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Old Wednesday, October 29, 2014
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Default Psychology Notes

Neurons, Hormones, and the Brain

Introduction:
The brain is an essential part of the nervous
system, a complex, highly coordinated network of
tissues that communicate via electrochemical
signals. We use our brains in virtually everything
we do, from keeping our heart beating to
deducing the existence of black holes. Within our
brains lie our deepest secrets, our earliest
memories, our most amazing capabilities, and the
keys to the mystery of consciousness itself.

Hippocrates (460–377 b.c.), the most famous
physician of the ancient world, first theorized that
our thoughts, feelings, and ideas came from the
brain, while others at the time thought the heart
and stomach were the seats of emotion. Today,
researchers are paying more attention to the roles
played by the brain and the hormones that affect
it in experiences such as mother-infant bonding,
religious ecstasy and prayer, extreme stress, and
meditation. Researchers now realize that though
our minds and brains may not be exactly the
same thing, they are intimately connected.

The Nervous System
The nervous system is a complex, highly
coordinated network of tissues that communicate
via electro chemical signals. It is responsible for
receiving and processing information in the body
and is divided into two main branches: the
central nervous system and the peripheral nervous
system.

(The Central Nervous System)

The central nervous system receives and
processes information from the senses. The brain
and the spinal cord make up the central nervous
system. Both organs lie in a fluid called the
cerebrospinal fluid , which cushions and nourishes
the brain. The blood-brain barrier protects the
cerebrospinal fluid by blocking many drugs and
toxins. This barrier is a membrane that lets some
substances from the blood into the brain but
keeps out others.

The Spinal cord nects the brain to the rest of
the body. It runs from the brain down to the
small of the back and is responsible for spinal
reflexes, which are automatic behaviors that
require no input from the brain. The spinal cord
also sends messages from the brain to the other
parts of the body and from those parts back to
the brain.
The brain is the main organ in the nervous
system. It integrates information from the senses
and coordinates the body’s activities. It allows
people to remember their childhoods, plan the
future, create term papers and works of art, talk
to friends, and have bizarre dreams. Different
parts of the brain do different things.

Damage to the Spinal Cord:

The spinal cord is what connects the brain and
body, and it is protected by the bones in the
spinal column. Injuries to the spinal cord can
cause serious problems, such as paralysis. Even
relatively minor damage to the spinal cord can
cause loss of feeling in parts of the body,
impaired organ function, and loss of muscular
control. Though spinal cord injuries are usually
permanent, current research into regenerated
axons and stem cells offers hope that one day
these injuries may be treated successfully.

The Peripheral Nervous System:

All the parts of the nervous system except the
brain and the spinal cord belong to the peripheral
nervous system. The peripheral nervous system
has two parts: the somatic nervous system and
the autonomic nervous system.

The Somatic Nervous System:

The somatic nervous system consists of nerves
that connect the central nervous system to
voluntary skeletal muscles and sense organs.
Voluntary skeletal muscles are muscles that help
us to move around.
There are two types of nerves
in the somatic nervous system:

•Afferent nerves carry information from the
muscles and sense organs to the central
nervous system.
•Efferent nerves carry information from the
central nervous system to the muscles and
sense organs.

The Autonomic Nervous System:

The autonomic nervous system consists of nerves
that connect the central nervous system to the
heart, blood vessels, glands, and smooth muscles.
Smooth muscles are involuntary muscles that
help organs such as the stomach and bladder
carry out their functions. The autonomic nervous
system controls all the automatic functions in the
body, including breathing, digestion, sweating, and
heartbeat. The autonomic nervous system is
divided into the sympathetic and parasympathetic
nervous systems.

•The sympathetic nervous system gets the body
ready for emergency action. It is involved in
the fight-or-flight response, which is the
sudden reaction to stressful or threatening
situations. The sympathetic nervous system
prepares the body to meet a challenge. It
slows down digestive processes, draws blood
away from the skin to the skeletal muscles,
and activates the release of hormones so the
body can act quickly.

•The parasympathetic nervous system becomes
active during states of relaxation. It helps the
body to conserve and store energy. It slows
heartbeat, decreases blood pressure, and
promotes the digestive process.

