AP Psychology 120 – 2011/2012
Unit #3 – Biological Bases of Behavior
Section 1 - Communication in the Nervous System
Your nervous system is a complex communication network in which signals are
constantly being transmitted, received and integrated.
Your nervous tissue is composed of 2 types of cells:
1. Glia – provides structural support, nourishment and insulation for neurons
2. Neurons - receive, integrate and transmit information. They are the basic links
that permit communication within the nervous system.
- Soma is the body of the neuron.
- Dendrites are the parts of the neuron that receive information
- The axon transmits signals away from the soma to other neurons, or muscles or
glands.
- The myelin sheath is the insulating material surrounding the axons.
- Terminal buttons are the ends of the axons that secrete chemicals called
neurotransmitters. These neurotransmitters serve as messengers that may
activate neighboring neurons.
- A synapse is the junction where information is communicated between neurons.
The points at which neurons interconnect.
- Essentially, information is received at the dendrite, is passed through the soma
and along the axon, and is transmitted to the dendrites of other cells at meeting
points called synapses.
The Neuron impulse (when a neuron is stimulated, using energy to send information)
-
-
-
-
Inactive neurons have a resting potential. This is a negative charge. The neuron
at rest is a tiny battery, a store of potential energy.
When a neuron activates, it creates an action potential. The neuron’s electrical
charge changes and becomes less negative or even positive. This shift travels
down the axon.
After firing, the neuron must rest. This is the neuron’s absolute refractory
period. After the refractory period, the neurons regain a negative charge.
Certain drugs, like anesthetics, prevent the neurons from firing. The neurons
aren’t able to rest after the refractory period because the positive ions are
blocked.
Neurons fire their entire potential. This is the All or None Law.
Neurons communicate the strength of a stimulus by how fast they fire. A strong
stimulus causes neurons to fire more quickly than a weaker stimulus.
The Synapse
-
-
-
-
Remember, the neural impulse functions as a signal. For that signal to have any
meaning for the system as a whole, it must be transmitted from the neuron to
other cells. This transmission takes place at special junctions called synapses,
which depend on neurotransmitters (chemical messengers).
Neurons don’t touch one another. The synaptic cleft is the space between a
neuron and the terminal buttons of another neuron. Signals have to cross this
gap to permit neurons to communicate.
When a neuron’s action potential reaches the terminal buttons, they release
neurotransmitters.
Neurotransmitters transmit information from one neuron to another.
Neurotransmitters go to receptor sites on the postsynaptic cell membranes of
the receiving cell.
The postsynaptic potential (PSP) is created when neurotransmitters combine
with receptors. It is a voltage change on the postsynaptic cell membrane.
Postsynaptic potentials do not follow the All or none Law. They are graded.
An excitatory PSP is a positive voltage shift. This increases the probability that
the postsynaptic neuron will fire.
An inhibitory PSP is a negative voltage shift. This decreases the probability that
the postsynaptic neuron will fire.
The neurotransmitters then either become inactive or are returned to the
presynaptic neuron through reuptake.
Neurotransmitters and behavior
- There are many different types of neurotransmitters. Specific neurotransmitters
work at specific kinds of synapses. Transmitters cannot bind to just any site on
the post synaptic membrane. The binding process acts like lock and key. Specific
transmitters can deliver signals only at certain locations on cell membranes.
- Agonists are chemicals that mimic the effect of neurotransmitters. Antagonists
are chemicals that oppose the effect of neurotransmitters.
-
Acetylocholine (Ach) is the neurotransmitter found in the motor neurons.
Monoamines are neurotransmitters that include dopamine, norepinephrine,
and serotonin.
Serotonin, for example, helps to regulate sleep. Dopamine is involved in
voluntary movement.
Abnormalities in levels of monoamines can cause psychological disorders.
For example, low levels of norepinephrine and serotonin can cause depression
and abnormal levels of dopamine can cause schizophrenia.
Drugs like cocaine affect people because they affect the levels of dopamine and
norepinephrine.
Endorphins are neurotransmitters that reduce pain and produce feelings of
exhilaration. They are similar to opiates.
Section 2 – Organization of the Nervous System
The human nervous system consists of the central nervous system and the peripheral
nervous system.
The central nervous system
- The CNS consists of the brain and the spinal cord.
- The spinal cord connects the brain to the peripheral nervous system.
- The CNS is protected by cerebrospinal fluid or CSF (to cushion the brain) and the
blood-brain barrier (to screen chemicals from the brain).
The peripheral nervous system
-
The peripheral nervous system is made up of all the nerves that lie outside the
brain and spinal cord.
-
The peripheral nervous system is divided into the somatic nervous system and
the autonomic nervous system.
The somatic nervous system is made up of nerves connected to voluntary
muscles and sensory receptors. These nerves are the cables that carry
information from receptors in the skin, muscles and joints to the central nervous
system and carry commands from the CNS to the muscles. These functions
require 2 kinds of nerve fibers.
In the somatic nervous system, afferent nerve fibers carry information to the
CNS (inward to the CNS from the periphery of the body). Efferent nerve fibers
carry information from the CNS (outward from the CNS to the periphery of the
body).
The autonomic nervous system is made up of nerves connected to the heart,
blood vessels and glands. It controls our automatic, involuntary functions that
people don’t normally think about, such as heart rate, digestion and
perspiration.
The autonomic nervous system is divided into the sympathetic division and
parasympathetic division.
The sympathetic division controls the body’s resources for emergencies, i.e. –
releasing adrenaline or withdrawing blood from limbs to the vital organs. It
creates the fight or flight response.
The parasympathetic division conserves the body’s resources i.e. – slowing
heart rate.
