ANAT 261 Lecture Notes - Papain, Basal Lamina, Desmocollin

49 views13 pages

For unlimited access to Class Notes, a Class+ subscription is required.

Naveen Sooknanan McGill Fall 2011
1
Muscle:
Muscular tissue’s structure is closely related to its function. Morphological features are related to
individual molecules. For example, sarcomeres of skeletal muscle give rise to characteristic
striations
In multicellular organisms, movement is dependent on muscle fibers (specialized cells).
They contract upon stimulation and are elongated in shape
o Muscle cells are elongated and contain a great deal of cytoplasmic filaments
Muscle originates from the mesoderm
o Differentiation by the ectoderms produces the skin nervous system and annexes
o Differentiation by the endoderm forms the digestive tract
o Differentiation of the mesoderm forms CT and muscular tissue
Differentiation occurs mainly by a process of cell lengthening and synthesis of
myofibrillar proteins
There is specialized terminology in muscles for things we have already seen:
o Sarcolemma means muscle cell membrane
o Sarcoplasm means muscle cell cytoplasm
o Sarcoplasmic reticulum means muscle ER
There are three different types of muscle: smooth muscle, striates skeletal muscle and striated
cardiac muscle
Smooth muscle is mainly found in the wall of blood vessels and organs (e.g. in arteries,
veins and the walls of the digestive tract)
o They have an elongated cell shape with a
central, round nucleus
o The cytoplasmic myofilaments are under the
power of LM, so we do not see them
o Spindle shaped cells will be observes in longitudinal section
Striated skeletal muscle (or simply skeletal muscle) contains cross striations (stripes)
which run perpendicular to the fiber
o One fiber is one long, multinucleated cell, and it can be as long as 5-30cm
Therefore they are very
elongated
These long cells are produced
because stem cells
differentiate during
development and fuse together
to form one long fiber
o The nuclei arte squished and are located at the periphery of the cell
o The myofilaments have a special configuration which allows us to see them in
LM in cross section
They appear as small dots within the cytoplasm
o The contain organized bands which we will talk about later
Striated cardiac muscle looks a lot like skeletal muscle, but has some important
differences
o The stem cells do not fuse together, meaning each cell only has one nucleus
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 13 pages and 3 million more documents.

Already have an account? Log in
Naveen Sooknanan McGill Fall 2011
2
o The nucleus is centrally located, and there is a pale staining “halo” around the
nucleus
o The same bands are visible here as in
skeletal muscle
o The cells are squished together, but
separating them are intercalated discs
This stains dark because it
contains the 2 PMs of the two adjacent cells
o The myofibrils are visible here as well
o The cytoplasm also becomes branched, unlike skeletal muscle which remain in
packed fibers
Plane of section is very important for these cells, because 90% of the sections we will see
are oblique and can sometimes be hard to distinguish
Smooth muscle, as we stated before, has spindle shapes cell and a centrally located nucleus:
In longitudinal section, this spindle shape, or fusiform (wider middle and tapered edges)
is really seen well. The nucleus is centrally located and is an oval shape
o There are no striations in smooth muscle, the cytoplasm appears clear, as no
myofilaments are visible
o These cells have only one nucleus each
In cross section, a variety of circular shapes can be seen, all differing in size. This is
because each cell is cut at a different location
o Some cells may be cut at the ends, which means we won’t see the nucleus
o Other will be cut in the center, and appear bigger, and will have a nucleus
o All cells are roughly the same size, and have a central, round nucleus in cross
section
o No myofibrils are present, which means the cytoplasm is clear
o There are no “halos” around the nuclei (unlike cardiac muscle)
Central nucleus
Appears to be missing
nucleus in cross section
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 13 pages and 3 million more documents.

Already have an account? Log in
Naveen Sooknanan McGill Fall 2011
3
Striated skeletal muscle is made of up very long cells called muscle fibers:
In longitudinal section, the A (dark) and I (light) bands can be seen very well
o The nuclei are flattened and elongated, and pushed to the periphery of the cell
Any nuclei outside of the fibers may be the nuclei of fibrocytes. These
nuclei are much darker
o These cells are multinucleated, so many nuclei will be seen in the longitudinal
section of one fiber
o There are visible striations in the muscle because of sarcomeres
In cross section, the cytoplasm will have tiny dots which are visible myofilaments
o The nuclei are small and round, and pushed to the edges of the cell
Sometimes, you will see more than one nucleus per cell
o Sometimes, blood vessels such as capillaries will be in between the fibers
They will be much smaller and tube shaped, and only have one nucleus
o The cells themselves appear almost round
A band
I band
Fibrocyte
Z line
Nucleus
Myofibrils give grainy
appearance
Capillary
Circular cells
Central, round nucleus
No grains in cytoplasm
Spindle shaped cells
Elongated central nucleus
No halo
No striations
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 13 pages and 3 million more documents.

Already have an account? Log in

Get access

Grade+
$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
1 Booster Class
Class+
$8 USD/m
Billed $96 USD annually
Homework Help
Class Notes
Textbook Notes
30 Verified Answers
Study Guides
1 Booster Class