Unit 3: Muscle Physiology Flashcards
1
Q
3 muscle types
A
- skeletal
- cardiac
- smooth
2
Q
skeletal muscle classification
A
striated, voluntary
3
Q
skeletal muscle description
A
- bundles of long, thick, cylindrical, striated, contracticle, multinucleated cells that extend the length of the muscle
4
Q
skeletal muscle typical location
A
attached to the bones
5
Q
skeletal muscle function
A
movement of body in relation to external environment
6
Q
cardiac muscle classification
A
striated, involuntary
7
Q
cardiac muscle desrciption
A
interlinked, short, slender, cylindrical, striated, branched, contractile cells connected by intercalated discs
8
Q
cardiac muscle location
A
heart wall
9
Q
cardiac muscle function
A
pumping blood out of heart
10
Q
smooth muscle classification
A
unstriated, involuntary
11
Q
smooth muscle description
A
loose network of short, slender, spindle-shaped, contractile cells arranged in sheets
12
Q
smooth muscle typical location
A
walls of hollow organs and tubes (stomach and blood vessels)
13
Q
smooth muscle function
A
movement of contents within hollow organs
14
Q
skeletal?
A
a
15
Q
cardiac?
A
b
16
Q
smooth?
A
c
17
Q
skeletal muscle histology
A
- epimysium
- endomysium
- fascicle
- nuclei
- muscle fibers
- blood vessels
- nerves
18
Q
skeletal muscle - epimysium
A
19
Q
skeletal muscle - endomysium
A
20
Q
skeletal muscle - fascicle
A
21
Q
skeletal muscle - perimysium
A
22
Q
skeletal muscle - nuclei
A
23
Q
skeletal muscle - muscle fibers
A
24
Q
skeletal muscle - blood vessels and nerves
A
25
muscle definition
group of fascicles
26
fascicles contain ... which ...
muscle fibers; extend the length of the muscle (tendon to tendon)
27
which tissue surrounds muscle fibers
connective tissue
28
synctia definition
multinucleated
29
sarcolemma
plasma cell membrane that encloses each muscle cell/fiber
30
endomysium
connective tissue that wraps individual muscle fibers
31
perimysium
connective tissue that wraps fascicles
32
fascicles
bundles of muscle fibers
33
epimysium
connective tissue that wraps the who muscle
34
(deep) fascia
a layer of thickened connective tissue that covers the entire muscle and is located over the layer of epimysium
35
what does skeletal muscle require to contract
stimulation by the nervous system
36
where does the nervous system communicate with the skeletal muscle
neuromuscular junction (NMJ)
37
neuromuscular junction (NMJ)
- impuls travels down the axon of the nerve
- reaches nmj, chemical transmitter acetylcholine is released
- muscle contraction
38
motor unit
an axon and muscle fibers it communicates with
39
what supplies efferent innervation to skeletal muscle
efferent arm of the somatic nervous system
40
motor neuron activity is ...
cholinergic, nicotinic, and only excitatory
41
cholinergic definition
relating to or denoting nerve cells in which acetylcholine acts as a neurotransmitter.
