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ORGANIZATION OF
THE NERVOUS
SYSTEM
Csilla Egri, KIN 306 Spring 2012
Gunther Von Hagen’s Body Worlds: The chess player
Outline
Introduction to the structure/function of central
nervous system (CNS)
Protection of CNS
Introduction to peripheral nervous system
(covered in more detail later)
Microanatomy: neurons
2
Divisions of the Nervous
System
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/8679.jpg
Enteric nervous system
3
CNS: Spinal cord5
Functions
1. Conducts afferent
stimuli from
sensory receptors
to the brain
2. Conducts efferent
stimuli from brain
to
effectors/muscles
3. Site of reflex
integration and
houses certain
central pattern
generators
CNS: Spinal cord input/output
Figure 4-8, B&L
6
Afferent fibre
Efferent fibre
*
* Part of the peripheral nervous system
*
*
*
*
CNS: Spinal cord tracts7
Silverthorn Figure 9-7
Tract: collection of axons that ascend/descend
spinal cord with a specific function
1. dorsal columns: ascending tracts that
transmits tactile and proprioceptive info
2. spinothalamic tract: ascending tract that
transmits info about pain, temp. and itch
3. lateral corticospinal tract: descending tract
that carries motor information to skeletal
muscle
1
2
3
9
CNS: Brain, three basic units
Illustrative guide to the
basic units of the brain:
Forebrain/midbrain/
hindbrain
CNS: Brain, five regions 10
http://www.ruf.rice.edu/~lngbrain/cglidden/middlelabnoline!!yes2use2.jpg
Regions grouped and named as they develop
in the embryo
Figure 10-6, B&B
Forebrain part 1:
Telencephalon11
Includes all of the cerebral cortex and the
internal nuclei such as the basal ganglia,
hippocampus, the olfactory bulb and the
amygdala
http://www.3icreative.com/wp-content/uploads/2011/03/telencephalon-limbic-
system-300x251.jpg
Telencephalon: Cerebral Cortex12
Outermost layer of the
cerebrum
Composed of 2-4mm of
gray matter
Up to 6 horizontal
layers with unique
neuronal projections
and functions
Figure 17-6 Kandel
Telencephalon: Cerebral Cortex
Silverthorn Figure 9-15
13
Central
Sulcus
Organized into functional lobes:
Cerebral Cortex: Broadman’s
Areas
Organization based on
physiological function
Important areas we will visit
later:
Area 4 = primary motor
cortex
Area 3,1,2 = primary
somatosensory cortex
Area 17 = primary visual
cortex
Area 41, 42 = primary
auditory cortex
14
Telencephalon: Basal Ganglia15
Functions
1. Motor control;
connections with motor
cortex and thalamus
2. Regulate initiation and
termination of
movements
3. Some role in attention,
memory and planning
Telencephalon: Amygdala &
Hippocampus16
Amygdala functions
1. Part of the limbic system
2. Associated with pleasure, fear,
addiction
3. Important in forming and storing
memories of emotional events
Hippocampus functions
1. Part of the limbic system
2. Important in formation of
memories, including spatial and
navigation memories
3. Damage to hippocampus can
result in anterograde amnesia
includes the thalamus and
hypothalamus
Telencephalon + diencephalon =
forebrain
Forebrain part 2: Diencephalon17
Thalamus functions
1. Main integrating centre for
sensory information
2. Receives input from basal
ganglia and cerebellum
Hypothalamus functions
1. Main control centre for the
autonomic nervous system
2. Close association with pituitary
gland, important functions in the
endocrine system (hormone
release)
3. Contains nuclei important in
regulation of circadian clock,
hunger, thirst, heart rate, and
temperature regulation
Two divisions:
a) tectum
superior colliculi
contain nuclei for visual
reflexes
inferior colliculi
contain nuclei for auditory
reflexes
b) tegmentum
substantia nigra
Release dopamine to basal
ganglia
red nucleus
Connections with cerebellum
for coordination of movement
Midbrain: Mesencephalon18
Hinbrain: Myelencephalon
Two divisions:
a) myelencephalon
medulla oblongata
Contains ascending
and descending
sensory and motor
tracts connecting the
cerebrum to the spinal
cord
Most spinal cord tracts
