Muscles Flashcards
1
Q
is skeletal muscle striated or unstriated
A
striated
2
Q
is skeletal muscle voluntary or involuntary
A
voluntary
3
Q
where is skeletal muscle found
A
attached to bones of skeleton
4
Q
function of skeletal muscle
A
movement of body in relation to external environment
5
Q
is cardiac muscle striated or unstriated
A
striated
6
Q
is cardiac muscle voluntary or involuntary
A
involuntary
7
Q
where is cardiac muscle found
A
wall of the heart
8
Q
function of cardiac muscle
A
pumping blood out of the heart
9
Q
is smooth muscle striated or unstriated
A
unstriated
10
Q
is smooth muscle voluntary or involuntary
A
involuntary
11
Q
where is smooth muscle found
A
in walls of hollow organs and tubes such as the stomach and blood vessels
12
Q
function of smooth muscle
A
movement of contents within hollow organs
13
Q
muscle
A
a group of fascicles
14
Q
what are fascicles
A
groups of muscle fibres
15
Q
sarcolemma
A
cell membrane that encloses each muscle cell
16
Q
endomysium
A
connective tissue that wraps each muscle fibre
17
Q
perimysium
A
connective tissue that wraps fascicles
18
Q
epimysium
A
the connective tissue that wraps the whole muscle
19
Q
fascia
A
a layer of thickened connective tissue covers the entire muscle and which is located over the layer of epimysium
20
Q
where does communication of neurotransmitters in muscle occur
A
at the neuromuscular junciton (NMJ)
21
Q
motor unit
A
an axon and the muscle fibres it communicates with
22
Q
what part of the nervous system supplies skeletal muscle
A
the efferent arm of the somatic nervous system
23
Q
motor end plate
A
specialised site on a muscle cell, where an α-motorneuron forms a synapse
24
Q
terminal buttons
A
fit into shallow depressions of the sarcolemma of individual muscle fibres
25
the cleft
the space between the terminal button and the motor end plate
26
transverse (T) tubules
folds of the sarcolemma
27
sarcoplasm
cytoplasm, contains many myofibrils
28
sarcoplasmic reticulum
smooth ER
29
what is a muscle fibre made from
composed of myofibrils which are made of repeating units of sarcomere which in turn are made of regular arrays of thick and thin filaments
30
what gives skeletal muscle a striated appearance
the thick and thin filaments in myofibrils
31
H zone of sarcomere
thick filament only
32
A band of sarcomere
thick filament and overlapping thin filament
33
I band of sarcomere
thin filament
34
name two contractile proteins
actin and myosin
35
name two structural proteins
titin and dystrophin
36
name two regulatory proteins
troponin-complex and tropomyosin
37
what are thin filaments made of
actin
38
F-actin
contractile protein
39
G-actin
has a binding site for myosin
40
three troponin-complex proteins
T, I and C
41
TnI function
binds to actin to hold the troponin-tropomyosin complex in place
42
TnT function
binds to tropomyosinm interlocking them to form a troponin-tropomyosin complex
43
TnC function
binds to calcium ions to produce conformational change in TnI
44
where is myosin head
towards I band
45
where is myosin tail
towards M line
46
what does the myosin head contain
- actin binding site
- nucleotide binding site for ATP and ATPase
47
what does the myosin tail contain
flexible hinge regions where they combine with other tails
48
how many myosins per thick filament
300
49
how many actin can one myosin bind to
6
50
titin functions
- supports protein in muscle
- anchors thick filaments between M line and Z line
- provides structural support and elasticity
- template for myosin assembly
51
what is happening to actin at rest
myosin binding sites are blocked by tropomyosin
52
what happens when Ca2+ is exposed to actin
- Ca2+ binds to TnC
- There is a conformational change in TnC
- this moves tropomyosin
- thus exposes myosin binding sites
53
cross bridge explanation
1. Actin binding: myosin cross bridge binds to actin
2. Power stroke: cross bridge bends pulling thin microfilament inward
3. Detachment: cross bridge detaches at end of power stroke and returns to original conformation
4. Binding: cross bridge binds to more distal actin molecle; cycles repeats
54
explain sliding filament mechanism
- needs overlapping thick and thin filaments
- neither thick nor thin filaments shorted
- filaments slide past eachother
- sliding is due to the cyclical formation and breaking of cross bridges
55
what happens within a sarcomere during contraction
