Download Nervous System Cells

Chapter 3
Biological Psychology
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Biological Psychology
• In this chapter we will examine:
– What are the components of the nervous
system?
– How does the brain create mental processes
and behavior?
“What we understand least is why brain activity
produces experience at all.” -- James W. Kalat
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Module 3.1
• Neurons and Behavior
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Introduction
• Explanations for Behavior
– The best theories in psychology explain
behavior in terms of development, or
physiology.
– Developmental explanations describe
changes during the life of an organism.
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Introduction
• Explanations for Behavior
– Physiological explanations describe
mechanisms that produce behaviors.
– We try to explain behavior in terms of the
activity of the cells of the nervous system.
– We will start by with how scientists measure
brain activity.
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Nervous System Cells
• Neurons
– You experience yourself as a single entity.
– Neuroscientists have demonstrated that
experience is the product of a nervous system
made up of an enormous number of discrete
cells.
– The cells that make up your nervous system
are called neurons.
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Nervous System Cells
• Neurons and communication
– Neurons are cells that receive and transmit
information electrochemically.
• Sensory neurons carry information from
sense organs to the central nervous
system.
• Neurons in the CNS process information,
interpret it, and send commands to
muscles, glands, and organs.
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Nervous System Cells
• The best estimate is that the human nervous
system has nearly 100 billion neurons.
• They aren’t the only type of cell in the system.
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Nervous System Cells
• Glia
– Glia support the neurons in many ways.
• They provide insulation, and remove waste
products and foreign bodies.
• They are 1/10th the size of the neurons, but
about 10 times as numerous.
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Nervous System Cells
• Anatomy of a neuron
– Neurons have a variety of shapes, but they all
have 3 basic parts.
• A cell body that contains the nucleus and
most of the organelles.
• The dendrites - branching structures that
receive transmissions from other neurons.
• The axon - a single, long, thin fiber with
branching tips.
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Nervous System Cells
• Axons
– The axon sends electrochemical messages to
neighboring cells.
• Most axons transmit information to the
dendrites or cell bodies of neighboring
neurons.
• Many axons have a coating of myelin,
which speeds up transmission.
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Nervous System Cells
• Nerve cell growth
– Neurons do not have a fixed anatomy.
• Researchers have found that neurons
constantly grow and lose branches to
dendrites and axons.
• This growth is related to new experiences
and learning.
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Nervous System Cells
• Action potentials
– Axons convey information by a combination of
electrical and chemical processes.
• This combination is called an action
potential.
• An action potential is a signal that travels
along the axon at a constant strength no
matter how far it travels.
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Neuron and Neural Impulse
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Nervous System Cells
• Action potentials
– The all-or-none law
• An action potential is an all-or-nothing
process – it’s either happening or not;
there’s no “sort of” action potential.
• This message reaches the brain at full
strength, but more slowly than regular
electrical conduction.
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Nervous System Cells
• Action potentials
– How an action potential works:
• An un-stimulated axon has resting
potential.
• Resting potential is an electrical
polarization across the membrane covering
the axon.
• A polarized axon is charged negatively (-70
millivolts) relative to the outside.
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Nervous System Cells
• Action potentials
– How an action potential works:
• Resting potential is maintained by the
sodium-potassium pump.
• Sodium is mostly concentrated outside the
neuron, and potassium mostly inside, and
they are held in place by the pump’s
special “gates.”
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Nervous System Cells
• Action potentials
– How an action potential works:
• The sodium-potassium pump sends
positively charged (+1) sodium ions out of
the cell and brings in a smaller number of
positively charged (+1) potassium ions.
• So the outside of the cell has more positive
charges than the inside.
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Nervous System Cells
• Action potentials
– How an action potential works:
• A message from a neighboring cell excites
part of the axon’s membrane the sodium
gates open and sodium enters the axon.
• This depolarization makes the charge
inside the cell positive.
• The neuron’s charge is briefly the same
inside and outside.
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Nervous System Cells
• Action potentials
– How an action potential works:
• The sodium gates shut quickly and
potassium ions leave the cell.
• The positive charge exits with them,
bringing the axon back to a polarized state.
• The sodium-potassium pump removes
excess sodium ions and recaptures the
exiled potassium ions.
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Concept Check
If a hamster and a seven-foot-tall human step on a
sharp object, which will respond faster? Why?
The hamster, because the action potential has a shorter distance to
travel.
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Nervous System Cells
• Synapses
– Communication between neurons occurs at
the synapses.
• Synapses are specialized junctions
between neurons.
