COORDINATION
Meaning
of coordination- this is the ability of living organisms to detect changes in their
internal and external environments and response to these changes
appropriately.
In animals,
coordination is achieved
by two systems; the nervous
system and the endocrine system, while in plants it is controlled by hormones.
Importance of coordination in living organisms
a. Enables living organisms to obtain necessary requirements from the environment.
b.
Organisms can avoid negative
stimuli that could
harm them
c. It brings about body balance
Sense organs.
A sense organ is
a mass of specialized sensory receptor cells
compacted together; they detect stimuli from the environment. There are five sense organs in mammals
which are the eye, the ear, the
tongue, the nose and the skin.
A particular
sense organ will only respond to a particular
stimulus.
Sensory receptors
Sensory receptors are specialized structures or cells in
the body that enable organisms to perceive and respond to various stimuli
from their external and internal environments. They play a crucial role in our ability to sense and
interact with the world around us.
Here are some key points about sensory
receptors:
Types of Sensory Receptors:
There are several types of sensory receptors, each
specialized for detecting specific
types of stimuli.
The main categories include:
i. Mechanoreceptors: These detect mechanical stimuli such as touch, pressure, vibration, and stretch.
Mechanoreceptors are found in the skin, muscles,
and internal organs.
ii. Chemoreceptors: These respond to chemical changes in the environment and are responsible for our sense of taste and smell.
Chemoreceptors are also found in internal organs, such as those involved in monitoring blood pH and oxygen levels.
iii. Photoreceptors: These are found in the eyes and are responsible for detecting light and translating it into visual
information.
iv. Thermoreceptors: Thermoreceptors detect temperature changes in the environment and in the body.
They help us sense hot and cold.
v. Nociceptors: Nociceptors are pain receptors. They respond to potentially harmful stimuli, such as
extreme temperatures or tissue damage.
vi. Proprioceptors: These receptors are located in muscles, tendons, and joints,
and they provide
information about the position and movement of body parts. This is essential for coordination and balance.
The mammalian eye.
Ø
This is an organ that perceives light.
Ø It contains light sensitive cells (photoreceptors) in a specialized
region calledretina.
Ø It lies in a cavity in a skull called orbit or eye socket. It offers protection
from injuries.
Ø
The eyeball is attached to the walls of the socket by muscles-
superior and
inferior oblique muscles and superior
and inferior rectus muscles.
Ø The oblique muscles
move the eye left and right while rectus moves the eye up and down.
Diagram of the eye (external parts)
This diagram
should only be drawn when you are told to draw
the internal parts of the sense organ used for vision
a.
Eyelids
Ø These are two thin folds of the skin found in front of the eyeball,
there is upper eyelid and lower eyelid.
Ø
They protect the external
surface of the eyeball against entry of foreign particles.
Ø They blink to keep the surface of the eye ball wet and lubricated.
Ø Beneath it is a tear gland which
secretes tears.
b.
Eye lashes
Ø These are relatively many long hairs found on the edge of the eyelids. It protects the eye from entry of
small foreign particles and dust.
c.
Eyebrows.
Ø Raised portions of the skin above the eye lids which has thickened hair. It prevents the entry of
dust particles and sweat into the eye.
Functions and
adaptations of the parts of the eye Sclera
Ø Outermost layer of the
eye.
Ø
It is white in color and is composed of elastic connective tissue.
Ø
It protects, supports
and maintains the shape of the eyeball.
Ø Continues and becomes
a transparent layer at the front of the
eye to form cornea.
Cornea
Ø
Is transparent front part of the eyeball and is
continuous with the sclera
Ø It is covered by a thin membrane called conjunctiva, it is convex
and transparent to reflect light.
Conjunctiva
Ø This is a transparent membrane which lies in the inner surface of
the eyelids.
Ø It covers and protects the cornea.
Ø It is a tough membrane
that protects the inner parts of
the eye
Ø It is also transparent to allow light to pass.
Choroid
Ø Is heavy pigmented layer located next to the sclerotic layer
Ø Choroid extends to the front of the eye to form ciliary
body and iris.
Ø It contains a dense network of blood vessels which supply oxygen and nutrients, and remove metabolic waste.
Ø
It also prevents the reflections of light
within the eye.
Iris
Ø This is a ring of contractile muscles which is continuous with the ciliary muscles
Ø Iris contains two sets
of the muscles namely circular
and radial.
Ø
Contraction and relaxation of circular and radial muscles
control the amount
of light entering
the eye.
