The document provides an overview of the organization of the nervous system. It discusses the central nervous system (CNS) which includes the brain and spinal cord, and the peripheral nervous system (PNS) which connects the CNS to sensory receptors and effector organs. The nervous system is composed of neurons and glial cells. Neurons have cell bodies, dendrites, axons and synaptic terminals. They communicate via electrical and chemical signals. The organization of the nervous system allows it to perform functions like sensation, movement, thinking and homeostasis.

1. NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
A REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
I. OVERVIEW:
A. Function: The nervous system consists of a group of organs and tissues that functions to control the body
and respond to internal and external environmental changes by
1. gathering sensory information (SENSORY INPUT)
2. integrating the sensory information (INTERGRATION)
3. activating the appropriate glands or muscles (MOTOR OUTPUT)
B. Structure: The nervous system is divided into two main components:
1. Central Nervous System (CNS) is composed of:
a. brain
b. spinal cord
2. Peripheral Nervous System (PNS)
a. components:
i. sensory receptors
ii. nerves: sensory nerves & motor nerves
iii. ganglia: dorsal root ganglia (sensory), parasympathetic ganglia (motor, autonomic), sympathetic
ganglia (motor, autonomic)
iv. motor endings
b. divisions:
i. sensory
ii. motor
• subdivided into
- somatic (voluntary control)
- autonomic (involuntary control) which is further subdivided into:
* parasympathetic
* sympathetic
* enteric
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2. NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
II. COMPONENTS OF NERVOUS TISSUE
A. CLASSIFICATION OF GLIAL CELL TYPES
Table 1: Classification and function of glial cells in the nervous system
CLASS SUBDIVISION CELL TYPES FUNCTION
Astrocyte i. nourishment
(Macroglia) ii. guidance
iii. synapse formation
iv. regulation of extracellular environment
(neurotransmitters, ions)
Ependymal cell circulation of CSF
CNS
(Macroglia)
Glia
Oligodendrocyte myelination of neuronal axons
(Macroglia)
Microglia phagocytes
Schwann cell myelination of neuronal axons
PNS
Satellite cell regulates extracellular environment
B. NEURONAL SHAPE AND STRUCTURAL ELEMENTS
1. CELL BODY (Nucleus + Soma (everything but the nucleus))
a. SOMA:
i. STRUCTURE: all organelles found in cells plus neurofilaments; plasma membrane (high levels
of chemically gated ion channels)
ii. FUNCTION: biosynthetic center; signal reception
b. Description of clusters of cell bodies (gray matter)
Clusters of cell bodies in the CNS = nuclei
Clusters of cell bodies in the PNS = ganglia
2. PROCESSES: projections or extensions that function to receive and transmit signals (dendrites) or
transmit and secrete neurotransmitters (axons)
a. Description of clusters of axons (white matter)
Clusters of axons in the CNS = tracts
Clusters of axons in the PNS = nerves
b. Classification and characteristics of neuron processes (Table 2)
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3. NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
II. COMPONENTS OF NERVOUS TISSUE
B. NEURONAL SHAPE AND STRUCTURAL ELEMENTS
2. PROCESSES
Table 2: Classification and characterization of neuron processes
TYPES CHARACTERISTICS ORGANELLES FUNCTION
same as soma i. reception of neuronal signals
Extensions: short
Branching: diffuse branching plasma membranes ii. transmission of signals to cell
contain chemically-gated body using short distance electrical
Myelination: none
ion channels signals (graded potentials)
Dendrite
DENDRITIC SPINES =
terminal endings of dendrites
conduction of electrical signals
Extensions: variable in length
Branching: variable
Myelination: variable
NERVE FIBERS = very long axons
AXON HILLOCK: origin of axon from cell body; trigger generates long distance electrical
signals (action potentials)
zone for action potential
AXON LENGTH: region same as soma except no conducts electrical signals away
RER, Golgi apparatus from cell body
after axon trigger zone to
