Transcript Brain Neurotransmitters

Stage 1 Psychology
Brain and Behaviour
Neurotransmitters
Human Nervous System
• The nervous system is
made up of several parts.
• The Central Nervous
System (CNS) is made up
of the areas encased by
bone-- the brain and
spinal cord.
• The Peripheral Nervous
System (PNS) includes
the rest of the nervous
system ("peripheral"
referring to the body
outside the CNS).
Where are they?
Types of Neurons
3 major types of neurons:
1. Sensory Neurons
Bring information from sensory receptors to the central nervous
system. i.e., Bring information from the eyes, ears, etc., as well
as from some organs within the body e.g., stomach. (PNS)
2. Interneurons
Neurons in the brain and spinal cord that serve as an
intermediary between sensory and motor neurons.
They carry information around the brain for processing.(CNS)
The majority of neurons are located in the brain - approx. 100 billion
3. Motor Neurons
Carry the information from the CNS to the appropriate muscles
to carry out behaviours. (PNS)
Neuron: 3 parts
1. Soma
(<-- Greek for “body”)
= the cell body which contains the nucleus,
cytoplasm, etc.
–
Everything needed for survival.
2. Dendrites (<-- Greek for “tree”)
= specialized branch-like structures used to receive
information from other neurons.
–
The more dendrites a cell has the more neurons it can
communicate with.
3. Axon (<-- Greek for “axle”)
= long, thin fibre that transmits signals away from the
soma to other neurons or to muscles or glands
– Tail-like fibre that extends from the soma to the
terminal buttons.
Structure of neurons
• Differ in size and shape
How do they work?
A. Flow of information within neurons
1. Receives input from other neurons/sense organs at the dendrites
2. Inputs are integrated and action potentials are generated in the
cell body, or soma
3. Output is conveyed to other neurons on the axon and across
synapses
What's involved in a neural impulse?
1) Ions
– Positively (+) and negatively (-) charged particles are called ions.
– Neural impulses involve Sodium (Na+) and Potassium (K+) ions.
2) Selectively permeable membrane
– the outer membrane of the neuron is not impermeable, but instead
selectively allows some small ions to pass back and forth.
3) Charge of the neuron
– Inside the neuron, the ions are mostly negatively charged.
– Outside the neuron, the ions are mostly positively charged.
– In this state (with mostly negative charge inside and positive
charge on the outside) the neuron is said to be Polarized.
4) Resting potential
• When the neuron is Polarized, it is in
a stable, negatively charged, inactive
state.
• The charge is approx. -70millivolts
• The neuron is ready to fire (receive
and send information).
5) Stimulus
• When stimulation occurs (e.g., hand
on hot iron) the information is from a
sensory receptor is brought to the
dendrites of a neuron.
6) Action potential
= a very brief shift in a
neuron’s electrical charge
that travels along an axon.
• Once the stimulation (e.g.,
the heat) reaches a certain
threshold the neural
membrane opens to allow
the positively charged ions
to rush in and the negative
ions to rush out. The
charge inside the neuron
then rises to approx. +40
mv.
7) Repolarization
= the neuron quickly restores its charge by pumping out the
positively charged ions and bringing back the negative ones.
• Can occur fast enough to allow up to 1,000 action potentials
per second. (60,000 per minute, 3,600,000 per hour, 86,400,000
per day etc.)
8) Absolute refractory period
= the minimum length of time after an action potential during
which another action potential cannot begin.
• During this period the charge inside the neuron drops to about 90 mv before being restored.
How do they work?
Flow of information between neurons
Synaptic cleft
the microscopic gap between
the terminal button of one
neuron and the cell
membrane of another neuron.
Neurotransmitters are
the chemicals which
carry the nerve impulse
from one neuron to
another.
•Excitatory
•Inhibitory
Neurotransmitters
• Acetylcholine
• Dopamine
• Norepinephrine
/Noradrenaline
• Serotonin
• GABA
• Endorphins
• Activates motor neurons controlling skeletal
muscles
• Contributes to the regulation of attention, arousal,
thirst and memory
• Has mostly excitatory effects (i.e., makes receiving
cells more likely to "fire").
