Muscle I, II, and III Objectives
1. The three types of muscle tissue are Skeletal, Cardiac, and Smooth.
Skeletal muscle causes movement/stature of the body. They act on
bone tissue to exert a force in a direction. They are striated muscle
tissue in that the myofibrils are organized and inline with one another.
They are multinucleate and can run long distances if need be. They
require an attachment point, usually bone. They are attached to bone
by tendons. Cardiac muscle does not attach to bone, but rather itself.
Cardiac muscle has a series of cellular connections that allow it to pull
on it self. The muscle has striation, but the fibrils are not long and
strait. They branch, enabling a cardiac myocyte to pull in multiple
directions. They are mononucleate and have 2 types of intercellular
connections on different aspects of the cell. The traverse connections
are the Intercalated Discs. They are a combination of the fascia
adherens and the desmosomes. The desmosomes are present where
there is no actin present. These ICDs allows for the conversion of
chemical energy (ATP) to mechanical energy (heart pumping). The
longitudinal aspect is populated by gap junctions so that all the
myocytes can “get the joke” at the same time. Cardiac muscles are
controlled by autonomic modulation, but mainly the Sinoatrial node
and atrioventricular node. The SA node generates and maintains the
beat of the heart. Smooth muscle is arranged in an anastomosing
arrangement, meaning they overlap and form an almost quilt like
appearance in longitudinal section. They are surrounded by a basal
lamina and reticular connective tissue. This allows them to pull and
squeeze on each other. They have a single nucleus that is placed
somewhat centrally. They are designed for a slow and steady
squeezing motion. They can be partially or fully contracted, but this
intermediate phase separates them from other muscle tissue, as they
cannot do this.
2. Skeletal and Cardiac muscle cells have sarcomeres, as their myofibrils
are arranged in a very specific pattern. Smooth muscle cells do not
have these organized bundles of myofibrils. Skeletal muscles are
multinucleate where as cardiac and smooth are both mononucleate.
Skeletal and Cardiac myocytes are not capable of mitosis but smooth
muscle is. Skeletal muscles do not have intercellular junctions, but
smooth and cardiac both have gap junction. Cardiac also have
intercalated discs. Because skeletal and cardiac cannot undergo
mitosis, they must find another way to regenerate. Skeletal have a set
of undifferentiated cells that can replace them. Cardiac cells are still
workin it out.
3. Epimysium contains dense irregular connective tissue. The
perimysium is also dense irregular as it is the septa from the
epimysium. The endomysium is comprised of loose connective tissue.
All three layers contain type 1 collagen, but the endomysium also
contains type IV collagen. This connective tissue brings in the
neurovascular bundles to oxygenate and innervate the muscle
4. Figure this out
5. The Triad is the combination of two enlarged terminal cisternae
flanking a Transverse tubule. This allows for rapid and diffuse
depolarization of the membrane.
6. The Z Line has three proteins. Z Protein provides the backbone of the
z disc. Attached to it is alpha actinin, which binds actin to the z disc
and cap Z which binds the (+) end of actin so it can prevent the
autopolymerization of actin.
7. The thin filament is mostly actin, however there are other proteins
associated with the thin filament. Tropomyosin wraps around the
actin chain like a rope cover the myosin-binding site. Troponin is a
three-subunit protein that interacts with tropomyosin. TnT binds with
Tropomyosin. TnI regulates the inhibition of myosin binding on the
actin molecule. TnC is a regulatory site that binds Ca++ and causes
the uncovering of the myosin binding site. Also associated with the
thin filaments is Nebulin. It acts as backbone for actin. Tropomodulin
is also affiliated with actin and binds the (-) end of the actin filament to
stabilize its size.
8. The thick filament is mostly myosin, however it does contain other
proteins. The myosin is responsible for the actual contraction of the
sarcomere. The essential light chain and regulatory light chains affect
the bending ability of the myosin flex points. C protein acts as a ring
binding the myosin strands together. Titin is an anchor protein that
holds the myosin band in the middle of the sarcomere. To keep the
sarcomeres separate, myomesin is present to bind and stabilize the
thick filaments location in relation to each other. Creatine kinase is
also at the m line of the thick filament for rapid reproduction of ATP.
9. Myomesin and Creatine Kinase are at the M Line. Myomesin keeps
thick filaments where they are supposed to be so that actin filaments
can over lap. Creatine Kinase is for local, rapid ATP regeneration.
10. I got this.
11. Actin Cap proteins are important because actin likes to
autopolymerize. The function of sarcomeres is dependent on the length
of actin molecules and therefore must remain constant.
12. The electrical event that occurs at the motor end plate of the neuron is
the systematic and rapid depolarization of the neuron that leads to the
release of neurotransmitters into the primary and secondary synaptic
clefts. This will cause the initial depolarization of the membrane by
the influx of Na+ by way of ligand-gated channels. The initial
depolarization will be further propagated by the voltage-gated Na+
channels. The influx of Na+ will turn DHPR and open up Ryanodine
receptors and allow for the release of a whole lot of Ca++ (unless you
are the USBME than it is caused by the increase in IP3 formation that
causes the opening of an IP3 ligand-gated Ca++ channel)
13. Signal transmission results in increased Ca++ (see above). The
increased calcium will interact with TnC and cause the exposure of the
myosin-binding site on actin.
14. ADP-Pi bound to myosin is in relaxed state and can bind to actin. The
binding causes the release of Pi which then causes the cocking of the
myosin head. The new conformation will release ADP and allow for
binding of ATP. When ATP binds, the myosin head will release the
actin filament. The myosin head remains in the tense position until
the ATP is cleaved to form ADP and Pi.
15. See Number 14
16. Muscle relaxation is not a passive process. The Ca++ must be actively
pushed back into the sarcoplasmic reticulum. Approximately 50% of
the ATP used in a muscle contraction series is consumed post
contraction
17. The muscle spindle is the apparatus used to sense the current state of
the muscle. They have efferent nervous signals (sent back to brain).
There are two types of muscle spindles and two types of efferent
nerves. The first type of spindle is the nuclear bag spindle. This cell
has many nuclei located in a central location giving the appearance of
a “bag of nuclei.” The second type of cell is a nuclear chain spindle.
The nuclei of this cell are centrally located, but are in a single file
chain. Only one nucleus can be seen in cross section. The two types of
efferent nerves are the annulospiral nerves and the flowerspray
nerves. The annulospiral nerves wrap around the nuclear bag fibers
and sense when the coils become loose indicating a lengthening of the
spindle fiber. The flower spray nerves sense stretching apart. They
are located on the nuclear bag and nuclear chain spindle.
18. The cardiac myocyte is a striated muscle cell however it is not linear.
It branches so that it may pull in multiple directions at one time. It is
not innervated by the voluntary nervous system, but rather modulated
by the autonomic nervous system. It does not have an Epi or
perimysium, but rather a tissue type more like the endomysium
sandwiched between cells. They are connected to each other which
give the characteristic rotational contraction. They are directly
connected by cell-cell junctions (Intercalated discs and gap junctions.)
19. The intercalated disc is along the transverse region of cardiac muscle.
They consist of desmosomes and fascia adherens. The desmosomes are
located where there are no actin filaments from a sarcomere to bind
too. The transverse region glues the cardiac myocytes together. The
lateral region is populated by gap junctions. These gap junctions allow
for intercellular communication.