Lab Activity 7

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Bone Histology

Martini Chapter 6

Lab Activity 7

Divisions of skeletal system


Axial skeleton
: in the
vertical axis of the body.
Consists of the skull, hyoid
bone, vertebral column
ribs and sternum.


Appendicular
skeleton
: skeleton
attached to the axial
skeleton

Bone features


Ones have many surface
features that have specific
names.


Grouped by
projections
,
depressions
, or
holes

in
the bone.


Some projections:


Some articulate with other
bones


Are attachment sites


Marking

Description

Example

Head

Bony expansion
carried on a
narrow neck

Femur

Condyle

Rounded
articular
projection

Condyle of
mandible

Facet

Smooth, nearly
flat articular
surface

Facet of ribs

Ramus

Armlike bar of
bone

Ramus of
mandible

Projections for Muscle & Ligament
Attachment

Process

Any bony
prominence

Trochan
ter

Very large, blunt,
irregularly
shaped process

Femur

Tuberosi
ty

Large, rounded
projection; may
be roughened

Tibia , ischia

Tubercle

Small, rounded
projection or
process

Adductor
tubercle of
femur (distal
end)

Crest

Narrow ridge of
bone; usually
prominent

Anterior
crest of tibia

Line

Narrow ridge of
bone, less
prominent than a
crest

Intertrochant
eric line

Spine

Sharp, slender,
often pointed
projection

Spinous
process of
vertebra

Epicond
yle

Raised area on
or above a
condyle

Medial
epicondyle
of femur



Bone

4


Organic and inorganic material


The
organic

portion is composed mostly of cells and
collagenous fibers (1/3 volume by weight)


The
inorganic

portion

consists mainly of hydroxyapatite.


Calcium salts
, which contribute hardness and rigidity.


Make bones as strong as steel or reinforced concrete.


intercellular matrix
of bone tissue is arranged in multiple
layers called
lamellae


Classification of Bones by Shape

5


Long bones
: longer
than they are wide

(e.g., humerus,
metacarpals )


Consists of a shaft
(diaphysis) plus 2
expanded ends
(epiphysis).

Features of Long bones

6


Hyaline cartilage


Covers joint surface of epiphysis


Cushions opposing bone ends


Absorb stress


Features of Long Bones

7


Diaphysis
: shaft forms the long axis of the bone


Wall of compact bone surrounding a
medullary

(marrow) cavity



Epiphyses
: expanded bone ends


Articulates with another bone


Exterior made of a thin layer of
compact bone


Interior made of
spongy bone

8

Bone Marrow

9


Marrow


Netlike mass of connective tissue that fills the spaces
of bone


Medullary cavities of long bones


Irregular spaces of spongy bone

Bone Tissues


Red Marrow

10


Hemopoietic

tissue


Formation of red blood cells, white blood cells, and blood platelets


In infants


Found in the medullary cavity and all areas of spongy bone


In adults


Found in the
diploë

of flat bones, and the head of the femur and
humerus

Bone Tissues


Yellow Marrow

11


As we age, the bone marrow is replaced by fat stores


Red becomes yellow marrow


Inactive in blood cell production


Functions in shock absorption

Structure of Short, Irregular, and Flat
Bones

12



Thin plates of

periosteum
-
covered compact bone
on the outside with
endosteum
-
covered spongy bone on the inside


Have no diaphysis or epiphyses


Contain bone marrow between the
trabeculae

Bone Membranes

13


Periosteum
: Double
-
layered

protective membrane


Outer fibrous layer is

dense irregular connective

tissue


Inner osteogenic layer is composed of osteoblasts and osteoclasts


Richly supplied with nerve fibers, blood, and lymphatic vessels, which
enter the bone via nutrient foramina


Secured to underlying bone by Sharpey’s fibers (strands of collagen)

Bone Membranes

14



Endosteum
: Delicate membrane covering internal surfaces of
bone


Covers the
trabeculae

of spongy bone in the marrow
cavities and lines the canals that pass through
compact bone.


Lines the medullary cavity


Contains both
osteoblasts and osteoclasts.


Classification of Bones by Shape

15


Short bones


Cube
-
shaped bones of
the wrist and ankle



Sesamoid bones


Bones that form within
tendons (e.g., patella)

Classification of Bones by Shape

16


Flat bones
: Thin,
flattened, and a bit
curved (e.g., sternum,
and most skull bones)

Sternum

Classification of Bones by Shape

17


Irregular bones
: bones
with complicated shapes
(e.g., vertebrae and hip
bones)


Sphenoid Bone

Classification of Bones by Shape

18



Wormian

or
sutural

bones:
Tiny bones between cranial
bones.


Vary in number and location
in different people

Bone Tissue:
Compact Bone

19



Bones are composed of both compact and spongy bone tissue


Compact bone

is found where great strength is
needed.


It makes up the external surfaces of all bones and the
shafts of long bones.



Bone Tissues:
Spongy Bone

20



Honeycomb of small needle
-
like pieces called
trabeculae
.


Organized in an open framework


Provides considerable strength with reduced weight


The open spaces between the
trabeculae

are filled with bone marrow




21

Note the gross differences between the spongy bone and the
compact bone in the above photo.

Do you see the trabeculae?

