Download Nervous Tissue

WHERE AM I?
Online Anatomy Module 1
INTRO & TERMS
CELL
EPITHELIUM
CONNECTIVE TISSUE
MUSCLE
NERVOUS SYSTEM
AXIAL SKELETON
APPENDICULAR SKELETON
MUSCLES
EMBRYOLOGY
101H NERVOUS STRUCTURES & TISSUE
CENTRAL
Brain
PERIPHERAL
Cranial nerves
Ganglia
Peripheral nerves
Cord
Receptors
Autonomic nerves
PNS - Peripheral Nervous System
NERVOUS STRUCTURES & NEURON
The systems are large and very extended to reach to all parts
of the body. The nerve cell/neuron forming the basis is a
greatly extended cell. The principal cell extension is the axon.
Neuron body
Brain
Cranial
nerves
Ganglia
Peripheral
nerves
Cord
Receptors
Autonomic
nerves
Axon
NEURON I
The neuron body or soma itself extends branching processes DENDRITES, to pick up different influences over a wide area
Neuron body
Axon
Dendrites
Axon and dendrites are tubular
extensions of the cell with very
sensitive plasma membranes
Dendrites (& soma) are
sensitive to the influence of
other nerve cells
Axons have a membrane that is
insensitive to such influences,
but transmits an electrical signal
NEURON II
Dendrites
Neuron body
Axon
The electrical signal that develops
on the dendrites & body and
propagates along the axon
membrane is based on the
coordinated actions of very many
ion channels
At the end of the axon branches,
the electrical signal causes the
release of chemicals from the
swelling - the SYNAPSE
The released chemical - the transmitter - acts on the dendritic
membranes of the next neuron in the chain to cause more
electrical activity
NEURON III
Axon
Axon often
branches to reach
several target cells
The myelin sheath is
absent from the fine
terminal branches of
the axon
The electrical signal that
propagates along the axon
membrane can be made to go
much faster by wrapping the
axon in lengths (segments) of a
fatty insulator - MYELIN
The myelin segments comprise a
myelin sheath
NEURON IV
Axon
The decision as to whether the
axon will ‘fire’ and propagate the
signal occurs right at the start of
the axon at the AXON HILLOCK
The axonal signal is termed the:
action potential
nerve impulse
axon firing
Marieb Fig
7.9, p 203
NEURON V
Axon
The axon + its myelin
sheath, if present, is the
NERVE FIBER
NEURON VI
synapse
soma
axon
axon hillock
dendrites
Neuron # 1
soma = cell body
preterminal
axonal branches
Neuron #
2 in chain
NEURON VII Properties of the parts
synapse
influence
soma
axon
transmissive
axon hillock & long reach
decisive
dendrites
receptive
preterminal
axonal branches
distributive &
more reach
NEURON VIII Multipolar type
These neurons are the majority
type - multipolar - because they
have several dendrites and
always just one axon
synapse
soma
axon
preterminal
axonal branches
axon hillock
dendrites
Neuron # 1
Bipolar neurons have just two
processes, one the axon
Marieb Fig
7.8, p 202
Neuron #
2 in chain
NEURON & GLIAL CELLS
The electrical signal that develops on the
dendrites & body and propagates along the
axon membrane is based on the coordinated
actions of very many ion channels
‘Space’
is filled
by glial
cells
The ions leaving & entering the neuron go
into an environment that has to be very tightly
controlled. The cells that create and maintain
this environment, and also feed and clean up
after the neurons, are GLIAL CELLS.
These glia are wrapped all around neuron
bodies, dendrites, axons and synapses.
