Psychology 131Chapter 2-Part 1

“I think; therefore I am.”• How to we translate the squiggly black lines on this page?• If you walk away from this lecture, how do you get to the next class, or

home later in the day?• What would happen if you were no longer capable of thoughts or

feelings? Why study the brain?• This is where it all begins• Makes us human, and sometimes, inhumane• Movement toward biopsychology

Neuroscience• The study of the biology of behavior and mental processes• A branch of science that deals with the structure and functioning of the

brain, nerves, and nervous tissue that form the nervous system• Primary purpose of neuroscience is to focus on learning and behavior as

it relates to the biological nature of the brain Brain = Information• Without information, we could not survive• Our cells take in sensory information that allows us to interpret the

outside world through our eyes, ears, and other sensory receptors• Our nervous system is a network of specialized cells that carries info to

and from all parts of the body• It uses chemical and electrical processes to convey that information

Central Nervous System• Our brain and spinal cord make up the central nervous system (“center

of everything”)• This is where the information is decoded and sent to various parts of the

body to be utilized as a response to stimuli• For example: smelling a foul odor

Neuron• These are the basic building blocks of the entire nervous system• About 100 billion or so in the human body (as much as the number of

stars in the galaxy)• Their job is to communicate electrochemical information throughout the

brain and the rest of the body• No two are alike, as unique as we are• They share three basic features:

1.) dendrites2.) cell body3.) axons

o Note: remember them in reverse order to understand how information flows “D, CB, A”

Dendrites• Greek for “little tree”• These are the branching areas in which info comes into the neuron• Receives neural impulses from other neurons• They act much like an antenna taking in the information and sending that

information to the cell body where it is then translated• Each neuron may have hundreds, even thousands of dendrites and their

branchings Cell Body• Aka the “soma” which is a Greek word for body• Receives info from the dendrites• This part of the neuron contains the nucleus• The cell body keeps the entire cell alive and functioning; life support

function• If enough stimulus is received in the cell body, the message is then

transmitted to the axon Axon• Long, tube-like structure that conveys impulses away from the neuron’s

cell body• Carries neural messages to other neurons, muscles, or glands• The axon operates on a principle called the “action potential”

Glial cells• These are the support structures that hold all of the neurons in place• These make up 90% of all cells found in the brain• They surround the neurons, provide clean-up tasks, and insulate the

neurons from one another so that their messages are not scrambled• New research shows that glial cells may also play a role in nervous

system communication Neural Transmission• When you consider neural transmission (the way in which messages move

back and forth between the brain and various parts of the body) think of the neuron’s cell body (soma) being clumped tightly in the spinal cord, and the axon’s “arms” spreading throughout the body.

Spinal Cord• A long bundle of neurons that serves two vital functions; consider a cross

section of the spinal cord (see page 54, Figure 2.5)1.) the outer section closest to the bone of the spinal column is composed mainly of axons and nerves (white in color)

o -purpose is to carry messages up to the brain, and back down to the body

2.) the inner part near the center of the spinal column is composed mostly of cell bodies

o -these cell bodies which are supported by glial cells, are responsible for reflexes

• -there are three types of neurons involved in this process known as the reflex arc and their sole purpose is to serve in a functional sense

a.) sensory neurons (aka afferent neurons)-carry messages from the senses to the spinal cordb.) motor neurons (aka efferent neurons)-carry messages from the

spinal cord to the muscles and glandsc.) interneurons- connects the sensory neurons to the motor neurons

• Direction of impulse

• neural transmission• The axons are able to remain bundled close together as they move to

various parts of the body without touching because of the myelin. • It is analogous to several wires running through a house that do not short

circuit because of the plastic coating on the outside. *The fact that there are so many axons bundled together also makes them less susceptible to damage because they are stronger together than on their own.• Structural components of the neuron• neural transmission: neurilemma• neurilemma is a membrane which covers the axon and myelin sheath. • It serves as a tunnel through which damaged fibers can repair themselves. • Consider this: the neurilemma for an axon that was connected to a severed

limb (such as a toe lost in an accident) may be able to regain some function and feeling if the limb is attached in enough time.

