BIOL 2401 Unit #3 Lecture Exam Ch. 10
What are the roles of smooth muscle tissue in systems throughout the body.
- In all systems, smooth muscle in blood vessels regulates blood pressure and flow. - In digestive and urinary systems, smooth muscle forms sphincters and produces contractions. - Smooth muscle also produces movements in the reproductive and glandular systems. - In the integumentary system, goose bumps are caused by arrector pili muscles of hair follicles.
Intermediate Fibers
- are mid-sized - have low myoglobin - have more capillaries than fast fiber, are slower to fatigue
Fast Fibers
- contract very quickly - have large diameter, large glycogen reserves, and few mitochondria - have strong contractions, fatigue quickly White muscle (mostly) -Pale (e.g.,chicken breast)
What forms of energy reserves do resting skeletal muscles contain?
-Adenosine triphosphate(ATP) •The active energy molecule -Creatine phosphate(CP) •The storage molecule for excess ATP energy in resting muscle ATP Generation (Glycogen) -Glycolysis: anaerobic breakdown of glucose to pyruvate in the cytosol (does not require oxygen) -Aerobic metabolism: provides 95% of the ATP demands of a resting cell, mitochondria absorb oxygen, ADP, phosphate ions & organic substrates (such as pyruvate) f/ the surrounding cytoplasm
Z line
-Bisects the I bands & mark the boundary between adjacent sarcomeres -Consist of proteins called actinins, which interconnect thin filaments of adjacent sarcomeres
A band
-Contains regions of overlapping thick (myosin) & thin (actin) filaments -the thick filaments are at the center of each sarcomere in this band -also includes portions of thin filaments & contain 3 subdivisions: 1. M Line 2. H Band 3. Zone of overlap
H band
-Is a lighter region on either side of the M line -Contains thick filaments only
I band
-Region of the sarcomere that contains thin filaments only -Extends from the A band of one sarcomere to the A band of the next sarcomere
Myofibrils
-cylindrical structure as long as the entire muscle fiber -encircled by branches of T tubules & the sarcoplasmic reticulum -the active shortening of these are responsible for skeletal muscle fiber contraction -organized into repeating subunits called sarcomeres
What two mechanisms are used to generate ATP from glucose in muscle cells?
1. Aerobic metabolism of fatty acids in the mitochondria: - the primary energy source of resting muscles - 34 ATP molecules produced per glucose molecule 2. Anaerobic glycolysis in the cytoplasm: - the breakdown of glucose from glycogen - primary energy source for peak muscular activity - 2 ATP molecules produced per molecule of glucose - skeletal muscles store glycogen
Identify the functional differences between skeletal muscle fibers and smooth muscle cells
1. Excitation-Contraction Coupling: Free calcium ions in the cytoplasm trigger smooth muscle contraction. In the sarcoplasm, calcium ions bind with the protein calmodulin, which activates the enzyme myosin light chain kinase, which breaks down ATP and initiates the contraction. 2. Length-Tension Relationships: Thick and thin filaments are scattered, so resting length is not related to tension development. The ability of smooth muscle to function over a wide range of lengths is called plasticity. 3. Control of Contractions: Smooth muscle cells are subdivided into multiunit smooth muscle cells, which are connected to motor neurons, and visceral smooth muscle cells, which are not. Visceral smooth muscle networks generally have rhythmic cycles of activity controlled by pacesetter cells. 4. Smooth Muscle Tone: Smooth muscles maintain normal levels of activity, which can be modified by neural, hormonal or chemical factors.
Identify the functional differences between skeletal muscle fibers and cardiac muscle cells.
1. automaticity (contraction without neural stimulation, controlled by pacemaker cells) 2. variable contraction tension controlled by the nervous system 3. extended contraction time 4. prevention of wave summation and tetanic contractions by cell membranes
What are six functions of skeletal muscle?
1.Produce skeletal movement 2.Maintain body position 3.Support soft tissues 4.Guard openings 5.Maintain body temperature 6.Store nutrient reserves
Describe the mechanisms by which muscle fibers obtain the energy to power contractions.
ATP Provides Energy for Muscle Contraction ›Sustained muscle contraction uses a lot of ATP energy ›Muscles store enough energy to start contraction ›Muscle fibers must manufacture more ATP as needed
Relate the types of muscle fibers to muscle performance, and distinguish between aerobic and anaerobic endurance.
Anaerobic endurance: Anaerobic activities (e.g. 50 meter dash or weightlifting) -use fast fibers, which fatigue within about 2 minutes of strenuous activity. -Frequent, brief, intensive workouts stimulate muscle hypertrophy, which improves anaerobic endurance. Aerobic endurance (prolonged aerobic activity) -is supported by mitochondrial activity, requiring oxygen and nutrients provided by circulating blood. -Improvements in aerobic endurance result from: 1. repetitive training to alter the neural responses of fast fibers 2. cardiovascular training
Describe the characteristics of skeletal muscle fibers
Are very long Develop through fusion of mesodermal cells (myoblasts) Become very large Contain hundreds of nuclei
End of muscle contraction
As calcium ion concentrations in the sarcoplasm fall, calcium ions detach from troponin, and the active sites are recovered by tropomyosin
Identify the components of the neuromuscular junction
Axon terminal: synaptic terminal of a neuron Motor end plate: -specialized region of the sarcolemma -contains chemically-gated Na+ channel (ACh membrane channel receptor) Synaptic cleft: -space in between the axon terminal & motor end plate Neurotransmitter: -chemical signal (acetylecholine or ACh)
What structural feature of skeletal muscle fiber propagates action potentials into the interior of the cell?
