An Ability of living things is responding to stimuli. In order this response to be effective various
implications must be met within the organism. Humans and animals rely mainly on stimuli from sight
and sound for communication although there are other senses that are involved between
communications.
DETECTING STIMULI
- A large number of cells in the human body have the role of detecting changes both internally and
externally. Receptor is the term used to describe the role of these specialised cells. Receptors are
involved many in different areas throughout the body. The skin contains four different types of
receptors which detect pain, pressure, heat and coldness. In the mouth there are five types of
receptors involved only in taste, as well as this there are 1000 different smelling receptors used in
detecting odours.
RESPONSE TO STIMULUS
-there are certain stages in which the body undergoes in order to detect different types of stimulus
from the external environment. First the stimulus causes a change in the external environment; a
specific sensor receptor detects their specific type of stimulus, specialised areas of the body turn this
response into energy, this energy is transformed into an impulse message, the message is received
and a response is carried out.
THE ANATOMY AND FUNCTION OF THE HUMAN EYE
CONJUNCTIVA- A protection layer for the surface of the Cornea
CORNEA- The front of the eyeball in which light enters before it is focused
SCLERA- The outer protection layer of the eyeball.
CHOROID- A cluster of blood vessels that act in carrying waste products out of the eye, and bring
oxygen and nutrients in.
RETINA- The structure of photoreceptors at the
back of the eye that allow light to be converted into
nerve impulses.
IRIS- The coloured part of the eye which contracts
and expands to control the amount of light that
enters the eye.
LENS- The lens is active in focusing the light onto
the photoreceptors.
AQUEOUS AND VITREOUS HUMOR- The fluids that fill up the spherical shape of the eye.
CILIARY BODY- a circular shaped ring that is active in focusing the lens.
OPTIC NERVE- nerve fibres that send impulses to the brain.
RANGE OF WAVE LEGNTHS OF THE ELECTOMAGNETIC SPECTRUM
The part of the electromagnetic spectrum that is visible to the human eye is known as the Visible
Spectrum. A typical human eye will respond to wavelengths from about 390 to 750 nanometres. This
spectrum is made up of the colours red, orange, yellow, green, blue, indigo and violet.
Different animals are able to detect different ranges of colours. Many vertebrates are not able to
tell the difference between colours. However some snakes and birds are able to see longer
wavelengths and can also detect heat via infrared-radiation. Some invertebrates can also detect
wavelengths of electromagnetic radiation. Some spiders are less sensitive to the red end of the
spectrum allowing them to see ultraviolet light.
CLARITY OF SIGHT
A clear picture within the human eye is important for maintaining visual communication. With an
unclear or distorted vision there can be problems involving judging depth, speed and distance.
Humans as a result have utilised the use of glasses to counter these problems correcting the failure
of the eye.
REFRACTION OF LIGHT- refraction is the result of light passing through a denser medium causing the
speed of the light to slow down. If the light hits the object at an angle the light rays will be bent or
refracted.
Refraction occurs in the eye in the cornea and the anterior and posterior surface of the lens.
ACOMMODATION OF THE EYE-In order for the lens to focus light from different distances onto the
retina the lens needs to change its shape in order to allow a certain amount of light inside the eye.
This process is known as accommodation. When the object is further away it is much easily
processed rather than close objects which may cause the muscles to contract, affecting the bending
of light.
The contracting of these muscles causes the eye to be rounder when focused on a near object and
flatter upon a distant object.
MYOPIA AND HYPEROPIA- Myopia (short sidedness) occurs when the eyeball naturally changes
shape. This causes light to focus in front of the retina rather than directly on the retina which causes
a blurred vision.
Hyperopia (farsightedness) occurs when light entering the eye focuses behind the retina, instead of
directly on it. An abnormally flat cornea or short eye can cause the light to enter the eye this way.
Both these conditions can be a result of hereditary factors and can be passed on through families.
Today these complications can be corrected by use of eyeglasses, contact lenses or surgery to
reshape the cornea.
CATARACTS-Cataract is the term used to describe the clouding of the lens which can affect the way
light is received to the retina causing problems with sight. Most cataracts are related to aging. Treatment
for Cataracts consists of replacing the damaged lens with synthetic lens to restore the lens's transparency.
