Download Muscle

Histology SSN
October 22, 2003
Muscle
Sarah Little
sjl2017
Grace Liu
gcl2008
SKELETAL MUSCLE
I. Organization
A. General
• Muscle fibers run parallel and straight
• Mucle tissue = many fasiciculi
• Fasicuclus = many fibers (cell)
• Muscle fiber = many fibrils
“Mucle fiber” is really a syncytium of small myoblasts
that form a large multinucleated cell
polygons shaped in cross section
nucleus at the outer edge of the fiber
B. Surrounding connective tissue
1) Endomysium
• Loose connective tissue that surrounds each
muscle fiber
• Reticular fibers
• Contains the smallest capillaries and neuronal
branches
2) Perimysium
• Connective tissue + fat + blood vessels and nerves
• Group fibers into fascicles
3) Epimysium
• Dense connective tissue that surrounds muscle groups. Large vessels and
nerves penetrate this to reach muscle fibers
II. Myofilaments & Striations
A. Types:
1) Thick: myosin
2) Thin: actin
B. Sarcomere = Basic Contractile Unit
C. Striations: Diagramed in sarcomere. Seen in entire muscle b/c myofibrils and
myofibrils are in register.
• H-band = myosin not overlapping actin
• A-band = all myosin (both overlapping and non-)
• I-band = actin not overlapping myosin
• Z disc = disc in center of I band from which actin extends
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Histology SSN
October 22, 2003
III. Function Tidbits
A. Musculotendinous junction = to dense regularly-arranged connective tissue
(tendon) i.e. collagen type I.
B. Triad = functions to deliver intracellular Ca++ to initiate contraction.
(2 triads/sarcomere)
1. (1) Transverse (T) Tubule = in-pocketing of plasma membrane
2. (2) cisternae of the Sarcoplasmic reticulum
C. Motor unit = neuron + muscle cells it innervates.
CARDIAC MUSCLE
I. Organization
• Fiber = one, mononuclear cell
• Central nucleus (can be seen in cross section too)
• Columns of cells are branched
II. Intercalated discs
A. Gap junctions
• Lateral portion
• Important for ionic continuity, to
coordinate contraction
B. Fasciae adherens
• Transverse portion
• Holds cells together at their ends
C. Desmosomes
• Lateral and transverse portions
• Keeps cells together
** Tight Junction = Zona occludans is not found in cardiac muscle
III. Functional
A. intrinsic rhythm - does not need ACh or norepinephrine for contraction
SMOOTH MUSCLE
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Histology SSN
October 22, 2003
I. Characteristics
• Surrounds the walls of ducts, blood vessels, GI tract, etc.
• Function to give an imprecise squeeze (staggered sheets of cells)
• Nuclei
• cigar-shaped
• lie in the middle of the fiber
• appear wrinkled or “puckered”
• Plane of section determines visibility of nuclei, cell width
• No striations because of diffuse contractile elements
• Gap junctions allow for united contractions
• Basal Lamina (Collagen IV) and Reticular Fibers (Collagen III) surround
individual fibers
II. Smooth muscle vs. Dense irregularly-arranged connective tissue
A. Color
• Smooth muscle is more purple because of combination of actin/myosin and
RNA (red + blue = purple)
• Connection tissue is more red because of purity of collagen
B. Nuclei
• Smooth muscle nuclei are inside cell
• Fibroblast nuclei are in between collagen fibers
C. Homogeneity
• Smooth muscle is composed only of muscle
• Connective tissue contains fibroblasts, macrophages, lymphocytes, etc., and
will therefore have a ragged appearance
Skeletal Muscle
Cardiac Muscle
Smooth Muscle
Striated
Yes
Yes
No
T Tubule Location
A-I junction
Z disk
Sarcoplasmic Reticulum:
2 cisternae in Triad
w/ T tubule
No
Anastamosing
network
Yes
Yes
Yes (limited)
No
Yes
thin filaments
thin filaments
thick filaments
Electrically coupled via
Gap Junctions?
Can regenerate?
level of Calcium
regulation
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Histology SSN
October 22, 2003
MUSCLE QUESTIONS
1)
Which of the following statements is FALSE?
a. The band marked “A” does not include actin filaments.
b. The M line is found in the band marked “A”.
c. During contraction, the length of the band marked “A” remains the same.
d. During contraction, the length of the band marked “B” is shortened.