Crisis Mode:

The sympathetic nervous system’s activation may
manifest as a rapidly thumping heart, sweaty
palms, pale skin, or panting breath—the kinds of
things we experience during a crisis. We may
experience these kinds of symptoms during a
panic attack, for example.


Neurons: Cells of the Nervous System:

There are two kinds of cells in the nervous
system: glial cells and neurons. Glial cells , which
make up the support structure of the nervous
system, perform four functions:
Provide structural support to the neurons
•Insulate neurons
•Nourish neurons
•Remove waste products
The other cells, neurons , act as the
communicators of the nervous system. Neurons
receive information, integrate it, and pass it
along. They communicate with one another, with
cells in the sensory organs, and with muscles and
glands.
•Each neuron has the same structure:
Each neuron has a soma , or cell body, which is
the central area of the neuron. It contains the
nucleus and other structures common to all
cells in the body, such as mitochondria.

•The highly branched fibers that reach out from
the neuron are called dendritic trees. Each
branch is called a dendrite. Dendrites receive
information from other neurons or from sense
organs.

•The single long fiber that extends from the
neuron is called an axon. Axons send
information to other neurons, to muscle cells,
or to gland cells. What we call nerves are
bundles of axons coming from many neurons.

•Some of these axons have a coating called the
myelin sheath . Glial cells produce myelin,
which is a fatty substance that protects the
nerves. When an axon has a myelin sheath,
nerve impulses travel faster down the axon.
Nerve transmission can be impaired when
myelin sheaths disintegrate.

•At the end of each axon lie bumps called
terminal buttons. Terminal buttons release
neurotransmitters, which are chemicals that
can cross over to neighboring neurons and
activate them. The junction between an axon
of one neuron and the cell body or dendrite of
a neighboring neuron is called a synapse.

Role of Myelin

People with multiple sclerosis have difficulty with
muscle control because the myelin around their
axons has disintegrated. Another disease,
poliomyelitis, commonly called “polio,” also
damages myelin and can lead to paralysis.
Communication Between Neurons
In 1952, physiologists Alan Hodgkin and Andrew
Huxley made some important discoveries about
how neurons transmit information. They studied
giant squid, whose neurons have giant axons. By
putting tiny electrodes inside these axons,
Hodgkin and Huxley found that nerve impulses
are really electrochemical reactions.

The Resting Potential:

Nerves are specially built to transmit
electrochemical signals. Fluids exist both inside
and outside neurons. These fluids contain
positively and negatively charged atoms and
molecules called ions . Positively charged sodium
and potassium ions and negatively charged
chloride ions constantly cross into and out of
neurons, across cell membranes. An inactive
neuron is in the resting state . In the resting state,
the inside of a neuron has a slightly higher
concentration of negatively charged ions than the
outside does. This situation creates a slight
negative charge inside the neuron, which acts as
a store of potential energy called the resting
potential. The resting potential of a neuron is
about –70 millivolts.

The Action Potential

When something stimulates a neuron, gates, or
channels, in the cell membrane open up, letting in
positively charged sodium ions. For a limited
time, there are more positively charged ions
inside than in the resting state. This creates an
action potential, which is a short-lived change in
electric charge inside the neuron. The action
potential zooms quickly down an axon. Channels
in the membrane close, and no more sodium ions
can enter. After they open and close, the channels
remain closed for a while. During the period when
the channels remain closed, the neuron can’t
send impulses. This short period of time is called
the absolute refractory period, and it lasts about
1–2 milliseconds. The absolute refractory period
is the period during which a neuron lies dormant
after an action potential has been completed.

The All-or-None Law

Neural impulses conform to the all-or-none law ,
which means that a neuron either fires and
generates an action potential, or it doesn’t.
Neural impulses are always the same strength—
weak stimuli don’t produce weak impulses. If
stimulation reaches a certain threshold, or
minimum level, the neuron fires and sends an
impulse. If stimulation doesn’t reach that
threshold, the neuron simply doesn’t fire.
Stronger stimuli do not send stronger impulses,
but they do send impulses at a faster rate.