- A band stays the same length
- I band shortens
- H zone shortens
- Sarcomere shortens
56
what does the cross bridge cycle depend on
ATP and Ca2+
57
explanation of the cross bridge cycle
58
steps from excitation to contraction
1. action potential in sarcolemma
2. action potential dowm T tubules
3. DHP receptors of T tubules open Ca2+ channels (ryanodine receptors)
4. Calcium increases in cytosol
5. Calcium binds to troponin shifting tropomyosin
6. Cross bridge cycling occurs
59
what happens if Ca2+ is maintained
- cross bridge cycle continues
- However, Ca2+ is rapidly pumped back into the SR by the SR/ER Ca2+ ATPase (SERCA)
- Therefore, based on the time-scale of the events there is a need for a continuous cycle of Excitation-Contraction to maintain the force
60
how does the cross bridge cycle use ATP
- splitting of ATP by myosin ATPase (for power stroke)
- binding of fresh ATP to myosin to cause dissociation
61
three sources of ATP for muscle
- immediate system - ATP and Creatine Phosphate
- Short term system - anaerobic or non-oxidative glycolysis
- Long term system - oxidative phosphorylation
62
use balanced equations to explain creatine phosphate and atp system
Creatine phosphate + ADP ← creatine kinase → Creatine + ATP
ATP + H2O ← ATPase → ADP + Pi+ H+ + energy
63
creatine phosphate and ATP system
- Creatine phosphate is the first source of ATP (10-30 seconds)
- Can provide 4-5 times the amount of ATP present in cell at rest
- One step process - very rapid
- Very limited amount - used up rapidly
64
use a balanced equation to explain anaerobic or non-oxidative glycolysis
Glucose → 2 lactic acid + 2 ATP
65
anaerobic or non-oxidative glycolysis
- When oxygen supply to muscle is limited (during intense exercise), anaerobic glycolysis is the primary source of ATP
- Breakdown of glucose, O2 is absent
- High intensity exercise (12-120 seconds)
- Rapid source of ATP
66
drawbacks of anaerobic or non-oxidative glycolysis
- only 2 ATP per glucose molecule
- limited glucose availability
- build up of lactic acid
67
oxidative phosphorlyation
- Primary energy source for light/moderate exercise (>2 mins)
- Muscles store a limited amount of glucose as glycogen
- Substrate of oxidative phosphorylation up to 30 minutes
- Glucose and fatty acids delivered to muscle by blood
- Dominant after 30 minutes
- Oxygen supply is adequate
- Occurs in mitochondria
68
twitch contraction
contraction produced in a muscle fibre in response to a single action potential
69
name the three phases of a muscle twitch
1. latent period
2. contraction phase
3. relaxation phase
70
explain the latent period of a twitch
- time from action potential in muscle to onset contraction
- few milliseconds
- exitation-contraction coupling
71
explain the contraction phase of a muscle twitch
- tension is increasing
- 10-100 milliseconds
- cross bridge cycle takes place repeatedly
72
explain relaxation phase of muscle twitch
- tension is decreasing back to zero
- longer than contraction phase
- calcium reuptake
73
isotonic contraction
load remains constant as muscle changes length
74
isometric contraction
muscle is prevented from shortening si tension develops at constant muscle length
75
explain how isometric and isotonic contractions occur together
- even if load is constant, isometric precedes isotonic phase of contraction
- as tension increases the isometric contraction continues until tension exceeds the load
- then isotonic contraction begins
- tension remains constant as muscle shortens
76
why is the load not generally constant
load changes as limb position changes
77
two things the level of force generated by muscle depends on
- factors affecting the force or tension generated by individual muscle fibres
- regulation of the force or tension generated by the whole muscle
78
name the factors that affect force or tension generated by individual muscle fibres
- frequency of stimulation
- fibre diameter
- changes in fibre length
- extent of fatigue
79
what regulates the force or tension generated by the whole muscle
the number of fibres contracting ie. recruitment
80
what is frequency of stimulation
frequency of action potentials in muscle fibres
81
two ways tension is increased
| frequency of stimulation
- treppe
- summation and tetanus
82
treppe
when independent twitches follow one another closely; peak tension increases to a constant level
83
