Transcript Biological Level of Analysis - Neurotransmission   Your brain is made up of cells. Brain cells come in two types:  neurons, which talk to.

Biological Level of Analysis - Neurotransmission


Your brain is made up of
cells.
Brain cells come in two
types:
 neurons, which talk to one
another and to the rest of the
body, and
 glial cells, which provide
essential support to keep the
whole show going.

There about 100 billion
neurons and many more
glial cells.
The Neuron

Signals within a neuron are carried by electricity.

To send electrical signals from one part of the neuron
to another, the neuron opens channels that allow the
ions to move across the membrane, creating a current
that carries an electrical signal down the membrane.

Neurons receive inputs through branched, treelike
structures called dendrites, which put together
information from a bunch of different sources.

The neuron then sends an electrical signal down a long,
wirelike structure, called an axon, which triggers a
chemical signal to another neuron, and so on.
The Neuron

Axons carry signals over long distances; your longest
axons run from your spine to the tips of your toes.

Each neuron in the brain receives chemical signals from
some neurons and sends chemical signals to others.

Communication between neurons relies on chemicals
called neurotransmitters, which are released from
small areas at the end of the axon when triggered by the
arrival of a spike.

Spikes are sudden increases in the electrical currents in
a neuron.
The Neuron

Every neuron makes and receives
up to several hundred thousand
chemical connections, called
synapses, with other neurons.

Neurotransmitters stick to
synaptic receptors on the
dendrites or cell bodies of another
neuron, triggering further
electrical and chemical signals.

All of these steps, from release to
detection, can take place in a
thousandth of a second.
The Neuron

For the brain to accomplish its many duties, neurons
have to take on very specific tasks. Each neuron
responds to a small number of events, such as hearing
a particular sound, seeing someone’s face, carrying out
a certain movement.

At any given moment, only a small fraction of your
neurons, distributed all over your brain, are active.

This fraction is ever shifting; the whole game of
thinking depends on which neurons are active and
what they are saying to each other and to the world.
Nucleus
Axon Hillock
The Neuron

Sensory neurons carry signals from the outer parts of
your body (periphery) into the central nervous system.
They are specified in the senses of taste, touch, hearing,
smell, and sight. They send messages from the sensory
receptors to the Central Nervous System.

Motor neurons carry signals from the central nervous
system to the outer parts (muscles, skin, glands) of your
body. Control muscle contractions.

Interneurons connect various neurons within the brain
and spinal cord. They carry information between motor
and sensory neurons.
The Neuron

Neurons transmit electrical signals called action
potentials.

Action potentials work a bit like a ‘Mexican
wave’

The presence of a myelin sheath on a neuron
changes the rate of transmission.

Synapses are the essential components of
communication in your brain.

Your thought patterns, basic abilities and functions,
and individuality are determined by how strong
these synapses are, how many of them you have,
and where they are.

Neurons use synapses to talk to each other within
the brain.

Only a small fraction of axons form their synapses
outside the brain or spinal cord, sending signals to
other organs of the body, including muscles.

Each neuron has direct synaptic contact with
several thousand other neurons.

Neurons do not touch each other, instead
contact is make through neurotransmitters.

Neurotransmitters are the chemical messengers
used by neurons to communicate with each
other.

It has been estimated that there are over 100
neurotransmitters.



Neurotransmitters are stored in the vesicles inside
the terminal button of the axon; the vesicles are
transported to the edge of the button – then released
into the synaptic gap
In the synapse – the neurotransmitter can bind with a
receptor if the receptor site is the right type and is
vacant. If enough of the neurotransmitter binds to
the receptor site, the neuron will ‘fire’ – transmit
information across the cell body electrically.
If the neurotransmitter is blocked or replaced, then
the messages change. This affects the physiological
system – cognition, mood, behaviour



When the information is received at the end of the
axon neuron, this chemical process is repeated.
Unused neurotransmitter is eventually absorbed
back into the neuron it came from (or enzymes
will remove it from the synaptic cleft). This is
called reuptake.
Certain drugs can be introduced to the nervous
system to encourage or prevent the production
or release of neurotransmitters.