2)
Which of these statements is FALSE about the muscle type at the pointer?
a. The cells in this muscle type are electrically coupled.
b. This muscle type utilizes a T-tubule system for calcium delivery.
c. This muscle type is not capable of regeneration.
d. Calcium regulation occurs at the level of thick filaments.
3)
Which figure(s) demonstrates smooth muscle?
a. Figure A&C
b. Figure A&D
c. Figure B&C
d. Figure B&D
4)
The structure at the pointer is composed of all of the following except:
a. desmosomes
b. tight junctions
c. gap junctions
d. fascia adherens
5)
This tissue contains…
a. actin, myosin, troponin
b. myosin, troponin, gap junctions
c. desmin, intercalated discs, calmodulin
d. actin, myosin, calmodulin
6)
The structure at the pointer is a:
a. site of calcium-binding protein (calsequestrin) and a Ca2+-activated-ATPase.
b. site of glycogen storage and degradation to glucose
c. site from while Ca2+ is passively transported during muscle relaxation
d. site into which calcium is released during muscle relaxation
e. form of rough endoplasmic reticulum
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Histology SSN
October 22, 2003
MUSCLE ANSWERS
1)
a. This is skeletal muscle. A marks the A band and B marks the I band. The A
band consists of myosin and some actin that overlaps the myosin. Thick
filaments of myosin anchor at the M line, which is found in the middle of the
H zone. The figure below demonstrates how the length of the A band stays the
same during contraction, while the I band gets shorter.
2)
d. This is cardiac muscle. The cells are electronically coupled via gap junctions,
thus allowing contractile signals to pass from cell to cell and allowing cardiac
muscle to behave as a syncytium. T tubules are used for calcium delivery in
both skeletal and cardiac muscle. Smooth muscle cells have no T tubule
system. Cardiac muscle is not capable of regeneration (mature cardiac muscle
cells do not divide). If injury to cardiac muscle tissue leads to death of cells,
fibrous connective tissue forms (scarring) with consequent loss of cardiac
function. Since tropomyosin and troponin wind around the actin filaments,
calcium regulation does not occur at the level of the thick filament.
3)
b. A is smooth muscle and B is skeletal muscle (from the esophagus). C is an EM
of skeletal muscle and D is an EM of smooth muscle. Skeletal muscle has
striations whereas smooth muscle does not. The EM in Figure C shows a
higher magnification of the H band, A band, I band, and Z line in a striated
muscle fiber. Figure C also shows a triad of T tubules and flanking terminal
cisternae, which is only found in skeletal muscle. Whereas skeletal muscle has
multiple, peripherally-located nuclei, smooth muscle has a single, centrally
located nucleus, as seen in Figure D.
4)
b. Pointer is at an intercalated disc. An intercalated disc does not have tight
junctions. The desmosomes are on both the transverse and lateral components
of the intercalated disc, while the fasciae adherens are on the transverse. Note
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Histology SSN
October 22, 2003
from Dr. Rothman: Gap junctions can also be a component of the transverse
portion of the disc but they are not as prevalent as on the lateral.
5)
d. This is smooth muscle. As in striated muscle, contraction is initiated by a rise
in calcium in the cytosol, but this does not act through a troponin-tropomyosin
complex on the actin filament. A rise in calcium stimulates a myosin lightchain kinase to phosphorylate one of the two light chains of myosin. When
this chain is phosphorylated, the myosin head can react with actin and
produce contraction. Intercalated discs are specific to cardiac muscle.
6)
a. This is an EM of skeletal muscle. The pointer is at the sarcoplasmic reticulum.
The sarcoplasmic reticulum (SR) provides a mechanism for the muscle cell to
regulate the concentration of cytosolic calcium. It is a modified smooth
endoplasmic reticulum that serves alternatively as a storage site and a source
of cellular calcium. Calcium is actively transported from the cytosol to the SR
through the activity of a Ca2+-dependent ATPase. Calsequestrin is a calciumbinding protein found in the SR that, as it’s name implies, functions in the
sequestion of calcium. Calcium is released from the SR during muscle
contraction and stored during relaxation. Glycogen is stored as particles or
droplets in the cytoplasm, which contains the enzymes required for the
synthesis and breakdown of glycogen.