42
nicotinic definition
related to or imitating the action of nicotine on neurons, esp. in blocking the cholinergic receptors of the autonomic ganglia
43
NMJ - muscle fiber
44
NMJ - NMJ
45
NMJ - terminal buttons
46
NMJ - axon terminal
47
motor end plate
the area of the muscle fiber surface where terminal buttons fit into shallow depressions of the sarcolemma of individual muscle fibers
48
the cleft
the space between the terminal button and the motor end plate
49
nmj sequence of events
1. action potential in a motor neuron is propagated to the terminal button
2. ap triggers the opening of voltage-gated Ca2+ channels and entry of Ca2+ into the terminal button
3. Ca2+ triggers release of acetylcholine by exocytosis from the vesicles
4. acetylcholine diffuses across the space separating the nerve and muscle cells and binds with receptor-channel specific for it on the motor end plate of the muscle cell membrane
5. nonspecific cation channels open due to binding leading to large movement of Na+ into the muscle cell and small movement of K+ outward
6. result is an end-plate potential; local current flow occurs between depolarized end plate and the adjacent membrane
7. local current flow opens voltage-gated Na+ channels in the adjacent membrane
8. Na+ entry reduces the potential to threshold initiating an action potential propagated through the muscle fiber
9. acetylcholine destroyed by acetylcholinesterase terminating the muscle cell's response
50
acetylcholinesterase
an enzyme on the motor end-plate membrane that destroys acetylcholine
51
transverse (T) tubules
folds of the sarcolemma
52
sarcoplasm
cytoplasm containing myofibrils
53
sarcoplasmic reticulum
smooth ER
54
skeletal muscle fiber organization
55
skeletal muscle fiber structure
regular striated patterns of filaments and organelles hint at functionality
56
what gives skeletal muscle a striated appearance
myofibrils
57
myofibril definition
orderly arrangement of thick and thin filaments (actin and myosin)
58
what do filaments form
sarcomeres
59
sarcomeres
- function unit
- z line to z line
60
myofibril parts
- z line
- m line
- a band
- h zone
- i band
- cross bridge
- thick filaments
- thin filaments
61
myofibril - z line
62
myofibril - m line
63
myofibril - a band
64
myofibril - i band
65
myofibril - crossbirdges
66
myofibril - thick filaments
67
myofibril - thin filaments
68
is h zone in myofibril thin filaments, thick filaments, or both?
thick filament (myosin) only
69
is a band in myofibril thin filaments, thick filaments, or both?
both
70
is i band in myofibril thin filaments, thick filaments, or both?
thin filament (actin) only
71
during contraction which part of a myofibril decreases in size due to more thin and thick filaments overlapping?
h zone
72
proteins of the sarcomere
- contractile proteins (actin and myosin)
- structural proteins (titin, dystrophin)
- regulatory proteins (troponin-complex, tropomyosin)
73
types of actin and their purpose
- F(ilamentous) actin is contractile
- G(lobular) actin has a myosin binding site
74
tropomyosin
- regulatory protein
- overlaps binding sites on actin for myosin
75
troponin-complex
- regulatory protein
- complex of three proteins [attaches to T(ropomyosin), attaches to I (actin), binds C (calcium) reversibly]
76
what makes up a thin filament in a sarcomere
- actin
- tropomyosin
- troponin
77
what makes up a thick filament in a sarcomere
bundles of myosin molecules bound at the tail
78
myosin tails point towards what
the m line
79
myosin heads point towards what
I band
80
what is the I band
thin filament near Z line
81
is titin present in thick or thin myofilaments
both
82
titin
- Z line to M line
- template for myosin assembly
- supports proteins in muscle
- anchors thick filaments between M and Z lines
- structural support and elasticity
83
parts of a single myosin molecule
- 2 identical myosin heavy chains
- 4 myosin light chains
- S1 head segment (ATPase activity, actin binding site)
- S2 tail segment (flexible hinge regions, combines with other tails)
- thick filament (contact 6 actin filament)
84
crossbridge cycle purpose
how muscles generate force
85
excitation-contraction coupling purpose
how muscle contractions are turned on and off
86
muscle cell metabolism
how muscle cells provide ATP to drive the crossbridge cycle
87
at rest, the skeletal muscle ...
myosin binding sites on actin blocked by tropomyosin
88
when Ca2+ is present, the skeletal muscle ...
