1
Q
a primary tissue type divided into:
- Skeletal Muscle
- Cardiac Muscle
- Smooth Muscle
A
Muscle Tissue
2
Q
- Includes only skeletal muscles (organs)
* Is not all muscle, only skeletal muscle bc all of the other muscle types belong to other systems
A
The Muscular System
3
Q
- Muscle tissue (muscle cells or fibers)
- Connective tissues
- Nerves
- Blood vessels
(this combination is necessary to make a functional skeletal muscle organ; which will shorten.) Shortening will allow you to move those bones relative to each other.
A
Skeletal Muscle Structures
4
Q
- Produce skeletal movements
- Maintain body position (postural muscles)
- Support soft tissues
- Guard body openings
- Maintain body temperature
A
Functions of Skeletal Muscles
5
Q
Muscles have 3 layers of connective tissues… what are they?
A
Epimysium
Perimysiun
Endomysium
6
Q
- a dense irregular connective tissue that is dominated by collagen fibers.
- Allows you to tie everything within the organ together,
- serves as a barrier for things that are trying to invade the organ)
A
Epimysium
7
Q
- Exterior collagen layer
- Connected to deep fascia
- Separates muscle from surrounding tissues
- Outermost most surface of the muscle organ
A
Epimysium
8
Q
- Holds the muscle fascicles together
- (Areolar connective Tissue)
- this form of loose connective tissue has enough collagen/elastic fibers to keep the fascicles where they need to be so they’re not sliding around within the muscle organ
A
Perimysium
9
Q
- Surrounds muscle fiber bundles (fascicles)
- Contains blood vessel and nerve supply to fascicles
- Between and around the muscle fascicles
A
Perimysium
10
Q
- Within the muscle fascicle,
- surrounds the individual muscle fiber,
- holds the muscle fiber within its fascicle relative to its neighbors so that it doesn’t slide around,
- primary purpose is to hold things to the muscle fiber, maintains important vital connections (neurons, stem cells, blood vessels,)
A
Endomysium
11
Q
- Surrounds individual muscle cells (muscle fibers)
- Contains capillaries and nerve fibers contacting muscle cells
- Contains satellite cells (stem cells) that repair damage
- Within the fascicles
- innermost
A
Endomysium
12
Q
• Muscles have extensive vascular systems that:
– supply large amounts of oxygen
– supply nutrients
– carry away wastes
A
Blood vessels
13
Q
Immature muscle cell
A
myoblast
14
Q
Skeletal muscle cells
A
fibers
15
Q
- Are very long
- Develop through fusion of mesodermal cells (myoblasts)
- Become very large
- Contain hundreds to thousands of nuclei
A
Skeletal Muscle Fibers
16
Q
- The cell membrane of a muscle cell
- Surrounds the sarcoplasm (cytoplasm of muscle fiber)
- A change in transmembrane potential begins contractions
- Lets you signal
A
Sarcolemma
17
Q
a signal that can travel across the sarcolemma and T Tubules (membrane)
A
Action Potential or Muscle impulse
18
Q
- Transmit action potential/muscle impulse through cell
- Allow entire muscle fiber to contract simulataneously
- Have same properties as sarcolemma
- Network of tubes
- Passes message to myofibrils
A
Transverse Tubules (T tubules)
19
Q
- Lengthwise subdivisions within muscle fiber
- Made up of bundles of muscle protein filaments (myofilaments)
- Myofilaments are responsible for muscle contraction (shortening)
A
Myofibrils
20
Q
made of the protein actin
A
Thin filaments
21
Q
made of the protein myosin
• Contain twisted myosin subunits
• Contain titin strands that recoil after stretching
A
Thick filaments
22
Q
- A membranous structure surrounding each myofibril
- Helps transmit action potential to myofibril (the myofibril doesn’t understand the message that the sarcolemma & T tubules sent) SR helps translate the message to contract
- Similar in structure to smooth endoplasmic reticulum
- Forms chambers (terminal cisternae) attached to T tubules
- Stores/release calcium ions and when the timing is right, it puts the calcium ions back into storage
A
Sarcoplasmic Reticulum
23
Q
Is formed by 1 T tubule and 2 terminal cisternae
A
A Triad
24
Q
- Concentrate Ca2+ (via ion pumps)
- Release Ca2+ into sarcomeres to begin muscle contraction
- (Stores calcium), when the signal arrives, (releases calcium), when the signal is gone, (put calcium back into storage) (SR
A
Cisternae
25
(One unit of the myofibril and they exist because of how the thin and thick are organized)
• The contractile units of muscle
• Structural units of myofibrils