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Histology SSN
October 22, 2003
NERVE
Shira Abeles, sra2013@columbia.edu
Katie Butler, kc361@columbia.edu
The Basics (fill in with presentation)
Nervous System Classifications (specific to this Histo lab)
Nervous System
CNS
Spinal Cord
Cerebellum
PNS
Cerebral Cx
ANS
(Ganglia)
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Somatic
Enteric
(Peripheral Nerve)
Histology SSN
October 22, 2003
Functions & Histological Features
CNS
Spinal Cord Cerebellum
Distinguishing *Butterfly
= gray matter
Feature
-- dorsal horn –
narrow, sensory
-- ventral horn –
wider, motor
*Purkinje
Cells
*Pyramidal
Cells
-
-- specialized
motor cortex;
polygonal in
shape, scattered
- large, round
cells; prominent
nucleoli;
wreathed in
satellite cells
Higher
processing
Sympathetic
& Parasympathetic
-
Functions
(general – you’ll
learn MUCH
more about this
when you study
Neuroanatomy)
White Matter
(axons)
eosinophilic
pear-flask
shaped;
UNIQUE
dendrites
mlcr layer
f(n):
outflow of
cerebellum
Transmits
signals to &
from brain;
site of reflex
control
Motor
coordination
*exterior,
axons
traveling to
& from brain
- axons cut in
*most interior
layer – looks
diffuse, w/in
granular layer
cross section in
spinal cord
preparation
Gray Matter
(cell bodies)
Cerebral Cx
*butterfly
- processes
from cell bodies
usually exit
gray matter in
plane of section
PNS
ANS
Ganglion
*Site of cell
bodies
Peripheral
Nerve
*Nerve
bundles
-- look for
axons in crosssection (round,
clear/ white
bodies
(myelin) with
central “dot”)
Somatic
motor &
sensory
(innervates
smooth muscle
& glands;
organ function)
*interior
N/A
N/A
*exterior
N/A
N/A
(don’t confuse
w/ outer,
molecular layer
of gray matter
(see below))
*molecular +
granular
layers
-
-
-
molecular
layer =
outermost,
pale
staining,
mostly
axons &
dendrites
granular
layer =
cellular,
basophilic
Purkinje
cells
separate the
two
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Histology SSN
October 22, 2003
Extraneuronal Cells
Function
Support
Myelin Production
Cells in CNS
Astroglia
Cells in PNS
Satellite Cells
- “star-shaped”
- structural support
extend processes to wrap
around capillaries form
BBB
-
Oligodendrocytes
Schwann Cells
- form myelin sheath that
-
cuboidal cells, surround cell
bodies IN AUTONOMIC
GANGLIA
Do Not Make Myelin
insulates axons
Connective Tissue
None – NO Collagen
Fibroblasts
Neuronal Supporting Structures
Function
CNS
PNS
Meninges:
For Peripheral Nerve
Supporting/Surrounding
Bundles Only:
Tissues:
Innermost Pia Mater – thin, direct contact Endoneurium – Vascular,
Middle
Outermost
with brain & SC
Arachnoid –“spider-web”;
sends delicate trabeculae to pia
(subarachnoid space is filled w/
CSF)
Dura Mater – “hard”; durable
outer covering
arround individual nerve fibers
Perineurium – Arrangers
axons into ‘fascicles’
Epineurium – binds ‘fascicles’
into ‘bundles’
Figure: Schematic of connective tissue layers in peripheral nerve
bundle.
Epineurium
binds fascicles
bundles
Fascicle
Perineurium
binds nerves
fascicles
Endoneurium
wraps individual
neurons
Peripheral Nerve Bundle
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Histology SSN
October 22, 2003
High-Yield Tips:
•
-
Peripheral Nerve vs. Smooth Muscle:
nerve tissue more compact and less eosinophilic
***nerve tissue wavy & bubbly – arises from myelin leaking out upon staining
•
-
Dendrites vs. Axons:
with Nissl staining, if see process that stains dark blue, dendrite, not axon. . . axons
contain no synthetic machinery and therefore do not stain w/ Nissl
•
-
Molecular Layer of Cerebellum vs. White Matter of Cerebellum (cerebellar
medulla)
Look for Purkinje cells. Purkinje cells are very distinct, and they demarcate the
border b/t molecular & granular layers of the cerebellum. The white matter of the
cerebellum resides underneath the basophilic granular layer.
