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

Divisions of the Nervous

System

http://faculty.washington.edu/chudler/nsdivide.html

4

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

Divisions of the Nervous

System

http://faculty.washington.edu/chudler/nsdivide.html

8

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

Divisions of the Nervous

System

http://faculty.washington.edu/chudler/nsdivide.html

21

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

Divisions of the Nervous

System26

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

Classifications of Neurons30

B&B Figure 10-3

Classifications of Neurons31

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