6 - Muscular Tissue Flashcards
(66 cards)
1
Q
3 muscle fiber types
A
- slow oxidative
- fast oxidative
- fast glycolytic
2
Q
3 phases of muscle twitch
A
- Latent period - events of E-C coupling
- Period of contraction - cross bridge formation, tension increases
- Period of relaxation - Ca re-entry into SR, tension declines to zero
3
Q
3 types of Muscle tissue
A
- skeletal, cardiac, smooth
4
Q
ATP generation - aerobic pathway
A
- energy source = glucose, pyruvic acid, fatty acid, amino acids
- uses O2
- produces 36 ATP per glucose, CO2, H2O
- Duration hours
5
Q
ATP generation - anaerobic pathway
A
- energy source = glucose
- does NOT use O2
- produces 2 ATP per glucose, lactic acid
- duration 30-60s
6
Q
ATP generation - direct phosphorylation
A
- energy source = CP
- does NOT use O2
- produces 1 ATP per 1 CP
- duration 15 secs
7
Q
ATP is regenerated by
A
- Direct phosphorylation of ADP by creatine phosphate CP
- Anaerobic pathway (glycolysis)
- Aerobic respiration
8
Q
Cardiac muscle cells
A
- branching chains of cells
- uninucleate or binucleate
- striations
9
Q
Cardiac muscle
A
- Only in the heart
- Striated
- Involuntary
- Intercalated discs = attachment for cardiac cells
10
Q
Common characteristics of muscle tissue
A
- Excitability – ability to receive & respond to stimuli
- Contractility – ability to shorten when stimulated
- Extensibility – ability to be stretched
- Elasticity – ability to recoil to resting length
11
Q
Dense bodies
A
- proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals
12
Q
Endomysium
A
- fine areolar CT surrounding each muscle fiber
13
Q
Endurance Training
A
- Aerobic (endurance) exercise
- Leads to increased:
Muscle capillaries
Number of mitochondria
Myoglobin synthesis
May convert fast glycolytic fibers into fast oxidative fibers
14
Q
Endurance Training
A
- Typically anaerobic
- Results in:
Muscle hypertrophy (increase in muscle fiber size)
Increased mitochondria
Myofilaments
Glycogen stores & CT
15
Q
Epimysium
A
- dense irregular CT surrounding entire muscle
- can form the tendon
16
Q
EPOC
A
- excess post exercise consumption
- replenishment of O2 reserves in muscles
- ex. breathing heavy post exercise
17
Q
Fast glycolytic fibers
A
- fast contraction
- fast ATPase activity
- low myoglobin, hgih glycogen stores
- recruitment order - third
- white colour
- large fibers
- few mitochondria
18
Q
fast oxidative fibers
A
- fast contraction
- fast ATPase activity
- high myoglobin
- recruitment order - second
- red-pink colour
- many mitochondria
19
Q
Features of a sarcomere
A
- Thick filaments – run the entire length of an A band (dArk band)
- Thin filaments – run the length of the I band & part way into A band (light band)
- Z disc – coin-shaped sheet of proteins that anchors the thin filaments & connects myofibrils to one another
- H zone – lighter midregion where the thick & thin filaments do not overlap
- M line – line of protein myomesin that holds adjacent thick filaments together
20
Q
Force of contraction is affected by
A
- Frequency of stimulation - increase frequency allows time for more effective transfer of tension to noncontractile components
- Number of muscle fibers stimulate (recruitment)
- Length-tension relationship - muscles contract most strongly when fibers are 80-120% of their normal resting length
- Relative size of fibers - hypertrophy of cells increase strength (ex. Strength training)
21
Q
Influence of load
A
- high load
- increase latent period, decrease contraction & decrease duration of contraction
22
Q
Influence of recruitment
A
- recruitment
- faster contraction & increased duration of contraction
23
Q
Is Endplate potential an action potential?
A
NO!!!