• Form visible patterns within myofibrils (thin/thick filaments)
(Responsible for the striations in the skeletal muscle/cardiac muscle slides)
Sarcomere
26
• A striped or striated pattern within myofibrils:
– alternating dark, thick filaments (A bands) and light, thin filaments (I bands)
(are found in that cardiac muscle slide and skeletal muscle slide. 0
Muscle Striation
27
– the center of the A band (The A band section)
| – at midline of sarcomere
M Line
28
– the centers of the I bands (the I band section)
| – at 2 ends of sarcomere
Z Line
29
* The densest, darkest area on a light micrograph
* Where thick and thin filaments overlap (interact)
* Where the actual work of shortening is done
* Most important part of the entire sarcomere
Zone of Overlap
30
* The area around the M line
| * Apart of the A band that Has thick filaments (no thin filaments )
H Zone
31
* Are strands of protein
* Reach from tips of thick filaments to the Z line
* Stabilize the filaments
* Prevents over stretching (proper alignment)
Titian
32
* Transverse tubules encircle the sarcomere near zones of overlap
* Ca2+ released by SR causes thin and thick filaments to interact (contract)
Sarcomere Function
33
– is 2 twisted rows of globular G actin
– the active sites on G actin strands bind to myosin
– looks like a pearl
F actin
34
– holds F actin strands together
– hold the G’s together to make the F (it holds them together to make the (active site) to face outwards towards tropomyosin)
Nebulin
35
– is a double strand
– prevents actin–myosin interaction
– (twisted rope)
Tropomyosin
36
– a globular protein
– binds tropomyosin to G actin (moves Tropomyosin out of the way if it has calcium) No calcium means Tropomyosin sits on the active site and myosin and actin cannot interact.
– controlled by Ca2+
Troponin
37
* Ca2+ binds to receptor on troponin molecule
* Troponin–tropomyosin complex changes
* Exposes active site of F actin
Initiating Contraction
38
– binds to other myosin molecules
tail
39
– made of 2 globular protein subunits
| – reaches the nearest thin filament
head
40
• During contraction, myosin heads:
– interact with actin filaments, forming cross-bridges
– pivot, producing motion
Myosin Action
41
– thin filaments of sarcomere slide toward M line
– between thick filaments
– the width of A zone stays the same
- Z lines move closer together
Sliding filament theory:
42
```
• Neural stimulation of sarcolemma:
– causes excitation–contraction coupling
• Cisternae of SR release Ca2+:
– which triggers interaction of thick and thin filaments
consuming ATP and producing tension
```
The Process of Contraction
43
• Is the location of neural stimulation
• Action potential (electrical signal):
– travels along nerve axon
ends at synaptic terminal
The Neuromuscular Junction
44
* Releases neurotransmitter (acetylcholine or ACh)
| * Into the synaptic cleft (gap between synaptic terminal and motor end plate)
Synaptic Terminal
45
• Acetylcholine or ACh:
– travels across the synaptic cleft
– binds to membrane receptors on sarcolemma (motor end plate)
– causes sodium–ion rush into sarcoplasm
– is quickly broken down by enzyme (acetylcholinesterase or AChE)
The Neurotransmitter
46
* Generated by increase in sodium ions in sarcolemma
* Travels along the T tubules
* Leads to excitation–contraction coupling
Action Potential
47
```
• Action potential reaches a triad:
– releasing Ca2+
– triggering contraction
• Requires myosin heads to be in “cocked” position:
loaded by ATP energy
```
Excitation–Contraction Coupling
48
1. Exposure of active sites
2. Formation of cross-bridges
3. Pivoting of myosin heads
4. Detachment of cross-bridges
5. Reactivation of myosin
5 Steps of the Contraction Cycle
49
• As sarcomeres shorten, muscle pulls together, producing tension
Fiber Shortening
50
• Depends on:
– duration of neural stimulus
– number of free calcium ions in sarcoplasm
– availability of ATP
Contraction Duration
51
* Ca2+ concentrations fall
* Ca2+ detaches from troponin
* Active sites are recovered by tropomyosin
* Sarcomeres remain contracted until an outside force pulls muscle to original length
Relaxation
52
• A fixed muscular contraction after death
• Caused when:
– ion pumps cease to function
– calcium builds up in the sarcoplasm
Rigor Mortis
53
– as a whole, a muscle fiber is either contracted or relaxed
The all–or–none principal
Bio 168 (2020)
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