Exam1Lec3SkeletalandSmooth Muscle Physiology Flashcards
1
Q
What are the three types of muscle
A
- Skeletal
- Smooth
- Cardiac
2
Q
Skeletal Muscle is _ _
A
NOT uniform
3
Q
What does skeletal muscle looks like?
A
Skeletal muscle is striated thus is appears to have stripes
4
Q
What are large muscle bundles composed of?
go down to the smallest unit of muscle
A
- Large muscle bundles are composed of individual muscle cells (myocytes or fibers) that each contain many myofibrils
- Myofibrils each contain many sarcomeres that are arranged end to end in series
- Each sarcomere is scomposed of actin, myosin and otehr moecylar machinery
5
Q
What is the smallest contracting frunctional unit of muscle
A
sarcomeres
6
Q
What is sarcomeres composed of?
A
actin and myosin
7
Q
What generates contractile forces?
A
sacromeres
8
Q
One sarcomeres is bounded by what?
A
two Z lines
9
Q
What are the two types of filaments (skeletal)
A
Thin filaments and thick filaments
10
Q
What are thin filaments of SM
A
actin helix with tropomyosin and triponin complex attached
11
Q
what are thick filaments SM?
A
Myosin II->ATPase enzyme
12
Q
What is the organization of a sarcomere
A
- I band: thin filaments only so actin
- H zone: thick filaments only so myosin heads
13
Q
Explain the neural control of skeletal muscle cell
A
Neuromuscular junction:
1. nerve axon innervating each muscle fiber
2. Releases acetylcholine (ACh
3. ACh binds to the AChR which is permeable to Na+, K+ and Ca+2
14
Q
What causes depolarization in skeletal muscle cells?
A
ACh receptors
15
Q
Explain the initiation of skeletal muscle contraction
A
when the muscle cell depolarizes, it will then:
1. Ca2+ release from the SR
2. Ca2+ bind to troponin C and initates a conformational change
3. Tropomysocin slides into the groove between the actin strands
4. Myosin can now bind actin which is the beginning of contraction
16
Q
Explain the cross bridge cycling of skeletal and smooth muscles
A
17
Q
What is needed to initiate contraction
A
Ca2+ is needed to move tropomyosin
18
Q
Where is ATP required?
A
cross-bridge cycling, the power stroke and force production
19
Q
explain the 3D structure of a myocyte
A
20
Q
explain the excitation-contraction coupling SM
A
- (+) charge is carried along the plasma membrane to the transverse tubules
- Depolatization activates the L-type Ca2+ channels located in the transverse tubules leading to a conformational change
- This induces a physical conformational change in the ryanodine receptors that are adjactent to the L-types but located in the SR
- As a result the RyR release Ca2+ into the cytosol
21
Q
What is not necessary for contraction for SM
A
influx of Ca2+ through the DHP receptors
22
Q
What is the sliding filament theory
A
sliding of actin on myosin heads
23
Q
What are the bands like when the muscle is relaxes?
A
- Z- bands become wider
- I-bands widen
- A-bands remain the same
- H-bands widen
24
Q
What are the band like when the musclee is contracted
A
- Z-bands move closer together
- I- bands narrow
- A-bands remain the same
- H-bands narrow
25
How does the skeletal muscle relax?
**SERCA**: Sacroplasmic endoplasmic reticulum ATPase
* a calcium pump that sequesters myoplasmic Ca2+ into the SR
* pumps 2 Ca2+ into lumen/ 1 ATP while extruding 2 H+
**Calsequestrin**: Ca2+ binding protein near RYR
**Sarcalumenin**: transfers Ca2+ from uptake sites to release sites
26
What is calsequestrin?
Ca2+-binding protein near RYR so you have ca when you want to contract
27
What are think filaments SmM
myosine but much less than SK
| only a forth
28
What are thin filaments SmM
Actin, tropomypsin, NO troponin
| NO BINDING TO TROPONIN C LIKE IN SM
29
What do intermediate filaments help with SmM contractile elements
* desmin ot vimentin, form a cytoskeletal nework connecting the dense bodies.
* Dense bodies also contain a- actinin, which binds actin
30
What can stimulate SmM contraction
1. hormones
2. neural
3. spontaneous electrical activity (APs)
4. mechanical (when you pull or poke, it will contract)
31
explain the neural control of SmM cells
* Some SMC: eye muscles, piloerector muscles in skin
* Most SMC: blood vessels visceral muscle
32
Explain multiunit and unitary neural control
multi: electrical isolations of cells allows finer motor control. (one inn to each smooth muscle cell)
Unit: one inn to multiple SmM cells. Gap juctions permit coordinated contraction
33
How does the initiation of SmM contraction happen?