causes of summation and tetanus
- Amount of tension developed depends on amount of calcium bound to troponin
- At high frequencies, release exceeds reuptake
- Calcium increases in cytosol
- Eventually saturate system
- All troponin molecules are bound to calcium
- Cross bridge cycle maxes out
- Maximum tetanic contraction
84
what is force generation capacity
inherent ability of muscle to generate force
85
what does force generation capacity depend on
the number of cross bridges in each sarcomere and geometrical arrangement of sarcomeres
86
what happens when there are more cross bridges in a sarcomere
more force is generated
87
what happens when more sarcomeres are in parallel
more force is generated
88
what happens when there is a greater fibre diameter
more filaments are present in the fibre and thus more force is generated
89
optimum length
- resting length of muscle at which fibres can develop greatest amount of tension
- sue to maximum overlpa of thick filament cross bridges and thin filaments
90
what causes a length greater than optimum
a decrease in cross bridge overlap
91
what causes a muscle length less than optimum
- thin filaments overlap eachother
- Z lines contact thin filaments
92
explain recruitment of motor units
- activation of motor neuron activates all muscle fibres in the motor unit
- increase in tension occurs in steps proportional to the size of motor units
93
motor unit size in muscles for delicate movements
small
94
motor unit size in muscles for strength
large
95
small fibre diamter
needed for weaker movements
96
large fibre units
needed for stronger movements
97
relation of motor unit and fibre diameter
- Small motor units → small fibres
- Large motor units → large fibres
98
motor unit size principle
small motor units are recruited first and large motor units are recruited last
99
what does muscle contraction speed depend on
rate of mysosin ATPase activity
100
3 types of muscle fibre
| contraction speed
- slow oxidative
- fast oxidative
- fast glycolic
101
slow oxidative fibre size and force
smallest
102
fast oxidative fibre size and force
intermediate
103
fasy glycolic fibre size and force
largest
104
composition of muscle fibre types within muscle
one muscle is made of a mixture of all three fibre types at different proportions depending on the function of the muscle
105
recruitment order of muscle fibre types
- slow oxidative
- fast oxidative
- fast glycolic
106
muscle fatigue
decline in a muscle's ability ti maintain a constant contraction force during repetition
107
seven causes of muscle fatigue
- low intensity exercise
- high intensity exercise
- very high intensity exercise
- strong and sustained contractions
- central fatigue
- build up of inorganic phosphates
- changes in ion distribution
108
low intensity exercise
| muscle fatigue
depetes energy reserves
109
high intensity exercise
| muscle fatigue
build up of lactic acid
110
very high intensity exercise
| muscle fatigue
depletion of acetylcholine
111
trong and sustained contractions
| muscle fatigue
compression of blood vessels
112
central fatigue
| muscle fatigue
psychological/neural fatigue
113
how do muscles increase in size
- no cell division
- increase in myofibrils
114
disuse atrophy
decrease in size due to loss of myofibrils
115
denervation atrophy
motor neuron is destoryed, meaning there is no excitation - atrophy due to misuse
116
hypertrophy
- increase in muscle size due to increase in myofibrils
- increase in production of actin and myosin
117
two skeletal muscle receptors
- muscle spindle
- golgi tendon organ
118
where are muscle spindles found
within muscle
119
what do muscle spindles detect
muscle length
120
where are golgi tendon organs found
within tendon
121
what do GTOs detect
muscle tension
122
what are extrafusual fibres found in
contractile cells of the muscle
123
what are extrafusal fibres innervated by
alpha motor neurons
124
where are intrafusal fibres found
muscle spindles
125
what are intrafusal fibres innervated by
gamma motor neurons
126
two types of sensory fibres found in muscle spindle
- Type Ia
- Tyoe II
127
describe type Ia sensory fibres
annulospiral endings that wrap around the central portion of the spindle
128
what do type Ia sensory fibres detect
muscle length and velocity
129
describe type II sensory fibres
flower-spray endings that are located around either end of the spindle
130
