Download Introduction to Psychology The Nervous System: Biological Control

Introduction to Psychology
The Nervous System: Biological
Control Center
Chapter 3
The Nervous System
 The brain not only thinks and
calculates but also feels and controls
motivation.
 The brain is connected to the spinal
cord, a thick bundle of long nerves
running through the spine.
 Individual nerves exit or enter the
spinal cord and brain, linking the
brain to every part of the body. Some
of these nerves carry messages from
the body to the brain to inform the
brain to regulate the body’s function
and the person’s behavior.
 Without the nervous system, the
body would be a mass of
uncoordinated parts that couldn’t
act, reason, or experience emotion.
Neurons
 The most important unit of the
nervous system is the
individual nerve cell known as
the neuron.
 In the early 1900’s, Santiago
Roman y Cajal, the scientist
that discovered neurons,
described them as “the
mysterious butterflies of the
soul”. Since then, we have
learned about the building
blocks of the nervous system.
Parts of the Neuron
 Neurons range in length from less than a
millimeter to more than a meter in length.
There are the same three parts in every
neuron.
 1) The cell body – contains a neuron’s
nucleus and other parts essential for the
cell’s preservation and nourishment.
 2) Dendrites – braches that extend out and
receive messages from other neurons.
 3) Axons – are branches at the other end of
the neuron that carry neural messages away
from the cell body and transmit them to the
next neuron. The messages usually stem
from the dendrite through the axon, but
can go the opposite direction.
 The human nervous system is made up of
100 billion neurons. The human body
contains trillions of neural connections,
most of them in the brain.
 Neuron is not the same as nerve. A nerve is
a bundle of many long neurons outside the
brain and spinal cord.
Neural Transmission
 Neurons are their own living wires, with
their own built-in supplies of electrical
power. Neurons are sacs filled with one
type of fluid on the inside and bathed in a
different type of fluid on the outside.
 These fluids are “soups” of dissolved
chemicals, including ions, the particles
that carry either negative or positive
electrical charge.
 There are more negative ions inside a cell.
This means the charge is negative. These
cells tend to attract positively charged
ions.
 The outside out of the cell becomes
saturated with positive ions, particularly
sodium (Na+). When neurons are in a
resting state, they are 10 times more
positively charged ions on the outside
than on the inside.
Neural Transmission
 Many ions are able to move freely through the cell
membrane of the neuron, but sodium ions cannot. The
membrane is said to be semipermeable in its normal
resting state-only some chemicals can pass through the
holes in the membrane. There is a balance as there are
both positive and negative aspects.
 While the neurons are in a resting state, they are said to
be electrically polarized.
 When a membrane is stimulated, positively charged
ions, rush into the neuron. This process is called
depolarization because the neuron is no longer mostly
negative on the inside.
 Depolarization creates a chain of events known as the
action potential. When sodium ions rush through, it
makes that part of the cell permeable. When the
sodium comes through the cell pumps it back out, bring
polarization back to the cell.
 This polarization lasts one ten-thousandths of a second.
Ramon y Cajal believed this was an “all-or-nothing
principle. He believed that all action potential was the
same. They now know that neurons transmit messages
through graded electrical potentials that vary in
magnitude.
Myelin Sheath and Neural
Transmission
 Many axons are encased in a white,
fatty coating called the myelin sheath.
This sheath insulates the axon and
greatly increases the speed at which
the axon conducts neural impulses.
 The myelin sheath continues to grow
until late adulthood. The layers are
thicker in females than in males. This
may be indicative of more efficient
neural processing of some kinds of
information by females.
 Multiple sclerosis destroys the myelin
sheath. These individuals have trouble
controlling their muscles; experience
fatigue, dizziness, and pain, as well as
suffer serious cognitive and vision
problems.
Neurotransmitters and Synaptic
Transmission
 Neurons are not connected to one
another, but are part of a complex
chain. One neuron influences the
next neuron through the synapse.
 The small space between two
neurons is known as the synaptic
space.
