Histo Lecutre 15
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Describe Skeletal Muscle cells
- Multinucleated cells
- Cells appear striated at the microscopic level due to orientation of contractile proteins
- Contraction provides voluntary movement
What are the 3 CT layers?
What are the functions of the CT?
- Nourishment via rich capillary and lymphatic network
- Transmist fores along muscle fibers
What is the of smallest muscle unit to largest muscle unit?
- Muscle fiber
- Muscle Fasciculus
- Whole muscle
What is a myofilament?
- Protein polymers responsible for contraction
- (e.g. action, myosin)
What is a myofibril?
Grouping of myofilaments within a muscle cell
What is a muscle fiber?
What is a muscl fasciculus?
Bundle of muscle fibers
What are myotendinous junctions?
- Connection of muscle and tendon
- Infoldings of cell membrane of muscle fibers
- Proides insertion sites for collagen fibers of tendon into muscle fibers
What are the three components of a sarcomere?
- Myosin (thick)
- Actin (thin)
What is Titin?
- Large protein polymer
- Assists with transmission of force during contraction
- Limits range of motion of sarcomere in tension
- Provides passive tension in resting muscle
- Maintains appropriate position of actin and myosin (binds Z-disc to M-line)
What are the 5 sarcomere landmarks?
- Z-line (disk)
- I band
- A band
- H band
- M line
What is the Z-disc?
Actin attaches here
What is the I band?
area of actin molecules only (staddles Z-line)
What is the A band?
Area of mysoin & action overlap
What is the H band?
Area of myosin only
What is the M line?
- Anchors central area of myosin within each sarcomere
- Contains creatine kinase - enzyme that adds high energy phosphates to ADP to make ATP
What is hypertrophy?
Number of myofilaments increases with training while number of muscle fibers stays the same
What is the Light Chain?
- Consists of area of ATPase function (globular head)
- Serves as connection site for actin
What is the Heavy chain?
Consist of helixes of filamentous protein polymers
Describe the Globular Head
Functions as an ATPase - enzyme that energies the the process of muscle contraction by fascilitating hydrolysis of ATP to release energy
- Globular protein polymer; bound to myosin at cross-bridges (on light chain of myosin)
- Globular proteins polymerized into long chains
Filamentous protein that exists within the "grooves" of actin filaments
What are three types of Troponin and their functions?
- TnT - binds tightly to tropomyosin
- TnC - contains Ca 2+ at binding site
- Tnl - inhibits actin/myosin interaction
Where is calcium stored in muscle cells?
Sarcoplasmic reticulum (terminal cisternae)
What are Transverse Tubules?
Invaginations of the sarcolemma that create a network of membranous tubules at each sarcomere of muscle fibers
Describe the Triad
- Complex of two terminal cisterns of SR and one T-tubule
- Area where sarcomere depolarization is transmitted to the membrane of SR
What happens when a motor neuron creates a depolarization of the sarcolemma at the NMJ?
- Depolarization is "transmitted" from the sarcolemma to the SR via the T-tubule system of the muscle fiber
- SR depolarization stimulates release of Ca2+ from cisterns
- Released Ca2+ binds to TnC (Allows cross-bridging between action and myosin)
- When depolarization is gone, Ca2+ actively returns from sarcoplasm to SR
What is the function of proprioceptors and where are they located?
- Used reflexively to maintain appropriate muscle tension for posture and regulation of opposing muscle groups
- Within straited muscle fibers
Spindles consist of a CT capsule that surrounds what?
- Intrafusal muscle fibers (modified muscle fibers)
- Bag fibers (dynamic and static stretch)
- Chain fibers (static stretch)
What do spindles monitor?
- Velocity and degree of muscle stretch and sends that info to the CNS
- -Transmits info using Ia and II affarent fibers
Aside from preventing quick muscle stretching, what else do muscle spindles help with?
Stimulate reflexive inhibition of anatagonist muscle to allow agonist muscles to contract without opposition
What do gamma motor neurons control?
"sensitivity" of the spindles to stretch
What is the Golgi Tendon Organ?
Sensory nerve ending imbedded in the collagen fibers of the myotendinous junction
What are the two functions of the GTO?
- Monitors force of contraction of the muscle and sends info to CNS via 1b efferent fibers
- Provides an inhibitory reflex that protects muscles from creating too much tension
What other components can be found in muscle cells?
- Glycogen - source of glucose for energy
- Myoglobin - Storage site for oxygen for aerobic respiration
What is a NMJ?
- Site of connection between the nerve fiber of a motorneuron and the muscle fibers of skeletal muscle ("motor end plate")
- Each nerve fiber contains terminal branches allowing it to synapse with up to several hundred muscle fibers
Name two NMJ synaptic characteristics
- Synaptic trough - invagination of muscle membrane
- Subneural clefts - folds within synaptic trough which increase surface area for NT receptors (Ach)
What is the job of mitochondria specifically within the NMJ?
Create ATP energy for acetylcholine synthesis and vesicle exocytosis
What does acetylcholine bind to in the subneural clefts?
What enzyme breaks down acetylcholine?
What is Myasthenia Gravis?
- Auto-immune disease in which anti-bodies "attack" Ach receptorsand render them nonfunctional
- Disease creates paralysis due to inability of muscle cell to react to nerve impulses
What is the treatment of Myasthenia Gravis?
Acetylcholinesterase inhibitors that reduce Ach degradation and increase Ach binding to remain functional receptors
What does nerve gas (sarin gas) do?
inhibits acetylcholinesterase and creates tonic muscle contraction
What are the three classifications of motor neurons?
- Alpha motor neuron - Extrafusal muscle fibers (skeletal muscle fibers)
- Gamma motor neuron - Intrafusal muscle fibers (muscle spindle). Generates muscle response to sensory input from muscle spindles
- C motor neuron - Autonomic nervous system fibers to smooth muscle
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