- Ca2+ binds to Troponin-complex
- conformational alteration in Troponin-complex
- moves tropomyosin
- exposes myosin binding sites
89
what does Troponinc C bind to in order to produce a corformational change in Troponin I
calcium ions
90
result of Troponin T binding to tropomyosin
troponin-tropomyosin complex
91
which binding holds the troponin-tropomyosin complex in place
troponin I binding to actin
92
troponin/tropomyosin/actin complex function
blocks interaction with myosin
93
troponin without Ca2+ (relaxed)
stabilize tropomyosin actin binding
94
troponin with Ca2+ (contracting)
destabilize tropomyosinactin binding --> cross bridge formation
95
how is a sarcomere shortened
z-lines of the extremes of the sarcomeres are pulled in
96
cross bridges and sarcomere shortening includes multiple cycles of
1. actin binding
2. power stroke
3. detachment
4. binding
97
sliding filament mechanism
- muscle contraction
- needs overlapping of thin and thick filaments
- neither thin or thick filaments shorten
- filaments slide past each other
- sarcomere contraction
98
crossbridge cycle due to…
sliding is due to cyclical formation and breaking of cross bridges
99
within a sarcomere during contraction
- a band stays the same length
- i band shortens
- h zone shortens
- sarcomere shortens
100
cross-bridge cycle depends on the presence of either:
- ATP
- Ca2+
101
cross-bridge cycle (ATP)
1. link of thin to thick filaments
2. power stroke, ADP is released from myosin
3. myosin binds to new ATP
4. thick and thin filaments detach
5. ATP hydrolysis, myosin re-energised
6. myosin head returns to cocked position
7. binding again
102
power stroke
myosin head moves propelling thin filament toward muscle center
103
cross-bridge cycle (ATP) binding again process
- myosin head returns to initial position
- myosin head undergoes conformational changes (high and low energy form)
- relies on ATP hydrolysis
104
excitation-contraction
sequence of events where an action potential in the sarcolemma causes contraction
105
excitation-contraction (no calcium)
- troponin holds tropomyosin over myosin binding sites on actin
- no cross bridges form
- muscle relaxed
106
excitation-contraction (calcium present)
- binds to troponin
- causing movement of troponin
- causing movement of tropomyosin
- exposing binding sites for myosin on actin
- cross bridges form
- cycle occurs, muscle contracts
107
excitation-contraction occurance depends on
- neural input from motor neuron
- Ca2+ release from the sarcoplasmic reticulum
108
steps from excitation to contraction
1. action potential in sarcolemma
2. action potential down T tubules
3. DHP receptors of T tubules open Ca2+ channels in lateral sacs of SR
109
if what continues, the crossbridge cycle continues
calcium
110
what pumps calcium back into the sarcoplasmic reticulum
sr/er ca2+ ATPase
111
there is a need for a continuous what to maintain a force in a muscle
cycle of excitation-contraction
112
dihydropyridine (DHP) receptor
- on t tubules
- voltage gated
- opens on depolarization
113
DHP receptors triggers what
opening of Ryanodine receptors (RyR) on SR
114
sarcoplasmic reticulum gating steps
1. DHP receptor opens on depolarization
2. triggers opening of RyR on SR
3. calcium channels in SR open
4. calcium released into cytosol
115
excitation to contraction coupling
116
the active generation of mechanical force in muscle is due to
interaction between actin and myosin
117
ATP is used by muscles for
1. cross-bridge cycle (splitting ATP by myosin ATPase; binding fresh ATP to myosin for dissociation)
2. active transport of calcium back into SR (relaxation)
118
sources of ATP
- anaerobic/non-oxidative glycolysis (short term)
- ATP-CP/creatine phosphate (immediate, anaerobic, lactate buildup)
- aerobic/oxidative phosphorylation (long-term, O2 needed)
119
creatine phosphate and ATP system
- first source of ATP
- limited amount, used rapidly (10-30 seconds)
- provides 4-5 times the amount of ATP present in cells at rest
- rapid one step process
120
anaerobic/non-oxidative glycolysis
- during intense exercise
- oxygen supply is limited, anaerobic exercise is primary ATP source
- O2 absent