 The neural message is carried across
the gap by chemical substances
known as neurotransmitters. Not all
neurotransmitters are excitable.
Some axons transmit inhibitory
substances across synapses, making
it difficult for the next neurons to
fire.
Neurotransmitters and Synaptic
Transmission
 Neurotransmitters are stored in tiny
packets called synaptic vesicles located in
the synaptic terminals, which are the
knob-like ends of the axons.
 When the action potential reaches the end
of the axon terminal, it stimulates the
vesicles to release the neurotransmitter
into the gap. The neurotransmitter floats
across the gap and “fits” into receptor
sites on the adjacent neuron’s membrane
like fitting into locks.
 Hundreds of different neurotransmitter
substances operate in different parts of
the brain, carrying out different functions.
Drugs can alter the transmission of a
neuron. Psychiatric drugs can control
anxiety, depression, and other
psychological problems.
 Some of the drugs can fit the receptor
sites much like the original
neurotransmitters. Some drugs can block
receptor sites.
Glial Cells
 Neurons are greatly outnumbered by a
second class of cells called glial cells.
 Glial cells help the neurons carry out their
function in three ways:
 1) New neurons grow from glial cells
throughout life.
 2) Glial cells support neurons and
transport nutrients from blood vessels to
neurons.
 3) Some glial cells produce the myelin
sheath that insulates axons.
 4) Glial cells also influence the
transmission of messages from one
neuron to another across synaptic gaps.
They can increase/decrease the speed of
synaptic transmission. The glial cells
absorb neurotransmitters from the
synaptic gap, release the neurotransmitter
into the synaptic gap, or by chemically
preparing the synapse for transmission.
Divisions of the Nervous System
 The two major divisions of the
nervous system are: 1) the Central
Nervous System and the 2) Peripheral
Nervous System.
 1) The Central Nervous System –
consists of the brain and the spinal
cord. The brain controls the functions
of the nervous system. The spinal
cord’s main job is to relay messages
between the brain and body. It also
processes reflexes.
 Example – withdrawing quickly from
a hot object. Reflexes are activated in
the spinal cord which reach a certain
neuron called the interneuron. This
gives a message to the muscles of
the limb to contract.
Divisions of the Nervous System
 2) The Peripheral Nervous System –
composed of the nerves that
branch from the brain and the
spinal cord to the body.
 Messages can travel across a
synapse only in one direction.
Those messages coming from the
body into the central nervous
system are carried by one set of
neurons, the afferent neurons.
Messages going out from the
central nervous system to the body
are carried by efferent neurons.
Divisions of the Peripheral Nervous
System
 The peripheral nervous system is
divided into two sections: 1) the
somatic nervous system, and 2)
autonomic nervous system.
 The peripheral nervous system –
carries messages from the
central nervous system to the
skeletal muscles that control
movements of the body. These
include voluntary and
involuntary movements. This
nervous system also receives
incoming messages from the
sensory receptors and transmits
them to the nervous system.
Divisions of the Peripheral Nervous
System
 The autonomic nervous system – is
composed of nerves that carry
messages to the glands and visceral
organs (heart, stomach, and
intestines). The autonomic nervous
system plays a key role in:
 1) Essential body functions –
regulates many essential functions
of the organs. E.g. heartbeat,
breathing, digestion, sweating, and
sexual arousal.
 2) Emotion – the autonomic system
is activated during times of stress.
This can create discomfort and make
someone feel nausea (flight or fight
syndrome).
Divisions of the Autonomic Nervous
System
 The autonomic nervous
system is composed of two
parts:
 1) the sympathetic nervous
system.
 2) the parasympathetic
nervous system.
The Sympathetic Nervous System
 The sympathetic nervous system prepares the
body for emergencies and times of stress. The
sympathetic nervous system activates organs
to improve our ability to respond to stress. In
other cases, it inhibits organs that are not
needed during times of stress.
 The sympathetic nervous system:
 1) Dilates (opens) the pupils of the eyes to let in
light.
 2) Decreases salivation.
 3) Speeds the beating of the heart.