• Now consider this: if the axons were in the brain or spinal cord, the likelihood of them being able to do any repair is almost nonexistent. This is because they lack the neurilemma found in outer axons that allows for repair to the extremities. Think about individuals that suffer from spinal cord injuries, or closed head injuries

• Neurilemma• Neural Impulses: The Messages within the Neuron• -messages in the neuron are driven by electrical charges

• -When the neuron is at rest, the semi-liquid solution in the cell body (soma) is composed of negatively charged ions

• the solution outside of the neuron is made up of positively charged ions. • Because the two charges are opposites, they will naturally be attracted to one

another. This is called the resting potential.• Neural Impulses: The Messages within the Neuron• -resting potential>>>>this happens when the transmembrane potential is at

rest• -ions can only move through a resting neuron by means of leak channels

which are always open• Two leak channels:

1.) sodium leak channel2.) potassium leak channel• Neural Impulses: The Messages within the Neuron• -cell membrane is more permeable to potassium (this means that potassium

ions move out of the cell more quickly than sodium ions)• -The membrane of the cell is permeable which means that substances can

move in or out of it. In the case of the charged ions, they can only move inside if the neuron is sending an active charge.

• Neural Impulses: The Messages within the Neuron• By an active charge we mean an action potential (when the neuron is active). • When the neuron is active, it means that it has been stimulated beyond its

threshold and it will continue with the action potential in an “all-or-none” fashion

• -in other words, once the neuron has been stimulated, it will continue sending the signal regardless of anything else going on at the time

• Neural Impulses: The Messages within the Neuron• -the threshold being broken means that it can have a strong stimulator (very

fast firing with many neurons involved), or a weaker stimulator (fewer neurons involved, less speed)----either way it goes, when the threshold is met, the action potential will occur and finish to send the appropriate signal

• How the action potential works• -consider a light tap on the wrist….the action potential has begun the

threshold has been met, but the number of neurons used will likely be less because the light tap will not trigger as many pain receptors

• -consider a second scenario, you get smacked very hard on the same hand, in the same spot…the action potential has also begun, but it will likely include a faster conduction of the neural impulse because there will more pain receptors in play, as well as larger area of the skin being covered

• How the action potential works• -In the resting state, known as the resting potential, the neuron is ready for a

stimulation which will open several gates that allow the oversize ions to penetrate the cell membrane and begin an electrical impulse.

• -when the neuron is triggered (action potential), the positive ions that were on the outside during rest, rush in and push out the negatively charged ions

• -this alteration of ions also induces the first gate that was opened, and now filled with positive ions, to trigger a reversal in electrical charge at the part of the axon closest to the soma (cell body)

• How the action potential works• -when the action potential gets to the end of the neuron branches off on the

inside into what are called axon terminals. • -at the end of each axon terminal, you will find what is known as a synaptic

knob• -the synaptic knob contains many synaptic vesicles (like a container) that

release neurotransmitters when an action potential reaches this part of the neuron

• How the action potential works• the synaptic vesicles contain different types of neurotransmitters based on

the neuron firing, and the neurotransmitters that are released fit like a key in a lock in the receptor sites of the adjoining dendrites

• -between the synaptic bulb at the end of the axon where the transmitters are released, and the dendrites with the receptor sites, you will find a gap in between them that is referred to as the synaptic gap (or synaptic cleft)

• How the action potential works• - the electrical charge from the action potential triggered the release of the

neurotransmitters, but the transfer from the releasing axon (presynaptic membrane) to the receptor site (on the postsynaptic membrane) is a purely chemical reaction

• -once the neurotransmitters are released into the synaptic gap, they float into the receptors sites that they “fit” into--- eliciting another action potential on the receiving neuron

• there are two types of neurotransmitters that are released• -those that turn a cell on (excitatory neurotransmitters), and those that turn

cells off (inhibitory neurotransmitters)• For example: an excitatory neurotransmitter may send a message to a muscle

in the body telling it to contract (excitatory); • a different neurotransmitter may tell that same muscle to relax, essentially

shutting it off (inhibitory neurotransmitter)• agonist• -an agonist is chemical substance that can mimic or enhance the effects of a

neurotransmitter on the receptor sites of the next cell• essentially tricking the body into reacting as if it were a normal bodily

chemical• For example: beta receptors that react by behaving as agonists to increase

the action of the neurotransmitter that stimulates the contraction of specific heart valves

