1. The Nervous System
Mr. Hunter
01/07/2013
Kennedy High School

2. Mr. Hunter
Anatomy and Physiology
01/15/13
• Objective(s)
• SWBAT
• List the major divisions of the Nervous System
• Describe the action of a nerve impulse / Action Potential
• Describe the structure and function of synapses.
• Review Concepts via Practice Problems
• Bell Ringer: List three possible stimuli that could generate
a nerve impulse.

3. • There are two principal divisions of the
nervous system.
Organs and Divisions
• The Central Nervous System (CNS)
• The Peripheral Nervous System (PNS)
• The CNS consists of the brain and the
spinal cord.
• The PNS consists of nerves which
extend from the spinal cord to the
peripheral parts of the body.
• A subdivision of the PNS is the
Autonomic Nervous System (ANS).
• ANS consists of structures that regulate
the body’s involuntary or automatic
functions ex. heart rate, smooth muscle
contractions, secretion of
hormones, enzymes, etc.

4. • The two types of cells found in the
Organs and Divisions Nervous System (NS) are neurons
and glia cells.
• Neurons conduct nerve impulses.
• Glia cells support neurons.
• Neuron consists of three main parts:
• Cell body
• Dendrites
• Axon

5. Cells of the Nervous • The main part of the neuron is the
System cell body.
• Branching projections are called
dendrites. Dendrites transmit
information to the neuronal cell
body.
• Axons are the long processes that
transmit information away from the
cell body.
• There are three types of neurons
named based on the direction in
which they transmit information.
• Sensory (afferent)
• Motor (efferent)
• Interneuron

6. Cells of the Nervous • Sensory neurons (afferent) transmit
System information to the CNS from all
regions of the body.
• Motor neurons (efferent) transmit
information in the opposite
direction- away from the CNS.
• They conduct impulses to muscle
and glandular epithelial tissue.
• Interneurons conduct impulses from
sensory neurons to motor neurons.
• They connect to form central
networks of nerve fibers and are
called central or connecting neurons.

7. Cells of the Nervous
• The axon is covered by myelin.
System • This is a white, fatty substance formed
by specialized cells called schwann cells
that wrap around axons outside the
CNS. The outer membrane of this type
of cell is called the neurilemma-plays
regenerative part in damaged axons.
• Myelin allows for saltatory conduction
of electrical transmissions.
• Nodes of Ranvier are interrupted
segments between schwann cells.
• Glia (glue) cells – one function is to hold
functioning neurons together and
protect them. They also coordinate the
functions of the NS.
• Glioma- common type of brain tumor.

8. • Glia vary in size and shape.
Types of glial cells • Astrocytes: resemble stars. Their
threadlike branches attach to neurons
and to small blood vessels holding both
structures together.
• Astrocyte branches form a two-layer
structure called the blood brain barrier
(BBB).
• BBB separates blood tissue and nervous
tissue. Protects brain from harmful
chemicals that might be found in the
blood.
• Microglia: smaller than astrocytes. They
remain stationary until brain tissue
becomes injured. They act as microbe
scavengers in the brain via phagocytosis.

9. • Oligodendrocytes hold nerve fibers
Types of glial cells together and they also produce
myelin sheaths around multiple
nerve cell axons in the CNS.
• Schwann cells are glia cells that
produce myelin sheaths on single
axons within the PNS.
• Assignment 01/07/13
• Pg. 195 # 1-4 Quick Check.

10. • A nerve can be defined as a group of
peripheral nerve fibers (axons) bundled
Nerves and Tracts
together.
• The fibers have a myelin sheath provided by
schwann cells.
• Because myelin is white, peripheral nerve
fibers often look white.
• Bundles of axons in the CNS are called
tracts. They are also myelinated and form
the white matter of the brain and spinal
cord.
• Brain and spinal cord tissue composed of
unmyelinated axons dendrites and cell
bodies is called gray matter due to its
appearance.

11. • Each axon in a nerve is surrounded
Nerves and Tracts by a thin wrapping of fibrous
connective tissue called
endoneurium.
• Groups of these wrapped axons are
called fascicles.
• Each fascicle is surrounded by a
thin, fibrous perineurium.
• A tough, fibrous sheath called the
epineurium covers the entire nerve.

12. • Only neurons can provide the rapid
Reflex Arcs communication between cells that is
necessary for sustaining life.
• Hormonal messages travel much
more slowly than neuronal
transmissions within the body. They
have to circulate via the blood
stream.
• Nerve impulses are also called action
potentials. The routes traveled by
nerve impulses are called neuron
pathways.
• A basic type of neuron pathway is
called a reflex arc.

13. • A simple kind of reflex arc consists of
Reflex Arcs two types of neurons: sensory
neurons and motor neurons.
• Three neuron arcs consists of:
sensory neurons, interneurons and
motor neurons.
• Reflex arcs allow impulse conduction
in only one direction.
• Impulse conduction starts mainly at
receptors.
• Receptors are the beginnings of
dendrites of sensory neurons. They
are located some distance away
from the spinal cord. (tendons,skin
mucous membranes etc.)

