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•The nervous system is a
network of cells that sense and
respond to stimuli in ways that
maintain homeostasis.
Dendrites
• The nervous system is
composed of:
• Neurons
• Neuroglial cells (also
known as neuroglia, glia,
and glial cells)
•Blood vessels
•Connective tissue
Cell body
Nuclei of
neuroglia
Axon
© Ed Reschke
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The function of the nervous system is to
coordinate all body systems! This is
accomplished by the transmission of signals
(electrochemical) from body parts to the
brain and back to the body parts.
•The two main anatomical divisions:
•Central Nervous System (CNS)
• Brain and spinal cord
•Peripheral Nervous System (PNS)
• All neural tissue outside CNS
• Afferent division (sensory input)
• Efferent division (motor output)
• Somatic nervous system
• Autonomic nervous system
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• Sensory Input Division (PNS)
• Receives sensory stimuli from sensory receptors (located at ends
of peripheral neurons)
• Once stimulated, receptors transmit impulse to
• Integrative Function (CNS)
• Involves interpretation of incoming sensory impulse in interneurons
• Motor impulse begins…
• Motor Division (PNS)
• Carries information to effectors (muscles and glands)
• Involves the response of a body part reacting to stimuli
**Divisions of the Motor Division**
• Somatic – carries information to skeletal muscle
• Autonomic – carries information to smooth muscle,
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cardiac muscle, and glands
Central Nervous System
(brain and spinal cord)
Brain
Peripheral Nervous System
(cranial and spinal nerves)
Cranial
nerves
Sensory division
Spinal
cord
Sensory receptors
Spinal
nerves
Motor division
(a)
(b)
Somatic
Nervous
System
Skeletal muscle
Autonomic
Nervous
System
Smooth muscle
Cardiac muscle
Glands
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
Input: sensory = sensory input
 Receptors monitor changes
 Changes called “stimuli” (sing., stimulus)
 Information sent by “afferent” nerves

Integration
 Information processed
 Decision made about what should be done

Output: motor = motor output
 Effector organs (muscles or glands) activated
 Effected by “efferent” nerves
Remember the difference between the English words
“affect” and “effect”
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
“The music affected her deeply.”
(Something is experienced: sensory)

“His protests had no effect.”
(Something is done or not done: motor)
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


