The Nervous System
The Haitian Zombie
http://www.youtube.com/watch?v=cXcjioLLvRQ
The Function of the Nervous
System

Major control and communication system
of the body

What other body systems communicate
with the nervous system?
• Works with the
muscular system
• Works with the
endocrine system
•Works with the
circulatory system
•Works with the
integumentary
system
•Works with the digestive system
There’s more…
Urinary system
 Skeletal system
 Respiratory system
 Reproductive system
 Immune system

Functions of the Nervous System

Sensory Input
◦ Gathering information by sensing stimuli

Integration
◦ Processes and interprets that information

Motor Output
◦ Response to the stimulus
◦ May activate muscles or glands
Organization of the Nervous
System

Central Nervous System
◦ Brain
◦ Spinal Cord

Peripheral Nervous System
◦ Nerves that connect the brain and spinal cord
to the rest of the body
Breakdown of the PNS

Sensory Division
◦ AKA: Afferent Division
◦ Carry information to the CNS

Motor Division
◦ AKA: Efferent Division
◦ Carry impulses away from the CNS
Breakdown of the Motor (efferent)
Division of the PNS

Somatic Nervous System
◦ Voluntary
◦ Skeletal muslces

Autonomic Nervous System
◦ Involuntary
◦ Cardiac & smooth muscles; glands; hormones
Breakdown of the Autonomic
Nervous System

Sympathetic Division
◦ Fight or Flight

Parasympathetic Division
◦ Rest and Digest
DRAW IT OUT!
Let’s make a flow chart to organize the complicated
nervous system.
The Cells of the Nervous Systems

Supporting cells called neuroglia
◦ Support, insulate, & protect neurons
◦ CNS & PNS have different “glia” or
supporting cells
◦ CANNOT transmit nerve impulses

Nerve cells called neurons
◦ Same for the CNS and PNS
Neuroglia of the CNS

Astrocytes
◦ Form a barrier
between neurons and
the blood capillaries
◦ Brace the neurons to
the blood supply
◦ Control the chemical
environment of the
brain

Microglia
◦ Spiderlike phagocytes
◦ Dispose of bacteria,
dead cells, and other
debris
Neuroglia of the CNS

Ependymal cells
◦ Ciliated cells
◦ Line the cavities of the
brain and spinal cord
◦ Circulate the
cerebrospinal fluid

Oligodendrocytes
◦ Wrap their extensions
tightly around nerve
fibers
◦ Form insulation
around neurons called
myelin sheaths
Neuroglia of the PNS

Satellite Cells
◦ Protect the neuron
cell bodies
◦ Provide cushion

Schwann Cells
◦ Form insulation
around the neurons
(myelin sheaths)
◦ Increases the speed of
nerve impulses!
Neurons = Nerve Cells
Highly specialized cells that transmit
messages in the form of electrical
impulses
 Every neuron has:

1. Cell Body
2. Dendrites
3. Axon
Neurons

Cell Body
◦ Metabolic center of
the cell
◦ Contains cell
organelles, except
centrioles
◦ Neurofibrils (cellular
filaments) and the
rough endoplasmic
reticulum called Nissl
Substance give the cell
its shape

Processes
(Extensions)
◦ Dendrites
 Can have hundreds of
branching dendrites
◦ Axons
 Only ONE axon
protruding from the cell
body,
 BUT axon can branch
 Can have many axon
terminals
Neuron

Dendrites
◦ Conduct impulses
toward the cell body

Axon
◦ Conduct impulses
away from the cell
body
◦ Axon terminals
contain hundreds of
tiny vesicles containing
neurotransmitters
Synapse
Junction where the axon terminal of the
PRESYNAPTIC neuron meets the
dendrites of the POSTSYNAPTIC neuron
 The two neurons don’t actually touch

◦ Synaptic Cleft- gap between adjacent neurons
Schwann Cells
Envelopes and rotates around an axon
 Most of the cell cytoplasm is toward the outside of
the cell
◦ Neurilemma
 Tight coil of plasma membrane closest to the axon

◦ Myelin Sheath

Nodes of Ranvier
◦ Gaps in the myelin
sheath along the
axon
Neuron Cell Body Location

Most are found in the CNS
◦ Nuclei- clusters of cell bodies in the CNS
◦ Tracts- bundles of nerve fibers running
through the CNS

Ganglia- collections of cell bodies in the
PNS
◦ Nerves- bundles of nerve fibers running
through the PNS
Neuron Classification

