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Glossary of Histology Test 1

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Created by brooke2008

can develop from endoderm, mesoderm, or ectoderm
Epithelia
1. Epithelial Membranes (Epithelia)
2. Epithelial Glands
2 Major Divisions of Epithelial Tissue
continuous sheets of cells that cover outer surfaces or line internal surfaces; attach to connective tissue by basement membrane; cells are joined as cell junctions; do not contain blood vessels
Epithelial Membranes

Epithelial Glands
Develop when epithelia invaginate into underlying connective tissue
How do nutrients and oxygen reach epithelial membranes?
By diffusing from blood vessels in connective tissue beneath the basement membrane
Functions of epithelia
1. Protection (skin)
2. Absorption (intestinal lining)
3. Secretion(stomach lining)

Types of epithelia
1. simple (1)
2. Stratified (2 or +)
3. Pseudostratified (1; appears stratified b/c cells are different heights; all cells are in contact with basement membrane)

Simple Epithelia
1. squamous (single, flattened)
2. Simple cuboidal (single, cube-shaped)
3. Simple columnar (tall, column-shaped)

mesothelium of body cavities, endothelium of blood vessels

Example of simple squamous
collecting tubules of kidney

Example of simple cuboidal
Often contains absorptive cells interspersed with secretory cells; small intestine, stomach lining
Example of simple columnar

goblet cells secrete mucus; absorptive cells have microvilli on luminal surface which facilitate nutrient absorption; microvilli give rise to striated border (light microscopy)
Simple columnar in small intestine
columnar cells may be ciliated with goblet cells interspersed between

Some parts of the lower respiratory tract
all columnar cells are mucus-secreting
Stomach lining
Simple Epithelia functions
absorption and secretion
Stratified epithelia function
protection
Stratified Epithelia
1. Stratified Squamous (multiple, outermost-squamous)
2. Stratified cuboidal (2 or 3, cuboidal)
3. Stratified columnar (several;, outermost-columnar)
4. Transitional (multiple, outermost-large rounded cells:often polyploid of binucleate)


Examples of Stratified Squamous
1. nonkeratinized (lining of vagina)
2. keratinized (skin epidermis)
Rare; Large ducts

Example of stratified columnar
lining of urinary bladder
Example of transitional
lining of large ducts
Example of stratified cuboidal
taller-either ciliated or goblet; shorter-basal, serve as stem cells for others
Pseudostratified ciliated columnar

lines most of upper respiratory tract
Example of pseudostratified ciliated columnar
ductus epididymis; lack true cilia; have nonmotile stereocilia; lacks goblet cells
Example of pseudostratified columnar

Types of Cell Junctions
1. tight junctions (only in epithelia)
2. adhering junctions
3. gap junctions

zonula occludens (tight junction)
forms a belt around cell perimeter near apical luminal) surface
forms a complete, tight seal; prevents passage of material across the epithelium (e.g. macromolecules are prevented from passing from intestinal lumen into intercellular space)
zonula occludens
tight junction that is restricted to specific area of cell perimeter forming an incomplete seal
fascia occludens
Example of fascia occludens
endothelium of blood vessels
Zonula adherens (adhering junctions)
belt-like junction around perimeter of cell; located just below zonula occludens on lateral aspect of contiguous cells; intercellular gap-filled with filamentous material
site of attachment for circumferential band of microfilaments located just deep to the membrane
zonula adherens
cells are joined as cell junctions; do not contain blood vessels
Epithelia
desmosome
macula adherens
small, circularjunction just below zonula adherens; series of button-like junctions, uneven row
macula adherens
seen on either side of opposed membranes
electron-dense plaques
serve as attachment sites for bundles of tonofilaments (intermediate filament)
plaques
between two plaques
fine electron-dense line; transmembrane linkers that extend across intercellular gap
seen between epithelial cells and basement membrane
hemidesmosomes (half-desmosomes)
Junctional complex (electron microscope)
zonula occludens, zonula adherens, and macula adherens
junctional complex (light microscope)
terminal bar
communications junctions; small circular regions of opposed cell membranes bridged by connexons
Gap Junctions (Nexuses)
Functions of gap junctions
permit direct cell-to-cell transfer of low molecular wt. nutrients and intracellular messengers (cAMP) and maintain electrical coupling b/w cells
tiny tubular channels that allow passage of ions and various small molecules from cell-to-cell; represent transmembrane proteins that interlock across the narrow gap
Connexons
beneath striated border of intestinal epithelial cells; horizontal network of microfilaments, intermediate filaments, spectrin, and some myosin
Terminal web
2 Types of Epithelial Glands
1. exocrine
2. endocrine
Components of exocrine glands
1. groups of specialized cells-secretory units; produce characteristic secretions
2. tubular ducts- convey secretions onto an epithelially-covered surface
Exocrine Gland classification
1. simple-single, unbranched duct
2. compound-branched duct system
example of simple gland
sweat gland
example of compound gland
pancreas
Secretory gland shapes
1. tubular gland- (tube-shaped)
2. alveolar (acinar) gland- rounded
3. tubuloalveolar gland- both types