- high intensity exercise (20-120 seconds)
- only 2 ATP/glucose
- limited glucose
- lactic acid build up (burning sensation)
121
oxidative phosphorylation
- primary source for light/moderate exercise (>2 minutes)
- muscle stores limited amount of glucose as glycogen
- glucose and fatty acid delivered to muscle by blood
- dominant after 30 minutes
- adequate oxygen supply
- occurs in mitochondria
122
mechanics of skeletal muscle contraction
- the twitch
- factors affecting generated force by individual muscle fibers
- force generation regulation by whole muscle
- length-velocity-load relationships
123
twitch contraction
- contraction produced in a muscle fiber in response to 1 AP
- all or nothing
- can be defined for a muscle fiber, motor unit, or whole muscle
124
phases of a muscle twitch
1. latent period (time from AP in muscle to onset of contraction; excitation-contraction coupling)
2. contraction phase (tension increasing, cross-bridge cycle taking place repeatedly, until apex of an arc)
3. relaxation phase (tension decreases to zero, longer than phase 2, calcium reuptake)
125
isotonic contraction
load remains constant as muscle changes length
126
isometric contraction
muscle is prevented from shortening, tension develops at constant muscle length
127
isometric twitch contraction
- length is constant
- contractile elements generate tension
- stretches series of elastic elements
- muscle does not shorten, load not lifted
128
isotonic twitch contraction
- constant tension
- load lifted as muscle shortens
129
are purely isometric contractions common
yes
130
are purely isotonic contractions common
- no
- even if a load is constant, isometric precedes isotonic contraction phase
- as tension increases, isometric contraction continues until tension exceeds the load
- isotonic contraction then begins
- tension remains constant as muscle shortens
131
is load constant, why
no, load changes as limb position changes
132
isokinetic definition
constant speed
133
isotonic and isokinetic contractions can be either ... or ...
- eccentric
- concentric
134
the level of force generated by muscle depends on
- factors affecting the force or tension generated by individual muscle fibers
- regulation of the force/tension generated by the whole muscle
135
factors affecting the force or tension generated by individual muscle fibers
- frequency of stimulation
- fiber diameter
- changes in fiber length
- extent of fatigue
136
recruitment definition
numbers of fibers contracting
137
increases in frequency of action potentials in muscle fibers increases tension in which two ways
- treppe
- summation and tetanus
138
treppe
independent twitches follow one another closely, peak tension increases to a constant level
139
cause of treppe
unknown, possibly increase in cystolic calcium
140
duration of action potential in an isometric twitch
2 ms
141
duration of a contraction in an isometric twitch
10-200 ms
142
effects of high frequency stimulation in a muscle contraction
summation and tetanus
143
label the twitch
144
label the summation
145
label the incomplete tetanus
146
label the complete tetanus
147
cause of summation and tetanus
- tension developed
- calcium increase in cytosol
- system saturation (all troponin molecules have calcium bound tp it, crossbridge cycle maces out, max tetanic contractions)
148
amount of tension developed depends on ...
amount of calcium bounded to troponin
149
force-generating capacity
inherent ability of muscle to generate force
150
force-generating capacity depends on
- number of crossbridges in each sarcomere and geometrical sarcomere arrangement
- more crossbridges per sarcomere = more force
- more sarcomeres in parallel = more force
151
optimum length in a length-tension relationship
- resting length of muscle at which fibers can develop greatest amount of tension
- due to maximum overlap of thick and thin filaments
152
non-optimum length in a length-tension relationship
- greater than optimum (decrease crossbridge overlap)
- less than optimum (thin filaments overlap, Z lines contact thick filaments)
153
muscle definition
bundle of muscle fibers
154
more fibers contract = ?
