Download Biological Processes Neurons

Biological Processes
Overview:
The Nervous System: Neurons
- Anatomy, communication, networks
CNS/PNS
The Brain
- Anatomy, localization of function
Methods to study the brain (Dr. Heidenreich)
Nervous system:
communication system of your body and brain
The basic unit of the nervous
system is a neuron
The nervous system contains
over 1000 billion
individual neurons
Your brain alone
consists of about 100
billion neurons
Neurons have both
chemical and
electrical processes
Neurons - how do they work?
(1) Your brain is almost
entirely made up of neurons,
specialized for different
behaviors
(2) Neurons are complex
cells that communicate
by
means of an
electrochemical “language”
(3) Activity in the neurons gets
passed from one to another in
a network
(4) Chemicals stimulate the cell to transmit an electrical impulse.
When the impulse reaches the end of the cell, chemicals are released
which are picked up by neighboring cells which stimulate those cells…
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Neurons have three basic parts
Dendrites
(1) Receives chemicals called
“neurotransmitters” from
neighboring cells and starts the
electrical signal
Axon
(2) Transmits the
electrical impulse down
the length of the cell
Terminal
buttons
(3) Releases
chemical
neurotransmitters to
neighboring cells
How neurons communicate
dendrites
Step1: chemicals (neurotransmitters)
enter through the dendrites
+++
---
Different
neurotransmitters have
different effects on the
neuron.
Some will make it more
likely to fire.
Others will make it less likely to fire.
Step2: Action potential
If enough of the excitatory (++) chemicals enter the dendrites, the neuron
will transmit an electrical signal down the length of the axon
Resting potential =
(1) Fluid inside
the neuron is
negatively
charged
Axon
(2) Fluid outside
has positive and
negative ions
When the message is positive, + ions
flow into cell and an electrical charge
travels down the neuron
This impulse is called an
action potential
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If enough of the inhibitory (- -) chemicals enter the dendrites, the neuron is
less likely to have an action potential
Resting potential =
(1) Fluid inside
the neuron is
negatively
charged
-
-
-
(2) Fluid outside
has positive and
negative ions
-
-
-
-
-
-
-
-
When the message is negative, ions flow into cell making the
inside more negative than the
resting potential and the cell is
less likely to fire
-
-
-
-
-
Step3: Neurotransmitter release
Sacs of chemicals (called
neurotransmitters) sit in the
terminal endings.
terminal
buttons
When the electrical signal
makes its way down the
axon….
…neurotransmitters are
released into the space
between nerve cells (the
synapse)
Synapse
…and are are picked up by
the dendrites of neighboring
neurons
How are neurotransmitters relevant to “real world” behavior?
Certain psychological and neurological
disorders may be linked to abnormal
levels of certain neurotransmitters
Depression may be linked to abnormally
low levels of serotonin
Alzheimer’s disease may be linked to
abnormally low levels of acetylcholine
Parkinson’s disease may be linked to
abnormally high levels of dopamine
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The neurons in your brain are highly interconnected.
It is really a communication network.
The networks are called neural nets.
They consist of as many as 1,000 billion neurons and
100,000 billion connections among neurons
The connections between neurons are key in many experiences and
behaviors. For example, learning serves to change the connections
and makes the network store information.
Action potentials only travel in one direction.
Each neuron is like an on and off switch. It either
fires or it doesn’t.
Each neuron connection carries information about
experience or behavior (pleasure, pain, hunger,
thirst, movements of your body, etc.)
…but what is most
important is a pattern of
activity across groups of
neurons
Your experiences and behaviors are a consequence of complex
patterns of activity in groups of neurons in your brain
The 100 billion neurons in
the brain can be thought of
as 100 billion “on-off”
switches
Neuron
10000
Neuron
10002
Neuron
10001
Neuron
10003
Neuron
10004
Neuron
10007
Each on-off pattern means
something different to the
brain
Neuron
10005
Neuron
10006
Neuron
10010
Neuron
10008
Neuron
10009
Neuron
10011
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Your experiences and behaviors are a consequence of complex
patterns of activity in groups of neurons in your brain
The 100 billion neurons in
the brain can be thought of
as 100 billion “on-off”
switches
Each on-off pattern means
something different to the
brain
Your experiences and behaviors are a consequence of complex
patterns of activity in groups of neurons in your brain
Brain images show these on-off patterns on a much larger scale…
How do these ideas help us learn about human behaviors?
McClelland’s work - video
What about neurons outside of the brain?
The central
nervous system
(CNS)consists of
the brain and
spinal cord
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What about neurons outside of the brain?
The peripheral
nervous system
consists of all the
other
nerve cells
of the body
The PNS and CNS work together to
process and react to stimuli in the
environment.
What about neurons outside of the brain?
interneurons
Sensory neurons take signals from
the PNS and send them to CNS.
Motor neurons take signals from
CNS and send them to the PNS.
This is known as a
reflex or a reflex arc
ANATOMY OF THE BRAIN
The brain is organized into two hemispheres.
Each hemisphere has four lobes.
