BIOLOGICAL BASES OF BEHAVIOR
UNIT III
NEURAL PROCESSING AND
THE ENDOCRINE SYSTEM
NEURONS: THE ORIGIN OF BEHAVIOR
• Neurons: cells in the nervous system that
communicate with one another to perform
information-processing tasks
• Components of neurons:
• Cell body – coordinates information-processing tasks
and keeps the cell alive
• Dendrites – receive information from other neurons
• Axon – transmits information to the other neurons,
muscles and glands
• Glial cells – support cells found in the nervous
system
• Some digest parts of dead neurons
• Some provide physical and nutritional support for neurons
• Myelin sheaths – an insulating layer of fatty material
around the axons of some neurons
• Formed by some glial cells
• Synapse: junction or region between the axon of one
neuron and the dendrites or cell body of another
THE SYNAPSE
TYPES OF NEURONS
• Sensory neurons – receive information from the
external world and convey it to the brain via the
spinal cord
• Motor neurons – carry signals from the spinal
cord to the muscles to produce movement
• Interneurons – connect sensory neurons, motor
neurons and other interneurons
• Most common
COMMUNICATING INFORMATION
WITHIN A NEURON
• Communication happens in two stages:
1. Conduction of an electric signal over
relatively long distances within neurons
2. Transmission of electric signals between
neurons over the synapse
COMMUNICATION -CONT• Neuron’s cell membrane is porous and allows ions (small
electrically charged molecules ) to flow in and out of the cell
• When at rest, channels that allow small, positively charged
potassium ions (K+) to pass are open
• Channels that allow the flow of other molecules are normally closed
• There are more potassium ions inside the neuron, so some K+
ions flow out leaving the neuron with fewer positively
charged molecules on the inside relative to the outside
• Resting potential – difference in electric charge between the
inside and outside of a neuron’s cell membrane
COMMUNICATION -CONT• Action potential – electric signal that is conducted along
the length of a neuron’s axon to the synapse
• Occurs only when an electric shock reaches a certain level, or
threshold
• When an electric charge is raised to the threshold value, the K+
channels briefly shut down and other channels that allow the
flow of sodium (Na+), another positively charged ion, are opened
• When an electric current passes down the length of a myelinated
axon, the charge “jumps” from node to node instead of travelling
down the entire axon
• Refractory period – time following an action
potential during which a new action potential
can’t be initiated
• After action potential reaches it’s maximum, K+ flows
out until the axon returns to resting potential
• Eventually an active chemical “pump” in the cell
membrane moves Na+ back outside the axon and K+
inside
ACTION POTENTIAL
THE ACTION POTENTIAL
SYNAPTIC TRANSMISSION BETWEEN
NEURONS
• Terminal buttons – knoblike structures that branch out
from most axons
• When the action potential reaches the terminal button, it
stimulates the release of neurotransmitters – chemicals that
transmit information across the synapse to a receiving neuron’s
dendrites
• Neurotransmitters float across the synapse and bind to sites on
the dendrites of the receiving neuron called receptors – parts of
the cell membrane that receive the neurotransmitter and initiate a
new electric signal
• Activation of receptors on the receiving neuron can cause a new
electric potential to be initiated, called synaptic transmission
• Neurotransmitters left in the synapse are cleared
up through one of three processes:
• Reuptake – neurotransmitters are reabsorbed by the
terminal buttons of the presynaptic neuron’s axon
• Enzyme deactivation – specific enzymes break down
and destroy specific neurotransmitters
• Autoreceptors – detect how much of a
neurotransmitter has been released into a synapse and
signal the neuron to stop releasing the
neurotransmitter when too much is present
SYNAPTIC TRANSMISSION
TYPES OF NEUROTRANSMITTERS
HOW DRUGS MIMIC
NEUROTRANSMITTERS
• Agonists – drugs that
increase the action of
a neurotransmitter
• Prozac blocks reuptake
of serotonin
• Antagonists – drugs
that block the
function of a
neurotransmitter
THE ORGANIZATION OF THE
NERVOUS SYSTEM
• Nervous system – interactive network of
neurons that conveys electrochemical
information throughout the body
• Made up of two divisions:
• Central nervous system (CNS) – brain and the spinal
cord
• Peripheral nervous system (PNS) – connects the CNS
to the body’s organs and muscles
• Also composed of two parts:
• Somatic nervous system – set of nerves that
conveys information into and out of the CNS
• Autonomic nervous system (ANS) – set of
nerves that carries involuntary and
automatic commands that control blood
vessels, body organs and glands
• Sympathetic nervous system – set of nerves that
prepares the body for action in threatening
situations
• Parasympathetic nervous system – helps the body
return to a normal resting state
THE HUMAN NERVOUS SYSTEM
SYMPATHETIC AND PARASYMPATHETIC
SYSTEMS
COMPONENTS OF THE CNS:
THE SPINAL CORD
• Some behaviors do
not require input
from the brain to the
spinal cord
• Spinal reflexes – simple
pathways in the
nervous system that
quickly generate
muscle contractions
COMPONENTS OF THE CNS:
THE BRAIN
THE HINDBRAIN
• Hindbrain – area of the brain that coordinates
information coming into and out of the spinal cord
• Sometimes called the brain stem – includes:
• Medulla – extension of the spinal cord into the skull that