Two glial cell types make the myelin
sheaths: a central kind & a peripheral one
NEURON & CNS GLIAL CELLS I
OLIGODENDROCYTE
synapse
soma
axon
Node of
Ranvier
Myelin segment
dendrites
for fast saltatory (jumping) conduction
Gap in the myelin is the Node of Ranvier
NEURON & CNS GLIAL CELLS II
ASTROCYTE
synapse
soma
axon
Myelin segment
dendrites
NEURON & PNS GLIAL CELLS I
synapse
SCHWANN CELL
soma
axon
Node of
Ranvier
dendrites
Myelin
segment
for fast saltatory conduction
NEURON & PNS GLIAL CELLS II
PNS SATELLITE CELL
synapse
soma
axon
Myelin
segment
dendrites
axon
}
AXONS, MYELIN, & GLIA in cross-section
myelinates
more than
one axon
either enfolding
several un-myelinated
axons
axon
or enclosing one
myelinated axon
axon
OLIGODENDROCYTE
}
SCHWANN CELLS
CNS MYELINATION I
OLIGODENDROCYTE
}
{
axon
Myelin lamellae
appear exactly concentric, but
are a spirally wrapped sheet
Oligodendrocyte
plasmalemma extends,
adheres, & becomes the next
myelin lamella
2
1
First, outer lip wraps;
then, inner lip extends
3
axon
Oligodendrocyte
process
Cytoplasm squeezed out
4
Transport of membrane
proteins and lipids for
membrane conversion
5
axon
Myelin lamellae
CNS MYELINATION II
Oligodendrocyte
CNS MYELINATION III
OLIGODENDROCYTE
}
{
axon
Myelin lamellae
appear exactly concentric, but
are a spirally wrapped sheet
Connection of plasmalemma
to outermost myelin lamella
is the OUTER MESAXON
Oligodendrocyte
plasmalemma extends,
adheres, & becomes the next
Intervening cytoplasm is resorbed, except
myelin lamella
for remnants at Nodes of Ranvier & clefts of
Schmidt-Lantermann
MYELINATED PERIPHERAL NERVE FIBER
AXOLEMMA
plasma membrane
of axon
SCHWANN CELL
MYELIN
In the periphery, the Schwann
cell similarly membrane-wraps
the axon, while coverting the
wrappings to compact myelin
layers/lamellae.
AXON
Two adjacent Schwann cells
leave an uncovered gap - the
Node of Ranvier
MYELINATED PERIPHERAL NERVE FIBER: Reinforcement
In the peripheral NS, two
strengthening steps are needed:
plasma membrane
of axon
MYELIN the construction of a basal
lamina & a fine connective tissue
sheath outside the Schwann cell
AXOLEMMA
BASAL LAMINA
AXON
ENDONEURIUM
delicate connective
tissue
SCHWANN CELL
MORE NERVOUS TISSUE COMPONENTS
NEURONS/NERVE CELLS
GLIAL CELLS
BLOOD VESSELS
Connective tissue
WRAPPINGS
The ion channels require large
amounts of energy from glucose &
oxygen to work the ion pumps, so
blood is urgently needed
So as not to interfere with the intimate
neuron-glia relations, the brain & cord
have only wrappings - no internal
connective tissue - making them very
squishy & vulnerable
NERVOUS STRUCTURES: Neuron bodies
Brain & Cord
have trillions of
nerve & glial
cells; protected
by layers of
defense
The neuron body keeps the
neuron alive so the bodies are
grouped for protection as well
as function
The grouped neuron
bodies (& glial cells) in
the peripheral system
are GANGLIA
Shown in two colors
for sensory &
autonomic
Ganglia get some protection from
the spine, holes in the skull, or
being in soft protected visceral
organs
BRAIN SUB-DIVISIONS I
The brain is subdivided into:
Cerebellum
Cerebral cortex = two
cerebral hemispheres
BRAIN IN CORONAL VIEW: layered defenses
SKIN
VENTRICLE
filled with fluid,
cushions
from inside
Marieb Fig
7.16 p 211
SKULL
CORTEX CORTEX
CEREBELLUM
DURA
Thick strong
connective
tissue stuck
to skull
SUBARACHNOID
SPACE filled
with
cushioning
fluid
fine ‘skin’ of connective tissue on the brain - PIA
PERIPHERAL NERVE - Bundles of nerve fibers
The idea of mutiple protective layers extends to the
connective tissue wrappings of individual axons,
bundles (fascicles) of axons (fibers), and the bundles
FASCICLE = bundle of nerve fibers
FASCICLE
Marieb Fig
7.20, p 218
PERIPHERAL NERVE - CONNECTIVE TISSUES Wrappings
The idea of mutiple protective layers extends to the
connective tissue wrappings of individual axons,
EPINEURIUM bundles (fascicles) of axons (fibers), and
the bundles
FASCICLE
PERINEURIUM