greater tension
155
in recruitment of motor units
- activation of motor neuron activates all muscle fibers in the muscle unit
- increase in tension occurs in steps proportional to size of motor units
156
muscles for delicate movements use ________ motor unites
small
157
muscles for strength use ________ motor unites
large
158
are the number of motor unites different in different muscles
yes
159
are small or large motor units recruited first
small
160
types of muscle fibers in skeletal muscle
- slow oxidative
- fast oxidative
- fast glycolic
161
muscle receptors
- muscle spindles
- golgi tendon organs
162
skeletal muscle fibers are classified according to
- contraction speed
- primary mode of ATP production
163
skeletal muscle fiber contraction speed is dependent on
rate of myosin ATPase activity
164
ATP hydrolysis
chemical reaction where a phosphate bond on ATP is broken by water, thereby releasing energy
165
fast skeletal muscle fiber contraction
myosin with fast ATPase activity
166
slow skeletal muscle fiber contraction
myosin with slow ATPase activity
167
fast fibers __________ and _________ two to three times faster than slow fibers
contract; relax
168
slow fiber contractions ______ 10 times longer than fast fibers
last
169
slow oxidative fiber type is __________ size and force
smallest
170
fast oxidative fiber type is __________ size and force
intermediate
171
fast glycolytic fiber type is __________ size and force
biggest
172
one muscle has a _________ of fiber types, but ....
mixture; proportions vary depending on function
173
in single motor units ...
all muscle fibers are the same type
174
skeletal muscle fiber type recruitment order
- slow oxidative
- fast oxidative
- fast glycolytic
175
fatigue
decline in a muscle's ability to maintain a constant contraction force during repetitive stimulation
176
muscle fatigue causes
- low intensity exercise (energy reserve depletion)
- high intensity exercise (lactic acid build up)
- strong, sustained contractions (blood vessel compression)
- very high intensity (depletion of acetylcholine)
- central fatigue (psychological/neural fatigue)
- other: build up of inorganic phosphates, ion distribution change
177
neuromuscular fatigue definition
depletion of acetylcholine causing fatigue
178
skeletal muscle use adaptations
- no cell division
- change in muscle size due to change in size of individual cells
179
skeletal muscle disuse atrophy
decrease in size (lose myofibrils)
180
skeletal muscle denervation atrophy
motor neuron destroyed, no excitation, atrophy due to lack of use
181
skeletal muscle hypertrophy
- increase in size (increase myofibrils)
- actin and myosin production increase
182
muscle hypertrophy definition
increase in muscle size
183
muscle spindle job
detect muscle length
184
golgi tendon organ within the tendon job
detect muscle tension
185
extrafusal fibers
- conscious control in the muscle
- muscle contractile cells
- responsible for skeletal muscle contraction
- innervated by alpha motor neurons
186
muscle v muscle spindle
muscle spindle includes intrafusal fibers
187
intrafusal fibers
- unconscious control
- adjust sensitivity of muscle sensors to stretch
- innervated by gamma motor neurons
188
sensory fibers in muscle spindle
- type 1a sensory fibers
- type 2 sensory ending
189
type 1a sensory fibers
annulospiral endings that wrap around the central portion of the spindle
190
type 2 sensory ending
flower-spray endings located around either spindle end
191
sensory fiber activity in a stretched muscle
high
192
sensory fiber activity in a relaxed muscle
consistent but neither high or low
193
sensory fiber activity in a contracted muscle
low
194
monosynaptic reflex loop
a reflex arc that provides direct communication between sensory and motor neurons innervating the muscle
195
example of a monosynaptic reflex loop
196
agonist
contracting muscle
197
antagonist muscle
relaxing or lengthening muscle
198
muscle activation steps
199
golgi tendon organ function
- information on whole muscle tension
- respond to alterations in muscle tension causing tendon tightening and joint uplifting
200
muscle spindles are ___________ to muscle fibers whereas golgi tendon organs are ___ _______
parallel; in series
201
we can feel muscle _________ but not muscle ________
tension; length
202
stretch intensity increases ?
action potential frequency
203
1b sensory (afferent) axons of golgi tendon organs
- advocates the presence of a more complex multi-synaptic positive/negative feedback in spinal cord
- 1b pathway to send info to brain through ascending pathways for further processing
204
intrafusal fiber function
modulate sensory activity in muscle spindle
205
golgi tendon organs are located in series with ___________ __________ to sense muscle tension
extrafusal fibers
206
where is smooth muscle found
walls of hollow organs
207
smooth muscle produces ...
