Transcript Biology and Behaviour 40s

Biophysiology
• Did everyone in the class describe the same
objects in the same way?
• Did everyone guess the same object?
• The nervous system underlies everything we
do. Understanding biology is fundamental to
understanding behaviour.
• We need to know the mechanics of sensation
before we can understand perception.
Is the center spinning?
Which intersections have white dots
and which are black?
Is it rotating?
Ignore the word and say the color
Are the horizontal lines parallel?
Which center dot is bigger?
Are the horizontal lines straight?
Count the spirals
Star or square?
COUNT THE F’S
• FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC COMBINED WITH THE
EXPERIENCE OF YEARS.
Straight or parallel?
Which center line is longer?
The Biological Bases of Behaviour
• In order to understand the mind, psychologists
must first understand how the body works
and is constructed.
• Before becoming a software engineer, you
must first know how a computer is put
together and how it works.
The basic hardware
• The nervous system is composed of billions of
cells called neurons.
• Neuron – individual cells that receive,
integrate, and transmit information.
• Humans are born with a fixed number of
neurons, Between 10 and 100 million.
• We lose an average of 10,000 per day, but
over a lifetime, that amounts to less than 2%
of the total.
Neurons
• Receptors – specialized structures capable of
turning stimuli in the environment into
electrical impulses in the body.
• Afferent nerves – nerves that transmit signals
into the brain.
• Efferent nerves – nerves that carry signals
from the brain to the muscles.
Brain
Impulse
Stimulus
Afferent
nerve
Receptor
Impulse
Efferent
nerves
Impulse
Muscle
• Sensory neurons carry signals from the outer parts of your body
(periphery) into the central nervous system.
• Motor neurons (motoneurons) carry signals from the central nervous
system to the outer parts (muscles, skin, glands) of your body.
• Receptors sense the environment (chemicals, light, sound, touch) and
encode this information into electrochemical messages that are
transmitted by sensory neurons.
• Interneurons connect various neurons within the brain and spinal cord.
• The simplest type of neural pathway is a monosynaptic (single
connection) reflex pathway, like the knee-jerk reflex. When the doctor
taps the the right spot on your knee with a rubber hammer, receptors
send a signal into the spinal cord through a sensory neuron. The sensory
neuron passes the message to a motor neuron that controls your leg
muscles. Nerve impulses travel down the motor neuron and stimulate the
appropriate leg muscle to contract. The response is a muscular jerk that
happens quickly and does not involve your brain. Humans have lots of
hard-wired reflexes like this, but as tasks become more complex, the
pathway "circuitry" gets more complicated and the brain gets involved.
• When a sensation reached the threshold – the
minimum strength required – a signal is
triggered in the dendrites of the neuron.
• Threshold – the minimum intensity required
to trigger a chain reaction in a neuron.
Synaptic Transmission
• Scientists had always believed that there was
some mechanism connecting two neurons
together.
• This was finally proven in 1920 by Otto Loewi.
• Lowei’s experiment proved that the
transmission from one neuron to the next
involved a chemical substance.
Synapse
• Synapse – the gap between the axon terminals
of the transmitting neuron and the dendrites
of the receiving neuron.
Synaptic Transmission
• As the impulse reaches the axon terminals,
tiny sacs of specialized proteins called synaptic
vesicles rupture at the surface of the terminal.
• These vesicles pop and release a chemical into
the synapse called a neurotransmitter.
Neurotransmitters
• Neurotransmitter – chemical substance that is
released at the terminal end of the neuron
that travel across the synapse and have an
excitory or inhibitory effect on the adjacent
neuron.
Receptors
• As each neurotransmitter crosses the synapse,
it lands on specialized receptor cells on the
dendrites of the next neuron.
• The receptors then lower the action potential
of the neuron.
• As each neurotransmitter reaches a receptor,
the action potential is lowered more and more
until the threshold is reached and an impulse
is triggered.
Lock and Key Model
• Each neurotransmitter is paired with the
special receptor at the end of the postsynaptic neuron. Each receptor can only be
activated by it’s paired neurotransmitter.
Reuptake
• Excess neurotransmitter in the synapse is
removed to prevent prolonged stimulus and
interference in two ways:
• Enzymes located in the synapse break down
the chemicals into smaller component parts.
• The axon terminal will reabsorb excess back
into the neuron cell.
The Nervous System
• The nervous system
constantly monitors,
controls and
maintains an optimal
state in the body
called homeostasis.