Axon
terminal
plasma membranes contain
voltage-gated Na channels
and voltage-gated
potassium channels
AXON TERMINAL: end of same as soma except no secretes neurotransmitters
RER, Golgi apparatus and
axons
higher concentrations of
BOUTONS = profusely
vesicles and mitochondria
branched terminals
plasma membranes contain
voltage-gated calcium
channels
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4. NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
II. COMPONENTS OF NERVOUS TISSUE
B. NEURONAL SHAPE AND STRUCTURAL ELEMENTS
3. CELL CLASSIFICATION AND FUNCTION OF NEURONAL CELLS
Table 3: Classification and function of neuronal cells in the nervous system
CLASS SUBDIVISION CELL TYPES FUNCTION
multipolar (multiple efferent, motor neurons (CNS  muscle); interneurons
dendritic extensions;
single axon)
based on
structure bipolar (fused specialized sensory neurons in retina or ear
dendrite & axon)
unipolar (single afferent, sensory neurons (receptor  CNS)
axon)
Neurons
motor neurons efferent, multipolar neurons (CNS  muscle)
(projection neuron)
based on
sensory neurons afferent, sensory unipolar neurons (receptor  CNS)
function
(projection neuron)
interneurons association, multipolar neurons between neurons in CNS
4. MYELIN SHEATH
a. STRUCTURE: a covering surrounding an axon that is formed by Schwann cells (PNS) or
oligodendrocytes (CNS)
i. in the PNS, the myelin sheath is segmented
• each segment is composed of one Schwann cell that wraps around the axon
• Nodes of Ranvier = uncovered axon membrane
• neurilemma: outer surface of myelin sheath; contains nucleus of Schwann cell
ii. in the CNS, the myelin sheath is continuous sheath
• one oligodendrocyte covers multiple axons for greater lengths
• Nodes of Ranvier are present but fewer in numbers
• no neurilemma
b. FUNCTION: provides insulation to promote faster conduction of electrical signals
c. DISEASE: Multiple sclerosis
i. autoimmune disease – inflammation and destruction of myelin sheaths
ii. useful links
http://www.bbc.co.uk/health/conditions/ms1.shtml
http://www.bbc.co.uk/devon/community_life/features/living_with_ms.shtml
http://www.allheadlinenews.com/articles/7004851125
http://news.bbc.co.uk/2/hi/health/4724414.stm
http://www.findarticles.com/p/articles/mi_m0EIN/is_2005_Sept_28/ai_n15635911
http://www.fredericknewspost.com/sections/features/display.htm?storyid=51932
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5. NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
III. LIFE AND DEATH IN THE NERVOUS SYSTEM
A. Neural Stem Cells & Differentiation
1. Neural stem cells
a. are present during prenatal development
http://www.mpg.de/english/researchResults/researchPublications/researchReports/EEB/200414_01
3.shtml
b. have been found in adult brains in two brain regions
i. subventricular zone (SVZ)
ii. hippocampus
2. Neural stem cells are pluripotent and can differentiate into macroglia and neurons.
3. Neural stem cells are under investigation as a possible therapy for neurodegenerative diseases such as
Parkinson’s or Alzheimer’s or brain injury.
http://www.sciencedaily.com/releases/2002/04/020415073115.htm
http://www.sciencedaily.com/releases/2005/09/050920074831.htm
http://www.ninds.nih.gov/news_and_events/news_articles/news_article_stroke_Notch.htm
http://www.helpforheadaches.com/articles/nihsheets/life-neuron.htm
B. Neuronal migration and axon guidance
1. Neurons migrate to site of final destination.
2. Glial cells and other neurons guide migrating neurons.
3. Neurons make connections with other neurons.
http://apu.sfn.org/index.cfm?pagename=brainBriefings_axonGuidance
C. Neuronal cell death
1. Neurons that make connections with other neurons integrate and mature.
2. Neurons that do not make connections die via apoptosis.
IV. NEURON COMMUNICATION
A. Synapses
1. Definition: junction between two neurons or a neuron and an effector cell
2. Structures: pre-synaptic membrane, post-synaptic membrane, synaptic cleft
B. Types of communication
1. Electrical
2. Chemical (neurotransmitters)
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6. NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
