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phgy215 final exam > module 4 > Flashcards

module 4 Flashcards

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1
Q

describe skeletal muscle

A

striated, under voluntary control

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2
Q

describe a muscle

A

made of individual muscle fibres, which run the entire length of the muscle

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3
Q

describe a muscle fibre

A

runs parallel to each other and are surrounded by connective tissues, a single cell, multi nucleated and have a large number of mitochondria

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4
Q

describe a myofibril

A

cell divided into contractile elements, light/dark bands give striation, organized into a cytoskeletal pattern of thick/thin filaments

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5
Q

what is an a band

A

dark bands, stacks of thick and thin filaments parallel to each other

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6
Q

what is an i band

A

light bands, made of thin filaments

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7
Q

what is the h zone

A

lighter portion of the a band, contains proteins that hold thick filaments together

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8
Q

what is the m line

A

proteins hold thick and thin filaments together in a stack, runs down centre of the h zone

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9
Q

what is the z line

A

vertical line in the middle of the i band, functional unit of a sarcomere

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10
Q

what is the function of a sarcomere

A

extends the length of the muscle fibre when growing by adding new sarcomeres to ends, creates cross bridges in the a band when thick and thin filaments overlap, 2.5um in width when relaxed

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11
Q

describe the thick filament

A

composed of myosin, motor proteins use ATP to move along actin filaments, has a long shaft with globular head for binding site

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12
Q

describe the thin filament

A

composed of actin (tropomyosin and troponin), made of spherical actin molecule to form the double helix structure

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13
Q

what is tropomyosin?

A

thin, double helix protein that lies end to end on the actin helix, covers binding site to prevent interaction of actin and myosin (regulatory protein)

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14
Q

what is troponin?

A

regulatory protein complex made of three polypeptides, one binds to tropomyosin, actin, and Ca++ (activates myosin ATPase activity and muscle contraction)

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15
Q

what is the sliding filament mechanism?

A

thin filaments move inwards over the thick filaments and z-lines move closer together. sarcomeres shorten and the whole muscle shortens

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16
Q

what are the four steps to the power stroke contraction?

A
  1. binding; myosin cross-bridge binds to actin molecule
  2. power stroke; myosin head bends, pulls thin myofilament inward
  3. detachment; cross-bridge detaches at end and returns to original formation
  4. binding; cross-bridge binds to more distal actin molecule, and the cycle repeats
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17
Q

describe the excitation-contraction coupling process

A

ACh is released into the neuromuscular junction, permeability changes and initiates action potential conducted across the entire muscle membrane (electrical signal to contraction)

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18
Q

what is sarcoplasmic reticulum?

A

runs parallel to fibres, has lateral sacs close to t-tubules and the ends for Ca++ storage, ryanodine receptors to sense depolarization and open Ca++ channels into the cytoplasm

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19
Q

what are t-tubules?

A

invaginations of plasma membranes at the junction of a and i bands. runs perpendicular, has dihydropyridine receptors on the surface as voltage sensors to sense depolarization

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20
Q

what occurs when calcium release is relaxed?

A

tropomyosin and troponin prevent cross-bridge formation by blocking myosin binding site on actin molecules

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21
Q

what occurs when calcium release is excited?

A

calcium enters the muscle fibre and binds to troponin causing a conformational change that results in tropomyosin moving out and exposing the binding site on actin molecules

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22
Q

what occurs when calcium release is relaxed after an excitation?

A

acetylcholinesterase removes any remaining ACh from the neuromuscular junction, stopping action potential generation

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23
Q

describe the process of cross-bridge cycling

A
  1. ATPase site binds to ATP, splits into ADP and inorganic phosphate, releases stored energy to myosin cross bridge
  2. Ca++ and troponin-tropomyosin complex exposes actin molecules for binding and power stroke
  3. no contraction, no Ca++
  4. power stroke completes, phosphate and ADP are released
  5. binding new ATP molecule causes cross bridge to detach, starting again
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24
Q

what is after death of cross-bridge cycling?

A

rigor mortis occurs due to Ca++ concentration increasing in cells and muscle remained contracted until out of ATP (since the death will eventually not produce any) and proteins decay