 4) Dilates the passageways (bronchi) of the
lungs to increase air flow.
 5) Inhibits the digestive tract (stomach,
pancreas, intestines)
 6) Releases sugar (glycogen) from the liver.
 7) Stimulates the secretion of epinephrine from
the adrenal glands.
 8) Inhibits contraction of the urinary bladder.
 9) Increases blood flow and muscle tension in
the large muscles.
The Para-sympathetic Nervous
System
 This system helps to maintain balance
regulation of the internal organs and the
large body muscles. When levels of physical
and emotional stress are low, it stimulates
maintenance activities and energy
conservation.
 1) Constricts (closes) the pupils of the eyes.
 2) Increases saliva to facilitate digestion.
 3) Slows the beating of the heart.
 4) Constricts the bronchi of the lungs.
 5) Activates the digestive tract.
 6) Releases bile from the liver to aid in
digestion of fats.
 7) Inhibits secretion of epinephrine from
the adrenal glands.
 8) Contracts the urinary bladder.
 9) Reduces blood flow and muscle tension
in the large muscles.
Structures and Functions of the Brain
 No function of the brain is
carried out solely by one part.
The brain can be viewed as
having three major parts: 1)
the hind-brain, 2) the
midbrain, and 3) the
forebrain.
 These parts of the brain are
divided into smaller sections.
Hindbrain and Midbrain:
Housekeeping Chores and Reflexes
 The hindbrain is the lowest part of the
brain, located near the base of the
skull. It tries to keep the body working
properly. There are three parts to this
portion of the brain:
 1) the Medulla
 2) the Pons
 3) the Cerebellum
 The medulla is a swelling just above the
top of the spinal cord, where the cord
enters the brain. It controls breathing
and a variety of reflexes.
 The pons is concerned with balance,
hearing, and some parasympathetic
functions.
Hindbrain and Midbrain:
Housekeeping Chores and Reflexes
 The cerebellum consists of two
rounded structures located to the
rear of the pons. It plays a key role
in coordination of complex muscle
movements and plays a role in
memory and learning.
 The reticular formation – is a set of
neurons that spans the medulla
and the pons. This plays a role in
maintaining muscle tone and
cardiac responsiveness to
changing circumstances.
Hindbrain and Midbrain:
Housekeeping Chores and Reflexes
 The midbrain – the small area
at the top of the hindbrain that
helps to control important
postural systems, especially
those that deal with the
senses. As an example, it
controls the movement of the
eyes.
Forebrain: Cognition, Motivation,
Emotion, and Action
 This portion of the brain deals
with two distinct areas.
 One area contains: the
thalamus, the hypothalamus,
and most of the limbic system.
 The other area made up of the
cerebral cortex, sits over the
lower parts of the brain.
Thalamus, Hypothalamus, and Limbic
System
 Thalamus – routes incoming
stimuli from the sense organs to
the appropriate parts of the brain
and links the upper and lower
centers of the brain.
 Hypothalamus – lies underneath
the thalamus, just in front of the
midbrain. It is involved in our
emotions and our motives. It
regulates the body’s temperature,
sleep, endocrine gland activity,
and resistance to disease. It
maintains a normal pace and
rhythm of such body functions
like blood pressure and heartbeat.
Thalamus, Hypothalamus, and Limbic
System
 The Limbic System contains:
 1) Amygdala – plays a role in emotion
and aggression. It helps to form
memories about emotionally charged
events.
 2) Hippocampus – helps in forming
new memories. It “ties together” the
sights, sounds, and meanings of
memories stored in various parts of
the cerebral cortex and is particularly
involved in spatial memory. Those
with Alzheimer’s disease will have
damage to this area.
 3) Cingulate cortex – works with the
hippocampus to process cognitive
information related to emotion.
Cerebral Cortex: Sensory, Cognitive,
and Motor Functions
 The largest structure in the forebrain
is the cerebral cortex. It is involved
in conscious experiences, voluntary
actions, language, and intelligence.