Sensory Neurons
◦ Carry impulses from sensory receptors TO
the CNS
◦ AKA Afferent Neurons
◦ Cell body is found in ganglion outside the
CNS
◦ What are Sensory Receptors?
 Found in cutaneous sense organs
 Sense touch, pressure, pain, temperature
 Proprioceptors detect stretch or tension in skeletal
muscles, their tendons, and joints
Neuron Classification

Motor Neuron
◦ Carries impulses from the CNS to the body
◦ AKA Efferent Neuron
◦ Cell body of the neuron is found in the CNS
Neuron Classification

Interneurons or Association Neurons
◦ Small neuron that is always located in the
CNS whose job is to connect the sensory and
motor neurons to complete the pathway
Structural Classification of Neurons
Based on the number of processes
extending from the cell body of the
neuron
 3 Types:

◦ Multipolar neuron- many extensions from the
cell body
◦ Bipolar neuron- one axon and one dedrite
◦ Unipolar neuron- one short single process
leaving the cell body
Structural Classification of Neurons
What do neurons do?

Irritability- ability to
respond to a stimuli
and convert it into a
nerve impulse

Conductivity- ability
to transmit an
impulse to other
neurons, muscles, or
glands
Nerve Impulse Video

http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter14/animation__the_nerve_impuls
e.html
Nerve Impulse

Membrane of a
resting (inactive)
neuron is polarized
◦ Fewer positive ions
inside the cell than
outside
◦ Major + ions that are
in the cell are K+
◦ Major + ions outside
the cell are Na+
Voltmeter = -70 mV
Nerve Impulse


When stimuli (light,
sound, touch, or
neurotransmitters
released from another
neuron) excite a neuron,
sodium channels open in
the membrane allowing
an inward rush of Na+
Depolarization- change
in polarity of the
membrane
◦ Locally, the inside is more
+ and the outside is less +
All or none response: Only if the stimulus is
strong enough and the Na+ influx is great enough,
will the neuron transmit an impulse (message)
Nerve Impulse
If signal is strong enough, an
action potential (nerve
impulse) is generated
 Action potential propagates
over the entire axon
 K+ ions rush out of the
neuron after Na+ rush in,
repolarizing the membrane

◦ Restores electrical conditions
to the resting state (more - on
the inside)

Sodium-Potassium pump
then restore the neuron to
the initial concentrations of
Na+ and K+
5 Step Nerve Impulse
1.
2.
3.
4.
5.
Resting membrane potential is more – inside
the cell than outside with more K+ inside the
cell and more Na+ outside the cell
Stimulus opens Na+ channels, allowing influx of
Na+ in cell initiating local depolarization
Generates action potential which travels down
the axon
Repolarization by K+ channels allowing K+ to
leave the cell, making the inside of the cell more
- than the outside
Na+/K+ pump restores ion concentrations to
more K+ in cell and more Na+ outside of the
cell
Nerve Impulse
What happens when the action
potential reaches the axon
terminals?
Ca2+ ions rush into the axon terminal of the
presynaptic neuron, causing tiny vesicles
containing neurotransmitters to be released
into the synaptic cleft
 Neurotransmitters then bind to the
receptors on the dendrites of the
postsynaptic neuron
 If enough neurotransmitters bind to the
dendrites, an action potential will result

Electrochemical Event
ACT IT OUT!
http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter14/animation__the_nerve_impuls
e.html
 Represent the membrane, Na+ and K+
ions, Na+ and K+ channels, Na/K pump

How does myelin sheath increase
the speed of a nerve impulse?

Saltatory conduction

http://www.youtube.com/watch?v=mOgHC5G
8LuI
Multiple Sclerosis (MS)
Antibodies specific
for protein in myelin
sheath
 Damaged myelin
forms scar tissue
forming hard plaque
or sclerosis
 Neurons are shortcircuited and
damaged

Myelination
Begins the 14th week
of development
 Continues into
adolescense
 Deficiencies in
nutrients can impair
myelination

Demyelination occurs
with age
Sodium Channel Blockers

If you block a sodium
channel and the
sodium cannot get
into the neuron
cell… what will
happen?






Does not allow
neurons to transmit
nerve impulses
Paralysis due to loss
of nerve function
TTX (tetrodotoxin)
Anesthetics
Treat cardiac
arythmias
Anti-epileptic drugs
Neurotoxins
TTX (tetrodotoxin)
 Too large to pass through the blood brain
barrier so often does not affect mental
function
 Binds to Na+ channels, preventing Na+
from generating an action potential
 Paralysis, slowed heart rate, slowed
respiration

Potassium Channel Blockers
Prolong
depolarization
 Use for heart
problems