The nervous system has two parts:
• The Central Nervous System – the brain and spinal
cord. The spinal cord consists of a large bundle of
nerve fibres that run down the back and transmit
signals between the body and the brain.
• The Peripheral Nervous System – includes the
smaller nerves that branch out from the spinal cord.
These nerves take information from the body’s
organs to the central nervous system and return
information to the organs.
The peripheral nervous system is
divided into two functions:
• Somatic division – concerned with the control
of the skeletal musculature and the
transmissions from the sense organs.
• Autonomic division – serves the structures
that are concerned with basic life processes
such as heart beat, contraction of the stomach
and intestines, and genital organs.
Brain structures
• Where the spinal cord meets the brain is the
brain stem, attached to the brain stem are two
structures;
• the cerebral hemispheres, which totally
envelope the brain stem
• the cerebellum which is attached further
down and is much smaller.
The brain itself can be divided into
three portions:
• The forebrain
• The mid-brain
• The hindbrain
The Hindbrain
• What two structures are located in the
hindbrain?
• The medulla and the cerebellum.
What are the functions of the two
parts of the hindbrain?
• The medulla controls heartbeat, circulation,
respiration, and other vital functions.
• The cerebellum controls balance and muscular
coordination.
The Midbrain
• What is the dominant structure in the
midbrain?
• The reticular formation.
How is the midbrain related to
sleep?
• It is related to activation of other parts of the
brain and when it is deactivated regulates
sleep.
The Forebrain
• What is the function of the thalamus?
• It coordinates and regulates information from
sensory organs and motor centers to the
cerebral cortex.
What is your guess as to the effect
of overstimulation of the
hypothalamus? Why?
• Because the hypothalamus controls behaviours
related to basic biological urges, overstimulation
would probably lead to someone who eats, drinks,
and sleeps too much and is probably inappropriate
frequently.
What is meant by “functional
summit”?
• Functional summit
refers to the most
complex, most capable,
and most sophisticated
part of the human body.
It is the part of the body
that is capable of the
most significant and
powerful actions.
What are the four lobes of the
cerebral hemisphere?
• Frontal, parietal, occipital, temporal lobes.
What is the function of the cerebral
cortex? Why do scientists believe that is a
recent development in evolution?
• The cerebral cortex is the location for higher brain
functions like thinking, memory, and planned and
voluntary action. Scientists believe it is a recent
evolutionary adaptation because many organisms
lack one like fish, and many have only the beginnings
of one like reptiles, and birds.
What do you think happened to
Leonard’s brain based on these
notes?
• Leonard must have suffered damage to his
basal ganglia when he was young because it is
the location of dopamine circuits and
Leonard’s condition improved after taking
synthetic dopamine.
Why do you think the limbic system
called the “old cortex”? What does this
mean about “human” behaviour?
• Because the limbic system is involved in
motivation and emotion, it is linked to more
primitive and basic functions whereas the
cerebral cortex is involved in rationality,
thinking, memory, and planning.
• This would lead us to believe that, based on
biology and brain functioning, what makes us
human is our higher brain functions. What
makes us more “advanced” is our rationality,
our thinking, and our premeditation; not our
emotions or our basic motivations.
The Cerebral Cortex
• The cerebral cortex is the key to human
intelligence.
• Without it, there can be no planning, no
complex speech, no complex sequence of
movement, no organizational perception.
Function zones
• The cortex is divided into two zones based on
their function:
• Projection areas – serve as receiving areas for
sensory information and as dispatching
centers for motor commands.
• Association areas – the remaining 2/3rds of
the cortex is devoted to higher mental
functions like planning, perceiving,
remembering, thinking, and speech.
Projection areas
• Motor projection areas of the cortex are
linked with control parts of the body.
• These can be mapped with a high degree of
accuracy to create a motor homonculus, or a
schema of the body as it is represented on the
cortex.
Motor homunculus
Sensory areas
• Each part of our body also has a designated
area of the cortex devoted to sensation –
called the somatosensory area.
• This map can be used to create a sensory
homunculus of the region of the brain devoted
to sensation.
Sensory homunculus
Sensory areas
• Other parts of the
cortex are devoted to
the different senses.
• These are the visual
cortex, and the
auditory cortex.
Association Areas
• Association areas are
related to complex
mental functions like
speech, thinking, and
remembering.
• The precise locations of
these activities can be
discovered through
lesions (damaged
tissue) in the brain.
Association Areas
Studying Localization
• The location of these lesions results in the loss
of a specific function.