It is the primary brain structure
related to the somatic nervous
system.
 The thin outer surface of the
cerebrum is a densely packed mass
of billions of cell bodies of neurons.
This portion is gray and is often
called the “gray matter of the
brain”. The fatty myelin underneath
this area gives neurons their white
appearance. These gray and white
areas can be seen in the MRI image.
Lobes of the Cerebral Cortex
 Frontal lobes – is located behind
your forehead, extending back to
the middle of your head. It plays a
key role in thinking, remembering,
making decisions, speaking,
predicting future consequences of
actions, controlling movement, and
regulating emotions.
 The frontal lobe also contains
Broca’s area (in the left cerebral
hemisphere), which is involved in
our ability to speak language. This is
named for French neurologist Paul
Broca. He performed autopsies on
non-fatal stroke patients that had
damage parts of their cerebral
cortex and had difficulty speaking.
The Frontal Lobe
 Persons with expressive aphasia
– understand what is said to
them, but have difficulty
speaking. This means damage
has occurred to Broca’s area.
 The frontal lobe also controls
some voluntary movement of
the body. Near the middle of the
top of the head, a strip called the
motor area runs across the back
portion of the frontal lobes.
Damage to this area can result in
paralysis or loss of motor
control.
The Frontal Lobe
 The frontal lobe also deals with
decisions and appropriate social
behaviors. This was revealed in
the case of Phineas Gage. (See
case study.)
 150 years later, psychologist
Christina Myers saw a similar case.
A 33 year-old man by the name of
J.Z. had a tumor removed from
the same area that Phineas Gage
was struck. After the surgery his
personality changed dramatically.
Whereas he was once honest,
stable, and a reliable
husband…he became dishonest,
irritable, irresponsible, and
grandiose in his beliefs.
The Parietal Lobe
 The parietal lobe is located
right behind the frontal lobe
on the top of your skull. There
is a strip that runs right next
to the motor strip known as
the sensorimotor strip.
 This strip tells us what our
hands and feet are doing and
gives us a sensation when
someone touches us. Different
parts of the strip serve us in
different areas of the body.
Temporal Lobes
 The temporal lobes stem backwards from
the area of your temples, occupying the
middle area at the base of the brain
beneath the frontal and parietal lobes.
 The temporal lobe contains the auditory
areas. These are just inside the skull by the
ears. They are involved in the sense of
hearing.
 Wernicke’s area – is located just behind the
auditory area in the left hemisphere. This
portion helps to understand spoken
language.
 Damage from strokes or injuries to this
area of the cortex results in Wernicke’s
aphasia. These people cannot make sense
out of language that is spoken to them by
others. They can make their own speech
sounds, but say it makes little sense.
Occipital Lobes
 These lobes are at the base of the
back of the head. It is the part of
the brain located farthest from
the eyes. The visual area is the
most important part of this lobe.
 This part of the brain plays an
essential role in processing
sensory information due to the
eyes. Damage to this area can
result in partial or complete
blindness.
 The unlabeled parts of the brain
not included with the lobes are
known as the association areas.
They work closely with other
nearby areas.
Images in the Brain at Work
 In the last 40 years, technology
has increased in order to be able
to view the living brain. We can
see electrical activity, magnetic
waves, and other forms of
radiation.
 Electroencephalogram (EEG) –
the technician places electrodes
on the person’s scalp and
electrical activity is recorded. This
is generally used to study a
person’s sleep cycle and to
diagnose medical conditions, such
as seizure disorder. Multiple EEG’s
can be used to create computer
generated maps in color.
Images in the Brain at Work
 PET scanning – positron emission
tomography. They can watch what
happens to the brain as different
chemicals enter the body.
 The best technology for the brain is
the MRI (magnetic resonance
imaging). This technique detects
magnetic activity from the nuclei of
atoms in living cells and creates
visual images of the anatomy of the
brain. Functional MRI – is capable of
measuring the changes in oxygen
because of the use by neurons that
reflect their activity level. There is
no exposure to radiation as there is
with PET.
