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25 Cards in this Set
- Front
- Back
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MU01 [a] Characteristics of muscle action potential:
A. RMP -90 mV B. APD 2 to 4 msec C. ERP 1 to 3 msec D. Conduction velocity 0.25 to 0.5 m/sec E. All of the above |
* A. Correct - resting membrane potential -90MV (Ganong 22nd ed p68)
* B. Correct - Action Potential Duration (APD) 2-4ms (Ganong 22nd ed p68) * C. Correct - should be ARP (not ERP) Absolute Refractory Period 1-3msec (Ganong 22nd ed p68) * D. Incorrect - Conduction Velocity is 5m/s (Ganong 22nd ed p68) * E. All of above correct - if D was 5m/s then the correct answer would be E, otherwise A, B and C appear correct |
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MU02 [ad] During muscle contraction:
A. Myosin heads hydrolyse ATP B. Z-lines move together C. Myosin cross-links & swivels 90 degrees D. Interaction between actin & tropomyosin occur E. Calcium passively passes into SR in relaxation |
ANSWER A
* A. Correct - Myosin head contains ATPase, ATP to ADP produces energy for stroke * B. correct - width A bands is constant, Z lines move closer together when muscle contracts and farther apart when stretched, except in isometric contraction * C. Incorrect - In the powerstroke the myosin head attaches to the actin at 90 degrees and subsequently bend to 45 degrees producing relative movement between the filaments * D. Incorrect - Interaction is between actin and myosin. Calcium binds to Troponin C, Troponin displaced laterally exposing binding site for actin. Myosin head binds to actin. * E. Incorrect - Contraction and relaxation both active processes, ATP consuming. Ca-Mg ATPase pumps move calcium back into sarcoplasmic reticulum |
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MU03 [a] Muscle spindle functions:
A. Increased gamma efferent tone smooths contraction B. Increased alpha efferent tone smooths contraction C. ? D. ? |
ANSWER A
* A gamma efferents supply muscle spindles (intrafusal fibres) * A beta efferents supply both intrafusal and extrafusal fibres. * A alpha efferents supply extrafusal fibres. * The muscle spindle functions as feedback mechanism to maintain muscle length. |
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MU04 [d]clonus (oscillation) of the muscle spindle is more likely with:
A. Increase in alpha-afferent discharge B. Increase in gamma-efferent discharge C. There is a delay in the circuit D. Increased tone E. All of the above |
Answer E
A. Alpha (or Ia/Ib) fibres are actually afferent fibres. Ia fibres located in muscle spindle (along with II fibres), these are rapid adapting, sense movement Ib fibres originate from Golgi tendon organs. These link to inhibitory interneurones to the motor neurones supplying the extrafusal fibres of the same muscle and to excitatory connections on the muscles antagonists. Stimulation of these fibres cause relaxation of the muscle, and as regulator of muscle force may contribute to clonus. B. A finding characteristic of states in which increased gamma efferent discharge is present is clonus. C. When the muscle is stretched in the case of hyperactive spindles the burst of discharges supplying the motor neurone causes the muscle to contract, stopping the spindle discharge. This causes a reduction in Ia stimulation and increase in Ib stimulation, causing the muscle to relax. However, the muscle is still stretched, and the cycle is repeated. The delay in the circuit is what gives clonus it's characteristic beat. D. Increased tone is generally a result of increased gamma efferent discharge, thus more likely to produce clonus. |
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MU05 [dk] In skeletal muscle:
A. Relaxation is due to passive Ca++ uptake by sarcoplasmic reticulum B. Contraction is due to Ca++ release from T tubules C. Contraction is due to Ca++ binding to tropomyosin D. Z lines move together in contraction |
ANSWER D
A : False, relaxation is via active Ca/Mg ATPase pump on SR B: False T-tubules transmit AP down to SR from sarcomella to cause SR Ca release C: False for contraction Ca binds to troponin C which causes conformation change in troponin T, moving troponin I from actin allowing tropomysin to reveal the myosin binding site on actin. D: true |
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MU06 [d] In smooth muscle:
A. Spontaneous pacemaker potentials are generated B. An action potential is required for contraction C. Ca++ is released from sarcoplasmic reticulum D. Multiple spiking action potentials occur with increased membrane potential |
ANSWER A
A. Smooth muscle found in most hollow viscera is functionally syncytial (def: pertaining to a multinucleate mass of protoplasm produced by the merging of cells - Dorlands Medical Dictionary ) and contains pacemakers that discharge irregularly. Smooth muscle found in the eye does not. But the majority does so CORRECT B. Visceral smooth muscle is unique (unlike other smooth muscle) in that it contracts when stretched in the absence of any extrinsic innervation. INCORRECT C. Ca 2+ is involved in the initiation of contraction of smooth muscle. Visceral smooth muscle has poorly developed sarcoplasmic reticulum, and the increase in the intracellular [Ca 2+] that initiates contraction is due primarily to Ca 2+ influx from the ECF via voltage-gated and ligand-gated ion channels. INCORRECT D. Increase in membrane potential results in decrease in number of action potentials, decrease in membrane potential results in increased number. INCORRECT |