• Chemicals released at the synapse excite
or inhibit neighboring cells, making action
potentials more or less likely.
• Synaptic activity is crucial to brain function.
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Nervous System Cells
• Synaptic transmission
• Excitatory messages cause the next cell to
“fire” - continue to carry the action potential.
• Inhibitory messages decrease the
likelihood the action potential will continue
to travel.
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Nervous System Cells
• Synapses
– Synaptic communication:
• Each axon bulges into a terminal bouton
(alternately spelled “button.”)
• When the action potential reaches the
terminal bouton, neurotransmitters are
released.
• A neurotransmitter is a chemical stored in
the neuron. It activates special receptors of
other neurons.
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Nervous System Cells
• Synapses
– Synaptic communication:
• There are many neurotransmitters.
Neurons use a particular neurotransmitter
or combination of them.
• Released neurotransmitters diffuse to the
surface of the postsynaptic neuron.
• They attach to receptors on the
dendrite/cell body of the neuron exciting or
inhibiting it.
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Nervous System Cells
• Synapses
– Synaptic communication:
• After the message is sent the
neurotransmitter detaches from the
receptors.
• The neurotransmitter may be reabsorbed
by the axon that released it (reuptake),
diffuse away, be removed from the body as
a waste product (metabolized), or remain in
the synapse.
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Concept Check
Learning and environmental challenges sometimes
produce branching in axons and dendrites of an
organism’s neurons. How would that affect the
number of synapses?
It would increase the number of synapses.
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Concept Check
• Dopamine is a neurotransmitter that excites
postsynaptic neurons. If a drug were injected
into an animal that blocked dopamine from
attaching to its receptors, what would happen to
the postsynaptic neurons?
They would be less likely to produce further action potentials.
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Neurotransmitters and Behavior
• New understanding of the role of
neurotransmitters has revolutionized the health
sciences.
– Drugs designed to act on a particular kind of
receptor in the nervous system can also have
specific effects on an organism’s functioning
and behavior.
– It is hypothesized that unusual behaviors or
dysfunctions may be due to lack or excess of
particular neurotransmitters.
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Neurotransmitters and Behavior
• Parkinson’s disease
– Parkinson’s disease is a condition in which
the individual has trouble with voluntary
movements including tremors, rigidity, and
depressed mood.
– This condition is related to gradual decay in a
system of axons that release the
neurotransmitter dopamine.
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Neurotransmitters and Behavior
• Parkinson’s disease
– Dopamine is a neurotransmitter that promotes
activity levels and facilitates movement.
– Symptoms of Parkinson’s disease can be
managed in mild cases with a drug called Ldopa, which is synthesized into dopamine by
the neurons.
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Neurotransmitters and Behavior
• The link is not always so clear though.
– The symptoms of attention-deficit disorder or
ADHD include impulsive, agitated behavior
and a short attention span.
– These symptoms suggest an oversupply of
dopamine.
– But there appears to be no relationship
between dopamine and ADHD.
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Concept Check
People suffering from schizophrenia are given
haloperidol, a drug that blocks activity at dopamine
synapses. How would haloperidol affect a person
with Parkinson’s Disease?
It would make the symptoms worse.
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Neurotransmitters and Behavior
• The neurotransmitter, whether in over-, under-,
or normal supply, is part of a complex system.
• What alleviates the problem may not reveal what
originally caused the problem.
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Module 3.2
• Drugs and Their Effects
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The Survey of Abused Drugs and Their Effects
• The biological basis of drug abuse and addiction
– Nearly all abused and addictive drugs
increase activity at the dopamine receptors in
the brain.
– These drugs increase the release of
dopamine, interfere with reuptake, stimulate
dopamine-releasing neurons or decrease
activity of dopamine-inhibiting ones.
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The Survey of Abused Drugs and Their Effects
• The biological basis of drug abuse and addiction
– Dopamine works on a small brain area, the
nucleus accumbens, that is central for
attention and habit-formation.
– Activities like gambling and video game
playing can have the same biological effects.
– Addiction is in the person, not in the drug.
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The Survey of Abused Drugs and Their Effects
– Stimulant drugs boost energy, heighten alertness,
increase activity and produce a pleasant feeling.
• Cocaine and amphetamine are examples of
stimulant drugs
• Cocaine decreases brain activity, which in turn
stimulates behavior.
• Free-base and crack cocaine allow the drug to
enter the nervous system more rapidly, thus
producing a more powerful “high” than powder
cocaine.
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The Survey of Abused Drugs and Their Effects
– Ritalin, which is prescribed for ADHD, is a
strong, slow-acting stimulant.
