An introductory lecture on the organization of the nervous system and its components.

1. ORGANIZATION OF
THE NERVOUS
SYSTEM
Csilla Egri, KIN 306 Spring 2012
Gunther Von Hagen’s Body Worlds: The chess player

2. 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

3. Divisions of the Nervous
System
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/8679.jpg
Enteric nervous system
3

4. Divisions of the Nervous
System
http://faculty.washington.edu/chudler/nsdivide.html
4

5. CNS: Spinal cord
5
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

6. CNS: Spinal cord input/output
Figure 4-8, B&L
6
Afferent fibre
Efferent fibre
*
* Part of the peripheral nervous system
*
*
*
*

7. CNS: Spinal cord tracts
7
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
1
2
3

8. Divisions of the Nervous
System
http://faculty.washington.edu/chudler/nsdivide.html
8

9. 9
CNS: Brain, three basic units
Illustrative guide to the
basic units of the brain:
Forebrain/midbrain/
hindbrain

10. 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

11. 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

12. Telencephalon: Cerebral Cortex
12
 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

13. Telencephalon: Cerebral Cortex
Silverthorn Figure 9-15
13
Central
Sulcus
 Organized into functional lobes:

14. 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

15. Telencephalon: Basal Ganglia
15
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

16. 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

17.  includes the thalamus and
hypothalamus
 Telencephalon + diencephalon =
forebrain
Forebrain part 2: Diencephalon
17
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

18. 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: Mesencephalon
18

19. 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

20. 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

21. Divisions of the Nervous
System
http://faculty.washington.edu/chudler/nsdivide.html
21

22. 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

23. Protection: Blood Brain Barrier
23
 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

24. Protection: Blood Brain Barrier
24
 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

25. Protection: Cerebrospinal Fluid
25
 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

26. Divisions of the Nervous
System26

27. Peripheral Nervous System
27
Autonomic Somatic
Parasympathet
ic
Sympathetic Sensory Motor
Rest and
digest
Flight or fight Afferent
neurons
carrying
information from
Efferent neurons
carrying
information from
the CNS to
 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

28. 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

29. Classifications of Neurons
29
 neurons can be classified by the following
characteristics:
B&B Figure 10-3

30. Classifications of Neurons
30
B&B Figure 10-3

31. Classifications of Neurons
31
B&B Figure 10-3

32. 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. 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