main barrier to
protect nerve fibers
ENDONEURIUM
around each myelinated
fiber or bundle of nonmyelinated fibers in the
FASCICLE
fat cells for padding
NERVES
Brain
The previous cross-section
of a nerve could be here
Cranial nerves
Peripheral nerves
Ganglia
Autonomic nerves
The nerve contains part of each contributing
nerve cell, but not the bodies & not the synapses
Protective wrappings: know the sequence outside-in
SKIN
SKULL
DURA
SUB-ARACHNOID
SPACE
EPINEURIUM
PERINEURIUM
ENDONEURIUM
PIA
CORTEX
CORTEX
CEREBELLUM
FASCICLE
NERVOUS TISSUE COMPONENTS
NEURONS/NERVE CELLS
GLIAL CELLS
BLOOD VESSELS
Connective tissue
WRAPPINGS
MORE CNS GLIAL CELLS
Marieb Fig
7.3, p 197
MICROGLIAL CELL
small reserve defensive
macrophages of CNS
CORTEX
CORTEX
EPENDYMAL CELLS
epithelium-like to line the ventricles
within the brain
CEREBELLUM
OLIGODENDROCYTE
axon
ASTROCYTE
Always be aware of where the discussion is in
the hierarchy of levels:
molecular,
organelle,
cellular,
tissue,
organ,
system,
whole person,
human population
this is made more difficult in the nervous system
because it goes everywhere, so also
Whereabouts in
the system am I?
NERVOUS STRUCTURES: Neuron bodies
The neuron body keeps the neuron
alive so the bodies are grouped for
protection as well as function
Brain & Cord
have trillions of
nerve & glial cells
In the brain & cord the
neuron bodies are
mostly segregated from
the nerve fibers (axons
& myelin), but to
separate functions
Where the neuron bodies
congregate has less myelin,
and is termed GREY MATTER
GRAY MATTER vs WHITE MATTER
Gray because
of little myelin
White because of many myelinated fibers
This is the fresh-tissue, naked-eye appearance.
Staining, e.g., of just myelin for brain atlases,
can reverse the intensity
BRAIN SUB-DIVISIONS I
The brain is subdivided into:
Cerebral cortex = two
cerebral hemispheres
Each fold of cortex has a core of
white matter sandwiched between
two layers of gray matter served by
the white-matter fibers
CEREBRUM one fold/gyrus
I
II
III
IV
V
GRAY MATTER
VI
}
WHITE MATTER
GRAY MATTER
The Roman numerals indicate that
the millions of neuron bodies are
not all the same, & make up six
distinguishable layers
SPINAL CORD: White & gray matter
The cord has many nerve cells, but also has many major
connection pathways so white matter is predominant & on the
outside
WHITE MATTER
GREY MATTER
in a characteristic
butterfly shape in the
cross-section
SPINAL CORD: More details
Two swellings
Cervical
enlargement
to serve arm
& hand
WHITE MATTER
Thoracic to
serve trunk &
sympathetic
autonomics
Lumbo-sacral
enlargement to
serve leg & foot &
pelvic viscera
GREY MATTER
dorsal horn - sensory
intermediate
/ lateral grey
ventral horn - motor
Central
canal
Ventral fissure/cleft with
anterior spinal artery
BODY CAVITIES II Dorsal
The bones of the skull are
organized to form the face and
a cranial cavity for the brain
The vertebrae making up the spine
have many surfaces for muscle to
attach and stabilize and move the
spine. But also, they each have a
hole. As the holes line up, they
create the spinal canal (cavity) for
the spinal cord
BRAIN SUB-DIVISIONS I
The brain is subdivided into:
Posterior
Cerebral cortex = two
cerebral hemispheres
Anterior
Cerebellum
Brain stem
Small, on midline, deep &
mostly within brain
(spinal cord)
Marieb Fig 7.12, p 206 note
additional region - diencephalon
BRAIN SUB-DIVISIONS II
Cerebral cortex = two
cerebral hemispheres
Anterior
Posterior
Cerebellum
Brain stem
Small, on midline, deep &
mostly within brain
Appreciate that one has left &
right lateral views of the brain
(Spinal cord)
INNERVATION = NEURON DEPLOYMENT
sensory
motor
CORTEX
cerebellum
B
R
A
I
NS
We can keep this orientation,
but distort the proportions a
little to create a brain-&-cord
framework for showing how
neurons actually are deployed
TE
M
C
O
R
D
PERIPHERAL-CENTRAL INTERDEPENDENCE
The nervous system is defined by the nonnervous organs and tissues that it serves.
