Lecture II' The Nervous System and Its Cells

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Lecture II. The Nervous System and Its Cells

• Bio 3411
• Friday
• August 28, 2009

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• T. Woolsey
• 3802 North Building
• 362-3601
• woolseyt_at_medicine.wustl.edu

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Readings

• NEUROSCIENCE 3rd ed, pp 1-22
• THE BRAIN ATLAS 3rd ed, pp 4-17
• References
• Jellison et al (2004). Diffusion tensor imaging
  of cerebral white matter a pictorial review of
  physics, fiber tract anatomy, and tumor imaging
  patterns. AJNR Am J Neuroradiol, 25356-369
• Ludwig, E., Klingler, J. (1956). Atlas cerebri
  humani. Der innere Bau des Gehirns dargestellt
  auf Grund makroskopischer Praparate. The inner
  structure of the brain demonstrated on the basis
  of macroscopical preparations. Boston, Little,
  Brown.
• Ramón y Cajal, S. (1988). Recollections of my
  life. New York Garland.
• ______________________
• (pdfs on course website http//artsci.wustl.edu
  /sdanker/index.html)

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Movie - vmjr-brain.mov
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• Overview
• A Few Facts
• Main Features of Nervous System
• Cells of Nervous System
• Importance in Health and in Disease

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Facts
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OrganWeight 2-3 of bodyO2 Consumption 20
of totalBrain Energy (Glucose) Utilization 20
of totalBrain Blood Flow 20 of heart output
at rest
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ElementsNeurons (nerve cells) 100
BillionGlia ( glue supporting cells) 1
TrillionSynapses (clasp) 1/1,000,000th of all
stars planets in the universe/person less
than the total of human synapses of people living
in the St.L area!!Genes 50 of 20,000-25,000
genes in the human genome are expressed only in
Brain70 of the balance are also expressed in
the nervous system the total is 85 of the
genome
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FeaturesBrain, Spinal Cord, Other
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THE BRAIN ATLAS 3rded, p. 8
Mid-line (sagittal) section through central
nervous system (CNS). Note the relationship
between vertebrae (BLACK), segments of the spinal
cord (RED) and spinal nerves (YELLOW).
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THE BRAIN ATLAS 3rd ed, p. 111
Magnetic Resonance Image (MRI) of head and neck
at the midline.
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Peripheral (PNS - outside the skeleton) Sensory
(sensation) Motor (movement) Autonomic
(involuntary) Enteric (gut)Central (CNS
-inside the skeleton) Spinal Cord (Spine) Brain
(Skull)
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Views of the human spinal cord and lower brain
stem. LEFT - Left lateral (side) showing segments
and spinal nerves. MIDDLE - Anterior (front)
view of spinal cord without showing
enlargements. RIGHT - Posterior (back) view of
spinal cord with roots, ganglia and nerves.
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THE BRAIN ATLAS 3rd ed, p. 49
Spinal Cord Segment
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THE BRAIN ATLAS 3rd ed, p. 20
Left Lateral (side) view of the human Brain
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THE BRAIN ATLAS 3rd ed, p. 9
The different regions of the brain from the
lateral (side) and median section (middle) human
brain. These brain regions are discernable in in
all vertebrates and in early embryos. (cerebral
cortex gold thalamus blue/purple midbrain
orange pons purple, cerebellum blue medulla
red/orange spinal cord green)
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THE BRAIN ATLAS 3rd ed, p. 58
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THE BRAIN ATLAS 3rd ed, p. 59
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THE BRAIN ATLAS 3rd ed, p. 6
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Components

• Gray Matter
• Cortex, Nuclei or Ganglia (groups of nerve cell
  bodies and neuropil) generally of similar
  function
• Neuropil - neuronal processes, synapses and glia

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Components

• White Matter
• Bundles (groups of myelinated axons see below
  that course in the same direction)
• Tracts (also groups of axons (myelinated and
  un-myelinated but indicates origin, destination
  and therefore function)

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Cerebrospinal Fluid (CSF)
The brain and spinal cord are bathed in a
colorless fluid called cerebrospinal fluid (CSF).
The fluid is made in chambers in the brain called
ventricles (blue). It circulates between all the
cells and their processes and in the space
between a membrane on the brain surface (called
the pia mater) and a membrane that is next to the
skull or spine (arachnoid mater) called the
subarachnoid space (gold).
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Components

• Other
• Blood Vessels (arteries, capillaries, veins and
  venous sinuses)
• Coverings - meninges (dura mater (tough mother),
  arachnoid (spider web like), pia
  (tender/affectionate))
• Cerebrospinal fluid (CSF - ventricles, canals,
  intercellular space, subarachnoid space)

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Movie - vmjr-brain.mov
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Cells of Nervous SystemNeurons, Contacts,
Support
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Santiago Ramón y Cajal (1851-1932) ca.
1892 Cajal (say kaahaal) shared the 1906 Nobel
Prize for discoveries indicating that the nervous
system was made up of individual contiguous
elements - the neurons.
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Cells of Nervous System

• Neurons
• Parts cell body (soma), dendrites (input
  processes), axon (output process)
• Types local circuit (90), projection (10)
• Variations stellate (star like) pyramidal
  (conical/triangular) famous guys - Purkinje,
  Betz, Cajal, Retzius, Mauthner
• All variations are correlated to particular
  functions.