Functions of the Hemispheres of the
Cerebral Cortex
 The cerebral cortex has 4 lobes,
which are in charge of different
functions.
 The cerebral cortex is also made
up of two separate halves called
the cerebral hemispheres. These
two hemispheres are linked by the
corpus callosum, allowing
communication between the two
sides of the brain. The left
hemisphere controls most of the
circumstances on the right side of
the body and vice versa.
Functions of the Left and Right
Central Hemispheres
 The areas that control language
are generally in the left
hemisphere given 90% of human
beings. The left side of the brain
tends to deal with logic.
 The right hemisphere seems to
be in control of understanding
space and the locations of items.
 The left side tends to handle
logic, reasoning, and analysis.
 The right side tends to handle
musical abilities, space, and
emotion.
Split Brains
 The largest and most important bridge
between the two hemispheres of the
brain is the corpus callosum. Sometimes,
when a person has bad seizures they will
sometimes cut the corpus callosum so
the seizure can’t move from one side of
the brain to the other.
 When the portions of the brain have been
disconnected, scientists have learned
much more about what each half does.
 Scientists have done experiments where
they show only one eye a word to see
how the person will react. Because
opposite sides of the brain are
responsible for opposite sides of the
body, the right eye would see and
understand words (the left hemisphere
of the brain). The left eye (the right
hemisphere) would not understand the
word.
Hemispheres of the Cerebral Cortex
and Emotion
 The cerebral cortex also deals with
emotional information.
 The right hemisphere – plays a role in
expression and perception of
negative emotions (fear, sadness, and
anger).
 The left hemisphere – plays a role in
the perception of positive emotions.
 In 1861, physician Paul Broca noticed
that patients that suffered a stroke in
the left cerebral hemisphere were
more likely to become depressed. This
is because this hemisphere tends to
deal with positive emotions. This is
not true all the time, though.
Plasticity of the Cortex
 Severe damage to the cerebral cortex often results in the loss of important
psychological functions. These can be recovered if the damage occurs early in
life. This is called plasticity in that other parts of the brain can take over this
lost portion.
 If a child loses a portion of the left hemisphere that is related to language,
portions of the right hemisphere will take over.
The Brain is a Developing System
 Our brain continues to change in structure
throughout our lives.
 The total weight of the brain does not
change much after early childhood.
 White matter (myelinated neural fibers)
increase in the cerebral cortex from
childhood through middle age. There is a
continued growth of myelin through
adolescence and early adulthood.
 Myelin increases the rate of neurons and
speeds the transmission of neural impulses.
 The gray matter (neural cell bodies) decrease
in the cortex at about the same rate from
childhood through the middle ages. This
happens because of neural pruning –
eliminating unneeded neural cells. This is
supposed to increase the efficiency of the
brain.
 After the 50’s, both gray and white matter
begin to decrease which results in memory
loss and cognitive speed loss.
Neurogenesis
 There are many neurons that
keep growing in areas of the
brain even during adulthood.
This is known as neurogenesis.
 These new neurons come from
glial cells in the brain that can
be transformed into neurons.
 These new neurons help with
learning and storing new
memories.
 Learning a new skill can cause
an average increase of 3% in
areas of the cortex.
Endocrine System: Chemical
Messengers of the Body
 The endocrine system – plays an
important role in communication and the
regulation of bodily processes. This
system consists of a number of glands
that secrete two kinds of chemical
messengers.
 Neuropeptides – many endocrine glands
secrete neuropeptides into the
bloodstream. These neuropeptides can
influence their functions. Neuropeptides
allow the endocrine glands to
communicate with one another. These
neuropeptides play important roles in
stress regulation, social bonding,
emotion, and memory.
 Hormones – chemical substances,
produced by endocrine glands that
influence internal organs, including the
brain.
Endocrine System: Chemical
Messengers of the Body
 The release of neuropeptides and
hormones by the endocrine
glands is regulated by several
systems of the brain through the
hypothalamus.
 The endocrine gland gives the
brain additional ways to control
the body’s organs. During times
of stress or emotional arousal,
neuropeptides and hormones
influence: metabolism, blood
pressure, blood-sugar level, and
sexual functioning.
The Pituitary Gland
 The pituitary gland is located by
the hypothalamus.
 The pituitary is thought to be the
body’s master gland because its
secretions help regulate the
body’s reactions to stress and
resistance to disease.
 This gland secretes hormones
that control blood pressure,
thirst, and body growth. Too
much or too little of the hormone
can make someone a “little
person” or a “giant”.
The Adrenal Glands
 The pair of adrenal glands sits
atop the two kidneys. They play a
role in emotional arousal and
secrete hormones important in
metabolism.
 When the adrenal glands are
stimulated by a hormone from the
pituitary gland or by the
sympathetic division of the
autonomic nervous system, the
adrenal glands secrete three
hormones that are important in
our reactions to stress:
 1) Epinephrine
 2) Norepinephrine
The Adrenal Glands
 Epinephrine and norepinephrine – stimulate
changes in the body to deal with physical
demands that require intense body activity,
including psychological threats or danger.
 These two adrenal hormones operate
differently. During times of stress, epinephrine
increases blood pressure by increasing heart
rate and blood flow.
 Norepinephrine increases blood pressure by
increasing heart rate and blood flow by
constricting the diameter of blood vessels in
the body’s muscles and by reducing the
activity of the digestive system.
 The adrenal glands also secrete the hormone
cortisol, which also activates the body’s
response to stress.
 The autonomic nervous system has two ways
of activating the internal organs: 1) by directly
affecting the organs and 2) by stimulating the
adrenals and other endocrine glands that then
influence the organs with their hormones.
Islets of Langerhans
 The islets of Langerhans are
embedded in the pancreas –
regulate the level of sugar in the
blood by secreting two
hormones that have opposing
action.
 Glucagon – causes the liver to
convert its stored sugar into
blood sugar and to dump it into
the bloodstream.
 Insulin – reduces the amount of
blood sugar by helping the
body’s cells absorb sugar in the
form of fat. Blood sugar level is
important given hunger motives
and it also determines how
energetic a person feels.
Gonads
 There are two sex glands: 1) ovaries
in females and 2) testes in males.
These glands secrete hormones
important in sexual arousal and are
important to the development of socalled secondary sex characteristics.
 Estrogen – is the sex hormone in
females.
 Testosterone – is the sex hormone in
males.
 Each sex has a certain amount of
each hormone, both estrogen and
testosterone.
 Testosterone influences the tendency
to be socially dominant in both sexes.
Sex hormones play a very important
factor in adolescence.
Thyroid Gland
 The thyroid gland is located just
below the larynx, or voice box,
which plays a role in the regulation
of metabolism.
 The thyroid gland secretes a
hormone called thyroxin.
 In children, the proper thyroid level
is important for mental
development.
 A serious thyroid deficiency in
childhood produces sluggishness,
poor muscle tone, and a rare type of
mental retardation known as
cretinism.
 In adults, people with low thyroxin
levels tend to be inactive and
overweight.
Parathyroid
 The four small glands embedded in
the thyroid gland are the
parathyroid glands.
 They secrete parathormone, which
helps the nervous system to
function.
 Parathormone controls the
excitability of the nervous system
by regulating ion levels in the
neurons.
 Too much parathormone inhibits
nervous activity and leads to
lethargy; to little of it may lead to
excessive nervous activity and
tension.
Pineal Gland
 The pineal gland is located between
the cerebral hemispheres, attached to
the top of the thalamus. Its primary
secretion is melatonin.
 Melatonin is important in the
regulation of biological rhythms,
including menstrual cycles in females
and the daily regulation of sleep and
wakefulness.
 Melatonin levels tend to be affected
by the amount of exposure to sunlight
and clock the time of day.
 Melatonin also seems to play a role in
regulating mood. Seasonal affective
disorder, a type of depression that
occurs most frequently in the winter
months, is thought to occur because
of the lack of light.