Ø It has pigments and determines the colour of the skin.
Ø
Ciliary body Contain ciliary muscles
that contract and relax to alter the shape of the lens.
Pupils
Ø
This is a hole or an opening in the iris which allows
light to enter the eye.
Mechanism of image
formation
Ø When light rays pass through
one media to another, of different intensities the rays are refracted meaning
that they are bend.
Ø
Rays from an external object
enter the eye, they pass through the cornea,
aqueous humour, pupil, the lens, vitreous humour and finally to the
fovea (the center of the retina) where the image is recorded as real,
upside down and smaller
than the object.
Ø Because all these media have different intensities and refract light
rays focusing them on the fovea
Ø Due to the series of multiple refractions, the image formed on the retina
is inverted and small in size than the object.
Ø
The image on the retina
stimulates the photoreceptor cells and a nerve
impulse is generated
and transmitted to the brain via the sensory neurons
in the optic nerve fibre.
Accommodation of the eye
This is the ability of the eye to focus both near and distant objects.
Ø During accommodation, the ciliary muscles relax and the tension of the suspensory ligament is
increased, this deceases the curvature of the lens
Ø The lens becomes
thin therefore allowing
light rays from a
distant object to be formed at the retina.
Ø When the eye is focusing on a near
object, the ciliary muscle contracts while the tension
of the suspensory
ligament is relaxed or decreases, this increases
the curvature of the lens
Ø In this case the lens becomes thick and more convex This allows light rays to be
focused into the retina.
The role of iris in controlling the amount of light entering the eye
During the accommodation of the eye in bright light entering the eye, in bright light, the circular muscles
of the iris contract and the pupil becomes
smaller.
In dim light, the radial muscles of the iris contract and the pupil become
larger.
Defects of the mammalian eye
and their corrections These are structural deviations of the eye
which alter the focusing mechanism of the eye.
The common eye defects are short-sightedness
and long sightedness.
I.
Short-sightedness (myopia)
A short sighted person
cannot focus a distant object properly,
but focuses near object properly.
Light rays
converge at appoint in front of the retina, this is caused
by along eyeball
Thus distant objects
appear blurred
This defect is corrected by using spectacles with concave lens.
Concave
lens diverge the rays before they reach the eye.
Fig Correction of short sight
II.
Long-sightedness (hypermetropia)
A long sighted person cannot focus properly on near objects, but focus on distant
objects properly.
The light rays from a near object converge at a point behind the retina
This caused by
eye ball being too
short.
Thus near objects appear
blurred meaning not clear.
This defect is corrected using spectacles with convexlens, the convex lens converges the light
rays before
they reach the eye.
Fig Correction of long sight
The mammalian
ear.
This is a complex
organ which performs
two functions, hearing
and maintenance of body balance.
Hearing – Is a process of being sensitive to sound waves and vibrations.
Body balance- The ear provides information on the animal’s position in space, for instance weather
the animal is upright or at an angle.
With this information the animal can make whatever
adjustments are necessary
to maintain balance.
The ear is divided into three regions
·
Outer ear
·
Middle ear
·
Inner ear.
Fig The internal
parts of the Ear
The outer ear.
This is filled
with air and consists of the following parts
i.
Pinna
This is the outermost funnel shaped part of the ear and is made up of cartilage. The function of the pinna
is to trap sound waves and direct
them to the ear canal.
ii.
Ear canal-external auditory meatus
This is the tube through which sound wave travels. The walls of ear tube secrets which traps dust
particles and micro-organisms. It directs
sound into ear drum.
iii. Ear drum- tympanic
membrane
Thin double
membrane that forms the boundary between the
outer ear and middle ear. It vibrates when hit by a sound wave. It converts sound waves into
vibrations and sends them to the middle ear.
The middle ear.
This is air filled cavity in the skull. It consists of three main
parts namely
i. Ear ossicles ii. Oval window iii. Eustachian tube.
i.
The ear ossicles
Are three tiny bones which link the ear drum with the oval window of the middle ear. They amplify
vibrations and transmit
them towards the middle
ear.
There are three ear ossicles which are;
Ø Malleus- hammer
Ø Incus- anvil
Ø Stapes- stirrup
ii.
Oval window
Ø
This is found at the end of
middle ear chamber
Ø It receives vibrations from the ear ossicles and transmits them to the inner ear
iii.
Eustachian tube
Ø Middle ear is connected to the pharynx by a tube called the Eustachian tube.