22

Compare compact and spongy bone as

viewed with the light microscope


Microscopic Structure of Compact
Bone


23



Bone tissue is composed of repeating, circular units called
Haversian

systems or
osteons



Osteons are the structural unit of compact bone


The substance of compact bone is formed from many osteons
cemented together



Oriented parallel to the long axis of the bone, and parallel to the
forces upon that bone



Microscopic Structure of Compact
Bone

24

Haversian System (Osteon)
Components

25



Concentric Lamella:

Weight
-
bearing, column
-
like matrix tubes
composed mainly of collagen that surround the central canal like rings
on a tree


Haversian
, or
central canal:

Central channel containing blood vessels
and nerves


Volkmann’s canals:

Channels lying at right angles to the central canal,
connecting blood and nerve supply of the
periosteum

to that of the
Haversian

canal


Interstitial Lamellae

26



Interstitial Lamellae

that are
not

part of an osteon


They are incomplete lamellae


They fill the gaps between forming osteons or are remnants of
osteons that have been cut through by bone remodeling


Circumferential Lamellae

27



Circumferential

lamellae are deep to the
periosteum


Extend around the entire circumference of the shaft

28

Concentric
lamellae


Microscopic Structure of
Compact Bone

29


Spider
-
shaped osteocytes

occupy
small cavities

known

as
lacunae

at the junctions of the lamellae.


Hair like canals called
canaliculi

connect the lacunae to each
other and to the central canal.


Canaliculi

allow the osteocytes to exchange nutrients, wastes,
and chemical signals to each other via gap junctions.

Microscopic Structure of

Spongy Bone

30


No osteons are present


Lamellae are irregularly arranged into plates called
trabeculae
.


Small needle
-
like pieces of bone


Have a lot of open space between them


Filled with bone marrow.


Trabeculae are interconnected by canaliculi


Trabeculae align precisely along lines of stress


Spongy Bone

31


Osteocytes are nourished
by diffusion from nearby
Haversian canals


The osteocytes are
connected by
canaliculi

Bone Cells

32



Bone tissue is a type of connective tissue, so it consist of cells plus a
significant amount of extracellular matrix.


Osteoprogenitor

Cells (
osteogenic

cells)


Undergo mitosis and become osteoblasts



Derived from mesenchyme

Osteoblasts

33


Bone
-
building cells.


Synthesize and secrete collagen fibers and other organic
components of bone matrix.


Releases calcium and phosphate ions for production of hydroxyapetite


Initiate the process of calcification.


Found in both the periosteum and the endosteum


Cannot undergo mitosis

Osteoblasts

34


The
blue arrows

indicate the
osteoblasts.


The yellow arrows
indicate the bone
matrix they’ve just
secreted.



O
steocytes


35


Mature bone cells

derived from
Osteoblasts that have become
trapped

by the secretion of matrix



Respond to stresses and remodel bone in response to those stresses


Maintain daily cellular activities


No longer secrete matrix


Cannot undergo mitosis


Will transform back to an osteoblast when bone
remodeling is needed.

Osteocytes

36


Yellow arrows

indicate
osteocytes: notice how
they are surrounded by
the pinkish bone matrix.


Blue

arrow shows an
osteoblast in the process
of becoming an
osteocyte.


Green
arrow: Osteoclast

Bone Cells

Osteoclasts

37


Huge cells derived from the fusion of as many as 50 monocytes or
macrophages (a type of white blood cell).


Function in bone
resorption

(i.e. destruction of bone matrix that is
part of normal bone growth, development, maintenance and
repair)


Breakdown of bone matrix with both acid phosphatase and HCL

Osteoclasts

38

Introduction to the Nervous System



The functional unit is the
neuron


These are the cells that
carry out the activity of
nervous tissue


Neuroglia

(glial cells) aid
neurons


Nervous System


Central Nervous System
(CNS)


brain and spinal
cord


Peripheral Nervous system
(PNS)
-

cranial and spinal
nerves, and ganglia

Neuron


3 main parts:


Axon


Dendrite


Cell body (
neurosoma
)


Neuroplasm

(cytoplasm)


Nissl

bodies (RER)


Nucleus


Axon hillock

Functions of neurons


Sensory (afferent
):
conduct impulses to CNS.


Convey info from the
external or internal body


Motor (efferent
)
conduct impulses away
from CNS


Interneurons

(association) neurons occur
between sensory and
motor neurons

Neuron Shapes


Classified according to
shape


Multipolar


Bipolar


Unipolar (
pseudounipolar
)

Synapses


Neurons transmit
information
electrochemically along the
length of the axon to the
synaptic knob
.


The junction is called the
synapse

and chemicals
called
neurotransmitters
move
across the synaptic cleft

PNS Neuroglia


Schwann cells
(
neurolemmoctye
) wrap
around the axon, leaving
small gaps between successive
cells called the
nodes of
Ranvier
.


Consist of a lipoprotein called
myelin and a series of
schwann

cells forms the
myelin sheath
.


Allows nerve transmission to
jump from node to node,
increasing speed called
saltatory

conduction

Histology of a Nerve

CNS Neuroglia


Oligodendrocytes

have
the same function in the
CNS as Schwann in PNS


Myelinated

nerve fibers
appear white so are called
white matter


CNS Neuroglia


The most common glial
cells are the
astrocytes
.


Form blood
-
brain barrier


Nourish neurons


Release nerve growth
factors among other things.


CNS Neuroglia


Microglia

are small,
phagocytic glial cells.


They resemble
macrophages as they engulf
microbes or damaged
tissue


CNS Neuroglia


Ependymal cells
line the
ventricles of the brain and
modify the cerebrospinal
fluid

Specialized Neurons


Pyramidal cells are found
in the cerebral cortex of
the brain


Purkinje cells are common
in the cerebellum.

The End


View structures on both models
and slides