Hitsology - Muscle Flashcards
Intrafusal fibers
- Modified muscle cells.
- Surrounded by fluid-containing periaxial space, which in turn is enclosed by capsule.
- The connective tissue elements of the capsule are continous with the collagen fibers of the perimysium and endomysium.
Two types of sensory receptors:
- Muscle spinldes
- Golgi tendon organs
Both act in concert to intergrate spinal reflex system
Extrafusal fibers
Skeletal muscle fibers surrounding the muscle spindle
Cardiac muscle
Centrally placed nucleus
- Two nuclei
- Ca. 50% of the volume of the cardiac muscle cell is occupied by mitochondria.
- Abundant supply of myoglobin
- Possesses inherent rythmicity
- Contract spontaneously
Atrial natriuretic peptide
A substance that functions to lower blood pressure
Quanta
- Is acetylcholine (ligand) liberated in larger quantities.
- Line the T tubule of cardiac muscle
Two types of smooth muscles
- Multiunit smooth muscle:
> Contract independently
> Each muscle cell had its own nerve sypply - Unitary (single unit, vascular) smooth muscle:
> Form gap junction with those of contigous smooth muscle cells, and nerve fibers form synapses with only a few of the muscle cell.
Substances manufactrured by smooth muscle cells for EC utilization
- Collagen
- Elastin
- GAGs
- Proteoglycans
- Growth factors
- In addition to its contractile infornations, som smooth muscle is capable of exogenous protein synthesis.
External lamina (basal lamina)
- Line both the primary synaptic cleft and the junctional fold.
- Each muscle cell is surrounded by an external lamina, with reticular fibers embedde in the external lamina
Smooth muscle fibers
- Are fusiform
- Elongated
- Oval nucleus with two or more nucleoli
Dense bodies
Visable atfter the H and E.
In smooth muscle fibers
Thick filaments of smooth muscle
Composed of myosin II
Thin filaments
Composed of actin
> With its associated caldesmon, a protein that blocks the active site of F- actin and tropomyoskine with the notable ab sent of tropomyosin
Hyperplasia
Sattelite cells that undergo mitotic activity subsequent is muscle injury
Hypertrophy
When satellite cells fuse with existing mucle cells
> Increasing muscle mass during skeletal hypertrophy
Voltage-gated calcium release channels
= junctional feet
- Located in terminal cisterna
What is responsible for the cross-striation of high and dark banding that are characteristic for skeletal muscles viewed in longitudinal section?
Myofibrils
What regulates muscle contraction?
Sacroplasmic reticulum
Power stroke
When the thin filament is dragged toward the center of sacromere as a result of ADP being released
What cause the release of the bond between actin and myosin II?
ATP binding to the S1 subfragment
Motor unit
Motor neuron and the muscle it controls?
Postsynaptic membrane
The muscle cell membrane
Axon terminal
- Covered by Schwann cells.
- Houses: mitochondria, SER and ca. 300’000 synaptic vesicles (containes acetylcholine)
Secondary synaptic cleft
= junctional folds
- Opens into the primary synaptic cleft.
- Is a further modification of the sacrolemma.
- Lined by basal lamina-like external lamina
- The sacroplasm in the vicinity of the secondary synaptic cleft is rich in glycogen, nuclei, ribosomes, and mitochondria.
Primary synaptic cleft
- Through-like structure occupied by the axon terminal.
- Lined by a basal lamina-like external lamina.
Neuromuscular junction
- Muscle-nerve junctions
- Composed of:
> An axon terminal
> A synaptic cleft
> Muscle cell membrane - Function: transmit a stimulus from the nerve fibers to the muscle cells
Active sites
Is where the fusion of acetylcholine (synaptic vesicle) occure along the presynaptic membrane
Somatic system
Skeltal muscle
Autonomic system
- Smooth muscle
- Cardiac muscle
- Glands
Striated muscles
- Skeletal
- Cardiac
Muscle fibers
Muscle cells
Investments of skeletal muscles
- Epimysium:
> Dense irregular collagenous connective tissue - Perimysium:
> Less dense collagenous connective tissue derive from epimysium.
> Surrounds bundles (fasicles) of muscle fibers. - Endomysium:
> Composed of reticular fibers and an external lamina (basal lamina)
> Surround each muscle cell
Tendons and aponeuroses
- Connect muscle to bone and to other tissues.
- Continous with connective tissue encasements of muscles and act in harnessing the contractile forces for motion.