Certain drugs can occupy receptor sites that
would normally receive a neurotransmitter. This
has an effect on the receiving neuron as well as
preventing the naturally occurring intended
communication between neurons.
Certain drugs prevent the reuptake of
neurotransmitters – allowing more time to bind
to receiving neurons

Read Information Box in textbook, pg27.

Monoamines:
 Acetylcholine (ACH) – involuntary muscle movement, learning
memory and sleep
 Norepinephreine (NE) – controls sympathetic nervous system,
involved in eating and alertness
 Dopamine (DA) – involved with movement, attention, learning
and memory.
 Serotonin (5-HT) – involved in inducing sleep, sensory
perception, temperature regulation, control of mood, appetite
and aggressive behaviour

Amino Acids:
 GABA – most common and is involved in most aspects of brain
functioning – from memory to sleep.

Peptides: there are over 50 peptide neurotransmitters



Neurotransmitter involved in motivation
(pleasure seeking), control of movement,
emotional response and addictive behaviour
Addictive drugs increase the levels of
Dopamine
Nicotine – the psychoactive ingredient in
tobacco – increases dopamine in the rewards
circuit creating a relaxing effect



L-Dopa – treatment of Parkinson’s disease –
triggers release of dopamine n the motor
cortex
Chlorpromazine (and other anti-psychotics) –
reduces symptoms of Schizophrenia by
reducing dopamine levels
Cocaine – intense feelings of pleasure and
faster cognitive activity – prevents reuptake
of Dopamine


fMRI scans used to study
brain areas involved in
the subjective
experience of pleasure.
Found the orbitofrontal
cortex was active when
people reported feeling
pleasure


Researchers concluded
that: dopamine & the
nucleus accumbens is
involved in pleasure seeking.
This could explain addictive
behaviour.
The orbitofrontal cortex
and endorphins perhaps
linked to the subjctive
experience of pleasure.




Earliest neurotransmitter discovered in the
1930s – released by motor neurons to activate
muscle fibres
Along with other – it forms a part of the
cholinergic system associated with higher
cognitive function (via interneurons)
Thus acetylcholine is linked to effects with
muscle contraction as well as the plasticity of
the hippocampus – and therefore development
of memory
Martinez & Kesner (1991) – see Crane p41
Aim: to investigate the role of ACh in memory
formation.
 Used rats trained to run a maze. Divided into three
groups:
 Group 1 – received scopolamine (blocks ACh
receptor sites inhibiting release of ACh)
 Group 2 - received physostigmine (blocks
production of enzyme cholinesterase which cleans
up ACh – leading to more Ach in the synaptic gap
 Group 3 – Control group

Results:
 Group 1 – problems finding way through the
maze & made more mistakes
 Group 2 – ran quickly through the maze & made
few mistakes. Faster than the control (group 3)
Evaluation
 Shows Ach is imporant in memory – rats showed
different memory capacity depending on Ach
level. Ach is ONE factor that affects memory –
but neurobiology of memory is complex
The hormone oxytocin is secreted by the
hypothalamus and released (1) into the blood
stream via the pituitary gland or
 (2) into the brain and spinal cord where it binds to
oxytocin receptors.
 Oxytocin acts primarily as a neurotransmitter
 Oxytocin has been linked to trusting other people.
 Experimental manipulation of oxytocin levels has
shown increase in trust.
 According to evolutionary psychologists, trust is an
important social tool in the relationship between
humans.

Trust is an adaptive mechanism as it helps humans to
form meaningful relationships at a personal and
professional level. Betrayal disrupts bonds of trust and
may result in avoidance of the person who has betrayed
you.
 Learning who to trust and who to avoid is important
for survival and the well-being of an individual. Humans
should also be able to move on after experiences of
breaching trust if long-term relationships and mental
well-being are to be preserved.
 Oxytocin could play a role in reducing fear reactions via
the amygdala that may arise as a consequence of
betrayal.