V. ORGANIZATION OF THE NERVOUS SYSTEM into regions that have discrete functions.
Table 4: Overview of the organization of the nervous system
SUB SUB-SUB-
REGION DIVISION STRUCTURE FUNCTION
DIVISION DIVISION
brain consciousness, perception,
thought, language, emotion,
voluntary movement,
maintaining homeostasis,
Central Nervous System (CNS)
memory, sleep
spinal cord 1. connects brain with PNS
2. controls reflexes
cranial nerves 1. sensation
spinal nerves
2. coordination b/n CNS
Peripheral Nervous System (PNS)
sensory receptors and the body
ganglia
motor endings 3. conduction
1. somatic sensory nerve conduction of impulses from
fibers receptors to CNS
Sensory (Afferent)
2. visceral sensory nerve
fibers
motor nerve fibers conduction of nerve
Motor (Efferent)
impulses from CNS to:
muscles & glands
voluntary (somatic) motor conducts impulses from
nerve fibers CNS to skeletal muscles
Somatic Nervous System
voluntary movement,
coordination, reflexes
involuntary (visceral) conducts impulses from
motor nerve fibers CNS to:
Autonomic Nervous System
cardiac muscle
autonomic ganglia smooth muscle
glands
Para- involuntary (visceral) maintenance –
sympathetic motor nerve fibers “rest & digest”
Sympathetic involuntary (visceral) emergency response –
motor nerve fibers “fight or flight”
involuntary (visceral) gut brain - regulation of
digestion
sensory and motor
nerves; neurons connected to CNS via
vagus nerve
Enteric
glial cells
same developmental origin
information processing as CNS
circuits
http://whyfiles.org/026fear/p
all neurotransmitters hysio1.html
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7. NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
Table 5: Structure and function of components of the CNS
COMPONENT STRUCTURE FUNCTION
Brain Gray matter (clusters of neuronal cell bodies and dendrites) - controls voluntary movement
(cerebrum)
White matter (clusters of myelinated fibers known as tracts) - interpretation and integration of
sensation (cerebrum)
Central cavity – filled with CSF and lined with ependymal - consciousness (cerebrum)
cells - cognition (cerebrum)
- maintains homeostasis
Meninges – protective membranes between skull and brain (hypothalamus)
- emotions
- sleep
- memory
Spinal Cord Nervous tissue that runs from the brain to the first and third i. connects brain with PNS
lumbar vertebrae ii. controls reflexes
iii. Spinal cord injury
Gray matter - H-shape gray area surrounding the central http://www.wingsforlife.com/?LN
canal consisting of cell bodies of the motor neurons (ventral G=en&id=163&zid=78
horn), sensory neurons (dorsal horn) and interneurons (dor-
sal horn).
White matter – white area surrounding the gray matter
which is composed of bundles of myelinated axons that ei-
ther are ascending or descending nerve fiber tracts.
Dorsal or ventral roots - bundles of afferent sensory neu-
ron axons (dorsal root) or bundles of efferent motor fibers
(ventral roots).
Spinal nerve – the fusion of dorsal and ventral roots.
Dorsal root ganglion -bundles of sensory neuron cell bodies
adjacent to the spinal cord
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8. NS3- REVIEW OF THE ORGANIZATION OF THE NERVOUS SYSTEM
Table 6: Structure and function of components of the PNS
COMPONENT STRUCTURE FUNCTION
specialized nerve endings (dendrites) sense pain, touch, pressure,
temperature skin, skeletal mus-
cle, tendons and visceral organs
Sensory receptors
sense organs (sensory neurons and associated vision, hearing, taste, smell,
cells) equilibrium
bundle of nerve axons
Nerves
i. mostly mixed sensory and motor fibers; but
some are purely sensory and purely motor
Cranial
ii. some also serve the parasympathetic division conduction of electrical signals
of the autonomic nervous system to and from CNS/PNS
i. mixed sensory and motor fibers; each nerve
is a fusion of the dorsal and ventral root
Spinal
ii. 31 pairs of spinal nerves emerge form the
spinal cord
bundles of sensory neuron cell bodies transmission of signals
Ganglia
bundles of sensory neuron cell bodies adjacent transmission of sensory infor-
Dorsal root
to the spinal cord mation to the CNS
bundles of motor neuron cell bodies of nerve maintains basal heart and respi-
Parasympa- fibers of the parasympathetic division of the au- ratory rates; conserves body en-
tonomic nervous system ergy
thetic
found adjacent to organ
bundles of motor neuron cell bodies of nerve response to emergency situa-
fibers of the sympathetic division of the auto- tions: responsible for dilated
nomic nervous system pupils, ↑ heart and respiratory
rates, ↑ blood pressure, bron-
Sympathetic
found adjacent to the spinal cord chio-dilation, ↑ blood glucose
levels
temperature control
control of muscle contraction
types of synapses between motor neuron and
Motor endings
target cell
forms neuromuscular junction = synapse be-
Skeletal
tween motor neuron and motor endplate of
muscle control muscle contraction and
skeletal muscle fiber
innervations relaxation
forms varicosities = synapse between motor
Visceral
neuron and visceral muscle (heart, gut) or
muscle and
control muscle contraction or
glands
gland
gland secretion
innervations
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