(A live brain in a jar has only stored
information to work with, and nothing to do
in any effective sense.) So there in the
‘periphery’ is where we shall start
The periphery to be considered first is the
body wall and its limb derivatives. These
defined ganglia & the cord. Sensory organs &
muscles of the head came later in evolution and
gave the head and brain their characteristics
We shall be talking electrical connections
NERVOUS STRUCTURES & TISSUE
CENTRAL
PERIPHERAL
Brain
Ganglia
Peripheral nerves
Cord
Receptors
But the central &
peripheral work together
so we’ll include
peripheral structures
CONVENTION FOR SHOWING NEURONS I
Here the neuron bodies are
represented with some dendrites
ending/synapse
axon
axon
neuron
body
Simplest schematic
synapse
101H NERVOUS STRUCTURES & TISSUE
CENTRAL
PERIPHERAL
Ganglia
Peripheral nerves
Receptors
PNS - Peripheral Nervous System
CONVENTION FOR SHOWING NEURONS II
Here the neuron bodies are
represented with some dendrites
axon
This type of ganglion
neuron has no dendrites
Motor synapse on muscle
synapse
touch receptor
SOMATIC INNERVATION
MOTOR
SENSORY
to detect external &
internal changes
To make muscle
contract, glands
secrete, etc
SKIN
BONE
Joint capsule
Tendon
Muscle
NEURON DEPLOYMENT making connections
sensory
motor
Cortex
Cerebellum
neuron
body
Receptors
movement
Nerve
touch
motor endings
Ganglion
MOTOR & SENSORY PATHWAYS
sensory
motor
Motor is for controlling
skeletal muscle
Sensory ‘knows’ what
skin receptors are
feeling
CORTEX
cerebellum
B
R
A
I
N
SOMA: Limb
& body wall
movement
touch
S
T
E Note chain of neurons
M
C
O
nerve
R
D
MOTOR & SENSORY PATHWAYS: # of NEURONS
sensory
motor
CORTEX
cerebellum
3
B
R
1
A
I
N
2
Note chains of neurons
S
T
E
M
C
O
R
D
2
1
Autonomic component of peripheral nerves
The flow of blood to skin
cerebellum & muscle needs to vary
B
Autonomic neurons
R
send axons to constrict
A
I
N vessel width
S ‘Autonomic’ - happens
T
E
without thought
M
CORTEX
C
SOMA
O
nerve
R
D
vasoconstriction
Afferent & Efferent components of peripheral nerves
CORTEX
cerebellum
Different axons are
carrying signals in to
the CNS & away from it
B
R
A
I
N
S
T
Afferent
E
M
Efferent
C
O
nerve
Marieb Fig
7.6, p 200
R
D
INNERVATION = NEURON DEPLOYMENT
sensory
motor
CORTEX
cerebellum
B
R
A
I
NS
We can keep this orientation,
but distort the proportions a
little to create a brain-&-cord
framework for showing how
neurons actually are deployed
TE
M
C
O
R
D
MEDIAN
(Midline)
TUBE MAN
Head - modification
of body wall + brain
& special senses +
start of two tubes
re
Al
Soma - body wall
& the limbs
- - - -
Viscera tubes,
modified tubes, &
