HCB Objectives 11
1.
Structural and functional differences between three muscles:
* See classroom handout
2.
Epimysium: dense, collagenous sheath of CT surrounding skeletal muscle; large
blood vessels supply epimysium
Perimysium: loose CT surrounding skeletal muscle fascicles; small branches of
blood vessels supply perimysium
Endomysium: loose CT surrounding myofibers connecting to the perimysium;
majority is composed of basal lamina surrounding myofibers
3.
Muscle: an anatomical structure with origin, insertion, innervation, and blood
supply
Fascicle: bundles of myofibers that compose muscle; fascicles are surrounded by
perimysium
Muscle fiber (myofiber): bundles of myofibrils that vary in diameter and travel
the length of the muscle; unbranched in skeletal and smooth muscle, branched in
cardiac
Muscle fibril (myofibril): a connection of sarcomeres that travels the length of
the muscle and is thus the region of contractile machinery
Sarcomere: functional unit of a myofibril and basic unit of striation, responsible
for contraction/relaxation of muscle, one sarcomere extends from one Z-line to
the next Z-line
Thick filament: myosin with globular head and long tail (heads make up
periphery, tails make up spine); head binds ATP and can bind actin
Thin filament: double-helical actin; unlike other actin due to presence of
troponin and tropomyosin
4.
Satellite cells:
a.
Function: repair and regenerate skeletal muscle cells
b.
Location: muscle fiber endomysium separate from muscle fiber; small,
round cells with dense nuclei (metabolically inactive)
5.
Sarcomere:
6.
T-tubules:
a.
Function: allows action potential to reach inside of cell and localize to
sarcoplasmic reticulum
b.
Location: junction between the A and I bands
c.
Structure: invaginations of the plasma membrane into the myofiber
Sarcoplasmic reticulum:
a.
Function: stores Ca2+ and releases Ca2+ when activated
b.
Location: two cisterns of sarcoplasmic reticulum will be found near Ttubules; near the A and I band junction
c.
Structure: smooth ER
Triad:
a.
Function: allows optimal release of calcium from a single action potential
by allowing action potential to quickly reach sarcoplasmic reticulum
causing a large release of calcium into the intracellular space
b.
Drawing:
7.
Sliding-filament mechanism of muscle contraction: Myosin binds actin in the
presence of Ca2+ and “walks down” the actin chain in the presence of ATP
Regulation mechanisms: Regulation can occur at the neuromuscular junction
(i.e. Botox at motor endplate), excitation-contraction coupling (i.e. problems in
SR Ca2+ channels), and stretch receptor feedback (i.e. muscle spindle).
Role of Ca2+: Ca2+ binds to troponin causing tropomyosin to shift off of the
myosin binding site of the thin filament. Thus, when Ca2+ is present, myosin can
bind actin.
Role of ATP: ATP allows myosin head to release from actin and move to next
binding site (facilitates the “sliding” of the filaments)
8.
Intercalated disk:
a.
Function: anchor sarcomeres, provide intracellular adhesion, and allow
rapid communication of signals
b.
Structure: unique to cardiac muscle, contains fascia adherens (similar to
zonula adherens), desmosome, and a gap junction
9.
Purkinje fibers:
a.
Function: long-range conduction of electrical signals from AV node
b.
Structure: modified cardiac myocytes with less developed contractile
machinery. Therefore, they appear puffy and pale (but still contain
sarcomeres!).