•Some ACh receptors stimulated by
Nicotine
Neurotoxins - disrupting acetylcholine (ACh)
and the transmission of information
between neurons
•
Some South American Indians use curare on the tips of
arrows for hunting. The curare binds to the receptor cites
where Ach binds, so the Ach cannot be received, this
results in paralysis and death.
•
The black widow spider uses venom that causes flood of
ACh into neuromuscular synapses which results in violent,
uncontrollable muscle contractions, paralysis, and death.
Neurotransmitters
• Acetylcholine
• Dopamine
• Norepinephrine
/Noradrenaline
• Serotonin
• GABA
• Endorphins
• Contributes to the control of voluntary movement,
• Inhibitory (i.e., decreasing action of receiving cell) or
excitatory, depending on receptor on receiving cell.
• Affects areas related to body movement; emotional
arousal, and "reward" systems, pleasurable emotions
• Neurotransmitter looked at most closely for drug
addiction.
•Parkinson’s Disease is associated with
decreased levels
•Schizophrenia associated with over-activity
at dopamine synapses
•Cocaine and Amphetamines elevate activity
at synapses
Parkinson’s
Disease
•
Parkinson's disease affects nerve cells in the parts of the brain called
the basal ganglia (pronounced BAY-sel GANG-lee-ah). This part of the
brain controls movement and balance in the body.
•
These nerve cells produce and store the neurotransmitter dopamine.
•
In Parkinson's disease, the cells that produce dopamine are damaged.
The instructions from the brain to the body about movement are
disrupted as dopamine decreases.
• Nerve cells in the basal ganglia send messages that signal the
body to move.
• In Parkinson's disease, many nerve cells are damaged. They do
not produce enough dopamine to carry signals properly.
PET scan of glucose metabolic function of the brain
Studying changes in motor control in
Parkinson’s Disease
Aiming task.
Aiming and pointing with the hand of forearm to a target in space
•
Examples of “kinematic
traces” of a patient with
Parkinson’s Disease
(PD), while "on" and
"off" medication in
comparison to the
performance to a
healthy age-matched
participant.
•
Note that the patient's
performance was
clearly slowed while
"off" medication. During
the "on" state, her
speed and ability to
accelerate improved,
but she could not
sustain this for the
whole duration of the
motion.
Neurotransmitters
• Acetylcholine
• Dopamine
• Norepinephrine
/Noradrenaline
• Serotonin
• GABA
• Endorphins
• Contributes to modulation of mood and arousal
• Mostly excitatory effects
• In the brain, has effects related to emotion, drive
states such as hunger, and general brain arousal.
•Cocaine and Amphetamines elevate activity
at synapses
• Acetylcholine
• Dopamine
• Norepinephrine
/Noradrenaline
• Serotonin
• GABA
Neurotransmitters
•
•
•
•
Involved in the regulation of sleep and wakefulness, eating,
aggression
Abnormal levels may contribute to depression and
obsessive-compulsive disorder
Inhibitory or Excitatory, depending on receptor
Plays some role in perception and higher-order thinking
(affected by hallucinogens)
• Endorphins
•Prozac and other newer antidepressants work by
increasing available serotonin
Neurotransmitters
•
Acetylcholine
•
Dopamine
•
Norepinephrine
/Noradrenaline
•
Serotonin
•
GABA
•
Endorphins
•
•
•
Inhibitory-- The brain's main inhibitory transmitter.
Found throughout the brain, GABA is necessary to keep
brain activity under control.
Under-activity of this neurotransmitter can lead to seizures.