secretes enzymes in a watery fluid
serous gland
secrets a viscous glycoprotein called mucus
mucous gland
both types of secretions are produced
mixed (seromucous gland)
example of serous gland
parotid gland
example of mucous gland
sublingal gland
example of mixed (seromucous) gland
submandibular gland
(H&E)
base contains large,spherical nucleus; cytoplasm-intensely basophilic due to RER abundance; apical-numerous eosinophilic granules filled with secretory enzymes
serous cell
(H&E)
base-flattened nucleus;cytoplasm-pale and vasculated due to abundance of secretory granules containing mucin
mucous cells
mucin
visualized by PAS-stain; becomes hydrated when released from cell to form mucus
mostly mucous cells with a small "cap" of of serous cells-serous demilume
mixed secretory units
processes that surround each secretory unit and cradles them; contraction expels secretions into the duct system
myoepithelial cell
secretion occurs via exocytosis; most common method
merocrine gland
example of merocrine gland
pancreas
entire cell and its contents form secretory product
holocrine gland
example of holocrine gland
sebaceous gland- cells in basal portion are displacedinto interior region as new cells arise in lining layer, displaced cells degenerate and accumulate lipid, disintegrated emerge as oily sebum
apical portion of cell membrane and associated cytoplasm are expelled as secretory product (possibly incorrect; now known to secrete via merocrine)
apocrine gland
example of apocrine gland
mammary gland
2 major components of exocrine glands
1. parenchyma- epithelial; secretory units and ducts
2. stroma-connective; gland, blood vessels, and nerves
connective tissue that encloses exocrine gland
capsule
consists of fibrous connective tissue, continuous with the capsule, subdivides the parenchyma into lobes (large) or lobules (small)
Septa
Intralobular ducts
lie within the parenchyma of the lobules; empty into interlobular ducts
Pathway for exocrine secretion
alveolus-> intercalated duct-> intralobular duct ->interlobular duct -> main duct
Exocrine secretion control
regulated by nerve impulses from ANS (both) and certain hormones
no ducts; secrete hormones directly into bloodstream that produces effects in distant tissue; surrounded by connective tissue capsule
endocrine glands
regulation of endocrine secretion
negative feedback
Loose Connective tissue
areolar tissue; binds and nourishes other tissues
made of intercelluar matrix (various fibers and ground substance) and cells
Loose Connective Tissue
3 types of fibers in intercellular matrix
collagen, reticular, and elastic
Type I collegen
collagen fibers
exhibit axial periodicity
collagen and reticular fibers
synthesized by fibroblasts in loose connetive tissue
type I collagen and type III collegen
1st step of collagen synthesis
formation of alpha-chains in RER
Alpha chains contain a high % of?
glycine, proline, hydroxyproline, and hydroxylysine
What determines collagen type?
amino acid sequence
3 alpha chains form?
1 procollagen molecule
Procollagen
passes through Golgi and transports to cell membrane thru secretory vesicles before discharging
How are collagen molecules yielded?
procollagen peptidase cleaves off short peptide sequences from both ends and yields collagen(tropocollagen) which spontaneously assemble into collagen fibrils
branching pattern; form a supporting network in myeloid and lymphoid tissues
reticular fibers
Type III collagen fibers
reticular fibers
produced by reticular cells in myeloid and lymphoid tissues
reticular fibers
PAS-positive; fibers are visible with silver stain
Reticular cells
Exhibit no axial periodicity
Elastic fibers
can be distinguished from other fibers when strained with orcein
elastic fibers
produced by fibroblasts in connective tissue
elastic fibers
precusor protein in elastic fibers? contains which amino acids?
elastin; desmocine and isodesmocine
a glycoprotein secreted by fibroblasts
fibrillin (in the form of fine microfibrils)
ground substance?
macromolecular (principally glycosaminoglycans-repeating disaccharides) meshwork with a large V of tissue fluid
What synthesizes glycosaminoglycans in loose connective tissue?
fibroblasts
proteoglycan
when sulfated glycosaminoglycans become covalently attahced as side chains to axial core proteins
principal unsulfated glycosaminoglycan in ground substance
hyaluronic acid
proteoglycans can be stained with?
basophilia and metachromasia
How do glycoproteins differ from proteoglycans?
1. carbohydrate moiety is not made of repeating dissacharides
2. protein component predominates
when blood passes through a capillary
hydrostatic pressure is greater at arterial end than venous end
contains dissolved gases and nutrients
interstitial fluid
has a lower osmotic pressure than blood; contains small amount of colloidal protein
tissue fluid
where tissue fluid is produced
arterial end of the capillary
where tissue fluid is resorbed
vemous end of capillary
lymph
fluid that collects in lymphatic capillaries
edema (swelling)
imbalance between production and removal of tissue fluid leading to an accumulation of fluid within affected tissues
Causes of edema
venous obstruction, lymphatic obstruction, increased capillary permeability, and decreased vascular protein
e.g. congestive heart failure
venous obstruction-impaired venous return->back pressure in capillaries->increases hydrostatic pressure and plamsa leakage
e.g. post-surgical trauma
backage of lymphatic capillaries->decrease in removal of excess tissue fluid
e.g. allergic inflammation
formation of gaps b/w endothelial cells in capillary wall->increase plasma leakage
e.g. liver failure
decreased vascular protein- reduction of colloiday protein->lower osmotic pressure->tissue fluid return reduction
middle part of basement membrane
lamina densa
what lamina densa consists of
laminin-5, type IV collagen (lacks axial periodicity), and proteoglycans
product of the cells to which the basement membrane attaches
lamina densa
top part of basement membrane
lamina lucida
integrins
chords that extend from lamina densa to cell membrane; composed of extracellular portions of cell adhesion molecules
lower level, next to basment membrane
lamina fibroreticularis
layer of basement membrane that contains reticular fibers(type III) and type IV collagen fibers
lamina fibroreticularis
proteins in basement membrane that anchor cells to basement membrane
laminin and fibronectin
Where are basement membranes found?
loose connective tisuue, muscle fibers, peripheral nerve fibers, endothelial mast cells, and fat cells
window-like openings in edothelial cells covered by a thin diaphragm
fenestrae
fenestrated capillaries
extra-permeable vessels
continuos capillaries
lack fenestrations
external to endothelium of capillaries and venules; insinuated in basement membrane
pericytes
pericytes
represent pluripotent cells that can produce new fibroblasts, smooth muscle cells, and endothelial cells
retain some of the potentiality associated with undifferentiated mesenchymal cells in embryo
pericytes
responsible for formation of scar tissue in fibrosis
fibroblasts
mature fibroblast
fibrocyte
a result of mature fibroblasts rarely dividing is?
new fibroblasts derive from pericytes
large phagocytic cells that form part of the mononuclear phagocyte system
macrophages
macrophages in loose connective tissue
histiocyte
multinucleated cells
foreign body giant cells
produced by plasma cells and can combine with antigens
antibodies
derived from certain lymphocytes and do not divide
plasma cells
large rounded cells that contain numerous granules that contain histamine and heparin
mast cells
rich capillary supply and abundance of mitochondria
brown fat
primary function is to metabolize triglycerides and generate body heat
primary function of body fat
most adipose tissue (10-20% in males and 15-25% in females)
white fat
synthesis, storage, and mobilization of triglycerides and provides thermal insulation
primary function of white fat
2 kinds of adipose tissue
white fat and brown fat
What provides an efficient store of fuel for cellular metabolism?
high colorie content of triglycerides
collagen fibers are oriented in the same direction
dense regular connective

