Student Submission -- Gen Psych the Neuron and the Brain

7/28/2019 Student Submission -- Gen Psych the Neuron and the Brain

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GENERAL PSYCHOLOGY



THE NEURON

It is clear that most of what we think of as our mental life involves the activities of the nervoussystem, especially the brain. This nervous

system is composed of billions of cells, the mostessential being the nerve cells or neurons. There are estimated to be as many as100 billion neurons in our nervous system!

A typical neuron has all the parts that any cellwould have, and a few specialized structuresthat set it apart.



The main portion of the cell is called the soma or cell

body. It contains the nucleus, which in turn containsthe genetic material in the form of chromosomes.Neurons have a large number of extensionscalled dendrites.

It is primarily the surfaces of the dendrites that receivechemical messages from other neurons. One extensionis different from all the others, and is called the axon.

The purpose of the axon is to transmit an electro-

chemical signal to other neurons, sometimes over aconsiderable distance.



In the neurons that make up the nerves running from

the spinal cord to your toes, the axons can be aslong as three feet!

Longer axons are usually covered with a myelin

sheath, a series of fatty cells which have wrapped

around an axon many times.

very end of the axon is the axon ending, It is there

that the electro-chemical signal that has travelled

the length of the axon is converted into a chemicalmessage that travels to the next neuron.



Between the axon ending and the dendrite of the next neuron is a very tiny gap called

the synapse For every neuron, there are

between 1000 and 10,000 synapses.



SPINAL CORD NUERON AXON ENDINGS



THE ACTION POTENTIALS

When chemicals contact the surface of a

neuron, they change the balance

of ions (electrically charged atoms) between

the inside and outside of the cell

membrane,When it reaches the axon, itinitiates the action potential, which is a

rapidly moving exchange of ions. The surface

of the axon contains hundreds of thousandsof miniscule mechanisms called ion

channels,



THE SYNAPSE When the action potential reaches the axon ending,

it causes tiny bubbles of chemicalscalled vesicles to release their contents into thesynaptic gap. These chemicals arecalled neurotransmitters .These sail across the

gap to the next neuron, where they find specialplaces on the cell membrane of the next neuroncalled receptor sites. The neurotransmitter actslike a little key, and the receptor site like a little

lock. When they meet, they open a passage wayfor ions, which then change the balance of ions onthe outside and the inside of the next neuron. Andthe whole process starts all over again.



THE SYNAPSE



THE TYPES OF NEURONS

Sensory neurons are sensitive to various non-neural stimuli. There are sensory neurons in the

skin, muscles, joints, and organs that indicate

pressure, temperature, and pain.

Motor neurons are able to stimulate muscle cellsthroughout the body, including the muscles of the

heart, diaphragm, intestines, bladder, and glands.

Inter neurons are the neurons that provideconnections between sensory and motor neurons,

as well as between themselves. The neurons of

the central nervous system, including the brain, are

all inter neurons



A fiber made up of many axons is called

a nerve. In the brain and spinal cord, areas

that are mostly axons are called whitematter , and it is possible to

differentiate pathways or tracts of these

axons. Areas that include large number of cell bodies are called gray matter .



I O N C H A N N E L

Cells have membranes

that are made of lipid

molecules (fats), andthey prevent most

things from entering or

leaving the cell. But all

over a cell membrane

are proteins that stick

out on both sides of the

cell membrane. Someof these are ion

channels



Some channels are called gates. They can,depending on their environment, open or close. For some, it's a matter of whatchemicals attach themselves to a part of the

gate. , it's a change in the positive-negativebalance that causes them to open or close.

One example of a chemical gate arethe receptor sites on the dendrites of aneuron: When a chemical called aneurotransmitter attaches itself to a spot onthe gate, the gate opens up to allow sodium

ions into the cell.



CHEM ICAL G ATES

CLOSED ION OPEN ION



R E C E P T O R S I T E S

CLOSED RECEPTOR OPEN RECEPTOR



ION PUMPS

Other ion channels arecalled pumps. They useenergy supplied by the cellto actually pump ions in or out of the cell, by force if youwill. These pumps push

sodium ions out of the cell,and potassium ions (K+) intothe cell. They are actuallymaintaining an imbalance of

these chemicals.