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Photograph of neurons stained by Golgis method
which fills processes of some cells with black
precipitates of heavy metals and Nissl which
stains all nuclei and neuronal cytoplasm blue.
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Pyramidal neuron (conical cell body) stained by
Golgis method. There are multiple processes that
resemble branches of trees (dendrites) and one
that resembles a wire (axon arrow). Inputs to
the cell are mainly on dendrites and the cell
body (soma) while outputs are mainly via the
axon. This the principal long axon (output) cell
in the cerebral cortex.
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Photograph of a Purkinje cell in the cerebellum
stained by Golgis method. The neuron has one
complex dendrite that resembles a sea fan
(arrow). Synapses on this cell type are estimated
to be about 0.5 Million.
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Cells of Nervous System

• Contacts (Synapses)

• Parts bouton or ending (contains vesicles
  (transmitters, modulators) and mitochondia),
  presynaptic membrane (dense in electron
  microscope) synaptic cleft postynaptic membrane
  (dense in electron microscope)

• Types asymmetrical Type I (postsynaptic
  membrane is thicker than presynaptic membrane
  spherical clear vesicles) these are excitatory
  synapses - on symmetrical Type II
  (postsynaptic membrane same as presynaptic
  membrane flattened clear vesicles) these are
  inhibitory synapses - off

• Variations large like to muscle, chalice in
  brain stem, climbing in the cerebellum
  intermediate small in passing or as a terminal.
  All variations relate to specific functions (like
  variations in hammers - sledge vs. jewelers).

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Photograph of the giant neuron in the brainstem
of the gold fish (Mauthner) stained by Bodians
method. Synapses on this cell type are
particularly easy to see. Much work on this cell
type contributed to understanding the structure
of the synapse before the electron microscope was
perfected.
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Electron micrograph of a synapse in the brain
stained with the heavy metal element osmium (Os)
which is lipophylic (stains lipids/fats). This
synapse is only about 2 micrometers across.
The main components of a synapse synaptic cleft
(space between the terminal and target process),
membrane thickenings on the terminal (pre) and
process (post), mitochondria and synaptic
vseicles (contain transmitter(s)).
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Most brain synapses (type I) have a wider cleft
(space between the terminal and target process),
thicker membrane densities on the terminal (pre)
and process (post) and rounder vesicles. Such
synapses are excitatory (on).
About 10 - 20 brain synapses (type II) have a
narrower cleft, thinner membrane densities on the
terminal (pre) and process (post) and flat
vesicles. Such synapses are inhibitory (off).
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A neuron (red) grown in tissue-culture. Green
shows proteins in processes from pre-synaptic
neurons. The green/yellow dots on the red neuron
indicate synapses. The inset shows a cartoon of
blue synaptic terminals contacting a neuron. The
picture gives a sense of the enormous numbers,
distribution and density of synapses on a nerve
cell. Neurons integrate information from
thousands of synapses from many different sources.
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Cells of Nervous System

• Glia (glue) or Supporting Cells
• Parts cell body (soma) and "short" processes
• Types astrocytes (star like) oligodendorcytes
  (fewer (oligo) branches (dendrites) microglia
  (small ones)
• Variations fleshy, fibrous (stringy),
  myelinating, non-myelinating
• All variations relate to specific functions.

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Cajals drawing of glia in the spinal cord.
B
C
A Ependyma (lining of the central canal of the
spinal cord)
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B Oligodendrocytes which myelinate axons in fiber
tracts
D
C Astrocytes - Protoplasmic (fleshy) in gray
matter
C
D Astrocytes - Fibrous
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NEUROSCIENCE (3rd ed, p.8, fig 1.5)
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THE BRAIN ATLAS 3rd ed, pp. 5, 7
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How Does This Work?
Please vote on the following propositionI think
that the TA can run up the stairs to the back row
of this auditorium in less than 10 seconds.
Yes ____
No ____
(Estimated elapsed time )
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ImportanceBiology, Disease
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• Biology
• Understanding the brain is THE major question in
  biology and science.
• Is it possible for the brain to understand
  itself?
• The brain like any organ has functions input,
  output, thought, communication.

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• Brain Diseases
• Interfere with brain functions as heart disease
  interferes with the circulation.
• Many diseases have a strong genetic component.
• Prevalence is high 15 - 30 of the
  population.
• Cost is high gtgt 2 Trillion/year in care, lost
  income, social services, etc., in the US.
• Impact (personal, family, societal) is
  persistent, pervasive, enormous, incalculable.

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• What this lecture was about
• A Few Facts
• (genes, size, energy)
• Main Features of Nervous System
• (brain, spinal cord, periphery)
• Cells of Nervous System
• (neurons, glia, contacts)
• Importance in Health and in Disease
• (bases, prevalence, impact)

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Movie - vmjr-brain.mov