e.g. of dense connective tissue
ligaments, tendons, and aponeuroses
collagen fibers are oriented in different directions
dense irregular connective
e.g. of dense irregular connective tissue
dermis of the skin and capsule of numerous organs
cells found in loose connective tissue
lymphocytes and eosiniphils
cartilaginous rings in the trachea and costal cartilage connecting ribs to the sternum
extraskeletal cartilage
found in articulating joints, where it provides a smooth, gliding surface at ends of articulating bones
articular cartilage
contains a few collagen fibers
hyaline cartilage
contains many collgen fibers
fibrocartilage
contains many elastic fibers
elastic cartilage
examples of hyaline cartilage
tracheal rings, costal cartilage, articulating surfaces in joints
cartilage consists of intercellular matrix, in which numerous chondrocytes are embedded; pearly-white
hyaline cartilage
perichondrium
fibrous connective tissue that surrounds sites in the body where cartilage will form
cells of the outer layer of the perichondrium
fibroblasts that produce collagen fibers (fibrous layer)
cells of the inner layer of the perichondrium
chondroblasts that produce cartilage matrix (chondrogenic layer)
after chondroblasts become surrounded by matrix they become?
chondrocytes
spaces in which chondrocytes live
lacunae
lacuna with a single chondrocyte
primary lacuna
chondrocyte that divides and produces daughter cell that resides in same lacuna
secondary lacunae
cell nest
formed by parent and daughter chondrocytes
cartilage growth from the inside out
interstitial growth
formation of cartilage by chondroblasts at the surface
appositional growth
perichondrium is absent in adults in?
articular surfaces
cartilage matrix
amorphous gel that contains large amounts of proteoglycans and type II collagen fibrils
produced by chondrocytes?
collagen and proteoglycans
What can bind a substantial amount of water in the matrix due to the particular macromolecular arrangement of the matrix?
proteoglycans
Monomers of ? attach to hyaluronic acid through?
proteoglycans; link proteins
proteoglycan aggregate
intermingles with collagen fibrils
2 reasons why proteoglycans can bind considerable amounts of water
1. many interstices b/w sulfated glycosaminoglycan side chains
2. there are many negative charges to hydrogen bond water molecules
cartilage matrix that immediately surrounds the lacunae; has a high concentration of sulfated glycosaminoglycans
territorial or capsular matrix
interterritorial matrix
stains less intensely than territorial matrix
capsular region
metachromatic and PAS-positive
How do chondrocytes within the matrix receive nutrients?
diffusion that is possible b/c of large volume of water trapped within matrix
examples of fibrocartilage
intervertebral discs and tendon insertions into cartilage
chondrocytes are arranged in longitudinal rows between bundles of type I collagen fibers
fibrocartilage
between chondrocytes, matrix is similar to capsular matrix of hyaline cartilage
fibrocartilage
perichondrium is absent in adult
fibrocartilage
examples of elastic cartilage
external ear and epiglottis
designed to withstand repeated bending
elastic cartilage
matix contains numerous elastic fibers and type II collagen fibrils
elastic cartilage
living cells embedded in an intercellular matrix in bone; occupy lacunae
osteocytes
contains more collagen than cartilage and is heavily mineralized with calcium salts
intercellular matrix of bone
Both bone and cartilage contain a fibrous connective tissue covering; in bone it is?
periosteum
highly vascularized
bone
canaliculi
fine channels that are part of the vasular nature of bone; radiate outward from lacunae
extend into regions where oxygen and nutrients are in greater supply
osteocyte processes
Why are osteocytes unable to divide?
because the intercellular matrix becomes mineralized soon after it is produced
How do all bones grow?
By apposition-depostion of bone on preexisting surfaces
intramembranous ossification
occurs directly in vascularized mesenchyme
endochondrial ossification
occurs indirectly by replacing a cartilage model
forms several flat bones of the cranium, as well as the mandible nd the clavicles
intramembranous ossification
mesenchymal cells
exhibit long, interconnected processes in developing embryo
What cells differentiate into osteoblasts and begin laying down intercellular matrix?
mesenchymal cells