accessory organs
& his Neuron
cvl
- -
-
diaphragm
u
o
Neuron - excitable, extended, fast influencer
SOMATIC INNERVATION
MOTOR
SENSORY
cutaneous
autononomic
proprioception
skeletal m
SKIN
BONE
Joint capsule
Tendon
Muscle
INNERVATION = NEURON DEPLOYMENT
sensory
motor
-
CORTEX
cerebellum
CONVENTIONS
B
ending
R
A
fiber
I
N
ST
neuron
body
E
M
C
SOMA
movement
touch
vasoconstriction
+
O
nerve
R
D
101H NERVOUS STRUCTURES & TISSUE
CENTRAL
PERIPHERAL
Ganglia
Peripheral nerves
Receptors
PNS - Peripheral Nervous System
Receptors & Sensory Information
sensory
motor
Receptors of many kinds tell
the brain & cord what is going
in the body & outside
Most of this information never
reaches consciousness
Tactile info from theneuron
skin
body
is an exception
Receptors
movement
Nerve
touch
motor endings
vasoconstriction
S
A
Ganglia
THICK, HAIRLESS SKIN
}
2 Receptors
EPIDERMIS
}
Meissner’s
corpuscle
Marieb Fig
4.3, p 96
DERMIS
Sweat gland
Pacinian
corpuscle
Pacinian
corpuscle
RECEPTORS: Cutaneous
(around
1 Peri-trichal
hair follicle)
Marieb Fig
7.7, p 201
2
Free endings
in epidermis
Merkel cell
5
6 Ruffini
corpuscle
encapsulated
3
Pacinian
corpuscle
encapsulated
Meissner’s
corpuscle
encapsulated
4
Meissner’s corpuscle
Receptors that are not inserted among the epithelial cells of
the epidermis, but are in the underlying connective tissue,
are mostly ‘encapsulated”, and have a typical structure
Supporting glia-like cells
Terminal impulsegenerating part of axon
Connective tissue capsule
Axon - peripheral branch of the axon of a sensory ganglion cell
1 Peri-trichal (around
“TOUCH” hair follicle)
RECEPTOR MODALITIES
hair displacement
3
Merkel cell
2
Free endings
TOUCH
COLD PAIN
Ruffini
6
corpuscle
Pacinian
corpuscle
TOUCH
4 Meissner’s
corpuscle
TOUCH
5
CT DISPLACEMENT*
VIBRATION
* slowly adapting
NERVOUS STRUCTURES
Peripheral
Central
PNS
CNS
RECEPTORS
CEREBRAL CORTEX
Sens GANGLIA
DIENCEPHALON
MOTOR ENDINGS
CEREBELLUM
Auton GANGLIA
BRAINSTEM
PLEXUSES
SPINAL CORD
NERVES
NEURAL RETINA
PERIPHERAL NERVE - CONNECTIVE TISSUES Wrappings
EPINEURIUM
PERINEURIUM
main barrier to
protect nerve fibers
FASCICLE
ENDONEURIUM
around each myelinated
fiber or bundle of nonmyelinated fibers in the
FASCICLE
fat cells (Black with
Osmium tetroxide
showing myelin rings)
vessels
PERIPHERAL NERVE - H&E versus OsO4 staining
Fat cells - clear & empty
H&E
Myelin sheaths
- Black rings
Nuclei - mostly
Schwann cells’
Myelin sheaths
- clear spaces
Axons - central dots
Fat cells - Black
OsO4
Axons - clear
Nuclei -unseen
Node
HISTOLOGY’S ORIENTATION PROBLEM
Cerebellum
Cortex
Small pieces from a
large complex system
Where am I?
