Lecture Notes 9.12.2018
NEUROSCIENCE –NEURONS
Nerve Communication
Activations of neurons in the brain help us interpret sensory cues.
Everything psychological is simultaneously biological
The power of the brain in terms of sense, emotions, thinking –comes from neural
communication: cells in the brain called neurons, that communicate to one another
through chemical messages.
How are Neural Messages Created?
A neuron consists of a cell body (soma) and two type
branching fibers:
o Dendrites are short bushes of fiber that take
information from outside of the cell and pass
on to the cell body.
o Axons are short or long extensions that take
info from the cell body and pass it on to the o
neurons or muscles/ glands, etc.
Lipids cover the axons of some neurons, called the myelin sheath that speeds up the
neural response. The most amount of myelin is in the frontal lobe (that controls
judgement). As we age, the development of the brain creates more myelin.
Action potential (the neural message) is the change in the voltage of the cell.
o The resting membrane potential (-70 mV) is when a nerve impulse is not being
transmitted. AT REST Positive Na+ ions are present outside the (in the cytoplasm)
and slightly positive K+ are present inside the cell;
thus, the cell is negatively polarized at -70 millivolts
(mV). All gated Na+ and K+ channels (voltage
gated) are closed.
The cell membrane is
permeable to K+ ions, and so
lots of K+ leaks out of the
neuron through K+ leak channels. The
membrane is partially permeable to Na+
ions, so they slowly leak into the neuron
through Na+ leak channels.
Because the cell wants to maintain a negative membrane potential, it
must pump K+ into the cell and Na+ outside of the cell at the same time.
o Depolarization makes the cell less polar (membrane potential gets smaller as ions
quickly begin to equalize the concentration gradient) after passing the threshold
, (-55 mV) to about +40 mv. Voltage-gated Na+ Channels activate and K+ channels
also activate.
Voltage-gated Na+ ions flow into the negatively charged cell membrane
and depolarizes the cell.
K+ channels also activate, K+ flows out of the cell, down the membrane.
o Repolarization brings the cell back to its resting potential. The cell becomes more
negatively charged. Voltage-gated Na+ channels close and K+ channels remain
open.
Na+ activation gates closed, stopping the inward flow of positive ions.
K+ channels also open, but there are more K+ exiting than entering the
cell, making the cell more negatively charged.
o Hyperpolarization makes the cell more negatively than its typical resting
membrane potential.
Because the K+ ion channels stay open, it continues to let positive ions
exit the cell. As the K+ closes, the Na-K Pump works to reestablish the
resting state.
Action potentials work on all-or-nothing basis, meaning that an action potential is either
triggered or not. If the threshold is passed, an action potential will occur, no matter the
strength of the stimulus.
o How quickly a signal is fired, tells us how strong the original stimulus is; the
stronger the signal the higher the action potential frequency.
There is a maximum frequency at which a single neuron can send action potential, and
that is determined by its refractory period.
o Absolute refractory period makes it impossible to send another action potential.
It helps direct the action potential down the axon, because only channels further
downstream can open and let in depolarizing ions.
o Relative refractory period is when the cell is hyperpolarized. For a signal to fire,
the initial triggering event would have to be bigger than normal in order to send
more action potentials along.
How is the Neural Message Communicated?
Action potential is carried towards the axon terminal, causes vesicles that contain
neurotransmitter (nt) molecules to move towards the synapse and releases chemical
messages across the synaptic gap. Nt binds to the receptor sites and open the Na+ ion
gated channels in order to allow the Na+ to flow into the cell membrane, and causes it
to depolarize and causes another action potential.
Types of Neurotransmitters
o Serotonin: affects mood, hunger, sleep and arousal.
o Dopamine: influences movement, learning, attention and emotion
o Acetylcholine (ACh): enables muscles action, learning and memory.
, o Norepinephrine: helps control alertness and arousal.
o Gamma Aminobutyric Acid (GABA): a major inhibitory neurotransmitter.
o Glutamate: excitatory neurotransmitter, involved in memory.
Two Effects of Neurotransmitters
o Excitatory: makes an action potential in receiving neuron more likely by
depolarizing the cell (e.g. glutamate, ACh).
o Inhibitory: makes an action potential less likely by hyperpolarizing the cell (e.g.
