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Biological Bases of Behavior
Transcript of Biological Bases of Behavior
A particular pathway in the brain may only use one or two
), and particular neurotransmitters may have particular
effects on behavior and emotion.
Cells make up almost everything in our body, and our neural system is no exception. The cells that make up our brain are known as
The Nervous System
central nervous system (CNS)
made up of the
brain and spinal cord
s the control center of the body. It
relays messages, processes information, and analyzes information.
Genetics, Evolutionary Psychology, and Behavior
Quick run down: All humans have
. We get 23 from our biological mother, and 23 from our biological father.
can be classified into
according to the
in which an impulse travels.
Sensory neurons (afferent) carry impulses from the sense organs to the spinal cord and brain
Motor neurons (efferent) carry impulses from the brain and spinal cord to muscles and glands.
Interneurons connect sensory and motor neurons, and carry impulses between them.
Although neurons come in all different shapes and sizes, they have certain features in
of a typical
cell body contains the nucleus and much of the cytoplasm
, and is responsible for much of the
of the cell.
from the cell body are short, branched extensions called
carry impulses from the environment or from other neurons TOWARD the cell body.
long fiber that carries impulses AWAY
from the cell body is called the
. The axon ends in a series of small swellings called
(located some distance from the cell body).
Neurons usually have dozens of dendrites, but only one axon.
In some neurons, the axon is surrounded by an
insulating layer of fatty tissue
known as the
gaps between the myelin sheath,
where the node is
, are called the
nodes of Ranvier.
(an electrical signal) moves along an axon, it
from one node to the next, which
increases the speed
at which the impulse can travel.
is similar to the
flow of electrical current
through a metal wire. Neurons generate this electricity from chemical events (like batteries). The
process involves the exchange of
When a neuron is at its
(when it's not transmitting an impulse), the fluid
of the axon has an excess of
charged ions, while the fluid
the axon membrane has more
charged ions. In short:
resting potential = (+) outside & (-) inside
When a neuron is actually
by signals from our senses or when triggered by chemical signals from neighboring neurons, it fires an impulse known as the
(a brief electrical charge that travels down its axon). This causes the positively charged sodium ions to
through the membrane into the axon.
that section of the axon, which causes the axon's next channel to open, and the next. This is because a
nerve impulse is
, which means that an impulse at any point causes an impulse at the next point (like falling dominoes).
The minimum level of a stimulus that is required to activate a neuron is called the
threshold (around -50mv)
. Any stimulus that is
than the threshold will
produce an impulse
, while any stimulus that is
not produce an impulse
(it's "all or nothing," very much like when you flush a toilet).
At the end of the neuron, the impulse reaches an axon terminal. Once here, the message "jumps"
from the axon terminal of one cell to the dendrite receptor of another
cell. A neuron may also
pass the impulse
along to a second cell. For example, motor neurons pass their impulses to muscle cells.
at which a neuron can t
ransfer an impulse
to another cell is called a
Neurons are able to
transmit these impulses
across a synapse to another cell through the use of special chemicals called
When an impulse arrives at an axon terminal, the
across to the neighboring cell to create a
However, there are ways to
the flow of neurotransmitters.
As a reminder, ions are electrically charged atoms and are either
(+) or (-).
The important ions in the nervous system are
potassium (K+), and chlorine (Cl-)
Impulses always flow
down the axon away from the cell body
toward the axon terminal.
, known as the
, the neuron
the positively charged sodium ions back
. Then, the neuron can fire again.
protects the brain, and the
protect the spinal cord.
The spinal cord is the
main communication link
between the brain and the rest of the body.
Thirty one pairs of spinal nerves
branch out from the spinal cord,
connecting the brain to all of the different parts of the body.
Certain kinds of information, including some kinds of
reflexes, are processed directly in the spinal cord.
quick, automatic response to a stimulus. Sneezing and blinking
are two examples of reflexes.
A reflex can also allow your body to
respond to danger immediately
, without spending time thinking about a response.
peripheral nervous system (PNS)
lies outside the central nervous system, and
consists of all the nerves and associated cells that are not part of the brain and spinal cord.