How much of what is
neuro
present can I see?
n body
Making the connections
mentally
Receptors
Nerve
motor endings
S
A
Ganglia
SENSORY PATHWAY
sensory
CORTEX
cerebellum
B
R
A
I
N
ST
E
M
C
O
nerve
touch
R
D
crosses midline
PATHWAYS OF AUTONOMIC MOTOR SYSTEM
Cranial gland
or eye smooth
muscle
Head vessels
Brain
stem
Para
V
C
Thor
Cord
Symp
C
P
ADRENAL
MEDULLA
Sacral
Cord
Para
I
S
C
E
R
A
CEREBRUM
1/2 one gyrus
Pia mater
I
Molecular layer
II
III
IV small stellate neurons
V pyramidal neurons
VI
Apical
dendrite
White matter
Basal
dendrites
PYRAMIDAL NEURON
Soma
Axon
VISCERAL TUBE CONSTRUCTION
Epithelium
Lamina
propria
}
Tunica
muscularis
nerve plexus
Tunica
adventitia
or serosa
vessel
Tunica
mucosa
GUT MOTOR INNERVATION intrinsic
with H & E staining, the only neural elements seen are the neuron
bodies & characteristic nuclei. The plexuses of fibers are unseen.
Meissner’s submucosal plexus
Rare neuron bodies of
plexus
submucosa
muscle
Auerbach’s myenteric plexus
Clumped
neurons of A’s
plexus
Unmyelinated autonomic nerve
neurons are multipolar, with dendrites!
AUTONOMIC “unmyelinated” NERVE in H&E
Small, pale, blueish, elongated;
‘purposeful’ track through pinker
connective tissue or muscle
Thin CT perineurium
X-section
Many nuclei (mostly of Schwann
cells) giving, with the fibers, an
undulating wavy character
Once they leave the nerve, individual fibers need special methods to
be seen
INTRAMURAL (Parasympathetic) GANGLION
like any other nervous gangion, is an aggregate of neuron
bodies & associated cells added to a nerve
Around the somas, the jumble
Neuron somas, with large pale of nuclei belong to satellite cells,
nucleus & prominent nucleolus Schwann cells, fibroblasts &
capillaries
Special methods are needed to show that the neurons are
multipolar to receive the pre-ganglionic synapses
INTRAMURAL (Parasympathetic) GANGLION
Post-ganglionic SYMPATHETIC fiber
Pre-gangionic
PARASYMPATHETIC fiber
Post-ganglionic
PARASYMPATHETIC fiber
Special methods are needed to show the plexus of autonomic
fibers to which the gangion neurons contribute
VOLUNTARY MOTOR PATHWAY I
CORTEX
motor
cerebellum
B
R
upper motor neuron
A
I
N
ST
E
M
C
O
muscle
movement
nerve
R
D
lower motor neuron
Motor end-plate
crosses midline
MOTOR END-PLATE or NEUROMUSCULAR/MYONEURAL JUNCTION
AXON
SCHWANN
CELL
AXOLEMMA
SARCOLEMMA
SYNAPTIC VESICLES
mitochondrion
synaptic
cleft
secondary/
junctional folds of
POST-SYNAPTIC MEMBRANE
SKELETAL MUSCLE FIBER/MYOCYTE
NEURON TYPES by SHAPE I
synapse
soma
MULTIPOLAR
axon
axon hillock
preterminal
axonal branches
The vast majority of neurons
are multipolar: hence, other
criteria for classification
dendrites
BIPOLAR
Dendrites’
function
transferred
PSEUDO-UNIPOLAR
receptive
NEURON TYPE DEPLOYMENT
sensory
CORTEX
motor
All long-axoned, except
cerebellum
B
R
Spinal interneuron
A
I
All shown: multi-polar
S T except
pseudoE
unipolar
M
DRG cell
C
O
nerve
R
D
N
movement
touch
vasoconstriction
NEURON DEPLOYMENT
sensory
motor
Appreciating how neurons
are used: problems are that
a neuron EXTENDS through
many named strucures, and
shares structures, e.g., here
motor & sensory in a nerve
Nerve
touch
NEURON DEPLOYMENT II
one neuron extends through
many named structures.