-
-
-
-
-
Section 3 – Researching the brain
Neuroscientists try to map out the structure and function of the brain. The structure of
the brain can be mapped out quite easily by examining and dissecting brains removed
from animals or deceased humans. Mapping brain function however, requires a working
brain. Therefore special research methods are needed to discover relations between
brain activity and behavior.
- The electroencephalograph (EEG) measures electrical activity in the brain.
Different brain wave patterns are associated with different mental activities.
- Lesioning - When people suffer brain damage, they develop lesions on their
brains. Neuroscientists can study the effects of these lesions.
- Electrical stimulation of the brain (ESB) involves sending electrical signals into
parts of the brain to stimulate or activate it. Most ESB research is done on
animals, but it is also a routine part of brain surgery.
Brain imaging
- A computerized tomography (CT) scan involves the use of computer enhanced
x-rays of the brain. The brain is x-rayed from many angles to produce an image
of the brain. It is used to look for abnormalities in brain structure among people
suffering from specific types of mental illness.
- A position emission tomography (PET) scan images brain function, not structure
like a CT scan. It maps the actual activity in the brain over time. Brain activity is
imaged by using radioactive chemicals.
- A magnetic resonance imaging (MRI) scan uses magnetic fields to map brain
structure and activity at the same time.
Section 4 – The Brain
The brain can be divided into 3 major regions – hindbrain, midbrain and forebrain.
The hindbrain
- The hindbrain includes the cerebellum, the medulla, and the pons. The medulla
and the pons are part of the brainstem.
- The medulla, attached to the spinal cord, controls unconscious functions like
circulation, breathing, coughing and sneezing.
- The pons (bridge) connects the brainstem with the cerebellum.
- The cerebellum (little brain) coordinates movement signals from the forebrain
and the senses from the body. It is critical to the coordination of movement and
to the sense of equilibrium or physical balance.
The midbrain
- The midbrain is the top of the brainstem. It is between the hindbrain and the
forebrain.
- The midbrain deals with senses and movement. It is an important centre for
dopamine production.
- The reticular formation deals with reflexes, breathing, pain perception and
sleep. It is also part of the hindbrain.
The forebrain
- The forebrain is the most complex part of the brain. It includes the thalamus,
hypothalamus, limbic system, and cerebrum.
- The thalamus is where all sensory information passes to the cerebral cortex.
-
-
-
-
-
The hypothalamus controls the autonomic nervous system, connects the brain
to the endocrine system, and regulates fighting, fleeing, feeding and mating.
The limbic system is involved in emotion, memory, and motivation. The limbic
system is not well understood.
The cerebrum is the largest and most complex part of the human brain. It
includes the brain areas that are responsible for the most complex mental
activities including learning, remembering, thinking and consciousness itself.
The cerebrum is divided into 2 halves called hemispheres – right and left halves
of the cerebrum. Each cerebral hemisphere is divided into 4 parts called lobes.
To some extent each of these lobes is dedicated to specific purposes. The 4 lobes
are:
Occipital lobe – at the back of the head includes the cortical area, where most
visual signals are sent and visual processing is begun (also called the primary
visual cortex)
Parietal lobe is forward of the occipital lobe. It includes the area that registers
the sense of touch, called the primary somatosensory cortex.
The temporal lobe includes primary auditory cortex for auditory processing.
The frontal lobe includes the primary motor cortex for movement and the
prefrontal cortex for planning, attention, and organizing.
Brian Plasticity – refers to the brains ability to change structure and function.
Neural wiring of the brain is flexible and constantly evolving. The brains plasticity
declined with age.
Section 5 – Cerebral laterality
Right and left hemispheres of the brain
-
-
-
The left hemisphere is better at verbal processing, such as language, speech,
reading and writing.
The right hemisphere is better at nonverbal processing, such as spatial and
musical tasks and visual recognition.
Although the left hemisphere is better at verbal processing, the right is also
involved. Although the right is better at non-verbal processing, the left is also
involved.
Each hemisphere’s primary connections are to the opposite side of the body.
Thus the left hemisphere controls and communicates with the right hand, right
arm, right leg, right eyebrow etc. In contrast, the right hemisphere controls and
communicates with the left side of the body.
Much has been learned through split-brain research, i.e. research on people who
have had brain surgery to cut the corpus callosum.
Section 6 – The Endocrine System (our body’s second communication system)
- The endocrine system consists of glands that release hormones into the
bloodstream to control bodily function, i.e. the pancreas releases insulin to
process sugar.
-
Much of the endocrine system is controlled by the hypothalamus.
The pituitary gland, connected to the hypothalamus, releases hormones to
stimulate other glands. It is sometimes called the “master gland.”
The endocrine system works with the nervous system.
Hormones (chemical substances released by the endocrine glands) are also
important in physical development. Hormones are similar to neurotransmitters
in many ways.
Section 7 – Heredity and Behaviour
Genetics
-
Chromosomes are strands of deoxyribonucleic acid (DNA) molecules that carry
genetic information. They are in every cell of your body.
Genes are DNA segments on chromosomes that are transmitted from parent to
child at conception. Each parent contributes 23 chromosomes.
Like chromosomes, genes work in pairs. Some genes are dominant, others are
recessive.
Genotype is a person’s genetic makeup. Phenotype refers to the way a person’s
genotype is demonstrated in physical appearance.
Polygenic traits require more than two genes, i.e. skin color.
Research methods and heredity
-
In family studies, researchers examine heredity by studying the traits of people
who are related to one another.
In twin studies, researchers examine heredity by studying the traits of identical
twins and fraternal twins.
In adoption studies, researchers examine heredity by studying traits of children,
their biological parents, and their adoptive parents.
Genetic mapping is the current research effort to determine the location and
function of all human genes.
Nature (heredity) and nurture (environments) are important to development.
Evolutionary psychology is based on the theory of evolution and knowledge of
genetics and heredity.