GABA)
, Lecture 9.17.18
POISONS & DRUGS –EFFECTS ON NEUROTRANSMITTERS (nt)
An antagonist blocks the action of a nt.
o Botox paralyzes the facial muscles, by preventing the ACh from stimulating a
neuron.
o Curare poison from a snake, that paralyzes the prey. Blocks the receptor sites for
Acetylcholine (ACh); it is like the nt but and prevents the action of the nt.
o The venom of a black widow spider causes ACh to flood across the synapse,
which leads to convulsions and sometimes leads to death.
An agonist stimulates the action of nt, by mimicking it.
Three Categories of Drugs
o Depressants –calms neural activity and slow body functions (e.g. Opioids &
Heroin)
o Stimulants –arouses neural activity and quicken body functions (e.g. Cocaine)
o Hallucinogens –distorts perceptions and create false sensations (e.g. LSD)
Case Study: Runner’s High
o Caused by the release of endorphins, a peptide nt that is involved in the control
of pain, binding to opioid receptor sites.
o May cause addiction, as the body stops making endorphins. Painful withdrawal
symptoms emerge after the addictive drug is discontinued because natural
endorphin production stops.
Cocaine is a stimulant
o Reuptake is a natural process in which excess nt are reabsorbed by the sending
neuron.
o Cocaine blocks the receptors of dopamine, norepinephrine and serotonin;
thereby, lifting mood and creating a rush.
o Selective Serotonin Reuptake Inhibitor (SSRI) antidepressants like Prozac blocks
reuptake of serotonin.
Marijuana (THC) stimulates cannabinoid receptor sites. Shortens the natural refractory
period of a neuron, after a stimulus, and causes heightened brain activity.
Alcohol (Depressant) facilitates GABA inhibitory activity and suppresses excitatory
glutamate.
o Causes looser judgements by preventing GABA.
o Glutamates (excitatory)
o GABA (inhibition)
Nicotine (stimulant) activates nicotinic receptors involved in learning and memory. It
improves the efficiency of info processing.
o Most addictive drug.
NEUROSCIENCE –NEURONS
Nerve Communication
Activations of neurons in the brain help us interpret sensory cues.
Everything psychological is simultaneously biological
The power of the brain in terms of sense, emotions, thinking –comes from neural
communication: cells in the brain called neurons, that communicate to one another
through chemical messages.
How are Neural Messages Created?
A neuron consists of a cell body (soma) and two type
branching fibers:
o Dendrites are short bushes of fiber that take
information from outside of the cell and pass
on to the cell body.
o Axons are short or long extensions that take
info from the cell body and pass it on to the o
neurons or muscles/ glands, etc.
Lipids cover the axons of some neurons, called the myelin sheath that speeds up the
neural response. The most amount of myelin is in the frontal lobe (that controls
judgement). As we age, the development of the brain creates more myelin.
Action potential (the neural message) is the change in the voltage of the cell.
o The resting membrane potential (-70 mV) is when a nerve impulse is not being
transmitted. AT REST Positive Na+ ions are present outside the (in the cytoplasm)
and slightly positive K+ are present inside the cell;
thus, the cell is negatively polarized at -70 millivolts
(mV). All gated Na+ and K+ channels (voltage
gated) are closed.
The cell membrane is
permeable to K+ ions, and so
lots of K+ leaks out of the
neuron through K+ leak channels. The
membrane is partially permeable to Na+
ions, so they slowly leak into the neuron
through Na+ leak channels.
Because the cell wants to maintain a negative membrane potential, it
must pump K+ into the cell and Na+ outside of the cell at the same time.
o Depolarization makes the cell less polar (membrane potential gets smaller as ions
quickly begin to equalize the concentration gradient) after passing the threshold
, (-55 mV) to about +40 mv. Voltage-gated Na+ Channels activate and K+ channels
also activate.
Voltage-gated Na+ ions flow into the negatively charged cell membrane
and depolarizes the cell.
K+ channels also activate, K+ flows out of the cell, down the membrane.
o Repolarization brings the cell back to its resting potential. The cell becomes more
negatively charged. Voltage-gated Na+ channels close and K+ channels remain
open.
