the left side. Although in many ways the two hemispheres are mirror images of
one another, there are functional distinctions between them. In most people, the
areas that control the development and use of language are located in the left
hemisphere, while areas that govern three-dimensional visualization and musical
and artistic creation are located in the right hemisphere.
Each hemisphere of the cerebrum is divided into four sections: the
frontal, parietal (top rear), temporal (lower), and occipital (rear) lobes. The
back part of the frontal lobe contains areas that govern movement of the
opposite side of the body. Damage to this region results in paralysis. In front
of this region is an area of the frontal lobe called the premotor cortex, where
complex movements are controlled. Still farther forward is the prefrontal cortex,
which exerts an inhibitory control over actions. Such distinctly human abilities
as foreseeing the consequences of an action, exercising self-restraint, and
developing moral and ethical standards depend on the normal functioning of the
prefrontal cortex. The parietal lobe, the part of the hemisphere that lies
behind the frontal lobe, contains the primary sensory cortex the part of the
brain. It receives sensory information from the opposite side of the body. Below
the frontal and parietal lobes is the temporal lobe, which is involved with
heari ng and memory. Behind the temporal lobe is the occipital lobe, the visual
center of the brain. Here the signals that come to the brain from the eyes are
put through very complex transformations in a process of analysis and
integration.
Cranial nerves are a group of 12 pairs of sensory, motor, or mixed
(having separate sensory and motor fibers) nerves that connect with the brain
stem and the lower parts of the brain.
The Endocrine System.
Endocrine glands secrete onto adjacent tissue where the hormone is
picked up by the blood, lymph system, or nerve cells and transported to the
target organ. The adrenals, thyroid, parathyroid, pituitary, hypothalamus,
pineal, and ovary are endocrine glands. The secretions of endocrine glands are
called hormones. Mixed exocrine and endocrine glands, which secrete in both ways,
include the liver, testes, and pancreas. Endocrine glands release extremely
small amounts because hormones are powerful substances. The activities of the
endocrine glands form one of the most complex systems in the body. Although each
gland has its own unique function, the glands are interdependent, and the
function of one depends on the activity of another. The hypothalamus produces
several hormones, including those that regulate pituitary activity. The
pituitary produces its own hormones that regulate growth and stimulate other
endocrine glands. The adrenals, thyroid, testes, and ovaries are dependent upon
pituitary stimulat ion. The hormones these glands produce govern metabolism,
blood pressure, water and mineral balance, and reproductive functions, and they
help defend against injury. The term hormone is derived from a Greek word
meaning ’stir up’.
Drugs Affecting Behaviour.
Many kinds of drugs are prescribed for anxiety, sleeping and nervous
disorders. Several types of sedative drugs induce sleep and cause intoxication.
These drugs although prescribed for sleep disorders and anxiety problems, can
also cause physical and psychological dependence. These include ethyl alcohol,
barbiturates, methaqualone, and many others.
There are of course everyday drugs that are consumed in enormous
quantities by millions of people. Caffeine, nicotine and alcohol are used daily
by a large number of people, to the extent where they could be classed as
addictive. Alcohol addiction is by far one of the most common addictions
globally. While there appears to be little evidence that using alcohol in
moderation does any damage, but excessive drinking is a major problem in many
countries causing many man hours of lost work, social and domestic violence
problems. Repeated heavy drinking can cause serious medical problems, liver
damage and irreversible brain damage in some cases.
SENSORY PROCESSES.
The term sensation refers to the process of receiving information in the
form of energy (light, heat, sound etc.) from the world outside and sorting it
out into the proper sense – vision, touch, hearing. Once that information has
been received, we interpret it and arrive at an understanding of what it means,
a process referred to as perception. Sensation and perception make up an
extensive information gathering system.
Each sense has it’s own receptors that constantly monitor our
environment. All sensory systems have certain characteristics: The sensory
system must be selective, which means that only certain types of incoming
information are processed. For example, we have more than one kind of receiver
for touch. One which responds to changes in temperature and one which responds
to damaged cells. The sensory system must have an adjustable speed. Nerve fibres
to the ear respond in less than a thousandth of a second because sudden noise
does not require analysis, as it does a speedy response. However, the visual
system will respond quickly to a blur as something comes towards us, a
potential danger, yet it will take it’s time when analyzing a complex scene.
The system must also be sensitive, but not too much. If our ears were too
sensitive we would hear blood running through artery at the base of the ear.
Sensory measurement must be reliable. Reliability comes from comparing incoming
stimulus with the conditions around us.
Vision.
The optic nerve delivers its impulses to a special area of the brain
called the visual center . This is where people “see” objects in the sense of
recognizing and reacting to what their eyes look at. In other words, seeing
always involves the brain’s visual center. Here sensation turns into perception.
The brain must learn by experience to analyze correctly the impulses it
receives from the eyes. For instance, the lens system of the eye, like that of a
camera, transmits its light pattern upside down. The brain has to learn that the
impulses received from the upper part of the retina represent the lower part of
the object sighted and vice versa.
In the brain also are located the centers that control all the eye’s
muscular movements, such as the opening and closing of the iris, the focusing of
the main lens, and the movement of the eyeball. The eyeball’s movement is
voluntary. Other eye adjustments are reflexes. Most individuals use both eyes
to see an object. This type of sensory perception is known as binocular vision.