when mesenchymal cells are surrounded by matrix they are called?
osteocytes
narrow spaces when filled with cytoplasmic processes of osteocytes
caniculi
after matrix is secreted...?
it begins to calcify
spicule
first piece of newly formed bone that exhibits an irregular shape
trabecula
when osteoblasts deposit more matrix onto the surface of the spicule, it enlarges
spongy (cancellous) bone
latticework structure; continued groth that leads to a network of trabeculae
appositional growth
osteoblasts on the surface of the trabeculae continue to lay down bone matrix
osteoclasts
resorbs bone; have the capacity to erode bone surfaces
osteoblasts
deposit matrix on surface of the spicule
bone remodeling
combination of bone deposition and resorption; eventually converts spongy bone to compact bone
osteogenic cells
have potential to become osteoblasts; line inside channels
osteon (haversian system)
concentric layers of lamellae of bone with cental haversian canal
represents the basic structural unit of compact bone
osteon (haversian system)
immature bone
first type of bone to be produced in prenatal life
have a higher concentration of osteocytes than mature bone
immature bone
woven bone
collagen fibers run in various directions in the matrix
coarsely-bundled bone
collagen fibers are arranged into think, parallel bundles in the matrix
fine-fibered or lamellar bone
mature bone
mature bone
presence of lamellae; orientation of collagen fibers is at right angles to adjacent lamella
Where osteogenic cells located?
periosteum(covers outer surface of bone) and endosteum (lines internal surfaces of bone)
examples of endosteum
cental canals, marrow cavities, and spaces of spongy bone
periosteum
outer fibrous layer and inner osteogenic layer
endosteum
osteogenic layer
when osteogenic cells proliferate they form?
osteoblasts (vascularized regions) or chondroblasts (avascular regions)
nondividing cells
osteoblasts
primary function is to form the organic constituents of bone matrix
osteoblasts
participate in the mineralization of bone matrix
osteoblasts
lower proteoglycan content and holds less water than cartilage matrix
bone matrix
type i collagen content is higher here?
bone matrix
calcification
deposition of insoluble calcium salts in the bone matrix
osteoid
new bone matrix that has not yet been calcified
calcification front
interface between osteoid zone and clacified bone
matrix vesicles
cell derived structures that are thought to initiate matrix calcification; found lying free in matrix; contain alkaline phosphatase
primary mineral component of bone (70% of wet weight)
hydroxyapatite

