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Behavioral Neuroscience

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Neuroanatomy
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ALS (Amyotrophic Lateral Sclerosis) – neurodegenerative disease that starts with
progressive symptoms, which involve muscle weakness and eventual paralysis
o Is idiopathic, which means that the cause of the disease is unknown
o What happens to the nervous system?
 Motor neurons in the spinal cord degenerate and die, which is what causes
motor weakness and paralysis
 Upper and lower motor neurons in the cortex both degenerate and die
 The motor neurons in the brain stem has motor neurons that control
breathing muscles, which degenerate and die, and it causes breathing
problems
o What is preserved in ALS?
 Autonomic nervous system
 Conscious perception and sensation (touch, sight, etc)
 Language
 “higher order cognition”
Divisions of nervous system:
o Central nervous system consists of the brain and spinal cord
o Peripheral nervous system consists of
o Nerves are bundles of axons
o Stimulating a motor nerve causes a muscle to contract
o Motor nerves arise from cells in the spinal cord and are called motor neurons
o In the spinal cord you see two matters, which are gray and white
 Gray matter contains cell bodies
 White matter consists of axons
o Command from the cortex and brain stem goes to the spinal cord then motor
nerve, which makes the muscle move
Human Brain
o The cerebral hemisphere/cortex includes four lobes:
 Frontal lobe is the most anterior region
 Parietal lobe is behind the frontal lobe and is divided from the frontal lobe
by the central sulcus
 Occipital lobe is the back of the brain
 Temporal lobe is on the side, below the parietal and frontal divided by the
sylvian fissure
o Brain surface has two types of surfaces
 Gyrus is a ridged or raised portion of the convoluted brain surface, which
is at the top
 Sulcus is a furrow of the convoluted brain surface, which is at the bottom
 Central sulcus is the boundary between the frontal and parietal lobes
o What does the cortex do?
 Conscious perception, voluntary motor control, language, and “higher
order cognition”
 Motor cortex is part of the parietal lobe and contains neurons that project
to the spinal cord
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Is responsible for motor control and have very long axons that go
from the cortex and brain stem, which projects to the spinal cord
 Lower motor neurons go from the spinal cord to the muscle
 Upper motor neurons go from the cortex to the spinal cord
Has two hemispheres:
 Right processes information from the left side of the body
 Controls muscles on the left side of body
 Left processes information from the right side of the body
 Controls muscles on the right side of body
 Corpus callosum is a bundle of axons that connects the right and left
hemispheres
Brain stem is involved with:
 Digestion, breathing, sleep, arousal, temperature control, and motor
control
 Damage to the brain stem would have dire consequences since it’s a small
structure
 It controls the autonomic nervous system, which controls glands and
muscles
Nervous system is divided into two parts:
 Central nervous system
 Peripheral nervous system consists of:
 Somatic nervous system
 Autonomic nervous system
Spinal cord carries sensory information from skin to brain
Neural Activity & Synapses
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Changes in the electrical potential (voltage) of a single neuron
Santiago Ramon y Cajal
o Spanish scientist and first neuroscientist
o Made the first drawings of neurons
Neurons have four parts/zones:
o Input zone – receives information from other cells through dendrites
o Integration zone – cell body (soma) where inputs are summed
o Conduction zone – single axon leads away from the cell body and transmits the
electrical impulse
o Output zone – axon terminals at the end of the axon communicate activity to other
cells
Neurons can have many dendrites but always only have one axon, which may have
multiple terminals
Luigi Galvani
o An Italian scientist who studied physiology
o When dissecting a frog realized there was some sort of electrical signal, which
made the frog move
o He stimulated a nerve with electricity which made the muscle contract
Ions
o Charged particles, for example Na+ while Clo The inside of a cell is negative relative to the outside because the cell tries to keep
Na+ outside
o The membrane acts as a barrier between the inside and outside
o Semi-permeable membrane is when the cell allows some Na+ to come through,
which makes the inside of the cell positively charged relative to the outside
o However, then the Na+ leaves and the cell is once again negative relative to the
outside
o There are multiple sodium channels which will allow for the ions to enter the cell;
however, it is normally closed and only occasionally opens (opens for a short
period of time)
o Action potential
 When the Na+ has entered, which forces an action
 Originates in the axon hillock
 Propagated along the axon
 Hillock is full of Na+ channels
 Axons are myelinated
 Has an all-or-none property, which means that the neuron fires at full
amplitude or not at all
o Resting potential is when cell is not active
o Threshold voltage is when the cell has to get to a certain voltage for there to be an