• Lesions can be discovered through:
• PET scan – Positron Emission Tomography
• CAT scan – Computerized Axial Tomography
• MRI scan – Magnetic Resonance Imaging
Localization - Phineas Gage
• Author: Damasio et al. 1994
• Type: Case Study, single subject, non-random sample, instrumental – it sought
to construct/confirm a hypothesis regarding localization of inhibition in the
brain as well as explaining the phenomena of his changed behaviour by what
his brain injury turned out to be once they could perform an autopsy.
• Aims: To discover the nature of the injuries to Gage’s brain and correlate those
injuries with the changes in his behaviour reported from the period –
disinhibition
• Method: Using modern technology, researchers reconstructed the injury to
Gage’s skull and compared those to historical accounts of his behaviour before
and after the injury.
• Conclusions: The reconstructed injury based on the skull of Gage indicated
damage to the pre-frontal lobe of the brain which corresponds with prior
knowledge of the localization of inhibition in the brain. This correlates
positively with the changes in behaviour of the subject described by the
historical accounts.
What do we know?
• Localization of brain function is not set,
• continually under study and subject to
revision as new information comes available.
https://www.youtube.com/watch?v=dFs9WO2B8uI
Neurotransmitters and behaviour
• We must remember how the nerve functions
Impulse
• Once the threshold is achieved in the cell
body, the protein “gates” of the axon open
and Na+ ions rush in.
• For 1 millisecond, the outside of the axon
body becomes – and the interior becomes +.
Propagation
• The polarity of the axon body is reversed as the
threshold is achieved.
• Gates in the cell membrane open briefly to let Na+
ions rush in.
• These gates quickly close and K+ ions slowly leak out
and the cell begins to actively pump Na+ ions back
out.
• This returns the cell to it’s resting state.
• The depolarization of the cell produces electric
currents that stimulate the threshold value in
neighboring regions as the impulse travels down the
axon.
All or None Law
• Once the impulse is triggered, the
intensity of the signal is constant.
• All or None Law – the stimulus
does not provide the energy of the
nervous impulse.
• This means that a stronger
sensation is caused by a greater
number of neurons being
stimulated, not a stronger impulse.
Pain
• The All or None Law is important for the study
of sensations like pain.
• Intense sensation can be caused by two
factors:
• A strong stimulus will trigger a higher
NUMBER of neurons to fire
• A strong stimulus will trigger a greater
FREQUENCY in the neuron impulse.
• The highest frequency in the human body is 1,000 impulses/second
• The list:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Neurotransmitters
Ach
5HT
GABA
NE
DA
Amphetamines
Curare
Endorphins
SSRIs
MAOIs
Cocaine
Benzodiazepines
You will be numbered by me
• Your assignment: Research and record the
function of the neurotransmitter/drug that
corresponds to your number.
• You will trade, compare and copy notes from
your classmates.
• A short quiz will follow
The Endocrine System
• Closely related to neurotransmitters,
hormones are chemical substances that have
an effect on structures elsewhere in the body.
• While neurotransmitters work across the
synaptic cleft 1/10,000mm wide, hormones
work across the entire body. They can have an
immediate and important impact on
behaviour.
Role of hormones
• Hormones are released by endocrine glands
and have specific effects on the body based on
the body’s need to maintain homeostasis.
They are vital to human development and
behaviour.
Master gland
• The hypothalamus regulates
the pituitary gland which
sends out a variety of
hormones for growth and
development. It is the “central
command” for other
endocrine structures.
• Eg. Gonadotrophins – direct
the formation of external
sexual organs in the
developing fetus.
The Endocrine
glands
Glands and their function
• Anterior
pituitary
• Often called the body’s master
gland because it triggers hormone
secretion in many of the other
endocrine glands.
• Prevents loss of water through
• Posterior
kidney
pituitary
• Affects metabolic rate
• Thyroid
• Islets in the • Affects utilization of glucose
pancreas
Glands and their function
• Adrenal cortex
• Adrenal medulla
• Ovaries
• Testes
• Various effects on metabolism; some
effects on sexual behaviour
• Increases sugar output of liver;
stimulates various internal organs in
the same direction as the sympathetic
branch of the ANS.
• One set of hormones (estrogen)
produces female sex characteristics
and is relevant to sexual behaviour.
• Another hormone (progesterone)
prepares uterus for implantation of
embryo.
• Produces male sex characteristics.
Relevant to sexual arousal.