Thus two images of the object are formed one on the retina of each eye. Impulses
from both images are sent to the brain. Through experience these impulses are
interpreted as two views of the same object. Because the eyes are about 2
inches apart from pupil to pupil and therefore are looking at the object from
different angles, the two views are not exactly alike. This is known as the
stereoscopic effect. If the object is far away, the difference between the
images is slight. If it is a few inches away, the difference is very great. The
brain makes good use of this phenomenon. It learns to judge the distance of an
object b y the degree of difference between the images it receives from the two
eyes. In the same way the brain perceives what is called perspective.
The Eye.
The retina is a soft, transparent layer of nervous tissue made up of
millions of light receptors. The retina is connected to the brain by the optic
nerve. All of the structures needed to focus light onto the retina and to
nourish it are housed in the eye, which is primarily a supporting shell for the
retina. When light enters the eye it passes through the lens and focuses an
image onto the retina. The retina has several layers, one of which contains
special cells named for their shapes rods and cones. Light-sensitive chemicals
in the rods and cones react to specific wavelengths of light and trigger nerve
impulses. These impulses are carried through the optic nerve to the visual
center in the brain. Here they are interpreted, and sight occurs. Light must
pass through the covering layers of the retina to reach the layer of rods and
cones. There are about 75 to 150 million rods and about 7 million cones in the
human retina. Rods do not detect lines, points, or color. They perceive only
light and dark
tones in an image. The sensitive rods can distinguish outlines or silhouettes
of objects in almost complete darkness. They make it possible for people to see
in darkness or at night. Cones are the keenest of the retina’s receptor cells.
Hearing.
In hearing the basic energy form is sound waves. Sound waves form at
various speeds, or frequencies. The frequency of any given tone is measured in
terms of the number of cycles per second. Sound travels slowly compared to light
at anything from 20-20,000 cycles per second. The sounds we hear have three
basic characteristics. Pitch, which is the frequency of the sound. Timbre,
determines the tonal quality . The loudness or intensity of the sound wave is
measured in decibels. The human ear can pick up sounds just above ‘0′ decibels,
otherwise there would be complete silence.
Decibel Table.
Decibels Noise Threshold
40 Quiet office Normal
60 Normal conservation Normal
75 Road Traffic Noisy
100 Subway Train Potential Damage
130 Rock Concert Human Pain Threshold
140 Aircraft Taking-off Human Pain Threshold
The Structure of the Ear.
The ear has three separate sections the outer ear, the middle ear, and
the inner ear. Each section performs a specific function, related to either
hearing or balance. The three parts of the outer ear are the auricle (also
called the pinna), the external auditory meatus (or ear canal), and the tympanic
membrane (or eardrum). The pinna collects sound waves from the air. It funnels
them into a tube, the external auditory meatus. This is a curved corridor that
leads to the tympanic membrane. The eardrum separates the external ear from the
middle ear. The middle ear is an irregular-shaped, air-filled space. A link of
three tiny bones, the ossicles, spans the middle ear. When sound waves strike
the outer surface of the eardrum, it vibrates. These vibrations are mechanically
transmitted through the middle ear by the ossicles, to the opening. This opening
is the round window. Like the eardrum, the round window’s membrane transmits
vibrations. It directs vibrations into the inner ear, where they enter a f luid
that fills a structure called the cochlea. This is a coiled tube that resembles
a snail’s shell. Within the cochlea is housed the true mechanism of hearing,
called the organ of Corti. It contains tiny hair-like nerve endings anchored in
a basilar membrane, which extends throughout the cochlea. The unattached tips of
these nerve endings are in contact with an overhanging membrane, called the
tectorial membrane. When vibrations pass into the inner ear, they cause waves to
form in the cochlear fluid. Receptor nerve cells in the organ of Corti are
highly sensitive to these waves. Other specialized nerve cells send the
electrochemical impulses produced by the wave motion into the cochlear branch of
the acoustic nerve. This nerve carries the impulses to the brain, where sound is
identified.
Taste.
It is widely accepted that there are four basic taste qualities, salty,
sour, sweet and bitter. It was originally thought that there was a sensory path
for each of these tastes. However it appears that there is a pattern of
activation in a number of different fibres providing the required sensory input
to the brain to distinguish these different tastes. The papillae on the surface
of the tongue are the receptors for these taste sensations.
Smell.
Deciphering the sensory information for the sense of smell is not
dissimilar to that of taste. In the olfactory area the nerve endings grow
through the mucous membrane which act as receptors to determine odors present in
the air we breathe.
Touch.
The skin or cutaneous sense has some 5 million sensors of at least 7
types throughout the human body. The three major types are Meissner’s corpuscles
which sense touch. The Pacinian corpuscle’s which determine movement and
vibration and the Krause end bulbs which sense changes in temperature.
Equilibrium and Proprioception.
Proprioception (kinesthesia), establishes the position of limbs and
underlies the ability to assume and maintain posture, to move about in the
environment, to manipulate objects and to be coordinated. These senses did not
figure prominently in the traditional account of senses because they have no
external sources of adequate stimulation. They do have identifiable and
understood sensory receptors. Both play an important role in maintaining posture
and balance.
PERCEPTION.
Perception is the primary process by which we obtain knowledge about the
world. It involves the activity of our senses in responding to external
stimulation. Perception is a skill or set of skills, not simply the passive
reception of external stimulation. The process of structuring these stimuli into
objects we can perceive is called perceptual organisation. There are a number
of principles to perceptual organisation.
Figure and Ground.
Gestalt psychologists identified the tendency to differentiate between
figure and ground. The figure being the part of an image which we notice
prominently, opposed to the background, the ground. This theory not only applies
to visual items, but