whenever osteoblasts are surrounded by bone matrix; nondividing
osteocytes
What interconnects neighboring osteocytes?
gap junctions
2 functions of osteocytes
1. maintain bone matrix 2. release calcium from bone matrix
nondividing, motile, multinucleated cells; resorb bone matrix
osteoclasts
derived fom monocytes
osteoclasts
Howship's lacunae or resorption bays
where some osteoclasts lie; recesses of bone surface
ruffled border
branching, finger-like processes that extend from osteoclast membrane onto the bone surface; represents portion of osteoclast activity resorbing bone
where are secretory vesicles containing hydrolytic enzymes released by exocytosis?
ruffled border
secretes organic acids to bring about local decalcification of bone matrix
ruffled border
possible participants in bone resorption
fibroblasts (secrete collagenase and phagocytose collagen fragments) and macrophages
Parathyroid hormone
raises blood calcium
calcitonin
lowers blood calcium
vitamin D metabolite
raises blood calcium
hypercalcemia
too high blood calcium levels
hypocalcemia
too low blood calcium levels
major site of action for PTH, CT, and vitamin D metabolite
osteoclast
stimulate bone resorption by osteoclasts
PTH and vitamin D metabolite
inhibits bone resorption by osteoclasts
CT
How do tubular bones form?
ossification of a temporary cartilage model (endochondrial ossification)
osteoporosis
net bone loss due to imbalance b/w bone formation and bone resorption; results in predisposition to bone fractures
rickets
caused by insufficient vitamin D; poor calcification of bone, which leads to skeletal deformities in infants
osteomalacia
rickets in adults
Why is vitamin D required?
for proper osteoclast activity and proper gut absorption of calcium and phosphate
scurvy
caused by insufficient vitamin C; results in decreased thickness of bone cortex and a corresponding fragility of the bone
Why is vitamin C (ascorbic acid) required?
collagen synthesis
3 factors that adversely affect bone formation
1. interference with organic matrix secretion
2. interference of matrix calcification
3. imbalance b/w bone formation and bone resorption