The axon is doing the extending
TRACT of
Cord - cuneate
DR GANGLION
touch
RAMUS of
PERIPHERAL
ROOT, dorsal
spinal
NERVE,
e.g. median PLEXUS, nerve, e.g.
e.g. brachial ventral
SPINAL NERVE
CUTANEOUS
PLEXUS
NEURON DEPLOYMENT III
one neuron extends through
many named structures.
The axon is doing the extending
1 CUTANEOUS PLEXUS
2 PERIPHERAL NERVE, e.g. median
3 PLEXUS, e.g. brachial
4 RAMUS of spinal nerve, e.g. ventral
5 SPINAL NERVE
6
DR GANGLION
7
ROOT, dorsal
}
8 CORD TRACT, cuneate
SPINAL CORD
Cervical
enlargement
to serve arm
& hand
WHITE MATTER
Thoracic to
serve trunk &
sympathetic
autonomics
Lumbo-sacral
enlargement to
serve leg & foot &
pelvic viscera
GREY MATTER
dorsal horn - sensory
intermediate
/ lateral grey
ventral horn - motor
Central
canal
Ventral fissure with
anterior spinal artery
DORSAL ROOT GANGLION
Pial connective tissue
Clumps of sensory neurons
Nerve-like Root
central axon unseen H&E
Satellite cells
around neurons
dorsal horn - sensory
Bundles of
myelinated fibers
Hallmarks: large round neurons;
separation of neurons from pale
myelinated nerve bundles
CNS STRUCTURES
sensory
motor
CORTEX
cerebellum
B
R
like CNS neuron somas
grouped in a NUCLEUS
GREY
A
I
N
ST
E
M
like CNS fibers
grouped in a TRACT
WHITE
C
O
movement
R
D
touch
vasoconstriction
CEREBELLUM
one folium
Pia mater
Molecular layer few neurons
Purkinje cells/neurons
Granule layer small neurons
White matter
Gray matter
Purkinje cell
Projection/output neuron
PNS STRUCTURES
sensory
N NE DRG AG
CORTEX
motor
B
R
A
I
N
S
T
E
M
C
O
Nerve endings
motor
Nerve
R
D
sensory
motor
Autonomic ganglion
DR ganglion
NEURON TYPES by SHAPE I
synapse
soma
MULTIPOLAR
axon
axon hillock
preterminal
axonal branches
The vast majority of neurons
are multipolar: hence, other
criteria for classification
dendrites
BIPOLAR
Dendrites’
function
transferred
PSEUDO-UNIPOLAR
receptive
RECEPTOR MODALITIES
1 Peri-trichal (around
hair follicle)
2 Free endings
“TOUCH” -hair displacement
TOUCH COLD PAIN
TOUCH
3
Merkel cell
4
Meissner’s corpuscle
5
Pacinian corpuscle
6
Ruffini corpuscle
Light TOUCH
VIBRATION
CT DISPLACEMENT*
* slowly adapting
TASTE BUD
Taste pore
Receptor cells
SS EPITHELIUM
Basal cell
Supporting cell
Axons of VII, IX or X
MUSCLE SPINDLE
Intra-fusal muscle fibers
Extra-fusal muscle fibers
often holds several
fibers of each type
ORANGE vs MENINGES
PEEL - DURA MATER
LINING OF PEEL & SPACE ARACHNOID
SKIN ON SEGMENTS PIA MATER
BRAIN IN CORONAL VIEW
CORTEX
VENTRICLE
with
Choroid
plexus
SKULL
DURA
Dural Falx
SUBARACHNOID
SPACE
Dural sinus
CEREBELLUM
Tentorium cerebelli
BLOOD FLOWS FOR THE BRAIN
Dural sinuses
Cerebral veins
Brain capillary
network
Arteries
Jugular veins
CSF PRODUCTION & FLOW
Dural sinus CSF returns to
blood: subarachnoid space
to dural sinus
CHOROID PLEXUS
in ventricles making
CSF from blood
Arteries
Jugular veins
CSF drains to
the outside of
the brain from
4th ventricle
CHOROID PLEXUS
CUBOIDAL EPENDYMAL EPITHELIUM
CAPILLARY
CSF
LOOSE CT
BASAL LAMINA
Choroid-plexus ependymal cells have tight junctions,
and ion pumps to drive water & some electrolytes
from blood to ventricle
CSF RETURN TO BLOOD I
CORTEX
Dural sinus
VENTRICLE
with
Choroid
plexus
SKULL
DURA
Dural Falx
SUBARACHNOID
SPACE CSF
How to return
CSF to blood?