cross over in the
pyramids
Contains nuclei that
regulate breathing,
blood pressure,
vomiting
19
Hinbrain: Metencephalon
b) metencephalon
pons
Contains pneumotaxic centre
which fine tunes breathing rate
Relays information between
cerebellum and cerebrum
cerebellum
Feedback center for execution
of motor movements
Controls posture and balance
reticular formation
Nuclei diffusely located through
the brainstem*
Regulates wakefulness and
muscle tone
20
*the term “brainstem” refers to the medulla oblongata, pons, and the midbrain
CNS Protection
Against physical
damage
Against chemical
damage
Both
Skull/vertebrae
-hard external
protection
Blood brain barrier
- Tight junctions
form physical
barrier across
capillaries
Cerebrospinal
fluid
-Shock absorption
-Stable ionic
composition
Meninges
-Pia mater
(innermost layer)
-Arachnoid mater
-Dura mater
22
Protection: Blood Brain Barrier23
CNS blood vessels prevent
paracellular diffusion of
macromolecules and ions
Capillary endothelial cells in the
brain are connected by tight
junctions to form a physical
barrier, with contribution from
astrocytes, pericytes & neurons
Specialized transporters required
for movement of most molecules
Small or lipophilic molecules and
gases can diffuse more easily
Caffeine, nicotine, heroin, CO2
Protection: Blood Brain Barrier24
Only a few, small regions of the brain
are without a blood brain barrier
Creates problems for delivering
therapeutic drugs to the brain
Methods for drug targeting include:
Manufacturing low molecular
weight drugs
Tagging the drug with ligand to
assist in receptor mediated
transcellular transport
Injecting drug directly into brain
matter
Protection: Cerebrospinal Fluid25
Fluid synthesized by the
choroid plexuses in each of
the four ventricles
Fills ventricles and
subarachnoid space
Less protein than
plasma with similar
electrolyte composition
(but more Cl-, less Ca2+
and K+)
Acts as a shock absorber
during impact
Removes waste, regulates
pH and maintains ionic
homeostasis of neuronal
microenvironment
Peripheral Nervous System27
Autonomic Somatic
Parasympathet
ic
Sympathetic Sensory Motor
Rest and
digest
Flight or fight Afferent
neurons
carrying
information from
sensory
Efferent neurons
carrying
information from
the CNS to
muscles
all parts of nervous system outside the dura mater
includes sensory receptors, peripheral portions of
spinal and cranial nerves (including those of the
ANS), and sensory ganglia
sensory ganglia are aggregates of nerve cells located
outside the CNS
Microanatomy: Neurons and Glial
cells28
Neurons
Convey electrical signals within
CNS and PNS
Glial cells
regulate neuron environment
& form the myelin sheath
around neurons
a) Astrocytes: regulate
neuron environment
b) Oligodendrocytes: form
myelin sheath in CNS
c) Schwann cells: form myelin
sheath in PNS
d) Ependymal cells: line the
ventricles, synthesize CSF
e) Microglia: monocytes of the
brain
Classifications of Neurons29
neurons can be classified by the following
characteristics:
B&B Figure 10-3
Objectives
After this lecture you should be able to:
List the types of neurons (afferent, efferent, sensory,
motor) contained in: dorsal root and ventral root
ganglion, ascending and descending tracts of the spinal
cord
List a major function of: frontal, parietal, temporal and
occipital lobes, reticular formation, medulla, pons,
midbrain, cerebellum, thalamus, hypothalamus, basal
ganglia, limbic system
Describe the modes of protection of the CNS
List the functions of various neurons and their respective
neuroglial cells
32
33
1. The __________________ is the main control centre
for regulating functions of the autonomic nervous
system, secretes a variety of hormones, and contains
nuclei important for regulation of hunger and
temperature regulation.
2. What kind of protection is offered by the cerebrospinal
fluid?
3. ____________________ are referred to as the
monocytes of the brain and become phagocytic cells
when activated in order to removed debris.
Test your knowledge