• antagonist• -an antagonist is a chemical substance that blocks or reduces a cell’s

response to the action of other chemicals or neurotransmitters; • drugs that block the effects of the natural chemical working within the body

• in this case it can have either an inhibitory effect, or an excitatory effect depending on the type of neurotransmitter that it is working to reduce or block

• -if an antagonist is working to block the effects of an inhibitory neurotransmitter, then it will allow an excitatory response to occur

• antagonist• Consider this: beta blockers are used for high blood pressure and they are

antagonists…..if their job is to prevent high blood pressure, then they would want to reduce or slow heart contractions to maintain a steady heart rate.

• The antagonist beta blocker would then work to block the effects of naturally occurring neurotransmitters that stimulate heart contractions in an effort to slow them, therefore causing a reduction in heart rhythm to reduce overall blood pressure.

• Neurotransmitters• 1.) acetylcholine• -this excitatory neurotransmitter is found between neurons and muscle cells• -it allows the muscles to contract• -if acetylcholine is blocked in some way, then the muscle will not be able to

move and will be paralyzed• i.e. from book; the blow darts used by South American Indians to paralyze;

this acts as an antagonist to acetylcholine because it block the effects of the neurotransmitter

• -too much acetylcholine (like the effects of a spider bite) could lead to over stimulation resulting in convulsions

• Neurotransmitters: GABA• 2.) GABA ( -aminobutyric acid)γ• -GABA is the most common inhibitory neurotransmitter in the brain• -helps calm anxiety• -alcohol acts as an agonist for GABA because it stimulates the release of this

neurotransmitter to calm the individual• Neurotransmitters: serotonin• 3.) Serotonin• -found in the lower part of the brain• -can be either excitatory or inhibitory• -serotonin is associated with sleep, mood, and appetite• -low levels of serotonin activity are also linked to depression• -SSRI’s and depressive symptoms• -involved in the effects of MDMA (ecstasy); works by blocking uptake and by

triggering the release of massive amounts of serotonin (Kaplan & Sadock, 2003)

• Neurotransmitters: dopamine• -this neurotransmitter is one of three catecholamines (the other two are

epinephrine and norepinephrine) • -associated with mental health disorders, as well as physical maladies

• -too much dopamine has been linked to schizophrenia (known as the Dopamine hypothesis); states that schizophrenia is related to excessive activity of dopaminergic neurons in the limbic system

• -hypothesis is based on studies in which people were given high doses of amphetamines to mimic the effects of dopamine, and were able to induce psychotic effects

• -too little dopamine is associated with Parkinson’s Disease• Neurotransmitters: Neuropeptides• -these neurotransmitters actually control the release of other

neurotransmitters• -an example of this special neurotransmitter is the endorphin• -endorphins are naturally occurring pain killers in the body that are released

in response to pain• -they act by binding to the receptors of axons that have given a signal for a

pain response; once the endorphins bind, they do not allow the cell to fire a pain signal and the pain sensation will actually subside

• Neurotransmitters: Neuropeptides• -endorphins are also released during exercise; can help regulate mood• -we have naturally occurring morphine receptors in the brain which is where

endorphins bind (endorphins are like natural morphine doses provided by our brain)

• -this is why drugs like heroin or morphine are so addictive…when a person takes an artificial morphine (heroin), it blocks the brain’s ability to block out pain which is why addicts experience withdrawals

• Reuptake• -this is the process where neurotransmitters are taken up again from the

synaptic gap and literally “sucked” back into the vesicles that they came out of

• -this is done to clean out the gap in order to get it ready for the next action potential

• -serotonin is associated with depression as we mentioned earlier; in the case of reuptake, if too much serotonin is lost in the reuptake process, this can affect a person’s mood leaving them depressed

• -SSRI’s are used to leave more of the serotonin in the synaptic gap in order for it to bind to receptor sites; the result is that more serotonin will elevate a person’s mood

• How the reflex arc works• -pain from a bee sting goes from the sensory neuron to the spinal cord where

it is redirected by the interneuron to the motor neuron which sends the message to move away from the sting and try to reduce the pain

