Muscle Tissue - Sheet1 Flashcards
smooth muscle
Functions: Contractility and Conductivity
No striations
No T-tubules
**Involuntary **
myofiber
muscle cells
myofibril
Tiny, cylindrical rods within the sarcoplasm of the muscle cell. Responsible for the appearance of cross-striations in muscle cells.
myofilament
A component of myofibrils that has three categories: 1) actin filaments (thin) 2) myosin filaments (thick) 3) Z-disk
sarcolemma
Plasma membrane. Nucleus located just inside the sarcolemma.
sarcoplasm;
cytoplasm of muscle fibers. Surrounds myofibrils and is beneath the sarcolemma
sarcoplasmic reticulum
Network of cisterns and/or membranous tubules running between and around myofibrils. Contains sarcoplasm.
actin
2 types…
G-actin (globular actin)–a globular monomer that polymerizes to form F-actin (Two helically-wound strands of polymerized G-actin)
myosin
thick, extends accross entire A-band, contains myomesin, C-protein, and others.
tropomyosin
Fibrous; arranged head to tail in a linear series.
Helically wound along grooves of F-actin helix
alpha-actinin
Component of the Z-disk
Holds actin filaments in register by binding them in parallel array
troponin complex
3 subunits:
TnT: binds entire troponin complex to tropomyosin
TnC: great affinity for Ca++
TnI: binds to actin, preventing actin-myosin interactions
T-tubule
part of the sarcolemma.
typically seen at A-I junctions.
triad
Facilitates transmission of electrical impulse from sarcolemma to interior depths of cell.
diad
Cardiac muscle? T-tubule + terminal portion of adjacent sarcoplasmic reticulum
nebulin
Long, non-elastic protein
Two molecules of nebulin wrap around each thin filament
Help anchor thin filament to Z-disk
titin
Helps position myosin filaments precisely within the sarcomere. Extends from each half of a myosin filament to the Z-disk Helps keep myosin fillaments centrally located by acting like a spring
caveolae
Pinocytotic-like invaginations of sarcolemma
Probably play the role of the T-tubules found in skeletal and cardiac muscle
May work in concert with sarcoplasmic reticulum to modulate Ca++ availability
dense bodies
Smooth muscle only!
Two locations: 1) Inner aspects of sarcolemma
2) Throughout cytoplasm
Comparable to Z-disks of skeletal & cardiac muscle Contain alpha-actinin
Serve as anchor sites for actin-myosin interactions as well as intermediate filaments (vimentin; desmin)
Z-disk
Dense-staining; narrow.
Distance between two Z-disks = a sarcomere
Sarcomere
functional unit of the myofibril. defined as that portion of a myofibril extending from Z-disk to Z-disk.
intercalated disk
Complex of several types of cell-to-cell junctions:
Gap junctions (nexuses)
Desmosomes Fascia adherens (serve as anchoring points for actin filaments)
I-band, A-band, H-band
I-band: narrower, light-staining band, becomes smaller; may disappear as muscle shortens.
A-band; broad, dark-staining band, represents myosin filaments, remains contant during contraction.
H-band: pale-staining and narrow, narrows and is eventually obliterated in contraction.
Junction of A and I band = ?
T (transverse) tubule
What are the three regulatory molecules in skeletal muscle?
- Troponin complex
- **tropomyosin **
- Ca++
Ca++ as a regultory ion
Binds to TnC induces a conformational shift in tropomyosin, exposing previously blocked active sites on the actin filament
In skeletal muscle, the breadth of the _____ stays the same during contraction, while the breadth of the _____ and ____ get shorter.
A band; I band and H band
Endomysium
Sheath of fine c.t. around individual muscle fibers
Fine reticular fibers and ground substance
Perimysium
Connective tissue sheath around groups of muscle fibers (fasicles)
_**Continuous with tendon fibers***_
Epimysium
Outermost sheath of c.t.;
surrounds entire muscle
Synaptic vesicles of skeletal muscle fibers
In axon terminals
Contain acetylcholine
Motor end plates (structure and function)
form myo-neural junctions
Golgi tendon organs (structure and function)
Structure: Spindle-shaped bodies comprised of collagen and enclosed by a thin capsule
Afferent (sensory) fibers penetrate between the collagen fibers
Sensitive to stretching forces on tendons (aka reflexes)
SYNAPTIC VESSICLES CONTAINING ________ WILL RELEASE UPON ________ AND INTERACT WITH ACETYLCHOLINE RECEPTORS. ACETYLCHOLINE IS BROKEN DOWN BY ACETYLCHOLINE ESTERASE.
ACETYLCHOLINE; Depolarization
describe what Purkinje fibers are and do
play a role in cardiac conduction system;
Contain more sarcoplasm
Nuclei more rounded
Large diameter
Lack T-tubules
More glycogen
Muscle spindle
Structure: ** Internal capsule** immediately surrounds intrafusal fibers; encloses inner axial space
External capsule surrounds internal capsule and creates (periaxial space) between inner and outer capsules
Skeletal Muscle Hypertrophy referes to what?
Due to increase in size of fibers, not number
cardiac muscle– significant characteristics
Striated (involuntary) with lots of MITO
Single nucleus/cell; centrally located—good diagnostic tool. Have intercalated disks.
Intercalated disks of cardiac muscle
Dark cross-bands; frequently appear step-like
Occur where a Z-disk should be observed
Mark spots of cell-cell attachments (i.e, at ends of cells)
Atrial granules
Unique to atrial cardiac muscle cells
Contain atrial natriuretic peptide which functions to lower blood pressure
Decreases renal tubules capability to resorb (conserve) sodium and water
Contractile mechanisms of smooth muscle
Ca++(probably stored in caveolae) + calmodulin form a complex –> activates myosin light chain kinase –> phosphorylates one of the two light chains associated with the myosin molecule head.
Innervation of smooth muscle
- sympathetic innervations: synaptic vesicles contain norepinephrine
- parasympathetic innervation: synaptic vesicles contain acetylcholine
- variations in numbers of cells in a group that are innervated