The Synapse

The gap between two cells at a synapse is called
the synaptic cleft. The signal-sending cell is
called the presynaptic neuron , and the signal-
receiving cell is called the postsynaptic neuron .
Neurotransmitters are the chemicals that allow
neurons to communicate with each other. These
chemicals are kept in synaptic vesicles, which are
small sacs inside the terminal buttons. When an
action potential reaches the terminal buttons,
which are at the ends of axons, neurotransmitter-
filled synaptic vesicles fuse with the presynaptic
cell membrane. As a result, neurotransmitter
molecules pour into the synaptic cleft. When they
reach the postsynaptic cell, neurotransmitter
molecules attach to matching receptor sites.
Neurotransmitters work in much the same way as
keys. They attach only to specific receptors, just
as certain keys fit only certain locks.
When a neurotransmitter molecule links up with a
receptor molecule, there’s a voltage change,
called a postsynaptic potential (PSP) , at the
receptor site. Receptor sites on the postsynaptic
cell can be excitatory or inhibitory:

•The binding of a neurotransmitter to an
excitatory receptor site results in a positive
change in voltage, called an excitatory
postsynaptic potential or excitatory PSP . This
increases the chances that an action potential
will be generated in the postsynaptic cell.

•Conversely, the binding of a neurotransmitter
to an inhibitory receptor site results in an
inhibitory PSP, or a negative change in
voltage. In this case, it’s less likely that an
action potential will be generated in the
postsynaptic cell.
Unlike an action potential, a PSP doesn’t conform
to the all-or-none law. At any one time, a single
neuron can receive a huge number of excitatory
PSPs and inhibitory PSPs because its dendrites
are influenced by axons from many other
neurons. Whether or not an action potential is
generated in the neuron depends on the balance
of excitation and inhibition. If, on balance, the
voltage changes enough to reach the threshold
level, the neuron will fire.
Neurotransmitter effects at a synapse do not last
long. Neurotransmitter molecules soon detach
from receptors and are usually returned to the
presynaptic cell for reuse in a process called
reuptake.

Neurotransmitters:

So far, researchers have discovered about 15–20
different neurotransmitters, and new ones are still
being identified. The nervous system
communicates accurately because there are so
many neurotransmitters and because
neurotransmitters work only at matching receptor
sites. Different neurotransmitters do different
things.

Neurotransmitter
Major functions
Excess is associated with
Deficiency is associated with
•Acetylcholine:
Muscle movement, attention, arousal, memory,
emotion
Alzheimer’s disease
•Dopamine:
Voluntary movement, learning, memory, emotion
Schizophrenia
Parkinsonism
•Serotonin:
Sleep, wakefulness, appetite, mood, aggression,
impulsivity, sensory perception, temperature
regulation, pain suppression
Depression
•Endorphins:
Pain relief, pleasure
•Norepinephrine:
Learning, memory, dreaming, awakening, emotion,
stress-related increase in heart rate, stress-
related slowing of digestive processes
Depression
•GABA
Main inhibitory neurotransmitter in the brain
Glutamate
Main excitatory neurotransmitter in the brain
Multiple sclerosis
•Agonists and Antagonists
Agonists are chemicals that mimic the action of a
particular neurotransmitter. They bind to
receptors and generate postsynaptic potentials.

Nicotine and Receptors;

Nicotine is an acetylcholine agonist, which means
that it mimics acetylcholine closely enough to
compete for acetylcholine receptors. When both
nicotine and acetylcholine attach to a receptor
site, the nerve fibers become highly stimulated,
producing a feeling of alertness and elation.
Antagonists are chemicals that block the action
of a particular neurotransmitter. They bind to
receptors but can’t produce postsynaptic
potentials. Because they occupy the receptor site,
they prevent neurotransmitters from acting.

Paralysis and Poison Arrows;

Curare is a drug that causes paralysis. As an
acetylcholine antagonist, it binds to acetylcholine
receptors at nerve-muscle junctions, preventing
communication between nerves and muscles.
Doctors sometimes use curare to immobilize
patients during extremely delicate surgery. South
American tribes have long used curare as an
arrow poison.

Studying the Brain:

To examine the brain’s functions, researchers
have to study a working brain, which means they
can’t use cadavers. Invasive studies, in which
researchers actually put instruments into the
brain, can’t be done in humans, though they can
be done occasionally during medically necessary
brain surgery. Researchers usually use invasive
techniques in animal studies.
There are two main
types of invasive animal studies:
•Lesioning studies: Researchers use an
electrode and an electric current to burn a
specific, small area of the brain.