- they are different
- end plate potential is at the NMJ, needs to reach threshold to propogate AP down the muscle cell
24
Q
isometric contraction
A
- no shortening, muscle tension increases but does NOT exceed the load
25
Isotonic contraction
- muscles shortens b/c muscle tension exceeds the load
26
Latent period
- time b/w AP initiation & beginning of contraction
27
length-tension relationship
* If muscle is already almost fully contracted - it won't create a lot of tension
* Excessively stretched – not great overlap, don't really generate a good amount of tension
* Optimal overlap -> muscle is about ½ contracted
28
Multiunit Smooth muscle
* Found in - large airways to lungs & large arteries, in arrector pili muscles attached to hair follicles, eye muscles of iris
* Characteristics:
Rare gap junctions
Infrequent spontaneous depol
Structurally independent muscle fibers
A rich nerve supply, with multiple fibers forms motor units
Graded contractions in response to neural stimuli
act more like skeletal
29
Muscle fatigue
- ionic imbalances - interfere w/ E-C coupling
- prolonged exercise damages SR & interferes w/ E-C coupling
30
Muscle fatigue from high intensity-short duration exercise
- produces rapid muscle fatigue
- Na-K pumps cannot restore ionci balances quickly enough
31
Muscle fatigue from low-intensity-long duration exercise
- produces slow-developing fatigue
- SR damaged & Ca regulation disrupted
32
Muscle functions
* Movement of bones or fluids
* Maintain posture & body position
* Stabilizing joints
* Heat generation (especially skeletal muscle)
33
Muscle responses are graded by...
* Changing the frequency of stimulation
* Changing the strength of the stimulus
34
Muscle tone
* Constant, slightly contracted state of all muscles
* Due to spinal reflexes that activate groups of motor units in response to input from stretch receptors in muscles
* Keeps muscles firm, healthy & ready to respond
35
myofilaments in smooth muscle
* Ratio of thick to thin is 1:13
* Thick filaments have myosin heads along their entire length
* No troponin complex - protein calmodulin binds Ca
* Myofilaments are spirally arranges, causing smooth muscle to contract in a corkscrew manner
36
Nebulin
- ruler in thick & thin filaments, helps maintain length of actin
37
Perimysium
- fibrous CT surrounding fascicles (groups of muscle fibers)
38
Peristalsis
* Alternating contractions & relaxations of smooth muscle layers that mix & squeeze substances through the lumen of hollow organs
39
Response to change in stimulus frequency
- low stimulation frequency -> unfused tetanus
- high stimulation frequency -> fused (complete) tetanus
40
Responses to change in stimulus strength
- contraction force is controlled by recruitment, brings more fibers into action
- size principle -> motor units w/ larger fibers are recruited as stimulus intensity increases
41
Role of Calcium in contraction
- low intracellular Ca - tropomyosin blocks active site on actin
- high intracellular Ca - Ca binds troponin, moves tropomyosin -> events of cross bridge cycling
42
Role of Calcium in Smooth muscle
* Ca binds to & activates calmodulin
* Activated calmodulin activates myosin (light chain) kinase (MLCK)
* Activated kinase phosphorylates & activates myosin II
* Cross bridge interacts w/ actin
43
Sarcomere
* Smallest contractile unit (functional unit) of a muscle fiber
* Regions of a myofibril b/w 2 successive z discs
* Composed of thick & thin myofilaments made up of contractile proteins
44
Sarcoplasmic reticulum
* Network of smooth endoplasmic reticulum (SER)
* Pairs of terminal cisternae form perpendicular cross channels
* Functions in the regulation of intracellular Ca2+ levels
45
Single Unit smooth muscle
* Cells of a single-unit (visceral muscle)
Contract rhythmically as a unit
Electrically coupled via gap junctions
Spontaneous AP
Are arranged in opposing sheets & exhibit Stress-relaxation response
46
Skeletal muscle
* Attached to bones & skin
* Voluntary (conscious control)
* Striated
* Powerful
* Remember: looks like dense regular but has striations
47
Skeletal Muscle cells
- single long cylindrical
- multinucleate
- striations
48
sliding filament theory
- relaxed state - thin & thick filaments overlap slightly
- contraction - myosin head binds actin, detach & binds again - moving filament towards M line
- H zones & I zones shorten, A band remains the same!!
