Exam 3 Skeletal and Smooth Muscle Flashcards
What percentage of the mass of a normal healthy adult comes from skeletal muscle?
40 %
What are some of the functions of skeletal muscle?
- Movement
- Expression
- Communication
- Body temperature regulation
- Effectors of neurons
- Store of ions, fluid, and proteins
- Storage of glycogen
What is glycogen and where is it stored?
- A long chain of glucose molecules
- Skeletal muscle and liver
What is a bone-bone connection called?
What are some examples?
- Ligament
- ACL, MCL, Patellar
What are muscle-bone connections called?
What is an example?
- Tendon
- Achilles
Exceptions: there are some intermediate tendons that connect muscle to muscle
What is a muscle cell called?
Muscle fiber
What is a group of muscle fibers called?
Fasiculous
What is a group of fasiculi?
Muscle Fiber
What are the internal cylinders of a muscle cell called?
What is contained within them?
How many are there per muscle cell?
- Myofibril
- Actin and myosin
- Over 200
What determines how many myofibrils a muscle fiber has?
The function of the muscle
Muscles needed for lots of strength have more myofibrils
Muscles needed for fine motor have less myofibrils
What is the functional unit of a myofibril?
What’s important about this structure?
Sarcomere
Has overlap of thin and thick filaments
What is a motor unit?
A group of muscle fibers controlled by a single motor neuron
Describe activation and function of small and large motor units?
- Typically small motor units are easier to excite and are activated first
- If more muscles are needed, then the large motor units are also excited
What type of muscle is used for sustained contraction?
What do they contain lots of?
- Type 1(slow)
- Mitochondria and myoglobin
What is myoglobin and its function?
What does this do to the appearance of the muscle?
- Very similar to hemoglobin and unloads oxygen from blood to muscles
- Iron containing protein that makes the muscle appear red
Ex: duck breast
What type of muscle is used for “fast twitch”?
How are they different from “slow” muscles?
- Type 2
- Have very little myoglobin making them appear white
- Have fewer mitochondria
Ex: chicken breast
Describe the differences in force of contraction over time for fast, intermediate, and slow muscles?
What are examples of each?
- Slow muscles take longer to get to full force but can contract longer (soleus)
- Fast muscles reach maximal force of contraction faster but contract for a short period (ocular)
- Intermediate muscles are somewhere in between fast and slow (gastrocnemius)
What is the cell wall of a muscle called?
Sarcolemna
What are muscles called that have bands of alternating light and dark colors?
Where are these found?
- Striated mucles
- Skeletal and heart muscles
What are the thick and thin filaments called in a sarcomere?
Thick = myosin
Thin = actin
What creates the two ends of the sarcomere?
What is it comprised of?
- Z disk
- Bundle of actin wraped around each other
What is the area of the sarcomere where there is only thin filaments?
What is its appearance?
I band
Light colored
Extends across both sides of the Z disk
What are the areas of the sarcomere containing only thick filaments?
What is its appearance?
H zone or band
dark colored
What is the area called on the sarcomere where the thick and thin filaments overlap?
A band
What is the large elastic connective tissue that helps provide structure to the sarcomere?
Titin (protein)
How does contraction of a myofibril effect the structures of a sacrcomere?
What is this contraction called?
Sliding Filament Mechanism
* Z bands move closer together
* I bands shrink
* H bands disappear
* A band remains the same width
How do long neurons transport needed proteins to the end of the axon where the synapse is?
They have tracks along the length of the axon where proteins and other information can be sent down from the nucleus to the terminal end of the neuron.
Skeltal muscles cannot use this system because of the contents of the myofibrils.
How do muscle fibers obtain needed proteins and other information if they cant use the “track” system via neurons?
They are multinucleated and have many nuclei along the length of the myofibrils.
What makes up a myosin filament?
How many are there per filament?
- Myosin molecules wrapped together
- 200 myosin molecules per myosin filament
How many chains are there per myosin molecule?
- 2 heavy chains in the tail
- 4 light chains in the head (2 essential and 2 regulatory)
What are the 2 different heads in the myosin molecule and their function?
- Regulatory light chains - regulate activity of essential light chains, used more in smooth muscle for phosphorylation
- Essential light chains - possess ATPase activity, has high affinity for the active sites on F-actin
What is the structure of an actin filament?
- F-actin strand: has active sites for binding myosin heads
- Tropomyosin strand: Blocks the active sites on the f-actin strand when the muscle is at rest
What is the troponin complex?
How does it work?