Ø It allows air to get in and out of the middle ear, thus equalizing pressure between inside and outside of the
ear drum thus prevent the ear drum from distortion.
Ø
It is usually closed
but opens during
the process of swallowing
The inner ear
Consists of a series of
fluid filled chambers which are;
i.
Chochlea
Ø This is a coiled tube filled with a fluid called endolymph.
Ø It has sensory cells which are connected to the brain through auditory
nerve. The part of the cochlea that actually responds
to sound is called organ of corti
ii. The semi-circular canal
Ø Are fluids filled tubular cavities and each has a swelling called
ampulla at one end. The three
semi-circular canals are at right angles with each other and occupy three different planes.
Ø They help to detect the movement of the head in any direction and thus help maintain balance
and posture.
The role of semi-circular canals in body balance.
When the head is rotated, nodded or held at any angle, the fluids in
the semi- circular canals
are moved.
This stimulates the sensory cells of
the ampullae.
An impulse is generated and transmitted by the auditory nerve to the
brain which interprets them and initiate a response which restores the body position.
Mechanism of hearing.
Ø
The pinna collects sound waves
and sends them to the ear drum, through the external auditory
meatus.
Ø
The ear drum vibrates and sends
the vibrations into the ear ossicles, malleus
to incus and finally to the
anvil.
Ø
In the middle ear the sound
waves are also amplified about 20 times by the ear ossicles because
of the following reasons.
a.
The high intensity of the bones
b. The lever like action of the ear ossicles
c. The oval window
being smaller than the ear drum
Ø The vibrations are send
to the oval window and finally to the
fluid of the inner ear. The fluid in the middle ear is called endolymph.
Ø The vibrations from this fluid stimulates the organ of corti which has hairs that are sensitive to sound
vibrations, thus an impulse is generated
and is sent to the brain. The organ of corti
discriminates Qualities
of sound according to their frequency.
Ø High frequency sounds are detected by organ of corti located at the base of the cochlea, while low
frequency sounds are detected by organ
of corti located at the apex of the cochlea
1.
Loudness
This is the magnitude or intensity of sound and is determined by the amplitude or strength of the sound
waves striking the ear drum.
2.
Pitch
This is the tone of the sound. It is determined by the frequency of the sound waves
Sound localization.
Ø To locate the direction of the sound, the two ears must work
together simultaneously.
Ø If sound waves comes from the front, both ears picks them at the
same time and the intensity of the
sound will be the same. But if the sound waves
comes from sides, then one ear will pick the sound waves earlier than the other.
The Tongue
Ø This is a specialized organ used to perceive taste, it consists of
group of specialized cells called taste buds.
Ø In mammals taste buds are found in raised portions of the tongue called
lingual papillae, while
in vertebrates, they are distributed at the walls of the buccal cavity.
Ø They are connected
by sensory fibres which are linked to the brain.
Ø The taste buds become stimulated and therefore generate a nerve impulse
to the brain.
There are four basic
taste stimuli that the human tongue has;
Ø Sweet- detected at the tip of
the tongue
Ø Sour- detected at the sides of
the tongue
Ø Bitter- detected at the back of
the tongue
Ø Salt detected all over the tongue
Tastes buds are
stimulated more by hot food than cold food because hot food has vapour which help in stimulation.
Taste is important in animals because it helps in distinguishing suitable
food and unsuitable foods substances.
The Nose
Ø The sensation of smell
is perceived by sensory cells located at the nasal
cavity.
Ø This is air filled space inside the nose.
Ø The sensory nerves are grouped together forming olfactory
epitheliums which consist of supporting cells and chemoreceptors.
Ø The chemoreceptors are surrounded by mucus glands.
Ø Dissolved substance in the film of mucus initiate a nerve impulse
which is transmitted tothe brain via olfactory nerve.
Ø In the olfactory lobe of the brain, the nerve impulse is interpreted as smell.
The Mammalian
Skin.
Ø The mammalian skin is made up of two main layers, the epidermis and the dermis.
Ø The dermis the part which carries sensory nerve cells and the receptors.
Ø The skin is composed of the following
receptors;
a)
Pain receptors
which detect pain
b) Touch
receptors which detect
touch
c) Pressure receptors which detect pressure
d) Thermal
receptors which detect
temperature
Ø The function of the connective tissue is to protect the nerve endings from mechanical damage and to help in the generation of a nerve impulse.