* Ca2+(4) initiates smooth muscle contraction by binding to calmodulin (not troponine C)
* So then the calmodulin binds to myosin light chain kinase (MLCK) to then phosphorylate myosin to be active
| Need: Ca2+ MLCK calmodulin
34
How much ATP does SmM cells need compared to SM cells
double one for initination of contraction and cross bridge cycling
35
While in skeltetal muscle T tubules carry charge to SR to stimulate Ca2+ release from internal stores, what does SmM cells do?
Caveolae bring external Ca2+ to the SR to induce more Ca to be released fro the SR
36
How does Smooth muscles relax?
1. Na-ca and exhanger and Ca2+ pump in the plasma membtane both extrude Ca2+ from the cell
2. Ca pump sequesters Ca within the SR
3. Ca is bound in the SR by calreticulin and calequestrin
4. Then you need myosine light chain phosphatase (MLCP) to remove phosphate from the myosin head to make it inactive
37
what are factors that affect force production in skeleton muscle?
1. initial length of muscle fiber
2. fiber type
3. motor unit recruitment
4. speed of contraction
5. muscle fiber arrangement
38
Explain the differe types of muscle actions (dynamic vs. static action)
Dynamic action
* **Concentric**: muscle developes tension adn muscle **shortens**. (muscle force> external force)
* **Eccentric**: muscle develops tesions and muscle **lengthens** (muscle force
39
How does muscle generate force without shortening
whole muscle has:
* Contracile elements and connective/elastic components
40
What is happening during isometric and eccentric
* elatic components are strethched which also contributes (**passively**) to the total muscle force
* Sarcomeres ratchet and pull towards their center which generates force (**actively**)
41
What is passive force mediated by
titin
42
What is titin
* elastic protein that runs from the Z line to the M line of the sarcomere (halfway)
* largest know protein. 3rd most abundant protein in muscle after actin and myosin
* acts as a molecular spring that is responsible for producing the passive force in muscle
43
Explain the length-tension relationship
* peak force-optimal overlap
* no active force-no overlap
* no force-myosin hits z disks
44
Explain the different in metabolic properties in fiber types
1. Primary Energy Pathways Utilized to Make ATP
Oxidative (Aerobic), Glycolytic or Combination
2. Determined by Differences in: # of Mitochondria, Capillary Density, Myoglobin Concentration, Enzymatic Activity
45
Explain the different in contractile properties in fiber types
1. . Speed of Contraction
* Myosin ATPase Activity –faster in type II isozyme
* Ca++ Cycling
2. Maximal Force Production
* number of cross bridges formed/cross sectional area
* Fiber Diameter (Contractile Elements)
* Rate of Cross Bridge Formation
* NOTE: Exercise increases size of myofibrils (hypertrophy), therefore sarcomeres are larger
3. Fatigue Resistance
* Depends on Energy Pathways Utilized
46
The mysosin ATPase activity is faster where?
faster in type II isozyme
47
What does exercise increase?
Increases size of myofibrils (hypertrophy), therefore sarcomeres are larger
48
Compare the flow vs fast twitch skeletal muscle fibers (fatigue, color, metabolism, mitochondria, glycogen)
49
What is the motor unit
all the muscle fibers inn by a single motor neuron
50
What is summation?
this is how muscle increases force
51
What is temportal summation?
increased frequency of stimulation of the motor units
52
What is spatial summation?
increased number of motor units that are recruited
53
What is recruitment?
not all muscle fibers are participating all the time; some are inactive
54
Explain more on temporal summation
* increased freq of stimulation
* increased action potential firing rate
* A single AP releases Ca2+ for a short duration to cause a twitch and can be summated
55
What is tetany and what does it lead to? (6 things)
stimulating a muscle with an AP before the muscle has had time to totally relax leads to:
1. Increased Ca2+ duration
2. New contraction occurs before preceding one is over
3. Force progressively increases
4. Fusion of the twitch contractions
5. Sustained contraction
6. Force is greatly amplified!!
56
What is spatial summation in SM
* All muscle fibers in a motor unit are activated simultaneously
* All or none
* However, not all motor units are active at the same time
57
What are the muscle energy sources during exercise?
1. **ATP**- - small but replenishable pool
2. **Creatine Phosphate**: ATP buffer system that keeps ATP constant
CPK
ADP + CP -> ATP + C
3. **Glycogen** – from muscle cells-> glycolysis = 3 ATP+ L.A.->aerobic oxidation = 37 ATP
4. **Plasma glucose** + glycogen
5. **Plasma FA, adipose TG’s**-> oxidative phosphorylation
58
Difference between tonic and phasic muscles
**Tonic**
* Continuously active to maintain a level of tone
* Examples: blood vessels, respiratory tract, some sphincters
* tone associated with action potentials
**Phasic**
* Rhythmic or intermittent contractions
* Examples: GI tract, urogenital, lymphatic
* action potential propagates from cell-to-cell
59
Test yourself: SM v SmM