•Electric stimulation of the brain: Researchers
activate a particular brain structure by using a
weak electric current sent along an implanted
electrode.
Because they cannot use such invasive
techniques on humans, researchers study human
brains in two ways:
They examine people with brain injuries or
diseases and see what they can and can’t do.
They use electroencephalographs (EEGs) ,
which can record the overall electrical activity
in the brain via electrodes placed on the scalp.
Recently, high-tech innovations have made
studying human brains easier. Researchers use
three types of imaging equipment to study the
brain:

•Computerized tomography (CT): In CT, a
number of x-rays are taken of the brain from
different angles. A computer then combines the
x-rays to produce a picture of a horizontal
slice through the brain.

•Magnetic resonance imaging (MRI): Both brain
structure and function can be visualized
through MRI scans, which are computer-
enhanced pictures produced by magnetic fields
and radio waves.

•Positron emission tomography (PET): For PET
scans, researchers inject people with a
harmless radioactive chemical, which collects
in active brain areas. The researchers then
look at the pattern of radioactivity in the brain,
using a scanner and a computer, and figure out
which parts of the brain activate during
specific tasks, such as lifting an arm or feeling
a particular emotion.

Structure and Functions of the Brain:

The brain is divided into three main parts: the
hindbrain, the midbrain, and the forebrain.

The Hindbrain:

The hindbrain is composed of the medulla, the
pons, and the cerebellum. The medulla lies next
to the spinal cord and controls functions outside
conscious control, such as breathing and blood
flow. In other words, the medulla controls
essential functions. The pons affects activities
such as sleeping, waking, and dreaming. The
cerebellum controls balance and coordination of
movement. Damage to the cerebellum impairs fine
motor skills, so a person with an injury in this
area would have trouble playing the guitar or
typing a term paper.

The Midbrain:

The midbrain is the part of the brain that lies
between the hindbrain and the forebrain. The
midbrain helps us to locate events in space. It
also contains a system of neurons that releases
the neurotransmitter dopamine. The reticular
formation runs through the hindbrain and the
midbrain and is involved in sleep and
wakefulness, pain perception, breathing, and
muscle reflexes.

The Forebrain:

The biggest and most complex part of the brain
is the forebrain, which includes the thalamus, the
hypothalamus, the limbic system, and the
cerebrum.

Thalamus:

The thalamus is a sensory way station. All
sensory information except smell-related data
must go through the thalamus on the way to the
cerebrum.

Hypothalamus:

The hypothalamus lies under the thalamus and
helps to control the pituitary gland and the
autonomic nervous system. The hypothalamus
plays an important role in regulating body
temperature and biological drives such as hunger,
thirst,reproductive organ, and aggression.

Limbic System:

The limbic system includes the hippocampus, the
amygdala, and the septum. Parts of the limbic
system also lie in the thalamus and the
hypothalamus. The limbic system processes
emotional experience. The amygdala plays a role
in aggression and fear, while the hippocampus
plays a role in memory.

Cerebrum;

The cerebrum, the biggest part of the brain,
controls complex processes such as abstract
thought and learning. The wrinkled, highly folded
outer layer of the cerebrum is called the cerebral
cortex. The corpus callosum is a band of fibers
that runs along the cerebrum from the front of the
skull to the back. It divides the cerebrum into two
halves, or hemispheres. Each hemisphere is
divided into four lobes or segments: the occipital
lobe, the parietal lobe, the temporal lobe, and the
frontal lobe:

The occipital lobe contains the primary visual
cortex, which handles visual information.
The parietal lobe contains the primary
somatosensory cortex, which handles
information related to the sense of touch. The
parietal lobe also plays a part in sensing body
position and integrating visual information.
The temporal lobe contains the primary
auditory cortex, which is involved in processing
auditory information. The left temporal lobe
also contains Wernicke’s area , a part of the
brain involved in language comprehension.
The frontal lobe contains the primary motor
cortex, which controls muscle movement. The
left frontal lobe contains Broca’s area , which
influences speech production. The frontal lobe
also processes memory, planning, goal-setting,
creativity, rational decision making, and social
judgment.