Included here are the
that pass through openings in the skull and stimulate regions of the head and neck, spinal nerves, and collections of
nerve cell bodies
peripheral nervous system
has two components:
somatic and autonomic.
somatic nervous system regulates activities that are under conscious control
(like the movement of our skeletal muscles).
Every time you lift your finger or wiggle your toes, you are using the
motor neurons of the somatic nervous system.
are also involved with
reflexes and can act with or without conscious control.
autonomic nervous system regulates activities that are automatic, or involuntary
, which means that the
of the autonomic nervous system
control functions of the body that are not under conscious control
(such as our glands and the muscles of our internal organs).
For instance, when you are
autonomic nervous system
speeds up your heart rate and the blood flow to the skeletal muscles, stimulates the sweat and adrenal glands, and slows down the contractions of the smooth muscles in the digestive system.
parts of the
autonomic nervous system:
sympathetic nervous system
parasympathetic nervous system
parasympathetic nervous systems have opposite effects on the same organ system
, and these opposing effects help
sympathetic nervous system prepares you to fight or run away
when faced with danger, while the
parasympathetic nervous system lets you "rest and digest."
neurotransmitters to bridge the gap between neurons
(any substance other than food that
changes the structure or function of the body
interferes with the action of neurotransmitters can
the functioning of the nervous system.
(such as ecstasy, cocaine, caffeine, meth, and nicotine)
increase heart rate, blood pressure, and breathing rate
. In addition, they increase the
release of neurotransmitters
at some synapses
in the brain.
This release leads to a fe
eling of energy and well-being. However, when the effects of stimulants wear off, the
brain's supply of neurotransmitters has been depleted
. The user quickly falls into fatigue and depression. Long term use can cause circulatory problems, hallucinations, and psychological dependence.
Even stronger effects are produced by drugs that act on neurons in the
pleasure centers of the brain.
On the other end of the spectrum,
depressants decrease the rate of functions regulated by the brain.
Depressants (such as alcohol and marijuana) slow down heart rate and breathing rate, lower blood pressure, relax muscles, and relieve tension.
enhance the effects of neurotransmitters that prevent some nerve cells from firing
. This calms parts of the brain that sense fear, and therefore relaxes the individual. However, as a result, the user can come to depend on the drug to relieve the anxieties of everyday life.
When depressants are used with alcohol (a double depressant dose), the results are often fatal because that combination can
depress the activity of the central nervous system until breathing stops.
Types of Brain Tools
an amplified recording of the waves of electrical activity that sweep across the brain's surface
Computed Tomography (CT):
a series of x-ray photographs taken from different angles and combined by a computer into a composite representation of a slice through the body (also known as a CAT scan)
Positron Emission Tomography (PET):
a visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task
Magnetic Resonance Imaging (MRI):
a technique that uses magnetic fields and radio waves to produce computer generated images of soft tissue (shows brain anatomy)
Functional MRI (fMRI):
a technique for revealing bloodflow, and therefore brain activity, by comparing successive MRI scans (shows brain function).
A deep groove
the cerebrum into right and left hemispheres. The hemispheres are
by a band of tissue called the
The largest and most prominent region of the human brain is the
The cerebrum is
responsible for the voluntary (or conscious) activities
of the body.
) and grooves (
) on the surface of each hemisphere greatly
increase the surface
area of the cerebrum.
of the cerebrum is divided into regions called
The lobes are named for the skull bones that cover them.
Each half of the cerebrum deals mainly with the
side of the body.
Sensations from the left side of the body go to the right hemisphere, and those from the right side of the body go to the left hemisphere.
Some studies have suggested that the
may be connected with
creativity and artistic ability
, whereas the
may be associated with
analytical and mathematical ability
there is more crossover than differentiation.
region of the brain is the
The cerebellum is located at the back of the skull.
to move muscles come from the
cerebellum ("little brain")
is the one that is responsible for
coordinating and balancing
the actions of the muscles so that the body can
move gracefully and efficiently.
Chickens have a
huge cerebellum relative to total volume of brain
, which is the reason they have such good body balance and can keep their head stable in one place even as their body moves.
connects the brain and spinal cord. Located just below the cerebellum, the brain stem
regulates the flow of information between the brain and the rest of the body.