– Caffeine, an ingredient in coffee, tea, and
many soft drinks, is a milder and less
dangerous stimulant drug.
– Cigarettes are nicotine delivery devices.
Nicotine is a powerfully addictive stimulant.
Smoking feels “relaxing” because between
cigarettes the smoker experiences
withdrawal, which more smoking temporarily
alleviates.
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Concept Check
If a person takes a drug that promotes the
production and release of dopamine, how would
the drug affect his or her response to cocaine?
It would probably enhance the effects of the
cocaine
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The Survey of Abused Drugs and Their Effects
• Depressants
– Depressants decrease physiological arousal.
• The most commonly used/abused depressants are
alcohol and tranquilizers.
• These drugs facilitates the transmission of the
neurotransmitter GABA.
• Alcohol is a class of chemicals that includes
methanol, ethanol, and propyl (rubbing) alcohol.
• Ethanol is found in liquor, wine, and beer.
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The Survey of Abused Drugs and Their Effects
• Depressants - Alcohol
– Alcohol has been consumed in world cultures
for millennia.
– It acts as a relaxant when consumed in small
amounts.
– In greater amounts, it can increase
aggressive and risk-taking behaviors.
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The Survey of Abused Drugs and Their Effects
• Depressants - Alcohol
– Excessive consumption of alcohol damages
the liver and other internal organs.
– It also causes memory impairment and loss of
motor control.
– Fetal alcohol syndrome, which can result
when pregnant women consumes alcohol, is
the number one preventable cause of mental
retardation in the United States.
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The Survey of Abused Drugs and Their Effects
• Depressants - Alcohol
– Alcohol abuse and dependence are worldwide public
health problems.
– They are more common in some cultures than in
others.
– Ethnic differences in alcohol consumption are related
to overall differences in lifespan. The relatively
greater rates of consumption among Native
Americans and African Americans may constitute part
of the reason for the shorter average lifespan in these
populations.
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The Survey of Abused Drugs and Their Effects
• Depressants – Tranquilizers
– Tranquilizers have been prescribed to help people
relax and fall asleep.
– They have also been used to suppress epileptic
seizures.
– Barbiturates proved to be so addictive and dangerous
that it they are rarely prescribed today.
– Benzodiazepines, a class including drugs like Valium,
are milder (but still highly addictive) drugs used for
anxiety management.
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The Survey of Abused Drugs and Their Effects
• Narcotics
– Narcotics produce drowsiness, insensitivity to pain,
and decreased responsiveness to environmental
stimuli.
• Opiates are one common type of narcotic.
• Opiates are derived from the opium poppy or
synthesized in the laboratory.
• They create a feeling of euphoria.
• Once the drug is used up, the person feels intense
withdrawal and a need to use the drug again.
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The Survey of Abused Drugs and Their Effects
• Narcotics
– Researchers have found that the human brain
produces chemicals called endorphins.
– They bind to opiate receptors and stimulate
dopamine production.
– Endorphins are released when an individual
experiences pain or stress.
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The Survey of Abused Drugs and Their Effects
• Marijuana
– Marijuana is classified as a narcotic, but
unlike opiates it intensifies sensory
experiences.
– It’s possible medical uses include suppression
of pain and nausea.
– It is a dangerous drug. It carries the same risk
of lung cancer as tobacco.
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The Survey of Abused Drugs and Their Effects
• Marijuana
– It impairs learning and memory. The active ingredient
in marijuana, THC, attaches to receptors in the
hippocampus, where memories are consolidated.
– Because of the political overtones, research studies
of marijuana are tainted by the agenda of the
researcher (pro or con) and may be unreliable.
– Marijuana is no more of a “gateway” drug than
tobacco and alcohol are.
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The Survey of Abused Drugs and Their Effects
• Hallucinogens
– Hallucinogens induce sensory distortions and false
sensory experiences.
– Peyote is a naturally derived hallucinogen. It plays an
important role in Native American religious
ceremonies.
– LSD is artificially manufactured. It alters serotonin
receptors. We don’t know how this leads to altered
sensory experiences.
– MDMA or ecstasy, acts as a stimulant at low doses
and a hallucinogen at high doses. This hallucinogen
poses great risk of brain damage.
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Psychoactive Drugs
• Drugs produce desirable or undesirable effects.
These effects are easy to understand and give
us greater insight into how the brain’s processes
manufacture “consciousness”
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Module 3.3
• Brain and Behavior
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The Major Divisions of the Nervous System
• The central nervous system and the peripheral
nervous system
– The central nervous system consists of the
brain and the spinal cord.