Because the whole muscle fiber must contract at the same time, the signal (action potential) is conducted through the cell by transverse tubules (T tubules) which have the same properties as the sarcolemma.
Fascicle
Bundle of muscle fibers surrounded by the perimysium
Identify the structural differences between skeletal muscle fibers and cardiac muscle cells.
Cardiac muscle is a striated muscle tissue found only in the heart. • Unlike skeletal muscle fibers, cardiac muscle cells (cardiocytes): 1. are small 2. have a single nucleus 3. have short, wide T tubules and no triads 4. have SR with no terminal cisternae 5. are aerobic (high in myoglobin and mitochondria) 6. have specialized contact points called intercalated discs • Intercalated discs join the cell membranes of adjacent cardiocytes with gap junctions and desmosomes. They maintain structure and enhance molecular and electrical connections. Action potentials travel easily across intercalated discs. Because heart cells are mechanically, chemically and electrically linked, the heart functions like a single, fused mass of cells.
Thin filaments
Composed primarily of actin Four Thin Filament Proteins: *F-actin (Filamentous actin) -Is two twisted rows of globular G-actin -The active sites on G-actin strands bind to myosin *Nebulin -Holds F-actin strands together *Tropomyosin -Is a double strand -Prevents actin-myosin interaction *Troponin -A globular protein -Binds tropomyosin to G-actin -Controlled by Ca2+
Thick filaments
Composed primarily of myosin -Contain twisted myosin subunits -Contain titin strands that recoil after stretching -The mysosin molecule •Tail: -binds to other myosin molecules •Head: -made of two globular protein subunits -reaches the nearest thin filament
Incomplete Tetanus
If rapid stimulation continues and the muscle is not allowed to relax, the twitches will reach a maximum level of tension called?
Complete tetanus
If stimulation frequency is so high that the muscle never begins a relaxation phase, the muscle reaches what? (continuous contraction)
Recruitment or Multiple Motor Unit Summation
In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated. This is called ?
Why is calcium necessary for skeletal muscle contraction?
Ion pumps concentrate calcium ions (Ca++) in the cisternae. The calcium ions are released into the contractile units of the muscle (sarcomeres) at the beginning of a muscle contraction. When calcium ions are released by the sarcoplasmic reticulum, thin and thick filaments interact. When a Ca++ ion binds to the receptor on a troponin molecule, the troponintropomyosin complex changes, exposing the active site of the F actin and initiating contraction.
What would happen if acetylcholinesterase were blocked?
Muscle would contract repeatedly The motor end plate would be stimulated continuously by acetylcholine, locking the muscle in a state of contraction
Myofilaments
Myofibrils consist of bundles of protein filaments, & contain 2 types: thin composed of actin & thick composed of myosin
Describe the organization of muscle at the tissue level.
Organization of Connective Tissues Muscle attachments Endomysium, perimysium, and epimysium come together: -at ends of muscles -to form connective tissue attachment to -bone matrix -i.e., tendon (bundle) or aponeurosis (sheet) Nerves -Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord) Blood Vessels -Muscles have extensive vascular systems that: -Supply large amounts of oxygen -Supply nutrients -Carry away wastes
Specify the functions of skeletal muscle tissue.
Producting movement Maintaining posture and body position Supporting soft tissues Guarding body entrances & exits Maintaining body temperature Storing nutrients
Wave Summation
Repeated stimulations before the end of the relaxation phase (stimulus frequency > 50 per second) causes increasing tension called a summation of twitches
Treppe
Repeated stimulations immediately after the relaxation phase (stimulus frequency < 50 per second) causes a series of contractions with increasing tension. This stair-step type increase in twitch tension is?
What is the functional unit of skeletal muscle?
Sarcomeres
Isometric contraction
Skeletal muscle develops tension, but is prevented from changing length
Why would a sprinter experience muscle fatigue before a marathon runner would?
Sprinting involves anaerobic endurance, whereas running a marathon depends more upon availability of substrates for aerobic respiration
The mechanism responsible for tension production in a muscle fiber
Tension of a Single Muscle Fiber depends on: -The number of pivoting cross-bridges -The fiber's resting length at the time of stimulation -The frequency of stimulation Length-tension relationship Number of pivoting cross-bridges depends on amount of overlap between thick & thin fibers Optimum overlap produces greatest amount of tension: -too much or too little reduces efficiency Normal resting sarcomere length: -is 75% to 130% of optimal length Frequency of stimulation: A single neural stimulation produces a single contraction or twitch which lasts about 7-100 milliseconds. Sustained muscular contractions require many repeated stimuli
Summarize the events involved in the neural control of skeletal muscle contraction and relaxation.
