1
Q
what is the classification of the muscle?
A
- skeletal muscle
- smooth muscle
- cardiac muscle
2
Q
what is the skeletal muscle activated by?
A
the somatic nervous system motor neuroons
3
Q
what is a motor unit?
A
the motor neuron and associated muscle fibres
4
Q
what is the neuromuscular junction (NMJ)?
A
chemical signaling synapse between motor neuron and skeletal muscle
5
Q
how is the skeletal muscle different to the other two types of muscle?
A
it is the only type of muscle that is under conscious voluntary control - must be activated by the CNS to contract
6
Q
what are sarcomeres?
A
contractile units containing actin and myosin; give skeletal muscle its striated appearance
7
Q
what is the sarcoplasmic reticulum?
A
well-developed Ca²⁺ storage network; releases calcium to trigger rapid, forceful muscle contraction
8
Q
define muscle
A
a group of fascicles
9
Q
muscle fibres extend length of muscle from —— to ——
A
tendon to tendon
10
Q
muscle fibres are made up of myofibrils; what are these?
A
myofibril are contractile threads within a muscle fiber composed of repeating sarcomeres
11
Q
what is the sarcolemma?
A
the plasma membrane
12
Q
what is the T-tubule system?
A
invaginations of the sarcolemma into the muscle fibre - this allows for the spread of action potential deep into the muscle
13
Q
what is the sarcoplasmic reticulum?
A
an intracellular organelle specialist for Ca2+ storage
14
Q
how is the skeletal muscle’s sarcoplasmic reticulum different from the other types of muscle?
A
the skeletal muscle has the best developed sarcoplasmic reticulum so has the fastest contraction time of all three types
15
Q
what does the smoothness and precision of movements determined by?
A
the number and timing of motor units that are activated
16
Q
which motor units are activated first in muscle contraction? why?
A
small motor units, as they are more easily activated
17
Q
what is meant by the collective nature of motor units?
A
the muscle fibres of a motor unit all contract together
18
Q
describe what happens to motor units as we age
A
- as individuals age, motor units within the body become larger
- this means more muscle fibres are innervated by each individual motor neuron
- having many smaller units allowed for more precise controlled movements; however, fewer but larger units allow for large development of force but less control over gradations in force
- so fine motor movements will become more difficult to perform
19
Q
how many categories of muscle fibres are there? what are the implications of this?
A
- there are 3 broad categories of muscle fibres, and hence of motor units
- these categories are based upon their histochemical characteristics
- the muscle fibres of a motor unit are all of the same type
20
Q
name the three categories of muscle fibres
A
- slow-twitch oxidative; red muscle
- fast-twitch oxidative-glycolytic; red muscle
- fast-twitch glycolytic; white muscle
21
Q
three characteristics of slow-twitch oxidative fibres
A
- slowly-contracting
- many mitochondria
- oxidative metabolism
22
Q
three characteristics of fast-twitch glycolytic fibres
A
- fast twitch time
- produce large amounts of tension
- rapid fatigue
23
Q
describe the different types of motor neurons that innervate the different types of muscle fibres
A
- small diameter motor neurons innervate slow oxidative fibres
- large diameter motor neurons innervate fast glycolytic fibres
24
Q
compare the excitability of small and large diameter motor neurons
A
small diameter motor neurons are more easily excited than large diameter motor neurons (lower levels of EPSP input)
25
describe the general anatomy of the neuromuscular junction
- terminal bouton = axon terminal (motor neuron)
- motor end plate = specialised muscle membrane at junction
- all motor neurons release Ach
- all synapses are excitatory
26
what does the activation of motor neurons depend on?
the summation of EPSPs/IPSPs
27
describe the steps of communication at the NMJ
1. action potential arrives at the terminal bouton
2. voltage-gated calcium channels open
3. calcium enters cell trigger the release of Ach
4. Ach diffuses across the cleft and binds to nicotinic receptors on the motor end plate
5. Ach binding triggers opening of channels for small cations (Na and K)
6. Net movement of positive charge in leads to depolarisation
7. this causes an action potential in the muscle cell
8. action potential spreads through the muscle causing contraction
28
how is the brain protected from toxins in the blood?
by the blood-brain barrier
29
what IS exposed to toxins in the blood?