nutrient artery
(derived from the periosteal bud)
enters medullary cavity thru wall of diaphysis; principal blood supply to a long bone
Where does supplemental blood supplies to bone come from?
periosteal artery, epiphyseal artey, and the metaphyseal artery
metaphyses
flared regions of long bones b/w epiphyses and diaphysis
What is present in Haversian canals?
a small arteriole, and venule, sometimes a single capillary, some nerves, NO LYMPHATICS
Zone of resting cartilage
no proliferation of chondrocytes; appearance is typical of hyaline cartilage
Zone of proliferating cartilge
chondrocytes are proliferating and are seen arranged in longitudinal rows of lacunae
zone of maturing cartilage
chondrocytes hypertrophy and produce large amounts of alkaline phosphatase for matrix vesicles
zone of calcifying cartilage
cartilage matrix becomes calcified and begins to break down; capillaries form medullary cavity below; osteogenic cells->osteoblasts and deposit bone matrix on remnants of calcified cartilage forming bony trabeculae with cores of calcified cartilage; formation of osteons in diaphysis; periosteum forms layers of bone outside of diaphysis; bone is remodeled
What is the adult structure of bone?
outer and inner diaphysis are covered by outer and inner circumferential lamellae which enclose compact bone; compact bone (cortex) consists of osteons and interstitial lamellae; Longitudinally b/w each osteon-> haversian canal; tranverse connections b/w are due to vessels running in Volmann's canals; spongy bone-inner diaphysis, surrounds medullary cavity; epiphysis-interior-spongy bone
secondary ossification centers
after birth; form in apiphyses; only in long bones; bone replaces cartilage on articular surfaces of joints and as a epiphyseal plate b/w epiphyses and diaphyses; in adult, epiphyseal plate->bone
Formation of cartilage model
mesenchymal cells differentiate into chondroblasts that eventually form a model consisting of hyaline cartilage surrounded by perichondrium; model grows by interstitial and appositional growth of cartilage
Formation of primary ossification center
at midsection, Ca salts deposit and impede diffusion; chondrocytes die or are altered; cartilage matrix breaks down; cells of inner layer of perichondrium->osteoblasts and produce bone matrix; perichondrium is now periosteum; subperiosteal vone surrounds midsection; blood vessels and osteogenic cells (periosteal bud) grow to interior of cartilage; osteogenic cells->osteoblasts that deposit bone matrix on calcified cartilage; region in midsection is primary cos
Formation of epiphyses and diaphysis
spongy bone forms when trabeculae contain cores of calcified cartilage; center is resorbed forming medullary cavity
Where is muscle tissue derived from?
mesoderm
3 different kinds of muscle
skeletal, cardiac, and smooth
skeletal muscle
striated and voluntary
cardiac muscle
striated and involuntary
smooth muscle
nonstriated and involuntary
muscle that elicits movement of the skeleton
skeletal muscle
found in the heart
cardiac muscle
found in the walls of the blood vessels and various hollow organs
smooth muscle
3 layers of skeletal muscle
epimysium, perimysium, and endomysium
epimysium
surrounds entire muscle
perimysium
continuous with epimysium; surrounds bundles of muscle fibers
fascicles
bundles of muscle fibers in perimysium
endomysium
continuous with perimysium; surrounds individual muscle fibers; contains capillaries and nerve fibers that supply muscle fibers
all connective tissue merge to form?
e.g. tendons, aponeuroses
muscle fibers
cells of skeletal muscle
sarcolemna
cell membvrane of muscle fibers
sarcoplasm
cytoplasm of skeletal fibers
A-bands
dark bands in muscle fibers
H-zone
pale region in middle of A-band (dark)
I-bands
light staining bands in muscle fibers
Z-line
thin line that bisects I-bands
myofibrils
causes striated pattern; has same banding pattern as muscle fiber
sarcomere
segment of myofibril from Z-line to Z-line; contractile unit of striated muscle
myofilaments
thin(actin) and thick (myosin)
only thin filaments connected at one end to the Z-line
I-band
thick filaments and overlapping thin filaments that extend
A-band
region of A-band where thin filaments do not extend; only thick filaments w/o overlapping thin filaments
H-zone
M-line
middle of H-zone; represents filamentous structures that interconnect the thick filaments
muscle contraction
width of A-band stays constant; H-zone and I-bands decrease in width
3 kinds of muscle fibers
red, white, and intermediate
red fibers (small diameter)
contain an abundant amt of myoglobin and many mitochondria
predominat in muscles that undergo sustained periods of activity
red fibers (dark meat)
white fibers (large diameter)
less myoglobin and less mitochondria
contract rapidly and fatigue rapidly
white fibers (white meat)
intermediate fibers
characteristics of red and white fibers
motor unit
one motor neuron, axonal branches, and muscle fibers they innervate
What is the strength of a muscle contraction dependant on?
how many motor units participate in the contraction
What innervates muscle fiber?
motor (effernt) axon
neuromuscular junction
site on muscle fiber where axon attaches
axon terminals
where axon touches sarcolemna and branches
motor end plate
axon terminals and underlying sarcolemna covered by Schwann cells
synaptic cleft
small depression of sarcolemna where each axon terminal of a motor end plate sits
junctional folds
invaginations of the sarcolemna; contains acetylcholinesterase
junctional folds
invaginations of the sarcolemna; contains acetylcholinesterase
junctional folds
invaginations of the sarcolemna; contains acetylcholinesterase

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