49
Slow oxidative fibers
- slow contraction
- slow ATPase activity
- high myoglobin
- recruitment order - first
- red colour
- many mitochondria
50
Smooth muscle
* In the walls of hollow organs (ex. Stomach, GI, airways)
* Not striated
* Involuntary
51
Smooth Muscle (microscopic structure)
- spindle shaped fibers
- endomysium only
- SR less developed
- Caveolae
- No sarcomeres, myofibrils or T tubules
52
Smooth muscle cells
- single fusiform
- uninucleate
- no striations
53
Steps in E-C coupling
1. AP is propagated along the sarcolemma & down T-tubules
Change in conformation of DHP receptors -> interacts w/ RyR1
2. Ca ions released
3. Ca binds to troponin & removes the blocking action of tropomyosin
4. Contraction begins
54
Steps in generation of AP at NMJ
1. Local depolarization - generation of end plate potential on the sarcolemma
- MUST reach threshold
2. Generation & propagation of the action potential
- Open Na channel, closed K channel -> Na going in, muscle cell getting more depolarized
3. Repolarization - Closed Na channel, open K channel
- K going out of cell, less +ve charge inside
55
Steps of contraction in smooth muscle
1. Ca enters from ECF via voltage-dependent/independent channels or from SR
2. Ca binds to & activates calmodulin
3. Activated calmodulin, activates MLCK
4. Activates myosin ATPase
5. Activated Myosin forms cross-bridge w/ Actin
56
Steps of Cross bridge cycling
1. Cross bridge formation - high-energy myosin head (ATP primed) attaches to thin filament
2. Working (power) stroke - myosin head pivots & pulls thin filament toward M-line
3. Cross bridge detachment - ATP attaches to myosin head & cross bridge detaches
4. Cocking of myosin head - energy from hydrolysis of ATP cocks the myosin head into high-energy state (recharges myosin)
57
Structure of Thick Filament
* 2 myosin
* Myosin tails - interwoven heavy polypeptide chains
* Myosin heads - connected to the tails are 2 polypeptide head groups that act as cross bridges during contraction
* ELC & RLC - can be manipulated, to improve muscle contraction ability, allows fast contractions
58
Structure of Thin Filament
- Twisted double strand of filamentous protein F-actin
- G-actin make up F-actin
- Tropomyosin & troponin - regulatory proteins bound to actin
59
T-tubules
* Invagination of sarcolemma
* Penetrate the cell's interior at each A band – I band junction
* Assoicate w/ the paired terminal cisterna to form triads that encircle each sarcomere
60
The overload Principle
* Forcing a muscle to work hard promotes increased muscle strength & endurance
* Muscles adapt to increased demands
* Muscle must be overloaded to produce further gains
61
Titin
- interacts w/ M-line throughout the length of Sarcomere (from Z disc to Z disc)
62
Triad Relationship
- T tubule proteins are voltage sensors (DHP receptor)
- SR foot proteins are gated channels (Ryanodine receptor)
- 2 receptors bind, release Ca2+ from SR cisternae
63
velocity/duration of contraction influenced by
- muscle fibre type
- load
- recruitment
64
What are the events at the Neuromuscular junction?
1. Action potential arrives at axon terminal of motor neuron
2. Voltage-gated Ca2+ channels open & Ca2+ enters axon terminal
3. Ca2+ causes synaptic vesicles to release Ach into synaptic cleft
4. Ach diffuses across synaptic cleft & binds to receptors on sarcolemma
5. Ach binding opens ion channels that allow Na into muscle fibre & K out
6. Ach effects are terminated by its enzymatic breakdown in synaptic cleft by acetylcholinesteras
65
what is a muscle twitch?
- response to a single brief threshold stimulus
66
What is excitation-cotnraction (E-C) coupling?
- sequence of events by which transmission of an AP along sarcolemma leads to sliding of myofilaments