•
-
Mnemonic: “Satellites are on the periphery of space.”
In other words, satellite cells are found in the peripheral nervous system.
•
Mnemonic: “Pyramidal cells are in the Cerebral Cortex.”
•
-
Mnemonic: “Schwann sounds like one”
One Schwann cell myelinates one PNS axon.
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Histology SSN
October 22, 2003
NERVE QUESTIONS
Questions 1-2 pertain to the structures at the pointers in Figures A and B.
1. Which of the following statements is correct regarding the cells at the pointers in Figures A
and B?
a. The cells are situated in white matter.
b. The cells are situated in a ganglion.
c. The cells are situated in the gray matter.
d. The cells are situated between the white and gray matter.
2. In Figure B the processes at the arrow are:
a. myelinated fibers.
b. axons.
c. collagen fibers.
d. dendrites
Question 3:
3. Which figure(s) demonstrates smooth muscle?
a. Figure A
b. Figure B
c. both Figures A and B
d. neither
Question 4:
4. The region at the pointer is required for: (choose all that apply)
a. protein synthesis.
b salutatory conduction.
c. insulation.
d. production of endoneurium.
Question 5:
5. All of the following characterize the organ depicted by the slide except:
a. Microglia
b. Myelinated axons
c. Fibroblasts
d. Oligodendrocytes
Question 6:
6. Which of the following is TRUE of the cell at the pointer?:
a. maintains stable microenvironment
b. resides in spinal cord.
c. is producing myelin.
d. transmits signals from molecular to granular layers.
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Histology SSN
October 22, 2003
NERVE ANSWERS
1. C. Cerebellum, Pointer A on Purkinje cell, Pointer B on Purkinje cell dendrite. This is
a Purkinje cell in the cerebellum, found at the junction between the molecular and
granular layers. The cell body lies in the granular layer. Its dendrites branch out in the
molecular layer.
2. D. The arrow points to the dendrites of the Purkinje cell in the molecular layer.
3. B. Figure A, peripheral nerve; Figure B, smooth musc. Peripheral nerve and smooth
muscle are hard to tell apart. Here are some distinctions:
-nerve tissue tends to be more compact, less eosinophilic, wavy and bubbly
because there are regions where myelin has leaked out.
-smooth muscle is more diffuse, more intense eosinophilic color.
4. B & C. Peripheral nerve, pointer on myelin sheath. The myelin sheath is layers of
lipid wrapping around the axon. It is required for saltatory conduction. It is also used for
insulation.
5. C. Figure depicts cerebral cortex. There are different support cells in the CNS and
PNS. This is a section from the CNS. There are fibroblasts in the PNS but not the CNS.
6. A. This is a satellite cell, found in autonomic ganglia. These PNS support cells do
not make myelin, while Schwann cells do. (Slide #83)
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Histology SSN
October 22, 2003
SKIN
Katie: Km2101
Jamie: Jmp2035
Functions: Resists Abrasion, Immunological Defense, Prevents Fluid Loss, Prevents
Fluid Absorption From Environment, and UV Protection.
Refer to Chapter 14 in Ross
EPIDERMIS
stratum corneum • fully keratinized (dead) epithelial cells, no nuclei, low H2O content
• sealed extracellular space
a) prevents evaporation
b) barrier against pathogens
• sqames, most superficial cells, sloughed off
stratum lucidum • only in thick skin; advanced keratinization
stratum
• keratinocytes here contain basophilic granules of keratohyalin
granulosum
a) leaks into extracellular space and acts to seal cell
b) this aids in waterproofing and protection of skin
• lamellar bodies with glycolipids are secreted (same function as
keratohyalin)
stratum
• cells attached to each other via desmosomes which gives spiny
spinosum
appearance to keratinocytes under LM
• spaces in between cells allow fluid from vessels in the dermis to
nourish the cells (epidermis is avascular!)