– The central nervous system communicates
with the rest of the body via the peripheral
nervous system.
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The Major Divisions of the Nervous System
• The central nervous system and the peripheral
nervous system
– The peripheral nervous system is composed
of bundles of axons between the spinal cord
and the rest of the body.
– There are two sets of subdivisions of the
peripheral nervous system.
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The Peripheral Nervous System
• The somatic nervous system and autonomic
nervous system
– The somatic nervous system is made up of
the peripheral nerves that communicate with
the skin and muscles.
– The autonomic nervous system controls the
involuntary actions of the heart, stomach, and
other organs.
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The Central Nervous System
• Embryological development
– During the embryonic stage, the vertebrate
nervous system forms out of a simple tube
with three lumps:
• The forebrain becomes the cerebral cortex
and other higher structures.
• The midbrain and hindbrain become the
brainstem.
• The forebrain dominates in humans.
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The Forebrain
• General structure
– The forebrain
• The forebrain has a left and right
hemisphere.
• Each controls sensation and motor
functioning on the opposite side.
• They communicate with each other through
a bundle of axons crossing between them,
the corpus callosum.
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The Forebrain
• Cerebral cortex
– The cerebral cortex
• The outer covering of the forebrain
• It’s composed of gray matter, the cell
bodies of the cortical neurons.
• The interior of the forebrain is composed of
white matter or axons of cortical neurons. It
is white because of its myelin coating.
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The Forebrain
• Cerebral cortex
– The four lobes of the cerebral cortex
• The areas of the cerebral cortex are shown
as four lobes: occipital, parietal, temporal,
and frontal.
• The occipital lobe is in the rear. It contains
many specialized areas for interpreting
visual sensory information.
• It has special areas for shape, color, and
motion vision.
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The Forebrain
• Cerebral cortex
– The four lobes of the cerebral cortex
• The parietal lobe is directly in front of the
occipital lobe.
• It contains the primary somatosensory
cortex which is specialized for body senses
and awareness of the location of body
parts.
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The Forebrain
• Cerebral Cortex
– The four lobes of the cerebral cortex
• The temporal lobes are located on the
sides of the head, near the ears.
• They are the main processing areas for
hearing and complex aspects of vision.
• The left temporal lobe contains important
areas for language processing and
comprehension.
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The Forebrain
• Other structures that lie under or near the
temporal lobe include the hypothalamus,
amygdala and hippocampus.
– The hypothalamus regulates emotional and
motivated behavior.
– The amygdala, an almond-shaped structure
crucial for emotional processing, is deep
inside the temporal lobes.
– The hippocampus is vital for memory
processing.
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The Forebrain
• Cerebral cortex
– The four lobes of the cerebral cortex
• The frontal lobes are in the front of the
brain.
• They contain the primary motor cortex,
important for control of fine movements.
• The foremost part, the prefrontal cortex, is
where organization, planning of action, and
aspects of memory are controlled.
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Concept Check
Which lobe is damaged if…
A person is unable to feel or locate the left side of
her body?
Right parietal lobe
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Concept Check
• Which lobe is damaged if…
• A person has difficulty with fine movements with
the right hand?
Left frontal lobe
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Concept Check
• Which lobe is damaged if…
• A person has loss of vision in the right visual
field?
Left occipital lobe
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Concept Check
• Which lobe is damaged if…
• A person has impaired emotional experience
and some hearing loss?
Temporal lobe
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Between the Spinal Cord and the Forebrain
• The hindbrain & midbrain
– The medulla, pons, and midbrain contain the
reticular activating system (or reticular
formation).
– The RAS regulates levels of arousal in the
brain.
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How the Cerebral Cortex Communicates with
the Body
• The hindbrain
– The cerebellum is important for coordination
and timing.
– It is also in charge of tasks that require
shifting of attention and discrimination
between stimuli.
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How the Cerebral Cortex Communicates with
the Body
• The hindbrain
– The medulla oblongata and pons are two
important structures in the hindbrain.
– They contain the axons that control breathing
and heart rate.
– They are also relay sensory information from
the head and sending motor messages back
to it.
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How the Cerebral Cortex Communicates with
the Body
• The spinal cord
• Reflex and voluntary responses are
conducted through the spinal cord.
• A reflex is a rapid, automatic response to a
stimulus. They usually originate in the
spinal cord.
• Voluntary responses originate in the brain
and travel via the spinal cord to the
muscles to carry out movements.
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How the Cerebral Cortex Communicates with
the Body
• The spinal cord
• The spinal cord communicates with the
body by means of sensory and motor
neurons.