Dural sinus
BLOOD
CSF RETURN TO BLOOD II
Dural sinus
CORTEX
VENTRICLE
with
Choroid
plexus
SKULL
Site of Next Fig
DURA
Dural Falx
SUBARACHNOID
SPACE
RETURN OF CSF: Arachnoid
DURA
dural-sinus blood
DURAL SINUS here Sup sagittal sinus
ARACHNOID
MEMBRANE
ENDOTHELIUM
ARACHNOID
TRABECULAE
PIA
ARACHNOID VILLUS
protruding into sinus
CORTEX
SUBARACHNOID SPACE
CORTEX
FALX
This Fig has appeared countless times without credit to its originator Lewis Weed of the Johns Hopkins U, so I am providing only his labels
Weed LH. The absorption of cerebrospinal fluid into the venous system. Am J
Anat 1923;31:191-221
VILLUS. Do I know you?
ARACHNOID VILLUS
SMALL INTESTINAL VILLUS
JOINT SYNOVIAL VILLUS
PLACENTAL CHORIONIC VILLUS
Many sub-types
CSF PRODUCTION, FLOW, & RETURN
Arteries
CHOROID PLEXUS in ventricles
making CSF from blood
CSF drains via foramina to the outside
of the brain from 4th ventricle
CSF returns to blood: subarachnoid space to dural sinus
Dural sinus
Jugular veins
CSF FLOW & RETURN: Problems
Arteries
CSF production
continues
CHOROID PLEXUS in ventricles regardless
OBSTRUCTIONS OF:
making CSF from blood
Flow between ventricles
Out of 4th ventricle
Dural-sinus uptake, e.g.
from meningitis
CSF drains via foramina to the outside
of the brain from 4th ventricle
CSF returns to blood: subarachnoid space to dural sinus
RAISED INTRACRANIAL PRESSURE Dural sinus
& Hydrocephalus in infant when cranial
vault bones not joined (synostosed)
Jugular veins
CNS VULNERABILITIES
SOFT & SQUISHY - EASILY BRUISED (no intrinsic c.t.)
CONFINED IN HARD BOX shared with blood, CSF (& tumor?)
URGENT NEED FOR OXYGEN & GLUCOSE for pumping ions
SUSCEPTIBLE TO TOXINS that can pass the blood-brain barrier
NO EFFECTIVE REPAIR of damage from trauma , raised
intracranial pressure, or interrupted blood supply
AXONAL TRANSPORT
FAST ANTEROGRADE 100 mm/day Carries materials
needed for the fast pace of
electrical activities of the neuron
SLOW ANTEROGRADE 4 mm/day Serves to move
the infrastructure of transport, e.g.,
replacement of tubulin dimers,
neurofilaments, mitochondria
RETROGRADE 20 mm/day Brings back to the soma
old materials for lysosomal destruction
& trophic and survival factors
derived from the target cell (neuron
or muscle) e.g. Nerve Growth Factor
Viruses,e.g., rabies, can also use this route
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Online Anatomy Module 1
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