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MU07 [efklop] Contraction in smooth muscle is different from skeletal muscle:
A. Source of Ca++ is different B. Force is greater in ?smooth muscle ?skeletal muscle C. Unable to produce same force of contraction D. Unable to maintain same duration of contraction E. Has prolonged latency F. Sarcomere of skeletal muscle is > smooth muscle G. Increased actin:myosin ratio H. Increased numbers of mitochondria I. More developed endoplasmic reticulum |
* A. Correct - entry of calcium from ECF via voltage-gated calcium channels, sarcoplasmic reticulum poorly formed
* B. ?? * C. ?? * D. Incorrect - Contraction must last for long periods, tonic contractions typical and effect of "latch-bridge" mechanism. * E. TRUE : longer due to lack of SR therefore slow to contract and slow to relax * F. Correct - no sarcomere in smooth muscle, no regular arrangement between fibrils of myosin, actin, tropomyosin, not arrange in regular arrays * G. Correct - smooth muscle 1/3 amount myosin; 2x amt actin, appears that greater amount of actin relative to mysoin * H. Incorrect - only few mitochondria in smooth muscle (high numbers in cardiac muscle), cellular metabolism depends largely on glycolysis * I. Incorrect - less well developed sarcoplasmic reticulum in smooth muscle |
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MU07b [q] Vascular smooth muscle differs from skeletal muscle in:
A. Different source of Calcium B. Absence of tropomyosin C. Contraction not dependant on interaction between actin and myosin D. Force developed is less |
ANSWER A
* A. Correct - Smooth muscle obtains its calcium from a different source compared with skeletal muscle. "Visceral smooth muscle generally has a poorly developed sarcoplasmic reticulum, and the increase in intracellular calcium concentration... is due primarily to Ca2+ influx from the ECF via voltage-gated Ca2+ channels" (Ganong ed 20, p.79) * B. Incorrect - Smooth muscle DOES contain tropomyosin, but does not contain troponin (Ganong ed 20, p78) * C. Incorrect - "Actin and myosin-II are present, and they slide on each other to produce contraction" * D. Incorrect - contractions are relatively slow, develop high forces and are maintained for longer durations when compared to striated muscle fibres |
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MU08 [el] Force developed during isotonic contraction is:
A. Dependent on the load condition B. Independent of the load condition C. Independent of muscle fibre length D. ? |
ANSWER A
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MU09 [f] Muscle :
A. The A band is dark because it contains thick actin filaments B. Myosin filaments are attached to the Z line C. Sarcomere is the area between 2 adjacent M lines D. ? |
ANSWER B
M line is attached to Z line via Titan to prevent over stretching and provide scaffolding this is also attached to cell wall allowing transmission of contraction, via desmin Z line : attachment between thin filaments (actin and tropomycin), sarcomere length, move closer together I band : surrounds Z line, just thin filaments, no overlap A band : follows I band, represents thick filament (overlapped and non overlapped parts) H band : follows A band, non overlapping part of thick filament, contains M line M line : inflection of thick filaments (myosin chains) Contraction Z-lines move closer I and H shorten A band stays the same (thick filaments cannot change length) |
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MU09b [hij] Isotonic contraction of a skeletal muscle fibre is not associated with a change in ? distance between:
A. Sarcomere length B. A bands C. I bands D. Z-lines move closer together E. M-lines move closer together |
ANSWER B
Isotonic contraction = same tension Isometric contraction = same length Everything shortens except A band |
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MU09c [k] During Isotonic contraction of a skeletal muscle fibre:
A. Calcium enters from the T tubular system near the myofibrils B. ? C. ? D. Z-lines move closer together E. |
ANSWER D
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MU10 [fgk] Tetany does NOT occur in cardiac muscle because:
A. Long absolute refractory period B. Acts as a syncitium C. Pacemaker signal can overcome any tetany D. ? E. ? |
Answer is A. Long absolute refractory period
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MU11 [gn] Sarcomere:
A. From I line to I line B. Actin filament attached to M line C. ? D. Z line crosses across myofibrils & from muscle fiber to muscle fiber E. Smooth muscle cells are larger than skeletal muscle cells |
All FALSE
A. The area between two adjacent Z lines is called a sarcomere. INCORRECT (Ganong pg 65) B. Z lines transect the fibrils and connect to thin filaments, which are made up of actin, tropomyosin and troponin (subunits I, C and T). INCORRECT (Ganong pg 65) D. Titin (large protien) connects Z lines to the M lines and provides scaffolding for the sarcomere. Desmin binds the Z lines to the plasma membrane. INCORRECT (Ganong pg 67) E. Smooth muscle fibres are about 2 - 5 micrometers in diameter and 20 - 500 micrometers in length, compared to skeletal muscle which are 20 times as thick and thousands of times as long. INCORRECT (Guyton, pg 95) |