peripheral tissues, including muscle
30
toxins that poison the NMJ fall into 3 types
1. nicotinic receptor blockers: muscle relaxants that block reflexive muscle contraction, eg poison dart (Curare), curariform drugs
2. exocytosis blocker: eg botox
3. Ach-esterase inhibition: continued depolarisation leads to paralysis, eg nerve gases and pesticides
31
what is the function of the crossbridge cycle?
how muscles generate force
32
skeletal muscle fiber - thin and thick filament
thin filament is made up of actin
thick filament is made up of myosin
33
structure of a sarcomere
actin and myosin are organised in overlapping arrangement with respect to one another in units called sarcomeres
34
how does muscle contraction link to sarcomeres?
muscle contraction = sarcomere shortening
35
describe sarcomere shortening
actin and myosin do not change length, instead slide past one another
36
describe the structure of the thick myofilament
- thick filament is made up of myosin molecules
- myosin head contains actin binding site and ATP binding site
37
describe the structure of the thin myofilament
- thin filament is made up of 2 strands of actin molecules
- actin molecule has a binding site for myosin
38
describe troponin and tropomyosin when there is no calcium
troponin holds tropomyosin over myosin binding sites on actin
- no cross bridges form between actin and myosin
- muscle is relaxed
39
describe troponin and tropomyosin when there is calcium present
calcium binds to troponin, causing movement of troponin, causing movement of tropomyosin, exposing binding sites for myosin on actin
- crossbridges form between actin and myosin
- cycle occurs, muscle contracts
40
describe the conformational changes that myosin undergoes
conformational changes swivelling back and forth relying on ATP hydrolysis
- high energy form: high affinity for actin
- low energy form: low affinity for actin
41
describe the cross bridge cycle
1. Power stroke begins when tropomyosin moves off the binding site
2. With increased Ca²⁺, myosin head and actin filament bind strongly
3. The power stroke occurs, with the myosin head moves and propelling the thin filament toward the centre of the muscle
4. Myosin release ADP at the end of the power stroke
5. Tight binding in the rigor state (eg rigor mortis)
6. ATP binds to myosin and myosin releases actin
7. Myosin hydrolyses ATP, so that its head is rotated to the cocked position
8. Myosin binds weakly to actin
42
define excitation-contraction coupling
sequence of events whereby an action potential in the sarcolemma causes contraction
43
excitation-contraction coupling is dependent on (2)
- neural input from motor neuron
- calcium release
44
describe the steps of excitation-contraction coupling
1. Ach is released from motor neurons
2. binding of Ach leads to Na+ entry, leading to muscle action potential
3. the action potential in the t-tubule leads to alteration of DHP receptor
4. the DHP receptor opens RyR Ca2+ release channel in the sarcoplasmic reticulum
5. Ca2+ enters the cytoplasm
6. Ca2+ binds to troponin allowing actin-myosin binding, and the power stroke occurs
45
how does termination of contraction occur?
- calcium must leave the binding sites
- to remove calcium from the cytosol, Ca2+ ATPase in the sarcoplasmic reticulum transports calcium from the cytosol into the sarcoplasmic reticulum
46
what is twitch contraction? how does this happen
- a muscle twitch is a single contraction-relaxation cycle
- to generate force you need to have many twitches working together
47
rise-time and duration of twitch force varies with
muscle fibre type
48
3 phases of muscle twitch
- latent period
- period of contraction
- period of relaxation
49
latent period
excitation-contraction coupling occurring
50
period of contraction
intracellular Ca2+ levels are high, cross bridge cycling is occurring
51
period of relaxation
intracellular Ca2+ levels fall, eventually tension gradually falls to 0
52
draw/label a graph of development of tension during one muscle twitch
53
what is summation?
in skeletal muscle, with increased AP frequency, successive twitches fuse with each other and do not allow the muscle to relax fully - thus, t he contractile force rises
54
what is tetanus?
when repeated stimulation can fuse into one continuous contraction
55
unfused tetanus
stimuli are far enough apart to allow muscles to relax slightly between stimuli
56
complete tetanus
muscle reaches steady tension - if muscle fatigues, tension decreases rapidly
57
where is smooth muscle found?
found in internal organs, blood vessels
58
examples of smooth muscles
vasculature, GI tracts, urinary, reproductive, and respiratory tracts, pupil
59
are smooth muscle arranged in sarcomeres?
no
60
what controls the smooth muscle?
