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Body Systems
Nervous System
Nervous System Functions
Sensory input – sense organs, receptors,
– afferent neurons
Integration – Central Nervous
– interneurons
Motor output – glands, muscles
– efferent neurons
The Neuron
 Consists
–Cell body
Label your diagram
The Nerve Impulse
Begins at dendrites, passes through to the
cell body and then through the axon,
terminating at the terminal branches
before the synapse.
The Nerve Impulse
Occurs as a result of both electrical and
chemical changes across the membrane of
the neuron.
Electrochemical nature of
Due to the presence of ions, a positive
electrical charge is present outside the
membrane. (excess of sodium ions)
A negative charge is present inside the
membrane. (mostly potassium ions)
Since both sodium (outside) and potassium
(inside) are both positive ions, how can one
side of the membrane be + and the other -?
Although diffusion
of ions will occur,
the membrane
actively pumps
 What do you call
the membrane
structures through
which the ions will
be pumped
Resting potential- unstimulated (-70 millivolts)
Action potential – channels open, Na+ ions
rush in, depolarization occurs.
What is the
Like a domino effect, once stimulated the
nerve impulse is an all or nothing response.
Repolarization – In response to the inflow of
Na+, K+ rushes out of the cell, followed by
closing of the Na+ channel gates.
Interpret the graph at
stage 4 with respect to
the events that are
Hyperpolarization – More K+ outflows than
is necessary, thus undershooting threshold,
more than repolarizing the membrane.
Refractory period – Although repolarized,
the neuron has a period when it is unable to
What has to occur to re-establish the
original conditions so that a neuron can fire
After the membrane
 Once
the impulse reaches the end of
the axon a different set of events has
to occur to allow the impulse to
continue to another neuron.
 This requires the crossing of the
Most transmissions across a
synapse are of a chemical
Synapse Summary
The gated channels for Ca2+ respond to
the action potential by opening up.
 In turn, the Ca2+ enters the cell and
triggers the release of neurotransmitters.
 The neurotransmitter crosses the synapse
and binds with protein receptors on the
next neuron membrane.
 Neurotransmitters degrade or are recycled
shortly after so as not to cause continuous
 Acetylcholine
– stimulates muscles to
contract at neuromuscular junctions.
At other junctions, acts as an
 Epinephrine, norepinephrine,
dopamine, serotonin (I) – all are
amino acid derivatives. Work
between neurons. First three may be
excitatory or inhibitory.
 GABA – inhibitory, within the brain.
Saltatory Conduction
 Neurons
with a myelin sheath
(Schwann cells) allow a much faster
conduction of impulses because the
impulse “jumps” between the gaps
(nodes of Ranvier) of the cells rather
than traveling along the whole length
of the axon.
The Bigger Picture
 Billions
upon billions of neurons and
other cells make up your nervous
system. Appearance can be
somewhat modified based on
location and function.
 CNS – brain, spinal cord
 Peripheral – all other nerves
– Somatic – sensory, motor
– Autonomic – sympathetic,
You are always on your mind!
This diagram illustrates the relative amount of brain mass
devoted to some important parts of the body. Why do you
think some areas require much more than others?