14. • The knee-jerk reflex is the simplest example
of a two neuron reflex arc.
Reflex Arcs • As a result of a tap on the patellar ligament
causes the quadriceps muscle to contract
via a neuronal pathway.
1. A nerve impulse is generated by stretch
receptors within the quadriceps.
2. It travels along the sensory neuron’s
dendrites to the cell body located in the
dorsal root ganglion (group of nerve cell
bodies located in the PNS)
3. The axon from the sensory neuron travels
from the cell body of the dorsal root
ganglion and ends near the dendrites of
another neuron located in the gray matter
of the spinal cord.
4. The nerve impulse stops at the synapse
(space that separates axon and dendrites)
5. Chemical signals are sent across the
synapse and connect with other dendrites

15. • and cell bodies located in the CNS gray
matter and axons outside the gray matter.
Reflex Arcs 6. The motor neuron synapses with an
effector which are muscles or glands – they
put the nerve signals” into effect.”
• The response to the impulse conduction
over a reflex arc is called a reflex.
• Complex reflexes may involve the actions
of three neurons.
• The end of the sensory neuron will synapse
with the dendrites of an interneuron
• located within the gray matter of the spinal
cord. The axon of that interneuron will
then synapse with the dendrites and cell
body of a motor neuron within the spinal
cord. The axons of the motor neuron lie
outside the spinal cord and will exit via the
anterior root of the spinal nerve and
terminate in the muscle(effector)

16. Withdrawl Reflex
• Interneurons are located
within the gray matter of
the brain or spinal cord.
•Three neuron reflex arcs
have two synapses.
•A Two-neuron refex arc
only has a sensory
neuron, a motor neuron
and one synapse between
them.

17. Nerve Impulses and the • Nerve impulse: self-propagating
Synapse wave of electrical disturbance that
travels along the surface of a
neuron’s plasma membrane.
• It is similar to a spark traveling along
a fuse.
• Nerve impulses have to be initiated
by a stimulus – a change in the
neuron’s environment. A stimulus
could possibly be on of the
following:
Environmental change(s)
• Pressure
• Temperature
• Chemical changes

18. Nerve Impulses and the • Due to the distribution of Na +
Synapse (sodium) and K+ (potassium) ions,
the resting neuron has a slight
positive charge on the outside of the
membrane and a slight negative
charge on the inside.
• This separation of electrical charges
is called polarization
• There is normally an excess of
sodium on the outside of the cell
than inside.
• When a portion of the membrane is
stimulated, Na+ ions will enter the
cell causing that region of the cell to
become temporarily positive –
outside becomes negative.

19. • This process is called depolarization.
Nerve Impulses and the
• This section of the membrane immediately
Synapse
recovers during a process of repolarization.
• However, depolarization has already
stimulated Na+ channels to open in the next
portion of the membrane. The Action
Potential continues along the axon in one
direction jumping from node to node until it
reaches the synaptic terminal of the axon.

20. Nerve Impulses and the
Synapse
• Transmission of nerve
signals from one neuron to
the next occurs across the
synapse.
• Impulses travel from the
presynaptic neuron to the
postsynaptic neuron.
•Impulses travel across the
synaptic cleft.
•Three structures that
make up a synapse:
•Synaptic knob
•Synaptic cleft
•Plasma membrane of
postsynaptic neuron

21. Nerve Impulses and the
Synapse
• synaptic knob – terminal
branch at the end of the
post synaptic neuron.
•Small vesicles contain
neurotransmitters.
•When a nerve impulse
arrives at the synaptic
knob, neurotransmitters
are released into the
synaptic cleft.
•The plasma membrane of
the postsynaptic neuron
contains receptors for the
neurotransmitter.

22. Nerve Impulses and the
Synapse
• The binding of the
neurotransmitter with the
receptors initiates an
impulse in the postsynaptic
neuron opening Na+
channels in the cell.
Therefore, the nerve signal
is transmitted to the
postsynaptic neuron.
•The neurotransmitter can
be :
•Taken back up by the
synaptic knobs
•Metabolized into inactive
chemicals

23. Neurotransmitters
•At least 30 different substances
have been identified as
neurotransmitters.
•Specific neurotransmitters are
localized in discrete groups of
neurons.
•Acetylcholine is released at some
synapses in the spinal cords and
at neuromuscular junctions.
•Norepinephrine, Dopamine and
Serotonin are grouped into
compounds called catecholamines
– involved in sleep motor
function, mood and pleasure
recognition.

24. Neurotransmitters
• Endorphins and Enkephalins are
released at spinal cord and
various brain synapses in the pain
conduction pathway.
•They inhibit the conduction of
pain impulses.
•Nitrous Oxide – neurotransmitter
that diffuses directly across the
plasma membrane instead of
being transported by vesicles.