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25
what are the three temporal periods of a contraction?
1. latent period; contraction 1-2 ms, is the delay before contraction starts, cross-bridge cycling is beginning 2. contraction time; cycling begins, takes time for sliding, peak tension is reached at 40-120 ms 3. relaxation time; Ca++ is removed, 50-200 ms
26
what are the three frequencies of stimulation?
1. single twitch; muscle fibre is restimulated after completely relaxed, second twitch is same magnitude as the first 2. twitch summation; fibre is restimulated before completely relaxed and both are added together 3. tetanus; rapidly twitches overlap, unfused contractions where muscles don't relax before next stimulus
27
what is sustained contraction?
motor units are stimulated by motor neurons at a high frequency at heavy weight
28
what is the less than optimal length?
contraction and tension decreases
29
what is the optimal length?
maximal number of cross bridge binding, thin do not overlap central region, maximal contraction
30
what is greater than optimal length?
overlap decreases, less tension, no contraction occurs
31
what is a isotonic contraction?
fibre tension remains constant as it changes length
32
what is isometric contraction?
fibre tension increases as it remains the same length (static muscle contraction)
33
what is concentric dynamic contraction?
produces tension while muscle shortens (lifting with bicep), everything shortens except the a band
34
what is eccentric dynamic contraction?
produces tension while the muscle lengthens (lowering with bicep), everything lengthens except the a band
35
what is central fatigue?
cns decreases activation of motor neurons, slowing down and cessation of activity even if muscle fibres are not fatigued (bored with activity, tired or lack of motivation)
36
what is muscle fatigue? four parts.
reduces contractile activity before ATP runs out 1. accumulation of ADP and phosphate from ATP hydrolysis, interferes with cross bridge cycling 2. accumulation of lactic acid inhibits enzymes of glycolysis reducing ATP and interferes with contraction coupling 3. accumulation of K+ causing membrane depolarization, less excitable fibres since Na-K pump cannot function without ATP 4. depletion of glycogen during exercise
37
what are the characteristics of slow twitch (type I) muscle fibres?
slow oxidative, a2 motor neurons, small, slow, resistant to fatigue, red (fast distance running)
38
what are the characteristics of fast twitch (type I) muscle fibres?
a1 motor neurons, large, fast, red/pale, fatigable (middle distance to sprint running)
39
describe the red muscle fibres
contain numerous mitochondria and are highly vascularized, lots of myoblobin to support high use of oxygen
40
describe the white muscle fibres
have few mitochondria and no myoglobin
41
what do muscle spindles do?
monitory changes in muscle length and are the key role of stretch reflexes, they are found in collections of intrafusal fibres found among extrafusal fibres
42
what are intrafusal fibres? what are extrafusal fibres?
lie within connective tissue and regular muscle fibres
43
how are muscle spindles innvervated?
innervated by gamma motor neurons, the central region contains sensory afferent fibres activated by stretch, and transmit information on muscle length and rate of stretch to CNS
44
what are golgi tendon organs?
respond to changes in muscle tension, receptors at junction of tendons and fibres responding to stretch and contraction
45
what are afferent neurons?
involved in spinal reflexes, maintain posture and protective movements (withdrawal)
46
what is the primary motor cortex?
fibres from pyramidal cells descend and terminate directly on motor neurons of the spinal cord. fine voluntary movements of the corticospinal motor system
47
what is the function of the brain stem?
regulates overall posture and involuntary movements of large muscle groups. multi-neuronal motor system influenced by motor regions of the cortex, cerebellum, and basal nuclei
48
what happens to muscle spindles if damaged?
affect detention of muscle length, hindering ability of afferent nerves to convey information to brain stem/primary motor cortex. hinders coordination of muscle activity
49
what happens if the brainstem nuclei is damaged?
result in decreased input on motor neurons, hindering voluntary movement
50
where are smooth muscle cells found?
walls of hollow organs and tubes, digestive system and the vasculature
51
where are cardiac muscle cells found?
heart
52
what is the structure of the smooth muscle? three filaments.
1. thick myosin filaments that are longer than those in skeletal muscle 2. thin actin filaments that do not contain tropomyosin 3. intermediated filaments that do not support contraction but rather cytoskeletal framework
53
describe smooth muscle cells
dense bodies throughout the cell and internal surface of plasma membrane, serves as anchor points for intermediate and contractile filaments. thick and thin filaments are at angles
54
describe smooth muscle contraction
lacks troponin, actin and myosin can't form cross bridges at rest
55
what are the 3 steps to smooth muscle contraction?
1. excitation, Ca++ enters the smooth muscle cell and binds to calmodulin (messenger protein) 2. Ca++ calmodulin complex binds and activates myosin light chain kinase 3. activated kinase phosphorylates myosin light chain, allows myosin to cross-bridge to actin
56
what is the calcium source from ECF?
voltage-gated dihydropyridine receptors in smooth muscle cells function as Ca++ channels, depolarization will open them into the ECF
57
what is the calcium source from SR?
Ca++ enters through voltage-gated channels and can activate calmodulin or increase Ca++ (CICR) by releasing it from the SR
58
what are single unit smooth muscles? found in?
fibres are electrically connected via gap junctions and become excited. found in hollow organs such as digestive system, reproductive system, urinary tracts, and small blood vessels
59
what are multi unit smooth muscles? found in?
neurogenic, nerves of autonomic system innervated by nerves to contract. found in walls of large blood vessels, lungs, hair follicles, and eye to adjust
60
what does myogenic mean?
single unit smooth muscle is self-excitable and does not require nerve stimulation
61
what are slow wave potentials?
caused by active transport of Ca2+ across the membrane, causing an oscillating wave of alternating hyperpolarization and depolarization. Action potential is generated and amplitude is influenced by neural and local factors
62
what are pacemaker potentials?
Autorhythmic cells contain If channels permeable to Na and K ions open and depolarize the cell. More positive, If channels close and Ca2+ channels open to continue depolarizing and fire action potential
63
what is the smooth muscle innervation?
ANS modifies rate and strength of contraction. Postganglionic autonomic neurons travel across the surface of smooth muscle cells and release neurotransmitters from varicosities
64
what is cardiac muscle characteristic?
action potentials last longer (200 msec compared to 2-5msec) and have joined branching network of fibres
65
what are some similarities between skeletal and cardiac muscle?
1.Striated with thick and thin filaments organized in sarcomeres 2. Contains troponin and tropomyosin where Ca2+ activates cross bridge activity 3. T-tubules and SR 4. Contains lots of mitochondria 5. Length-tension relationship
66
what are some similarities between smooth and cardiac muscle?
1. Ca2+ comes from ECF and SR 2. Interconnected gap junctions allow spread of excitation 3. Innervated by ANS to modify rate and strength of contraction

phgy215 final exam (2 decks)

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