Follow instructions listed to complete the
brain web quest online.
Place worksheet on pg. 105 of notebook.
Color-code AND label brain on pg. 104 of
notebook.
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• Structural & functional unit of the nervous system;
• Cells that transmit nerve impulses
• Vary in length and size of their axons and dendrites
• AKA nerve cell
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• Dendrite: branching filaments that conduct nerve impulses towards the
cell body
• Cell body: central part of the nerve cell containing the nucleus
• Axon: the long thin process that carries nerve impulses away from cell
body
**Nerve: bundle of axons
• Myelin sheath: covering of fatty material which is an insulating
membrane that surrounds the axon
• Nodes of Ranvier: gaps between myelin that allow impulses to move
quickly up the axon
• Axon terminal: structure at the end of an axon that produces
neurotransmitters to transmit the nerve impulses across the synapse
• Synapse: connection between adjacent neurons
**Neurotransmitter: chemical secreted into the gap between neurons at
a synapse
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Chromatophilic
substance
(Nissl bodies)
Dendrites
Cell body
Nucleus
Nucleolus
Axonal
hillock
Synaptic knob of
axon terminal
Impulse
Neurofibrils
Axon
Nodes of Ranvier
Myelin (cut)
Axon
Schwann
cell
Nucleus of
Schwann cell
Portion of a
collateral
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• White Matter
• Contains myelinated
axons
• Considered fiber tracts
• Gray Matter
• Contains unmyelinated
structures
• Cell bodies, dendrites
Dendrite
Unmyelinated
region of axon
Myelinated region of axon
Node of Ranvier
Axon
Neuron
Neuron
cell body nucleus
Enveloping
Schwann cell
Schwann
cell nucleus
Longitudinal
groove
Unmyelinated
axon
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• Sensory Neurons (PNS)
• Afferent neurons
• Carry impulse from sense receptor to CNS
Central nervous system
Peripheral nervous system
• unipolar/bipolar
Cell body
• Skin & sense organs
Dendrites
Sensory
• Interneurons (CNS)
Cell body
receptor
Axon
Axon
• Link sensory neurons to
(central process)
(peripheral process)
motor neurons
Sensory (afferent) neuron
Interneurons
• Aka association/relay
neurons
Motor (efferent) neuron
Axon
• Multipolar
• Motor Neurons (PNS)
• efferent neurons; multipolar
• Carry impulses away from CNS to effectors
• Effectors = muscles & glands
Effector
(muscle or gland)
Axon
Axon
terminal
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Due to structural differences, neurons can be classified into three
(3) major groups:
• Bipolar neurons – two extensions; one fused dendrite leads
toward cell body and one axon leads away from cell body
ex. Specialized parts of eyes, nose, & ears (sensory)
• Unipolar neurons – one process from cell body; forms central
& peripheral process; only distal ends are dendrites
ex. Cell bodies in ganglia outside brain & spinal cord
• Multipolar neurons – many extensions; many dendrites lead
toward cell body and one axon leads away from cell body
ex. Most common neuron (99%)
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Neurogila are accessory cells of the nervous system form
supporting network for neurons (“nerve glue”)
1) Schwann Cells
• Equivalent to oligodendrocytes
•Produce myelin found on peripheral myelinated neurons
• Speed up neurotransmission
2) Satellite Cells
• Support clusters of neuron cell bodies (ganglia)
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These cells provide the bulk of brain & spinal cord tissue:
1) Microglial cells
• looks like “spider”
• Phagocytic cell
3) Oligodendrocytes
• looks like “eyeball”
• produces myelin
2) Astrocytes
4) Ependymal cells
• star shaped
• epithelial-like layer
• Scar tissue
• Ciliated
•Induce synapse formation
• Line fluid filled cavities in
• Connect neurons to blood vessels brain and spinal cord
• Part of Blood Brain Barrier
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Fluid-filled cavity
of the brain or
spinal cord
Neuron
Ependymal
cell
Oligodendrocyte
Astrocyte
Microglial cell
Axon
Capillary
Myelin
sheath (cut)
Node of
Ranvier
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Cell body injury results in death of neuron, but axons my regenerate.
Skeletal
muscle fiber
Motor neuron
cell body
Changes
over time
Site of injury
Schwann cells
Axon
(a)
Distal portion of
axon degenerates
(b)
Proximal end of injured axon
regenerates into tube of sheath cells
(c)
Schwann cells
degenerate
(d)
Schwann cells
proliferate
(e)
Former connection
reestablished
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Neurons exhibit both excitability and conductivity. The
transmission of a nerve impulse along a neuron from one end to
the other occurs as a result of electrical changes across the
membrane of the neuron.
The membrane of an unstimulated neuron is polarized—that is,
there is a difference in electrical charge between the outside and
inside of the membrane. The inside is negative with respect to the
outside.
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Polarization is established by maintaining an excess of
sodium ions (Na +) on the outside and an excess of
potassium ions (K +) on the inside. A certain amount of
Na + and K + is always leaking across the membrane through
leakage channels, but Na +/K + pumps in the membrane
actively restore the ions to the appropriate side.
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The main contribution to the resting membrane potential (a
polarized nerve) is the difference in permeability of the resting
membrane to potassium ions versus sodium ions. The resting
membrane is much more permeable to potassium ions than to
sodium ions resulting in slightly more net potassium ion diffusion
(from the inside of the neuron to the outside) than sodium ion
diffusion (from the outside of the neuron to the inside) causing the
slight difference in polarity right along the membrane of the axon.
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Other ions, such as large, negatively charged proteins and
nucleic acids, reside within the cell. It is these large,
negatively charged ions that contribute to the overall
negative charge on the inside of the cell membrane as
compared to the outside.
In addition to crossing the membrane through leakage
channels, ions may cross through gated channels. Gated
channels open in response to neurotransmitters, changes
in membrane potential, or other stimuli.
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1. Resting Potential: When a neuron is not conducting electrical
signals, it is said to be “resting”.
2. Depolarization: A stimulus triggers stimulus-gated Na+ channels
to open and allow inward Na+ diffusion. As the threshold
potential is reached, voltage-gated Na+ channels open. The
magnitude of action potential peaks when voltage-gated Na+
channels close.
3. Repolarization: Voltage-gated K+ channels open, allowing
outward diffusion of K+.
4. Hyperpolarization: Too many K+ rush out of the cell. After a
brief period of hyperpolarization, the resting potential is
restored by the sodium-potassium pump and the return of ion
channels to their resting state.
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If threshold potential is surpassed, the full peak of the
action potential is always reached.
If threshold potential is not surpassed, no action potential
will occur at all.
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http://highered.mheducation.com/sites/0072495855/student_view0/
chapter14/animation__the_nerve_impulse.html
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http://outreach.mcb.harvard.edu/animations/actionp
otential_short.swf
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• Nerve impulses pass from
neuron to neuron at synapses,
• These nerve impulses move
from a pre-synaptic neuron
(axon terminal) to a postsynaptic neuron (dendrite).
Note:
•two neurons do not touch
•There is a gap between them
= synaptic cleft
Synaptic
cleft
Impulse
Dendrites
Axon of
presynaptic
neuron
Axon hillock of
Postsynaptic neuron
Axon of
presynaptic
neuron
Impulse
Cell body of Impulse
postsynaptic
neuron
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Direction of
nerve impulse
• Neurotransmitters are
released when impulse
reaches synaptic knob
Axon
Ca+2
Synaptic knob
Synaptic
vesicles
Presynaptic neuron
Ca+2
Cell body or dendrite
of postsynaptic neuron
Mitochondrion
Ca+2
Synaptic
vesicle
Vesicle releasing
neurotransmitter
Axon
membrane
Neurotransmitter
Synaptic cleft
Polarized
membrane
Depolarized
membrane
(a)
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1= Presynaptic Neuron
2= Axon Terminal
3= Synaptic Knob
4= Mitochondria
5= Vesicles
6= Synaptic Cleft
7= Receptors
8= Postsynaptic Neuron
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1= Presynaptic Neuron
2= Exocytosis
3= Neurotransmitters
4= Synaptic Cleft
5= Postsynaptic Neuron
6=Postsynaptic Receptor
7= Endocytosis
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Neurotransmitters (NT) = chemical messengers
•At least 300 different NTs
•Some neurons produce/release only one, while others release many
•Most typical NT is Acetylcholine (Ach)
- released by all motor neurons
Other NTs include:
-monoamines (modified amino acids)
• widely distributed in brain
•play role in emotional behavior/ circadian rhythm
•present in some motor neurons of the ANS
•Ex. Epinephrine, norepinephrine, dopamine, serotonin,
histamine
-unmodified amino acids
• Ex. Glutamate, GABA
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• Neurotransmitters cross the synaptic cleft and react with
specific molecules called receptors in the postsynaptic neuron
membrane.
• Effects of neurotransmitters vary with their location in the
nervous system
• Some neurotransmitters may open ion channels (excitatory) and
others may close ion channels (inhibitory).
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http://highered.mheducation.com/sites/0072495855/student_
view0/chapter14/animation__transmission_across_a_synaps
e.html
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http://outreach.mcb.harvard.edu/animations/synaptic.swf
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