continuous contractions of relatively low force
208
is smooth muscle voluntary or involuntary
involuntary
209
what controls smooth muscle
nervous system, hormones, and local metabolites
210
smooth muscle cells
- contractile cells
- uninucleated
- no troponin
- dense bodies
- alow myosin ATPase
- myosin has light chains
- little sarcoplasmic reticulum
211
smooth muscle contraction
- no bare portion of myosin
- acting pulled across longer distances in opposite directions
- anti-parallel crossbridges
- contraction requires Ca2+ not troponin
212
smooth muscle classifications
- single unit (visceral)
- multiunit
213
single unit (visceral) smooth muscle
- contracts as a single unit
- most common
- tonic or phasic
- myogenic (pacemaker or slow wave potentials)
- digestive, reproductive, urinary tracts, uterus
- small blood vessels
- functional synctia
- linked by gap junctions
214
multiunit smooth muscle
- phasic and neurogenic
- discrete units function independently
- walls of large blood vessels, small lung airways, eye muscle, base of hair follicles
- no gap junctions
- each functional unit is activated separately (separate innervations)
215
phasic smooth muscle
contracts in bursts
216
tonic smooth muscle
maintains tone
217
neurogenic
initiation of contraction orginated in nervous tissue
218
myogenic
initiation of contraction originated in muscle tissue
219
function syncytia
a unit of contraction comprised of a network of electrically connected cardiac muscle cells
220
smooth muscle excitation-contraction coupling steps
1a. opening of Ca2+ channels in plasma membrane
1b. calcium triggers release of calcium from sarcoplasmis reticulum
2. Ca2+ binds with Calmodulin to form Ca-Calmodulin
3. Ca-Calmodulin activates MLCK (myosin light chain kinase) activation causing myosin phosphorylation
4a. unphosphorylated myosin light chain -> no myosin ATPase activity -> no crossbridge activity
4b. phosphorylated myosin light chain -> myosin ATPase active -> crossbridge coupling -> contraction
221
in skeletal muscle, Ca2+ targets ? via ?
actin; troponin/tropomyosin system
222
in smooth muscle, Ca2+ targets ? via ?
myosin; calmodulin and MLCK process
223
myosin ATPase is ___ __ ____ __ ________ in smooth muscle compared to skeletal muscle
10-100x slower
224
smooth muscle relaxation
1. phosphatase enzyme removes phosphate from myosin
2. calcium removed from cytoplasm (Ca2+ -ATPase, calcium pumps or Ca2+ -Na+ exchanger)
225
phosphatase is _____________ active and competes with _____ thus ? is needed to activate MLCK
continuously; MLCK; high Ca2+ concentration
226
smooth muscle is innervated by ...
ANS (sympathetic and/or parasympathetic)
227
smooth muscle may be ...
excitatory or inhibitatory
228
smooth muscle neurotransmitter is released from ...
varicosities
229
gap junctions function
allow electrical signal transmitter from one cell to neighboring cell
230
is smooth muscle able to contract by hormonal/chemical stimulation
yes
231
how is cardiac muscle similar to skeletal muscle
- striated with sarcomeres
- troponin and tropomyosin regulation
- T tubules
- sarcoplasmic reticulum
- similar to slow oxidative fibers (myoglobin, mitochondria, slow and fatigue resitant)
232
how is cardiac muscle similar to smooth muscle
- gap junctions with intercalated disks
- pacemaker cells
- innervated by ANS
- influenced by hormones, paracrines, adjacent cells
- Ca2_ from ECF and SR
233
why is there no summation in cardiac muscle
long refractory period
234
functional benefit of no cardiac muscle summation
summation would not allow the heart to relax after each beat to fill with blood