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MU12 [fghlopq] The soleus muscle:
A. High glycogen stores B. Few mitochondria C. Large nerve fibre D. Long duration of contraction E. Large muscle fibre (OR: Large muscle diameter) F. High capacity for glycolysis |
ANSWER D
The soleus muscle has fatigue resistant (red) muscle fibres - and, in contrast, the gastrocnemius tends to have white muscle fibres. Fatigue resistant muscles are red because of high myoglobin content. These type of muscle fibres have high mitochondrial content (therefore aerobic metabolism), slow myosin ATPase (therefore strong sustained contractions up to 100ms), and low levels of glycolytic enzymes (unable to function anaerobically by glycolysis). Fast twitch muscle fibres are at least twice the diameter of slow twitch fibres. |
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MU13 [g] Skeletal muscle action potential:
A. Na & K conductance begin to increase at same time B. Units of conductance are mA/cm3 C. ? |
Both FALSE
A: Sodium conductance increases first then potassium conductance (same as in nerve AP's ) B: Units of conductance are mmho/cm2 |
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MU14 [i] An increase in force of a skeletal muscle contraction is initially achieved by:
A. Recruitment of nerve fibres B. Recruitment of muscle fibres C. Recruitment of motor units D. Increased intracellular calcium E. None of the above |
ANSWER C
Factors responsible for Grading of muscle contraction * recruitment of motor units * frequency of discharge of motor nerves * length of muscle fibre * the asynchronous firing of motor units |
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MU14 [i] An increase in force of a skeletal muscle contraction is initially achieved by:
A. Increased calcium release in contracting myocytes B. Recruitment of myofibres C. Recruitment of motor units D. Increasing force of skeletal muscle contraction is due to |
ANSWER C
Factors responsible for Grading of muscle contraction * recruitment of motor units * frequency of discharge of motor nerves * length of muscle fibre * the asynchronous firing of motor units |
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MU15 [io] In a large nerve fibre, the typical action potential duration is:
A. 0.03 millisecs B. 0.3 millisecs C. 3 millisecs D. 30 millisecs E. 300 millisecs |
ANSWER B
AP duration A fibres : 0.4-0.5 ms B fibres : 1.2 ms C fibres: 2 ms |
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MU16 [j] The muscular contractions in skeletal muscle working at what level of
efficiency? A. 10% B. 15% C. 35% D. 50% E. 75% |
ANSWER D
Efficiency= work done/total energy expenditure Isotonic contraction 50% Isometric contraction 0% |
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MU17 [j] Annulospiral endings are involved in:
A. afferent to receptors measuring tension B. afferent to receptors measuring length C. supply to intrafusal & extrafusal fibres D. ? |
ANSWER B
Muscle Spindle -extrafusal and intrafusal -measure stretch/length -Ia and II fibres, large and myelinated -sensitivity is modulated by A gamma efferents Golgi Apparatus -located in tendons -measures tension -Ib afferent axon is a large diameter, myelinated axon |
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MU18 [kq] Denervated muscle extrajunctional receptors differ from the motor end plate receptors…
A Have 1 alpha subunit B Open for shorter time C Not produced in the end plate D. ? E None of the above |
ANSWER E
* A. Incorrect - extrajunctional and junctional nictoinic receptors both have two alpha subunits, gamma unit substituted for epsilon unit in extrajunctional nicotinic receptor (Miller 6th edn, p871) * B. Incorrect - extrajunctional receptors have a 2-10 fold longer opening time than mature junctional receptors (BJA CEPD reviews Vol 2, No.5 2002) * C. Incorrect - extrajunctional or immature receptors may be expressed anywhere in the muscle membrane (Miller 6th edn p871) * D. ? * E. If A, B, C and D all incorrect, then E would be correct answer. |
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An immediate available energy source in muscle is:
A. ATP in all 3 muscles B. ATP in smooth, phosphorylcreatine in skeletal and cardiac muscle C. Skeletal muscle uses creatine, cardiac and smooth use ATP D. Skeletal and cardiac muscle uses creatine and smooth muscle uses ATP E. All muscles utilise creatine |
ANSWER A
All muscle uses ATP for contraction. Skeletal muscle has phosphocreatinine as a 'store' replenish ATP (up to 8 contractions) |
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MU20 [p] Cardiac muscle is different from skeletal muscle because of:
A. Fast Ca channels B. Slow Ca channels C. Fast Na channels D. Actin and myosin E. ? |
ANSWER B
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MU21 [qr] Intrafusal fibres
A. Shorter than extrafusal fibres B. Measure tension in muscle C. Contain contractile elements |
ANSWER C
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