Download The Nervous System

The Nervous System
Homework
Objectives
 Identify the role of the nervous system.
 Recognize that the basic cellular unit of
the nervous system is the neuron.
 Distinguish between sensory and motor
neurons.
 Explain the roles of the brain, spinal
cord, and peripheral nerves.
The Nervous System
 Let’s see those hands: What is the
nervous system? What does it do?
Nervous System
 The nervous system mediates
communication among different parts of
the body, and mediates the body’s
interactions with the environment.
 The nervous system is one of two major
control and communication networks for
the body.
 What are some parts of the nervous system
that you know about?
Nervous System
 The nervous system includes brain,
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spinal cord, nerves, etc. We’re going to
focus today on its most basic unit, and
get up to those organs tomorrow.
 The cells that carry messages as part of
the nervous system are neurons. They
are the basic unit of the system.
 In order to understand how they work, you
need to know their basic anatomy.
Neurons
 A neuron is a one-
way
communication
system. Messages
are received by
one end, and
transmitted by the
other.
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Neurons
 The arrow indicates
an electrical
impulse. Neurons
work like a long
chain of dominoes.
 The dendrite is made
to fire an electrical
impulse when it’s hit
by a chemical.
 The impulse travels
down the axon…
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Neurons
 … The
impulse
reaches the end,
where it makes the
neuron release
chemicals into the
synapse.
 On the other end of
the synapse are the
dendrites of another
neuron.
 That electrical
impulse = an action
potential.
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Neurons
 All action potentials are the same,
there’s no actual information in the
action potential.
 But each neuron has its own function. So
the brain will be able to recognize, “if
neuron #15734793 fired an action potential,
that means that there was heat being
applied to that section of the skin.” In this
case, neuron #15734793 doesn’t fire if
there’s cold or pressure being applied.
Neurotransmission
 New vocab: Neurotransmitter: A
chemical used by one neuron to signal
another neuron.
 http://science.education.nih.gov/supple
ments/nih2/addiction/activities/lesson2_
neurotransmission.htm
Neurotransmission
 Important things to notice in order to
understand how a drug works:
 The two neurons aren’t touching each other,
there’s a space (synapse) between the end of one
and the beginning of the next.
 The dendrite has proteins that the
neurotransmitters bind to. That’s how it
recognizes that it’s being signaled, and starts a new
action potential.
 The neurotransmitters aren’t used up. They’re
released to go back to the original neuron, to wait
until another signal is to be transmitted.
Neurons
 How could this neuron system be used
by the body to maintain homeostasis?
Neurons
 How could this neuron system be used by the
body to maintain homeostasis?
 Neurons and negative feedback loops: Some
neurons activate their action potentials when they
detect rising body temperature.
 The end of their chain activates another chain of
neurons, this one leading to the blood vessels of
the skin. The end of this new chain signals the
blood vessels to dilate, releasing excess heat.
 When the original heat-sensing neurons stop
sensing excess heat, their action potentials stop,
and the blood vessels stop being stimulated and
can go back to normal.
Neurons
 A helpful way to understanding how
body systems work is to understand why
things can go wrong.
 What is a drug?
Neurons
 A helpful way to understanding how
body systems work is to understand why
things can go wrong.
 What is a drug?
 A drug is any substance which alters the
body’s normal function.
 We’re going to look at psychoactive drugs,
drugs that alter the normal functions of the
nervous system.
Neurons and Drug Action
 What could be ways that the normal
action of a neuron could be changed, to
produce a change in how often they
send their signal?
 Demo
Neurons and Drug Action
 http://science.education.nih.gov/supple
ments/nih2/addiction/activities/lesson3_
cocaine.htm
Neurons and Drug Action
 Different psychoactive drugs have
different modes of action, affect
different kinds of neurons and
neurotransmitters, but the common
thread is that they change the frequency
of the action potential.
 Examples:
Neurons and Drug Action
 Opiates, THC, alcohol: Increase the number
of impulses by mimicking normal
neurotransmitter.
 Methamphetamines: Release neurotransmitter
from vesicles with or without an impulse.
 Nicotine: Release more neurotransmitter per
impulse.
 Cocaine, amphetamine: Block reuptake.
 LSD, caffeine: Block postsynaptic receptor.
Specific Example: THC
 THC is a cannabinoid, a chemical which
mimics neurotransmitters called anandamide.
Anandamides are the neurotransmitters of
choice in the following areas of the brain,
consider what interference would result in:
 Limbic system & hippocampus (memory and
learning)
 Amydgala (strength/mildness of emotions,
integrating emotion and action)
 Cerebellum (movement & coordination)
 Plus other areas involved in pain and hunger
 It makes even more sense when you consider
what anandamides usually are used for:
THC
 Anandamides are usually used during sleep. These pathways involve
the calming and settling process, tuning down emotional responses,
turning down pain recognition, encouraging you to eat when you get
up, turning off memory and learning (a part of why you don’t
remember dreams well).