the ANS
61
describe the functioning of the smooth muscle
- must operate over a range of length
- layers may run in several directions
- contracts and relaxes much more slowly
- uses less energy
- sustains contractions for extended periods
62
classification of smooth muscle
by location: vascular, gastrointestinal, urinary, respiratory, reproductive, ocular
by communication with neighbouring cells:
- single-unit smooth muscle/visceral smooth muscle
- multi-unit smooth muscle
63
single-unit smooth muscles
- found in the intestinal tract and blood vessels
- exhibits spontaneous activity (but also activated by the ANS)
- able to actively exert tension in the absence of external stimulation
64
multi-unit smooth muscle
- found in large airways and arteries
- each fiber acts individually
- heavily innervated
- generally, contracts only when nervous supply is stimulated
65
smooth muscle lacks; therefore
specialised receptor regions
- Ca2+ is from the extracellular fluid and sarcoplasmic reticulum
- Ca2+ initiates a cascade ending with phosphorylation of myosin light chain and activation of myosin ATPase
66
describe the smooth muscle excitation-contraction coupling
1. opening of calcium channels in the plasma membrane
2. calcium triggers the release of calcium from sarcoplasmic reticulum
3. calcium binds to calmodulin
4. Ca-calmodulin activates MLCK
5. MLCK phosphorylates myosin
6. crossbridge cycling
67
how does relaxation of the smooth muscle happen?
- phosphatase removes phosphate from myosin
- calcium removed from cytoplasm (Ca-ATPase, Ca-Na counter transport)
68
what are the two types of cardiac muscle cell?
contractile cell and conductive cells
69
AP duration in ventricles
300 ms
70
describe the shape of the AP in the cardiac muscle?
The cardiac action potential has a prolonged plateau due to slow Ca²⁺ channel opening. This maintains depolarization for ~300 ms, allowing sufficient Ca²⁺ entry for a forceful contraction from a single action potential. The shape and duration reflect changing membrane permeability to Na⁺, Ca²⁺, and K⁺ ions.
71
cardiac contractile cell AP last for almost as long as
the contraction and relaxation
72
three ways to change or not change cardiac muscle contraction
- unable to increase force of contraction by motor unit recruitment or by enhanced excitation/contraction coupling
- unable to increase force of contraction by increasing stimulation frequency to tetanus
- increase force of contraction by increasing muscle (Starling law)
73
describe excitation-contraction coupling for the cardiac muscle
- significant Ca2+ source from ECF, rest from SR
- contractile proteins in presence of increased cytosolic [Ca2+] power contraction (systole)
- Ca2+ pump in the SR removes Ca2+ from cytosol allowing for relaxation (diastole)
- Na+/Ca2+ membrane exchange removes Ca2+ from cytosol allowing for diastole
74
Digitalis
Digitalis inhibits the Na⁺/K⁺-ATPase on the cardiac myocyte membrane
→ Intracellular Na⁺ increases
→ This reduces activity of the Na⁺/Ca²⁺ exchanger (NCX)
Normally NCX brings Na⁺ in and pumps Ca²⁺ out
→ Less Ca²⁺ is extruded from the cell
→ Intracellular Ca²⁺ increases
→ More Ca²⁺ is taken up into the sarcoplasmic reticulum
→ More Ca²⁺ released with each action potential
→ Stronger myocardial contraction
75
classification of smooth muscle
by location: vascular, gastrointestinal, urinary, respiratory, reproductive, ocular
by communication with neighbouring cells:
- single-unit smooth muscle/visceral smooth muscle
- multi-unit smooth muscle
PSL300
flashcards
Decks in class (55)
# Cards
-
L140
-
L216
-
L340
-
L431
-
L532
-
L638
-
L733
-
L857
-
L930
-
L1041
-
L1138
-
L1227
-
L1362
-
L1453
-
L1546
-
L1646
-
L1756
-
L1824
-
L1971
-
L2053
-
L2174
-
L2286
-
L2344
-
L2457
-
L2563
-
L2644
-
L2748
-
L2832
-
L2926
-
L3042
-
L3127
-
L3248
-
L3375
-
638
-
733
-
857
-
930
-
1041
-
1138
-
1228
-
1453
-
1546
-
1824
-
1971
-
2053
-
2174
-
2286
-
2563
-
2644
-
2748
-
270
-
2832
-
3127
-
3248
-
3375