As a result of this technology on society, people who are affected by cataract blindness can be
treated and their sight can be restored in a matter of minutes. Cataracts affect millions of people
worldwide and can cause significant problems for the elderly which without cure may lead to their
loss of independence or in many instances their unnecessary death. With the improvement of
technology and the education of this problem the effectiveness of the intraocular lens can be
increased and an increasing number of surgeons are able to perform this surgery. With the mass
production of these lenses treatment can be provided for many people throughout the world
including people in third world nations who this condition is affecting the most.
DEPTH PERCEPTION-The perception of depth may be a result of the positioning of the eyes on the
head.
Predatory Animals; the eyes are placed at the front of the head allowing them to see greater depth
and distance. Examples of this are jungle cats and most birds.
Herbivores; These animals on the other hand have eyes mounted on the sides of their head allowing
them to keep a look out for predators from almost every angle. However they cannot see distance
and depth as effectively as other animals. Examples include deer and buffalo.
LIGHT TRANSFORMED INTO AN ELICTRICAL IMPULSE
Photoreceptor cells; certain types of nerve cells located in the retina that contain light sensitive
pigments. The significance of these cells to the eye is they have the ability to convert light into
complex messages that the brain is able to interpret. Rods and cones make up the photoreceptors in
this area. Cones work more effectively in bright light and their main function is to detect colour and
visual acuity while rods on the other hand are better suited for detecting shape and movement,
distinguishing shades of light and dark and help us see in low lit and dark areas, hence nocturnal
animals will have a much larger ratio of rods than humans allowing them to see better at night,
example, the eyes of the tawny owl are approximately 100 times more sensitive at night than those
of humans. The structures of invertebrates’ photoreceptors in most cases are different in structure
to that of vertebrates. The reason for this is that some invertebrates including arthropods may have
thousands of lenses and multiple eyes. Some invertebrates such as flatworms have simple light
receptors and do not see complete images only variations of light and dark.
HUMAN PHOTORECEPTORS IN THE EYE
The human eye has a much larger amount of rods than cones,
making our sight much more effective during the day or with
large amounts of light. The human eye has 125 million rods and
6.5 million cones. Cones are spread around the central fovea
and the macula lutea. Rods on the other hand are more
concentrated around the retina.
PHOTORECEPTORS IN MAMMALS
The photoreceptors in other mammals are almost identical to that of a human consisting primarily of
rods and cones. Depending on the ratio of rods and cones these mammals might have the ability to
see more effectively in the dark, or even as a result of having no cones may only see in black and
white. This is evident in rats.
PHOTORECEPTORS IN INSECTS
The structures of insects’ eyes are considerably different as
most insects have thousands of lenses with each one
focusing light on a smaller number of photoreceptors.
Ommatidium contains a cluster of photoreceptor cells
surrounded by support cells and pigment cells. These
pigments absorb certain colours of incoming light and make
nerve impulses similar to humans. Some insects are even
able to distinguish colour.
COMPARISON-The photoreceptors in mammals work using different pathways and structures to that
of insects and flatworms. However the photosensitive cells do contain similarities across all three
different organisms.
TYPES OF CONES-Pigments in cones are almost the same as the ones in rods except they require
bright light and reform faster than that in rods. There are three types of cones that contain pigments
sensitive to blue, green or red light.
People who have a lack of colour pigments in their cones may be colour blind causing them to not be
able to process this colour or colours.
Many animals use colour as an important tool for communication. Many animals including bird
species utilise the use of colour in order to signal times of breeding and to tell male and female
apart. Animals also use colour via camouflage to hunt or avoid predation. Although for many of
these scenarios communication through colour is only effective if the animal has colour vision.
SOUNDWAVES- apart from electromagnetic waves which are detected by sight, sound waves are
detected by vibrations. Sound waves are very useful and popular for communication.
Sound can be used for communication when all other means of communication cannot be detected;
this makes soundwaves very effective at night, without vision or from a distance. Most animals can
effectively detect sound waved and create them which makes this type of communication easy and
efficient.