NEUROTRANSMITTERS



Neurotransmitters are the chemicalswhich allow the transmission of signals

from one neuron to the next across

synapses. They are also found at theaxon endings of motor neurons, where

they stimulate the muscle fibers



ACETYLCHOLINE

Acetylcholine was the first neurotransmitter to bediscovered. It was isolated in 1921 by a German biologist

named Otto Loewi, who would later win the Nobel Prize for

his work. Acetylcholine has many functions: It is

responsible for much of the stimulation of muscles, including

the muscles of the gastro-intestinal system. It is also found

in sensory neurons and in the autonomic nervous system,

and has a part in scheduling REM (dream) sleep. On a more

serious note, there is a link between acetylcholine and

Alzheimer's disease: There is something on the order of a90% loss of acetylcholine in the brains of people suffering

from Alzheimer's, which is a major cause of senility.



NOREPINEPHRINE

In 1946, a Swedish biologist by the name of Ulf vonEuler discovered norepinephrine . Norepinephrineis strongly associated with bringing our nervoussystems into "high alert." It is prevalent in thesympathetic nervous system, and it increases our

heart rate and our blood pressure. Our adrenalglands release it into the blood stream, along withits close relative epinephrine (aka adrenalin). It isalso important for forming memories. Stress tends

to deplete our store of adrenalin, while exercise tends to increase it. Amphetamines ("speed") workby causing the release of norepinephrine, as wellas other neurotransmitters called dopamine and

seratonin..



DOPAMINE

Another relative of norepinephrine and epinephrineis dopamine, discovered to be a neurotransmitter in

the 1950s by another Swede, Arvid Carlsson.

Dopamine is strongly associated with reward

mechanisms in the brain. Drugs like cocaine, opium, heroin, and alcohol increase the levels of

dopamine, as does nicotine. If it feels good,

dopamine neurons are probably involved! too little

dopamine in the motor areas of the brain areresponsible for Parkinson's disease, which involves

uncontrollable muscle tremors.



GABA

In 1950, Eugene Roberts and J. Awaparadiscovered GABA (gamma aminobutyric acid),which is also usually an inhibitoryneurotransmitter. GABA acts like a brake to the

excitatory neurotransmitters that lead toanxiety. People with too little GABA tend tosuffer from anxiety disorders, and drugs likeValium work by enhancing the effects of

GABA. Lots of other drugs influence GABAreceptors, including alcohol and barbituates. If GABA is lacking in certain parts of the brain,epilepsy results.



GLUTAMATE

Glutamate is an excitatory relative of GABA. It is the most common

neurotransmitter in the central nervous

system - as much as half of all neurons in thebrain - and is especially important in regards

to memory. Curiously, glutamate is actually

toxic to neurons, and an excess will kill them,Sometimes brain damage or a stroke will

lead to an excess and end with many more

brain cells dying than from the original

trauma



SEROTONIN

Serotonin is an inhibitory neurotransmitter thathas been found to be intimately involved inemotion and mood. Too little also leads to anincreased appetite for carbohydrates (starchyfoods) and trouble sleeping, which are also

associated with depression and other emotionaldisorders. It has also been tied to migraines,irritable bowel syndrome, and fibromyalgia.

serotonin also plays a role in

perception. Hallucinogens such as LSD,mescaline, psilocybin, and ecstasy work byattaching to seratonin receptor sites and therebyblocking transmissions in perceptual pathways



ENDORPHIN

In 1973, Solomon Snyder and Candace Pertof Johns Hopkins discovered

endorphin. Endorphin is short for

"endogenous morphine."It is also the

neurotransmitter that allows bears and other

animals to hibernate. Consider: Heroin

slows heart-rate, respiration, and metabolism

in general - exactly what you would need tohibernate. Of course, sometimes heroin

slows it all down to nothing: Permanent

hibernation.



