Chapter 10 Flashcards
(33 cards)
Functions of Skeletal Muscle
Body movement
- Move bones, make facial expressions, speak, breathe, swallow
Maintenance of posture
- Stabilize joints, maintain body position
Protection and support
- Package internal organs and hold them in place
Regulating elimination of materials
- Circular sphincters control passage of material at orifices
Heat production
- Help maintain body temperature
Example: Skeletal muscles allow us to walk and run.
Characteristics of Muscle
Responsiveness (excitability)
- To chemical signals, stretch, and electrical changes across the plasma membrane
Conductivity
- Local electrical change triggers a wave of excitation that travels along the muscle fiber
Contractility
- Shortens when stimulated
Extensibility
- Capable of being stretched between contractions
Elasticity
- Returns to its original resting length after being stretched
Additional Information: Muscle cells have the ability to contract and relax.
Skeletal Muscle
Skeletal muscle—voluntary, striated muscle attached to one or more bones
Striations—alternating light and dark transverse bands
- Results from an overlapping of internal contractile proteins
Voluntary—usually subject to conscious control
Muscle cell, muscle fiber (myofiber)—as long as 30 cm
Example: Biceps muscle is a type of skeletal muscle.
Structural Organization of Skeletal Muscle
Tendons are attachments between muscle and bone matrix
- Endomysium: areolar CT around muscle cells
- Perimysium: dense irregular CT around muscle fascicles
- Epimysium: dense irregular CT surrounding entire muscle
- Continuous with collagen fibers of tendons
- In turn, with connective tissue of bone matrix
Collagen is somewhat extensible and elastic
- Stretches slightly under tension and recoils when released
- Resists excessive stretching and protects muscle from injury
- Returns muscle to its resting length
- Contributes to power output and muscle efficiency
Structural organization is important for muscle function.
The Muscle Fiber
Sarcolemma—plasma membrane of a muscle fiber
- Has T-tubules (transverse tubules) that extend deep into the cell
- Sarcolemma and its T-tubules have voltage-gated ion channels that allow for conduction of electrical signals
Sarcoplasm—cytoplasm of a muscle fiber
- Organelles plus contractile proteins
Myofibrils—long protein bundles that occupy the main portion of the sarcoplasm
- Glycogen: stored in abundance to provide energy with heightened exercise
- Myoglobin: red pigment; stores oxygen needed for muscle activity
The sarcolemma is essential for muscle function.
Myofilaments
Thick filaments—made of several hundred myosin molecules
- Shaped like a golf club
- Two chains intertwined to form a shaftlike tail
- Double globular head
- Heads directed outward in a helical array around the bundle
- Heads on one half of the thick filament angle to the left
- Heads on the other half angle to the right
- Bare zone with no heads in the middle
Myosin is a key component of thick filaments in muscle fibers.
Structure of thin filament
Troponin complex
G actin
Tropomyosin
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Structure of thick filament
Myosin head
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Components of sarcomere
Sarcomere—segment from Z disc to Z disc
A band
H zone
M line
I band
Z disc
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Motor neurons and motor units
Somatic motor neurons
Somatic motor fibers
Motor unit
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Neuromuscular junction
Neuromuscular junction (NMJ)
Synapse
Synaptic knob
Synaptic cleft
Motor end plate
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What is the function of the motor end plate?
Region of sarcolemma with many ACh receptors
Example: The motor end plate is where the synaptic vesicles release ACh into the synaptic cleft.
What is the role of the Schwann cell at the Neuromuscular Junction?
Envelops and isolates all of the NMJ from surrounding tissue fluid
Example: The Schwann cell helps protect the NMJ from external influences.
What happens during exocytosis at the Neuromuscular Junction?
Synaptic vesicles release ACh into the synaptic cleft
Example: Exocytosis is a crucial process for neurotransmitter release.
What is the significance of the basal lamina at the Neuromuscular Junction?
Thin layer of collagen and glycoprotein separating Schwann cell and muscle cell from surrounding tissues
Example: The basal lamina provides structural support and isolation.
What are electrically excitable cells?
Muscle fibers and neurons
Electrically excitable cells are cells that exhibit voltage changes in response to stimulation
What is electrophysiology?
The study of the electrical activity of cells
Define voltage (electrical potential)
A difference in electrical charge from one point to another
What is the resting membrane potential?
About -90 mV
Maintained by sodium-potassium pump
What is an action potential?
A quick up-and-down voltage shift from the negative RMP to a positive value, and back to the negative value again
Seen in an active stimulated cell
What are the four major phases of contraction and relaxation in skeletal muscle fibers?
Excitation, excitation-contraction coupling, contraction, relaxation
What is rigor mortis?
Hardening of muscles and stiffening of body beginning 3 to 4 hours after death
Peaks about 12 hours after death
What are the two main pathways of ATP synthesis?
Anaerobic fermentation and aerobic respiration
What is Myasthenia Gravis?
An autoimmune disease where antibodies attack neuromuscular junctions and bind ACh receptors together in clusters
Effects usually first appear in facial muscles