In a medium such as air there are variations of pressure, which are created by the vibration of an
object. When these waves are created the air surrounding it will vibrate, when the eardrum vibrates
as a result, the brain interprets this vibration as sound. Sounds with short wavelengths have higher
frequencies and sounds with long wavelengths have lower frequencies, both short and long
wavelengths can vary in volume or loudness.
HUMAN LARYNX-The larynx is also known as the voice box and
is composed of vocal cords which consist of muscles and
ligaments. With the larynx working together with the tongue,
lips, nose and air which travels from the lungs humans are
able to communicate by a differentiation of sounds which are
recognised by other humans. Air that comes from the lungs
travels to the larynx which can open and shut in order to
create vibrations which are amplified later within the throat,
mouth and nose.
DETECTION OF VIBRATIONS
In order for communication by soundwaves to be effective an organism must be able to produce
sound as well as detect sound.
Mammals- one fifth of mammals including bats, dolphins and toothed whales use echolocation to
navigate the environment around them. Most mammals have developed hearing satisfactory for
communication and as well as this are able to produce sound. The main way of hearing sound is by
specialised organs on the head that are able to detect vibrations, example ears in humans.
Insects- Not all insects are capable of hearing, in fact only a small minority of species have the
capability. Most of these insects also have ears which detect vibrations but they are located in
different areas of the body, example crickets have ears located on their legs while grasshoppers and
cicadas have them on their abdomens. Insects also have much more sensitive hearing allowing them
to hear sounds in the ultrasonic region.
Fish- fish receive sound waves from a series of tunnels in the inner ear which contain sound
receptors, this is called a labyrinth. As well as this fish can also detect vibrations by a lateral line of
receptors which are sensitive to movement in the surrounding water.
STRUCTURE AND FUNCTION OF THE MAMMALIAN EAR
STRUCTURE
FUNCTION
Pinna- the flap
Collects sound waves from a wide area and funnels the sound into the
external ear passage
Tympanic
membrane – ear
drum
Stretched across the end of the auditory canal; separates the outer ear from
the middle ear. Sound waves cause the tympanic membrane to vibrate.
These vibrations are then conveyed from the tympanic membrane to the
oval window by three tiny bones called the ear ossicles.
Ear ossicles
Three intricately formed bones- the hammer, anvil and stirrup- transmit
sound waves to the inner ear. (Sound vibrations travel well through bone.)
Oval window and
Round window
The oval window and round window are two thin membranes. Sound reaches
the inner ear at the oval window. Pressure is then transmitted in the fluid in
the tympanic canal. This pressure causes the round window, at the end of
the tympanic canal, to bulge outwards. The oval window helps to amplify the
pressure of the sound vibrations.
Cochlea- snail like
spiral coiled tube, in
the inner ear
The cochlea contains the receptors for sound and the vestibular apparatus
that is associated with a sense of balance. As a result of the round window
bulging outwards, fluid in the cochlear tubes vibrates.
Organ of Corti
Contains the auditory receptor cells
Auditory nerve
Transmits the sound vibrations to the brain
(Excel HSC biology- Diane Alford and Jennifer Hill- page 123-124 table 4.1)
EUSTACHIAN TUBE- the middle ear and the pharynx are connected by the Eustachian tube. This tube
also is important in equalising the pressure on both sides of the ear drum. This tube is closed except
at times of muscle movement in the mouth, an example of this is swallowing.
THE PATH OF A SOUND WAVESoundwaves come into contact with the outer ear and reach the eardrum into the middle ear. The
ear ossicles transmit vibrations to the inner ear at the oval window. Through the spiral cochlea the
vibrations reach the round window. The impulse reaches the auditory nerve to the auditory area of
the cerebrum.
When sound energy reaches the tympanic membrane it is transformed into mechanical energy of
the ossicles. When it reaches the Corti it is transformed into electrochemical energy.
HAIR CELLS IN THE ORGAN OF CORTIThe sound receptors in the organ of Corti are hair cells.
The movement of the hair cells depends on the
frequency of vibrations in the sound that reaches the
ear. Low frequency sounds travel further down to the
cochlea as sounds of high frequency pass through the
basilar membrane.