The Contraction Cycle 1.Contraction cycle begins 2.Active-site exposure 3.Cross-bridge formation 4.Myosin head pivoting 5.Cross-bridge detachment 6.Myosin reactivation Relaxation -Ca2+concentrations fall -Ca2+detaches from troponin -Active sites are re-covered by tropomyosin
Contraction cycle & cross-bridge formation
The Contraction Cycle has 5 steps: 1. Exposure of active sites 2. Formation of cross-bridges 3. Pivoting of myosin heads 4. Detachment of cross-bridges 5. Reactivation of myosin
M line
The center of the A band (middle) -Proteins connect the central portion of each thick filament to neighboring thick filaments -Dark-staining proteins help stabilize the position of the thick filaments
Identify the structural components of a sarcomere.
The contractile units of muscle Functional units of myofibrils Form visible patterns within myofibrils *The A Band (dark, thick filaments) M line: -The center of the A band -At midline of sarcomere The H Band: -The area around the M line -Has thick filaments but no thin filaments Zone of overlap: -The densest, darkest area on a light micrograph -Where thick and thin filaments overlap *The I Band (light, thin filaments) Z lines: -The centers of the I bands -At two ends of the sarcomere Titan: -Are strands of protein -Reach from tips of thick filaments to the Z line -Stabilize the filaments
Describe the three connective tissue layers associated with skeletal muscle, the epimysium, perimysium and endomysium.
They are connective tissues and the collagen fibers blend together to form bundles (tendons) or broad sheets (aponeuroses) to provide firm attachments to bone •Epimysium: dense layer of collagen fibers that surrounds the entire muscle •Perimysium: divides the skeletal muscle in series of compartments that contain bundle of muscle fibers called fascicles •Endomysium: surrounds individual muscle cells (muscle fibers)
How would a drug that blocks acetylcholine release affect muscle contraction?
Would interfere w/ cross bridge formation & contraction would be prevented
Excitation-contraction coupling
a motor neuron releases ACh, which allows an electrical event to be transferred to the muscular system Muscle fiber contraction is initiated by neural stimulation of a sarcolemma, causing? The cisternae of the sarcoplasmic reticulum release calcium ions, which trigger the interaction of thick & thin filaments, consuming ATP and producing a pulling force called tension.
Sarcoplasm
cytoplasm of the muscle fiber & has characteristic membrane potential
Where would you expect to find the greatest concentration of calcium in resting skeletal muscle?
in cisternae of the sarcoplasmic reticulum The cytosol contains low calcium in resting skeletal muscle
What would happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to calcium ions?
increased strength of contraction & decreased ability to relax cytosolic concentration of Ca2+ would increase & the muscle would contract & bc the amount of calcium ions in the cytosol must decrease for relation to occur, it might prevent the muscle from relaxing completely
Sustained tension
is less than maximum tension, allowing some motor units to rest in rotation.
Sarcoplasmic reticulum
membrane complex that forms a tubular network around each myofibril
Transverse tubules
narrow tubes whose surfaces are continuous w/ the sarcolemma & extend deep into the sarcoplasm, & form passageways through the muscle fiber
Sarcolemma
plasma membrane of a muscle fiber & surrounds the sarcoplasm
Slow Fibers
small diameter, rich in myoglobin, and very vascular - are slow to contract, slow to fatigue - have small diameter, more mitochondria - have high oxygen supply - contain myoglobin (a red pigment that binds oxygen) Red muscle (mostly) -Dark (e.g.,chicken legs)
The neuromuscular junction.
special intercellular connection between axon branches and a skeletal muscle fiber the synapse between a motor neuron & a skeletal muscle cell (fiber) & enables communication between the nervous system & a skeletal muscle fiber
Maximum Tension
when all motor units reach tetanus, but this can only be sustained for a very short time.
Identify the structural differences between skeletal muscle fibers and smooth muscle cells
• Smooth muscle is a nonstriated tissue which forms around other tissues in almost every organ system The internal organization of actin and myosin in smooth muscle is different from that in the striated muscles. Smooth muscle cells: 1. are long and slender 2. are spindle shaped, with a single, central nucleus 3. have no T tubules, myofibrils or sarcomeres 4. have scattered myosin fibers, with more heads per thick filament 5. have thin filaments attached to dense bodies 6. transmit contractile force from cell to cell through dense bodies 7. have no tendons or aponeuroses
Isotonic Eccentric contraction
•If muscle tension < load (resistance): -muscle lengthens
Isotonic Concentric contraction
•If muscle tension > load (resistance): -muscle shortens
Isotonic contraction
•Skeletal muscle changes length: -resulting in motion Concentric = muscle shortens Eccentric = muscle lengthens
Muscle tone
•The normal tension and firmness of a muscle at rest •Muscle units actively maintain body position, without motion •Increasing muscle tone increases metabolic energy used, even at rest