Na+ activation gates closed, stopping the inward flow of positive ions.
K+ channels also open, but there are more K+ exiting than entering the
cell, making the cell more negatively charged.
o Hyperpolarization makes the cell more negatively than its typical resting
membrane potential.
Because the K+ ion channels stay open, it continues to let positive ions
exit the cell. As the K+ closes, the Na-K Pump works to reestablish the
resting state.
Action potentials work on all-or-nothing basis, meaning that an action potential is either
triggered or not. If the threshold is passed, an action potential will occur, no matter the
strength of the stimulus.
o How quickly a signal is fired, tells us how strong the original stimulus is; the
stronger the signal the higher the action potential frequency.
There is a maximum frequency at which a single neuron can send action potential, and
that is determined by its refractory period.
o Absolute refractory period makes it impossible to send another action potential.
It helps direct the action potential down the axon, because only channels further
downstream can open and let in depolarizing ions.
o Relative refractory period is when the cell is hyperpolarized. For a signal to fire,
the initial triggering event would have to be bigger than normal in order to send
more action potentials along.
How is the Neural Message Communicated?
Action potential is carried towards the axon terminal, causes vesicles that contain
neurotransmitter (nt) molecules to move towards the synapse and releases chemical
messages across the synaptic gap. Nt binds to the receptor sites and open the Na+ ion
gated channels in order to allow the Na+ to flow into the cell membrane, and causes it
to depolarize and causes another action potential.
Types of Neurotransmitters
o Serotonin: affects mood, hunger, sleep and arousal.
o Dopamine: influences movement, learning, attention and emotion
o Acetylcholine (ACh): enables muscles action, learning and memory.
, o Norepinephrine: helps control alertness and arousal.
o Gamma Aminobutyric Acid (GABA): a major inhibitory neurotransmitter.
o Glutamate: excitatory neurotransmitter, involved in memory.
Two Effects of Neurotransmitters
o Excitatory: makes an action potential in receiving neuron more likely by
depolarizing the cell (e.g. glutamate, ACh).
o Inhibitory: makes an action potential less likely by hyperpolarizing the cell (e.g.
GABA)
, Lecture 9.17.18
POISONS & DRUGS –EFFECTS ON NEUROTRANSMITTERS (nt)
An antagonist blocks the action of a nt.
o Botox paralyzes the facial muscles, by preventing the ACh from stimulating a
neuron.
o Curare poison from a snake, that paralyzes the prey. Blocks the receptor sites for
Acetylcholine (ACh); it is like the nt but and prevents the action of the nt.
o The venom of a black widow spider causes ACh to flood across the synapse,
which leads to convulsions and sometimes leads to death.
An agonist stimulates the action of nt, by mimicking it.
Three Categories of Drugs
o Depressants –calms neural activity and slow body functions (e.g. Opioids &
Heroin)
o Stimulants –arouses neural activity and quicken body functions (e.g. Cocaine)
o Hallucinogens –distorts perceptions and create false sensations (e.g. LSD)
Case Study: Runner’s High
o Caused by the release of endorphins, a peptide nt that is involved in the control
of pain, binding to opioid receptor sites.
o May cause addiction, as the body stops making endorphins. Painful withdrawal
symptoms emerge after the addictive drug is discontinued because natural
endorphin production stops.
Cocaine is a stimulant
o Reuptake is a natural process in which excess nt are reabsorbed by the sending
neuron.
o Cocaine blocks the receptors of dopamine, norepinephrine and serotonin;
thereby, lifting mood and creating a rush.
o Selective Serotonin Reuptake Inhibitor (SSRI) antidepressants like Prozac blocks
reuptake of serotonin.
Marijuana (THC) stimulates cannabinoid receptor sites. Shortens the natural refractory
period of a neuron, after a stimulus, and causes heightened brain activity.
Alcohol (Depressant) facilitates GABA inhibitory activity and suppresses excitatory
glutamate.
o Causes looser judgements by preventing GABA.
o Glutamates (excitatory)
o GABA (inhibition)
Nicotine (stimulant) activates nicotinic receptors involved in learning and memory. It
improves the efficiency of info processing.
o Most addictive drug.