action potential (low or high and it effects how easy it is to get a reaction)
 What determines the threshold is when the channels in the cell (voltage
gated channels) recognizes the voltage changing
o Voltage is the measure of electrical potential
o Nodes of Ranvier
 Little gaps in the myelin sheath (acts as insulation) and contain the Na+
channels
o Dendrites contain receptors which open in response to neurotransmitters and these
receptors allow the passage of Na+
 Some channels known as ligand channels open up when a neurotransmitter
(from other cells) attaches itself to it
 Influx of Na+ causes change in voltage in dendrite
 Excitatory post-synaptic potential are light changes in voltage
 If a whole bunch of neurotransmitters start firing (activity and input in the
dendrites) then there will be an influx of Na+ in the cell, which will cause
the voltage to reach the threshold and eventually generate the action
potential
 Neurons generate action potential when EPSP’s push neuron past
threshold
o The differences between action potential and EPSP
 Location – action potential starts in the axon whereas the EPSP’s are in
the dendrites
 Channels – the action potential is caused by a voltage gated channel
whereas the EPSP is caused by the ligand gated channel
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Amplitude – action potential is always all or nothing, but require the same
voltage whereas EPSPs depend on the amount of stimulus and their sizes
vary
o Epilepsy
 A chronic condition where an individual has seizures
 A seizure is uncontrollable neural activity in the brain and can be either:
 Generalized – when a person is catatonic, may cause death
 Partial – when a certain location is affected
 Neural activity is measured by the EEG
 There needs to be a balance between excitatory and inhibitory, but when
having a seizure, the excitatory part wins
Neurotransmitters
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Neurotransmitters are inside vesicles
o A chemical that has to be synthesized in a neuron, sent to the axon and all the way
down to the axon terminal (pre-synaptic); released at axon terminal and released
by action potential (post-synaptic)
o It then travels across the synaptic cleft and the neurotransmitter will stimulate the
post-synaptic receptor (only glutamate), which creates a transient signal
(neurotransmitter will bind to the receptor briefly and then decouples from the
receptor)
Most neurotransmission in the brain involves two neurotransmitters
o Glutamate
 Main excitatory neurotransmitter in brain
 When glutamate channel opens it stimulates glutamate receptors
 Causes Excitatory Post Synaptic Potential (EPSP)
 Allows the passage of Na+, which allows activity
o GABA
 Main inhibitory neurotransmitter in brain
 Stimulates GABA receptors
 Causes Inhibitory Post Synaptic Potential (IPSP)
 Allows the passage of Cl-, which inhibits activity
Drugs
o Anti-seizure drugs stimulate GABA receptors as well as alcohol
o All neurotransmitters are endogenous and agonist
o Some drugs exist in nature that act like neurotransmitters
 Ex. Muscimol is derived from mushrooms and acts on GABA receptors
o Endogenous – chemicals naturally created/present within the body
o Exogenous – chemicals introduced from outside the body
o Agonist – a chemical that will bind to/stimulate a receptor
 All neurotransmitters are agonists as well as some natural compounds
o Antagonist – a chemical that binds to a receptor but blocks it from stimulating
 Ex. Ketamine is a sedative that blocks glutamate receptors
o Two types of neurotransmitters:
 Directly change voltage like Glutamate and GABA
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Neuromodulators have indirect effects on cell activity:
 Dopamine
o Activated when one receives an award, released during
“salient events”
o Involved in mood, decision making and movement
(Parkinson’s disease)
o Cocaine and amphetamine affect dopamine
o DAT (dopamine transporter)
o Drugs that block DAT (stays in cleft) increases dopamine
signal
o Neuroleptics block dopamine receptors and act as antipsychotics
o Psychostimulant drugs affect two processes at
synapse/regulate neurotransmitter release:
o Reuptake
 Transporters in pre-synaptic site picks up the
neurotransmitter and gets it back in the terminal
o Autoreceptors
 Located on the axon terminal
 Detects the amount of dopamine
 Serotonin
o Involved in sleep, mood & anxiety, as well as digestion
o SSRI’s (Selective serotonin reuptake inhibitor) increase
serotonin activity and improves mood
o The serotonin transporter removes serotonin from synapse
o Degradation is when the neurotransmitter is transformed,
which breaks it down; the degradation of serotonin by
enzymes (MAO)
o Drugs that block MAO prolong serotonin signal
 Cannabinoids
o Affects cognition, mood, appetite, and pain
o Transmission that goes from the dendrite to the axon
terminal is called retrograde signaling
 An endocannabinoid inhibits further release of
cannabinoid
o Drugs that block cannabinoid receptors improves memory
o Drugs that simulate cannabinoid receptors alters cognition
o released and then inhibits further dopamine release
Caffeine blocks adenosine receptors, which prevents negative-feedback
loop and prolong dopamine signal
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