Download Chapter Two - Texas Christian University

Chapter Two
The Biological Perspective
Biological Psychology
--branch of psychology concerned with
the links between biology and
behavior.
Neuroscience-
Neural Communication
Neuron - basic building block of the nervous system.
Components that make up the neuron
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Cell Body- the neurons life support center. Dendritebranching fibers located on the cell body, that receives
information from other neurons.
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Axon-single, slender, fiber extending from the cell body
carrying outgoing messages to other neurons, muscles,
or glands in the form of neural impulses.
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Tract-group of axons bundled together that carry
information to a specific area (i.e. spinal cord tract)
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Myelin sheath- layer of fatty substance made by the
oligodendrocytes and schwann cells that insulate certain
axons and speeds up the transmission of the neural
impulse
Types of Neurons
• Sensory (afferent) Neurons- neurons that
collect messages from sense organs and
carry those messages to the spinal cord or
brain.
• Motor (efferent) Neurons-neurons that carry
messages from the spinal cord or the brain
to the muscles and glands
• Interneurons (association) Neurons- neurons
that carry messages from one neuron to
another.
Neural Impulse-method of
communication between neurons
• A neural impulse is an electrical
charge that travels down the axon
causing the neuron to fire.
• This electrically charged impulse
allows the neuron to communicate with
other neurons and is called an Action
Potential
Composition of Intra and Extracellular Fluid
• Electrically charged ions on either side of the
membrane. Intra-cellular fluid is predominately
negative and extra-cellular fluid is predominately
positive in relation to each other.
• Intra-cellular fluid-Higher concentration of:
– Negative Ion-(Cation)-A– K+
• Extra-cellular fluid– Na+
– Cl-
Action Potential
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Resting Potential- small negative electrical charge across the neuron
due to the concentration of positive ions on the outside and negative
ions on the inside.
Due to negative electrical charge, the neuron at rest is said to be in a
state of polarization.
Incoming signals from other neurons stimulate receiving neurons at
the dendrites through binding of Neurotransmitter.
When the NT binds, local channels open and briefly change the
polarity which results in a graded potential.
When there are enough graded potentials in succession, channels
open allowing positive ions from the outside to enter the interior of
the neuron.
Entrance of the positive ions into the cell body depolarizes the
neuron, changing the interior from negative to more positive, setting
off a chain reaction that eventually sends an electrical charge (action
potential), down the axon.
Selective Permeability
• Neuron is semi-permeable, meaning some ions
can flow freely in and out while other ions cannot
due to different types of channels which are
open or closed.
• Channels-( open when neuron is at rest)
– Both K+ and Cl- channels are open while neuron is at
rest and freely cross the semi-permeable membrane.
– Although the K+ and Cl- ions are free to move in and
out of the neuron when it is at rest, whether ions
move in or out is influenced by the electrical and
concentration of ions.
• Pumps-Na+/K+ pump
-3 Na+ ions are pumped out
-2 + ions are pumped in
-helps to maintain the concentration and electrical
gradient.
Voltage gated Channels
• Voltage gated channels are closed when
membrane is at rest
• Voltage gated channels begin to open when
there is a change in the voltage of the neuron.
• Different voltage gated channels open and close
and different times.
– Sodium (Na+) channels-open FIRST and more
quickly than K+ initiate depolarization
– Potassium ions (K+)- open later than Na+ gates, but
close more slowly-contribute to hyperpolarization
through the efflux ( leaving the cell ) of K+ = neuron
becomes more negative..
Propagation of Action Potential
aka. When the Neuron fires.
• Neurotransmitters stimulate the neuron via dendrites,
which influence the opening and closing of voltage
channels.
– Action potential is a sequence of events
– Na+ channels open first, allowing positive ions to rush in and
allowing the inside of the neuron to be more positive.
• Graded potential -stimulation via NT is not always
enough to open enough gates to cause a change in
polarity that is enough to reach threshold. Therefore a
brief sudden change in polarity is a graded potential and
the neuron remains at rest.
Action Potential
• Threshold Potential- As more NT
stimulates the dendrites, we see a
summation of graded potentials, which isis
enough to begin the sequence of events
that changes the polarity of the neuron
when the neuron reaches threshold.
• All or None Response- once the axon
reaches threshold it fires, it does not fire at
any greater speed or stronger response. It
either fires, or it does not.
Sending the Message to other cells.
• Propagation- the action potential begins at the
axon hillock of the soma and continues down
the axon.
• As Na+ gates open the electrical impulse
continues to travel down the axon.
• As Na+ gates close, no more positive ions can
enter from the Na+ gates.
• K+ gates open later, and stay open longer
which allows K+ to leave the neuron while it has
a positive charge.
C
Hyperpolarization
• The action potential sequence takes less
than one-thousandth of a second.
• After the action potential fires, the neuron
re-polarizes to its former resting state.
• After the Na+ voltage gated channels
close, the K+ voltage gated channels
remain open, allowing the neuron to be
more negative than resting potential which
is called Hyperpolarization.
Repolarization
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Absolute Refractory Period- period
after the neuron fires when it will not
fire again no matter how strong the
signal. (Neuron is hyper-polarized)
Relative Refractory Period-period
after firing when the cell is returning
to its normal polarized state (negative)
and will fire again only if the incoming
signal is much stronger than usual.
