Download The Nervous System and The Brain

The Nervous System and The
Brain
Neuroscience and Behavior
Modules 3 & 4
Early Theories - Phrenology
- Bumps on the skull tell
us nothing about the
brain’s underlying
functions
- Some assumptions
were true…different
parts of the brain DO
control different parts of
behavior
The Nervous System
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An electrochemical communication system
that enables us to think, feel and act
How do we study the Nervous
System?
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Clinical Observation – Direct clinical observation of
patients with brain damage or disease - Ex. Phineas
Gage
http://www.youtube.com/watch?v=kc213mMSsjY
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Invasive Techniques – Since 1850, experimenters
have opened the skull and “invaded” the brain while the
patient is still alive
Brain Tissue can be stimulated with electricity,
chemicals, heat or cold. In addition, it can be
lesioned, or destroyed in place
Brain Tissue can also be ablated, or removed
with a vacuum or scalpel. It can also be
transected, meaning isolated or cut.
Neuroimaging Techniques
 EEG
– Electroencephalogram –
Detects electrical currents in the
brain making possible early
evaluation of issues
Neuroimaging Techniques cont’d
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PET Scan – Positron Emission Tomography
– Patient is injected with a safe dose of
radioactive sugar. Brain cells that are
particularly active will consume more (or
perhaps none) of the substance.
The brain activity is measured by an
imaging computer
Neuroimaging Techniques cont’d
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CAT Scan – Computerized Axial
Tomography – A narrow X-ray beam is
aimed through the patient’s head & hits a
detector on the other side. Brain tissue
has different densities, and blocks the
beam to different degrees. The computer
then constructs a picture that reveals
damaged or dead tissue.
http://en.wikipedia.org/wiki/File:64_slice_scanner.JPG
Neuroimaging Techniques cont’d
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MRI – Magnetic Resonance Imaging – Safer
than a CAT Scan because there are no X-Rays.
The nuclei at the center of atoms have their
own resonant frequencies. If they are perturbed,
the bounce around, and return to their normal
position.
The MRI disturbs the atoms of the brain, and
the computer assembles a detailed picture that
may reveal tumors, tissue degeneration, clots
and leaks, etc.
http://videos.howstuffworks.com/tlc/29321-understanding-brain-mri-video.htm
Neurons and their Messages
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Neural Pathways – Information travels in
the Nervous System through three types
of neurons
Sensory or Afferent Neurons (Inward) –
Sends information from the body’s tissues
and sensory organs inward to the spinal
cord and brain for information
Neurons and their Messages cont’d
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Interneurons – This processing involves a second class
of neurons of the brain and spinal cord (CNS).
Motor or Efferent Neurons – Sends instructions to the
body’s tissues and extremities
Mnemonic Device – SAME
http://www.youtube.com/watch?v=wK3VUQTRIBg&NR=1&safety_mode=tr
ue&persist_safety_mode=1&safe=active
The easiest example is the simple reflex – Ex. Touching
a hot stove http://www.youtube.com/watch?v=1OYKegnG8Lo&NR=1
Nervous system vid 1:00
http://www.youtube.com/watch?v=iBnGeDzTYD4&feature=related&safety_mode=tru
e&persist_safety_mode=1&safe=active
Generating a Neural Impulse
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Each neuron consists of a cell body
(Soma) and one or more branching
fibers. The fibers are of two types:
Dendrites – Receive information from
sensory receptors, or other neurons
Axons – Pass information along to other
neurons
***Dendrites – Short; Axons – Long ***
Neurons and their messages
Generating a Neural Impulse – cont’d
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A layer of fatty cells called the Myelin Sheath
insulates and speeds up their impulses
When does a neuron fire?
When the neuron is stimulated by pressure,
heat, light or chemical messages from adjacent
neurons. This impulse is called the action
potential.
Action Potential is a brief electrical charge that
travels down the neuron like a spark down a
fuse. The signals trigger an impulse if the
stimulus exceeds a minimum intensity called the
Threshold – See handout on Action Potential
Generating a Neural Impulse –
cont’d
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Increasing the stimulus above the threshold will not
increase the intensity of the impulse. The neuron’s
reaction is an “All or None Response” – Like firing a
gun – either it fires, or it doesn’t
***Reaction Time Experiment***
http://www.bbc.co.uk/science/humanbody/sleep/sheep/
How do you know the difference between getting
touched with a feather, or getting hit with a punch?
More neurons can fire, and fire more often
Generating a Neural Impulse – cont’d
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There are tiny gaps, less than a millionth
of an inch wide. This junction is called
the…
Synapse
If the neurons don’t touch, how does one
neuron pass information to the next?
Through chemical messengers called
neurotransmitters
For a second, the neurotransmitter
unlocks tiny gates like a “Lock and Key”
system - http://www.youtube.com/watch?v=90cj4NX87Yk
Generating a neural impulse – cont’d
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One of the best understood
neurotransmitters is Acetylcholine (ACh)
Acetylcholine is the neurotransmitter at
every junction between a motor neuron
and a muscle. When ACh is released to
the muscle cells, the muscle contracts. If
ACh is blocked, muscles cannot contract.
Ex. Curare – Poison that occupies and
blocks ACh receptor sites leaving the
neurotransmitter unable to affect the
muscles – result is paralysis.
Monkey http://www.youtube.com/watch?v=0P-FuwMDq5s&feature=related
Generating a neural impulse – cont’d
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Ex. Botulin – Poison that causes paralysis by
blocking the release of ACh http://www.youtube.com/watch?v=OX2ECc1lNFc
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***Opposite – Venom of a Black Widow Spider
*** - Causes a flood of Ach which leads to
muscle contractions and convulsions
Endorphins – “Morphine Within” – Natural
opiate-like neurotransmitter linked to pain
control and pleasure. Most commonly released
during exercise (“Runner’s high”)
If endorphins lessen pain, and boost mood, why
not simply take morphine? – Handout of
common neurotransmitters – “Must Know 5”
http://www.youtube.com/watch?v=TjrBdKXgYFY
Divisions of the Nervous System
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Neurons function through several sub-systems –
The Central Nervous System (CNS) includes
all the neurons in the brain and spinal cord
The Peripheral (On the outside) Nervous
System (PNS) – Links the CNS with the body’s
sense receptors, muscles and glands
The PNS has two components: The Somatic
Nervous System and the Autonomic
Nervous System
Divisions of the Nervous System – cont’d
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The Somatic transmits sensory input (touch
and taste for example) to the CNS from the
outside world and directs motor or muscle
output, such as our voluntary movements
The Autonomic influences glands and the
muscles of our internal organs. Usually operates
on its own – “Autonomously” – Activities such as
heartbeat, digestion, glandular activity, etc.
The Autonomic Nervous System also has
subcomponents
The Nervous System
Peripheral Nervous System
Somatic Nervous System
Central Nervous System
Autonomic Nervous System
Brain
Sympathetic Nervous System
Parasympathetic Nervous System
Spinal Cord
Divisions of the Nervous System – cont’d
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The Sympathetic Nervous System – Arouses
us for defensive action. It accelerates your
heartbeat, slows digestion, raises your blood
sugar, and cools you with perspiration.
When the stress is over, your
Parasympathetic Nervous System produces
the opposite effects and calms you down
http://www.youtube.com/watch?v=8PWH
745MMMY
The Brain