Lecture 3 - Muscle Histology Flashcards
Three types of muscle tissue
Skeletal
Cardiac
Smooth
Sarcolemma
muscle cell membrane
Other cell types= plasmalemma (plasma membrane)
Sarcoplasm
Cytoplasm of the muscle Cell
Sarcoplasmic reticulum
similar to smooth endoplasmic reticulum, storage site for calcium
Sarcosomes
Term of mitochondria within a muscle cell
Contractile Proteins
actin(thin) and myosin (thick)
Examples of Movement of actin and myosin for each type of muscle
skeletal- ex. movement of limbs
cardiac- ex. movement of blood
smooth- ex. movement of bolus (involuntary)
Connective tissue organization
Epimysium
Perimysium
Endomysium
(outer to inner)
Epimysium (type of CT)
Surrounds an ENTIRE muscle; dense irregular CT
Perimysium (type of CT)
Surrounds a muscle FASCICLE; dense irregular CT, Neurovascular structures course through the perimysium
Endomysium (Composition)
surrounds a SINGLE muscle or fiber/cell; mainly comprised of reticular fibers; capillaries and nerves terminals course through endomysium
Muscle unit and CT
CT investments are continuous with the tendon
form a strong muscolotendinous unit that allows muscle contraction forces to be transmitted
Contraction force path
Muscle->tendon->bone -> movement of bone segments
Skeletal muscle general features
Each muscle fiber contains many nuclei (MULTINUCLEATED)
located peripherally, adjacent to sarcolemma
Myofibrils and Sarcomeres
each muscle fiber/cell contains many myofibrils
each myofibril contains many sarcomeres
Sarcomere
repetitive subunit of skeletal ms
Actin and myosin are two major proteins that contribute to each sarcomere
Sarcomere composition
Several proteins
- actin (thin)
- myosin (thick)
- tropomyosin
- tropo
- titin
tropomyosin
wraps around actin
titin
stabilizes myosin at Z disc
M-line
middle of sarcomere; includes myosin binding protein that holds myosin in place
H-zone
corresponds to location of myosin (only)
A-band
corresponds to entire length of myosin
I band
corresponds to location of actin (only)
z disc
each sarcomere extends from Z disc to Z disc
alpha actin
stabilizes actin at the z disc
Contractile mechanism
involves actin, myosin, tropomyosin, troponin
tropomyosin in relaxtion
it wraps around actin
blocks binding site on actin for myosin head
troponin in relaxation
holds tropomyosin in place
during contraction
Ca2+ binds to troponin
- troponin changes conformation
- tropomyosin moves away from the active site on actin
- myosin binds to actin
- ATP provides energy for power stroke
- SHORTENS sarcomere
Neuromuscular Junction AP path
- AP travels down axon to terminal
- Opens Voltage Gated Ca2+ channels
- Ca2+ triggers release of ACh
- ACh traverses synaptic cleft, binds to ACh receptors on the sarcolemme (Motor end plate)
- Na+ ion channels open, enters Na+
- Depolarizing potential
- action potential initiated in muscle cell
- AP propagated along muscle cell plasma membrane
How does AP reach myofibrils deep in the sarcomere?
T-tubules: invaginations of the sarcoplasm
- permit AP to reach deep into muscle fiber
- Surrounded on both sides by the Sarcoplasmic reticulum cistern
- AP triggers release of Ca2+ from SR
Triad
Located in Skeletal Muscle
2 sarcoplasmic reticulum cisterns surrounding 1 T tubule
Contraction vs relaxation and Ca2+
Ca release = contraction
Ca sequestered in SR = relaxation
Contractile mechanism summary
Action potential in motor axon -> action potential in sarcolemma
travels down T-tubule and
triggers Ca+2 release from SR -> Ca+2 binds to troponin ->
conformational change in
troponin which moves tropomyosin
and uncovers the myosin binding
site (on actin) ->myosin head binds to actin ->
via energy release from ATP->
muscle contraction (power stroke
Relaxation summary
no more signal of ACh on terminal -> Ca2+ transported back into SR -> tropomyosin recovers active site on actin
Cardiac muscle vs Skeletal
Both Striated,
Cardiac not a regular structure,
Cardiac has 1 or 2 central nuclei,
Cardiac has cytoplasmic cone - location of glycogen/mitochondria
cardiac is small in length
intercalated disc at interface of cardiac muscle cells
Intercalated Disc (what is it describe structure)
seen as dark lines between “ends” of cardiac muscle cells (unique to cardiac), has elevations and depression (looks like waves at the end)
intercalated disc components (with location)
fascia adherens - located at the end
desmosomes - located at the end
gap junctions - laterally located, and provide continuity for quick potentials
Dyads
T- Tubules that dont have flanking cisterns. There is one T tuble and one SR.
This is located in Cardiac Muscle only
Smooth Muscle Location and Structure
No striations
Seen many places, blood vessels, urinary, eye, lung
spindle shaped cells taper on long axis
one signel nucleus
Contraction of smooth muscle Shape
Contracted called corkscrew shape
Fiber Orientations in Smooth Muscle
Inner Circular Layer - go around muscle - so they look like long cells in cross setion
Longitudinal - Organized in parllel to muscle - so look like cell circles going in to the page in a cross section
Dense Bodies
Located along the sarcolemma and in sarcoplasm. Similar to Z discs and bind actin
Dense Plaques
Aka Focal Adhesions
Junctions between cells.
They are dense bodies with an additional proteins connecting to adjacent cells
allows for communication of neighbor cells of contraction
Caveolae
Slight invaginations in the smooth muscle
location of calcium channels
are close to the sarcoplasmic reticulum
influx of calcium results in more calcium from sarcoplasmic reticulum
Gap Junctions in Smooth Muscle
Electrically and chemically couple the smooth muscle
for paristalsis