coordinates heart rate, circulation and respiration
• Reticular formation – brain structure that regulates sleep,
wakefulness and levels of arousal
• Cerebellum – large structure that controls fine motor skills
• Thalamus – directs messages to the sensory receiving areas in the
cortex and transmits replies to the cerebellum and medulla
• Pons – relays information from the cerebellum to the rest of the
brain
THE HINDBRAIN
THE MIDBRAIN
THE FOREBRAIN
• Highest level of the brain
• Controls complex cognitive, emotional,
sensory and motor functions
• Divided into two main parts:
• Cerebral cortex – outermost layer of the brain
• Subcortical structures – areas of the forebrain
housed under the cerebral cortex near the
center of the brain
SUBCORTICAL STRUCTURES
• Limbic system – located below the
cerebral hemispheres
• Associated with emotions and drives
• Amygdala – involved in many emotional processes,
particularly the formation of emotional memories
• Hippocampus – plays a role in the storage of
memories
SUBCORTICAL STRUCTURES -CONT• Thalamus – sits on top of the brain stem and
serves as a relay station
• Like a server in a computer network
• Hypothalamus – regulates body temperature,
hunger, thirst and sexual behavior
• Basal ganglia – large neuron clusters that work
with the cerebellum and cerebral cortex to
control and coordinate voluntary movements
THE FOREBRAIN
THE CEREBRAL CORTEX
• Divided into two hemispheres
• Each controls the opposite side of the body
• Corpus callosum – thick band of nerve fibers that
connects large areas of the cerebral cortex on each
side of the brain and supports communication of
information across the hemispheres
• Hemispheres are subdivided into four areas/lobes
•
•
•
•
Occipital lobe – processes visual information
Parietal lobe – processes information about touch
Temporal lobe – hearing and language
Frontal lobe – has specialized areas for movement,
abstract thinking, planning, memory and judgment
• Motor cortex – area at the back of the frontal lobe that
controls voluntary movements
• Sensory cortex – area at the front of the parietal lobes
that registers and processes body touch and
movement sensations
• Association areas – areas of the cerebral cortex that are
composed of neurons that help provide sense and
meaning to information registered in the cortex
• Are usually less specialized and more flexible than neurons in
the primary areas
THE BRAIN AND LANGUAGE
• Aphasia – impairment of language, usually
caused by left hemisphere damage either to
Broca’s area or to Wernicke’s area
• Broca’s area – controls language and expression
• Usually in the left frontal lobe
• Directs muscle movements involved in speech
• Wernicke’s area – controls language reception
• Usually in left temporal lobe
• Plasticity – the brain’s ability to change,
especially during childhood, by reorganizing
after damage or by building new pathways
based on experience
OUR DIVIDED BRAIN
• Split brain – results
from surgery that
isolates the brain’s
two hemispheres by
cutting the fibers
connecting them
Left visual
field
Right half of
each eye
Right
hemisphere
Right visual
field
Left half of
each eye
Left
hemisphere
• Some things to remember about the brain’s
hemispheres:
• There is no activity to which only one hemisphere
makes a contribution
• Logic is not confined to the left hemisphere and
creativity and intuition are not exclusive properties of
the right hempishere
• It is impossible to educate one hemisphere at a time
• There is no evidence that people are purely “leftbrained” or “right-brained”
HOW WE STUDY THE BRAIN
• Brain lesioning – abnormal disruption in the
tissue of the brain resulting from injury or
disease
• Is done with laboratory animals to determine the
function of different parts of the brain
• Strokes and brain injuries create lesioned areas in the
brain
• Electrical activity within the brain is measured
with an electroencephalogram (EEG)
• Multiple electrodes are attached to the outside of the
head
• Advantages:
• Can detect very rapid changes in electrical activity, allowing
analysis of stages of cognitive activity
• Disadvantages:
• Provides poor spatial reasoning of the source (cells, brain
region) of electrical activity
• Neuroimaging techniques
• PET (positron mission tomography) scan –
indicates specific changes in neuronal activity by
detecting where a radioactive form of glucose
goes while the brain performs a given task
• Advantage – provides visual image corresponding to
anatomy
• Disadvantages:
• Requires exposure to low levels of radioactivity
• Not as clear as an MRI
• Cannot follow changes faster than 30 seconds
• CT (computed tomography) scan – series of X-rays
taken from different angles and combined by
computer into a composite representation of a slice
through the body
• MRI (magnetic resonance imaging) – show brain
anatomy
• fMRI (functional MRI) – can reveal brain’s functioning
and structure
FMRI SCAN OF A CONCUSSION
GENETICS, EVOLUTIONARY
PSYCHOLOGY AND BEHAVIOR
BEHAVIOR GENETICS
• Chromosome – strands of DNA wound around each
other in a double-helix configuration
• DNA – complex molecule containing the genetic
information that makes up the chromosomes
• Genes – biochemical units of heredity that make up the
chromosomes
TWIN AND ADOPTION STUDIES
• Identical twins – develop from a single fertilized
egg that splits in two
• Also called monozygotic twins
• Share 100% of their genes
• Fraternal twins – develop from separate
fertilized eggs
• Also called dizygotic twins
• Share about 50% of their genes
• Likelihood increases with use of fertility treatments
and genes