Brain Hemispheres:

Lateralization refers to the fact that the right and
left hemispheres of the brain regulate different
functions. The left hemisphere specializes in
verbal processing tasks such as writing, reading,
and talking. The right hemisphere specializes in
nonverbal processing tasks such as playing
music, drawing, and recognizing childhood
friends.
Roger Sperry , Michael Gazzaniga, and their
colleagues conducted some of the early research
in lateralization. They examined people who had
gone through split-brain surgery , an operation
done to cut the corpus callosum and separate the
two brain hemispheres. Doctors sometimes use
split-brain surgery as a treatment for epileptic
seizures.

Control of the Body:

Because of the organization of the nervous
system, the left hemisphere of the brain controls
the functioning of the right side of the body.
Likewise, the right hemisphere controls the
functioning of the left side of the body.
Vision and hearing operate a bit differently. What
the left eye and right eye see goes to the entire
brain. However, images in the left visual field
stimulate receptors on the right side of each eye,
and in-formation goes from those points to the
right hemisphere. Information perceived by the
right visual field ends up in the left hemisphere.
In the case of auditory information, both
hemispheres receive input about what each ear
hears. However, information first goes to the
opposite hemisphere. If the left ear hears a sound,
the right hemisphere registers the sound first.
The fact that the brain’s hemispheres
communicate with opposite sides of the body
does not affect most people’s day-to-day
functioning because the two hemispheres
constantly share information via the corpus
callosum. However, severing the corpus callosum
and separating the hemispheres causes impaired
perception.

Split-Brain Studies:

If a researcher presented a picture of a Frisbee to
a split-brain patient’s right visual field,
information about the Frisbee would go to his left
hemisphere. Because language functions reside in
the left hemisphere, he’d be able to say that he
saw a Frisbee and describe it. However, if the
researcher presented the Frisbee to the patient’s
left visual field, information about it would go to
his right hemisphere. Because his right
hemisphere can’t communicate with his left
hemisphere when the corpus callosum is cut, the
patient would not be able to name or describe
the Frisbee.
The same phenomenon occurs if the Frisbee is
hidden from sight and placed in the patient’s left
hand, which communicates with the right
hemisphere. When the Frisbee is in the patient’s
left visual field or in his left hand, the patient may
not be able to say what it is, although he would
be able to point to a picture of what he saw.
Picture recognition requires no verbal language
and is also a visual-spatial task, which the right
hemisphere controls.

The Endocrine System:

The endocrine system, made up of hormone-
secreting glands, also affects communication
inside the body. Hormones are chemicals that
help to regulate bodily functions. The glands
produce hormones and dump them into the
bloodstream, through which the hormones travel
to various parts of the body. Hormones act more
slowly than neurotransmitters, but their effects
tend to be longer lasting.
The pituitary gland , which lies close to the
hypothalamus of the brain, is often called the
master gland of the endocrine system. When
stimulated by the hypothalamus, the pituitary
gland releases various hormones that control
other glands in the body. The chart below
summarizes the better known hormones along
with some of their functions.
Hormone
Produced by
Involved in regulating
Thyroxine
Thyroid gland
Metabolic rate
Insulin
Pancreas
Level of blood sugar
Melatonin
Pineal gland
Biological rhythms, sleep
Cortisol , Norepinephrine, Epinephrine, Adrenaline
Adrenal glands
Bodily functions during stressful and emotional
states
Androgens
Testes (and ovaries and adrenal glands to a
lesser extent) in
Estrogens
Ovaries (and testes and adrenal glands to a
lesser extent)
Ovaries (and testes and adrenal glands to a
lesser extent)
Preparation of uterus for implantation of fertilized
egg.






dear Aspirants the day before yesterday I shared here my psychology notes but this thread belong to medical. actualy i wrote some notes in my cell with same names (endocrine system) one belong with medical and 2nd from psychology but unfortunately medical notes has been shared here by mistake so please excuse my mistake this time next time i will
care .now i m trying to delete this thread but i
can't find delete option i think there is no option of
deleting ?and sorry if my post waste your precious
time.
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