 So, taking THC which mimics an anandamide activates these
pathways while the person is awake. Hence, calmness/stupor,
lack of pain, hunger, lack of integration between emotion and
action, lack of coordination, not feeling emotions strongly, and
difficulty with forming memories and learning.
 THC withdrawal then makes sense in context: irrationality and
outbursts, difficulty re-coordinating the learning processes, etc.
 The withdrawal symptoms take time to dissipate as neurons try to
return to normal activity, though truly chronic use can prevent
that.
Neurons and Drug Action
 Understanding how psychoactive drugs
are related to neurons and
neurotransmitters also lets you
understand dependence and withdrawal.
 Consider that, to maintain homeostasis,
neurons have mechanisms by which they
can reduce their sensitivity to
neurotransmitters.
Neurons and Drug Action
 Understanding how psychoactive drugs
are related to neurons and
neurotransmitters also lets you
understand dependence and withdrawal.
 Consider that, to maintain homeostasis,
neurons have mechanisms by which they
can reduce their sensitivity to
neurotransmitters.
 Now, what will neurons probably do when
exposed to those different drugs
repeatedly?
Neurons and Drug Action
 And why do you think it is that, after
giving up a drug that had effect A on the
user, they tend to have the opposite of
effect A during withdrawal?
 A can be a lot of things. Happiness,
concentration, elevated heart rate, etc.
Neurons and Drug Action
 So, psychoactive drugs can have a variety
of effects. It depends on dosage and
route of administration, among other
things, but effects include:
 Influence on neuronal action, as we just
discussed
 Altering the brain’s ability to metabolize
glucose (cocaine and others do this) - what
would be the result?
 Even neuron death (alcohol, meth, ecstasy
among others) - why might that happen?
Neurons and Drugs
 Knowing what they do about drugs and
their effect on neurotransmission, though,
has also allowed scientists to develop
psychoactive drug regimes for treatment
purposes.
 How could a psychoactive drug like
morphine reduce pain?
 In people with chronic clinical depression,
who don’t release enough of the
neurotransmitter serotonin, how could a drug
treat that condition?
Neurons and Drugs
 Neurons and neurotransmission are at the center
of research on:
 ADHD:
http://videos.howstuffworks.com/discoveryhealth/14425-human-atlas-adhd-video.htm
 Chronic depression
 Alcoholism & Addiction
 Schizophrenia
 Acute life events: can you use neurotransmission to
explain why people often remain depressed after an
acute event, like death or torture, even if they’re not
thinking about it anymore or don’t “feel” bothered?
Neurons
 So you know that neurons communicate
axon-to-dendrite. This means that what
you get is a long chain of neurons, like an
extended game of telephone or dominoes.
 A long bundle of neurons is called a nerve.
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Nerves
 The body is riddled with a huge network of
nerves, all with different functions.
 Sensory nerves send information to the brain:
they detect and inform the command center of
stimuli, like pressure, heat, moisture,
damage…
 Your tongue is equipped with sensory nerves to
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carry messages that they’ve detected tastes like
salt or sweet.
 Your optic nerve sends messages that its
photoreceptors have sensed light.
Nerves
 Then, there are motor nerves send information
from the brain to the body: nerves whose
signal is a command, like “dilate this blood
vessel,” “contract this muscle,” “relax that
muscle.”
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Nerves
 This network of sensory and motor
nerves woven throughout the body is
called the peripheral nervous system.
 What does peripheral mean?
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Nervous System
 But of course, those sensory nerves send
their message somewhere, and the
motor nerves get their message from
somewhere. You know where, right?
CNS
 The central nervous system receives and
processes stimuli and issues responses.
It’s comprised of the brain and the
spinal cord.
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CNS
 The brain is the major command center.
It’s a huge complicated bundle of
neurons (for everyone but this guy), and
each area has a different function.
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Brain
 There are areas which control breathing, body
temperature, etc. The higher cognitive
functions - memory, emotion, learning - are
also there.
 Why can’t I just read definitions of things? Why
do Ms. Stang and our teachers make us read and
listen and write and do problems and activities and
homework and labs with them?
 Because what learning actually is is a new
connection. You don’t make a new neuron, you
connect existing dendrites & axons.
 So the more different ways that you encounter or do
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something, the more new connections you make, the
more learning, the more likely it is that you will be able
to access the memory.
Spinal Cord
 The spinal cord carries messages to and
from the brain, and it also has some
control functions, like reflexes.
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Sense Organs
 Other organs generally considered to be
part of the nervous system are certain
sensory functions, like your eyes and
aspects of your ears and chemical
senses.
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