Aim
 To investigate the role of oxytocin after breaches
of trust in a trust game.
Procedure
 The participants played a trust game used by
economists and neuroscientists to study social
interaction.
 The "investor" (player 1) receives a sum of money
and must decide whether to keep it or share it with
a "trustee" (player 2). If the sum is shared the sum is
tripled. Then player 2 must decide if this sum should
be shared (trust) or kept (violation of trust).


fMRI scans were carried out on 49 participants.
They received either oxytocin or placebo via a
nasal spray.
Participants played against different trustees in
the trust game and against a computer in a risk
game. In 50% of the games their trust was
broken. They received feedback on this from the
experimenters during the games.

Participants in the placebo group were likely to show less
trust after feedback on betrayal. They invested less.

Participants in the oxytocin group continued to invest at
similar rates after receiving feedback on a breach of
trust.

The fMRI scans showed decreases in responses in the
amygdala and the caudate nucleus. The amygdala is
involved in emotional processing and has many
oxytocin receptors. The caudate nucleus is associated
with learning and memory and plays a role in rewardrelated responses and learning to trust.



Oxytocin could explain why people are able to
restore trust and forgive in long-term
relationships.
Scanner research is merely mapping brain
activity but nothing definite can be said about
what it really means at this point in science.
Giving oxytocin like this in an experiment may
not reflect natural physiological processes.
The function of oxytocin is very complex




Cortisol is a hormone produced by the adrenal
cortex in response to stress and to restore
homeostasis (the body’s normal balance). Chronic
stress may result in prolonged cortisol.
It increases blood sugar and suppresses the
immune system
Has been associated with both depression and
memory problems.
MRI shows that elevated levels of cortisol can
damage the hippocampus




Aim: To investigate how levels of cortisol
interfere with verbal declarative memory.
Procedure: A self-selected sample (recruited
through advertisement) of 51 normal and
healthy people aged 18-30 was used.
It was a randomized, controlled, double-blind
experiment running for four days.
All participants gave informed consent.




There were three experimental conditions:
1. A high level of cortisol (tablet of 160 mg
per day), equivalent to cortisol levels in the
blood as a consequence of a major stressful
event.
2. A low level of cortisol (tablet of 40 mg per
day), equivalent to cortisol levels in the
blood as a consequence of a minor stressful
event.
3. A placebo (tablet of no active ingredient).



The high-level group performed worse on the
verbal declarative memory test than the lowlevel group.
They performed below placebo levels after day
1.
The low-level group (mild stress) showed no
memory decrease.


This was a controlled randomized experiment
so it was possible to establ ish a cause-effect
relationship between levels of cortisol and
scores on a verbal declarative memory test.
Ethical issues were observed with informed
consent. The negative effect of taking high
dosages of cortisol was reversible so no harm
was done.

Stress as a Psychobiological Process

Hans Selye (1956) first argued for the General
Adaptation Syndrome - a model of stress reponse
after experimenting on laboratory animals involving a
variety of stressors including toxins, physical restraint,
extreme heat and bacterial infections.

The GAS model proposes that there is the same bodily
response to ALL stressors.

The Syndrome refers to a typical combination of
factors that make up the stress response.






Alarm mobilises the body for swift action - such as the 'fight or
flight' response.
Occurs over seconds or minutes in response to a sudden stressor
Heart rate, blood pressure increase, increase in blood sugar from
the liver for extra energy
Increased tension in the muscles
Respiration deepens
Blood increases ability to clot

Very severe response can be life threatening - a heart attack can
occur when the body goes into shock.

If stressor disappears or body returns to resting level - adaptation
has been successful



Occurs when stressor persists
Hormones from pituitary gland and adrenal
cortex increase
Alarm systems disappear giving appearance of
return to normal physiological functioning but arousal is still high as resistance to stressor
is raised






Occurs when stressor persists but the body’s
defences can no longer cope.
Adrenal glands cease to function normally
Blood sugar levels drop
Symptoms that occur with alarm stage such as
raised blood pressure can appear irreversibly
Followed by a massive decline in resistance
Can lead to Psychosomatic illnesses (such as
stomach ulcers, heart disease, hypertension)