Synapse & Synaptic Transmission
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As the action potential travels down the axon it reaches the
terminal buttons at the end of the axon.
Terminal button –tip of the axon from which the neural
impulse is released out into the synapse in the form of
chemicals called neurotransmitters.
Synapse- tiny gap between the axon tip of one neuron and
the dendrite or cell body of the next neuron.
Neurotransmitter Release – release of chemicals from axon
terminals into the synapse when the neural impulse reaches
the end of the axon.
Vesicles –tiny sacs filled with NT that release the NT into the
synapse, where it binds to receptor sites on the receiving
neuron.
Binding of the NT sends a chemical signal which activates
the next neuron by binding at the receptor sites.
Types of Synapses
• Excitatory Synapse-synapse at which a
neurotransmitter causes the receiving cell
to fire.
• Inhibitory Synapse-synapse at which a
neurotransmitter causes the receiving cell
to stop firing  cessation of pain signal.
• It is not the NT that is excitatory or
inhibitory, but rather the synapse to which
the NT binds.
Drugs and Neurotransmitters
• Drugs are synthesized molecules that are
similar enough in shape to a specific
neurotransmitter, so that the drug can fit into
the receptor site.
• Agonists-chemical substances that can mimic
or enhance the effects of the
neurotransmitters on the receptor site of the
next cell.
• Antagonist-chemical substance that blocks or
reduces the cells response to the action of
other chemicals or neurotransmitters.
Drug Effects
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AgonistExcitatory synapse
AgonistInhibitory synapse
AntagonistExcitatory synapse
AntagonistInhibitory synapse
Re-uptake
Re-uptake inhibitor
How Neurotransmitters influence Us
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Acetylcholine (Ach)-triggers muscle
contraction.
Dopamine-NT involved with voluntary
movement, learning, memory and
emotions.
Serotonin_primarily involved in mood
and depression. Also important in
regulation of sleep and appetite.
Endorphins (endogenous morphine)natural opiate released in response to
pain and vigorous exercise
Central Nervous system
• Includes all of the neurons in the brain and
spinal cord. Two main areas of the CNS:
– Brain
– Spinal Cord
Subdivisions of the brain
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Central Core- earliest part of the brain to
develop.
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Hindbrain: point where the spinal cord enters
the skull. Contains the medulla, pons and
cerebellum
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Medulla-controls basic body functions such as
breathing, heart rate, and blood pressure.
Pons- maintains the bodies sleep wake cycle
Cerebellum-sense of balance and coordinating the
bodies actions
Thalmus-major sensory relay center, integrates
and shapes incoming signals
Hypothalamus-governs hunger thirst, sex drive
and body temperature.
Limbic System
• Located on top of and around the central
core.
• Composed of a set of structures that impose
additional controls over instinctive behaviors
regulated by the central core.
• Associated with emotions such as fear and
aggression, and drives such as food and sex
– Hippocampus-formation of new memories
– Amygdala-governs emotions related to self
preservation
Cerebral Cortex
• More highly developed in humans than in any other
animal.
• Literally covers the central core and limbic system
• Divided into two cerebral hemispheres, right and left.
Each hemisphere is further divided into four lobes.
• The central fissure runs sideways form ear to ear
and separates the primary somatosensory cortex
from the primary motor cortex.
• Primary somatosensory cortex-receives sensory
messages from the entire body.
• Primary motor cortex-sends messages from the
brain to muscles and glands
Functional Lobes of the Cerebral Cortex
 Four lobes, two in each hemisphere, for example, right and
left frontal lobe, etc.
 Occipital - Receives and processes visual information.
Damage: “blind sight”
 Temporal -Regulates hearing, smell, balance and
equilibrium, emotion and motivation, some language
comprehension and complex visual processing such as
recognizing faces. Damage: prosopagnosia
 Parietal – Receives sensory information from all over the
body and registers these messages in the primary
somatosensory cortex. Regulates spatial and mathematical
abilities. Damage: neglect.,
 Frontal lobe- executive function--receives and coordinates
messages from the other three lobes. Also appears to play
a key role in personality, motivation, persistence, affect
(mood) and character traits such as moral character:
Damage: Phineas Gage
Spinal Cord
• Consists of soft jelly-like bundles of axons,
protected by the vertebrae
• Two pathways-descending motor, ascending
sensory
• Motor-carries information from the brain controls
internal organs, muscles, and autonomic nervous
system
• Sensory-carries information from the organs and
extremities to the brain.
• Reflex-circuit that does not require input from the
brain…sensory fibers send info to the spinal cord
where interneurons pass info to motor fibers
causing withdrawl reflex, before brain has registered
what has happened.
Peripheral Nervous system• (def). the sensory and motor neurons that
connect the CNS to the rest of the body.
Autonomic
• Sympathetic
• Parasympathetic
Somatic•
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ENDOCRINE SYSTEM
• (def)-chemical communication system,
slower than electrical, consists of glands that
secrete hormones into the blood- stream.
• Hormones• Endocrine glands–
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Thyroid gland ParathyroidPineal glandPancreasPituitary glandAdrenal gland-