what do type II sensory fibres detect
onlt muscle length
131
two steps of the stretch reflex pathway
- afferent input from sensory endings of muscle spindle fibre
- alpha motor neuron output to regular skeletal muscle fibre
132
explain alpha-gamma coactivation
- stretch reflex pathway
- gamma motor neuron output to contractile end portions of spindle fibre
- descending pathways coactivate alpha and gamma motor neurons
133
how do GTOs sense muscle tension
- They are afferent fibres lying within the tendons
- Respond to alterations in muscle tension
- Muscle tension causes tendon tightening and uplift to joint
- The increased tension in the tendon stretches GTO
- Stretch intensity increases action potential frequency (afferent signals delivered centrally and therefore interpreted consciously)
- Meaning we can feel muscle tension but not muscle length
134
where are smooth muscles found
walls of hollow organs
135
what type of contractions do smooth muscles produce
- continuous contractions of relatively low force
- contraction of whole muscle mass
136
what kind of control does smooth muscle have
involuntary - influenced by nervous system, hormones and local metabolites
137
describe a smooth muscle cell (5 points)
- contractile units
- one nucleus
- dense bodies
- slow myosin ATPase
- little sarcoplasmuc reticulum
138
phasic
smooth muscle which contracts in bursts
139
tonic
smooth muscle which maintains tone
140
neurogenic
initiation of contraction is orginated in nervous tissue
141
describe single unit smooth muscle
- most common type
- tonic or phasic
- muscle fibres are activated synchronously
- they contract together as a single unit
142
where are single unit smooth muscles found
digestive, reproductive and urinary tracts and small blood vessels
143
how are fibres in single-unit smooth muscles connected
gap junctions
144
how are fibres in single-unit smooth muscles connected
gap junctions
145
describe multi-unit smooth muscle
- phasic and neurogenic
- discrete units which function independently
- few, if any gap junctions
146
where is multi-unit smooth muscle found
walls of large blood vessels, small airways of lung, muscles of eye, base of hair follicles
147
describe the innervation of multi-unit smooth muscle
each functional unit is activated separately ie. recieves its own innervation
148
steps of excitation-contraction coupling of smooth muscle
1. opening of calcium channels in plasma membrane
2. Calcium triggers release of calcium from sarcoplasmic reticulum
3. Calcium binds to calmodulin
4. Ca2+-Calmodulin activates MLCK enzyme (myosin light chain kinase)
5. MLCK phosphorylates myosin
6. Cross-bridge cycling
149
describe relaxation of smooth muscle
1. Phosphatase enzyme removes phosphate from myosin
2. Calcium removed from cytoplasm
150
why is a high level of Ca2+ needed to activate MLCK
because phosphatase is continuously active and cometes with MLCK
151
descrive neural regulation of smooth muscle contraction
- Innervated by autonomic nervous system
- May be excitatory or inhibitory
- Target cell response depends on receptor type
- Neurotransmitter is released from varicosities
- Gap junctions allow transmission of electrical signal from one cell to neighbouring cells
152
descrive non-neural regulation of smooth muscle contraction
- Some smooth muscles are able to actively exert tension in absence of external stimulus
- If intracellular Ca2+ levels are high enough to maintain constant level of cross-bridge activity - thus maintaining tone
- Sometimes smooth muscles are able to contract by hormonal/other chemical stimulation
153
similarities between skeletal and cardiac muscle
- Striated - contains sarcomeres
- Troponin and tropomyosin regulation
- Has T tubules
- Has sarcoplasmic reticulum although it’s not as well developed
- Similar to slow oxidative fibres
- Myoglobin
- Mitochondria
- Fatigue resistant
154
similarities between smooth and cardiac muscle
- Gap junctions (within intercalated discs)
- Pacemaker cells
- Innervated by autonomic nervous system
- Influenced by hormones, paracrines (influenced by adjacent cells)
- Calcium comes from ECF and SR
155
why is there no summation in cardiac muscle
- action potential lasts almost as long as tension
- thus ling refractory period
156
benefit of no summation of cardiac muscle
summation would not allow the heart to relax after each beat to fill with blood