THE CENTRAL NERVOUS SYSTEM



THE SPINAL CORD

The spinal cord runs from the base of theskull all the way down the spine to the "tail

bone." There are motor pathways coming

down from the brain and sensory pathways

going up to the brain.

The spinal cord has another very important

function: Reflexes ,a reflex is the connection

of sensory neurons, via inter neurons, tomotor neurons.



THE SPINAL CORD OF THE HUMAN



For example, there are pain sensors in your

fingers. If you hold your finger over a flame

for a period of time, the pain will trigger motor

neurons to pull your finger away. It is true

that you can over-ride this reflex with "willpower," but as the example intentionally

shows, it isn't easy!

Reflexes do much more than just get your finger out of the fire: A great deal of

movement is accomplished through reflexes.



THE BRAIN

The brain is traditionally divided into threeparts, the hindbrain, the midbrain, and the

forebrain. This drawing is roughly what it

would look like if you sliced your brain

straight down the middle, like a part in your hair. The front of the brain is on the left, the

back on the right:

The hindbrain or brain stem consistsof three parts.



Before the 20th century, there was only oneway to see the brain: Open up the skull. Of course, with the assistance of a talentedmedical artist or, later, a good photograph,

this provides us with a particularly goodview. For the most part, however, itrequired a dead patient! Fortunately, wenow have a number of imaging techniquesthat allow us to see what is going on insidethe brain of a living human being.



X-rays were the first things used to look at aliving brain. While some details are visible,the nature of the brain is such that it is not aparticularly good subject for the X-ray.

The CT scan (computer tomography) or CATscan involves taking a large series of x-raysfrom various angles, and then combiningthem into a three-dimensional record on acomputer. The image can be displayed andmanipulated on a computer screen.



The PET scan (positron emission tomography)works like this: The doctor injects radioactiveglucose ("sugar water") into the patient’sbloodstream. The device then detects therelative activity level - that is, the use of glucose- of different areas of the brain. The computer generates an image that allows the researcher to tell which parts of the brain are most active

when we perform various mental operations,whether it’s looking at something, countingoutloud, imagining something, or listening tomusic!



PARTS OF THE BRAIN

The first is the medulla, which is actually an

extension of the spinal cord into the skul.

The upper part of the medulla contains a pinky-

sized complex of nuclei called the reticular

formation. It is the regulatory system forsleep, waking, and alertness.

The second part is the pons, which means

bridge in Latin. The pons sits in front of themedulla, and wraps around it to the back. It is

primarily the pathways connecting the two

halves of the next part, which is called the

cerebellum.



The cerebellum, which means "little brain" in

Latin, is in fact shaped like a small brain, and

it is primarily responsible for coordinatinginvoluntary movement. It is believed that,

when you learn complex motor tasks, thedetails are recorded in the cerebellum.

The midbrain is, in human beings, the

smallest part of the brain. It connects thehindbrain to the forebrain, and contains

several pathways important to hearing and

vision. It is much larger in lower animals



The largest and, for psychologists, most

interesting part of the brain is

the forebrain. It starts with the thalamus,

which is practically in the center of your

head. The thalamus is like a switchingstation, conducting signals from the body up

to the relevant parts of the higher brain, and

down from the brain to the lower brain andspinal cord.



The MRI (magnetic resonance imaging) workslike this: You create a very strong magnetic field

which runs through the person from head to

toe. This causes the spinning hydrogen atoms

in the person’s body to line up with the magneticfield.

Since different tissues have different relative

amounts of hydrogen in them, they give adifferent density of energy signals, which the

computer organizes into a detailed three-

dimensional image. This image is nearly as

detailed as an anatomical hoto ra h!



MRI OF THE AUTHOR'S EXCEPTIONALLY LARGE BRAIN



PARTS OF THE BRAIN



RIGHT AND SIDE VIEW OF THE BRAIN BOTTOM PART OF THE BRAIN



CAT SCAN/PET SCAN/M.R.I. IMAGES

Student Submission -- Gen Psych the Neuron and the Brain

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