Parietal
Left Hemisphere
Occipital Lobe
Right
Hemisphere
Top View
Lobe
Temporal
Lobe
Frontal
Lobe
Right View:
Right
Cerebral Hemisphere
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Localization of function: DIFFERENT PARTS OF THE
BRAIN SEEM TO DO DIFFERENT THINGS
There are front-back differences…
RECEPTION
perceptions,
interpretations
Back
Front
EXPRESSION
actions, plans
More Localization of function…
THE BRAIN IS ORGANIZED INTO FOUR LOBES
Touch/Movement
Parietal Lobe
Vision
Cognitive
Frontal Lobe Functions
Occipital Lobe
Temporal Lobe
Language & Hearing
Right View: Right
Cerebral
Hemisphere
Even more localization of function… THE BRAIN IS ORGANIZED
INTO “PROJECTION AREAS” AND “ASSOCIATION AREAS”
somatosensory
motor
Impulses from the sense
organs are sent to the
primary sensory areas
“Association Area” organizes
and integrates information
across projection areas
visual
auditory
Impulses from the primary
motor area are sent to the rest
of the body
An important lesson:
Equal areas of body do not receive equal brain space
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Different parts of the somatosensory cortex receive nerve
impulses from different parts of the body.
foot
knee
chest
hand
face
What do you notice about how the somatosensory cortex is organized?
Why do you think the hands have so many cells devoted to them?
Different parts of the motor cortex send out nerve impulses to
different parts of the body.
foot
knee
chest
hand
face
The motor cortex is organized the same way as the sensory cortex in an
adjacent area of the brain.
Brain function is also lateralized
Lateralization of function:
DIFFERENT HALVES OF THE BRAIN
SEEM TO DO DIFFERENT THINGS
Damage to the left
hemisphere leads
to difficulties in
language tasks
Damage to the
right hemisphere
leads to difficulty
in spatial tasks
LANGUAGE
SPATIAL ABILITIES
(like producing and
understanding
words)
(like reading maps)
Top View
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It is important that the two hemispheres of the brain receive
and process the same information about the world
The corpus callosum is a band of tissue
that connects the two hemispheres of the
brain. It allows for fast and efficient sharing
of information.
LANGUAGE
SPATIAL ABILITIES
(like producing and
understanding
words)
(like reading maps)
…but what would happen if
someone did not have a
corpus callosum?
Would one hemisphere of the
brain know something that
the other did not?
How could we find out?
We would need to find people without a corpus collosum (such people
exist) and present them with information so that only one hemisphere of
their brain received it.
The organization of
the visual system
provides one way for
us to do this…
Left
Visual
Field
Right
Visual
Field
Vision is not divided by
eye. Instead it is divided
by visual field.
Left
Visual
Cortex
Right
Visual
Cortex
When stimulation occurs in only ONE visual field
ONLY the OPPOSITE visual cortex receives the image
In order to do this, the
participant is instructed
to stare straight ahead
and the image is
flashed very briefly
Why does it have to be
flashed so quickly?
Left
Visual
Field
Left
Visual
Cortex
Right
Visual
Field
Right
Visual
Cortex
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Let’s say we briefly flash an image in the RIGHT visual field...
What did
you see?
In this case the image
goes to the LEFT
HEMISPHERE, which
has access to the words
to describe what is
being seen.
A bird
LANGUAGE
SPATIAL
ABILITIES
Let’s say we briefly flash an image in the LEFT visual field...
What did
you see?
In this case the image
goes to the RIGHT
HEMISPHERE, which
DOES NOT have
access to the words to
describe what is being
seen.
I don’t
know
LANGUAGE
SPATIAL
ABILITIES
Lateralization of function: motor control
LEFT
HEMISPHERE
RIGHT
HEMISPHERE
Controls
movement of
and
processes
stimulation
from
Controls
movement of
and
processes
stimulation from
the RIGHT
SIDE of the
body
the LEFT SIDE
of the body
Contralateral control
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This is what happened to Phineas Gage...
Notice what part of the brain is injured...
Excerpts from Descartes’ Error: Emotion, Reason,
and the Human Brain, By Antonio Damasio
“The rod enters his left cheek, pierces the base
of the skull, traverses the front of the brain,
and exits at high speed through the top of the
head. The rod has landed more than a hundred
feet away, covered in blood and brains”
What happened to Gage after the accident?
After being transported to a nearby doctor, Gage
“…got out of the cart himself, with a little
assistance from his men”
However… he was somehow different….
Before the accident Gage was: “wellbalanced, a shrewd businessman, controlled,
considerate, and soft spoken..”
After the accident he was: “fitful, irreverent,
profane, irritable, demanding, and unable to
plan for the future”
According to his doctor “the equilibrium or
balance…between his intellectual faculty and
his animal propensities” has been destroyed
He could no longer function as a foreman of the railroad site.
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What can we (as scientists interested in the influence of the
brain on behavior) learn from this?
Two key questions:
What part of the brain did he injure?
How did it affect his behavior?
Conclusion: This part of the brain (the
frontal lobe) has something to do with
decision making, planning, social
interaction, personality, etc.
Summary of Biological Processes:
(1) Neuron fires through electrical and chemical
processes
(2) Action potential starts process for sending info to
other neurons
(3) Activity of neurons across the network = behavior
(4) Brain function localized and lateralized lobes/hemispheres
(5) Brain function studied by clinical cases, brain
recordings, and experimental methods
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