RANGE OF FREQUENCES DETECTED AS SOUND –
MammalsThe range in which humans can hear ranges from 20-20000Hz
Bats hearing ranges from 100000-120000Hz
Marine mammals have different hearing ranges which give them unique communication qualities.
Examples of this consists of dolphins and porpoise’s which can hear sounds as high as 150000Hz
Animals which use sound for communication over long distances use low frequency sound waves
because they are able to travel further. (Whales)
Animals which use sound for precise location and communication over shorter distances may use
high frequency sound waves. (Bats in echolocation)
SONIC SHADOWThis term is used to describe how sound being projected on a certain angle may cause one ear to
receive more sound than the other, which as a result makes the receiving of soundwaves in humans
more effective while facing the source of sound.
HEARING AIDS- hearing aids will not benefit all people
who suffer from problems of hearing including those
who have nerve deafness. Instead it is aimed at
people who have hearing problems from the middle
or outer ear. A hearing aid is powered by electricity
and by use of a microphone, earpiece and amplifier
attempt to recreate a louder sound wave which can
be heard by the person using this device. The
microphone captures the sound being projected
around the ear, and the amplifier increases the
volume of this sound. When this sound is adjusted to
the right amount depending on the person’s previous
ability to hear, the sound is transferred into the
earpiece which assists the person in hearing sound.
The effectiveness of hearing aids has been internationally recognised and people from all over the
world turn to hearing aids for assistance in specific types of hearing problems.
COCHLEAR IMPLANT- A cochlear implant or bionic ear is a device used to assist people who are
severely hard of hearing. The device consists of a microphone which picks up sound from the
environment, a speech processor which filters the sound and sends electrical sound signals through
a thin cable to the transmitter, and a transmitter which by electromagnetic induction transmits
sound to the internal device.
The internal device consists of a stimulator and receiver which are secured in the patient’s skull; this
converts the signals into electric impulses and sends them through an internal cable to electrodes.
The receiver is attached to the cochlea which send the impulses to the nerves in the scala tympani
and then directly to the brain through the auditory nerve system.
Hundreds of thousands of people have used this device as an alternative for hearing problems;
however it is not available to everyone because of the high cost and the ongoing maintenance costs.
Another issue is that the device must be re-programmed a number of times for a variety of
situations which can be frustrating and take up a lot of time.
For more information
~ http://www.bionicear.com.au
~’Cochlear implants in the second and third millennia’ Australasian Science, 1999, pp. 26-29
NERVES- The nervous system is made up of neurones or nerve cells, these
nerve cells are made up of dendrites, an axon and a cell body. The axon
and dendrites are joined together. Myelin sheath acts as an insulation
layer over the axon. The size of neurons differs in relation the task they
are set to carry out. A nerve is a bundle of neuronal fibres.
NEURONS-the job of neurons
is to send signals by
electrochemical changes in
their membrane. These signals
are carried out from the cell
body to the axon and the cross
over to other neurons creating
a chain reaction.
NERVE THRESHOLD-this is the term used to describe the minimum stimulus required to generate a
response in the nerve cell. This minimum threshold is important because without this, nerves would
not have an idea of when and how rapidly to respond creating difficulty in the message process. This
is known as action potential.
CEREBRUM DETECTION OF LIGHT AND SOUNDThe cerebrum is a big clump of the
brain. The cerebral cortex is the
surface area of the cerebrum. The
left and right hemispheres are
connected from the inside by the
corpus callosum which is consisted
of a large bundle of nerve fibres.
The medulla oblongata is located
near the spinal chord and controls
basic functions in the body,
example breathing.
The cerebellum is located behind
the medulla oblongata and
coordinates movement, posture
and balance.
INTERPRETING SIGNALS FOR CO-ORDINATIONThroughout this website there may be an understanding of how signals such as light and sound are
interpreted by the brain and bring about a response.
However sensory signals have been known in some instances to be wrongly interpreted. Examples of
this are in optical illusions where 2D objects can be mistaken for 3D objects.
Some orchids are able to trick male wasps into thinking the flower is a female wasp in order to
pollinate the orchid. Without proper sensory signals wasps may rapidly decline in numbers by not
actually creating new offspring.
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