• Langerhans cells (involved in the immune system) found here
• in upper part synthesis of keratohyalin granules and lamellar
bodies begins
stratum
• contains stem cells from which new keratinocytes arise by mitosis
germinativum
a) these cells are relatively small, cuboidal to low columnar
(basalis)
b) look for mitotic cells with basophilic appearance
• melanocytes are dendritic cells that synthesize melanin
a) melanin protects from UV radiation
b) can be distributed to surrounding keratinocytes
DERMIS
papillary layer
(loose CT)
• blood vessels, nerves, lymphatics found here
• dermal papillae project into the epidermis
• Meissner’s corpuscles (in dermal papillae); mostly in fingertips
a) encapsulated; two point discrimination
• bulb of the hair follicle (see page 385 in Ross)
a) matrix of hair follicle is equivalent to the basal layer of
epidermis
b) melanocytes contribute melanin granules
c) sebaceous glands (always associated with hair follicle)
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Histology SSN
October 22, 2003
i.
ii.
secrete sebum between shaft and follicle
holocrine secretion—cell is stuffed with product
and necroses
d) arrector pili (smooth muscle bundle)
i.
hair pulled to vertical position
ii.
goosebumps due to skin depression
Reticular layer
(dense CT)
• eccrine sweat glands (coiled tubular glands—not associated with
hair follicles)
a) secretion contains salts and IgA
b) secretory portion in subcutaneous tissue
i.
secretory tubules: acidophilic layer of
myoepithelium contracts to expel secretion
ii.
myoepithelium – sympathetic innervation
c) ducts extend to epidermis
i.
excretory ducts: TWO layers of cuboidal cells
ii.
remove salt – final sweat hypotonic
iii.
corkscrew path in epidermis
• Pacinian corpuscle (found in deeper dermis and hypodermis)
i.
encapsulated
ii.
senses vibration, deep pressure
HYPODERMIS
subcutaneous
tissue
• loose CT, many glands, ducts, blood vessels, lymphatics
• abundant adipose tissue
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Histology SSN
October 22, 2003
SKIN QUESTIONS
1. In the stratum basalis, ________ are found. They attach keratinocytes to _________.
a.
b.
c.
d.
Hemidesmosomes, basal lamina
Desmosomes, basal lamina
Hemidesmosomes, other keratinocytes
Desmosomes, Langerhans cells
2. What is the function of the structure at the pointer?
a.
b.
c.
d.
senses light touch.
pain and temperature sensation.
deep pressure and vibration sensation.
increases rate of neuronal transmission.
3. The structure is a(n) ________; it is located in the _________ layer, and its ducts
terminate in the ________.
a.
b.
c.
d.
sebaceous gland, hypodermal, stratum granulosum.
eccrine sweat gland, dermal, stratum granulosum.
eccrine sweat gland, dermal, stratum corneum.
sebaceous gland, hypodermal, stratum corneum.
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Histology SSN
October 22, 2003
SKIN ANSWERS
1. Lab 8, slide 2
a) Choice A is correct
b) Choice B is not correct because desmosomes attach keratinocytes to other
keratinocytes.
c) Choice C is not correct because hemidesmosomes attach keratinocytes to
the basal lamina.
d) Choice D is not correct because Langerhans cells are involved in the
immune response and does not form desmosomes with neighboring
keratinocytes.
2. Lab 8, slide 17 (pointer on Pacinian Corpuscle)
a) senses light touch – NO. This better describes a Meissner’s corpuscle,
which senses 2 point discrimination.
b) pain and temp. sensation – NO. This describes free nerve endings in the
epidermis.
c) deep pressure and vibration sensation – YES.
d) increases rate of neuronal transmission – partly true. At best, this answer
is only partly correct, as the STRUCTURE is the corpuscle. A myelin
sheath (composed of Schwann cells) surrounds the nerve axon entering the
corpuscle and does ensure an increased rate of transmission relative to
transmission in unmyelinated nerves – but the myelin sheath only extends
for one or two nodes. The inner core of the corpuscle is composed of
lamellae of attenuated Schwann cells, while the outer core of the corpuscle
is composed of lamellae of extra-corpuscular endoneurial cells. Lymphlike fluid and collagen sit between the lamellae; displacement of lamellae
causes an action potential – so the Schwann cells are also involved in
whether the transmission will happen at all (their role is not limited to
ensuring speed).
3. Lab 8, slide 14
a) Choice A is not correct because sebaceous glands are only associated with
hair follicles.
b) Choice B is not correct because if this were true, sweat would have to
percolate to the outer surface of the epidermis.
c) Choice C is correct.
d) Choice D is not correct because, again, sebaceous glands are only
associated with hair follicles.
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