Skeletal And Smooth Muscle Histology (MODULE 3) Flashcards
Sarc/o
Flesh
Cyt/o
Cell
My/o
Muscle
Fibr/o
Fiber
Disc/o
Flatten surface
Fasci/o
Fascia/Bundle
Striat/o
Stripe/Line
Act/o
Movement/Ray
Myos/o
Muscle
Trop/o
Change
Pon/o
Bridge
Kinesi/o
Movement
Tract/o
Draw/To pull
Con-
Peri-
Epi-
Together/with
Around/outer
Upon/over
-in
Denote protein
-ium
Membrane or Tissue
-tion
Act of or process of
-mere
Part or segment
Name the 4 types of tissues, and the 3 types of muscle tissue.
Tissues
1. Epithelial
2. Connective
3. Muscle
4. Nerve
Muscle Tissue
1. Skeletal
2. Cardiac
3. Smooth
Microfilament = Actin Filament
Describe the actin filament structure. (G-actin vs F-actin)
- Has 2 strands (helical structure, like a rope; diameter approx. 6nm) —> very fine filament
- Each strand is assembled from bead-like subunits, called G-actin (G=globular) or the arctic monomer —> polymerized into a strand, called F-actin (F=fibrous) —> two strands wrap around each other to form a the microfilament (or actin filament)
T or F
Smooth endoplasmic reticular has non ribosomes on their surface
T
Muscle Vocabulary:
Sarcoplasm
Sarcolemma
Sarcoplasmic reticulum -
Sarcoplasm - the sytoplasm of a muscle cells. It is the gel-like substance that fills the space between the muscle fibers and contains various organelles, proteins, and nutrients essential for muscle function.
Sarcolemma - the plasma membrane of a muscle cells. It surrounds muscle cell and acts as a barrier, controlling the movement of ions and other molecules in and out of the cell.
SR- specialized type of smooth endoplasmic reticulum found in muscle cells. Its main function is to store and regulate the levels of calcium ions which are crucial for muscle contraction.
Skeletal muscle has ________ nuclei.
Its shape is…
Multiple
Long cylindrical shape
T or F
Smooth muscle cells have one long nucleus and is staggered
T
T or F
Skeletal muscle originates from embryonic dermontamal cells
F!
Originate from embryonic mesenchymal cells
T or F
Muscle fibers are multinucleated cells
T
This is because the myoblasts come together to form a skeletal muscle. Each myoblast has a nucleus
T or F
Satellite cells come from myoblasts
T
What is the epimysium and what collagen types make up this layer?
It is the outermost layer of the skeletal muscle.
Collagen types I and III and fibroblasts, nerve, BV.
The perimysium is the covering layer of ________. The entire structure is covered by the __________ layer.
Fascicles
Epimysium
Look at slide #12 and identify skeletal muscle layers.
Look over slide #14 and 15
T or F
Fiber is bigger
Fibril is smaller
T
The A band within the structure of a myofibril has all the ________ in it. It also has overlapping ________ in it.
Primarily Myosin
Overlapping actin
The I band is going to comprise of what protein?
Actin
NO MYOSIN
What is the Z disc on the structure of a myofibril?
An arrangement of proteins that anchors the actin filaments to the middle
What and where is the H zone?
What and where is the M line?
H zone is the area where the actin do not overlap (when relaxed there is a large gap). Located within the A band. When contracted the actin moves inwards. (Sliding filament theory)
- Only myosin is present in this region because the actin overlapping.
Within the H zone there is another set of proteins that work to keep the myosin filaments together this is referred to as the M line.
Overview of Actin
- Made of individuals G-actin/Globular actin subunits
- G-actin polymerizes to form F-actin/ Fibrous actin
- Every G-actin monomer has a ‘myosin-binding site’
- Two F-actin chains intertwine
- It occupies the I-band of the sarcomere
Protiens of the myofibril: ACTIN
F-actin associates with 2 regulatory proteins __________ and _________.
Tropomyosin and Troponin
Protiens of the myofibril: ACTIN
__-_______ + _________ + _______ together make the ‘thin filament’
F-actin + tropomyosin + troponin together make the ‘thin filament’
What is the function of Tropomyosin?
What is the function of Troponin? What are the three subunits of troponin?
Tropomyosin = found on thin filaments (actin filaments) and functions to regulate the interaction between actin and myosin.
Troponin = Has three subunits
1st subunit: (TnC) - interacts with Ca+
2nd subunit: middle (TnI) - transfers conformational change of Ca+ between TnC and TnT
3rd subunit: attached to actin (TnT)- interacts with Tropomyosin
T or F
Myosin has an actin binding site and ATP-binding site
T
Within the sarcomere the I band is composed of ________.
Actin that does not overlap with myosin
From Z disc to Z disc it is the area referred to as?
