number of cross bridges that can be formed in turn depends on the degree of overlap between the thick filaments and thin filaments present in the sarcomere. |
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Term
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Definition
| A brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron |
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Term
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Definition
| a brief delay between application of the stimulus and the beginning of the contraction. |
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Term
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Definition
1. the action potential propagates along the sarcolemma.
2. Ca++ are being released from the SR
*since the contraction cycle has not yet begun, no tension is produced |
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Term
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Definition
1. The filaments start to exert tension
2. shortening begins |
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Term
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Definition
tension begins to fall due to the active transport of calcium ions back into the SR.
-the actual duration of the periods depends on the type of muscle (fast-twitch vs. slow-twitch muscles) |
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Term
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Definition
If two stimuli are applied (one immediately after the other), the muscle will respond to only the first stimulus.
-When a muscle fiber receives enough stimulation to contract, it temporarily loses its excitability and cannot respond for a time. |
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Term
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Definition
- Our muscle contractions are relatively smooth and vary in strength based on the demands placed on them
*variations in the degree of muscle contraction are called graded responses:
-muscle contraction can be graded in two ways:
1. By changing the frequency (speed) of stimulation -ATP-
2. By changing the strength of the stimulus -higher voltage- |
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Term
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Definition
-the increase in peak tension will continue over the first 30-50 simulations
*after that, the amount of tension produced will remain constant
-treppe (the rise) may be due to a gradual increase in the concentration of calcium ions in the sarcoplasm.
*this is the basic for warming up |
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Term
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Definition
The phenomenon in which stimuli arriving at different times cause larger contractions:
-due to additional Ca++ released from the SR
-also due to the stretch of the elastic elements |
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Term
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Definition
When skeletal muscle is stimulated at a rate 20-30 times per second, it can only partially relax between stimuli:
-the result is a sustained but wavering contraction known as unfused (incomplete) tetany |
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Term
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Definition
When skeletal muscle is stimulated at a rate of 80-100 stimuli per second, the result is fused (complete) tetany (a sustained contraction in which individual twitches cannot be discerned)
-almost all normal muscular contractions involve complete tetanus of the participating muscle. |
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Term
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Definition
| The force exerted on an object by a contracting muscle |
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Term
| Muscle tension depends on.. |
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Definition
-The tension produced by the stimulated muscle fibers
-the total number of muscle fibers stimulated |
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Term
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Definition
| if tension develops but the load is not moved. (same length) |
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Term
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Definition
| if the tension developed overcomes the load and muscle shortening occurs. (same tension)Used for body movements and for moving external objects. |
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Term
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Definition
a somatic motor neuron plus all the skeletal muscle fibers it stimulates
*all the muscle fibers in one motor unit contract in unison.
It depends on:
-how large the motor units are and
-how many motor units are activated at the same time.
*Muscle that control precise movements consist of many small motor units.
*Muscle that control large-scale and powerful movements have larger motor units. |
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Term
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Definition
| The process in which the number of active units is increased. |
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Term
| Asynchronous motor unit summation |
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Definition
The various motor neurons to a whole muscle fibers asynchronously.
* this pattern of motor unit activity delays muscle fatigue
*the weakest motor units are recruited first, with progressively stronger motor units being added if the task requires more force. |
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Term
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Definition
-to sustain muscle tone, small groups of motor units are alternately active and inactive in a constantly shifting pattern.
*muscle tone is due to spinal reflexes that activate first one group of motor units and then another in response to activation of stretch receptors in muscles and tendons.
*a muscle with little or no muscle tone appears limp and flacid, while one with moderate tone is firm and solid. |
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Term
| Muscle tone is important... |
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Definition
-stabilizing the position of bones and joints (muscles of balance and posture)
-preventing sudden uncontrolled changes in positions of bones and joints. |
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Term
| Concentric isotonic contraction |
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Definition
| a muscle shortens and pulls on another structure to produce movement and to reduce the angle at a joint. (i.e tendon) |
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Term
| Eccentric isotonic contraction |
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Definition
| When the overall length of a muscle increases during a contraction. (Move arm down) |
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Term
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Definition
important for maintaining posture and for supporting objects in a fixed position, important in stabilizing some joints as others are moved.
-in isometric contractions tension is generated without shortening of the muscle. |
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Term
| Contraction of muscle requires a great amount of ATP for: |
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Definition
1)powering the contraction cycle
2)pumping CA++ back into the SR to achieve muscle relaxation
3)other metabolic reactions |
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Term
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Definition
Unique to muscle fibers
-the enzyme creatine kinase catalyzes the transfer of one high energy phosphate group of ATP to creatine forming creatine phosphate and ADP.