Contains 3 protiens
* Troponin I: Binds to actin
* Troponin T: Binds to tropomysoin
* Troponin C: Binds to calcium with 4 binding sites
When troponin C is bound by calcium, the configuration changes, causing a twisting or unraveling of the filaments that exposes the actin active sites
Describe the “resting” or cocked state of the myosin head?
ATP binds to the myosin head and puts tension on the head, “cocking” it, making it ready to bind to myosin. This leaves an ADP and Pi group on the head.
Explain/draw cross bridge cycling?
Ca++ binds to tropomyosin C to reveal the active sites on actin during step 3
What is the resting state of our heart sarcomeres?
Why is this necessary?
They are typically understretched
This is so that when more pressure or volume is added to the heart muscle, the sarcomeres can stretch to add more force of contraction (starling forces)
How do you obtain total tension?
Total tension = passive + active tension
X = total tension, Y = active tension, Z = passive tension
What tension is the weight providing?
How does the tension change during contraction?
How could we calculate the total force generated by contraction (active tension)?
- Passive tension
- Tension increases with contraction
- Subtract the mass of the weight from the total tension measured
Describe the load velocity relationship?
Where is the important?
- The heavier the load, the slower the contraction speed
- In the heart, when someones BP is high (high afterload) the slower the velocity of contraction (longer time to eject blood)
-Can lead to problems with filling bc systole is taking longer
Describe temporal summation?
By increasing the rate of simulation of the neuron, there is an additive effect that increases the strength of muscle contraction until ~40Hz (tetany). This additive affect is due to calcium not having enough time to be removed from the sarcoplasm between stimuli, increasing the force of contraction. After ~40Hz the calcium receptors become saturated, and the muscle cannot contract more.
What is the equivalent structure of the z disk in smooth muscles?
Dense bodies
Anchor neighboring cells, comprised of wound actin filaments
Describe the set up of visceral smooth muscle?
What is the other name for it?
Where are these found?
- Also called unitary, makes up the vast majority of smooth muscle
- Smooth muscles cells are attached by gap junctions that allows for the cells to contract as a unit
- Found in the intestinal smooth muscle
Describe the set up of mutli-unit smooth muscle?
Where are these used?
- The cells are not connected by gap junctions, they require neurotransmitters to be activated
- This allows for delicate control of the muscles
- Found in the cilliary muscle and iris
What is indicated by 1? What is its function? What is the other name for this layer?
- Adventitia
- Structural support connective tissue of vascular smooth muscle
- Tunica externa
What is number 2? Where is it found? What is the other name for this layer?
- Endothelium
- Found in all of our vascular smooth muscle
- Tunica intima
What is the difference in the set up of myosin heads in smooth muscle compared to skeletal muscle?
What does this allow?
- The myosin heads are aligned on one actin molecule without a gap (M line).
- This allows for much greater shortening of the muscle which can produce a strong contraction
What is the difference between activation of actin in smooth muscle and skeletal muscle?
Be able to describe the pathway.
In skeletal muscle the active sites on actin are hidden by the tropomyosin complex and are revealed to bind with myosin when ca++ binds to Troponin C.
In smooth muscle the active sites are always visible and require phosphorylation of the regulatory light chain in order to cause muscle contraction.
How is contraction ended in smooth muscle?
- Calcium removed from sarcoplasm by SERCA, PMCA (plasma membrane calcium ATPase), and NCX
- Phosphate group removed from MLC by myosin phosphatase
- Phosphate group eventually will fall off on their own
Describe how nitrates affects vascular smooth muscle cells?
- Nitrates increase the release of NO
- NO increases the activity of guanylyl cyclase
- This increases cGMP
- cGMP increases PKG which adds phosphate groups to MLCK and Ca+ entry channels to prevent contraction
Describe how NO is produced in the endothelium and its affect of vascular smooth muscle cells?
- NT like ACh and bradykinin bind to mACh-R on endothelium
- Causes release of Ca from SR that binds to calmodulin
- Ca-calmodulin increases the activity of eNOS
- eNOS converts L-arginine to NO
Describe activation of alpha1 receptors in VSMC?
What can activate this pathway?
NE and 5-HT
What is this graph showing? Where is it found?
- Pacemaker activity of smooth muscle action potentials
- Happens in the intestine (muscle cramps; come in waves)
How much of calcium during cardiac contraction is from the SR and ECF?
80% from the SR
20% from the ECF
Describe cholinergic and adrenergic activation in the heart?
- Beta increases Adenylyl cyclase which increases cAMP - increases PKA - increases contraction and HR
- mACh-R inhibits Adenylyl cyclase - decreases cAMP - and decreases PKA (this is different than mACh at the nodes that are tied to potassium channels)