Sarcomere
Explain the association of Sarcoplasm reticulum and T-tubules
SR - is the smooth ER of the skeletal muscle fiber/skeletal muscle cell, and it stores Ca.
T-tubules - extend down from the Sarcolemma, surround the myofibril around the junction of the I and the A bands. The cisternae of the sarcoplasmic reticulum are seen on both sides of the T-tubules - which together make a Triad (SER cisternae and the T-tubule in the middle)
The entire muscle is covered by a layer of dense connective tissue called the _____________. The ____________ is present just under the ‘deep fascia’ and __________ connects to the bone and the muscle.
Epimysium
Tropomyosin wraps around the twisted F-actin and lies in the groove between the 2 F-actin chains. It is different from the protein called ‘Myosin’. What binds to tropomyosin?
Troponin
Myosin protien molecule is made of 2 _______ twisted around each other and 2 ________ ______.
2 tails
2 globular heads
What happens when a motor nerve initiates an AP? Explain the process.
- It depolarizes the Sarcolemma.
- This depolarization travels through the T-tubules and triggers the release of Ca from the adjacent cisternae of the sarcoplamsic reticulum into the Sarcoplasm.
- The calcium binds to the TnC subunit of troponin, this causes a displacement of the tropomyosin and exposes the MMyosin - binding sites on the F-actin. The showing heads will interact with the actin fibers through these sites.
- A series of binding and unbinding events of the myosin heads to the F-actin causes the sliding of myosin bundles over the arctic fibers, causing contraction of the sarcomere.
*Look over slides of muscle microscopic images and be able to label portions of the them (such as slide 26)
Explain the events of muscular contraction.
Such as: membrane depolarisation - Ca release - displacing tropomyosin
- Nerve impulse triggers release of acetylcholine (ACh a neurotransmitter) from the synaptic knob (terminal end of the axon) into the synaptic cleft at the neuromuscular junction
- ACh binds to the ACh receptors on the Sarcolemma causing depolarization of the Sarcolemma - which spreads to the T-tumbles. This triggers the release of Ca from the SER cisternae into the Sarcoplasm.
- Ca+ ions bind to troponin. Troponin causes a conformational change of tropomyosin and cause it to move away from the myosin - binding sites on the F-actin. The exposed myosin - binding sites are now available for the myosin to bind to.
The sliding filament theory…..
First in class notes…..
Second online notes……
The SFT.
1. Free myosin heads are bound to ATP on their ATP-binding sites
2. ATP is broken down and the energy produced is stored in the myosin head. At this point, the myosin head will have ADP bound to it since it has already broken down the ATP.
3. ADP+Pi bound myosin head can now bind to Actin forming a ‘cross-bridge’. When myosin head binds to actin, it brings a conformational change in the myosin head and causes it to pivot. The energy for piloting comes from the hydrolysis of ATP that had occurred before the myosin-actin crossbridge was formed.
4. After pivoting, the myosin head loses its ADP and attracts an ATP-binding to ATP cause the myosin to detach from the actin.
5. The cycle of attachment and detachment contributes as long as there is Ca and ATP in the vicinity.
6. Numerous scales cause the sarcomere to shorten as the myosin slides over the actin bringing the Z-discs closer.
7. A single muscle contraction is a result of hundreds of cycles of attachment and detachment of myosin heads.
Online resource
1. Resting state: in a relaxes muscle, the actin and myosin filaments are partially overlapped in a region called the sarcomere, which is the smallest unit of muscle contraction. The myosin filaments have tiny projections called cross-bridges that are in a “ready” position to interact with actin.
- AP: when a muscles is stimulated by an electrical impulse, it triggers the release of calcium ions from the sarcoplasmic reticulum inside the muscle cell.
- Calcium activation: the release of calcium binds to a protein called troponin on the actin filaments. This causes a conformational change that exposes binding sites on actin forming the myosin cross-bridges.
- Cross-Bridge Formation: myosin heads attach to these exposed binding sites on actin, forming cross-bridges.
- Power Stroke: once the myosin head binds to actin it pivots and pulls the actin filament toward the center of the sarcomere. This movement is called the power stroke and shortens the sarcomere, which is what leads to muscle contraction. During this, ADP and inorganic phosphate are released.
- ATP binding: after the power stroke, ATP binds to the myosin heads, cause it it to detach from the actin filament.
- Re-cocking the myosin head: the ATP is then hydrolyzed into ADP and phosphate, which provides the energy to “re-cock” the myosin head, positioning it for the next cycle.
When the neural impulse stops, the Ca+ levels in the Sarcoplasm diminish - Ca+ goes back into the SER - Ca+ not bound to troponin anymore - so tropomyosin swings back into the grooves of the actin fiber covering the myosin - binging sites- myosin cannot bind to actin and the muscle relaxes.