• -the message in the above example goes as far as the spinal cord and the back down to save precious time to keep you safe and enact your reflexes

• -if the same message had to got to your brain, it would waste more time that is needed to aid you immediately…hence the importance of the reflex arc

• Effects of Drugs on Neurotransmitters• stimulates the neuron to release a chemical message to the next cell

• inhibiting the release of the neurotransmitter; drugs of abuse alter the way that the CNS functions

• -different drugs can interact with several neurotransmitters in different combinations; the end result is that the variety of mechanisms that are potentially endless

• Tolerance • -is built once the brain makes attempts to return to normal functioning and

will no longer achieve the initial desired effect• Cross Tolerance • -when the body also becomes tolerant to the effects of other drugs that have

the same mechanism of action• Blood Brain Barrier • -protects the brain from: • 1.) toxins • 2.) infections• 3.) unfamiliar organisms, as well as • 4.) regulating which molecules will be allowed to enter the brain• NMDA (N-methyl-D-aspartate)• -neurotransmitter, which under normal conditions binds to receptor sites• -alcohol blocks the entry of calcium atoms through the ion channels normally

activated when NMDA binds to these sites• -alcohol is able to depress the actions of the CNS by blocking the effects

ofNMDA while facilitating GABA• Marijuana• -euphoria like state caused by marijuana use is due to an increase in the

release of dopamine• THC(Delta-9-tetrahydrocannaboid) • -is the main ingredient in pot and influences the cannaboid receptors found in

the brain• -interferes with the normal functioning of the cerebellum (which is

responsible for motor functions such as balance, posture, and movement coordination)

• Marijuana• -once marijuana is ingested, THC is distributed throughout the body affecting

the heart, lungs, and brain• -the remaining unmetabolized THC stays in the fatty tissue of the body• -chronic administration of THC has shown permanent damage to the

hippocampus—suggesting a proneness to memory impairment• -suggested that long-term use of marijuana may cause changes in the limbic

system---resulting in heightened arousal of emotions while withdrawing from THC

• Cannabis Receptors • -found in the brain—generally in the hippocampus• -hippocampus induces memory• -marijuana use affects short-term memory while under the influence• -influence the brain’s ability to

• 1.) memory• 2.) concentration• 3.) cognition• 4.) coordinated movement• 5.) perception of time and depth• Cocaine• -depression and cocaine use is likely due to the lack of re-absorption of the

neurotransmitters dopamine, norepinephrine, or serotonin• -diencephalon is affected by cocaine use, resulting in a higher-than-normal

body temperature• -prefrontal cortex and amygdale are also affected by cocaine use• -regular cocaine users are at risk for struggling to learn new information and

to accurately recall past events• Down Regulation • -excessive build-up of dopamine reducing number of active receptors• -this causes the craving to ingest more to bring back the level of dopamine

that the brain needs• Disorders Related to Alcohol/Drug |Abuse• Korsakoff’s Syndrome • -alcohol related disease• Characterized by: • impairment of memory, • abnormal eye movement, • difficulty walking (ataxia), and • confusion• -caused from a severe loss of brain cells located within the anterior superior

temporal cortex of the brain• Treatments• Methadone • -opiate substitute and a synthetic narcotic analgesic• Positives of methadone include:• decline in heroin use• drug associated problems tend to decrease• psych depression declines• commission of drug related crimes is reduced• increase in permanent employment• Treatments• LAAM (L-alpha-acetyl-methadol) • -another treatment for heroin/narcotic abuse• -metabolized in the liver resulting in a much longer duration, therefore being

used much less often than a methadone treatment• Treatments• Naloxone and Nalorphine -used to block the sensation of being high and

initiate immediate withdrawal symptoms• Treatments

• Diazepam - this is a benzodiazepine (sedative); injected into a person trying to detoxify themselves after alcohol abuse; curbs symptoms such as:– delirium– tremors– convulsions

• Treatments• Antabuse • -inhibits the enzyme aldehyde dehyrogenase• -this causes the alcohol to convert itself into acetylaldehyde• - acetylaldehyde then builds up in the body causing severe physical reactions

such as projectile vomiting, nausea, breathing difficulties, etc.• -makes ingesting alcohol unpleasant because of the side effects which result

from the antabuse