Skeltal muscle
Multinucleated -> nuclei peripherally located Voluntary contraction Rich vascular supply - A lot of myoglobin pigments = red - Myoblast are precusors of skeletal muscle fibers - Myotubes - Myofibrils -> myofilaments - Continous capillaries - Red, white, or intermediate
Satellite cells
- Have a single nucleus and act as regenerative cells in shallow depressions on the muscle cell’s surface, sharing teh muscle external lamina
- Chromatin network of the satellite cell nucleus is denser and coarser then that of the muscle fibers
During muscle contraction
- I band = narrower
- H band = dissapears
- Z disks = move closer
- A band = nothing happens
T-tubules in skeletal muscles
- 2 terminal cisternae
- Terminal cisternae have voltage-gated calcium release channels (junctional feet) in their membrane.
- Transverse tubules
- Lie in the plane of the junction of the A and I bands
Thin filaments
Composed primarly of actin
Thick filaments
Composed of myosin II
Myomesin and C protein
Found in the M-line
The center of which is occupied by a thick filament
Hexagon
The structural organization of myofibrils is maintained largerly by fibe proteins:
- Titin
- “Alpha”-actin
- Cap Z
- Nebulin
- Tropomodulin
The heavy chains
- Cleaved by trypsin into:
- Light meromyosin
- Heavy meromyosin
- Read more p. 165
Huxley’s sliding filament theory
Is about how the thin filaments slide past the thick filaments during contraction
Acetylcholine receptors
- Located in the vicinity of the presynaptic active sites.
- Are ligand-gated ion channels
Acetylcholineterase
- Enzyme in the external lamina lining the primary and the secondary synaptic clefts
- Degrade acetylcholine to:
- Acetate
- Choline
=> Reestablishment of the resting potential
- Hint: terase = tear up (sounds like)
Choline acetyl transferase
Within the axon terminal, the acetylcholine is synthesized from activated acetate (product in mitochondria) and the recycled choline, a reaction catalyzed by choline acetyl transferase.
Cardiac muscle recieve calcium from:
- SER/ sacroplasmic reticulum
- Bore on the T-tubules that permit ECM with Ca2+ to enter the cardiac muscle via the T-tubules.
- External lamina: negatively charged coating the T-tubules store calcium for instantenous release.
- Calcium can enter the cell through calcium-sodium channels
Golgi tendon organs
= Neurotendinous spindles
- Composed of:
> Wavy collagen fibers
> Nonmyelinated continuation of a single type Ib axon that ramifies as free nerve ending in the intersices between the collagen fibers.
Organelles for cardiac muscle
- ECM -> Primary calcium source for cardiac muscle contraction
- SER -> Ca2+ supply for the cardiac muscle
-> Do not form terminal cisternae - T-tubules with small terminals of SER
=> Dyad
Smooth muscle (1)
- No striations
- Do not possess a system of T-tubules
- Location: Hallow vicera (gastrointestinal tract, some of the reproductive tract, and the urinary tract), walls of blood vessles, larger ducts of compound glands, respiratory passages, small boundles within the dermis of the skin.
Smooth muscle (2)
- Not under voluntary control
- Regulated by the autonomic nervous system, hormones, and local physiological conditions.
- = Involuntary muscle
Fine structure of smooth muscle
- Thin and thick filaments
- Heavy meromyosin heads (S1)
- Myosin II + actin = contractions of long duration
- All-or-none law does not apply to smooth muscle
- Intermediate filaments which consist of vimetin and desmin
- Caveolae -> associated with the cell membrane. Act as T-tubules. Regulates the cytosolic free calcium ion concentration.
Neuromuscular junction
Is composed of an axon terminal, a synaptic cleft, and the muscle cell membrane
Intercalated disk
- End-to-end junction between cardiac muscle cells
- Transverse portion:
> Fasciae adherentes
> Desmosomes abound - Lateral postion:
> Rich in gap juction - Thin myofilaments attach to the fasciae adherens
- Gap junctions -> Rapid flow of information
Gap junction
- Cardiac muscle cells
- Smooth muscle cells
- Neurons
- Skeletal muscles DO NOT have gap junction
Unitary (single-unit, vascular) smooth muscle form gap junctions with those of contigous smooth muscle cell
Dystrophin
A protein that binds to actin
Caldesmon
A protein that blocks the active site of F-actin
F-actin
- A major component of each thin filament
- Is a polymer of globular G-actin units
- Two chains of F-actin wound around each other in a tight helix
Myofibrils
- Held with one another with intermediate filaments desmin and vimetin
- Dystrophin binds to actin
Myofibrils -
- A-bands:
> Dark bands
> Anisotropic with polarized light
- I-bands:
> light bands
- Isotropic with polarized light
- H-bands:
> Pale
> Bisected by a thin M line (H&M)
- I-band bisected by Z disk (line)
- Z disk = sacromereRead page 172-173
Muscle spindles
Read
- Muscle contraction and relaxation
- Energy source for muscle and myotendious junctions
Les 182-184
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