• The sensory neurons carry information
from the extremities of the body to the
spinal cord and brain.
• Motor neurons transmit messages from the
central nervous system to the muscles and
glands.
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Measuring Brain Activity
• Methods for viewing and mapping the brain
include:
– Electroencephalographs and
Magnetoencephalographs (EEGs and MEGs)
record electrical and magnetic activity in the
brain.
– These do not visualize brain activity.
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An EEG records momentary changes in electrical potential from the scalp,
revealing an average of the activity of brain cells beneath each electrode.
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Measuring Brain Activity
• Methods for viewing the brain include:
– Positron emission tomography (PET) - a
high-resolution picture of brain activity using
radioactive chemicals injected into the
bloodstream.
– The color of the image indicates the level of
activity: red areas are most active, followed by
yellow, green, and blue for the least active
areas.
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A PET scan of the human brain. Red shows areas of most-increased
activity during some task; yellow shows areas of next most-increased
activity.
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Measuring Brain Activity
• Methods for looking at and mapping the brain
include:
– Functional magnetic resonance imaging
(fMRI) uses magnetic detectors to measure
the amounts of hemoglobin and oxygen in
different areas of the brain.
– Highly active areas of the brain appear to use
more oxygen in fMRI images.
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This brain scan was made with functional magnetic resonance imaging
(fMRI). Participants looked at words or pictures and judged whether each item
was abstract or concrete, living or nonliving. Yellow shows the areas most
activated by this judgment; red shows areas less strongly activated.
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The Peripheral Nervous System
• The autonomic nervous system
• The autonomic nervous system is division
of the peripheral nervous system closely
linked with the spinal cord.
• The individual has little control over this
division’s responses, hence “autonomic.”
• It has two subdivisions.
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The Peripheral Nervous System
• The autonomic nervous system
– The divisions of the autonomic nervous
system
• The sympathetic nervous system is the
crisis management center.
• It increases heart and respiration rate and
prepares the body for fight or flight.
• It’s controlled by a chain of neurons lying
just outside the spinal cord.
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The Peripheral Nervous System
• The autonomic nervous system
– The divisions of the ANS
• The parasympathetic nervous system runs
long-term survival-related functions,
nutrition, and energy conservation.
• It decreases heart rate, increases digestive
activities, and promotes restorative
processes.
• It is controlled by neurons at the upper and
lower levels of the spinal cord.
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The Endocrine System
• The endocrine system is under the control of the
nervous system.
– It’s a system of glands that release hormones
into the bloodstream.
– Hormones are chemicals that affect mood,
behavior, and anatomy.
– Some neurotransmitters act as hormones. For
example, epinephrine, is called adrenaline
when it is acting as a hormone in the
bloodstream.
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Experience and the Brain
• Nerve cell generation/Plasticity
– Neurons are generated later in life (to a
limited extent).
• It was once thought that all neurons
developed well before birth.
• Stem cells - undifferentiated cells growing
in some brain areas are capable of
developing into neurons in older organisms.
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Experience and the Brain
• Nerve cell generation
– Neuronal generation is very limited in scope.
• The action of stem cells seems to be
stimulated after some types of brain
damage, so their purpose may be in part
compensatory.
• The growth of new neurons is much more
limited than other body cells.
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Experience and the Brain
• Learning changes the brain
– We know, because we can “see” the brain
and its activity, that practicing behaviors
(learning to play a musical instrument, for
example) changes the structure of the brain
by altering the cortical neurons.
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Experience and the Brain
• The “binding problem”
– We still don’t understand how the different
parts of the brain produce a unified
experience of objects or events, since the
areas of the brain that help us analyze our
experience are not directly interconnected.
– It is amazing that people can lose just one
aspect of vision; for example, color, motion, or
the ability to recognize faces.
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Experience and the Brain
• The two halves of the brain
– Work with individuals who have had the “splitbrain” operation (severing the corpus
callosum) to control seizures provides
evidence that the two hemispheres are highly
specialized.
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Experience and the brain
• The two halves of the brain
– The right hemisphere communicates with the
left in order to name the objects in its visual
field.
– The left hemisphere works with the right to
synthesize details into a whole picture (e.g.,
combining the parts of a face into a whole
recognizable image).
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Visual-Spatial Processing
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The Brain and the Self
We are still learning about the brain, but we now
understand that IT is composed of many separate
areas with separate abilities.
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The Brain and the Self
If you lose part of the brain, you lose part of your
unique experience.
Brain activity and mind are inseparable. One is the
other.
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