chapter 10 Flashcards
a primary tissue type divided into:
- Skeletal Muscle
- Cardiac Muscle
- Smooth Muscle
Muscle Tissue
- Includes only skeletal muscles (organs)
* Is not all muscle, only skeletal muscle bc all of the other muscle types belong to other systems
The Muscular System
- 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.
Skeletal Muscle Structures
- Produce skeletal movements
- Maintain body position (postural muscles)
- Support soft tissues
- Guard body openings
- Maintain body temperature
Functions of Skeletal Muscles
Muscles have 3 layers of connective tissues… what are they?
Epimysium
Perimysiun
Endomysium
- 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)
Epimysium
- Exterior collagen layer
- Connected to deep fascia
- Separates muscle from surrounding tissues
- Outermost most surface of the muscle organ
Epimysium
- 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
Perimysium
- Surrounds muscle fiber bundles (fascicles)
- Contains blood vessel and nerve supply to fascicles
- Between and around the muscle fascicles
Perimysium
- 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,)
Endomysium
- 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
Endomysium
• Muscles have extensive vascular systems that:
– supply large amounts of oxygen
– supply nutrients
– carry away wastes
Blood vessels
Immature muscle cell
myoblast
Skeletal muscle cells
fibers
- Are very long
- Develop through fusion of mesodermal cells (myoblasts)
- Become very large
- Contain hundreds to thousands of nuclei
Skeletal Muscle Fibers
- The cell membrane of a muscle cell
- Surrounds the sarcoplasm (cytoplasm of muscle fiber)
- A change in transmembrane potential begins contractions
- Lets you signal
Sarcolemma
a signal that can travel across the sarcolemma and T Tubules (membrane)
Action Potential or Muscle impulse
- 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
Transverse Tubules (T tubules)
- Lengthwise subdivisions within muscle fiber
- Made up of bundles of muscle protein filaments (myofilaments)
- Myofilaments are responsible for muscle contraction (shortening)
Myofibrils
made of the protein actin
Thin filaments
made of the protein myosin
• Contain twisted myosin subunits
• Contain titin strands that recoil after stretching
Thick filaments
- 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
Sarcoplasmic Reticulum
Is formed by 1 T tubule and 2 terminal cisternae
A Triad
- 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
Cisternae
(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
• 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
– the center of the A band (The A band section)
– at midline of sarcomere
M Line
– the centers of the I bands (the I band section)
– at 2 ends of sarcomere
Z Line
- 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
- The area around the M line
* Apart of the A band that Has thick filaments (no thin filaments )
H Zone
- Are strands of protein
- Reach from tips of thick filaments to the Z line
- Stabilize the filaments
- Prevents over stretching (proper alignment)
Titian
- Transverse tubules encircle the sarcomere near zones of overlap
- Ca2+ released by SR causes thin and thick filaments to interact (contract)
Sarcomere Function
– is 2 twisted rows of globular G actin
– the active sites on G actin strands bind to myosin
– looks like a pearl
F actin
– 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
– is a double strand
– prevents actin–myosin interaction
– (twisted rope)
Tropomyosin
– 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
- Ca2+ binds to receptor on troponin molecule
- Troponin–tropomyosin complex changes
- Exposes active site of F actin
Initiating Contraction
– binds to other myosin molecules
tail
– made of 2 globular protein subunits
– reaches the nearest thin filament
head
• During contraction, myosin heads:
– interact with actin filaments, forming cross-bridges
– pivot, producing motion
Myosin Action
– 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:
• 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
• Is the location of neural stimulation
• Action potential (electrical signal):
– travels along nerve axon
ends at synaptic terminal
The Neuromuscular Junction
- Releases neurotransmitter (acetylcholine or ACh)
* Into the synaptic cleft (gap between synaptic terminal and motor end plate)
Synaptic Terminal
• 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
- Generated by increase in sodium ions in sarcolemma
- Travels along the T tubules
- Leads to excitation–contraction coupling
Action Potential
• Action potential reaches a triad: – releasing Ca2+ – triggering contraction • Requires myosin heads to be in “cocked” position: loaded by ATP energy
Excitation–Contraction Coupling
- Exposure of active sites
- Formation of cross-bridges
- Pivoting of myosin heads
- Detachment of cross-bridges
- Reactivation of myosin
5 Steps of the Contraction Cycle
• As sarcomeres shorten, muscle pulls together, producing tension
Fiber Shortening
• Depends on:
– duration of neural stimulus
– number of free calcium ions in sarcoplasm
– availability of ATP
Contraction Duration
- 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
• A fixed muscular contraction after death
• Caused when:
– ion pumps cease to function
– calcium builds up in the sarcoplasm
Rigor Mortis
– as a whole, a muscle fiber is either contracted or relaxed
The all–or–none principal