The medulla is the lower half of the brain stem, and is involved in the control of
blood pressure, heart rate, breathing, and swallowing
Areas of the Cerebral Cortex
(front) of the frontal lobe is known as the
, and is thought to play a critical role in directing thought processes such as
judgment, pursuing goals, and emotional control.
In most people, the
; one of the two special areas responsible for
(in some left-handed people the language centers are in the right hemisphere).
is in the frontal lobe and is responsible for
controlling the muscles involved in producing speech
to Broca's area might leave us
unable to make the muscle movements needed for speech.
thin vertical strip at the back
of the frontal lobe is called the
. This part of the cerebral cortex
sends signals to our muscles controlling our voluntary movements.
are behind the frontal lobe, but still on the top of the brain. They
contain the sensory cortex
, which is located right behind the motor cortex in the frontal lobe.
The sensory cortex is a thin, vertical strip that receives incoming touch sensations from the rest of the body.
are at the very back of our brain, and their job is to
interpret messages from our eyes in our visual cortex
. Impulses from the retinas in our eyes are sent to the visual cortex to be interpreted.
temporal lobes process sound sensed by our ears.
Sound waves are processed by the ears, turned into neural impulses, and interpreted in our auditory cortices.
Sound is not lateralized like the visual cortex is; sound received by the left ear is processed in the auditory cortices in both hemispheres.
second language area
is located in the temporal lobe, and is called
Wernicke's area interprets both written and spoken speech
Damage to this area would affect our ability to understand language. Our speech may sound fluent, but lack the proper syntax and grammatical structure needed for meaningful communication.
sit on top of the medulla and are involved in
relaxation and the control of facial expressions
, and acts as a
between the medulla and the midbrain.
habitual muscle movements
, such as tracking a target with our eyes or playing the saxaphone.
refers to our brain's
ability to modify
itself after some type of
Our brains are most plastic when we are young children.
The brain's plasticity is also good news to those who are
blind or deaf.
Blindness and deafness makes unused areas of the brain
available for other uses
This can also be seen in
patients (people who have had their
corpus callosum severed
; often due to intense issues with epilepsy)
When shown the
hollow face illusion
, people will mistakenly perceive the inside of the mask as a protruding face. Yet, research participants will unhesitatingly (and accurately) reach into the inverted mask to flick off a speck on the face inside the inverted mask, which suggests the
unconscious mind knows the truth
of the illusion.
All of our
processing occurs simultaneously on
multiple parallel tracks.
For instance, driving a car on a familiar route you may go into "
" (your hands and feet do the driving, but your mind may be rehearsing the upcoming day). Running on auto pilot allows your
(your mind's CEO) to
monitor the whole system
and deal with new challenges, while many
automatically take care of
(like washing your hair in the shower).
Try tapping a steady
hand while simultaneously tapping a steady
You can't do it!
Both tasks require conscious attention
, which can be in only one place at a time.
are made of
(our universal genetic code), and contain genes (small segments of the giant DNA molecules). We have around 20,000 active genes;
some genes can be expressed while others can be inactive.
Environmental events can "turn on" genes
, and when that happens, genes provide the code for creating protein models (the building blocks of physical development)
We are 99.99% genetically identical
to every person on the planet (yes, including the person next to you), and share around 50% of our genes with bananas
...But some of us are
than 99.99% identical
However, researchers believe that some of the
differences in the appearance and behavior
of identical twins are due to
changes in the activation of genes
rather than the genes themselves. These are known as
changes because they
change how the genome operates
without changing its actual sequence. Our epigenomes therefore refer to the set of unique operating instructions that run each of our genomes' 'hard drive' differently.
"Heredity deals the cards; environment plays the hand"
--Psychologist Charles Brewer
Natural selection in a nutshell: If a gene
(not this kind
then it is
likely to be passed on
to the offspring so that they may increase their chances of having their own offspring.
mistakes in the organism's DNA) are often responsible for the appearance of certain advantageous traits
...This definitely accounts for what we view as "
." This schema can vary with cultural preferences (often amplified by media)
Evolutionary psychology's opinion on: