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Chapter II
BIOLOGICAL FOUNDATIONS OF PSYCHOLOGY
If the human brain were so simple that we could understand it, we would be so simple
that we couldn’t.
- Lyall Watson
Ψ Basic Life Processes
 these are activities/characteristics that are exhibited by all the cells of the human
body
a] IRRITABILITY – the ability to react to stimulus; refers to the “FIRING” of a nerve
b] CONDUCTIVITY – the ability to conduct impulses from one point to another
c] CONTRACTILITY – the ability to contract or relax in order to move (ie. Muscle cell)
d] METABOLISM – this is the process of building PROTOPLASM from food for cell
growth and repair; metabolism also refers to the breaking down of
food into simpler substances to release energy
e] REPRODUCTION – the process where cells repair and reproduce themselves; the
nucleus splits into two equal parts, each of the parts is identical
to the mother cell
Ψ Neurons and Nerves


The NERVE CELL is considered as the building blocks of the nervous system.
Although they differ markedly in size and appearance, they have certain common
characteristics:
The main parts of the Nerve Cell are the AXONS, DENDRITES, CELL BODY
AND SYNAPSE
o The Axons and Dendrites allow the neurons to communicate with each
other. The AXONS conduct the information/impulse away from the cell
body while the DENDRITES conduct information/impulse and brings them
toward the cell body.
o The SYNAPSE is the area where impulses transfer from one neuron to
another; the gap itself is known as the SYNAPTIC GAP
o The SYNAPSE are the slender collaterals located at the end of the axons;
this term is used to refer to the whole area which is actually a junction
between the axon and the next cell body/dendrite
o At its end, the axon branches into a number of fine collaterals that end in
a small swelling called SYNAPTIC TERMINALS. When the impulses
travel down the axon, it triggers the release of chemicals called
NEUROTRANSMITTERS.
o The neurotransmitter then crosses the SYNAPTIC GAP (gap between the
synaptic terminals where the neurotransmitters will cross), and once they
have crossed, it stimulates the adjacent neuron and it in turn makes the
receiving neuron send out an impulse
o In most of the neurons, the axon is coated with a whitish substance
known as the MYELIN SHEATH. The presence of the myelin sheath
hastens the speed of conduction of the neural impulse.
Ψ Types of Neurons
Sensory Neurons
- transmit impulses received by the receptors to the central nervous system (spinal
cord). The RECEPTORS are specialized cells located in the sense organs,
muscles, skin, and joints. They (receptors) detect physical or chemical changes
and translate these events into impulses that travel along the sensory neurons.
- Sensory neurons are also known as AFFERENT NEURONS
Motor Neurons
- carry outgoing signals from the brain or spinal cord to the effector organs, namely
muscles and glands
- Motor neurons are also known as EFFERENT NEURONS
Interneurons
- receive signals from the sensory neurons and send impulses to other
interneurons or to motor neurons. Interneurons are found only in the brain, eyes
and spinal cord.
- They are responsible for what is know as thought; they carry
information/impulses within the nervous system
- Interneurons are also known as ASSOCIATIVE NEURONS

A nerve is a bundle of elongated axons belonging to hundreds or thousands of
neurons. A single nerve may contain axons from both sensory and motor
neurons.
Ψ Nerve Impulse
 The NERVE IMPULSE is the form by which messages are transmitted within
o They involve some electro-chemical reactions within the nerve fiber
o It is caused by a swapping of positive and negative charges between the
inner and outer surface of the neuron
o The nerve impulse will have the same potential regardless of the strength
of the activating stimulus
 In its resting state, the neuron is said to be in the state of POLARIZATION; in this
state, there are more positive charges in its outer surface while it has more
negative charges in its inner surface
o When the neuron is adequately stimulated, the polarization breaks down
(interchanging of charges), thus allowing a nerve impulse to go through.
 All psychological processes are responses of organisms to stimulation. This is
represented by the formula:
S
- O - R
Where:
S – the stimuli that arouses the organism
O – the reaction of the organism
R – the response of the organism
 Stimulus – any factor that causes the organism to react
Synaptic Transmission
 The synaptic junction between neurons is of tremendous importance because it
is there that nerve cells transfer signal.
 A single neuron fires when the stimulation exceeds a certain Threshold level.
o The THRESHOLD is the intensity or strength of the stimulus before the
nerve will fire
o The strength of the neural impulse is constant and cannot be triggered by
a stimulus unless it reaches the threshold level
ALL-OR-NONE PRINCIPLE
- once a nerve impulse is fired, its STRENGTH IS CONSTANT irregardless of the
activating stimulus
- all it needs is for the strength of the stimulus to reach the threshold level
 The All-or-None principle states that a neuron will fire with its maximum strength
or not at all
 neurons do not directly connect at a synapse; there is a slight gap (Synaptic
Gap) across which the signal must be transmitted. Generally, neurotransmitters
are responsible for transmitting the signals.
SYNAPTIC VESSICLES
- the nerve impulse which travels down the axons are the ones which stimulates
the synaptic vesicles
- once the synaptic vesicles are stimulated, it releases the
NEUROTRANSMITTERS, which in turn diffuse across the synaptic gap and bind
to the NEURORECEPTOR MOLECULES. The neurotransmitter molecules bind
themselves to the neuroreceptor molecules in the cell membrane of the receiving
neuron. The interlocking of the neurotransmitter molecules to the neuroreceptor
molecules then changes the neuron’s permeability of the receiving neuron.
o If the neurotransmitter has an EXCITATORY effect, this locking would
cause the neuron to increase its permeability in the direction of
depolarization;
o Other neurotransmitters are inhibitory and decrease permeability, thereby
preventing depolarization
 after the neuron has fired, the neuron is said to be in its ABSOLUTE
REFRACTORY PERIOD
o during this time, under no circumstances will the neuron fire another
impulse and not even the strongest stimulus will trigger it
o this allows the nerve to recover (go back to the state of polarization)
 After a few moment, the neuron will gradually undergo recovery and the neuron
is now in its PARTIAL REFRACTORY PERIOD
o In this state, the neuron has partially recovered and recovery continues
until it becomes normal again
o During this time, a neuron may fire an impulse IF the second stimulus is
stronger the one which triggered it before;
o The increasing strength of the stimulus would increase the frequency of
discharge thus activating more fibers
Reflexes
 they are known as the simplest synaptic arrangements
 reflexes are simple, inborn and automatic responses of some parts of the body
 when a reflex occurs, the transfer between sensory to motor neurons NO
LONGER PASS THROUGH THE BRAIN; impulses cross via a SENSORY
MOTOR ARC
 Reflexes are significant for the behavior of humans and this usually is for the
organism’s protection
o PUPILLARY REFLEX – or the narrowing of the pupils of the eye in
response to excessive illumination; a protective reflex
o GAGGING REFLEXES – occurs when an object is placed on the back of
the tongue; a protective reflex
o SALIVATION – or watering of the mouth
o KNEE JERK – reflexes of the spinal cord
o FLEXION REFLEXES – such as withdrawal of the hand from a hot object
or of the foot from a pointed object
o EXTENSION REFLEXES – stiffening of the legs to support one’s weight
in standing, walking and running
ORGANIZATION OF THE NERVOUS SYSTEM
Nervous System
Peripheral Nervous System
Central Nervous System
Brain
Spinal Cord
Somatic System
Sympathetic System
Autonomic System
Parasympathetic System
CENTRAL NERVOUS SYSTEM
 consists of the BRAIN and the SPINAL CORD; acts as the decision-maker
 the tracts and pathways of nerves run between the spinal cord and they are
covered with a protective substance called MYELIN (a whitish substance that
protects the axons and also hastens transmission of impulses)
 WHITE MATTER – area in the Central nervous system where myelin is in
abundance (mostly the nerves in the spinal cord)
 GRAY MATTER – area in the central nervous system where cell bodies are in
abundance (mostly in the brain)
PERIPHERAL NERVOUS SYSTEM
 controls all parts of the nervous system that lie outside the central nervous
system
 is not a coordinating system. The main function is to conduct impulses to and
from the central nervous system.
 Composed of two major divisions: the somatic and autonomic
AUTONOMIC NERVOUS SYSTEM
 the nerves of the ANS run to and from the internal organs, regulating processes
as respiration, heart rate and digestion; the ANS also play a role in emotion
 the activities of this area of the nervous system are SELF-REGULATING even
when a person is asleep.
 Motor system that supplies impulses to most of the INTERNAL ORGANS and
SMOOTH MUSCLES
 There is little or no control from the person
 Has two divisions: the sympathetic and parasympathetic, which are often
antagonistic in their actions; the normal state of the body (somewhere between
extreme excitement and vegetative placidity) is maintained by the balance
between these two systems
SOMATIC NERVOUS SYSTEM
 Includes the sensory system and the motor nerves that activate skeletal
(voluntary) muscles responsible for movements
 transmit information about external stimulation from the skin, muscles and joints
to the central nervous system; they make us aware of pain, pressure, and
temperature variations
 the motor nerves of the somatic system carry impulses from the central nervous
system to the muscles of the body, where they initiate action
 the SNS controls all the skeletal muscles (area of VOLUNTARY CONTROL), as
well as involuntary adjustments in posture and balance
SYMPATHETIC NERVOUS SYSTEM
 tends to act as a unit; during emotional excitement, it simultaneously speeds up
the heart, dilates the arteries of the skeletal muscles and heart, constricts the
arteries of the skin and digestive organs, and causes perspiration. It also
activates certain endocrine glands to secrete hormones that further increase
arousal
 becomes active when one is in danger or when preparing to engage in an athletic
contest
 the SyNS is focused on using body resources particularly in times of need (fightor-flight) response
PARASYMPATHETIC NERVOUS SYSTEM
 tends to affect one organ at a time. If the sympathetic system is thought of as
dominant during violent and excited activity, the parasympathetic may be thought
of as dominant during quiescence. It participates in digestion, and in general,
maintains the functions that conserve and protect bodily resources
 connected to same organs as SyNS
 restores body resources in preparation for the next event

While the sympathetic and parasympathetic systems are usually antagonistic to
one another, there are some exceptions to this principle. For example, the
sympathetic system is dominant during fear and excitement; however, a notuncommon parasympathetic symptom during extreme fear is the involuntary
discharge of the bladder or bowels. Another example is the complete sex act in
the male, which requires erection (parasympathetic) followed by ejaculation
(sympathetic). Thus although the two systems are often antagonistic, they
interact in complex ways.
Structure of the Brain
Central Core – includes most of the brain stem
Medulla
 first slight enlargement of the spinal cord as it enters the skull
 it is a narrow structure that controls breathing and some reflexes that help the
organism maintain an upright posture
 at this area, major nerve tracts CROSS OVER to the opposite hemisphere
Thalamus
 the thalamus consists of two egg-shaped groups of nerve cell nuclei; located just
above the brain stem
 acts as the RELAY STATION between the five senses and directs the impulses
to the appropriate areas of the cerebrum
 also plays and important role in SLEEP and WAKEFULNESS
Hypothalamus
 a small structure located just below the thalamus
 centers in the hypothalamus governs activities such as EATING, DRINKING and
SEXUAL ACTIVITY
 also governs the ENDOCRINE SYSTEM that maintains HOMEOSTASIS
(balance)
 plays an important role in EMOTION and our response to stress-producing
situations
 its control on the endocrine system (though its influence on the pituitary gland)
extends in the release of HORMONES, especially those that are involved in the
“fight-or-flight” response (to help the person deal with emergencies); it also acts
as the STRESS CENTER in recognition of it s special role in mobilizing the body
for action
 the hypothalamus is also knotted to play a key role in governing sexual behavior
and there are evidences that suggest that homosexuality is related to this part of
the brain
Reticular System
 this is a network of neural circuits that extends from the LOWER BRAIN STEM
up to the THALAMUS
 plays an important role in controlling our state of arousal (when electrodes are
stimulated in some areas, animals either goes to sleep or is awakened)
 it also plays a role in our ability to FOCUS our attention to a particular stimuli
 the RS also acts as a FILTER – it filters impulses whether it will be sent to the
cerebral cortex (conscious level) or not
Cerebellum
 a convoluted structure, located just above the medulla
 concerned primarily with the COORDINATION OF MOVEMENT.
 Known as the “little brain”
 Damage to the cerebellum results in jerky, uncoordinated movements
Limbic System
 these are a number of structures that together are together called the limbic
 closely interconnected with the hypothalamus and appears to impose additional
controls over some of the instinctive behaviors regulated by the hypothalamus
and brain stem
 in mammals, the limbic system seems to inhibit some of the instinctive patterns,
allowing the organism to be more flexible and adaptive to changes in the
environment
Hippocampus
 plays a special role in memory
 research show that it is critical for the storage of new events such as lasting
memories, but it is not necessary for the retrieval of older memories (when a
person undergoes an operation, he will have no difficulty in recognizing old
friends, recall earlier experiences, or perform skills learned early in life but he will
have little recall of events that happened in the year prior to the operation and will
not remember events and people he meets after the operation)
 also involved in emotional behavior (lesions in some areas will cause the
organism to react with rage, and with some areas, it would inhibit the display of
aggression and show no hostility even when attacked)
Cerebrum
 is a highly convoluted structure, more so in humans than in any other organism
 the outer layer is called the Cerebral Cortex (in Latin, cortex which “bark”)
 the cerebrum is divided into the right and left cerebral hemispheres; the
division of the cerebrum into these hemispheres represent the most important
developments of the human brain which cannot be found in animals
Cerebral Hemispheres
 it considered as the seat of consciousness and of the higher mental processes,
such as language and abstract thinking.
 The outer layer consists of the cortex, gray in color because its constitution is
primarily of neuron cell bodies and dendrites
 It has an internal white color composed of axons that connect areas of the
hemispheres with each other and with other parts of the brain
 In the cerebral cortex, one can find a series of depressions and ridges which
form the so-called convolutions; the convolutions increase the area of the brain;
the brain becomes highly convoluted due to the proportion of growing brain
tissues relative to the fixed size of the cortex


Each of the cerebral hemispheres is divided into four lobes:
o Frontal Lobe
o Parietal Lobe
o Occipital Lobe
o Temporal Lobe
the lobes of the brain are subdivided by way of the fissures;
o Central Fissure or Fissure of Rolando – divides the frontal from the
parietal lobe
o Lateral Fissure or Fissure of Sylvius – separates the temporal lobe
o Parieto-Occipital Fissure – divides the parietal lobe from the occipital
lobe
CORTICAL AREAS AND THEIR FUNCTIONS
Motor Area
 this is located in front of the central fissures; this is there areas where the motor
impulses go
 controls the bodily movements (voluntary movements)
 each hemisphere governs the opposite side of the body; an electrical stimulation
on any part would produce movement on specific parts of the body
 in an upright position, the upper part of the motor area controls the lower part of
the body such as the toes and legs while the lower part of the motor area is the
speech motor area known as the Broca’s area which integrates and coordinates
our speech (found in the left hemisphere of the brain, near the temporal lobe – it
is located in the left hemisphere since this is concerned with understanding
speech and to write and understand written words
Somatosensory Area
 Known as the “body-sense area;” all feelings like heat, cold, touch, pain and the
sense of body movement are represented here
 Located at the parietal lobe, just at the back of the central fissure
 Most of the nerve fibers in the pathways that radiate to and from the
somatosensory and motor areas cross to the opposite side of the body and when
stimulated at one side, it will produce movement on the opposite side of the body
 The amount of somatosensory or motor area associated with a particular part of
the body is directly related to its sensitivity an use
Visual Area
 located at the back of each occipital lobe; this area is mainly composed of optic
fibers and neural pathways. Some of the optic fibers from the right eye, go to the
right cerebral hemisphere, whereas others cross over at a junction called the
optic chiasma and go to the opposite hemisphere (this arrangement holds true
for the left eye as well). As such, damage to the visual area of one hemisphere
will result in blind fields in the left sides of both eyes, causing a loss of vision to
the right side of the environment
Auditory Area
 found on the surface of the temporal lobe at the side of each hemisphere
 it is involved in the analysis of complex auditory signals and is particularly
concerned with the temporal patterning of sound, as in human speech
 both ears are represented in the auditory areas on both sides of the cortex;
however, connections to the contralateral side are stronger
Association Areas
 large areas of the cerebral cortex that are not directly concerned with sensory or
motor processes; primarily concerned with memory, thought and language;
occupies the largest area in the cortex
o Frontal Association Area
- parts of the frontal lobes in front of the motor area
- this area appears to play an important role in thought processes
required for problem solving
- Human beings who have suffered damage to the frontal association
areas can perform many intellectual tasks normally. The ability to
use language probably enables them to remember the correct
response. However, they encounter difficulties when they need to
shift frequently from one strategy to another while working on a
problem
o Posterior Association Area
- Located near the various primary sensory areas and appear to
consist of subareas, each serving a particular sense.
- For example: the lower portion of the temporal lobe is related to
visual perception. Damage in this area produces deficits in the
ability to recognize and discriminate different forms. It does not
cause loss of visual acuity, but the individual “sees” sees the forms
(and can trace the outline) but cannot identify the shape or
distinguish it from a different form (Goodglass & Butters, 1988)
THE ENDOCRINE SYSTEM
Working in conjunction with the nervous system to control bodily functions and
behavior are the endocrine of ductless glands. These involve the process of
homeostasis.
 HOMEOSTASIS : the maintenance of biochemical balance in the body
carried out
through the various chemical secretions known as
hormones.
 HORMONES : are directly secreted by these glands into the blood stream
and play an important role in the utilization of food, growth of living tissue,
conservation of energy, and development of sexual maturity.
PITUITARY GLAND (hypophysis). It is a small gland suspended directly under
the optic chiasma at the base of the brain. This is called the master gland of the body
because it secretes hormones that control the activities of other glands. Although its
structure is very complex, only two parts need to be distinguished, the anterior and the
posterior lobes.
The anterior lobe secrete several important hormones which have to do with
growth, the formation of milk, and the functioning of other endocrine glands.
Oversecretion (hyperpituitarism) of the growth hormone of somatotrophin in early
childhood results in giantism or overdevelopment of the entire skeleton.
THYROID GLAND. It is located at the base of throat, near the Adam’s apple in
the males. It is a flat gland like a butterfly and secretes two known hormones: thyroxine
and idothyroxine. Disorders of the thyroid gland may be due to the oversecretion of
these hormones, which leads to hyperthyroidism, or undersecretion which leads to
hypothyroidism. In hyperthyroidism, there is augmented metabolism, and, consequently,
rapid physiological processes like accelerated heartbeat, increases temperature, flushed
and moist skin. The person becomes irritable, easily exhausted, and prone to loss of
weight. Hypothyroidism, on the other hand, results in cretinism if it occurs during
childhood. A cretin is characterized by arrested physical and mental development. If
hypothyroidism occurs after the person has reached adulthood, it results in myxedema
which is characterized by slowing of motor activity, increase of weight, slowing of
speech, yellowing of the skin and thickening of the lips.
ADRENAL GLANDS. Located on top of each kidney. Each gland is composed of
two parts: the center or medulla and the outer layer or cortex. The medulla secretes two
hormones known as adrenalin or epinephrine and noradrenalin or norepinephrine,
which serve to give us extra energy needed during emergencies and prolonged stress.
These hormones produce many of the same effects as are produced by the sympathetic
nervous system.
ISLETS OF LANGERHANS. It is found in the pancreas which is located just
posterior to the stomach and attached by a duct to the intestinal tract. Through the duct it
delivers a pancreatic secretion in to the digestive tract, thereby aiding digestion. In
addition to the digestive enzyme, the Islets of Langerhans produces hormones insulins
and glucogen which increase the permeability of cells to sugar (glucose) in the blood.
Thus, when present in normal amounts in the blood, insulin ensures that the various
tissues of the body get enough glucose as fuel for the work they have to do. Because
the nervous system, particularly the brain, consumes glucose almost exclusively for its
activities, insulin and glucagon are of primary importance in nervous functions.
When the supply of insulin is below normal (hypoinsulinism) as in diabetes
mellitus, the blood sugar level mounts because of the non-utilization of sugar by the
cells. Consequently, the nervous system is deprived of its essential fuel, with the that its
metabolic rate and general level of activity falls. On the other hand, where there is
oversupply of insulin (hyperinsulinism), there is rapid utilization of sugar in the blood
resulting in extreme weakness, cold clammy sweating, and causing the individual to
collpase.
GONADS. During the period of embryonic development prior to the third month
of prenatal development, we are neither female nor male. At the third month, we begin to
differentiate; the sex glands develop.
Sex glands differ in males and females. The male sex glands are the testes.
They secrete a hormone known as testosterone which promotes male secondary sex
characteristics that make the male look typically masculine. The female sex glands are
the ovaries. They secrete estrogen and progesterone. Estrogen is responsible for the
appearance of the secondary sex characteristics which make a girl look typically
feminine. Progesterone stimulates the thickening of the uterine lining in preparation for
pregnancy.
PARATHYROID GLANDS Attached to the posterior surface of the thyroid glands
are the parathyroid glands. These glands secrete the hormone parathormone which
controls the valance of various minerals in the blood stream, particularly calcium.
Deficiency of this hormone leads to low calcium content of the blood resulting in tetany
which is characterized by stiffening of the hands and fingers, muscle cramps, and
irritability. Too much parathormone raises the calcium in the blood, causing lethargy and
sometimes unconsciousness.
References:
Atkinson, et.al. (2000). Hilgard’s Introduction to Psychology. 13th ed.
Asia: Harcourt, Inc.
Bustos, et.al. (1999). Introduction to Psychology. 3rd ed.
Katha Publishing