•Depressant drugs (Valium, alcohol, barbiturates)
work by increasing GABA activity
Neurotransmitters
• Acetylcholine
• Dopamine
• Norepinephrine
/Noradrenaline
• Serotonin
• GABA
• Endorphins
•
•
Resemble optiate drugs in structure and affects
Contribute to pain relief and perhaps some pleasurable emotions
•Morphine and opium work by mimicking
endorphins at synaptic receptors
Neurochemical basis of drug action
Caffeine as a psychoactive drug
• Caffeine is a central nervous system stimulant.
• In moderate doses, caffeine can:
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increase alertness
reduce fine motor coordination
cause insomnia
cause headaches, nervousness and dizziness
• In massive doses, caffeine is lethal (80 to 100 cups of coffee in
rapid succession)
• About 6 hours for one half of the caffeine to be eliminated.
• Caffeine can cause physical dependence. Typical withdrawal
symptoms = headache, fatigue and muscle pain.
Caffeine is psychoactive because it mimics a
neurotransmitter
• Caffeine belongs to the xanthine chemical group.
• Adenosine is a naturally occurring xanthine in the brain that is
used as a neurotransmitter at some synapses.
• One effect of caffeine is to interfere with adenosine at multiple
sites in the brain including the reticular formation.
Caffeine as preventative therapy for
Parkinson’s Disease?
• Honolulu Heart Program,
• 8,004 Japanese-American men over a 30 year period.
• Incidence of Parkinson's disease lower in those who drank
coffee.
• Consumption of caffeine from other sources such as green tea,
black tea, chocolate and soda was also associated with a lower
risk of Parkinson's disease.
Caffeine
• How could it work?
When adenosine receptors are blocked, levels of the
neurotransmitter dopamine increase. Caffeine may protect
against Parkinson's disease by blocking adenosine receptors,
thus increasing the amount of dopamine in the brain.
Alcohol is a central nervous
system depressant
• In low doses, alcohol produces:
*
*
*
*
*
*
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a relaxing effect (inhibits anxiety)
reduces tension
lowers inhibitions
impairs concentration
slows reflexes
impairs reaction time
reduces coordination
• In medium doses, alcohol produces:
* slur speech
* cause drowsiness
* alter emotions
• In high doses, alcohol produces:
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vomiting
breathing difficulties
unconsciousness
coma
•Structure of ethanol
Alcohol works via many neurotransmitters:
•
Alcohol acts at many sites, including the reticular formation, spinal
cord, cerebellum and cerebral cortex, and on many neurotransmitter
systems.
•
Some of the effects of alcohol on neurotransmitters are:
1.
2.
3.
1.
2.
Increased concentration of norepinephrine and dopamine (D=pleasure
centres)
Decreased transmission in acetylcholine systems
Potentiates GABA receptor sites (inhibitory) (sedative)
Increased production of beta-endorphin in the hypothalamus
Alters serotonin transmission (behaviour inhibitor) (aggression, sexual
activity)
Role of myelin in behaviourMultiple Sclerosis
• MS is thought to be an autoimmune disease that affects the
central nervous system (CNS).
• In MS, myelin is lost, leaving scar tissue called sclerosis (also
known as plaques or lesions). Sometimes the nerve fiber itself is
damaged or broken.
• Magnetic resonance imaging brain scan showing areas of
abnormal tissue (arrows) in multiple sclerosis
Cognitive symptoms of MS
• The MS symptoms that usually grab the spotlight are the
physical ones—balance, gait, muscle control, bladder control,
vision, numbness.
• In the last decade, evidence on how MS may affect cognition
• 40% to 60% of people with MS develop some degree of
“cognitive dysfunction”. Most people who are affected have mild
problems.
• Cognitive dysfunctions arise when lesions (or areas of MS
damage) occur in certain locations in the cerebral hemispheres,
the “thinking” part of the brain.
Common cognitive symptoms of MS:
• Poorer memory for recent events and information
• Fluency with words may be diminished.(word search <-memory )
• When a lot of information is coming all at once, processing may
take longer.
• Judgment and problem solving may be slower or less reliable.
Some people with MS-caused cognitive problems have difficulty
analyzing a situation, coming up with a solution, and carrying it
out.