Upon death, the mitochondrial activity stops - not enough ATP to support the sliding, so the myosin that is bound to actin remains attached and does not detach. This cases the muscles to become rigid. This is referred to as?
Rigor Mortis
Smooth muscle is under the control of what innervation?
Autonomous innervation
Myosin is a ________ protein. This means?
Motor
It is going to utilise ATP to become pre-charged. When not in motion the myosin heads break down ATP —>ADP + P (phosphate). During this breakdown there is energy stored in the myosin head. Now the myosin head will form its cross bridge (myosin head is binding to a site on the actin molecule).
How does the myosin heads detach from the actin molecule?
The myosin head bends (changes its shape) and cause itself to loose the ADP+Pi energy it has.
Smooth muscle can also be referred to as ________ _______.
Visceral muscle.
*look at microscopic picture of muscles and be able to identify
What are dense bodies?
Within smooth muscle. It is aggregations of alpha actin proteins. They allow for action filaments to anchor.
*Anchor actin filaments
What is reticulin? What does it normally cover?
Collagen type 3
SMOOTH Muscles
T or F
A sarcomere is the contractile unit of a muscle
T
T or F
Actin and myosin are involved in cytokinesis, separating cells during cell division.
T
T or F
Actin and myosin are the essential contractile proteins of all muscle cells
T
T or F
Smooth muscle contraction is involuntary
T
T or F
Numerous fascicles together make a skeletal muscle fiber
F
T or F
Rough ER is the sarcoplasmic reticulum that stores Ca++ in muscle cells
F
Role in Muscle Contraction:
When the muscle is at rest, calcium is stored in the SR, bound to proteins like calsequestrin.
Upon muscle stimulation, the T-tubules (transverse tubules) transmit the action potential into the muscle cell. This causes the SR to release its stored calcium into the sarcoplasm.
The calcium binds to the troponin complex on the actin filament, causing a conformational change that exposes binding sites for myosin, triggering contraction.
The rough ER is primarily involved in the synthesis and folding of proteins, especially those that are secreted or embedded in membranes. It is studded with ribosomes on its surface, which are responsible for protein synthesis, but it does not play a significant role in calcium storage.
*** calcium ions are mainly stored in the sarcoplasmic reticulum (SR) in muscle cells, which is a specialized form of the smooth endoplasmic reticulum
T or F
Skeletal muscle cell/fiber is multi-nucleated
T
T or F
The Sarcolemma is the cytoplasm of the muscle cell
F
T or F
The TnT subunit of Troponin is responsible for Ca++ binding
F
T or F
The T-tubules are inward tubular extensions of the Sarcolemma
T
Which of the following best defines a sarcomere?
A. A protien that enables muscle contraction by binding with calcium ions.
B. The main contractile unit of muscle fiber in the skeletal muscle
C. The outer membrane of a muscle cell that helps with nutrient absorption
B
Which of the following is the correct breakdown of the word “tropomyosin” into its word parts?
A. Tropo- (muscle) + -sin (energy)
B. Tropo- (muscle) + -myo- (turn/change) + -sin (structure)
C. Tropo- (turn/change) + -myos- (muscle) + -in (protein)
D. Tropo- (movement) + -myos- (protein) + -in (enzyme)
C
What does the prefix “fibro-“ refer to in medical terminology?
A. Muscle
B. Blood vessel
C. Fiber or connective tissue
D. Nerve
C
T or F
A sarcomere is Z disk to Z disk
T
T or F
A myosin head is only bound to one unit at one time
T
It is bound to actin until ATP binds to it. Then it re leases. ADP and Phosphate then come off, creating a slide.
*Swings back, and myosin head binds again and pivots
When could the sliding filament not happen?
If calcium cannot be accepted. There is no place for myosin heads to bind. *other involvements that would hinder the detaching of the myosin heads
Explain cross - bridge..
Explain power stroke …..
Cross-Bridge Formation:
Cross-bridge refers to the connection formed between myosin (thick filament) and actin (thin filament) in muscle fibers.
When a muscle is stimulated to contract, calcium ions are released inside the muscle fibers. This allows the myosin heads (part of the myosin thick filaments) to bind to specific sites on the actin filaments. This binding forms the “cross-bridge.”
The binding site on actin is exposed when tropomyosin (a protein that usually blocks these sites) is moved by troponin, which is regulated by calcium ions.
Power Stroke:
Once the cross-bridge is formed, the myosin head undergoes a conformational change, pulling the actin filament towards the center of the sarcomere (the structural unit of muscle fibers).
This action is known as the power stroke, where the myosin head rotates and pulls actin, causing the muscle to contract. During this, the myosin head releases a phosphate group (previously bound during the cross-bridge formation), which powers the stroke.
As the myosin head moves, it also releases ADP (adenosine diphosphate) and generates a small force, which shortens the muscle fiber.
Smooth muscles are found in …
Tube like organs
(NOT the heart)
