Download Chapter 3 Biological Aspects of Psychology

TOPIC OVERVIEW
Chapter 3
Biological Aspects of
Psychology
What branch of psychology
studies this?
• Biological
psychology:
researches the
physical and
chemical changes
that cause, and
occur in response
to, behavior and
mental processes
(p. 59 of book)
“Nervous Ned”
• Your basic neuron consists of a nerve cell
body and all its parts
• What makes Ned excited?
• Contact with other neurons = chemistry
•
The Nervous System
– Neurons & neurotransmitters
•
Organization of the Nervous System
– Central & Peripheral Nervous System
•
Brain and behavior
– Areas of brain & their function
•
Right Brain/Left Brain Lateralization
– Tendency for each hemisphere to excel at a function
•
Chemistry of Psychology
– How neurotransmitters affect behavior
– How does the endocrine system affect behavior?
The Nervous System
• What makes the Nervous System work?
• Nerves or Neurons!!
– A cell that receives signals from other neurons or
sense organs, processes signals and sends to
other neurons, muscles or glands
• 3 functions: input > processing > output
Meet Nervous Ned the Neuron!
• I have a big family (1
trillion)
• Some of them live in
the city (Central
Nervous System)
• Others live in the
country (Peripheral
Nervous System)
• We all stick together
thanks to Glia
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“In Glia We Trust”
Think of Glia as the
“glue” that binds us
Or
• Glia: cells in the
nervous system that
hold neurons
together and help
them communicate
with one another
Neuron Structure
– Cell body - contains:
• Nucleus - cells genetic
info
• Mitochondria structures that turn
oxygen & glucose to
sugar
– Dendrites – receive
information
– Axon – carry signals
away from cell body;
sending end
A simple reflex
OUCH!
Figure 3.1
Structure of the neuron. Neurons are the communication links of the nervous system. This diagram highlights
the key parts of a neuron, including specialized receptor areas (dendrites), the cell body (soma), the fiber
along which impulses are transmitted (axon), and the junctions across which chemical messengers carry
signals to other neurons (synapses). Neurons vary considerably in size and shape and are usually densely
interconnected.
HOW DOES THE NEURON
WORK SO WELL?
• Ability to communicate efficiently due to 2
features:
– “Excitable” surface membrane of some fibers
– and the tiny gap between neurons, called a
synapse
• “Excitable” = the ACTION POTENTIAL
What is the action potential?
• Not this type of
action!
• An abrupt wave of
electro-chemical
changes traveling
down an axon when
a neuron becomes
depolarized
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Action Potential
• Background: cell membranes and
chemicals (p 62)
Action Potential
• Background cont.
– Molecules with a positive charge are attracted to
those with a negative charge
– Cell membrane has a semipermeable
barrier: lets some chemical molecules
pass through but blocks others
– The attraction causes a force called an
electrochemical potential which drives the positively
charged molecules toward the inside of the cell
– Many of the molecules carry a positive
or negative electrical charge
– Cell membrane keeps out many of the positively
charged molecules but some are allowed to enter by
passing through special openings called channels
(gates) that are normally closed
– The cell is usually pumping out the
positively charged molecules making the
inside of the cell more negative
(polarized)
Action Potential
• Changes in environment around cell (e.g.,
stimulation) can depolarize part of its
membrane causing the gate to swing open
and allow the positively charged molecules to
rush in
What happens when a neuron is
stimulated?
• The neural impulse (action potential) occurs
• When this brief charge reaches the end of the
axon, it finally causes the terminal buttons to
release chemicals
Action Potential
•
When this happens, the next area of the axon becomes
depolarized, causing the next gate to open, creating a wave of
changes in electrochemical potential that spreads rapidly down
the axon
•
This abrupt wave of electrochemical change is called an action
potential
After the Action Potential
• Absolute Refractory Period: minimum
length of time after an action potential
during which another action potential
cannot begin
• All-or-none law: if a neuron is sufficiently
stimulated, it will fire.
• Resting potential: when neuron is not firing it
maintains a negative charge (polarized)
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How was the action potential
discovered?
• Hodgkin & Huxley (1952) studied the
giant squid
– Fluids inside and outside neuron
• Electrically charged particles
(ions)
–Neuron at rest – negative
charge on inside compared
to outside
»-70 millivolts – resting
potential
Figure 3.2 The neural impulse. The electrochemical properties of the neuron allow it to transmit signals. The
electric charge of a neuron can be measured with a pair of electrodes connected to a device called an
oscilloscope, as Hodgkin and Huxley showed with a squid axon. Because of its exceptionally thick axons, the
squid has frequently been used by scientists studying the neural impulse. (a) At rest, the neuron is like a tiny
wet battery with a resting potential of about –70 millivolts. (b) When a neuron is stimulated, a brief jump in its
electric potential occurs, resulting in a spike on the oscilloscope recording of the neuron’s electrical activity.
This change in voltage, called an action potential, travels along the axon like a spark traveling along a trail of
gunpowder.
Neural Communication requires • Myelin sheath – a fatty substance that
wraps around some axons and increases
the speed of the action potential
• Terminal Buttons – at the end of axon;
secrete neurotransmitters
• Neurotransmitters – chemical messengers
• Synapse – the place where an axon of one
neuron meets the membrane (on a
dendrite or cell body) of another neuron
How do neurons actually
communicate?
• To send signal, neuron uses chemical couriers called
neurotransmitters (NT)
• Neurons don’t touch at synapse but are separated by
- the synaptic cleft: microscopic gap between terminal
button of one neuron and the cell membrane of
another neuron
Figure 3.3
The synapse. When a neural impulse
reaches an axon’s terminal buttons, it
triggers the release of chemical
messengers called neurotransmitters.
The neurotransmitter molecules diffuse
across the synaptic cleft and bind to
receptor sites on the postsynaptic
neuron. A specific neurotransmitter
can bind only to receptor sites that its
molecular structure will fit into, much
like a key must fit a lock.
How do neurons actually
communicate?
• NT binds to receptor sites on the receiving neuron
• The receptors open allowing positive sodium ions to
enter and excite or inhibit the action potential
• Receptor sites are tuned to recognize and respond to
some neurotransmitters and not others
• Electrical signals can’t jump this gap. Instead, the
neuron that is sending the message across the gap
releases neurotransmitters into the synaptic cleft
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