-when the muscle needs energy, the reverse reaction takes place.
*this allow rapid formation of ATP |
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Term
| Anaerobic Cellular Respiration |
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Definition
Series of ATP producing reactions that do not require oxygen.
* A series of reactions known as glycolysis, quickly break down each glucose molecule into two molecules of pyruvic acid. |
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Term
| Aerobic Cellular respiration |
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Definition
Takes place in the mitochondria, and requires the presence of oxygen.
-36 molecules of ATP are produced from each molecule of glucose
*this is sufficient for prolonged activities. |
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Term
| Sources of muscle tissue oxygen |
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Definition
1)oxygen that diffuses into muscle fibers from the blood.
2)oxygen released by myoglobin within muscle fibers. |
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Term
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Definition
| The inability of a muscle to contract forcefully after prolonged activity |
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Term
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Definition
| added oxygen needed over and above the resting oxygen consumption, that is taken into the body after exercise. |
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Term
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Definition
| the greater the load, the longer the latent period, the slower the contraction, and the shorter the duration of contraction |
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Term
| Muscle performance recruitment |
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Definition
| the more motor units contracting, the faster and more prolonged the contraction |
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Term
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Definition
They produce rapid and powerful contractions of relatively brief duration.
*large in diameter
*contain densely packed myofibrils
*large glycogen stores
*few mitochondria
*anaerobic
*they fatigue easily |
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Term
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Definition
Designed to continue contracting for extended periods.
*they take 3 times as long to contract after stimulation
*abundant mitochondria
*extensive capillary supply
*high concentrations of myoglobin |
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Term
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Definition
| Muscles dominated by fast fibers appears pale |
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Term
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Definition
| Muscle dominated by slow fibers are rich in myoglobin |
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Term
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Definition
enlargement of a stimulated muscle
-this occurs in muscles that have been repeatedly stimulated to produce near maximal tension.
-the number of muscle fibers does not change |
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Term
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Definition
principle tissue in the heart wall.
-have same arrangement of actin and myosin and same bands, zones and Z discs as skeletal muscle fibers.
-ends of cardiac muscle fibers connect to adjacent fibers by intercalated discs
*the intercalated discs contains desmosomes (help stabilize the adjacent cells) and gap junctions (allow small molecules to move from one cell to another)
-longer contraction period than skeletal muscle
-involuntary
-almost completely dependent on aerobic metabolism |
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Term
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Definition
-spindle shaped
-lack transverse tubules, myofibrils and sarcomeres.
-the thin filaments are attached to dense bodies
*dense bodies attach adjacent smooth muscle cells to each other. |
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Term
| Visceral smooth muscle tissue |
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Definition
| -single unit smooth muscle has electrically coupled fibers that contract synchronously an often spontaneously |
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Term
| Visceral smooth muscle tissue locations |
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Definition
Found in:
-walls of small arteries and veins
-walls of hollow viscera:stomach, intestines, uterus, urinary bladder
*autorythmic
-they lack a direct contact with any motor neuron |
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Term
| Multiunit smooth muscle tissue |
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Definition
Consists of individual fibers, each with their own motor neuron connected to more than a single motor neuron.
-stimulation of one motor unit fiber causes contraction of that fiber only.
-stimulation is via autonomic nerves or hormones. |
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Term
| Multiunit smooth muscle tissue location |
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Definition
Found in the walls of large arteries, airways, and in arrector pilli.
*not usually found in the digestive tract. |
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Term
| Contraction of Smooth Muscle |
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Definition
1. excitation contraction coupling
2.length-tension relationship
3. control of contraction |
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Term
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Definition
| a cytoplasmic calcium binding protein |
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Term
| myosin light chain kinase |
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Definition
a kinase enzyme
-the thin filaments lack troponin and son are always ready for contraction |
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Term
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Definition
| Smooth muscle can both shorten and stretch to a greater degree than other muscle types |
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Term
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Definition
| Both multiunit and visceral smooth muscle tissues have tone |
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Term
| Regeneration of muscle tissue |
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Definition
-Skeletal muscle fibers cannot divide and have limited powers of regeneration.
-Cardiac muscle fibers cannot divide or regenerate.
-Smooth muscle fibers have limited capacity for division and regeneration. |
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Term
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Definition
| the replacement of muscle fibers by fibrous scar tissue. |
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